Neuroscience 282 (2014) 198–216

REVIEW

THE ANTERO-POSTERIOR HETEROGENEITY OF THE VENTRALTEGMENTAL AREA

M. J. SANCHEZ-CATALAN, a,b J. KAUFLING, c,d

F. GEORGES, c,d P. VEINANTE a,b AND M. BARROT a,b*

a Institut des Neurosciences Cellulaires et Integratives,

Centre National de la Recherche Scientifique, Strasbourg, France

bUniversite de Strasbourg, Strasbourg, France

cCentre National de la Recherche Scientifique, Interdisciplinary

Institute for Neuroscience, UMR 5297, Bordeaux, France

dUniversite de Bordeaux, Interdisciplinary Institute for

Neuroscience, UMR 5297, Bordeaux, France

Abstract—The ventral tegmental area (VTA) is a brain region

processing salient sensory and emotional information, con-

trolling motivated behaviors, natural or drug-related reward,

reward-related learning, mood, and participating in their

associated psychopathologies. Mostly studied for its dopa-

mine neurons, the VTA also includes functionally important

GABA and glutamate cell populations. Behavioral evidence

supports the presence of functional differences between

the anterior VTA (aVTA) and the posterior VTA (pVTA), which

is the topicof this review.Thisantero-posterior heterogeneity

concerns locomotor activity, conditioned place preference

and intracranial self-administration, and can be seen in

response to ethanol, acetaldehyde, salsolinol, opioids

includingmorphine, cholinergic agonists including nicotine,

cocaine, cannabinoids and after local manipulation of GABA

and serotonin receptors. It has also been observed after viral-

mediated manipulation of GluR1, phospholipase Cc (PLCc)and cAMP response element binding protein (CREB) expres-

sion, with impact on reward and aversion-related responses,

on anxiety and depression-related behaviors and on pain

sensitivity. In this review, the substrates potentially underly-

ing these aVTA/pVTA differences are discussed, including

theVTAsub-nuclei and the heterogeneity in connectivity, cell

types and molecular characteristics. We also review the role

of the tail of the VTA (tVTA), or rostromedial tegmental

nucleus (RMTg), which may also participate to the observed

antero-posterior heterogeneity of the VTA. This region, partly

located within the pVTA, is an inhibitory control center for

dopamine activity. It controls VTA and substantia nigra dopa-

mine cells, thus exerting a major influence on basal ganglia

http://dx.doi.org/10.1016/j.neuroscience.2014.09.0250306-4522/� 2014 IBRO. Published by Elsevier Ltd. All rights reserved.

*Correspondence to: M. Barrot, Institut des Neurosciences Cellul-aires et Integratives, CNRS UPR3212, 5 rue Blaise Pascal, 67084Strasbourg, France. Tel: +33-388-456-633.

E-mail address: mbarrot@inci-cnrs.unistra.fr (M. Barrot).Abbreviations: aVTA, anterior VTA; CNQX, 6-cyano-7-nitroquinoxaline-2,3-dione; CREB, cAMP response element bindingprotein; EM-1, endomorphin-1; NMDA, N-methyl-D-aspartate; PLCc,phospholipase Cc; pVTA, posterior VTA; RMTg, rostromedialtegmental nucleus; tVTA, tail of the VTA; VTA, ventral tegmental area.

198

functions. This review highlights the need for a more

comprehensive analysis of VTA heterogeneity.

This article is part of a Special Issue entitled: Ventral

Tegmentum & Dopamine. � 2014 IBRO. Published by

Elsevier Ltd. All rights reserved.

Key words: dopamine, ventral tegmental area, tVTA,

behavior, drugs of abuse.

Contents

Introduction 198

VTA antero-posterior functional heterogeneity 199

GABA transmission 199

Ethanol, acetaldehyde and salsolinol 199

Ethanol behavioral studies 199

From ethanol to acetaldehyde and salsolinol 201

Neurochemical studies 202

Electrophysiological studies 202

Opioids 203

Cholinergic system 204

Cocaine 204

Other drugs 205

Affect and pain 205

Neuroanatomy of the VTA 205

Definition of the VTA 205

The VTA and the A10 dopamine cell group 206

Cytoarchitectonic subdivisions of the VTA 206

BASES for the aVTA/pVTA differences 207

The tVTA 209

Detecting the tVTA 209

tVTA control of dopamine cells 210

tVTA and behavior 210

Conclusion 211

Acknowledgments 211

References 211

INTRODUCTION

The ventral tegmental area (VTA) is studied for its

implication in a wide range of functions including the

processing of salient sensory and emotional information,

the control of motivated behavior, natural or drug-related

reward, reward-related learning, mood, and their

associated psychopathologies (Nestler and Carlezon,

2006; Fields et al., 2007; Grace et al., 2007; Bromberg-

Martin et al., 2010; Hong, 2013; Creed et al., 2014;

Gillies et al., 2014; Ikemoto and Bonci, 2014; Meye and

M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216 199

Adan, 2014; Nikulina et al., 2014; Overton et al., 2014;

Walsh and Han, 2014). While most work related to the

dopamine cells of the VTA, recent attention has also been

given to the GABA and glutamate cell populations

(Roeper, 2013; Creed et al., 2014; Morales and Root,

2014). Beyond this cellular heterogeneity, behavioral evi-

dence has accumulated since the late nineties supporting

the presence of a major antero-posterior heterogeneity

within the VTA (Ikemoto, 2007). The functional difference

between the anterior VTA (aVTA) and the posterior VTA

(pVTA) is particularly supported by studies of the locomo-

tor, rewarding and reinforcing properties of various drugs

of abuse. However, the substrate underlying such aVTA/

pVTA differences remains elusive, with hypotheses based

on neuroanatomy, connectivity and cellular and molecular

heterogeneity. Moreover, in the past decade, an inhibitory

control center for midbrain dopamine cells was identified

and named the tail of the VTA (tVTA) or rostromedial teg-

mental nucleus (RMTg). The tVTA is partly located within

the pVTA and thus should also be considered when

studying the antero-posterior heterogeneity of the VTA.

In this review, we will first describe the behavioral and

physiological evidence supporting the antero-posterior

heterogeneity of the VTA. Indeed, historically, the first

data highlighting the importance of the VTA antero-

posterior functional heterogeneity came from

experiments of behavioral pharmacology. Most of these

studies did a direct side-by-side comparison of intra

aVTA and pVTA drug injections. We will then provide

information on the possible bases for such

heterogeneity, including the presence of subnuclei within

the VTA and the presence of potential differences in

connectivity, in cell types and in molecular cell

characteristics. It is indeed important to also consider

the available information on VTA anatomical

heterogeneity, even though no direct link has been

established yet between the antero-posterior functional

heterogeneity and the precise VTA subnuclei. Last, we

will summarize the present knowledge on the tVTA, a

structure with its most rostral portion within the pVTA

and extending caudally beyond the VTA, that exerts a

major control over the activity of mesencephalic

dopamine cells. The tVTA may have a critical role in

basal ganglia functions. While published work has not

directly compared the aVTA, pVTA and tVTA, some

evidence suggests that the latter structure might be

mediating some of the functions that were previously

attributed to the pVTA.

VTA ANTERO-POSTERIOR FUNCTIONALHETEROGENEITY

GABA transmission

A third of a century ago, it was observed that injections of

GABA modulators in the VTA had different effects on

locomotor activity depending on the injection site (Arnt

and Scheel-Kruger, 1979) (Table 1). Agonists of GABAA

receptors increased locomotor activity when delivered in

the pVTA but not in the aVTA, while GABAA antagonists

increased activity when delivered in the aVTA but not

the pVTA. In the late nineties, Ikemoto et al. observed that

Wistar rats self-administered antagonists of the GABAA

receptor, such as picrotoxin and bicuculline, into the

aVTA but not into the pVTA (Ikemoto et al., 1997b;

Ikemoto, 2005), whereas they self-administered the

GABAA agonist muscimol into the pVTA but not into the

aVTA (Ikemoto et al., 1998). These data (Table 1) high-

lighted the presence of a prominent functional heteroge-

neity at the level of the GABAergic transmission along

the antero-posterior axis of the VTA. However, it may

be challenging to control for the anatomical selectivity of

local injections, due to the diffusion of injected com-

pounds. Thus, the rewarding effects of GABAA antagonist

in the aVTA were later proposed to be associated with the

supramammillary nucleus, a hypothalamic area anterior

to the VTA and that plays also a role in reward

(Ikemoto, 2005, 2010). Nevertheless, differences in the

consequences of pVTA and aVTA manipulations

remained valid, and these first functional data on the ante-

ro-posterior heterogeneity of the VTA opened the path to

other studies, in particular in the field of ethanol action and

alcoholism (Table 1). It should be noted that, for a long

time, the ‘‘aVTA’’ and the ‘‘pVTA’’ were functionally com-

pared without the frontier between them being anatomi-

cally defined. A study on the response to cocaine

showed that the aVTA/pVTA limit in rats was around

�5.5 mm from the bregma, which neuroanatomically cor-

responds to the position of the interpeduncular nucleus

below the VTA ((Olson et al., 2005), see cocaine section

below).

Ethanol, acetaldehyde and salsolinol

Ethanol behavioral studies. Manipulations of the VTA

can modify the ethanol intake in rats (Hodge et al., 1993;

Katner et al., 1997). While rats directly self-administer eth-

anol into the VTA, this reinforcing property displays a

neuroanatomical selectivity (Fig. 1, Table 1). Indeed, rats

self-administer ethanol into the pVTA but not into the

aVTA (Rodd-Henricks et al., 2000, 2003; Rodd et al.,

2004b, 2005d; Ding et al., 2014), and the infusion of etha-

nol into the pVTA also increases the rat locomotor activity

(Sanchez-Catalan et al., 2009). Considering data obtained

in a strain of alcohol-preferring rats, the preferential sensi-

tivity of the pVTA may be relevant to the vulnerability to

alcohol. Alcohol-preferring rats self-infuse lower doses of

ethanol into the pVTA than Wistar rats (Rodd et al.,

2004a), and the dose of ethanol eliciting self-infusion in

the pVTA is even lower after chronic ethanol drinking

(Rodd et al., 2005b,c).

Ethanol can act through several ion channels and

neurotransmitter systems (Morikawa and Morrisett,

2010), a major mediator of its action being the GABAergic

system. In this context, the alcohol intake (Melon and

Boehm, 2011) and the conditioned place preference to

ethanol (Bechtholt and Cunningham, 2005) may be

decreased by a manipulation of GABAA or GABAB recep-

tors in the pVTA respectively. However another study was

also supportive of an influence of aVTA GABAA receptors

on ethanol intake (Nowak et al., 1998). Despite the pVTA

selectivity for ethanol self-administration, it should be

noted that the oral ethanol intake and the locomotor effects

Table 1. Selected behavioral data on the aVTA, the pVTA and the tVTA. Abbreviations: aVTA, anterior VTA; CPA, conditioned place aversion; CPP,

conditioned place preference; FST, forced swim test; ICSA, intracranial self-administration; pVTA, posterior VTA; tVTA, tail of the VTA; VTA, ventral

tegmental area

In the aVTA In the pVTA References

Ethanol Rat Does not support ICSA Supports ICSA Rodd et al., 2000, 2004b

(2005d), Ding et al. (2014)

Supports ICSA Rodd et al. (2003, 2004a,

2005b,c), Ding et al. (2009c,

2012c)

Increases locomotor activity Sanchez-Catalan et al. (2009),

Marti-Prats et al. (2010, 2013)

Acetaldehyde Rat Does not support ICSA Supports ICSA Rodd et al. (2002, 2005d)

Increases locomotor activity Sanchez-Catalan et al. (2009)

Salsolinol Rat Does not support ICSA Supports ICSA Rodd et al. (2008)

Increases locomotor activity &

sensitization

Hipolito et al. (2010)

Supports CPP Hipolito et al. (2011)

Opioid Rat Supports weak ICSA, not CPP, & weakly

increases locomotor activity

Supports ICSA, CPP & increases

locomotor activity

Zangen et al. (2002)

Mouse Supports CPP Terashvili et al. (2004)

Cholinergic

agonists

Rat Carbachol supports weak ICSA & does not

support CPP

Carbachol & neostigmine support

ICSA, carbachol supports CPP

Ikemoto and Wise (2002)

Nicotine does not support ICSA Nicotine supports ICSA Ikemoto et al. (2006)

Nicotine & carbachol supports

ICSA

Farquhar et al. (2012)

Carbachol increases locomotor

activity

Ikemoto et al. (2003)

Cocaine Rat Does not support ICSA Supports ICSA Rodd et al. (2005a)

Mouse Supports ICSA David et al. (2004)

D9THC Rat Does not support ICSA & CPP Doesn’t

increase locomotor activity

Supports ICSA, CPP & increases

locomotor activity

Zangen et al. (2006)

AMPA Rat Supports CPA Doesn’t support CPA Ikemoto et al. (2004)

GABAA Rat Antagonists support ICSA Antagonists do not support ICSA Ikemoto et al. (1997b), Ikemoto

(2005)

Agonists do not support ICSA Agonists support ICSA Ikemoto et al. (1998)

Antagonists but not agonists increase

locomotor activity

Agonists but not antagonists

increase locomotor activity

Arnt and Scheel-Kruger (1979)

5-HT3 Rat Agonists do not support ICSA Agonists support ICSA Rodd et al. (2007)

GluR1 Rat Favors morphine CPP Favors morphine CPA Carlezon et al. (2000)

PLC! Rat Favors morphine CPP Favors morphine CPA Bolanos et al. (2003)

Increases sucrose preference Decreases sucrose preference

Increases anxiety-like behavior No effect on anxiety-like behavior

No effect on FST Decreases immobility latency in

FST

No effect on foot-shock response Increases foot-shock sensitivity

Increases morphine sensitization Does not affect morphine

sensitization

Bolanos et al. (2005)

CREB Rat Favors morphine & cocaine CPP Favors morphine & cocaine CPA Olson et al. (2005)

mCREB Favors morphine & cocaine CPA Favors morphine & cocaine CPP

tVTA & behavior

Opioid Rat Supports ICSA & CPP Jhou et al. (2012)

Activation Mouse Supports active, passive and conditioned avoidance Stamatakis and Stuber (2012),

Lammel et al. (2012)

Rat Supports CPA Jhou et al. (2013)

Inhibition (I) or

lesion (L)

Rat Suppresses cocaine-induced avoidance behavior in runway test (I, L)

Supports ICSA (I) Jhou et al. (2012)

Inhibits fear-conditioned freezing, passive response to predator odor & anxiety-

like behavior (L)

Jhou et al. (2009a)

Increases motor coordination & motor skill learning (L) Bourdy et al. (2014)

200 M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216

of ethanol may be modified by microinjections of GABA

agonists or antagonists into the aVTA (Nowak et al.,

1998; Boehm et al., 2002; Moore and Boehm, 2009).

The reinforcing properties of ethanol in the pVTA

depend on the dopaminergic system. Indeed, the

co-infusion of the D2 agonist quinpirole into the pVTA,

Fig. 1. Schematic of the behavioral action of ethanol, acetaldehyde and salsolinol in the aVTA and the pVTA. The aVTA/pVTA limit in rats is around

�5.5 mm from the bregma, which neuroanatomically corresponds to the presence of the interpeduncular nucleus below the VTA. Various receptors

can influence the behavioral consequences of the pVTA microinjections. Abbreviations: 5-HT, 5-hydroxytryptamine; aVTA, anterior ventral

tegmental area; CPP, conditioned place preference; ICSA, intracranial self-administration; IP, interpeduncular nucleus; pVTA, posterior ventral

tegmental area.

M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216 201

which would inhibit the dopamine system by stimulating

local autoreceptors (Ford, 2014), prevents the local self-

administration of ethanol (Rodd et al., 2004b, 2005d).

The self-administration can then be reinstated by the

co-infusion into the pVTA of the D2 antagonist sulpiride

(Rodd et al., 2004b). Moreover, at terminal fields, the

blockade of D1 and D2 dopamine receptors in the nucleus

accumbens shell, the ventral pallidum or the medial pre-

frontal cortex, but not in the nucleus accumbens core,

reduces the pVTA ethanol self-administration (Ding

et al., 2014). This role of the dopaminergic system is

not limited to the self-administration of ethanol into the

pVTA. Indeed, the oral intake of ethanol and ethanol

seeking behavior are both reduced by the pVTA microin-

jection of a D2 agonist (Nowak et al., 2000; Hauser et al.,

2011). Pre-treatment with the D1 antagonist SCH23390 in

the pVTA also decreases ethanol intake, but does not

alter ethanol-seeking (Czachowski et al., 2012). Interest-

ingly, while ethanol is not directly self-administered in

the aVTA, the local manipulation of the dopaminergic sys-

tem can influence some ethanol-related behaviors. Thus,

the aVTA microinjection of D2 agonists reduces ethanol

intake but not ethanol-seeking behavior (Nowak et al.,

2000; Hauser et al., 2011).

The pVTA self-administration of ethanol is also locally

influenced by other transmitter systems, including the

opioid, the 5-HT, the cholinergic (nicotinic), the

glutamatergic and the cannabinoid systems, reflecting

the complex regulation of VTA activity. The endogenous

opioid system is intimately associated with ethanol

addiction (Gianoulakis, 2009), and opioid antagonists are

even used as a treatment for alcoholism (Spanagel and

Kiefer, 2008). The intra-pVTA administration of an opioid

antagonist prevents the locomotor-activating effects of

intra-pVTA ethanol in rats (Sanchez-Catalan et al.,

2009), and decreases ethanol-induced conditioned place

preference in mice (Bechtholt and Cunningham, 2005).

Various intra-pVTA 5-HT3 antagonists can also reduce

the pVTA ethanol self-administration (Rodd-Henricks

et al., 2003; Rodd et al., 2005d), the pVTA self-administra-

tion of a mixture of ethanol and cocaine (Ding et al., 2012c)

and the oral self-administration of ethanol (Rodd et al.,

2010), while the 5-HT3 antagonists had no effect on oral

ethanol self-administration when delivered into the aVTA

(Rodd et al., 2010). In fact, rats will even self-administer

a 5-HT3 agonist in the pVTA but not in the aVTA (Rodd

et al., 2007). The pVTA ethanol self-administration is also

attenuated by the co-infusion of a 5HT2A antagonist

(R96544), but not by a 5HT1B antagonist (GR55562)

(Ding et al., 2009c). An intra-pVTA microinjection of nico-

tine can favor ethanol seeking, which is prevented by a

nicotinic (mecamylamine) or 5-HT3 receptor antagonist

(zacopride) (Hauser et al., 2014). An intra-pVTA adminis-

tration of the glutamate antagonist CNQX (6-cyano-7-

nitroquinoxaline-2,3-dione) also reduces ethanol-seeking,

but without affecting ethanol intake (Czachowski et al.,

2012). Last, the local cannabinoid system also influences

ethanol action, since the administration of a CB1 agonist

(WIN 55–212) into the pVTA, but not into the aVTA, alters

the time-course of binge-like ethanol intake in mice

(Linsenbardt and Boehm, 2009). These various interac-

tions may also participate in a cross-vulnerability between

alcohol and other drugs of abuse.

In addition, the hyperpolarization-activated cyclic

nucleotide–gated (HCN) ion channels have also been

proposed as a molecular target of ethanol (Brodie and

Appel, 1998; Okamoto et al., 2006), and their overexpres-

sion in the pVTA increases voluntary ethanol intake in rats

(Rivera-Meza et al., 2014).

From ethanol to acetaldehyde and salsolinol. Signifi-

cant evidence implicates the first metabolite of ethanol,

acetaldehyde, in the mechanisms underlying the

psychopharmacological effects of ethanol (Correa et al.,

2012). In fact, it has been demonstrated that acetalde-

hyde has rewarding properties per se (Correa et al.,

2012). The relevance of the role of acetaldehyde in the

VTA is further supported by the local presence of the

enzymatic machinery necessary to metabolize ethanol

(Moreno et al., 1995; Sanchez-Catalan et al., 2008).

Rats self-administer acetaldehyde into the pVTA

(Fig. 1) but not the aVTA, and the co-administration of

the D2/3 agonist quinpirole is able to block this intra-

pVTA acetaldehyde self-administration (Rodd-Henricks

et al., 2002; Rodd et al., 2005d). Acetaldehyde microin-

jection into the pVTA also increases locomotor activity

202 M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216

in rats, which is prevented by an intra-pVTA pre-treatment

with a l-opioid receptor antagonist (Sanchez-Catalan

et al., 2009). The critical role of acetaldehyde in pVTA eth-

anol action is demonstrated by the pharmacological use

of an acetaldehyde sequestering agent, D-penicillamine.

Indeed, the locomotor activity induced by an intra-pVTA

ethanol administration can be reduced by D-penicillamine

(Marti-Prats et al., 2010). Moreover, a low dose of intra-

pVTA ethanol can even induce motor depressant action

after pre-treatment with D-penicillamine or with sodium

azide, a catalase inhibitor blocking the transformation of

ethanol into acetaldehyde. Interestingly, this depressant

effect can be prevented by the local microinjection of

the GABAA antagonist bicuculline (Marti-Prats et al.,

2013). Similarly, pre-treatment with the aldehyde dehy-

drogenase inhibitor cyanamide, which reduces the acetal-

dehyde degradation, stimulates motor activity in response

to the intra-pVTA administration of a normally non-

effective dose of ethanol (Marti-Prats et al., 2013). These

studies suggest that acetaldehyde is involved in the

activating effects of ethanol in the pVTA, while the non-

metabolized ethanol would display a motor depressant

action through GABAA receptors (Marti-Prats et al.,

2013). The use of sequestering-agents of acetaldehyde

proves to be a useful pharmacological tool to assess the

role of this metabolite in ethanol effects. The recent dem-

onstration that the intra-pVTA administration of D-penicil-

lamine can block relapse in a preclinical model of alcohol

deprivation (Orrico et al., 2013) also suggests a therapeu-

tic potential for these compounds.

The acetaldehyde is also a highly reactive compound.

In the presence of dopamine, a condensation reaction

leads to the production of salsolinol (1-methyl-6,7-

dihidroxy-1,2,3,4-tetrahydroisoquinoline) (Fig. 1), which

has been implicated in some of the neurobiological

effects of ethanol (Hipolito et al., 2012). Thus, a salsolinol

microinjection into the pVTA is sufficient to increase the

locomotor activity of rats in a dose-dependent manner,

this action being blocked by an intra-pVTA pre-treatment

with the opioid antagonist naltrexone or with the selective

l-opioid antagonist b-funaltrexamine (Hipolito et al.,

2010). When repeated, the intra-pVTA administration of

salsolinol leads to locomotor sensitization (Hipolito et al.,

2010) and induces conditioned place preference

(Hipolito et al., 2011). Furthermore, rats self-administer

salsolinol directly into the pVTA, but not into the aVTA,

this self-administration being impaired by pre-treatment

with the D2 agonist quinpirole or the 5-HT3 antagonist

ICS205–930 (Rodd et al., 2008). The reinforcing proper-

ties of salsolinol are thus similar to those of acetaldehyde

and of ethanol itself but they can be seen at much lower

doses (Rodd-Henricks et al., 2000, 2002, 2003; Rodd

et al., 2004b, 2005d; Sanchez-Catalan et al., 2009), high-

lighting salsolinol as an important and likely candidate to

mediate the neurobiological effects of ethanol. (Table 1)

Neurochemical studies. While there is agreement that

ethanol administration into the aVTA does not influence

dopamine levels in the nucleus accumbens (Ericson

et al., 2008) (more specifically in the nucleus accumbens

shell (Ding et al., 2009b)), there are discrepancies

concerning the consequences of pVTA administration,

some authors observing increased dopamine levels in

the nucleus accumbens shell (Melis et al., 2007; Ding

et al., 2009b), whereas others did not observe changes

when sampling the transition zone between the core

and the shell (Ericson et al., 2008). The ethanol injection

into the pVTA but not the aVTA was also proposed to

increase extracellular dopamine levels in the ventral palli-

dum and in the medial prefrontal cortex (Ding et al.,

2011). When repeated, the infusion of ethanol into the

pVTA sensitizes the dopaminergic response, further

increasing extracellular dopamine levels in the nucleus

accumbens shell (Ding et al., 2009b); and cross-sensitiza-

tion between drugs of abuse can also be observed, as

repeated pVTA administration of nicotine increases the

effect of a pVTA ethanol administration on the nucleus

accumbens shell dopamine levels (Ding et al., 2012b).

In line with an interaction between ethanol action and

the cholinergic system, the antagonism of nicotinic recep-

tors by mecamylamine in the aVTA blocks the dopamine

level increase in the nucleus accumbens after intra-

accumbens ethanol perfusion (Ericson et al., 2008).

Interestingly, acetaldehyde and salsolinol

administered into the pVTA increase the extracellular

dopamine levels in the nucleus accumbens shell (Melis

et al., 2007; Hipolito et al., 2011; Deehan et al., 2013), sup-

porting the idea that the properties of these compounds are

similar to the ones of ethanol. The stimulation of the dopa-

minergic transmission by an intra-pVTA salsolinol adminis-

tration can be blocked by the pVTA pre-treatment with the

l-opioid antagonist b-funaltrexamine, which parallels the

behavioral action of salsolinol (Hipolito et al., 2011).

The pVTA dopamine levels are also associated with

spontaneous preference for alcohol. Indeed, the basal

pVTA dopamine levels are lower in a strain of alcohol-

preferring rats compared to their Wistar controls (Liu

et al., 2006). However, when exposed to alcohol drinking,

the alcohol preferring rats display increased basal pVTA

dopamine levels (Engleman et al., 2011). This could sug-

gest that the alcohol intake in these rats may be driven by

compensatory mechanisms in order to reach a higher

steady-state of dopaminergic activity. Such a hypothesis

is attractive and would be in agreement with a ‘‘self-med-

ication’’ hypothesis, suggesting that alcohol helps these

animals reach an optimized ‘‘hedonic set-point’’. Explor-

ing this hypothesis will require further research.

Finally, ethanol may not only recruit the dopamine

system. Acute and repeated systemic ethanol

administration as well as chronic ethanol drinking

increases the extracellular levels of glutamate in the

pVTA (Ding et al., 2012a, 2013).

Electrophysiological studies. Despite behavioral

evidence, electrophysiological studies do not usually

differentiate between the anterior and the pVTA

dopamine neurons. Some recent studies, however,

assessed the effects of ethanol and its derivates on

dopamine neurons of the aVTA and the pVTA. These

dopamine neurons have similar electrophysiological

features, although different responses to ethanol (Guan

et al., 2012). In ex vivo brain slices, ethanol inhibits the

M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216 203

dopamine neurons of the aVTA whereas it stimulates the

ones of the pVTA (Melis et al., 2007, 2013; Guan et al.,

2012). This latter effect is due to a reduction of the GAB-

Aergic influence on pVTA dopamine neurons (Guan et al.,

2012), which thus favors the disinhibition of dopamine

cells (Johnson and North, 1992). Likewise, voluntary eth-

anol intake increases the number of active dopamine neu-

rons in the pVTA of alcohol-preferring rats (Morzorati

et al., 2010). As this action of alcohol is associated with

a reduced pVTA sensitivity of N-methyl-D-aspartate

(NMDA) receptors in the pVTA, it is more likely due to a

disinhibitory mechanism rather than to the recruitment of

excitatory inputs (Fitzgerald et al., 2012).

Behavioral and neurochemical studies have shown

that acetaldehyde and salsolinol have stimulating

properties into the pVTA (Rodd-Henricks et al., 2002;

Rodd et al., 2008; Sanchez-Catalan et al., 2009; Hipolito

et al., 2010, 2011). Accordingly, it has been observed that

they enhance the activity of the pVTA dopamine neurons

(Melis et al., 2007; Xie et al., 2012; Xie and Ye, 2012).

Moreover, the acetaldehyde derived from ethanol has

been proposed to be responsible for the activating effect

of ethanol on dopamine cells (Melis et al., 2013). Salsolin-

ol was proposed to enhance dopamine activity through an

opioid-dependent mechanism (Xie et al., 2012), however

an action on VTA glutamate inputs was also suggested

(Xie and Ye, 2012).

Opioids

Opioids have both dopamine-dependent and dopamine-

independent activating and rewarding properties. In the

Fig. 2. Schematic of the manipulations of the aVTA and the pVTA sustaini

preference (CPP) and stimulating locomotor activity (activity), local elec

consequences of viral-mediated local expression of GluR1, PLCc, CREB an

bregma, which neuroanatomically corresponds to the presence of the

hydroxytryptamine; aVTA, anterior ventral tegmental area; CPA, conditioned

test; IP, interpeduncular nucleus; pVTA, posterior ventral tegmental area.

VTA, the opioids can recruit dopamine cells through a

disinhibitory mechanism (Johnson and North, 1992;

Jalabert et al., 2011). While some authors observed no

significant correlation between the VTA antero-posterior

placement of morphine injection and the resulting place

conditioning (De Jaeger et al., 2013), data from other

groups support the idea that opioids can have different

behavioral consequences depending on the antero-

posterior level within the VTA (Zangen et al., 2002;

Jhou et al., 2012). Indeed, endomorphin-1 (EM-1) induces

intracranial self-administration, conditioned place prefer-

ence and increases locomotor activity when administered

into the pVTA (Zangen et al., 2002; Terashvili et al., 2004)

(Fig. 2, Table 1), whereas it displays weaker intracranial

self-administration and stimulating effects and fails to

induce conditioned place preference when delivered into

the aVTA (Zangen et al., 2002).

Similar to ethanol studies, this aVTA/pVTA dichotomy

associated with local microinjections does not mean that

the aVTA cannot influence systemic drug response.

Indeed the reversible inactivation of the aVTA by

lidocaine decreases morphine-induced conditioned place

preference (Moaddab et al., 2009). Moreover, the inacti-

vation of the aVTA, but not of the pVTA, by GABA ago-

nists impairs heroin-conditioned immunomodulation

(Hutson et al., 2014). Last, the inactivation of AMPA

receptors by CNQX delivery into the aVTA blocks the

morphine-induced place conditioning and the heroin

self-administration, although it does not modulate those

behaviors (but it modulates the motor-activating effects)

when the AMPA antagonist is administered into the pVTA

(Shabat-Simon et al., 2008).

ng intracranial self-administration (ICSA), inducing conditioned place

trophysiological response of dopamine cells (DA), and behavioral

d mCREB. The aVTA/pVTA limit in rats is around �5.5 mm from the

interpeduncular nucleus below the VTA. Abbreviations: 5-HT, 5-

place aversion; D9THC, D9tetrahydrocannabinol; FST, forced swim

204 M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216

A set of studies using viral vector-mediated expression

of various proteins in the aVTAor in the pVTAare important

to mention here. Thus, the overexpression of the GluR1

subunit of the AMPA receptor (Carlezon et al., 2000), of

the phospholipase Cc (PLCc) which is implicated in the

intracellular cascade activated by neurotrophic factors

(Bolanos et al., 2003) or of the transcription factor cAMP

response element binding protein (CREB) (Olson et al.,

2005)modulates in oppositeways the rewarding properties

of a low dose of morphine depending whether this overex-

pression is performed in the aVTA or in the pVTA. When

GluR1, PLCc or CREB are overexpressed in the aVTA,

the rewarding properties ofmorphine as evaluated by place

conditioning are enhanced, while the same dose of mor-

phine becomes aversive if these proteins are overexpres-

sed in the pVTA (Carlezon et al., 2000; Bolanos et al.,

2003; Olson et al., 2005). These data are further reinforced

by the fact that the aVTA or the pVTA overexpression of

mCREB, a dominant negative form of CREB acting as an

antagonist, leads to consequences that are opposite to

the ones of CREB overexpression (Olson et al., 2005),

i.e. an aversion to a low dose of morphine if overexpressed

in aVTA and an enhancement of morphine reward if over-

expressed in the pVTA. The opposite action of the aVTA

and the pVTA manipulations on morphine place condition-

ing was particularly striking after the PLCc overexpression

(Bolanos et al., 2003); furthermore, the PLCc overexpres-

sion in the aVTA, but not in the pVTA, also enhanced

morphine-induced locomotor sensitization (Bolanos et al.,

2005). As neurotrophic factors in the VTA have been

related to the effects of drug of abuse (Nikulina et al.,

2014), the PLCc data suggest that the action of neurotro-

phic factors might also depend on the considered antero-

posterior level within the VTA.

Cholinergic system

The cholinergic system is a key modulator of the VTA

dopamine cells (Faure et al., 2014), but the behavioral

effect of cholinergic agents may vary depending on the

VTA subregions. Thus, nicotine, the cholinergic agonist

carbachol and the acetylcholinesterase inhibitor neostig-

mine support intracranial self-administration in the pVTA

of rats (Ikemoto and Wise, 2002; Ikemoto et al., 2003,

2006; Farquhar et al., 2012) (Fig. 2, Table 1), whereas

the intracranial self-administration of carbachol is weaker

(Ikemoto and Wise, 2002) and the intracranial self-admin-

istration of nicotine does not occur (Ikemoto et al., 2006)

into the aVTA.

The pVTA self-administration of carbachol is

prevented by a muscarinic (scopolamine), a nicotinic

(dihydro-b-erythroidine) or a D1 receptor (SCH23390)

antagonist (Ikemoto and Wise, 2002), and the pVTA

self-administration of nicotine by a nicotinic antagonist

(mecamylamine) and a D2 agonist (quinpirole) (Ikemoto

et al., 2006). Furthermore, the administration of carbachol

into the pVTA also induces locomotor activity, conditioned

place preference and c-Fos expression in several brain

regions (Ikemoto and Wise, 2002; Ikemoto et al., 2003;

Schifirnet et al., 2014). Some discrepancies are however

present concerning the ability of carbachol to induce con-

ditioned place preference into the aVTA (Ikemoto and

Wise, 2002; Schifirnet et al., 2014), which may be related

to the definition of ‘‘aVTA’’. Indeed, a recent study pro-

posed the presence of an aVTA (supporting carbachol

conditioned place preference), a mid-VTA (lacking such

conditioned response) and a pVTA (supporting carbachol

conditioned place preference) along the VTA antero-pos-

terior axis (Schifirnet et al., 2014). However, it may be dif-

ficult to discriminate aVTA from lateral hypothalamus

effects with very rostral injection sites.

The microinjection of a mGlu2/3 receptor agonist

(LY379268) or mGlu5 receptor antagonist (2-methyl-6-

(phenylethynyl)pyridine, MPEP) into the pVTA

decreases nicotine intravenous self-administration in

Wistar rats (Liechti et al., 2007; D’Souza and Markou,

2011), further highlighting the role of the pVTA in the rein-

forcing properties of nicotine.

Ex vivo electrophysiological studies have also

suggested that nicotine preferentially activates

dopamine neurons of the pVTA, whereas nicotine effect

is weaker on neurons from the aVTA, which is likely due

to a different expression of nicotinic receptors (Li et al.,

2011; Zhao-Shea et al., 2011).

Overall, these studies provide evidence of an

activating effect of cholinergic agonists in the VTA, and

most importantly within the pVTA.

Cocaine

Rodents self-administer cocaine into the pVTA (David

et al., 2004; Rodd et al., 2005a) (Fig. 2, Table 1), but

not in the aVTA (Rodd et al., 2005a). This pVTA self-

administration of cocaine can be blocked by systemic

pre-treatment with a D1 (SCH23390) or a 5HT1B

(GR127935) antagonist, by the co-infusion of a 5HT3

(ICS205–930) antagonist, or by the co-infusion of the

D2/3 agonist quinpirole (David et al., 2004; Rodd et al.,

2005a).

While the pVTA preferentially supports intracranial

cocaine self-administration, both the aVTA and the

pVTA can influence systemic cocaine effects. For

example, the inhibition of the aVTA (but not of the

pVTA) by muscimol increases the motivation for cocaine

intake (as shown by higher breaking-point in self-

administration), and also decreases the number of

cocaine self-infusions under a FR1 fixed ratio,

suggesting an enhanced rewarding effect of cocaine

(Lee et al., 2007). Moreover, cocaine place conditioning

can also be suppressed by the microinjection of a

l-opioid agonist into the aVTA, but not into the pVTA,

while microinjections into the pVTA, but not the aVTA,

suppress cocaine-induced locomotor activity (Soderman

and Unterwald, 2008). These data could suggest a possi-

ble dissociation between the pathways underlying the

rewarding and the locomotor effects of cocaine. However,

the dopaminergic lesion of the medial pVTA (sparing the

parabrachial pigmented nucleus of the VTA) (Ouachikh

et al., 2013), but not of the aVTA (Ouachikh et al.,

2014), impairs cocaine-induced conditioned place prefer-

ence. The respective roles of the aVTA and the pVTA in

cocaine responses are thus complex, which may also

reflect the complexity of the feed-forward and feed-back

circuitry of the ventral tegmentum and basal ganglia.

M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216 205

Similarly to morphine place conditioning, the aVTA

and the pVTA manipulations of the transcription factor

CREB have opposite actions on cocaine place

conditioning (Olson et al., 2005). A viral-mediated overex-

pression of CREB in the rat aVTA favors place preference

for a threshold dose of cocaine, while the same dose

becomes aversive if CREB is overexpressed in the pVTA;

and these effects are mirrored after the expression of the

dominant negative mCREB (Olson et al., 2005). This

study was particularly important as it also searched for

the limit between the aVTA and the pVTA in rats. For this,

the viral vectors for CREB or mCREB expression were

injected at different antero-posterior levels within the

VTA, and the response to cocaine was tested in the place

conditioning paradigm. An inflexion point was observed

between the rewarding and aversive effects of cocaine,

around �5.5 mm from the bregma, which neuroanatomi-

cally correspond to the location of the interpeduncular

nucleus below the VTA. This transition point is similar to

the one that was more recently observed between the

lack or presence of conditioned place preference after

intra-VTA carbachol administration (Schifirnet et al.,

2014).

Other drugs

An opposite modulation of brain stimulation reward has

been observed after blocking NMDA and AMPA

receptors in the VTA. The changes in reward threshold

positively correlated with the VTA antero-posterior

position of a NMDA antagonist injection, while it

negatively correlated with the antero-posterior position

of an AMPA antagonist injection (Ducrot et al., 2013).

The influence of AMPA antagonism was thus stronger in

the aVTA. Interestingly, intra-aVTA infusions of AMPA

itself were also reported to induce conditioned place

avoidance, while intra-pVTA AMPA infusions had no

effect (Ikemoto et al., 2004).

D9tetrahydrocannabinol can induce locomotor activity

and conditioned place preference and can support

intracranial self-administration when delivered into the

pVTA but not into the aVTA (Zangen et al., 2006)

(Table 1).

Affect and pain

Recent attention has been given to the heterogeneity of

the VTA cells (Roeper, 2013; Morales and Root, 2014)

and of the projection pathways originating from the VTA

(Lammel et al., 2014; Walsh and Han, 2014), particularly

concerning reward, aversion and depression. Similarly,

the aVTA/pVTA differences are not limited to the effect

of rewarding or locomotor activating substances (Figs. 1

and 2, Table 1). For example, the overexpression of

PLCc in the aVTA, but not in the pVTA, increased the

anxiety-like behavior in an elevated plus-maze, while the

pVTA overexpression, but not the aVTA one, decreased

the latency to immobility in the forced swim test

(Bolanos et al., 2003). These data partially dissociated

the influence on anxiety and depression-related behav-

iors, which may be further supported by the fact that the

aVTA overexpression of PLCc increased sucrose

preference, while the overexpression in the pVTA blunted

it. These findings should also be considered in the context

of VTA neurotrophic factors and mood disorders (Nikulina

et al., 2014; Walsh and Han, 2014), as PLCc participates

to the intracellular signaling cascade activated by these

factors.

Last, some data also report differences in the control

of pain-related responses along the antero-posterior

extent of the VTA. Thus, pVTA PLCc overexpression in

rats lowered the foot-shock thresholds inducing a jump

response, while an aVTA overexpression did not affect it

(Bolanos et al., 2003). Experiments on tail shocks’ thresh-

olds inducing vocalizations also showed aVTA/pVTA dif-

ferences in the control of such responses. The

microinjection of the cholinergic agonist carbachol into

the pVTA strongly increased the shock intensity neces-

sary to elicit a vocalization (Schifirnet et al., 2014), which

was prevented by either nicotinic (mecamylamine) or

muscarinic (atropine) antagonists. No influence was

observed at more anterior levels (designed in this article

as ‘‘midVTA’’), and an increase in the shock intensity elic-

iting vocalization was again observed more rostrally

(designed in this article as ‘‘aVTA’’) but in this case only

mecamylamine prevented it.

NEUROANATOMY OF THE VTA

All the behavioral findings reported above provide

convincing evidences for the functional antero-posterior

heterogeneity of the VTA. This raises the question of

the morphofunctional substrate of such heterogeneity.

Among the parameters to consider, the neuroanatomy

of the VTA (for review: (Yetnikoff et al., 2014)) is a critical

one.

Definition of the VTA

The first occurrence of the VTA in the literature is due to

Tsai in 1925 (Tsai, 1925). In its description of the opos-

sum brain, he identified with Nissl and Golgi staining a

region lateral to the interpeduncular nucleus as the trigo-

num interpeduncular. This region included the mamillary

peduncle, the medial lemniscus and the nucleus tegmenti

ventralis (presently VTA). This latter nucleus constituted

the medial part of the trigonum interpeduncular and it

spanned from the cerebral peduncle to the ventral tip of

the substantia nigra.

Before Tsai’s study, the fusiform aspect of the cells of

the nucleus tegmenti ventralis had led it to be considered

as a part of the substantia nigra (Kosaka and Hiraiwa,

1915; Castaldi, 1923). Accordingly, it has also been des-

ignated as the nucleus niger suboculomotorius (Hassler,

1937). However, the small size of the cells as well as

the close proximity to the mamillo- and the olfacto-

tegmentalis tracti suggested specific anatomical and

functional features for the nucleus tegmenti ventralis;

but whether the nucleus tegmentis ventralis belonged or

not to the substantia nigra remained an issue that was

long discussed. This debate was also due to the cytoar-

chitectonic heterogeneity of the region, and to the diffi-

culty to clearly differentiate it from the substantia nigra

compact part in primates as compared to rodents. In the

-4.80 mm

Rfr

SuMM

scpmlcp

aVTA

SNL

SNC

SNRmpPBP

206 M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216

fifties, Nauta’s work confirmed Tsai conclusions, by show-

ing that some brain structures, such as the lateral hypo-

thalamus, project to the VTA but not to the substantia

nigra. The ‘‘ventral tegmental area of Tsai’’ was then men-

tioned for the first time by Nauta in 1958 (Nauta, 1958)

(For historical review see: (Oades and Halliday, 1987)).

-5.30 mm

-5.80 mm

-6.30 mm

-6.80 mm

scp

aoptIF

RLi

PN

R

PBP

mlcp

mp

aVTA

SNR

SNC

SNL

Rscp

ml

cp IP

pVTA PBP

PN

IF

RLiCLi

mp

SNR

SNC

SNL

RRF

tVTA

Rscp

SNRSNC

mlcp

pn

PNIPIF

pVTA PBP

RLiCLi

tVTA

IP

pn

RRFxscp

PPTgtth

ml

MM

The VTA and the A10 dopamine cell group

Dopamine was detected in the central nervous system at

the end of the fifties (Montagu, 1957; Wei-Malherbe and

Bone, 1957), then in neurons in 1962 (Carlsson et al.,

1962). This led to the classification, on a neurochemical

basis, of 12 catecholaminergic cell groups in the brain

(Dahlstrom and Fuxe, 1964).

However, the cytoarchitectonic frontiers of brain

structures do not always fit with neurochemically

identified cell groups. In Dahlstrom and Fuxe definition

(Dahlstrom and Fuxe, 1964), areas A1–A7 correspond

to noradrenergic regions and areas A8–A12 to dopami-

nergic regions, with five additional dopaminergic regions

later identified (A13–A17). Even though dopamine cells

form an uninterrupted continuum through the midbrain,

three groups were locally defined: A8 associated with

the retrorubral field, A9 with the substantia nigra compact

part, and A10 with the VTA. The A10 group was distin-

guished from the two others based on specific inputs,

notably described by Nauta (for review: (Ikemoto,

2007)). The connectivity thus influenced the definition of

mesencephalic cell groups, and the terms VTA and A10

were often synonymous in the literature; even though

the A10 group stricto sensu is only composed of the dopa-

mine cells of the VTA. In the eighties, it was proposed to

extend the definition of the A10 group (Hokfelt et al.,

1984), by including in it the dopamine neurons of the ret-

rorubral nucleus, of the lateral hypothalamus, of the dor-

sal raphe and of the periaqueductal gray. While some

continuity may be observed between these cell groups,

this distinction which further separated the notion of

VTA from the A10 group was not followed and is not pres-

ently used.

parabrachial pigmented n.

paranigral n.

interfascicular n.

rostral and caudal linear n.

tail of the ventral tegmental area

Fig. 3. Schematic of the organization of the rat VTA. The five

subdivisions of the VTA, as firstly described by Phillipson (1979a,b,c),

are shown on frontal plates of the rat brainstem modified from rat

brain atlases, from the aVTA (top) to the pVTA (bottom). The recently

defined tVTA is also presented. The anteroposterior distance from the

Bregma is indicated above each plate. The aVTA/pVTA limit in rats is

around �5.5 mm from the bregma, which neuroanatomically corre-

sponds to the presence of the interpeduncular nucleus below the

VTA. Abbreviations: aopt, accessory optic tract; aVTA, anterior VTA;

CLi, caudal linear nucleus; cp: cerebral peduncle; fr, fasciculus

retroflexus; IF, interfascicular nucleus; IP, interpeduncular nucleus;

ml, medial lemniscus; MM, medial mammillary nucleus; mp, mam-

millary peduncle; PBP, parabrachial pigmented nucleus; pn, pontine

nuclei; PN, paranigral nucleus; PPTg: pedunculopontine tegmental

nucleus; pVTA, posterior VTA; R, red nucleus; RLi, rostral linear

nucleus; RRF, retrorubral field; scp, superior cerebellar peduncle;

SNC, substantia nigra, compact part; SNL, substantia nigra, lateral

part; SNR, substantia nigra, reticular part; SuMM, supramammillary

nucleus, medial part; tth, trigeminothalamic tract; tVTA, tail of the

VTA; xscp, decussation of the scp; VTA, ventral tegmental area.

Cytoarchitectonic subdivisions of the VTA

The subdivisions of the VTA were defined on

neuroanatomical and functional basis. Historically, the

first subdivisions were cytoarchitectonic, based on the

heterogeneity of the morphology and orientation of cells

bodies of the VTA and of their neuritis. Functional

distinctions were observed more recently.

Three studies published in 1979 divided the VTA of

Tsai in five nuclei (Phillipson, 1979a,b,c) (Fig. 3). Using

Golgi staining, two lateral nuclei were identified: the para-

nigral nucleus and the parabrachial pigmentosus nucleus

(presently parabrachial pigmented nucleus), which are

rich in dopamine cells. These nuclei are present over a

large part of the rostrocaudal extent of the VTA. The para-

nigral nucleus is in a zone just above the anterolateral part

of the interpeduncular nucleus, and it is mostly composed

of fusiform, medium-sized cell bodies and of smaller cells

with few spiny dendrites. The limits of the parabrachial

pigmented nucleus are more difficult to define as this

M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216 207

subregion of the VTA is found dorsally and/or dorsolater-

ally to the paranigral nucleus depending on the antero-

posterior level. It also constitutes the lateral limit between

the VTA and the substantia nigra. One of the types of cell

bodies is in fact similar to the fusiform neurons found on

the dorsal tiers of the substantia nigra compact part.

Other neurons of the parabrachial pigmented nucleus

have a medium-sized globular cell body with numerous

radial dendrites. Three median nuclei have been pro-

posed in the VTA: the interfascicular, the rostral linear

and the caudal linear nuclei. The interfascicular nucleus

extends over the whole antero-posterior extent of the

VTA and it is composed of round and densely packed

cells, smaller than in the rest of the VTA. Overlying it in

its anterior part is the rostral linear nucleus, containing

the largest cells of the VTA, and in its posterior part, the

caudal linear nucleus.

This architectonic parcellation of the VTA into five sub-

regions still remains valid, but other subdivisions have

also been proposed (for review of VTA subdivisions,

see: (Halliday and Tork, 1986; Oades and Halliday,

1987; Fallon and Loughlin, 1995; Ikemoto, 2007)). In this

context, the recent work from Ikemoto is particularly sig-

nificant. Based solely on the cytoarchitectonic dimension

of the VTA, four lateral nuclei were proposed (Ikemoto,

2007). These include the classical paranigral nucleus

and parabrachial pigmented nucleus, rich in dopamine

cells (Phillipson, 1979a,b,c; Halliday and Tork, 1986;

Oades and Halliday, 1987), as well as two additional

nuclei: the parafascicular retroflexus area, and the tVTA

(Perrotti et al., 2005; Kaufling et al., 2009; Jhou et al.,

2009b). In this latter case, only the rostral third of what

is now known as the tVTA/RMTg was really described.

The parafascicular retroflexus area is the most anterior

part of the VTA, with a low density of dopamine cells, con-

tinuous with those of the lateral hypothalamus and of the

supramamillary nucleus. This area is thus composed of

the most anterior part of the paranigral nucleus and of

the parabrachial pigmented nucleus. These two nuclei

are indeed difficult to differentiate at this anterior level,

while they are clearly distinguished in the mid third of

the VTA. Then, in the posterior part of the VTA, another

group of cells localized dorsolaterally to the interpeduncu-

lar nucleus can be seen, based on a Nissl staining. This

region was previously included in the paranigral nucleus,

but data from the last decade converge to designate it as

a distinct region: the tVTA or RMTg (Perrotti et al., 2005;

Kaufling et al., 2009; Jhou et al., 2009a,b; Bourdy and

Barrot, 2012).

This recent analysis of VTA subregions (Ikemoto,

2007) also highlights a classical problem in the definition

of the VTA: do the median nuclei (the interfascicular,

the rostral linear and the caudal linear nuclei) really

belong to the VTA or should they be associated with other

structures such as the raphe nuclei? Different authors

(Swanson, 1982; Kalivas, 1993; Ikemoto, 2007) would

consider that these three median nuclei are not part of

the VTA. Thus, while the VTA and the A10 dopamine

group are often used as synonyms, the VTA would only

include the lateral nuclei (the paranigral nucleus and the

parabrachial pigmented nucleus), while the A10 group of

cell would also include the three median nuclei (Kalivas,

1993). Ikemoto also designated the rostral linear nucleus

and the caudal linear nucleus as raphe nuclei, which is

also the case since the 4th edition (1998) of the Paxinos

and Watson atlas of the rat brain (Paxinos and Watson,

1998, 2007). Last, it is to be noted that in the recent ver-

sions of the rat and of the mouse brain atlases (Paxinos

and Watson, 2007; Franklin and Paxinos, 2008) a parain-

terfascicular nucleus has also been identified in the mid to

posterior third of the VTA. The parainterfascicular nucleus

is wedged between the paranigral nucleus and the par-

abrachial pigmented nucleus. This name has then been

reused by different groups (over 35 references can be

presently retrieved under Google Scholar) in rats

(Colussi-Mas and Schenk, 2008; Nair-Roberts et al.,

2008; Wang and Morales, 2008; Brischoux et al., 2009;

Zhang et al., 2014) and in other species (Reyes et al.,

2012; Cavalcanti et al., 2014; Schweimer et al., 2014).

Accordingly, a recent cytoarchitectonic and chemoarchi-

tectonic reanalysis of the mouse midbrain dopamine cell

groups has been done (Fu et al., 2012).

Despite the obvious existence of different anatomical

subdivisions within the VTA, the question and the study

of their respective functions has not yet really been

addressed. This is likely due to the difficulty in

selectively manipulating these groups of cells, due to

their relatively small size, proximity and mostly shared

neurochemistry. Recent progress has allowed the study

of selected VTA cell populations based on their

neurochemistry and/or connectivity (for example

mesolimbic vs. mesocortical) (Roeper, 2013; Lammel

et al., 2014; Walsh and Han, 2014), leading to major sci-

entific advances. However, these studies did not differen-

tiate yet between VTA subnuclei. The search for specific

molecular markers of these sub-regions would allow

major progress in the field, by making possible to perform

promoter-driven selective targeting of VTA subregions.

BASES FOR THE aVTA/pVTA DIFFERENCES

The aVTA and the pVTA cannot be considered as

separate brain structures per se. The functional

differences that exist between them are thus likely to be

based on the preferential targeting of different VTA

subnuclei (see above), on differences in connectivity, on

differences in the proportion of the various cell types

(dopamine, GABA, glutamate, neuropeptides. . .), and on

the differential expression of membrane receptors and

channels.

Different afferents and/or efferents for the aVTA and

the pVTA are likely to contribute to the functional

differences. The inputs/outputs of the VTA are well

described (Yetnikoff et al., 2014), even though detailed

differences between VTA subnuclei or along the VTA

antero-posterior axis are yet to be completed. A widely

studied projection of the VTA dopamine cells is the ventral

striatum, with the nucleus accumbens constituting the

densest efferent target of VTA cells. This VTA-ventral stri-

atum projection displays a preferential, but not exclusive,

posteromedio-anterolateral topography (Phillipson and

Griffiths, 1985; Heimer et al., 1991; Berendse et al.,

208 M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216

1992; Haber and Fudge, 1997; Haber et al., 2000; Hasue

and Shammah-Lagnado, 2002; Ikemoto, 2007, 2010) that

could partly explain why the pVTA is a preferential sub-

strate for the intracranial self-administration of various

substances. The aVTA and lateral portions of the VTA

preferentially innervates the lateral part of the ventral stri-

atum, formed by the lateral olfactory tubercle and the lat-

eral parts of the shell and of the core of the nucleus

accumbens, whereas the pVTA and the medial portions

of the VTA preferentially projects to the medial part of

the ventral striatum, formed by the medial olfactory tuber-

cle and the medial shell of the nucleus accumbens

(Ungerstedt, 1971; Heimer et al., 1991, 1997; Berendse

et al., 1992; Usuda et al., 1998; Hasue and Shammah-

Lagnado, 2002; Zhou et al., 2003; Ikemoto, 2007,

2010). In the mouse, the antero-posterior analysis of the

VTA dopamine cells projecting to various forebrain

regions also showed a lack of projection from the cau-

dal-most part of the VTA to the lateral shell (Lammel

et al., 2008). A topographical organization is also

observed for the VTA projections to the dorsal striatum,

which mostly arise in the lateral part of the VTA and pref-

erentially the lateral aVTA (Ikemoto, 2007). Similarly, the

striato-pallidal projections to the VTA also display a topo-

graphical organization, with an antero-posterior gradient

and an inverted dorso-lateral gradient (for review see:

(Yetnikoff et al., 2014)). The relation between the VTA

and the prefrontal cortex still deserves a more detailed

analysis. The meso-accumbens and meso-cortical

pathways are mostly segregated (Deniau et al., 1980;

Fallon, 1981; Lammel et al., 2008). In the rat, meso-corti-

cal cells are distributed throughout the VTA (Deniau et al.,

1980), but non-dopamine meso-cortical cells (TH-nega-

tive projecting to the cingulate cortex) appear to be more

frequently observed in the aVTA (Swanson, 1982). In the

mouse, dopamine meso-cortical projections to the prelim-

bic and infralimbic cortices preferentially arise from the

medial pVTA, and non-dopamine ones from the aVTA

and from cells in the caudal-most part of the VTA (see

supplemental data in Lammel et al., 2008). The neuro-

chemical nature of VTA cell types may thus be important

to consider. Moreover, it would be useful to determine

whether the prelimbic, infralimbic and cingulate compo-

nents of the meso-cortical projections arise or not from

the same cells, and/or display a topographical organiza-

tion within the VTA. Differences in the serotonergic

(Herve et al., 1987) inputs have also been proposed, as

well as for cholinergic inputs from the laterodorsal teg-

mental nucleus that differently target meso-accumbens

and meso-cortical neurons (Omelchenko and Sesack,

2005). It is also noteworthy that some aspects of the

pVTA strongly innervate the aVTA, and that the paranigral

nucleus project to the interfascicular nucleus (Ferreira

et al., 2008), highlighting the existence of intra-VTA cir-

cuitries. However, there are few studies aimed at provid-

ing a precise analysis of input heterogeneity within the

VTA; and a comprehensive re-assessment of the VTA

subnuclei connectivity would be likely useful to the field.

The VTA contains a relatively large number of

neurons, between 10,000 and 20,000 dopamine

neurons unilaterally in the rat according to different

studies (Swanson, 1982; German and Manaye, 1993;

Nair-Roberts et al., 2008), constituting around 2/3 of the

VTA neuronal population (Swanson, 1982; German and

Manaye, 1993; Harris and Nestler, 1996; Nair-Roberts

et al., 2008). GABA cells and glutamate cells (Morales

and Root, 2014; Yetnikoff et al., 2014), including gluta-

mate-dopamine cells, are also present in the VTA. Thus,

a differential distribution of the VTA cell types along the

antero-posterior axis could be an important factor under-

lying the functional differences observed between the

aVTA and the pVTA after local manipulations. The distri-

bution of dopamine cells indeed differs along the antero-

posterior and medio-lateral axes (Swanson, 1982;

Fallon and Loughlin, 1995; Ikemoto, 2007; Nair-Roberts

et al., 2008). While the dopamine neurons are present

throughout the rostro-caudal extent of the VTA, they are

more prevalent in the pVTA. Tyrosine hydroxylase-immu-

noreactive cells are particularly dense in the antero-lateral

part of the pVTA, in the paranigral and the parabrachial

pigmented nuclei. This density progressively decreases

rostrally and caudally to this region. A decreasing latero-

medial gradient is also present; however, another region

rich in dopamine neurons is also observed in the midline

nuclei, corresponding to the interfascicular and the caudal

linear nuclei. These midline cell bodies are much smaller

but more densely packed than the lateral VTA neurons.

While the pVTA is richer in dopamine cells, the aVTA is

relatively richer in GABA neurons (Olson et al., 2005;

Ikemoto, 2007; Olson and Nestler, 2007) and the VTA

glutamate (VGluT2-positive) neurons are also more pres-

ent within the anterior midline nuclei even though that are

found in each VTA subnucleus (Morales and Root, 2014).

Different antero-posterior gradients between neuronal cell

types could partly explain differences in responses after

local drug administration.

It has also been proposed that neurons of the aVTA

and of the pVTA may express different types of

receptors or different subunits of a same receptor.

Inactivating GABAA receptors in aVTA is for example

reinforcing, while activating these receptors is

reinforcing in the pVTA (Ikemoto et al., 1997b,1998).

The perfusion of GABAA antagonists into the aVTA also

increases the extracellular levels of dopamine in the

nucleus accumbens, suggesting that GABAA receptors

tonically inhibit the aVTA dopamine neurons projecting

to the nucleus accumbens (Ikemoto et al., 1997a), and

more specifically to the nucleus accumbens shell (Ding

et al., 2009a). Thus, GABAA receptors might be differently

localized in the aVTA and in the pVTA, being on dopa-

mine neurons in the aVTA but on inhibitory interneurons

in the pVTA. However, such differences in the location

of the GABA receptors has not been demonstrated, and

another explanation could be that intra-pVTA GABA

agents could also modulate nearby tVTA GABA neurons

that are known to control the activity of midbrain dopa-

mine cells (Barrot et al., 2012; Bourdy and Barrot,

2012). The pVTA dopamine neurons projecting to the

nucleus accumbens seem to be under tonic inhibition

through D2 receptors, since the pVTA administration of

the D2 antagonist sulpiride increases the extracellular

dopamine levels in nucleus accumbens (shell and core),

M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216 209

but also locally into the pVTA (Ding et al., 2009a). It has

also been shown that the activation of 5HT3 receptors

has a stronger action on dopamine levels in the pVTA

than in the aVTA (Liu et al., 2006). The aVTA/pVTA differ-

ences in behavior, or in changes in extracellular dopa-

mine levels or dopamine cell activity, that are observed

after local manipulation of GABA, dopamine, serotonin,

cannabinoid, opioid and nicotinic receptors (see the

‘‘VTA antero-posterior functional heterogeneity’’ section)

might reflect some differences in the distribution of these

receptors, but specific analyses are still needed to evalu-

ate this.

THE tVTA

In the past decade, a new mesopontine region associated

to the VTA has been defined: the tVTA or RMTg (Perrotti

et al., 2005; Kaufling et al., 2009; Jhou et al., 2009a,b;

Barrot and Thome, 2011; Bourdy and Barrot, 2012). As

the tVTA is partially embedded in the paranigral nucleus

of the VTA and exerts a major control on the activity of

dopamine cells, it is likely a new actor to consider when

studying and/or interpreting functional antero-posterior

differences of the VTA.

Detecting the tVTA

Experimentally, the easiest way to visualize the tVTA in

rats is to expose them acutely or chronically, either

through injections or self-administration procedures, to a

psychostimulant drug, such as cocaine, amphetamines

(D-amphetamine, methamphetamine, or (±)-3,4-methylen-

edioxymethamphetamine (MDMA)) or even modafinil,

and to process the midbrain for immunohistochemistry

against either cFos or FosB/DFosB (Scammell et al.,

2000; Perrotti et al., 2005; Geisler et al., 2008; Jhou

et al., 2009a,b; Kaufling et al., 2009, 2010a,b; Rotllant

et al., 2010; Zahm et al., 2010; Lecca et al., 2011; Matsui

and Williams, 2011; Cornish et al., 2012; Lavezzi et al.,

2012). Within the posterior part of the VTA, a cluster of

Fos-positive nuclei can be observed after exposure to

any of these drugs. This cluster is located dorso-laterally

tVTA

Fig. 4. Schematic of the consequences of tVTA manipulations. Abbreviatconditioned place preference; DA, dopamine; FC, fear conditioning; ICSA,

posterior VTA; tVTA, tail of the VTA; VTA, ventral tegmental area.

to the interpeduncular nucleus, in a subpart of the region

that is designated as the paranigral nucleus in the rat brain

atlas (Paxinos and Watson, 2007) (Figs. 3 and 4). Both

immunohistochemistry against the GABA synthesizing

enzyme, glutamic acid decarboxylase (GAD67) (Olson

andNestler, 2007), andNissl staining (Ikemoto, 2007) sup-

port the idea that this cluster of cells should be differenti-

ated from the surrounding paranigral nucleus. This highly

localized Fos staining extends caudally, beyond borders

of the VTA as defined by 6th edition of the rat brain atlas

(Paxinos and Watson, 2007). In fact, some difference is

even present between this continuous cell group and the

posterior-most drawings of the ‘‘VTA’’ in this atlas. Indeed,

the Fos-stained cell group shifts dorsally along its antero-

posterior axis (Kaufling et al., 2009, 2010b) (Figs. 3 and

4), following the position of the superior cerebellar pedun-

cle fibers, laterally to the median raphe nuclei. At some

point it is even partly embeddedwithin the superior cerebel-

lar peduncle. At this level, it might correspond to the ‘‘inter-

stitial nucleus of the decussation of the superior cerebellar

peduncle’’ newly proposed in the plates 89–92 of the rat

brain atlas (Paxinos andWatson, 2007). This mesopontine

group of cells, starting within the pVTA and spanning over

1 mm along the antero-posterior axis in rats, corresponds

to the tVTA or RMTg (Perrotti et al., 2005; Kaufling et al.,

2009; Jhou et al., 2009a,b; Lavezzi and Zahm, 2011;

Barrot et al., 2012; Bourdy and Barrot, 2012).

The psychostimulant-induced Fos staining allows an

easy visualization of the tVTA because surrounding

structures are unstained and because almost no staining

is present in the tVTA of control animals. It is to be noted

that the Fos induction in the tVTA is selectively observed

after exposure to arousing psychostimulant drugs, but it is

not present after exposure to various other drugs. Indeed,

the opiate morphine, ethanol, the benzodiazepine

diazepam, the cannabinoid D9-tetrahydrocannabinol, the

NMDA antagonists and dissociative drugs ketamine and

phencyclidine (PCP), the antidepressants reboxetine,

nortriptyline, venlafaxine, and fluoxetine, the 5-HT

releaser dexfenfluramine, and the anticonvulsants

valproic acid and gabapentin, do not induce Fos in the

tVTA (Perrotti et al., 2005; Kaufling et al., 2010b). A lack

ions: aVTA, anterior VTA; CPA, conditioned place aversion; CPP,

intracranial self-administration; IP, interpeduncular nucleus; pVTA,

210 M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216

of tVTA Fos expression is also observed after exposure to

stress (Perrotti et al., 2005), to the exception of electric

foot-shocks that induce a tVTA Fos response (Jhou et al.,

2009a; Brown and Shepard, 2013).

Based on connectivity, the tVTA has also been

observed in monkeys (Hong et al., 2011) and in mice

(Stamatakis and Stuber, 2012; Wasserman et al., 2013).

However, the borders of this structure are not yet been

clearly defined in these species, and the psychostimu-

lant-induced Fos that is often used in rats might be less

pertinent to visualize the tVTA in mice (unpublished

observations).

tVTA control of dopamine cells

The tVTA is mostly composed of GABA neurons (Perrotti

et al., 2005; Olson and Nestler, 2007; Kaufling et al.,

2009; Jhou et al., 2009b; Balcita-Pedicino et al., 2011),

with a notable expression of the l-opioid receptor (Jhou

et al., 2009b; Jalabert et al., 2011). Afferents of the tVTA

mostly arise in brain regions that also project to the VTA

(Kaufling et al., 2009; Jhou et al., 2009b); even though

inputs to the VTA and to the tVTA likely originate from dif-

ferent cell populations within these brain regions. For

example, the tVTA inputs from the dorsal raphe and the

locus cœruleus are non-aminergic and those from the lat-

eral hypothalamus are mostly non-orexinergic (Kaufling

et al., 2009), and the VTA and tVTA inputs from the lateral

habenula preferentially arise from its medial and lateral

subdivisions respectively (Goncalves et al., 2012). Pres-

ently, the most studied input to the tVTA remains the lat-

eral habenula (Herkenham and Nauta, 1979; Jhou et al.,

2009a, 2013; Brinschwitz et al., 2010; Balcita-Pedicino

et al., 2011; Hong et al., 2011; Goncalves et al., 2012;

Lammel et al., 2012; Stamatakis and Stuber, 2012;

Good et al., 2013; Stamatakis et al., 2013). The output

from the tVTA targets relatively few forebrain regions.

One of the main forebrain outputs is the lateral hypothal-

amus. The efferents of the tVTA are more prominently

directed toward the brainstem, in particular toward the

dopamine cell areas (the VTA, the substantia nigra com-

pact part, and to a lesser extent the retrorubral field)

(Ferreira et al., 2008; Jhou et al., 2009a,b; Kaufling

et al., 2010a; Balcita-Pedicino et al., 2011; Bourdy and

Barrot, 2012). This connectivity and the fact that tVTA

fibers do form synapses with dopamine cells of the VTA

(Balcita-Pedicino et al., 2011) and of the substantia nigra

compact part (Bourdy et al., 2014) and the results of elec-

trophysiological analyses support the hypothesis that the

tVTA may be an inhibitory control center for dopamine cell

activity (Hong et al., 2011; Jalabert et al., 2011, 2012;

Lecca et al., 2011; Matsui and Williams, 2011; Bourdy

et al., 2014).

The stimulation of the tVTA inhibits midbrain

dopamine cells, while its inhibition increases their firing

(Hong et al., 2011; Jalabert et al., 2011; Lecca et al.,

2011, 2012; Matsui and Williams, 2011; Melis et al.,

2013; Bourdy et al., 2014), which indicates the presence

of both phasic and tonic controls. This inhibitory control

can also be recruited by the stimulation of the lateral

habenula inputs to the tVTA (Hong et al., 2011; Lammel

et al., 2012; Stamatakis and Stuber, 2012), and a

VTA-lateral habenula-tVTA feedback loop has been

recently proposed (Good et al., 2013; Jhou et al., 2013;

Stamatakis et al., 2013).

Both morphine and the l-opioid agonist, DAMGO, can

inhibit the tVTA cells (Lecca et al., 2011; Matsui and

Williams, 2011; Matsui et al., 2014). Moreover, the

l-opioid receptors expressed by the tVTA GABA cells

and their terminals within the VTA are critical to the acute

recruitment of dopamine neurons by opiates (Jalabert

et al., 2011; Matsui and Williams, 2011; Matsui et al.,

2014). This led to the proposal that the classic disinhibi-

tion model for acute opiate action on dopamine cells

should be updated (Johnson and North, 1992; Barrot

et al., 2012; Bourdy and Barrot, 2012). The inhibitory

action of a cannabinoid agonist on tVTA neurons (Lecca

et al., 2011., 2012) supports the idea that the role of the

tVTA in disinhibition models could also be extended to

cannabinoids.

It remains to be explored whether the tVTA exerts a

differential inhibitory control on the aVTA and on the

pVTA, which could also participate to VTA antero-

posterior functional heterogeneity. Moreover, no

information is available yet on developmental aspects

of the tVTA, either concerning the origin of the tVTA

cells or the development of the tVTA inhibitory

innervations of the VTA and of the substantia nigra.

Such information would be useful to the field, for

example to appreciate whether the tVTA participates to

the known heterogeneity in dopamine neuron activity

across age or across individuals (Marinelli and

McCutcheon, 2014).

tVTA and behavior

The above data are supportive of a particular role of the

tVTA in the response to opiates. This role is behaviorally

confirmed by the fact that rats preferentially self-

administer EM-1 and develop conditioned place

preference to this opioid when it is microinjected into

the tVTA (Jhou et al., 2012) but not into surrounding

regions. The local administration of EM-1 likely inhibits

tVTA GABA cells. Accordingly, the inhibition of the tVTA

by local muscimol administration also sustains self-

administration (Jhou et al., 2012). For both EM-1 and

muscimol, this reinforcing effect decreases with the dis-

tance of the cannula from the tVTA core. These findings

led to reconsideration of previous reports of intra-pVTA

muscimol (Ikemoto et al., 1998) and EM-1 (Zangen

et al., 2002; Terashvili et al., 2004) reinforcing and

rewarding properties (see section on ‘‘VTA antero-pos-

terior functional heterogeneity’’), and suggest that these

properties might in fact have been due to an inhibition

of what has been designed as the tVTA a few years

later. The question is open as to whether other findings

previously associated with the manipulation of the pVTA

should be revisited by taking the tVTA into consideration

(Fig. 4, Table 1).

The tVTA has also been associated with the coding of

errors in reward prediction (Hong et al., 2011), but the

largest set of behavioral data in relation to the tVTA con-

cerns aversive and avoidance-related responses. Lesion

of the tVTA inhibits fear-conditioned freezing, passive

M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216 211

(but not active) response to a predator odor, and the anx-

iety-like behavior in an elevated plus-maze (Jhou et al.,

2009a). It also suppresses cocaine-induced avoidance

behavior in a runway operant paradigm (Jhou et al.,

2013). Reciprocally, the pharmacological stimulation of

the tVTA by AMPA is sufficient to induce a conditioned

place aversion (Jhou et al., 2013), and the stimulation of

the lateral habenula terminals in a midbrain region that

includes the tVTA induces active, passive and condi-

tioned avoidance of the stimulation (Lammel et al.,

2012; Stamatakis and Stuber, 2012).

It should also be considered that the tVTA control not

only the VTA, but also the substantia nigra compact part.

In this context, a lesion of the tVTA chronically stimulates

the nigrostriatal pathway and increases the motor

coordination performances and the motor learning in a

rotarod task (Bourdy et al., 2014). These last data high-

light the critical influence that the tVTA has on basal gan-

glia circuitry and function.

CONCLUSION

There is strong evidence for a functional antero-posterior

heterogeneity of the VTA. However, the morphofunctional

substrate(s) for this heterogeneity is(are) not clearly

identified yet. Differences related to the sub-regions of

the VTA, including the recently defined tVTA, and how

they may be differently inserted into larger brain

circuitries is likely critical. The neurochemical and

molecular heterogeneity of VTA cell populations are also

important to be considered. Important progress,

benefiting from technical advances, has recently been

made in relation to some aspects of VTA heterogeneity.

Many questions remain unanswered. Detailed re-

assessments of the VTA cytoarchitecture across

species, of the definition of its sub-nuclei, of their cell

composition and of their connectivity and of the

molecular heterogeneity of these cells, are required.

These, together with the search for specific molecular

markers that would also allow designing transgenic

tools, are among challenges that need to be addressed

in order to progress in our understanding of the

physiological and pathophysiological influences of the

VTA.

Acknowledgments—Supported by the Centre National de la

Recherche Scientifique, Universite de Strasbourg, Universite

Bordeaux Segalen, and by the Agence Nationale de la Recher-

che (ANR-11-bsv4-002). We thank Pr. Paul Bolam for his com-

ments on the manuscript.

REFERENCES

Arnt J, Scheel-Kruger J (1979) GABA in the ventral tegmental area:

differential regional effects on locomotion, aggression and food

intake after microinjection of GABA agonists and antagonists. Life

Sci 25:1351–1360.

Balcita-Pedicino JJ, Omelchenko N, Bell R, Sesack SR (2011) The

inhibitory influence of the lateral habenula on midbrain dopamine

cells: ultrastructural evidence for indirect mediation via the

rostromedial mesopontine tegmental nucleus. J Comp Neurol

519:1143–1164.

Barrot M, Thome J (2011) Discovering a new anatomical structure in

the brain: implications for neuropsychiatry and therapy. World J

Biol Psychiatry 12(S1):19–22.

Barrot M, Sesack SR, Georges F, Pistis M, Hong S, Jhou TC (2012)

Braking dopamine systems: a new GABA master structure for

mesolimbic and nigrostriatal functions. J Neurosci

32:14094–14101.

Bechtholt AJ, Cunningham CL (2005) Ethanol-induced conditioned

place preference is expressed through a ventral tegmental area

dependent mechanism. Behav Neurosci 119:213–223.

Berendse HW, Groenewegen HJ, Lohman AH (1992) Compartmental

distribution of ventral striatal neurons projecting to the

mesencephalon in the rat. J Neurosci 12:2079–2103.

Boehm 2nd SL, Piercy MM, Bergstrom HC, Phillips TJ (2002) Ventral

tegmental area region governs GABA(B) receptor modulation of

ethanol-stimulated activity in mice. Neuroscience 115:185–200.

Bolanos CA, Perrotti LI, Edwards S, Eisch AJ, Barrot M, Olson VG,

Russell DS, Neve RL, Nestler EJ (2003) Phospholipase Cgamma

in distinct regions of the ventral tegmental area differentially

modulates mood-related behaviors. J Neurosci 23:7569–7576.

Bolanos CA, Neve RL, Nestler EJ (2005) Phospholipase C gamma in

distinct regions of the ventral tegmental area differentially

regulates morphine-induced locomotor activity. Synapse

56:166–169.

Bourdy R, Barrot M (2012) A new control center for dopaminergic

systems: pulling the VTA by the tail. Trends Neurosci

35:681–690.

Bourdy R, Sanchez-Catalan MJ, Kaufling J, Balcita-Pedicino JJ,

Freund-Mercier MJ, Veinante P, Sesack SR, Georges F, Barrot

M (2014) Control of the nigrostriatal dopamine neuron activity and

motor function by the tail of the ventral tegmental area.

Neuropsychopharmacology. http://dx.doi.org/10.1038/npp.2014.

129.

Brinschwitz K, Dittgen A, Madai VI, Lommel R, Geisler S, Veh RW

(2010) Glutamatergic axons from the lateral habenula mainly

terminate on gabaergic neurons of the ventral midbrain.

Neuroscience 168:463–476.

Brischoux F, Chakraborty S, Brierley DI, Ungless MA (2009) Phasic

excitation of dopamine neurons in ventral VTA by noxious stimuli.

Proc Natl Acad Sci U S A 106:4894–4899.

Brodie MS, Appel SB (1998) The effects of ethanol on dopaminergic

neurons of the ventral tegmental area studied with intracellular

recording in brain slices. Alcohol Clin Exp Res 22:236–244.

Bromberg-Martin ES, Matsumoto M, Hikosaka O (2010) Dopamine in

motivational control: rewarding, aversive, and alerting. Neuron

68:815–834.

Brown PL, Shepard PD (2013) Lesions of the fasciculus retroflexus

alter footshock-induced cFos expression in the mesopontine

rostromedial tegmental area of rats. PLoS One 8:e60678.

Carlezon Jr WA, Haile CN, Coppersmith R, Hayashi Y, Malinow R,

Neve RL, Nestler EJ (2000) Distinct sites of opiate reward and

aversion within the midbrain identified using a herpes simplex

virus vector expressing GluR1. J Neurosci 20:RC62.

Carlsson A, Falck B, Hillarp NA (1962) Cellular localization of brain

monoamines. Acta Physiol Scand Suppl 56:1–28.

Castaldi L (1923)Studdi sulla strutturae sulosviluppodelmesencefalo. I

ricerche in Cavia cobaya. Arch Ital Embrio 20:23–225.

Cavalcanti JR, Soares JG, Oliveira FG, Guzen FP, Pontes AL, Sousa

TB, Cavalcante JS, Nascimento Jr ES, Cavalcante JC, Costa MS

(2014) A cytoarchitectonic and TH-immunohistochemistry

characterization of the dopamine cell groups in the substantia

nigra, ventral tegmental area and retrorubral field in the rock cavy

(Kerodon rupestris). J Chem Neuroanat 55:58–66.

Colussi-Mas J, Schenk S (2008) Acute and sensitized response to

3,4-methylenedioxymethamphetamine in rats: different behavioral

profiles reflected in different patterns of Fos expression. Eur J

Neurosci 28:1895–1910.

Cornish JL, Hunt GE, Robins L, McGregor IS (2012) Regional c-Fos

and FosB/DeltaFosB expression associated with chronic

methamphetamine self-administration and methamphetamine-

seeking behavior in rats. Neuroscience 206:100–114.

212 M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216

Correa M, Salamone JD, Segovia KN, Pardo M, Longoni R, Spina L,

Peana AT, Vinci S, Acquas E (2012) Piecing together the puzzle

of acetaldehyde as a neuroactive agent. Neurosci Biobehav Rev

36:404–430.

Creed MC, Ntamati NR, Tan KR (2014) VTA GABA neurons

modulate specific learning behaviors through the control of

dopamine and cholinergic systems. Front Behav Neurosci 8:8.

Czachowski CL, Delory MJ, Pope JD (2012) Behavioral and

neurotransmitter specific roles for the ventral tegmental area in

reinforcer-seeking and intake. Alcohol Clin Exp Res

36:1659–1668.

D’Souza MS, Markou A (2011) Metabotropic glutamate receptor 5

antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP)

microinfusions into the nucleus accumbens shell or ventral

tegmental area attenuate the reinforcing effects of nicotine in

rats. Neuropharmacology 61:1399–1405.

Dahlstrom A, Fuxe K (1964) Localization of monoamines in the lower

brain stem. Experientia 20:398–399.

David V, Segu L, Buhot MC, Ichaye M, Cazala P (2004) Rewarding

effects elicited by cocaine microinjections into the ventral

tegmental area of C57BL/6 mice: involvement of dopamine D1

and serotonin1B receptors. Psychopharmacology (Berl)

174:367–375.

De Jaeger X, Bishop SF, Ahmad T, Lyons D, Ng GA, Laviolette SR

(2013) The effects of AMPA receptor blockade in the prelimbic

cortex on systemic and ventral tegmental area opiate reward

sensitivity. Psychopharmacology (Berl) 225:687–695.

Deehan Jr GA, Engleman EA, Ding ZM, McBride WJ, Rodd ZA

(2013) Microinjections of acetaldehyde or salsolinol into the

posterior ventral tegmental area increase dopamine release in

the nucleus accumbens shell. Alcohol Clin Exp Res 37:722–729.

Deniau JM, Thierry AM, Feger J (1980) Electrophysiological

identification of mesencephalic ventromedial tegmental (VMT)

neurons projecting to the frontal cortex, septum and nucleus

accumbens. Brain Res 189:315–326.

Ding ZM, Liu W, Engleman EA, Rodd ZA, McBride WJ (2009a)

Differential effects of dopamine D2 and GABA(A) receptor

antagonists on dopamine neurons between the anterior and

posterior ventral tegmental area of female Wistar rats. Pharmacol

Biochem Behav 92:404–412.

Ding ZM, Rodd ZA, Engleman EA, McBride WJ (2009b) Sensitization

of ventral tegmental area dopamine neurons to the stimulating

effects of ethanol. Alcohol Clin Exp Res 33:1571–1581.

Ding ZM, Toalston JE, Oster SM, McBride WJ, Rodd ZA (2009c)

Involvement of local serotonin-2A but not serotonin-1B receptors

in the reinforcing effects of ethanol within the posterior ventral

tegmental area of female Wistar rats. Psychopharmacology (Berl)

204:381–390.

Ding ZM, Oster SM, Hall SR, Engleman EA, Hauser SR, McBride WJ,

Rodd ZA (2011) The stimulating effects of ethanol on ventral

tegmental area dopamine neurons projecting to the ventral

pallidum and medial prefrontal cortex in female Wistar rats:

regional difference and involvement of serotonin-3 receptors.

Psychopharmacology (Berl) 216:245–255.

Ding ZM, Engleman EA, Rodd ZA, McBride WJ (2012a) Ethanol

increases glutamate neurotransmission in the posterior ventral

tegmental area of female Wistar rats. Alcohol Clin Exp Res

36:633–640.

Ding ZM, Katner SN, Rodd ZA, Truitt W, Hauser SR, Deehan Jr GA,

Engleman EA, McBride WJ (2012b) Repeated exposure of the

posterior ventral tegmental area to nicotine increases the

sensitivity of local dopamine neurons to the stimulating effects

of ethanol. Alcohol 46:217–223.

Ding ZM, Oster SM, Hauser SR, Toalston JE, Bell RL, McBride WJ,

Rodd ZA (2012c) Synergistic self-administration of ethanol and

cocaine directly into the posterior ventral tegmental area:

involvement of serotonin-3 receptors. J Pharmacol Exp Ther

340:202–209.

Ding ZM, Rodd ZA, Engleman EA, Bailey JA, Lahiri DK, McBride WJ

(2013) Alcohol drinking and deprivation alter basal extracellular

glutamate concentrations and clearance in the mesolimbic system

of alcohol-preferring (P) rats. Addict Biol 18:297–306.

Ding ZM, Ingraham CM, Rodd ZA, McBride WJ (2014) The

reinforcing effects of ethanol within the posterior ventral

tegmental area depend on dopamine neurotransmission to

forebrain cortico-limbic systems. Addict Biol. http://dx.doi.org/

10.1111/adb.12138.

Ducrot C, Fortier E, Bouchard C, Rompre PP (2013) Opposite

modulation of brain stimulation reward by NMDA and AMPA

receptors in the ventral tegmental area. Front Syst Neurosci 7:57.

Engleman EA, Keen EJ, Tilford SS, Thielen RJ, Morzorati SL (2011)

Ethanol drinking reduces extracellular dopamine levels in the

posterior ventral tegmental area of nondependent alcohol-

preferring rats. Alcohol 45:549–557.

Ericson M, Lof E, Stomberg R, Chau P, Soderpalm B (2008) Nicotinic

acetylcholine receptors in the anterior, but not posterior, ventral

tegmental area mediate ethanol-induced elevation of accumbal

dopamine levels. J Pharmacol Exp Ther 326:76–82.

Fallon JH (1981) Collateralization of monoamine neurons:

mesotelencephalic dopamine projections to caudate, septum,

and frontal cortex. J Neurosci 1:1361–1368.

Fallon JH, Loughlin SE (1995) Substantia nigra. In: Paxinos G, editor.

The rat nervous system, 2nd edition. San Diego: Academic Press.

Farquhar MJ, Latimer MP, Winn P (2012) Nicotine self-administered

directly into the VTA by rats is weakly reinforcing but has strong

reinforcement enhancing properties. Psychopharmacology (Berl)

220:43–54.

Faure P, Tolu S, Valverde S, Naude J (2014) Role of nicotinic

acetylcholine receptors in regulating dopamine neuron activity.

Neuroscience 282:86–100.

Ferreira JG, Del-Fava F, Hasue RH, Shammah-Lagnado SJ (2008)

Organization of ventral tegmental area projections to the ventral

tegmental area-nigral complex in the rat. Neuroscience

153:196–213.

Fields HL, Hjelmstad GO, Margolis EB, Nicola SM (2007) Ventral

tegmental area neurons in learned appetitive behavior and

positive reinforcement. Annu Rev Neurosci 30:289–316.

Fitzgerald GJ, Liu H, Morzorati SL (2012) Decreased sensitivity of

NMDA receptors on dopaminergic neurons from the posterior

ventral tegmental area following chronic nondependent alcohol

consumption. Alcohol Clin Exp Res 36:1710–1719.

Ford CP (2014) The role of D2-autoreceptors in regulating dopamine

neuron activity and transmission. Neuroscience 282:13–22.

Franklin KBJ, Paxinos G (2008) Mouse in brain stereotaxic

coordinates, 3rd edition. San Diego, CA: Academic Press.

Fu Y, Yuan Y, Halliday G, Rusznak Z, Watson C, Paxinos G (2012) A

cytoarchitectonic and chemoarchitectonic analysis of the

dopamine cell groups in the substantia nigra, ventral tegmental

area, and retrorubral field in the mouse. Brain Struct Funct

217:591–612.

Geisler S, Marinelli M, Degarmo B, Becker ML, Freiman AJ, Beales

M, Meredith GE, Zahm DS (2008) Prominent activation of

brainstem and pallidal afferents of the ventral tegmental area by

cocaine. Neuropsychopharmacology 33:2688–2700.

German DC, Manaye KF (1993) Midbrain dopaminergic neurons

(nuclei A8, A9, and A10): three-dimensional reconstruction in the

rat. J Comp Neurol 331:297–309.

Gianoulakis C (2009) Endogenous opioids and addiction to alcohol

and other drugs of abuse. Curr Top Med Chem 9:999–1015.

Gillies GE, Virdee K, McArthur S, Dalley JW (2014) Sex-dependent

diversity in ventral tegmental dopaminergic neurons and

developmental programing: a molecular, cellular and behavioral

analysis. Neuroscience 282:69–85.

Goncalves L, Sego C, Metzger M (2012) Differential projections from

the lateral habenula to the rostromedial tegmental nucleus and

ventral tegmental area in the rat. J Comp Neurol 520:1278–1300.

Good CH, Wang H, Chen YH, Mejias-Aponte CA, Hoffman AF,

Lupica CR (2013) Dopamine D-4 receptor excitation of lateral

habenula neurons via multiple cellular mechanisms. J Neurosci

33:16853–16864.

M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216 213

Grace AA, Floresco SB, Goto Y, Lodge DJ (2007) Regulation of firing

of dopaminergic neurons and control of goal-directed behaviors.

Trends Neurosci 30:220–227.

Guan Y, Xiao C, Krnjevic K, Xie G, Zuo W, Ye JH (2012) GABAergic

actions mediate opposite ethanol effects on dopaminergic

neurons in the anterior and posterior ventral tegmental area. J

Pharmacol Exp Ther 341:33–42.

Haber SN, Fudge JL (1997) The primate substantia nigra and VTA:

integrative circuitry and function. Crit Rev Neurobiol 11:323–342.

Haber SN, Fudge JL, McFarland NR (2000) Striatonigrostriatal

pathways in primates form an ascending spiral from the shell to

the dorsolateral striatum. J Neurosci 20:2369–2382.

Halliday GM, Tork I (1986) Comparative anatomy of the ventromedial

mesencephalic tegmentum in the rat, cat, monkey and human. J

Comp Neurol 252:423–445.

Harris HW, Nestler EJ (1996) Immunohistochemical studies of

mesolimbic dopaminergic neurons in Fischer 344 and Lewis

rats. Brain Res 706:1–12.

Hassler R (1937) Zur pathologie der paralysis agitans und des

postenkephalitischer parkonsonismus. J Psychol Neurol

48:387–476.

Hasue RH, Shammah-Lagnado SJ (2002) Origin of the dopaminergic

innervation of the central extended amygdala and accumbens

shell: a combined retrograde tracing and immunohistochemical

study in the rat. J Comp Neurol 454:15–33.

Hauser SR, Ding ZM, Getachew B, Toalston JE, Oster SM, McBride

WJ, Rodd ZA (2011) The posterior ventral tegmental area

mediates alcohol-seeking behavior in alcohol-preferring rats. J

Pharmacol Exp Ther 336:857–865.

Hauser SR, Deehan Jr GA, Toalston JE, Bell RL, McBride WJ, Rodd

ZA (2014) Enhanced alcohol-seeking behavior by nicotine in the

posterior ventral tegmental area of female alcohol-preferring (P)

rats: modulation by serotonin-3 and nicotinic cholinergic

receptors. Psychopharmacology (Berl) 231:3745–3755.

Heimer L, Zahm DS, Churchill L, Kalivas PW, Wohltmann C (1991)

Specificity in the projection patterns of accumbal core and shell in

the rat. Neuroscience 41:89–125.

Heimer L, Alheid GF, de Olmos JS, Groenewegen HJ, Haber SN,

Harlan RE, Zahm DS (1997) The accumbens: beyond the core-

shell dichotomy. J Neuropsychiatry Clin Neurosci 9:354–381.

Herkenham M, Nauta WJH (1979) Efferent connections of the

habenular nuclei in the rat. J Comp Neurol 187:19–47.

Herve D, Pickel VM, Joh TH, Beaudet A (1987) Serotonin axon

terminals in the ventral tegmental area of the rat: fine structure

and synaptic input to dopaminergic neurons. Brain Res

435:71–83.

Hipolito L, Sanchez-Catalan MJ, Zornoza T, Polache A, Granero L

(2010) Locomotor stimulant effects of acute and repeated

intrategmental injections of salsolinol in rats: role of mu-opioid

receptors. Psychopharmacology (Berl) 209:1–11.

Hipolito L, Marti-Prats L, Sanchez-Catalan MJ, Polache A, Granero L

(2011) Induction of conditioned place preference and dopamine

release by salsolinol in posterior VTA of rats: involvement of mu-

opioid receptors. Neurochem Int 59:559–562.

Hipolito L, Sanchez-Catalan MJ, Marti-Prats L, Granero L, Polache A

(2012) Revisiting the controversial role of salsolinol in the

neurobiological effects of ethanol: old and new vistas. Neurosci

Biobehav Rev 36:362–378.

Hodge CW, Haraguchi M, Erickson H, Samson HH (1993) Ventral

tegmental microinjections of quinpirole decrease ethanol and

sucrose-reinforced responding. Alcohol Clin Exp Res

17:370–375.

Hokfelt T, Johansson O, Goldstein M (1984) Chemical anatomy of the

brain. Science 225:1326–1334.

Hong S, Jhou TC, Smith M, Saleem KS, Hikosaka O (2011) Negative

reward signals from the lateral habenula to dopamine neurons are

mediated by rostromedial tegmental nucleus in primates. J

Neurosci 31:11457–11471.

Hong S (2013) Dopamine system: manager of neural pathways. Front

Hum Neurosci 7:854.

Hutson LW, Szczytkowski JL, Saurer TB, Lebonville C, Fuchs RA,

Lysle DT (2014) Region-specific contribution of the ventral

tegmental area to heroin-induced conditioned

immunomodulation. Brain Behav Immun 38:118–124.

Ikemoto S, Kohl RR, McBride WJ (1997a) GABA(A) receptor

blockade in the anterior ventral tegmental area increases

extracellular levels of dopamine in the nucleus accumbens of

rats. J Neurochem 69:137–143.

Ikemoto S, Murphy JM, McBride WJ (1997b) Self-infusion of

GABA(A) antagonists directly into the ventral tegmental area

and adjacent regions. Behav Neurosci 111:369–380.

Ikemoto S, Murphy JM, McBride WJ (1998) Regional differences

within the rat ventral tegmental area for muscimol self-infusions.

Pharmacol Biochem Behav 61:87–92.

Ikemoto S, Wise RA (2002) Rewarding effects of the cholinergic

agents carbachol and neostigmine in the posterior ventral

tegmental area. J Neurosci 22:9895–9904.

Ikemoto S, Witkin BM, Morales M (2003) Rewarding injections of the

cholinergic agonist carbachol into the ventral tegmental area

induce locomotion and c-Fos expression in the retrosplenial area

and supramammillary nucleus. Brain Res 969:78–87.

Ikemoto S, Witkin BM, Zangen A, Wise RA (2004) Rewarding effects

of AMPA administration into the supramammillary or posterior

hypothalamic nuclei but not the ventral tegmental area. J Neurosci

24:5758–5765.

Ikemoto S (2005) The supramammillary nucleus mediates primary

reinforcement via GABA(A) receptors.

Neuropsychopharmacology 30:1088–1095.

Ikemoto S, Qin M, Liu ZH (2006) Primary reinforcing effects of

nicotine are triggered from multiple regions both inside and

outside the ventral tegmental area. J Neurosci 26:723–730.

Ikemoto S (2007) Dopamine reward circuitry: two projection systems

from the ventral midbrain to the nucleus accumbens-olfactory

tubercle complex. Brain Res Rev 56:27–78.

Ikemoto S (2010) Brain reward circuitry beyond the mesolimbic

dopamine system: a neurobiological theory. Neurosci Biobehav

Rev 35:129–150.

Ikemoto S, Bonci A (2014) Neurocircuitry of drug reward.

Neuropharmacology 76 Pt B:329–341.

Jalabert M, Bourdy R, Courtin J, Veinante P, Manzoni OJ, Barrot M,

Georges F (2011) Neuronal circuits underlying acute morphine

action on dopamine neurons. Proc Natl Acad Sci U S A

108:16446–16450.

Jhou TC, Fields HL, Baxter MG, Saper CB, Holland PC (2009a) The

rostromedial tegmental nucleus (RMTg), a GABAergic afferent to

midbrain dopamine neurons, encodes aversive stimuli and inhibits

motor responses. Neuron 61:786–800.

Jhou TC, Geisler S, Marinelli M, Degarmo BA, Zahm DS (2009b) The

mesopontine rostromedial tegmental nucleus: a structure targeted

by the lateral habenula that projects to the ventral tegmental area

of Tsai and substantia nigra compacta. J Comp Neurol

513:566–596.

Jhou TC, Xu SP, Lee MR, Gallen CL, Ikemoto S (2012) Mapping of

reinforcing and analgesic effects of the mu opioid agonist

endomorphin-1 in the ventral midbrain of the rat.

Psychopharmacology 224:303–312.

Jhou TC, Good CH, Rowley CS, Xu SP, Wang HK, Burnham NW,

Hoffman AF, Lupica CR, Ikemoto S (2013) Cocaine drives

aversive conditioning via delayed activation of dopamine-

responsive habenular and midbrain pathways. J Neurosci

33:7501–7512.

Johnson SW, North RA (1992) Opioids excite dopamine neurons by

hyperpolarization of local interneurons. J Neurosci 12:483–488.

Kalivas PW (1993) Neurotransmitter regulation of dopamine neurons

in the ventral tegmental area. Brain Res Brain Res Rev

18:75–113.

Katner SN, McBride WJ, Lumeng L, Li TK, Murphy JM (1997) Alcohol

intake of P rats is regulated by muscarinic receptors in the

pedunculopontine nucleus and VTA. Pharmacol Biochem Behav

58:497–504.

214 M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216

Kaufling J, Veinante P, Pawlowski SA, Freund-Mercier MJ, Barrot M

(2009) Afferents to the GABAergic tail of the ventral tegmental

area in the rat. J Comp Neurol 513:597–621.

Kaufling J, Veinante P, Pawlowski SA, Freund-Mercier MJ, Barrot M

(2010a) Gamma-aminobutyric acid cells with cocaine-induced

DeltaFosB in the ventral tegmental area innervate mesolimbic

neurons. Biol Psychiatry 67:88–92.

Kaufling J, Waltisperger E, Bourdy R, Valera A, Veinante P, Freund-

Mercier MJ, Barrot M (2010b) Pharmacological recruitment of the

GABAergic tail of the ventral tegmental area by acute drug

exposure. Br J Pharmacol 161:1677–1691.

Kosaka K, Hiraiwa K (1915) Zur anatomie der sehnervenbahn und

ihrer zentren. Folia Neurobiol (leipzig) 9:367.

Lammel S, Hetzel A, Hackel O, Jones I, Liss B, Roeper J (2008)

Unique properties of mesoprefrontal neurons within a dual

mesocorticolimbic dopamine system. Neuron 57:760–773.

Lammel S, Lim BK, Ran C, Huang KW, Betley MJ, Tye KM,

Deisseroth K, Malenka RC (2012) Input-specific control of reward

and aversion in the ventral tegmental area. Nature 491:212–217.

Lammel S, Lim BK, Malenka RC (2014) Reward and aversion in a

heterogeneous midbrain dopamine system. Neuropharmacology

76 Pt B:351–359.

Lavezzi HN, Zahm DS (2011) The mesopontine rostromedial

tegmental nucleus: an integrative modulator of the reward

system. Basal Ganglia 1:191–200.

Lavezzi HN, Parsley KP, Zahm DS (2012) Mesopontine rostromedial

tegmental nucleus neurons projecting to the dorsal raphe and

pedunculopontine tegmental nucleus: psychostimulant-elicited

Fos expression and collateralization. Brain Struct Funct

217:719–734.

Lecca S, Melis M, Luchicchi A, Ennas MG, Castelli MP, Muntoni AL,

Pistis M (2011) Effects of drugs of abuse on putative rostromedial

tegmental neurons, inhibitory afferents to midbrain dopamine

cells. Neuropsychopharmacology 36:589–602.

Lecca S, Melis M, Luchicchi A, Muntoni AL, Pistis M (2012) Inhibitory

inputs from rostromedial tegmental neurons regulate

spontaneous activity of midbrain dopamine cells and their

responses to drugs of abuse. Neuropsychopharmacology

37:1164–1176.

Lee DY, Guttilla M, Fung KD, McFeron S, Yan J, Ranaldi R (2007)

Rostral-caudal differences in the effects of intra-VTA muscimol on

cocaine self-administration. Pharmacol Biochem Behav

86:542–549.

Li W, Doyon WM, Dani JA (2011) Acute in vivo nicotine administration

enhances synchrony among dopamine neurons. Biochem

Pharmacol 82:977–983.

Liechti ME, Lhuillier L, Kaupmann K, Markou A (2007) Metabotropic

glutamate 2/3 receptors in the ventral tegmental area and the

nucleus accumbens shell are involved in behaviors relating to

nicotine dependence. J Neurosci 27:9077–9085.

Linsenbardt DN, Boehm 2nd SL (2009) Agonism of the

endocannabinoid system modulates binge-like alcohol intake in

male C57BL/6J mice: involvement of the posterior ventral

tegmental area. Neuroscience 164:424–434.

Liu W, Thielen RJ, Rodd ZA, McBride WJ (2006) Activation of

serotonin-3 receptors increases dopamine release within the

ventral tegmental area of Wistar and alcohol-preferring (P) rats.

Alcohol 40:167–176.

Marinelli M, McCutcheon JE (2014) Heterogeneity of dopamine

neuron activity across traits and states. Neuroscience

282:176–197.

Marti-Prats L, Sanchez-Catalan MJ, Hipolito L, Orrico A, Zornoza

T, Polache A, Granero L (2010) Systemic administration of

D-penicillamine prevents the locomotor activation after intra-

VTA ethanol administration in rats. Neurosci Lett 483:

143–147.

Marti-Prats L, Sanchez-Catalan MJ, Orrico A, Zornoza T, Polache A,

Granero L (2013) Opposite motor responses elicited by ethanol in

the posterior VTA: the role of acetaldehyde and the non-

metabolized fraction of ethanol. Neuropharmacology 72:

204–214.

Matsui A, Williams JT (2011) Opioid-sensitive GABA inputs from

rostromedial tegmental nucleus synapse onto midbrain dopamine

neurons. J Neurosci 31:17729–17735.

Matsui A, Jarvie BC, Robinson BG, Hentges ST, Williams JT (2014)

Separate GABA afferents to dopamine neurons mediate acute

action of opioids, development of tolerance, and expression of

withdrawal. Neuron 82:1346–1356.

Melis M, Enrico P, Peana AT, Diana M (2007) Acetaldehyde

mediates alcohol activation of the mesolimbic dopamine system.

Eur J Neurosci 26:2824–2833.

Melis M, Carboni E, Caboni P, Acquas E (2013) Key role of salsolinol

in ethanol actions on dopamine neuronal activity of the posterior

ventral tegmental area. Addict Biol. http://dx.doi.org/10.1111/

adb.12097.

Melon LC, Boehm 2nd SL (2011) GABAA receptors in the posterior,

but not anterior, ventral tegmental area mediate Ro15-4513-

induced attenuation of binge-like ethanol consumption in C57BL/

6J female mice. Behav Brain Res 220:230–237.

Meye FJ, Adan RA (2014) Feelings about food: the ventral tegmental

area in food reward and emotional eating. Trends Pharmacol Sci

35:31–40.

Moaddab M, Haghparast A, Hassanpour-Ezatti M (2009) Effects of

reversible inactivation of the ventral tegmental area on the

acquisition and expression of morphine-induced conditioned

place preference in the rat. Behav Brain Res 198:466–471.

Montagu KA (1957) Catechol compounds in rat tissues and in brains

of different animals. Nature 180:244–245.

Moore EM, Boehm 2nd SL (2009) Site-specific microinjection of

baclofen into the anterior ventral tegmental area reduces binge-

like ethanol intake in male C57BL/6J mice. Behav Neurosci

123:555–563.

Morales M, Root DH (2014) Glutamate neurons within the midbrain

dopamine regions. Neuroscience 282:60–68.

Moreno S, Mugnaini E, Ceru MP (1995) Immunocytochemical

localization of catalase in the central nervous system of the rat.

J Histochem Cytochem 43:1253–1267.

Morikawa H, Morrisett RA (2010) Ethanol action on dopaminergic

neurons in the ventral tegmental area: interaction with intrinsic ion

channels and neurotransmitter inputs. Int Rev Neurobiol

91:235–288.

Morzorati SL, Marunde RL, Downey D (2010) Limited access to

ethanol increases the number of spontaneously active dopamine

neurons in the posterior ventral tegmental area of nondependent

P rats. Alcohol 44:257–264.

Nair-Roberts RG, Chatelain-Badie SD, Benson E, White-Cooper H,

Bolam JP, Ungless MA (2008) Stereological estimates of

dopaminergic, GABAergic and glutamatergic neurons in the

ventral tegmental area, substantia nigra and retrorubral field in

the rat. Neuroscience 152:1024–1031.

Nauta WJ (1958) Hippocampal projections and related neural

pathways to the midbrain in the cat. Brain 81:319–340.

Nestler EJ, Carlezon WA (2006) The mesolimbic dopamine reward

circuit in depression. Biol Psychiatry 59:1151–1159.

Nikulina EM, Johnston CE, Wang J, Hammer Jr RP (2014)

Neurotrophins in the ventral tegmental area: role in social

stress, mood disorders and drug abuse. Neuroscience

282:122–138.

Nowak KL, McBride WJ, Lumeng L, Li TK, Murphy JM (1998)

Blocking GABA(A) receptors in the anterior ventral tegmental area

attenuates ethanol intake of the alcohol-preferring P rat.

Psychopharmacology (Berl) 139:108–116.

Nowak KL, McBride WJ, Lumeng L, Li TK, Murphy JM (2000)

Involvement of dopamine D2 autoreceptors in the ventral

tegmental area on alcohol and saccharin intake of the alcohol-

preferring P rat. Alcohol Clin Exp Res 24:476–483.

Oades RD, Halliday GM (1987) Ventral tegmental (A10) system:

neurobiology. 1. Anatomy and connectivity. Brain Res

434:117–165.

Okamoto T, Harnett MT, Morikawa H (2006) Hyperpolarization-

activated cation current (Ih) is an ethanol target in midbrain

dopamine neurons of mice. J Neurophysiol 95:619–626.

M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216 215

Olson VG, Zabetian CP, Bolanos CA, Edwards S, Barrot M, Eisch AJ,

Hughes T, Self DW, Neve RL, Nestler EJ (2005) Regulation of

drug reward by cAMP response element-binding protein:

evidence for two functionally distinct subregions of the ventral

tegmental area. J Neurosci 25:5553–5562.

Olson VG, Nestler EJ (2007) Topographical organization of

GABAergic neurons within the ventral tegmental area of the rat.

Synapse 61:87–95.

Omelchenko N, Sesack SR (2005) Laterodorsal tegmental

projections to identified cell populations in the rat ventral

tegmental area. J Comp Neurol 483:217–235.

Orrico A, Hipolito L, Sanchez-Catalan MJ, Marti-Prats L, Zornoza T,

Granero L, Polache A (2013) Efficacy of D-penicillamine, a

sequestering acetaldehyde agent, in the prevention of alcohol

relapse-like drinking in rats. Psychopharmacology (Berl)

228:563–575.

Ouachikh O, Dieb W, Durif F, Hafidi A (2013) Differential behavioral

reinforcement effects of dopamine receptor agonists in the rat with

bilateral lesion of the posterior ventral tegmental area. Behav

Brain Res 252:24–31.

Ouachikh O, Dieb W, Durif F, Hafidi A (2014) Anterior ventral

tegmental area dopaminergic neurons are not involved in the

motivational effects of bromocriptine, pramipexole and cocaine in

drug-free rats. Behav Brain Res 262:1–7.

Overton PG, Vautrelle N, Redgrave P (2014) Sensory regulation of

dopaminergic cell activity: phenomenology, circuitry and function.

Neuroscience 282:1–12.

Paxinos G, Watson C (1998) The rat brain in stereotaxic

coordinates. CA: San Diego.

Paxinos G, Watson C (2007) The rat brain in stereotaxic

coordinates. CA: San Diego.

Perrotti LI, Bolanos CA, Choi KH, Russo SJ, Edwards S, Ulery PG,

Wallace DL, Self DW, Nestler EJ, Barrot M (2005) DeltaFosB

accumulates in a GABAergic cell population in the posterior tail of

the ventral tegmental area after psychostimulant treatment. Eur J

Neurosci 21:2817–2824.

Phillipson OT (1979a) A Golgi study of the ventral tegmental area of

Tsai and interfascicular nucleus in the rat. J Comp Neurol

187:99–115.

Phillipson OT (1979b) The cytoarchitecture of the interfascicular

nucleus and ventral tegmental area of Tsai in the rat. J Comp

Neurol 187:85–98.

Phillipson OT (1979c) Afferent projections to the ventral tegmental

area of Tsai and interfascicular nucleus: a horseradish peroxidase

study in the rat. J Comp Neurol 187:117–143.

Phillipson OT, Griffiths AC (1985) The topographic order of inputs to

nucleus accumbens in the rat. Neuroscience 16:275–296.

Reyes S, Fu Y, Double K, Thompson L, Kirik D, Paxinos G, Halliday

GM (2012) GIRK2 expression in dopamine neurons of the

substantia nigra and ventral tegmental area. J Comp Neurol

520:2591–2607.

Rivera-Meza M, Quintanilla ME, Bustamante D, Delgado R,

Buscaglia M, Herrera-Marschitz M (2014) Overexpression of

hyperpolarization-activated cyclic nucleotide-gated channels into

the ventral tegmental area increases the rewarding effects of

ethanol in UChB drinking rats. Alcohol Clin Exp Res 38:911–920.

Rodd-Henricks ZA, McKinzie DL, Crile RS, Murphy JM, McBride WJ

(2000) Regional heterogeneity for the intracranial self-

administration of ethanol within the ventral tegmental area of

female Wistar rats. Psychopharmacology (Berl) 149:217–224.

Rodd-Henricks ZA, Melendez RI, Zaffaroni A, Goldstein A, McBride

WJ, Li TK (2002) The reinforcing effects of acetaldehyde in the

posterior ventral tegmental area of alcohol-preferring rats.

Pharmacol Biochem Behav 72:55–64.

Rodd-Henricks ZA, McKinzie DL, Melendez RI, Berry N, Murphy JM,

McBride WJ (2003) Effects of serotonin-3 receptor antagonists on

the intracranial self-administration of ethanol within the ventral

tegmental area of Wistar rats. Psychopharmacology (Berl)

165:252–259.

Rodd ZA, Bell RL, Melendez RI, Kuc KA, Lumeng L, Li TK, Murphy

JM, McBride WJ (2004a) Comparison of intracranial self-

administration of ethanol within the posterior ventral tegmental

area between alcohol-preferring and Wistar rats. Alcohol Clin Exp

Res 28:1212–1219.

Rodd ZA, Melendez RI, Bell RL, Kuc KA, Zhang Y, Murphy JM,

McBride WJ (2004b) Intracranial self-administration of ethanol

within the ventral tegmental area of male Wistar rats: evidence for

involvement of dopamine neurons. J Neurosci 24:1050–1057.

Rodd ZA, Bell RL, Kuc KA, Zhang Y, Murphy JM, McBride WJ

(2005a) Intracranial self-administration of cocaine within the

posterior ventral tegmental area of Wistar rats: evidence for

involvement of serotonin-3 receptors and dopamine neurons. J

Pharmacol Exp Ther 313:134–145.

Rodd ZA, Bell RL, McQueen VK, Davids MR, Hsu CC, Murphy JM, Li

TK, Lumeng L, McBride WJ (2005b) Prolonged increase in the

sensitivity of the posterior ventral tegmental area to the reinforcing

effects of ethanol following repeated exposure to cycles of ethanol

access and deprivation. J Pharmacol Exp Ther 315:648–657.

Rodd ZA, Bell RL, McQueen VK, Davids MR, Hsu CC, Murphy JM, Li

TK, Lumeng L, McBride WJ (2005c) Chronic ethanol drinking by

alcohol-preferring rats increases the sensitivity of the posterior

ventral tegmental area to the reinforcing effects of ethanol.

Alcohol Clin Exp Res 29:358–366.

Rodd ZA, Bell RL, Zhang Y, Murphy JM, Goldstein A, Zaffaroni A, Li

TK, McBride WJ (2005d) Regional heterogeneity for the

intracranial self-administration of ethanol and acetaldehyde

within the ventral tegmental area of alcohol-preferring (P) rats:

involvement of dopamine and serotonin.

Neuropsychopharmacology 30:330–338.

Rodd ZA, Gryszowka VE, Toalston JE, Oster SM, Ji D, Bell RL,

McBride WJ (2007) The reinforcing actions of a serotonin-3

receptor agonist within the ventral tegmental area: evidence for

subregional and genetic differences and involvement of dopamine

neurons. J Pharmacol Exp Ther 321:1003–1012.

Rodd ZA, Oster SM, Ding ZM, Toalston JE, Deehan G, Bell RL, Li TK,

McBride WJ (2008) The reinforcing properties of salsolinol in the

ventral tegmental area: evidence for regional heterogeneity and

the involvement of serotonin and dopamine. Alcohol Clin Exp Res

32:230–239.

Rodd ZA, Bell RL, Oster SM, Toalston JE, Pommer TJ, McBride WJ,

Murphy JM (2010) Serotonin-3 receptors in the posterior ventral

tegmental area regulate ethanol self-administration of alcohol-

preferring (P) rats. Alcohol 44:245–255.

Roeper J (2013) Dissecting the diversity of midbrain dopamine

neurons. Trends Neurosci 36:336–342.

Rotllant D, Marquez C, Nadal R, Armario A (2010) The brain pattern

of c-fos induction by two doses of amphetamine suggests different

brain processing pathways and minor contribution of behavioural

traits. Neuroscience 168:691–705.

Sanchez-Catalan MJ, Hipolito L, Guerri C, Granero L, Polache A

(2008) Distribution and differential induction of CYP2E1 by

ethanol and acetone in the mesocorticolimbic system of rat.

Alcohol Alcohol 43:401–407.

Sanchez-Catalan MJ, Hipolito L, Zornoza T, Polache A, Granero L

(2009) Motor stimulant effects of ethanol and acetaldehyde

injected into the posterior ventral tegmental area of rats: role of

opioid receptors. Psychopharmacology (Berl) 204:641–653.

Scammell TE, Estabrooke IV, McCarthy MT, Chemelli RM,

Yanagisawa M, Miller MS, Saper CB (2000) Hypothalamic

arousal regions are activated during modafinil-induced

wakefulness. J Neurosci 20:8620–8628.

Schifirnet E, Bowen SE, Borszcz GS (2014) Separating analgesia

from reward within the ventral tegmental area. Neuroscience

263:72–87.

Schweimer JV, Coullon GSL, Betts JF, Burnet PW, Engle SJ,

Brandon NJ, Harrison PJ, Sharp T (2014) Increased burst-firing of

ventral tegmental area dopaminergic neurons in d-amino acid

oxidase knockout mice in vivo. Eur J Neurosci. http://dx.doi.org/

10.1111/ejn.12667.

Shabat-Simon M, Levy D, Amir A, Rehavi M, Zangen A (2008)

Dissociation between rewarding and psychomotor effects of

opiates: differential roles for glutamate receptors within anterior

216 M. J. Sanchez-Catalan et al. / Neuroscience 282 (2014) 198–216

and posterior portions of the ventral tegmental area. J Neurosci

28:8406–8416.

Soderman AR, Unterwald EM (2008) Cocaine reward and

hyperactivity in the rat: sites of mu opioid receptor modulation.

Neuroscience 154:1506–1516.

Spanagel R, Kiefer F (2008) Drugs for relapse prevention of

alcoholism: ten years of progress. Trends Pharmacol Sci

29:109–115.

Stamatakis AM, Stuber GD (2012) Activation of lateral habenula

inputs to the ventral midbrain promotes behavioral avoidance. Nat

Neurosci 15:1105–1107.

Stamatakis AM, Jennings JH, Ung RL, Blair GA, Weinberg RJ, Neve

RL, Boyce F, Mattis J, Ramakrishnan C, Deisseroth K, Stuber GD

(2013) A unique population of ventral tegmental area neurons

inhibits the lateral habenula to promote reward. Neuron

80:1039–1053.

Swanson LW (1982) The projections of the ventral tegmental area

and adjacent regions: a combined fluorescent retrograde tracer

and immunofluorescence study in the rat. Brain Res Bull

9:321–353.

Terashvili M, Wu HE, Leitermann RJ, Hung KC, Clithero AD,

Schwasinger ET, Tseng LF (2004) Differential conditioned place

preference responses to endomorphin-1 and endomorphin-2

microinjected into the posterior nucleus accumbens shell and

ventral tegmental area in the rat. J Pharmacol Exp Ther

309:816–824.

Tsai CE (1925) The optic tracts and centers of the opossum,

didelphis virginiana. J Comp Neurol 39:173–219.

Ungerstedt U (1971) Stereotaxic mapping of the monoamine

pathways in the rat brain. Acta Physiol Scand Suppl 367:1–48.

Usuda I, Tanaka K, Chiba T (1998) Efferent projections of the nucleus

accumbens in the rat with special reference to subdivision of the

nucleus: biotinylated dextran amine study. Brain Res 797:73–93.

Walsh JJ, Han MH (2014) The heterogeneity of ventral tegmental

area neurons: projection functions in a mood-related context.

Neuroscience 282:101–108.

Wang HL, Morales M (2008) Corticotropin-releasing factor binding

protein within the ventral tegmental area is expressed in a subset

of dopaminergic neurons. J Comp Neurol 509:302–318.

Wasserman DI, Wang HG, Rashid AJ, Josselyn SA, Yeomans JS

(2013) Cholinergic control of morphine-induced locomotion in

rostromedial tegmental nucleus versus ventral tegmental area

sites. Eur J Neurosci 38:2774–2785.

Wei-Malherbe H, Bone AD (1957) Intracellular distribution of

catecholamines in the brain. Nature 180:1050–1051.

Xie G, Hipolito L, Zuo W, Polache A, Granero L, Krnjevic K, Ye JH

(2012) Salsolinol stimulates dopamine neurons in slices of

posterior ventral tegmental area indirectly by activating mu-

opioid receptors. J Pharmacol Exp Ther 341:43–50.

Xie G, Ye JH (2012) Salsolinol facilitates glutamatergic transmission

to dopamine neurons in the posterior ventral tegmental area of

rats. PLoS One 7:e36716.

Yetnikoff L, Lavezzi HN, Reichard RA, Zahm DS (2014) An update on

the connections of the ventral mesencephalic dopaminergic

complex. Neuroscience 282:1–12.

Zahm DS, Becker ML, Freiman AJ, Strauch S, Degarmo B, Geisler S,

Meredith GE, Marinelli M (2010) Fos after single and repeated

self-administration of cocaine and saline in the rat: emphasis on

the Basal forebrain and recalibration of expression.

Neuropsychopharmacology 35:445–463.

Zangen A, Ikemoto S, Zadina JE, Wise RA (2002) Rewarding and

psychomotor stimulant effects of endomorphin-1: anteroposterior

differences within the ventral tegmental area and lack of effect in

nucleus accumbens. J Neurosci 22:7225–7233.

Zangen A, Solinas M, Ikemoto S, Goldberg SR, Wise RA (2006) Two

brain sites for cannabinoid reward. J Neurosci 26:4901–4907.

Zhang D, Dragomir A, Akay YM, Akay M (2014) Nicotine exposure

increases the complexity of dopamine neurons in the

parainterfascicular nucleus (PIF) sub-region of VTA. J Neuroeng

Rehabil 11:103.

Zhao-Shea R, Liu L, Soll LG, Improgo MR, Meyers EE, McIntosh JM,

Grady SR, Marks MJ, Gardner PD, Tapper AR (2011) Nicotine-

mediated activation of dopaminergic neurons in distinct regions of

the ventral tegmental area. Neuropsychopharmacology

36:1021–1032.

Zhou L, Furuta T, Kaneko T (2003) Chemical organization of

projection neurons in the rat accumbens nucleus and olfactory

tubercle. Neuroscience 120:783–798.

(Accepted 10 September 2014)(Available online 18 September 2014)