Hippocampus and serotonin

The Hippocampus and Serotonin Receptors:

A table of contents

• Characteristics of the Raphe Nuclei• Function of the Raphe Nuclei• Malfunction of the hippocampus in depression• Serotonin Receptors (5-HTRs) and Signal

Transduction• 5-HT innervations in the hippocampus• Signal Transduction of the pyramidal cells• Summary

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A table of contents



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Major depression is one of the most common mood disorders(over 20% of U.S. for over 18 yo during life, NIH).

Symptoms: A loss of interest, Change of mood representations, Impairment of social, occupational, or educational function, Sleep problem(Insomnia or hypersomnia), indecisive, Suicidality, Worthlessness(DSM-IV, 1994)

Why Serotonin?:

Low levels of serotonin in the patients(Serotonin-deficiency theory)[Lacasse, Plos Med., 2005]

Strong evidence:

Selective Serotonin Reuptake Inhibitors(SSRI) -> induction of extracellular serotonin increase

•　 Major antidepressant drugs(about -70%)

However, detailed etiology is still unknown.

What is depression? And What’s the cause

Aim of This Independent StudySome discrepancies:

1) A slow effect of SSRI on mood even after acute treatment[Harmer, BJPsychiatry, 2009]

2) SSRI is not completely effective(Dopamine theory, BDNF theory)[Dunlop, Arch Gen psychiatry, 2006;Trivedi, The New England Journal of Medicine, 2006]

On the other hand….(several indication)

1)15 subgroups of Serotonin (5-HT) receptor family and different effect on neurons

2) Region-dependent distribution of the receptors

3) Strong Serotonergic innervations related with several brain regions in the depression patients(the hippocampus, the basal ganglia, and the amygdala).

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Serotonergic projections

Presumption of depression

Presumption:

• Neuronal network might cause differential effect on multiple brain regions due to different receptor types of serotonin.

Purpose of this seminar

• Summary of detailed survey of serotonin innervations

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A table of contents

• Characteristics of the Raphe Nuclei• Serotonin Receptors (5-HTRs) and Signal

Transduction• Malfunction of the hippocampus in depression• 5-HT innervations in the hippocampus• Signal Transduction of the pyramidal cells• Summary

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Serotonin (5-HT)

• One of monoamine neurotransmitters

• 5-HT, tryptophan, and melatonin are related metabolites.

• Breathing rhythms, heart rate, locomotion, circadian rhythms, emotions, and neurogenesis.

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General Characteristics of Raphe NucleiClassification:

The raphe nuclei: serotonin (5-HT) containing neuron clusters(Midline of the brainstem)

•　 Subdivisions in rats:

B1: Raphe Pallidus, B2: Raphe Obscurus, B3: Raphe magnus, B4: Raphe Obscurus(dorsolateral part), B5: Raphe Pontis, B6: Dorsal Raphe Nucleus(caudal part), B7: Dorsal Raphe Nucleus(Principal part), B8:Median Raphe Necules(Main party), B9:Dorsal Pontine Tegmentum

• 85% of 5-HT neurons in Rostral(B7, B8) part of human brains[Hornung, J. Chemi. Neuroana. 2003]

9[Siegel, 2008]

Fig 2 Caudal part(B1-3), Rostral(B7, B8)[Stahl S., 1996] revised by CNS

General Characteristics of Raphe Nuclei

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[Vertes and Linley, International Congress Series, 2007]

Dorsal Raphe(DR) projections in rat:the ventral tegmental area(VTA), the substantia nigra pars compacta(SNc), some regions of hypothalamus, amygdala complexes, dorsal and ventral striatum, lateral septum(LS), the entorhinal(EC), medial orbital (MO) and the medial prefrontal cortex (mPFC), the hippocampus. (anterograde tracer with PHA-L[Vertes and Linley, 2007])

Median Raphe(MR) projections in rat:the interpeduncular nucleus, VTA, medial mammillary nucleus, parts of the midline and intralaminar thalamus, the lateral habenula, septum, ventral striatum(Nucleus accumbens), the hippocampus, medial septum (MS)[Vertes J.Comp. Neurol, 1999; Vertes and Linley, 2007].

DR: cell size(30-40um), fusiform, darkly stained

MR: cell size(10-12um), oval, lightly stained[Verte., 2007]

Blue: dopaminergic nucleiRed: Amygdala relatedOrange: Basal GangliaBrown: hippocampus

Reciprocal links between DRN and MRN

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DRN

MRN

“We are brothers and friends, but…”

Glu application into the DRN[Mokler, 2009]

unknown

Glu application into the MRN[Mokler, 2009]

Mutual connections in rats and hamster[Vertes and et al., 1988, 1991, 1999; Tisheler and Morin, Brain Res., 2003]

The mean of extracellular 5-HT: DRN(15.6 ± 2.4 fmol/20ul = 0.78 ± 0.12 nmol/l; n = 16), MRN(10.6 ± 1.3 fmol/20ul = 0.53 ± 0.065 nmol/l; n=16)[Mokler, Brain Res., 2009]

Putative Firing rate of 5-HT neurons: DRN(1.34 ± 0.09 Hz), MRN(0.54 ± 0.05 Hz)[Judge., etal, Neurochemi., 2006]

DRN affects MRN, but MDR does not affect much.

Function of DRN -Patience and Impulsivity-Patience and Impulsivity

1. Activation 5-HT Neurons in DRN during waiting delayed rewards

2. Negative correlation between 5-HT activity and Wait Error.

Omission trials counted by removal of nose-poking.

13[Miyazaki et al., Mol Neurobiol, 2012]

Disruption of theta rhythms by stimulation of Serotonergic neurons in MRN

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MS – DBB: Medial septum-diagonal band of BrocaLHA: Lateral hypothalamic areaHypocretin: Orexin

Theta Rhythms (4 - 10 Hz): relationship with memory consolidation in the hippocampus and possible to be induced by stress

Induction of Inescapable foot shook by MS-DBBPrevention of theta rhythms by lesion of MS – DBB[]

[Hsiao et al., Behavioral Brain Resarch,2012]

(cited from UCLA facility)

[Hsiao et al., Behavioral B. Res., 2013]

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Malfunction of hippocampal neurogenesis hypothesis

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Slow effect of SSRI or Antidepressant drugs (AD) -> Morphological changes (?)

[Berton, Nature Neuro., 2006]

• Brain-Derived Neurotrophin Factor (BDNF) -> Induction of Neuro-proliferation -> Promotion of Neurogenesis• Decrease of BDNF by stress in hippocampus[Smith et al., 1995]

• BDNF mRNA promotion by AD drugs[Nibuya, J. Nuro., 1995]

Chronic ADs increase neurogenesis in Rat hippocampus[Malberg, J. Neuro., 2000]

Measurement of helplessness and anxiety

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The Forced Swim Test:Check immovability of mice

Normal: Try to avoid waterAbnormal: Be quiet.

Interpretation: immovability shows despair.

The Novelty Suppressed Feeding (NSF) test

Check amount of foods in a novel environment after removal of feeding.

Interpretation: hesitation for rewards shows level of anxiety of a new environment.

Malfunction of hippocampal neurogenesis hypothesis

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The novelty suppressed feeding[Kuteeva, Springer, 2010].

Selective inhibition of neurogenesis -> Prevention of Antidepressant Drugs effects[Santarelli et al., Science,

2003]

[Bremner JD., CNS, 2002]

Hippocampal volume reduction in depression patients

A table of contents



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Serotonin Receptors

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Subtypes Agonists Antagonists G protein Localization Function

5-HT1A Tetalin, 5-MeO- DMT, BAY, 8-OH-DOAT

Spiperone, WAY-100135

Gi(AC↓, open K+), Go(close Ca2+)

Hippocumpus,the lateral septum,entorhinal and cingular cortices, dorsal raphe nucleus

Autoreceptor, Heteroreceptor

5-HT1B (unselective) TFMPP, CGS12066B,Sumat riptan, L694247

Isamoltane, GR-55562, SB 224289, SB-236057

Gi(AC↓) SN,globus pallidus,caudate putamen,ventral pallidum,entopeduncular nucleus,hippocampus, cortex,VTA

Autoreceptor

5-HT1D Sumatriptan, PNU 109291, BRL 15572

GR-127935 Gi(AC↓) SN,globus pallidus,caudate putamen,ventral pallidum,entopeduncular nucleus,hippocampus, cortex,VTA

Autoreceptor

5-HT1E Gi(AC↓) The caudate,putamen amygdala,and cortical areas(Bruinvels, 1994)

5-HT1F Gi(AC↓) hippocumpus cortical areas

5-HT2A DOI, DOB, α-Me5- HT

ritanserin(vgedo ,1989)

Gq(PLC)↑ Cortex, claustrum, hippocampus, hypothalamus, basal ganglia

Post synaptically expressed

5-HT2C SB-243213(Blackbu rn et al., 2002)

Mesulergine, SB-242084, RS-102221

Gq(PLC)↑ the chroid plexus, the frontal cortex,the limbic system,hippocumpus,septum,hypot halamus, striatum,nucleus accumbens,rhombencephalon,spin al cord [Filip, 2009;Hoyer,

2002]

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Subtypes Agonists Antagonists G protein Localization

5-HT3 α-Me-5-HT

DAU 6215Zacopride, Odanserton, GranisotronZatosetron

None(Ion channels-influx Na+, Ca2+, efflux K+)

the caudal medulla, forebrain, SN, N. AC, prefrontl cortex, striatum

GABA-containing cells in neocortex, olfactory cortex, hippocampus, amygdala

5-HT4 SC-53116

SDZ-205557GR-125487

Gs(AC↑) limbic regions, the olfactory system, striatum, medial habenula, hippocampus

5-HT5A Gi/o(AC↓) Hippocampus, hypothalamus, olfactory bulb, cortex, thalamus, striatum, pons

5-HT5B ? Habenula, raphe nucleui, hippocampus(in rodents); pseudogene(in humans)

5-HT6 Lisuride, ColozapineSB271046

Gs(AC↑) Striatum, olfactory tubercle, N. Acc,

5-HT7 LSD Clozapine, Amitryptline Gs(AC↑) hypothalamus, thalamus, brain stem, striatum, cerebral cortex.

[Filip, 2009;Hoyer, 2002]

Serotonin receptors and Signal Transduction

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[Berumen et al., The Scientific World Journal,2012]

Serotonin Receptors and Signal Transduction

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24[Berumen et al., The Scientific World Journal,2012]

Serotonin Receptors and Signal Transduction

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[Berumen et al., The Scientific World Journal,2012]

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A table of contents



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Hippocampus and 5-HT Ascending Projections

CC: Central Gray

GCL: granule cell layer

Mo: Molecular layer of Dentate Gyrus

PCL: Pyramidal Layer

SLM: Stratum lacunosum-moleculare

SR: Stratum radiatum

SOr: Stratum oriens29

Mouse Brain(cited from NeuroDigi)

PHA-L 5-HT fibers[Morin et al., 1999] PHA-L MR fibers to hippocampus[Morin et al., 1999]

PHA-L MR fibers in ventral Hippocampus[Vertes, 1999]

MR fibers in dorsal

Hippocampus[Vertes,

1999]

Serotonin Receptor Expression in the mouse hippocampus

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5-HTR

Hippo. Localization

1A granular, pyramidal N., and some glia (Presynaptic R as well)

1B Presynaptic N. of DRN or MRN

2A granular, pyramidal, and astrocytes

2C CA3 pyramidal.

3A CA2 and C3 Pyramidal N.

4 Cholinergic axon

5A Astrocytes

5B CA1 pyramidal cells

7 CA1 neurons

Serotonin Receptor Expression in the mouse hippocampus

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GCL: Granule cell layer, GluML: molecular layer,

Hilus:

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SSRI induces neurogenesis[Santralli, 2003]-> 5-HT increase in DG.

Q1. Which receptor is dominant?Assumption(As) . Maybe 5-HT1AR, and linking to inhibition of AC.

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Q1. Which receptor is dominant?Assumption(As). Maybe 5-HT1AR, and linking to inhibition of AC.

Q2. Express where?

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Q2. Express where?a) Induction of neurogenesis by 5-HT1A agonist in DG[Grabiec, 2009].b) Inhibition of cell proliferation by 5-HT1A antagonist[Radley, JJ., 2002].

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Q2. Express where?a) Induction of neurogenesis by 5-HT1A agonist in DG[Grabiec, 2009].b) Inhibition of cell proliferation by 5-HT1A antagonist[Radley, JJ., 2002].

As: 1. GABA > PyramidalHow b) happen?

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Q2. Express where?a) Induction of neurogenesis by 5-HT1A agonist in DG[Grabiec, 2009].b) Inhibition of cell proliferation by 5-HT1A antagonist[Radley, JJ.].


2. Pyramidal > GABA5-HT1A G protein activates cAMP?

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Q2. Express where?a) Induction of neurogenesis by 5-HT1A agonist in DG[Grabiec, 2009].b) Inhibition of cell proliferation by 5-HT1A antagonist[Radley, JJ.].


2. Pyramidal > GABA5-HT1A G protein activates cAMP?

3. Other receptors? Other G proteins?

4. 5-HT increase in DG?

Signal Transduction of Pyramidal neurons

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Unknown

[Dumen et al., 2012]

Summary

• 1. Serotonergic neurons project to the basal ganglia, the amygdala complex, the hippocampus, and others.

• 5-HT affect neurogenesis as well as anxiety.• Differential 5-HTRs’ expression in

hippocampus.• A causal receptor is still unknown.

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40Dance of the Rats[17c, Germany]

Discussion Time

Health & Medicine

Hippocampus and serotonin