Compulsive Drug-Seeking Behavior and Relapse : Neuroadaptation, Stress, and Conditioning Factors

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Compulsive Drug-Seeking Behavior and Relapse

Neuroadaptation, Stress, and Conditioning Factors

FRIEDBERT WEISS,a ROBERTO CICCOCIOPPO,b LOREN H. PARSONS,a

SIMON KATNER,a XIU LIU,a ERIC P. ZORRILLA,a GLENN R. VALDEZ,aOSNAT BEN-SHAHAR,c STEFANIA ANGELETTI,b ANDREGINA R. RICHTERd

aDepartment of Neuropharmacology, The Scripps Research Institute, La Jolla,California 92037, USAdDepartment of Molecular Neurobiology, Institute of Molecular Pharmacology,10315 Berlin, Germany

ABSTRACT: The development of addiction and vulnerability to relapse fol-lowing withdrawal is proposed to be the result of neuroadaptive processeswithin the central nervous system that oppose the acute reinforcing actionsof drugs of abuse. These changes lead to impairment in the mechanismsthat mediate positive reinforcement and the emergence of affective chang-es such as anxiety, dysphoria, and depression during withdrawal. Consid-erable evidence exists implicating perturbations in DA and 5-HTtransmission in the nucleus accumbens—neurochemical systems that areactivated by cocaine and ethanol self-administration and deficient duringwithdrawal—as potential substrates for these affective changes. In addi-tion, growing evidence suggests that enhanced CRF release in the centralnucleus of the amygdala represents a mechanism underlying the anxiogen-ic and stress-like consequences of withdrawal that are common to all drugsof abuse. A growing body of evidence also implicates dysregulation of thenon-neuroendocrine CRF stress system within the central nucleus of theamygdala as a common factor in the anxiogenic and aversive consequencesof withdrawal from drugs of abuse. Moreover, a possible link may exist be-tween long-lasting abnormalities in CRF function in the CeA and vulner-ability to relapse during protracted abstinence. Another presumablycritical element contributing to the chronic relapsing nature of drug addic-tion is the learned responses to drug-related stimuli. The long-lasting effi-

bCurrent address: Department of Pharmacological Sciences and Experimental Medicine, Uni-versity of Camerino, 62032 Camerino, Italy.

cCurrent address: Department of Psychology, University of California, Santa Barbara, CA93106, USA.

Address for correspondence: Friedbert Weiss, Department of Neuropharmacology, TheScripps Research Institute, La Jolla, CA 92037.

[email protected]

2 ANNALS NEW YORK ACADEMY OF SCIENCES

cacy of drug- and alcohol-associated contextual stimuli in eliciting drug-seeking behavior in animal models of relapse resembles the endurance ofconditioned cue reactivity and cue-induced cocaine craving in humans andconfirms a significant role of learning factors in the long-lasting addictivepotential of cocaine. With cocaine, D1-dependent neural mechanisms with-in the medial prefrontal cortex and basolateral amygdala may be impor-tant substrates for the motivating effects of drug-related environmentalstimuli. With ethanol, available data suggest a role for opioid receptors inthe mediation of conditioned drug-seeking behavior. Finally, conditioningfactors (i.e., exposure to drug-associated stimuli) and stress can interact toaugment vulnerability to relapse. This finding emphasizes that it will beimportant to consider the simultaneous effects of multiple environmentaltriggers for relapse in the development of treatment and medicationstrategies.

KEYWORDS: Addiction, drug; Cocaine; Compulsive drug-seeking behav-ior; CRF; Dopamine; Drug-seeking behavior; Ethanol; Self-administra-tion; Reinstatement; Serotonin

INTRODUCTION

Drug addiction is a chronic relapsing disorder characterized by compulsivedrug-seeking and use. The long-lasting nature of this compulsion and thehigh rates of recidivism present a considerable challenge in the treatment ofdrug and alcohol addiction such that understanding the neurobiological basisof relapse has emerged as a central issue in addiction research. Two majortheoretical positions exist to explain the persistence of addictive behavior andthe vulnerability to relapse associated with drug and alcohol addiction:homeostatic hypotheses and conditioning hypotheses.

Homeostatic hypotheses relate relapse risk to neuroadaptive changes anddisruption of neuroendocrine homeostasis that are thought to underlie anxi-ety, mood dysregulation, and somatic symptoms that accompany acute with-drawal and that can persist for considerable periods of time during what hasbeen referred to as the “protracted withdrawal” phase. This view, therefore,implicates alleviation of discomfort and negative affect as a motivational ba-sis for relapse. Conditioning hypotheses are based on observations that re-lapse is often associated with exposure to drug-related environmental stimuli.This view holds that specific environmental stimuli that have become associ-ated with the rewarding actions of a drug by means of classical conditioningcan elicit subjective states that trigger resumption of drug use. The homeo-static and conditioning hypotheses are not mutually exclusive. In fact, ho-meostatic and conditioning factors are likely to exert additive effects in thatexposure to drug-related environmental stimuli may augment vulnerability torelapse conveyed by homeostatic disturbances. The experiments to be de-

3WEISS et al.: COMPULSIVE DRUG-SEEKING BEHAVIOR

scribed were designed to study the neurochemical alterations that may under-lie withdrawal symptoms and vulnerability to relapse after chronic drugabuse. In addition, these studies examine the role of conditioning factors andtheir neurobiological basis in the development of long-lasting relapse risk.

DYSREGULATION OF NEURAL MECHANISMS THATMEDIATE REWARD

Growing evidence suggests that chronic drug use can produce profoundchanges in neural mechanisms that mediate positive reinforcement. This is il-lustrated, for example, by findings that most drugs of abuse acutely facilitatethe rewarding effects of intracranial self-stimulation,1–3 whereas withdrawalafter chronic use leads to impairment in the rewarding efficacy of electricalbrain stimulation4–9 and behavioral disruptions (e.g., see refs. 10 and 11) be-lieved to be indicative of dependence and withdrawal. Similarly, rats givenprolonged access to cocaine or heroin will escalate their drug intake on a dai-ly basis and show long-lasting enhancement in the intake of cocaine or heroinacross different unit doses;12,13 this effect has been interpreted to reflect neu-

FIGURE 1. Effect of 12-hour unlimited-access cocaine self-administration and sub-sequent withdrawal on extracellular 5-HT and DA levels in the nucleus accumbens asmeasured by microdialysis. (Reprinted with permission from Ref. 18.)


roadaptive dysregulations, resulting in increased hedonic or reward “setpoint” rather than tolerance. Findings such as these have given rise to theview that compulsive drug-seeking behavior may be the result of adaptiveprocesses within the central nervous system that oppose the acute reinforcingactions of drugs, leading to both a “blunting” of mechanisms that mediatepositive reinforcement and the emergence of affective changes (e.g., anxiety,dysphoria, and depression) during withdrawal that may motivate continueddrug use or relapse.14–16

Functional changes within the brain reward circuitry that may contribute tothese behavioral changes include abnormalities in dopaminergic and seroton-ergic transmission in the nucleus accumbens. For example, rats given 12hours of unlimited access to cocaine show significant decreases in extracel-lular dopamine (DA) and serotonin (5-HT) levels within the nucleus accum-bens during subsequent withdrawal as measured by microdialysis (FIG. 1).These synaptic monoamine deficits emerge within 2 hours of withdrawal anddo not recover within 10–12-hour monitoring periods.17,18 Previous evidencelinks dysfunctions in mesolimbic DA transmission with behavioral abnor-malities such as dysphoria and anergia (e.g., see refs. 19 and 20), and deficitsin serotonergic transmission with disorders such as depression, panic disor-

FIGURE 2. Effects of local 5-HT administration by reverse microdialysis on extra-cellular DA levels in the nucleus accumbens of rats. Perfusate concentrations of up to 10nM had no significant effect in drug-naïve controls (Cocaine Naïve) and in rats that hadreceived only 3-hour limited daily access to cocaine during self-administration training(Cocaine Trained). By contrast, local 5-HT (10 nM) application significantly increasedextracellular DA concentrations as measured after 6 hours of withdrawal following a 12-hour session of unrestricted cocaine self-administration (12-hour). (Reprinted with per-mission from Ref. 18.)


der, and insomnia (e.g., see refs. 21–23). Because these conditions are alsocommon cocaine withdrawal symptoms (e.g., see refs. 24–26), the postco-caine deficits in extracellular DA and 5-HT may represent a neurochemicalbasis for these aspects of the cocaine withdrawal syndrome. In particular, thefinding of synaptic DA deficiency during withdrawal complements evidencethat the D2 agonist bromocriptine effectively reverses postcocaine deficits inbrain stimulation reward27 and confirms a link between withdrawal-associat-ed impairments in mesolimbic DA neurotransmission and attenuated brainstimulation reward.

In addition, recent findings show that neural systems involved in the medi-ation of the reinforcing actions of drugs of abuse become dysregulated in amultidirectional manner, and these changes may set the stage for further dis-ruption rather than allow the functioning of these systems to recover. For ex-ample, although synaptic levels of dopamine show a deficiency duringcocaine withdrawal, dopamine release shows a profound sensitization18

(FIG. 2) to the well-established permissive or facilitatory function of seroto-

FIGURE 3. Locomotor response of rats to the 5-HT1B agonist RU 24969 (1 mg/kg,sc) after different times of withdrawal from IV cocaine self-administration (0.25 mg/in-fusion). Data shown are from three groups of rats: (1) drug-naive catheterized animals(Cocaine-Naïve); (2) rats given 21 consecutive daily 3-hour cocaine self-administrationsessions (Limited-Access); and (3) animals given 20 consecutive 3-hour self-administra-tion sessions, followed by an extended 12-hour self-administration session on day 21(Extended-Access). Data represent the total number of cage-crossings (mean ± SEM)during a 2-hour period following RU 24969 administration. The dashed line correspondsto the mean locomotor response of the Cocaine-Naive group to RU 24969 across all testdays and is provided as a comparison for the motor responses of the Limited-Access andExtended-Access groups. §Significant reduction in locomotor activity relative to Co-caine-Naive controls (p <0.05). *Significant enhancement in the motor response to RU24969 vs. Cocaine-Naïve controls.


FIGURE 4. Effects of ethanol withdrawal and operant alcohol self-administrationon DA efflux in the nucleus accumbens. Rats in the Dependent group (C) were made de-pendent on ethanol via an ethanol (8.7% w/v) liquid-diet regimen. Nondependent rats (B)were pair-fed with ethanol-free liquid diet and trained to self-administer either ethanol orwater in daily 30-minute limited-access sessions. Dialysate DA levels are compared tothose in Ethanol-Naive rats (A) trained to self-administer water only. Average water in-take in this group was negligible (<0.8 ml) and is not shown. Amounts of self-adminis-tered ethanol (10% w/v) during 10-minute intervals for the Dependent (solid bars) andNondependent (open bars) groups are shown at the bottom of the figure. A, B, and Cshow dialysate DA concentrations during the last hour of ethanol- (or control) diet avail-


nin on dopamine release in the nucleus accumbens.28,29 Similarly, the seroto-nin 5-HT-1B receptor, which is thought to play a role in the reinforcing actionsof cocaine by modulating the release of GABA in the ventral tegmental area,shows biphasic alterations with subsensitivity during acute cocaine with-drawal and supersensitivity during protracted withdrawal30 (FIG. 3). The ini-tial subsensitivity presumably reflects an adaptive “downregulation” of 5-HT-1B receptors that develops during long-term cocaine self-administrationto compensate for the sustained cocaine-induced increases in synaptic sero-tonin levels. The supersensitivity at later time points may be a consequenceof a compensatory upregulation of 5-HT1B receptors in response to postco-caine deficits in extracellular 5-HT. These findings implicate alterations in 5-HT-1B receptor function in both the cocaine withdrawal syndrome and thepersistent behavioral and neurochemical sensitization that is often associatedwith chronic cocaine exposure.

Monoamine deficits similar to those associated with cocaine withdrawalhave been reported during withdrawal from ethanol in dependent rats. Acti-vation of meso-accumbens DA neurotransmission has been widely implicat-ed in the acute reinforcing effects of ethanol (for review see refs. 31 and 32).Whereas ethanol self-administration increases the release of DA from the nu-cleus accumbens in nondependent rats,33 this effect shows tolerance in thedependent state.34 Moreover, significant deficiencies in accumbal DA release(FIG. 4) and decrements in mesolimbic neuronal activity are commonly ob-served during ethanol withdrawal.34–37 Interestingly, rats given the opportu-nity to self-administer ethanol during withdrawal regulate their ethanol intakein a manner that restores extracellular DA concentrations in the nucleus ac-cumbens to pre-withdrawal levels (FIG. 4), and this observation identifies ac-cumbal DA neurotransmission as a possible factor in ethanol-maintainednegative reinforcement and, by extension, in continued abuse anddependence.34

Neuroadaptive changes similar to those observed with dopamine have beenreported in serotonergic systems after chronic ethanol exposure. Whereasethanol self-administration acutely enhances the release of 5-HT from the nu-cleus accumbens,38 ethanol withdrawal in dependent rats is associated withprogressive suppression of 5-HT release in this brain region.34 These findings

ability (BSL) and during the last 60 minutes of an 8-hour withdrawal period (WD), fol-lowed by a 1-hour period of response-contingent ethanol (10% w/v) availability (Self-Administration). In Nondependent rats, ethanol self-administration produced a signifi-cant increase in DA efflux (p <0.05). In Dependent rats, DA levels decreased significant-ly during withdrawal below pre-session values and levels in Ethanol-Naïve controls (p<0.001). Ethanol self-administration at the end of the withdrawal period restored DA lev-els to pre-withdrawal values. (Modified with permission from Ref. 34.)


of serotonergic deficiencies during withdrawal are consistent with clinicalstudies that revealed deficits in 5-HT synthesis, turnover, or receptor functionin alcoholics39–41 and support the hypothesis that impaired 5-HT function isan important neurochemical element in alcohol abuse and dependence.42

DYSREGULATION OF BRAIN STRESS SYSTEMS

Chronic drug abuse produces neuroadaptive changes not only within sys-tems implicated in the acute reinforcing effects of ethanol, but also withinother motivational systems, notably brain stress-regulatory mechanisms.Stress has an established role in the initiation and maintenance of drug abuseand is a major determinant of relapse in abstinent individuals.43–46 The signif-icance of stress in drug-seeking behavior has also been amply documented inthe animal literature. Physical, social, and emotional stress can facilitate ac-quisition or increase self-administration of cocaine,47–49 heroin,50 andethanol51–53 in rodents and nonhuman primates. Stressful stimuli have alsobeen shown to elicit reinstatement of cocaine, heroin, and ethanol-seekingbehavior in drug-free animals after extinction,54–56 and these findings provideexperimental support for the role of stress in relapse.

Traditionally, stress-related drug-seeking behavior was thought to be me-diated by activation of the hypothalamic-pituitary-adrenal (HPA) axis. How-ever, growing evidence suggests that the nonneuroendocrine corticotropin-releasing factor (CRF) system in the central nucleus of the amygdala (CeA)may play a significant independent role in the regulation of the addictive be-havior associated with stress. The CeA is rich in CRF immunoreactive cellbodies, terminals, and receptors, and this neuronal CRF system has been im-plicated in the mediation of behavioral and emotional responses to stressfulstimuli.57,58 For example, immobilization stress elevates extracellular CRFlevels in the CeA,59,60 whereas intra-CeA injection of the CRF receptor an-tagonist α-helical CRF9-41 reduces the behavioral signs of anxiety producedby social and environmental stressors.61,62 Anxiety and stress-like symptomsare central to drug and alcohol withdrawal syndromes. Considering the evi-dence of a role of CRF neurons in the CeA in the regulation of emotional andanxiogenic effects of stress, it is likely that anxiogenic and stress-like conse-quences of withdrawal from drugs of abuse may be mediated by the CRF sys-tem in the CeA as well.

Consistent with this possibility, extracellular CRF levels in the CeA, asmeasured by microdialysis, are substantially elevated during acute ethanol andcocaine withdrawal63,64 as well as during antagonist-precipitated withdrawalfrom chronic cannabinoid65 and morphine (Richter, Zorrilla, Schulkin, andWeiss, unpublished observations) treatment (FIG. 5), and functional antago-


nism of CRF transmission in the CeA attenuates aversive and anxiogenic-likebehavioral manifestations of alcohol66 and opiate withdrawal.67

Overall, these findings identify activation of CRF neurons in the CeA as acommon neurobiological mechanism for anxiogenic and stress-like symp-toms that accompany withdrawal from drugs of abuse. These findings alsomay have general implications concerning the neurobiological basis of drugaddiction. Activation of CRF neurotransmission in the CeA not only has beenimplicated in the anxiogenic effects of drug and alcohol withdrawal, but alsomay play a role in reward deficits and “dysphoria” as measured by brain stim-ulation reward thresholds68 that are a common consequence of withdrawalfrom drugs of abuse.69 Thus, changes in the regulation of the activity of theCRF system within the CeA may represent a critical neuroadaptive mecha-nism responsible for the development of dependence and compulsive drug-seeking behavior.

FIGURE 5. Extracellular CRF in the central nucleus of the amygdala (CeA) duringcocaine, ethanol, and cannabinoid withdrawal as measured by microdialysis. (5A) Mean(± SEM) CRF concentrations (expressed as percentage of baseline values) in the CeA ofrats at baseline, during a 12-hour cocaine self-administration session, and during a sub-sequent 12-hour withdrawal period (Cocaine Group). CRF levels in rats with the samehistory of cocaine self-administration training, but not given access to cocaine on the testday, are shown for comparison (Control Group). During cocaine self-administration,CRF concentrations in the cocaine group were decreased by about 25% relative to con-trols. Termination of access to cocaine resulted in a significant increase in CRF efflux thatbegan approximately 5 hours postcocaine and reached about 400% of pre-session base-line levels at the end of the withdrawal session. *p <0.05; **p <0.01; ***p <0.001. (Mod-ified with permission from ref. 64.)


Perturbations in non-neuroendocrine CRF mechanisms may have a rolenot only in acute but also in protracted withdrawal. A recent study examinedthis possibility by determining regional CRF tissue content in the amygdalafrom 1 day to 6 weeks after withdrawal from cocaine or ethanol in rats after3 weeks of exposure to an ethanol-containing liquid diet or after two 12-hourperiods of unrestricted access to intravenous cocaine.70 In both ethanol- andcocaine-withdrawn rats, CRF tissue content in the amygdala was significant-ly decreased during acute withdrawal (day 1). The initial deficiency in CRFtissue content was followed by a progressive increase in CRF content duringsubsequent postdrug test intervals with significantly elevated CRF levels 6weeks postwithdrawal (FIG. 6). The decrease in CRF tissue content duringacute withdrawal (day 1) is consistent with the increase in CRF output at theextracellular level, shown in FIGURE 5. Although the isolated measurement ofpeptide tissue levels performed here does not provide information as towhether this change was the result of altered release, synthesis, storage, ormetabolism, previous data suggest that the reduced amygdalar CRF tissue

FIGURE 5B. Effects of ethanol withdrawal on CRF levels in the rat CeA. Rats hadbeen made dependent by a chronic ethanol liquid-diet procedure (EtOH dependent). Ex-periments began with collection of basal fractions during which ethanol-containing liq-uid-diet diet was still available. At the end of this period, the bottle containing ethanoldiet was replaced by control diet. CRF measurements then were performed over four 2-hour periods alternating with 2-hour nonsampling periods for a total of 12 hours. CRFlevels significantly (p <0.01) increased during the withdrawal period up to 900% overlevels in nondependent rats, pairfed with control-diet (Control). (Modified with permis-sion from ref. 59.)


FIGURE 5D. Effects of morphine withdrawal on extracellular CRF in the CeA.Withdrawal was precipitated by administration of naltrexone (0.1 mg/kg, NTX) in ratsprepared with chronic morphine pellet implants. (From Richter, Zorrilla & Weiss, unpub-lished observations.)

FIGURE 5C. Effects of cannabinoid withdrawal, precipitated by the CB1 receptorantagonist SR 141716A (3 mg/kg) on CRF release from the CeA in rats pretreated for 14days with HU-210 (100 µg/kg/day), a cannabinoid CB1 agonist. Cannabinoid withdrawalinduced by SR 141716A (Long-Term HU-210 + SR 141716A) produced a significant (*p<0.005) transient increase in CRF release compared to vehicle-injected rats (Long-TermHU-210). (Modified with permission from ref. 108.)


content on the first day of withdrawal59 reflects depletion secondary to with-drawal-induced activation of CRF release.64,71,72

The neurochemical basis and functional significance of the rebound in-crease at later stages of protracted withdrawal (week 6) are presently unclear.With cocaine, it is known that chronic exposure per se does not persistentlyelevate CRF mRNA levels in the amygdala.73 However, the long-term persis-tence of withdrawal-induced changes in CRF synthesis within the amygdalahas, to our knowledge, not yet been studied. Reductions in CRF1 receptorbinding sites have been reported during acute cocaine withdrawal, but thesechanges returned to normal within 10 days of withdrawal.74 Considering thelate rebound increase in CRF tissue levels, alterations in CRF binding sites orbinding properties may, nonetheless, (re)emerge at later stages of withdrawal.Thus, it will be important to establish more systematically the mechanism un-derlying the apparent long-lasting dysregulation in amygdalar CRF suggest-ed by the whole-tissue data. The functional significance of increased CRFtissue content currently remains, similarly, unclear. Here, it is important toexamine the profile of CRF release in response to environmental challengesand corresponding changes in behavioral reactivity to stressors at differentstages of protracted withdrawal. Interestingly, preliminary results suggestthat 6 weeks postwithdrawal, ethanol-dependent rats may be more sensitive

FIGURE 6. Corticotropin-releasing factor-like immunoreactivity (CRF-IR) in tis-sue homogenates of rat amygdala measured 24 hours (day 1) and 6 weeks after ethanolor cocaine withdrawal. CRF-IR was measured following withdrawal from 24–28 days ofmaintenance on a chronic ethanol liquid diet (left panel) or after two 12-hour sessions ofunrestricted access to IV cocaine conducted on 2 consecutive days (right panel). *p<0.01, ** p <0.005, p <0.001 vs. drug-naïve controls.


to the anxiogenic-like effects of mild stressors, an effect that can be reversedby central pretreatment with a CRF receptor antagonist (G. Valdez and G.F.Koob, unpublished observations), and it will be important to determine in fu-ture studies whether such changes in stress reactivity translate into greatersusceptibility to stress-induced reinstatement of drug-seeking behavior.

FIGURE 7. Lever-press responses during self-administration training, extinction,and reinstatement sessions at an active (top) and inactive (bottom) lever. Training Phase:Rats were trained to associate two distinct discriminative stimuli (SD) with the availabil-ity of intravenous cocaine (COC + S+; �) vs. nonrewarding, saline vehicle solution (SAL+ S-; �). Two cocaine and one saline session were conducted daily in random sequencein the presence of the respective SD. Training was continued until stable cocaine-rein-forced responding was obtained. Responses for cocaine in the two daily drug-reinforcedsessions were identical and, therefore, pooled. Only data for the final 3 days of the train-ing phase are shown. Extinction Phase: Withholding of cocaine and the associated SD

(S+) resulted in extinction of responding as defined by a criterion of 5 or fewer responses/session over 3 consecutive test days. The extinction criterion was reached within 16.4 ±3.8 days. Only data for the last 3 days of this phase are shown (�). Reinstatement Phase:Reinstatement tests were conducted at 3-day intervals. Presentation of the cocaine S+

alone reliably elicited and maintained responding at the same level previously maintainedby cocaine (�). Responding remained at (Day 1) or returned to (Day 31) extinction levelswhen rats were presented with the nonreward SD (S−; open symbols). (Modified with per-mission from Ref. 109.)


CONDITIONING FACTORS AND VULNERABILITYTO RELAPSE

The data just discussed identify neuroadaptive changes in brain circuitriesand perturbations in stress systems as important elements in compulsivedrug-seeking behavior and dependence. Another important factor in the long-lasting addictive potential of drugs of abuse is the conditioning of their re-warding actions with specific environmental stimuli. Environmental cues re-peatedly associated with the subjective effects of drugs of abuse includingalcohol can evoke drug craving (see refs. 75–79) or elicit automatic behavior-al responses80,81 that ultimately may lead to relapse. Learned responses todrug-related stimuli may therefore contribute critically to the high rates of re-lapse associated with cocaine and other drug addictions.

Data from operant response-reinstatement models developed to investigatedrug-seeking behavior associated with exposure to drug-related environmen-tal cues in rats indicate that discriminative stimuli predictive of cocaine,82

ethanol,83,84 or heroin85 availability reliably elicit strong recovery of extin-guished drug-seeking behavior in the absence of further drug availability. Theresponse-reinstating effects of these stimuli show remarkable resistance toextinction with repeated exposure86 and, in the case of cocaine, they can stillbe observed after several months of forced abstinence (FIGS. 7 and 8). Addi-tionally, in the case of ethanol, drug-seeking behavior induced by ethanol-predictive discriminative stimuli was found to be enhanced in genetically al-cohol-preferring P rats compared to alcohol-nonpreferring (NP) and non-selected Wistar rats.87 This observation demonstrates that geneticpredisposition towards heightened ethanol intake is reflected also by greatersusceptibility to the motivating effects of ethanol cues (i.e., enhanced drug-seeking under conditions in which behavior is not directly reinforced by eth-anol itself). Together, these findings strongly support the hypothesis thatlearned responses to drug-related stimuli are a significant factor in long-last-ing vulnerability to relapse. Moreover, considering the endurance of the mo-tivating actions of these drug-predictive stimuli, it appears that contextualcues that act as discriminative stimuli for drug availability are particularly ef-fective in eliciting and sustaining drug-seeking behavior and therefore maybe a critical environmental factor in compulsive drug-seeking behavior andvulnerability to relapse.

NEUROBIOLOGICAL BASIS OF CONDITIONEDDRUG-SEEKING BEHAVIOR

Cocaine. Neurochemical, neuroanatomical, and pharmacological studieshave identified dopamine-rich brain regions including the basolateralamygdala, nucleus accumbens, and prefrontal cortex as likely sites for the


mediation of the motivating effects of cocaine-predictive contextual stimuli.Specifically, responding at a previously active, cocaine-paired lever elicitedby a drug-associated discriminative stimulus led to increased Fos protein ex-pression in the basolateral amygdala and medial prefrontal cortical regions(areas Cg1 and Cg3) as well as increased release of dopamine in the nucleusaccumbens and basolateral amygdala.82,88 Both the behavioral effects andFos expression induced by the drug-predictive stimulus were reversed by pre-treatment with the selective dopamine D1 receptor antagonists SCH 39166

FIGURE 8. Responses at an active (top) and inactive (bottom) lever during self-administration training, extinction, and reinstatement sessions. Reinstatement tests wereconducted either immediately (A) after completion of extinction training or after an addi-tional 4 months of abstinence (B) during which time the rats remained confined to theirhome cages. Self-Administration: Cocaine-reinforced (�) and saline/nonreinforced (�) re-sponses across the final 3 days of self-administration training. Extinction: Mean responsesduring the last 3 days of the extinction phase. The rats required on average 15 ± 2.8 days toreach an extinction criterion of no more than 4 responses/session over 3 consecutive days.Reinstatement: Responses during exposure to a cocaine- (S+) or saline- (S−) associated dis-criminative stimulus and exposure to the S+ preceded by 10 µg/kg (IP) of the D1 antagonistSCH 39166 (S+

SCH). Compared to extinction performance, presentation of the S+ signifi-cantly increased responding, whereas the S- had no effect. SCH 39166 attenuated the effectof the S+, and responding in this condition was not statistically different from extinctionlevels. **p <0.01: different from Extinction and S− conditions; ++p <0.01: different fromthe S− condition. (Reprinted with permission from Ref. 88.)


and SCH 23390 (FIGS. 8, 9, and 10). These findings identify medial prefrontalcortical brain regions and the basolateral amygdala as candidate sites for themediation of cue-induced cocaine-seeking behavior and suggest that the D1receptor may represent an important neuropharmacological substrate for themotivating effects of cocaine-related stimuli.

The persistence of the behavioral effects of cocaine-associated contextualstimuli observed in these studies resembles the persistence of conditioned cuereactivity and cue-induced craving in humans89 that has been implicated as acritical factor in high rates of recidivism.90 In this regard, it is also importantto note that the distribution of Fos activation induced by the cocaine cueclosely parallels data from brain imaging studies in humans showing neuralactivation within the amygdala and anterior cingulate cortex during cue-in-duced cocaine craving.91–93 The correspondence between the results of thesebrain imaging studies and the distribution of Fos immunoreactivity associat-ed with exposure to a cocaine-predictive stimulus in rats offers the promisethat the response reinstatement models employed in these will provide a validand effective future research tool for the elucidation of the neural mecha-nisms underlying long-lasting relapse risk associated with exposure to drug-related cues.

FIGURE 9. Effects of the D1 antagonist SCH 23390 on responding induced by a dis-criminative stimulus for cocaine (S+). SCH 23390 dose-dependently reversed the effects ofthe S+. For comparison, the figure also shows the average number of responses during thelast 3 days of the cocaine self-administration (SA) and extinction (EXT) phases as well asresponses in the presence of the stimulus associated with cocaine nonreward (S−). *p <0.05,significant linear trend over dose levels; +p <0.05, different from the EXT and S- conditions;&p <0.01, different from cocaine-reinforced responses (SA). (Reprinted with permissionfrom Ref. 88.)


Ethanol. Studies of the neuropharmacological substrates for the response-reinstating actions of ethanol-associated stimuli have focused on opioid re-ceptors. Opiate antagonists inhibit the self-administration of ethanol in a va-riety of animal models, suggesting that opioid pathways in the brainparticipate in the mediation of ethanol-seeking behavior (e.g., see refs. 94–100). More importantly, a growing number of clinical studies suggest that thenonselective opiate antagonist naltrexone is an effective pharmacological ad-junct for reducing craving and relapse rates in human alcoholics.101–103

Consistent with these clinical data, the behavioral effects of ethanol-asso-ciated contextual stimuli have been found sensitive to pharmacological ma-nipulation of opioid receptors.83,87,104 Naltrexone effectively and dosedependently reversed the response-reinstating effects of the ethanol cues.87

Naltrexone reversed cue-induced alcohol-seeking behavior not only in non-dependent animals, but also in rats that had previously been made dependent

FIGURE 10. Fos immunoreactive nuclei in rats after exposure to the cocaine S+, S−,and S+ preceded by administration of SCH 39166 (S+

SCH) in the immediate (a and c) and4-month delayed (b and d) tests. Compared to the S− control condition, the number of Fosimmunoreactive nuclei was significantly increased after exposure to the cocaine S+ in thebasolateral amygdala and medial prefrontal cortex (areas Cg1 and Cg3) in both the immme-diate and delayed testing conditions. SCH 39166 reversed the effects of the cocaine S+ onFos expression. *p <0.05, **p <0.01: different from the S− condition. +p <0.05, ++p <0.01:different from the S+ condition. (Reprinted with permission from Ref. 88.)


on ethanol via a vapor inhalation procedure and were tested 3 weeks after eth-anol withdrawal. Interestingly, however, the dose response function for naltr-exone’s effects was shifted to the right in these animals.105 This observationpoints towards the possibility that the mechanisms by which opiate receptorsparticipate in the mediation of alcohol craving and relapse show sensitizationin rats with a history of ethanol dependence.

Investigations aimed at determining whether mu or delta receptors mayhave a preferential and perhaps selective role in the anti-relapse effects of thenonselective agent naltrexone have revealed that the selective delta antagonistnaltrindole dose-dependently attenuated drug-seeking behavior elicited byethanol-associated discriminative stimulus without altering responses gener-ated by the presentation of a water-associated discriminative stimulus. A se-lective mu antagonist, naloxonazine, also dose-dependently suppressed thecue-induced ethanol-seeking behavior. However, at the lowest effective dose,this mu antagonist also produced a nonselective behavioral suppression as re-flected by a reduction in responding associated with a water-associatedcue.106 Overall, these findings support the hypothesis that endogenous opioidreceptors play possibly a central role in conditioned ethanol-seeking behaviorand relapse and suggest that the delta receptor may be a promising target toexplore for the treatment of alcohol craving and relapse.

INTERACTIONS BETWEEN CONDITIONING FACTORSAND STRESS

In humans, relapse risk involves multiple determinants that are likely to in-teract. For example, exposure to drug cues may augment vulnerability to re-lapse imparted by protracted withdrawal symptoms resulting fromneuroadaptive changes in dependent individuals. Interactive effects exacer-bating relapse risk may also exist between the motivating effects of stress anddrug-related cues.

Recent work addressing these issues has confirmed that additive interac-tions between the response-reinstating effects of ethanol-associated cues andstress can indeed be demonstrated and that these effects are enhanced in ratswith a history of ethanol dependence.107 Rats were trained to self-administerethanol, and each ethanol delivery was paired with brief presentation of a dis-crete cue light (CS). The animals were then made dependent via an ethanolvapor procedure. During the last 2 days of the dependence induction, the ratswere removed from the vapor chambers each day for 12 hours, but allowed tooperantly self-administer ethanol with response-contingent presentation ofthe ethanol CS. After withdrawal, ethanol-reinforced responding was extin-guished, and the reinstatement of alcohol-seeking behavior was studied under


three conditions: during response-contingent presentation of the CS alone,after exposure to 10 minutes of intermittent footshock stress alone, and dur-ing response-contingent presentation of the CS after exposure to footshock.Under these conditions, neither the ethanol CS alone nor the footshock aloneproduced significant alcohol-seeking behavior in nondependent rats. Howev-er, the ethanol CS elicited strong responding in animals that had been subject-ed to footshock stress before the session. In contrast to their effects innondependent rats, both the ethanol CS alone and the footshock stress aloneproduced significant drug-seeking behavior in previously dependent rats. Ad-ditionally, in these animals, response-contingent presentation of the ethanolCS after footshock exposure substantially enhanced the interactive effects ofthese stimuli compared to those in nondependent rats and produced synergis-tic effects on ethanol-seeking behavior (FIG. 11).

Central administration of a CRF antagonist (D-Phe-CRF(12-41)) substan-tially deceased the response-reinstating effect of stress but not the ethanolCS. In contrast, a nonselective opioid antagonist (naltrexone) significantlysuppressed the response-reinstating effect of the ethanol CS but not stress.Both drugs were effective in diminishing the response-reinstating effect ofthe combination of stress and the ethanol CS. These data confirm the role of

FIGURE 11. Effects of an ethanol-paired conditioned stimulus (EtOH CS), a phys-ical stressor (Footshock Stress), and an ethanol CS preceded by footshock (FootshockStress + EtOH CS) on the recovery of responding at a previously active lever. SA: Meanethanol-reinforced responses during the last 3 days of ethanol availability (30-minute ses-sions). *p <0.05; **p <0.01, compared to Extinction responses. +p <0.05, performance ofPost-dependent vs. Non-dependent rats in the Footshock Stress + EtOH CS condition.


CRF in stress-induced reinstatement of alcohol-seeking behavior and the roleof opioid receptors in cue-induced relapse in rats with a history of ethanol de-pendence. Moreover, these observations confirm that a history of dependenceexacerbates cue- and stress-induced alcohol-seeking behavior and that differ-ent motivationally relevant environmental triggers may exert additive effectson relapse risk. Moreover, with regard to the development of pharmacother-apeutic strategies for the prevention of relapse, the results suggest that it willbe important to consider treatment drug combinations that protect individualsfrom the effects of more than a single environmental risk factor.

REFERENCES

1. ESPOSITO, R.U., A. MOTOLA & C. KORNETSKY. 1978. Cocaine: acute effects onreinforcement thresholds for self-stimulation behavior to the medial forebrainbundle. Pharmacol. Biochem. Behav. 8: 437.

2. HUBNER, C.B. & C. KORNETSKY. 1992. Heroin, 6-acetylmorphine and mor-phine effects on threshold for rewarding and aversive brain stimulation. J.Pharmacol. Exp. Ther. 260: 562.

3. BAUCO, P. & R.A. WISE. 1994. Potentiation of lateral hypothalamic and mid-line mesencephalic brain stimulation reinforcement by nicotine: examinationof repeated treatment. J. Pharmacol. Exp. Ther. 271: 294.

4. SCHULTEIS, G., A. MARKOU, M. COLE & G.F. KOOB. 1995. Decreased brainreward produced by ethanol withdrawal. Proc. Natl. Acad. Sci. 92: 5880.

5. MARKOU, A. & G.F. KOOB. 1991. Post cocaine anhedonia: an animal model ofcocaine withdrawal. Neuropsychopharmacology 4: 17.

6. LEITH, N.J. & R.J. BARRETT. 1976. Amphetamine and the reward system: evi-dence for tolerance and post-drug depression. Psychopharmacologia 46: 19.

7. KOKKINIDIS, L. & B.D. MCCARTER. 1990. Postcocaine depression and sensiti-zation of brain stimulation reward: analysis of reinforcement and perfor-mance effects. Pharmacol. Biochem. Behav. 36: 463.

8. SCHAEFER, G.J. & R.P. MICHAEL. 1986. Changes in response rates and rein-forcement thresholds for intracranial self-stimulation during morphine with-drawal. Pharmacol Biochem Behav. 25: 1263.

9. EPPING-JORDAN, M.P., S.S. WATKINS, G.F. KOOB & A. MARKOU. 1998. Dra-matic decreases in brain reward function during nicotine withdrawal. Nature393: 76.

10. WOOLVERTON, W.L. & M.S. KLEVEN. 1988. Evidence for cocaine dependencein monkeys following a prolonged period of exposure. Psychopharmacology94: 288.

11. KLEVEN, M.S. & W.L. WOOLVERTON. 1991. Effects of continuous cocaineadministration on schedule-controlled behavior in rhesus monkeys. Behav.Pharmacol. 2: 471.

12. AHMED, S.H. & G.F. KOOB. 1998. Transition from moderate to excessive drugintake: change in hedonic set point. Science 282: 298.


13. AHMED, S.H., J.R. WALKER & G.F. KOOB. 2000. Persistent increase in themotivation to take heroin in rats with a history of drug escalation. Neuropsy-chopharmacology 22: 413.

14. KOOB, G.F. & F.E. BLOOM. 1988. Cellular and molecular mechanisms of drugdependence. Science 242: 715.

15. KOOB, G.F., P.P. SANNA & F.E. BLOOM. 1998. Neurobiology of drug addiction.Neuron 21: 467.

16. WISE, R.A. 1996. Neurobiology of addiction. Curr. Opin. Neurobiol. 6: 243.17. WEISS, F., A. MARKOU, M.T. LORANG & G.F. KOOB. 1992. Basal extracellular

dopamine levels in the nucleus acumbens are decreased during cocaine with-drawal after unlimited-access self-administration. Brain Res. 593: 314.

18. PARSONS, L.H., G.F. KOOB & F. WEISS. 1995. Serotonin dysfunction in thenucleus accumbens of rats during withdrawal after unlimited access to intra-venous cocaine. J. Pharmacol. Exp. Ther. 274: 1182.

19. FIBIGER, H.C. 1991. The dopamine hypothesis of schizophrenia and mood dis-orders: contradictions and speculations. In The Mesolimbic Dopamine Sys-tem: From Motivation to Action. :615. John Wiley & Sons. Chichester, UK.

20. WILNER, P. 1995. Dopaminergic mechanisms in depression and mania. In Psy-chopharmacology: The Fourth Generation of Progress. :921. Raven Press.New York.

21. CHARNEY, D.S. & G.R. HENINGER. 1986. Serotonin function in panic disorders:the effect of intravenous tryptophan in healthy subjects and patients withpanic disorder before and during alprazolam treatment. Arch. Gen. Psychiatry43: 1059.

22. CHARNEY, D.S., S.W. WOODS, J.H. KRYSTAL & G.R. HENINGER. 1990. Seroto-nin function and human anxiety disorders. Ann. N.Y. Acad. Sci. 600: 558.

23. MELTZER, H.Y. & M.T. LOWY. 1987. The serotonin hypothesis of depression.In Psychopharmacology: The Third Generation of Progress. :513. RavenPress. New York.

24. GAWIN, F.H. & H.D. KLEBER. 1986. Abstinence symptomatology and psychiat-ric diagnosis in cocaine abusers. Arch. Gen. Psychiatry 43: 107.

25. WEDDINGTON, W.W., B.S. BROWN, C.A. HAERTZEN, et al. 1990. Changes inmood, craving, and sleep during short-term abstinence reported by malecocaine addicts. Arch. Gen. Psychiatry 47: 861.

26. GILLIN, J.C., L. PULVIRENTI, N. WITHERS, et al. 1994. The effects of lisuride onmood, craving, and sleep during acute withdrawal from cocaine and amphet-amine. Biol. Psychiatry 35: 843.

27. MARKOU, A. & G.F. KOOB. 1992. Bromocriptine reverses the elevation inintracranial self-stimulation tresholds observed in a rat model of post-cocaineanhedonia. Neuropsychopharmacology 7: 213.

28. BENLOUCIF, S. & M.P. GALLOWAY. 1991. Facilitation of dopamine release invivo by serotonin agonists: Studies with microdialysis. Eur. J. Pharmacol.200: 1.

29. PARSONS, L.H. & J.R. JUSTICE. 1993. Perfusate serotonin increases extracellu-lar dopamine in the nucleus accumbens as measured by in vivo microdialysis.Brain Res. 606: 195.

30. PARSONS, L.H., P.P. SANNA & G.F. KOOB. 1998. 5-HT1 receptor function isbiphasically altered during abstinence from cocaine self-administration. Soc.Neurosci. Abstr.


31. WEISS, F. 2000. Neuroadaptive changes in neurotransmitter systems mediatingethanol-induced behaviors. In National Institute on Alcohol Abuse and Alco-holism Research Monograph No. 34. :261. National Institutes of Health Pub-lication No. 00-4520. Bethesda, MD.

32. SAMSON, H.H. 1992. The function of brain dopamine in ethanol reinforcement.In Alcohol and Neurobiology: Receptors, Membranes, and Channels. :91.CRC Press. Boca Raton, FL.

33. WEISS, F., M.T. LORANG, F.E. BLOOM & G.F. Koob. 1993. Oral alcohol self-administration stimulates dopamine release in the rat nucleus accumbens:genetic and motivational determinants. J. Pharmacol. Exp. Ther. 267: 250.

34. WEISS, F., L.H. PARSONS, G. SCHULTEIS, et al. 1996. Ethanol self-administra-tion restores withdrawal-associated deficiencies in accumbal dopamine andserotonin release in dependent rats. J. Neurosci. 16: 3474.

35. ROSSETTI, Z.L., F. MELIS, S. CARBONI, et al. 1992. Alcohol withdrawal in ratsis associated with a marked fall in extraneuronal dopamine. Alcohol:. Clin.Exp. Res. 16: 529–532.

36. DIANA, M., M. PISTIS, S. CARBONI, et al. 1992. Profound decrement ofmesolimbic neuronal activity during ethanol withdrawal syndrome in rats:electrophysiological and biochemical evidence. Proc. Natl. Acad. Sci. USA90: 7966.

37. SHEN, R.Y. & L.A. CHIODO. 1993. Acute withdrawal after repeated ethanoltreatment reduces the number of spontaneously active dopaminergic neuronsin the ventral tegmental area. Brain Res. 622: 289.

38. YOSHIMOTO, K., W.J. MCBRIDE, L. LUMENG & T.-K. LI. 1992. Ethanolenhances the release of dopamine and serotonin in the nucleus accumbens ofHAD and LAD lines of rats. Alcohol. Clin. Exp. Res. 16: 781.

39. LINNOILA, M., M. VIRKKUNEN, M. SCHEININ, et al. 1983. Low cerebrospinalfluid 5-hydroxyindoleacetic acid concentration differentiates impulsive fromnonimpulsive violent behavior. Life Sci. 33: 2609.

40. THOMSON, S.M., JR. & B.A. MCMILLEN. 1987. Test for decreased serotonin/tryptophan metabolite ratios in abstinent alcoholics. Alcohol 4: 1.

41. LEE, M.A. & H.Y. MELTZER. 1991. Neuroendocrine responses to serotonergicagents in alcoholics. Biol. Psychiatry 30: 1017.

42. LEMARQUAND, D., R.O. PIHL & C. BENKELFAT. 1994. Serotonin and alcoholintake, abuse, and dependence: clinical evidence. Biol. Psychiatry 36: 326.

43. MARLATT, G.A. 1985. Relapse prevention: introduction and overview of themodel. In Relapse Prevention: Maintenance Strategies in the Treatment ofAddictive Behaviors. :3. Guilford. London.

44. MCKAY, J.R., M.J. RUTHERFORD, A.I. ALTERMAN, et al. 1995. An examinationof the cocaine relapse process. Drug Alcohol Dep. 38: 35.

45. WALLACE, B.C. 1989. Psychological and environmental determinants ofrelapse in crack cocaine smokers. J. Subst. Abuse Treat. 6: 95.

46. BROWN, S.A., P.W. VIK, T.L. PATTERSON, et al. 1995. Stress, vulnerability andadult alcohol relapse. J. Studies Alcohol 56: 538.

47. GOEDERS, N.E. & G.F. GUERIN. 1994. Non-contingent electric shock facilitatesthe acquisition of intravenous cocaine self-administration in rats. Psychophar-macology 114: 63.

48. HANEY, M., S. MACCARI, M. LE MOAL, et al. 1995. Social stress increases theacquisition of cocaine self-administration in male and female rats. Brain Res.698: 46.


49. RAMSEY, N.F. & M. VAN REE. 1993. Emotional but not physical stressenhances intravenous cocaine self-administration in drug naive rats. BrainRes. 608: 216.

50. SHAHAM, Y. & J. STEWART. 1994. Exposure to mild stress enhances the rein-forcing efficacy of intravenous heroin self-administration in rats. Psychophar-macology 111: 523.

51. NASH, J., JR. & R.P. MAICKEL. 1988. The role of the hypothalamic-pituitary-adrenocortical axis in post-stress-induced ethanol consumption by rats. Progr.Neuropsychopharmacol. Biol. Psychiatry 12: 653.

52. MOLLENAUER, S., R. BRYSON, M. ROBINSON, et al. 1993. EtOH Self-adminis-tration in anticipation of noise stress in C57BL/6J mice. Pharmacol. Bio-chem. Behav. 46: 35.

53. HIGLEY, J.D., M.F. HASERT, S.J. SUOMI & M. LINNOILA. 1991. Nonhuman pri-mate model of alcohol abuse: effect of early experience, personality, andstress on alcohol consumption. Proc. Natl. Acad. Sci. USA 88: 7261.

54. SHAHAM, Y. & J. STEWART. 1995. Stress reinstates heroin-seeking in drug-freeanimals: an effect mimicking heroin, not withdrawal. Psychopharmacology119: 334.

55. AHMED, S.H. & G.F. KOOB. 1997. Cocaine- but not food-seeking behavior isreinstated by stress after extinction. Psychopharmacology 132: 289.

56. LE, A.D., B. QUAN, W. JUZYTCH, et al. 1998. Reinstatement of alcohol-seekingby priming injections of alcohol and exposure to stress in rats. Psychophar-macology (Berl) 135: 169.

57. DUNN, A.J. & C.W. BERRIDGE. 1990. Physiological and behavioral responsesto corticotropin-releasing factor administration: is CRF a mediator of anxietyor stress responses? Brain Res. Brain Res. Rev. 15: 71.

58. KOOB, G.F., S.C. HEINRICHS, F. MENZAGHI, et al. 1994. Corticotropin releasingfactor, stress and behavior. Semin. Neurosci. 6: 221.

59. MERLO PICH, E., M.T. LORANG, M. YEGANEH, et al. 1995. Increase of extracel-lular corticotropin-releasing factor-like immunoreactivity levels in theamygdala of awake rats during restraint stress and ethanol withdrawal as mea-sured by microdialysis. J. Neurosci. 15: 5439.

60. MERALI, Z., J. MCINTOSH, P. KENT, et al. 1998. Aversive and appetitive eventsevoke the release of corticotropin- releasing hormone and bombesin-like pep-tides at the central nucleus of the amygdala. J. Neurosci. 18: 4758.

61. HEINRICHS, S.C., E. MERLO PICH, K.A. MICZEK, et al. 1992. Corticotropin-releasing factor reduces emotionality in socially defeated rats via direct neu-rotropic action. Brain Res. 581: 190.

62. SWIERGIEL, A.H., L.K. TAKAHASHI & N.H. KALIN. 1993. Attenuation of stress-induced behavior by antagonism of corticotropin- releasing factor receptors inthe central amygdala in the rat. Brain Res. 623: 229.

63. MERLO PICH, E., G.F. KOOB, W. VALE & F. WEISS. 1994. Release of corticotro-pin releasing factor (CRF) from the amygdala of ethanol-dependent rats mea-sured with microdialysis. Alcohol. Clin. Exp. Res. 18: 522.

64. RICHTER, R.M. & F. WEISS. 1999. In vivo CRF release in rat amygdala isincreased during cocaine withdrawal in self-administering rats. Synapse 32:254.

65. DE FONSECA, F.R., M. CARRERA, M. NAVARRO, et al. 1997. Activation of corti-cotropin-releasing factor in the limbic system during cannabinoid withdrawal.Science 276: 2050.


66. RASSNICK, S., S.C. HEINRICHS, K.T. BRITTON & G.F. Koob. 1993. Microinjec-tion of a corticotropin-releasing factor antagonist into the central nucleus ofthe amygdala reverses anxiogenic-like effects of ethanol withdrawal. BrainRes. 605: 25.

67. HEINRICHS, S.C., F. MENZAGHI, G. SCHULTEIS, et al. 1995. Suppression of cor-ticotropin-releasing factor in the amygdala attenuates aversive consequencesof morphine withdrawal. Behav. Pharmacol. 6: 74.

68. MACEY, D.J., A.M. BASSO, J. RIVIER, et al. 1997. Corticotropin releasing factor(CRF) decreases brain stimulation reward in the rat. Soc. Neurosci. Abstr. 23:521.

69. KOOB, G.F. 1999. Stress, corticotropin-releasing factor, and drug addiction.Ann. N.Y. Acad. Sci. 897: 27.

70. VALDEZ, G.R., E.P. ZORILLA, G.F. KOOB & F. WEISS. 2000. Influence of pro-tracted ethanol abstinence on corticotrophin-releasing factor systems and theHPA axis in dependent rats. Soc. Neurosci. Abstr. 26: 1821.

71. MERLO PICH, E.M., G.F. KOOB, M. HEILIG, et al. 1993. Corticotropin releasingfactor release from the mediobasal hypothalamus of the rat as measured bymicrodialysis. Neuroscience 55: 695.

72. SARNYAI, Z., E. BIRO, J. GARDI, et al. 1995. Brain corticotropin-releasing fac-tor mediates ‘anxiety-like’ behavior induced by cocaine withdrawal in rats.Brain Res. 675: 89.

73. ZHOU, Y., R. SPANGLER, K.S. LAFORGE, et al. 1996. Corticotropin-releasingfactor and type 1 corticotropin-releasing factor receptor messenger RNAs inrat brain and pituitary during “binge”-pattern cocaine administration andchronic withdrawal. J. Pharmacol. Exp. Ther. 279: 351.

74. AMBROSIO, E., L.G. SHARPE & N.S. PILOTTE. 1997. Regional binding to corti-cotropin releasing factor receptors in brain of rats exposed to chronic cocaineand cocaine withdrawal. Synapse 25: 272.

75. CHILDRESS, A.R., R.N. EHRMAN, A.T. MCLELLAN & C.P. O’BRIEN. 1988. Con-ditioned craving and arousal in cocaine addiction: a preliminary report, inNIDA Research Monograph 81. :74. US Government Printing Office. Wash-ington, DC.

76. EHRMAN, R.N., S.J. ROBBINS, A.R. CHILDRESS & C.P. O’BRIEN. 1992. Condi-tioned responses to cocaine-related stimuli in cocaine abuse patients. Psy-chopharmacology 107: 523.

77. MONTI, P.M., D.J. ROHSENOW, A.V. RUBONIS, et al. 1993. Alcohol cue reactiv-ity: Effcts of detoxification and extended exposure. J. Stud. Alcohol. 54: 235.

78. POMERLEAU, O.F., J. FERTIG, L. BAKER & N. COONEY. 1983. Reactivity toalcohol cues in alcoholics and non-alcoholics: implications for the stimuluscontrol analysis of drinking. Addict. Behav. 8: 1.

79. STORMARK, K.M., J.C. LABERG, T. BJERLAND, et al. 1995. Autonomic cuedreactivity in alcoholics: the effect of olfactory stimuli. Addict. Behav. 20:571.

80. MILLER, N.S. & M.S. GOLD. 1994. Dissociation of “conscious desire” (crav-ing) from and relapse in alcohol and cocaine dependence. Ann. Clin. Psychia-try 6: 99.

81. TIFFANY, S.T. & B.L. CARTER. 1998. Is craving the source of compulsive druguse? J. Psychopharmacol. 12: 23.

82. WEISS, F., C.S. MALDONADO-VLAAR, L.H. PARSONS, et al. 2000. Control ofcocaine-seeking behavior by drug-associated stimuli in rats: effects on recov-


ery of extinguished operant responding and extracellular dopamine levels inamygdala and nucleus accumbens. Proc. Natl. Acad. Sci. USA 97: 4321.

83. KATNER, S.N., J.G. MAGALONG & F. WEISS. 1999. Reinstatement of alcohol-seeking behavior by drug-associated discriminative stimuli after prolongedextinction in the rat. Neuropsychopharmacology 20: 471.

84. KATNER, S.N. & F. WEISS. 1999. Ethanol-associated olfactory stimuli reinstateethanol-seeking behavior after extinction and modify extracellular dopaminelevels in the nucleus accumbens. Alcohol. Clin. Exp. Res. 23: 1751.

85. GRACY, K.N., L.A. DANKIEWICZ, F. WEISS & G.F. KOOB. 2000. Heroin-specificcues reinstate heroin-seeking behavior in rats after prolonged extinction.Pharmacol. Biochem. Behav. 65: 489.

86. WEISS, F. & R. CICCOCIOPPO. 1999. Enduring conditioned reactivity to cocainecues: Effects on extinguished operant responding, forebrain dopaminerelease, and fos immunoreactivity. Behav. Pharmacol. 10(Suppl 1): S99.

87. CICCOCIOPPO, R., S.N. KATNER & F. WEISS. 1999. Relapse induced by alcohol-associated environmental stimuli after extinction in rats. Alcohol. Clin. Exp.Res. 23(Suppl): 52A.

88. CICCOCIOPPO, R., P.P. SANNA & F. WEISS. 2001. Cocaine-predictive stimulusinduces drug-seeking behavior and neural activation in limbic brain regionsafter multiple months of abstinence: reversal by D1 antagonists. Proc. Natl.Acad. Sci. USA. In press.

89. CHILDRESS, A.R., A.V. HOLE, R.N. EHRMAN, et al. 1993. Cue reactivity andcue reactivity interventions in drug dependence. NIDA Res. Monogr. 137: 73.

90. O’BRIEN, C.P., A.R. CHILDRESS, R. EHRMAN & S.J. ROBBINS. 1998. Condition-ing factors in drug abuse: Can they explain compulsion? J. Psychopharmacol.12: 15.

91. CHILDRESS, A.R., P.D. MOZLEY, W. MCELGIN, et al. 1999. Limbic activationduring cue-induced cocaine craving. Am. J. Psychiatry 156: 11.

92. GARAVAN, H., J. PANKIEWICZ, A. BLOOM, et al. 2000. Cue-induced cocainecraving: neuroanatomical specificity for drug users and drug stimuli [In Pro-cess Citation]. Am. J. Psychiatry 157: 1789.

93. MAAS, L.C., S.E. LUKAS, M.J. KAUFMAN, et al. 1998. Functional magnetic res-onance imaging of human brain activation during cue-induced cocaine crav-ing. Am. J. Psychiatry 155: 124.

94. GONZALES, R.A. & F. WEISS. 1998. Suppression of ethanol-reinforced behav-ior by naltrexone is associated with attenuation of the ethanol-inducedincrease in dialysate dopamine levels in the nucleus accumbens. J. Neurosci.18: 10663.

95. ALTSHULER, H.L., P.E. PHILLIPS & D.A. FEINHANDLER. 1980. Alterations ofethanol self-administration by naltrexone. Life Sci. 26: 679.

96. FROEHLICH, J.C., M. ZWEIFEL & J. HART. 1991. Importance of delta opioidreceptors in maintaining high alcohol drinking. Psychopharmacology 103:467.

97. HUBBELL, C.L., S.H. MARGLIN, S.J. SPITALNIC, et al. 1991. Opioidergic, sero-tonergic, and dopaminergic manipulations and rats’ intake of a sweetenedalcoholic beverage. Alcohol 8: 355.

98. KORNET, M., C. GOOSEN & J.M. VAN REE. 1991. Effects of naltrexone on alco-hol consumption during chronic alcohol drinking and after a period ofimposed abstinence in free-choice drinking rhesus monkeys. Psychopharma-cology 104: 367.


99. HYYTIÄ, P. & J.D. SINCLAIR. 1993. Responding for oral ethanol after nalox-one treatment by alcohol-preferring AA rats. Alcohol.: Clin. Exp. Res. 17:631.

100. DAVIDSON, D. & Z. AMIT. 1996. Effects of naloxone on limited-access etha-nol drinking in rats. Alcohol.: Clin. Exp. Res. 20: 664.

101. O’MALLEY, S.S., A.J. JAFFE, G. CHANG, et al. 1992. Naltrexone and copingskills therapy for alcohol dependence. Arch. Gen. Psychiatry 49: 881.

102. VOLPICELLI, J.R., A.I. ALTERMAN, M. HAYASHIDA & C.P. O’BRIEN. 1992.Naltrexone in the treatment of alcohol dependence. Arch. Gen. Psychiatry 49:876.

103. O’BRIEN, C.P., L.A. VOLPICELLI & J.R. VOLPICELLI. 1996. Naltrexone in thetreatment of alcoholism: a clinical review. Alcohol 13: 35.

104. WEISS, F. & R. CICCOCIOPPO. 1999. Environmental stimuli potently reinstatealcohol-seeking behavior: effect of repeated alcohol intoxication. Soc. Neuro-sci. Abstr. 25: 1081.

105. WEISS, F. & R. CICCOCIOPPO. 1999. Environmental stimuli potently reinstatealcohol-seeking behavior: effects of repeated alcohol intoxication. Soc. Neu-rosci. Abstr. 21: 1081.

106. ANGELETTI, S. & F. WEISS. 2000. Cue-induced reinstatement of ethanol-seek-ing behavior in P, Wistar, and NP rats. Soc. Neurosci. Abstr. 26: 786.

107. LIU, X. & F. WEISS. 2000. History of ethanol dependence determines long-term vulnerability to “relapse” induced by stress and ethanol-related cues inrats. Alcohol: Clin. Exp. Res. 24: 51A.

108. RODRIGUEZ DE FONSECA, F., M.R.A. CARRERA, M. NAVARRO, et al. 1997.Activation of corticotropin-releasing factor in the limbic system during can-nabinoid withdrawal [see comments]. Science 276: 2050, 1997.

109. WEISS, F., R. MARTIN-FARDON, R. CICCOCIOPPO, et al. 2001. Enduring resis-tance to extinction of cocaine-seeking behavior induced by drug-related cues.Neuropsychopharmacology. In press.

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Compulsive Drug-Seeking Behavior and Relapse : Neuroadaptation, Stress, and Conditioning Factors