Alcohol Withdrawal and ConditioningHilary J. Little, David N. Stephens, Tamzon L. Ripley, Gilyana Borlikova, Theodora Duka, Manja Schubert,

Doris Albrecht, Howard C. Becker, Marcello F. Lopez, Friedbert Weiss, Colin Drummond,Michelle Peoples, and Christopher Cunningham

This review contains the proceedings from a symposium held at the RSA conference in 2003 on “AlcoholWithdrawal and Conditioning.” The presentations covered a range of interactions between conditioningand alcohol withdrawal, in both animal behavior and the clinic. Dr. D.N. Stephens first described his studiesexploring the consequences of alcohol dependence and repeated experience of withdrawal on the condi-tioning process. His data suggested that repeated withdrawal from moderate alcohol intake impairsamygdala-dependent mechanisms for learning about aversive events. Dr. H. Becker then detailed studiesexamining the consequences of repeated ethanol withdrawal experience on subsequent ethanol drinkingbehavior in mice, and conditions in which motivational properties of odor cues that are associated withdifferent phases of ethanol withdrawal influence such relapse behavior. The data suggested that cuesassociated with acute withdrawal or “recovery” from withdrawal may serve as modulating factors in influ-encing subsequent ethanol drinking behavior, and that the timing of the cues determines their conse-quences. Dr. F. Weiss described recent findings from animal models of relapse that suggested the efficacyof alcohol-associated contextual stimuli in eliciting alcohol-seeking behavior resembles the endurance ofconditioned cue reactivity and cue-induced cocaine craving in humans. The interactive effects of stress andethanol-related environmental stimuli were found to be dependent on concurrent activation of endogenousopioid and corticotropin-releasing factor systems. Conditioning factors (i.e., exposure to drug-associatedstimuli) and stress could therefore interact to augment vulnerability to relapse. Dr. C. Drummond thenaddressed the clinical aspects of conditioning during alcohol withdrawal and described studies showingexposure of alcoholics to alcohol-related cues elicited greater subjective and physiological responses thanexposure to neutral cues. The former responsivity showed a relationship with a measure of motivation todrink alcohol. Finally, Dr. C. Cunningham provided a summary of the concepts involved in the presenta-tions and discussed the conditioning processes that affect behavior during and after alcohol withdrawal.

Key Words: Alcohol Withdrawal, Conditioning, Learning.

LEARNING HAS LONG been recognized to play animportant role in alcohol abuse and alcoholism, but

the effects of chronic alcohol consumption on conditioningprocesses have only recently been studied. Conditioning andprior experience are crucially important in determiningwhether and when alcohol consumption takes place andthere is increasing evidence that the processes involved inconditioning are altered by prior alcohol dependence and

withdrawal. Such factors interface with neuroadaptivechanges that play a significant role in perpetuating drink-ing, as well as underlying the ability of environmental cuesto trigger relapse after periods of abstinence. The contri-butions to this symposium highlight the recent discoveriesmade on the influences of alcohol withdrawal on condition-ing and the importance of such data in relation to thealcohol dependence process and relapse drinking.

THE EFFECTS OF ALCOHOL DEPENDENCE ANDWITHDRAWAL ON AVERSIVE CONDITIONING

D.N. Stephens, T.L. Ripley, G. Borlikova, T. Duka,M. Schubert, and D. Albrecht

Alcohol-seeking and other aspects of alcoholics’ behav-ior may be mediated by simple conditioning processes. Towhat extent are these influenced by the patient’s previoushistory of taking alcohol? Clinical, as well as animal labo-ratory experimental studies, indicates that repeated expe-rience of detoxification results in profound behavioralchanges, associated with neurobiological changes in severalbrain regions. The best documented of such changes is theincreased propensity to seizures experience following mul-

Departments of Pharmacology and Addictive Behaviour, George’s Hospi-tal Medical School, Cranmer Terrace, London, SW17 ORE, U.K. (HJL, CD,MP); Department of Psychology, University of Sussex, Brighton, UK (DNS,TLR, TD); Institute of Physiology (Charité), Humboldt University, Berlin,Germany, Charleston Alcohol Research Center (MS, DA); Department ofPsychiatry and Behavioral Sciences, Medical University of South Carolina(HCB, MFL); Department of Veterans Affairs, Charleston, South Carolina29425 (HCB); Department of Neuropharmacology, The Scripps ResearchInstitute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (FW); De-partment of Behavioral Neuroscience and Portland Alcohol Research Center,Oregon Health and Science University, Portland, OR, 97239 (CC).

December 23, 2004; January 11, 2005.Reprint requests: Hilary J. Little, Departments of Pharmacology and Addictive

Behaviour, St. George’s Hospital Medical School, Cranmer Terrace, London,SW17 ORE, U.K.; Fax: �44-208-725-2675. E-mail: hilary.little@sghms.ac.uk

Copyright © 2005 by the Research Society on Alcoholism.

DOI: 10.1097/01.ALC.0000156737.56425.E3

0145-6008/05/2903-0453$03.00/0ALCOHOLISM: CLINICAL AND EXPERIMENTAL RESEARCH

Vol. 29, No. 3March 2005

Alcohol Clin Exp Res, Vol 29, No 3, 2005: pp 453–464 453

tiple withdrawals. This so-called “kindling” of convulsantactivity has been suggested to reflect changes in efficiencyof nervous transmission in the amygdala (Carrington et al.,1994; Pinel et al., 1975; Pinel and Van Oot, 1975; Pinel,1980). The amygdala is crucially implicated in the forma-tion of associations between discrete environmental eventsand aversive stimuli, and the expression of fear reactions,through its projections to brainstem structures governingbehavioral, autonomic and endocrine responses to threat.It is thus of importance whether periods of repeated with-drawal from alcohol also affect emotional competence, andPavlovian conditioning of emotional events.

We have studied the effect of multiple withdrawals fromalcohol on fear conditioning. High alcohol intakes wereinduced in Hooded Lister rats by providing them chroni-cally with a 7% alcohol-containing diet which the ratsreceived as their sole source of nutrition for either 24 dayscontinuously, followed by a 2-week withdrawal period be-fore behavioral analyses (single withdrawal group), or withthe treatment interrupted for 2 additional withdrawal pe-riods, each 3 days in length, during which time the animalsreceived control diet (repeat withdrawal group). A third,control, group was given access to control diet for 24 days,and were pair fed to the single withdrawal group to stabilizebody weight.

The acquisition of a conditioned emotional response wasimpaired in the repeat withdrawal group. In control ani-mals, presentation of a tone, or flashing light, conditionedstimuli (CS�) which predicted mild foot shock, resulted incessation of ongoing behavior, in our case, lever pressing toobtain food reward (Stephens et al., 2001). The impairmentof this response in the repeat withdrawal group is consistentwith altered amygdala function. When the shock intensitywas increased in steps over a period of 5 weeks, the repeatwithdrawal rats eventually showed some evidence of behav-ioral suppression in response to the CS�. Whether thiseventual acquisition reflected the higher shock levels, orthe prolonged training period is not clear. In a subsequentexperiment (Ripley et al., 2003a) we were able to show that.if the rats were trained on the conditional emotional re-sponse task prior to alcohol exposure and withdrawal, thenthe repeated withdrawal rats were not impaired in expres-sion of the response. This suggests effects of withdrawal onlearning the relationship between the CS� and the shock,rather than blunted fear responses. Interestingly, however,the repeated withdrawal animals showed a slight impair-ment in extinction of the CS�-shock association, when theCS� was presented repeatedly in the absence of the shockreinforcer. In this experiment, two stimuli were used duringtraining, a tone, and a light; for half the animals the tonesignaled shock, while the light had no predictive value (CS);for the other half, the light predicted shock, while the tonehad no predictive value. Following the extinction proce-dure, the significance of the stimuli was reversed, so thatthe former CS� became the CS-. The rats were required tolearn this new association several weeks after they had

undergone the alcohol withdrawal procedure. Once again,the repeated withdrawal rats were impaired in learning thenew association. This series of experiments suggests thatthe repeated withdrawal procedure impairs the learning ofassociations, but if learning took place prior to alcoholexposure, there was no impairment in the expression of theconditioned response.

Fear conditioning depends upon information processingin amygdala. As a result of conditioning, the CS� affectsthe outflow from the lateral amygdala to the central nu-cleus (Fanslow et al., 1999). This, in turn, induces activity inoutput pathways eliciting diverse symptoms of fear andanxiety. In keeping with this model, increases in the num-ber of neurons showing Fos immunoreactivity in the centraland basal nuclei of the amygdala were seen following anacoustic signal previously conditioned to shock (Beck andFibiger, 1995; Hamamura et al., 1997; Hall et al., 2001).

We reasoned that if the repeated withdrawal treatmentimpaired learning of CS-US associations, presentation ofthe tone as a CS� to these animals would not induce c-fosexpression in pathways involved in fear conditioning. Con-sistent with the prediction, after exposure to the tone CS�both the control and single withdrawal animals showed highlevels of c-fos expression in the core and shell of theaccumbens and in the basolateral and central nuclei of theamygdala. However, c-fos was expressed in fewer neuronsin the repeat withdrawal group. Similar, though not statis-tically reliable, patterns were seen in lateral nucleus of theamygdala (Stephens, Ripley and Borlikova, unpublishedfindings). These results suggest the repeat withdrawal ex-perience, but not an equivalent amount of continuous al-cohol exposure, impaired the formation of associationsbetween a tone stimulus and an aversive event. This isconsistent with our behavioral observations (Stephens etal., 2001; Ripley et al., 2003a).

These observations are commensurate with alteredtransmission within the amygdala, though there appear tobe differences between the consequences of repeated with-drawal and electrical kindling. There are similarities be-tween electrical kindling of seizures and alcohol withdrawalseizures, and they cross-sensitize. In the case of fear con-ditioning, repeated alcohol withdrawal and electrical kin-dling of the basolateral amygdala have opposite effects.Repeated withdrawal impairs fear conditioning, while incontrast electrical kindling facilitated fear conditioning(Ripley et al., 2003b). Recent studies suggest that the cen-tral nucleus may also function independently of the lateralnuclei, as it receives highly processed sensory input fromentorhinal cortex and related areas (see Killcross, 2003 fora review). It thus seems possible that the major effects ofrepeated withdrawal from alcohol on fear conditioning aremediated by the central amygdala, rather than the lateralaspects.

By what mechanism does repeated alcohol withdrawallead to impaired fear conditioning? Long-term potentiation(LTP) has been proposed as a mechanism whereby synaptic

454 LITTLE ET AL.

transmission is facilitated as a result of use. In associativeLTP, transmission in the pathway carrying informationabout the CS� is facilitated as a result of it being activatedcontemporaneously with the pathway signaling the uncon-ditioned stimulus (US). This basic mechanism may be thebasis for the formation of associations. If two independentpresynaptic neurons synapse on to the same postsynapticelement (say, a spine), then activity in one may provide thenecessary depolarization to remove the Mg2� block in an-other, allowing NMDA receptor-mediated transmissionthrough the second synapse. Increased probability of pre-synaptic activity in the second synapse would then result inactivation of the postsynaptic element. If synapse 1 carriesinformation about an aversive event (the unconditionedstimulus, US), and synapse 2 information about a condi-tioned stimulus (CS) occurring contemporaneously withthe US, then, following synaptic strengthening, activationof the synapse carrying information about the CS may havesimilar postsynaptic consequences as activating the synapsecarrying information about the US did prior to strengthen-ing. This type of LTP is found in the pathway from medialgeniculate body to the lateral nucleus of the amygdala,which is thought to mediate conditioning of fear responsesto acoustic stimuli. Tetanic stimulation of the medial genic-ulate body also results in a long-lasting potentiation of afield potential in the lateral amygdala elicited by a naturallytransduced acoustic stimulus (Rogan and LeDoux, 1995;Rogan et al., 1997). The stimulation coincidence parame-ters necessary for induction of LTP in the lateral amygdalaclosely resemble those required for the formation of asso-ciations between CS and US in fear conditioning experi-ments (Bauer et al., 2001). Taken together, these experi-ments suggest that that LTP-like mechanisms underlieamygdala-mediated fear conditioning. Why then shouldalcohol withdrawal affect such a mechanism?

Acute alcohol treatment is associated with facilitation ofGABAergic inhibitory mechanisms, while alcohol is also anNMDA antagonist. During chronic alcohol exposure, trans-mission in glutamatergic systems is facilitated to compen-sate for these two major actions of alcohol, resulting inpartial tolerance to alcohol’s sedative effects. Followingwithdrawal from alcohol, the glutamatergic system contin-ues to be overactive, and this overactivity is no longerbalanced by alcohol’s effects on GABAergic systems. Wesuggest that this imbalance in the direction of glutamatergicexcitatory transmission might have consequences similar tooveractivation of glutamatergic synapses that occurs duringLTP.

The apparent paradox of heightened seizure sensitivity,and exaggerated anxiety responses during withdrawal, butimpaired fear conditioning, could then be accounted for ifrepeated experience of withdrawal induces synaptic plastic-ity. This would result in facilitated transmission, but re-duced capacity for the further plasticity necessary for learn-ing. Information regarding discrete cues, such as the CSs inour experiments, is relayed to the lateral amygdala from

sensory cortex and sensory thalamus (Pitkanen et al., 1997).LTP occurs in the pathway from the external capsule to thelateral nucleus of the amygdala (Chapman et al., 1990).High frequency stimulation of the medial geniculate inputto the amygdala also results in a long-lasting potentiation offield potentials in the lateral amygdala elicited by a natu-rally transduced acoustic stimulus (Rogan et al., 1997). Wetherefore compared excitability and plasticity in the amyg-dala of rats that had undergone repeat, or a single with-drawal (unpublished experiments). We observed reliableincreases in signal in the lateral amygdala following in-creased intensity of stimulation of the external capsuleaccessory pathway. These input-output curves were shiftedto the left in slices from rats that had undergone repeatedwithdrawal, consistent with increased efficiency of synaptictransmission. Such changes could in principle account forincreased sensitivity to seizures following repeated with-drawal. Furthermore, such increased efficiency might implythat fear-related stimuli activating these pathways might bemore effective in eliciting anxious responses following re-peated withdrawal, as reported in both humans (George etal., 1990; Krystal et al., 1997) and some animal models(Overstreet et al., 2002). However we did not find thatdiscrete stimuli conditioned to foot-shock prior to alcoholexposure were more effective in suppressing behavior inrats that subsequently underwent repeated withdrawal(Ripley et al., 2003a).

As well as leftward shifts in the input-output curves,repeated withdrawal reduced the ability to support LTP. Inthe case of the lateral amygdala, both single and repeatwithdrawal groups showed equally reduced capacity forLTP. These observations are consistent with reduced ca-pacity for associative learning following repeated withdraw-als from alcohol. However, while both single withdrawaland repeated withdrawal treatments gave rise to similarsize reductions in LTP, in our behavioral fear conditioningexperiments we have found repeated withdrawal impairedconditioning more than single withdrawal (Stephens et al.,2001; Ripley et al., 2003a). Nevertheless, these electrophys-iological data provide an interesting parallel to the condi-tioning deficits. The entire set of electrophysiological andbehavioral data might be reconciled by suggesting thatrepeat withdrawal increases efficiency of synaptic connec-tions, leading to facilitation of synaptic transmission, butreduced capacity for further plasticity.

The results described here refer to aversive conditioning,but similar mechanisms may underlie appetitive condition-ing. Recently we found deficits in aspects of appetitiveconditioning which would be consistent with impairmentsof function in central, though not lateral, amygdala (Ripleyet al., 2004; Duka et al., 2004)). Taken together, thesefindings suggest a mechanism whereby chronic alcoholtreatment and withdrawal may lead to a deficit in function-ing of the central amygdala with consequences for associa-tive learning. Such deficits may have implications for the

ALCOHOL WITHDRAWAL AND CONDITIONING 455

use of conditioning approaches to behavioral therapies foralcoholics.

CONDITIONED ETHANOL WITHDRAWAL EFFECTS ONETHANOL DRINKING BEHAVIOR IN MICE

Howard C. Becker and M. F. Lopez

Associative learning mechanisms are generally acceptedas playing an important role in influencing a variety ofethanol-related behaviors, including motivation for ethanolconsumption. Pavlovian conditioning procedures have mostcommonly been employed to study place or taste condition-ing where ethanol is administered as the unconditionedstimulus (Cunningham et al., 2000; Drummond et al., 1990;Littleton, 2000). These studies have demonstrated that eth-anol is capable of inducing both conditioned preferencesand aversions depending on various experimental parame-ters and conditions (Broadbent et al., 2002; Chester et al.,2003; Cunningham and Niehus, 1997; Cunningham et al.,2002; Cunningham et al., 2003). In contrast, fewer studieshave examined whether withdrawal from ethanol exposurecan serve as an unconditioned stimulus supportive ofconditioning.

Ethanol withdrawal produces an aversive state charac-terized by physiological signs of stress, as well as dysphoriaand other subjective measures of discomfort (e.g., anxiety,agitation) (Becker, 2000; De Witte et al., 2003). These signsand symptoms wax and wane over time following differenttime courses during the ethanol withdrawal period, andtheir magnitude has been shown to intensify with the rep-etition of withdrawal episodes (Ballenger and Post, 1978;Becker and Littleton, 1996; Malcolm et al., 2000).

Animals have been shown to be capable of detecting andprocessing internal cues related to ethanol withdrawal. Forexample, the interoceptive cues associated with ethanolwithdrawal have been demonstrated to acquire discrimina-tive stimulus properties, and generalize to the aversive/angiogenic state produced by drugs such as pentylenetetra-zol (Gauvin et al., 1992; Lal et al., 1988). Additionally,ethanol withdrawal has effectively served as the uncondi-tioned stimulus in different models of place conditioning(Cole et al., 1999; 2000; Gauvin et al., 1997). The fact thatmany withdrawal symptoms progressively intensify with re-peated such experiences suggests that cues associated withwithdrawal may become more salient and, therefore, morelikely to influence ethanol-related behaviors through asso-ciative processes. To our knowledge, the effect of condi-tioned withdrawal cues on ethanol drinking behavior hasnot been explored.

We have previously demonstrated that mice trained todrink ethanol in a limited access procedure significantlyincrease their ethanol intake after experience with repeatedchronic ethanol exposure and withdrawal episodes in com-parison to mice that did not experience chronic ethanolexposure and withdrawal (Becker and Lopez, 2004, Lopezand Becker, 2003). Using this model along with a Pavlovian

conditioning procedure, this study was designed to examinewhether presentation of a cue previously associated withethanol withdrawal influences subsequent voluntary etha-nol intake.

Adult male C57BL/6J mice were first trained to drinkethanol (15% v/v) under a limited access schedule (2 hr/day). A sucrose fading procedure was used to stabilizeintake and, thereafter, 15% ethanol was presented in a freechoice situation with water. The daily sessions started 30min prior to the start of the dark phase of the light/darkcycle; food and water were freely available throughout thestudy. Once stable baseline intake was established (2.5–3.0g/kg), mice were separated into groups based on chronicethanol exposure and conditioning treatments. One set ofanimals received four cycles of 16 hr chronic exposure toethanol vapors in inhalation chambers. For differentgroups of these ethanol-exposed mice, an odor cue wasassociated with either acute withdrawal (8 hr followinginhalation treatment) or protracted withdrawal (32 hr fol-lowing chronic ethanol treatment) (EWD-8hr odor andEWD-32hr odor groups, respectively). Another group ofmice experienced repeated ethanol exposures with no odorcue presentation during the withdrawals (EWD-no odor).A separate set of animals was similarly treated (odor andno-odor conditions), but placed in control (air) inhalationchambers (C-8/32hr odor and C-no odor groups, respec-tively). The odor cue (banana) was presented on a satu-rated cotton ball placed on the cage top (out of reach) for30 min. After the conditioning trials (repeated cycles ofchronic ethanol exposure and withdrawal conditioning), allanimals were given the opportunity to self-administer eth-anol in the presence of the odor cue. Data were analyzed bycomparing ethanol intake for the different groups collapsedover the last 5 days of baseline and the 5 consecutive dailytest sessions following the withdrawal conditioning phase ofthe study.

As expected, ethanol intake during baseline (prior towithdrawal conditioning) was not significantly different be-tween groups (overall mean � SEM ethanol intake: 2.72 �0.10, p � 0.05). We have previously shown that this level ofintake results in blood ethanol levels that are physiologi-cally relevant (50–60 mg/dl) (Becker and Lopez, 2004,Lopez and Becker, 2003). Analysis of the no-odor (condi-tioning control) groups revealed that the ethanol-exposedmice consumed more ethanol than the air-exposed controlgroup during the test phase of the study (F(1,13) � 5.04, p� 0.05). Further, ethanol intake in the EWD-no odorgroup was significantly greater after the inhalation treat-ment compared to its intake during baseline, while ethanolconsumption in the air-exposed control group (C-no odor)did not differ between baseline and test phases of the study(mean � SEM ethanol intake (g/kg) for EWD-no odor andC-no odor groups: baseline � 2.92 � 0.15, test � 3.43 �0.20 and baseline � 2.92 � 0.22, test � 2.77 � 0.18,respectively). These results corroborate our previous find-ings demonstrating increased voluntary ethanol consump-

456 LITTLE ET AL.

tion following repeated chronic ethanol exposure/with-drawal experience (Becker and Lopez, 2004, Lopez andBecker, 2003). Additionally, the results suggest that pre-sentation of a novel odor stimulus during test sessions didnot disrupt ethanol consumption, nor the enhanced intakeexhibited by the ethanol-exposed group.

Analysis of ethanol intake during test sessions for theodor conditioning groups revealed significant differencesbetween groups depending on when conditioning occurred(F(2,20) � 3.76, p � 0.05). Similar to results obtained fromthe EWD-no odor group, ethanol intake in the presence ofan odor cue that was previously associated with protracted(32 hr) withdrawal was elevated in comparison to the cor-responding control group (mean � SEM ethanol intake(g/kg) for EWD-32hr odor and C-8/32hr odor groups: base-line � 2.49 � 0.23, test � 3.17 � 0.21 and baseline � 2.67� 0.20, test � 2.68 � 0.29, respectively). However, thisenhanced ethanol intake following chronic ethanol expo-sure was eliminated if limited access to ethanol during thetest phase was presented in the presence of an odor cuethat was previously associated with acute (8 hr) withdrawal(mean � SEM ethanol intake (g/kg) for EWD-8hr odorgroup: baseline � 2.70 � 0.11, and test � 2.73 � 0.15).Thus, following the conditioning phase of the study, etha-nol intake did not significantly differ between EWD-8hrodor, C-8/32hr odor, and C-no odor groups, and intake didnot change from their respective baseline levels. In con-trast, ethanol consumption was significantly greater forEWD-32hr odor and EWD-no odor groups in comparisonto the other groups, as well as their own baseline levels ofintake (p � 0.05).

Collectively, these results indicate that cues associatedwith different phases of ethanol withdrawal may exert dif-ferential effects on subsequent voluntary ethanol drinking.While presentation of an odor cue that was previouslypaired with acute (peak) withdrawal did not suppress in-take compared to control conditions, it did prevent en-hancement of ethanol drinking that has been demonstratedto occur as a function of chronic ethanol experience. Thus,although one cannot firmly conclude that the odor cueacquired aversive properties as a result of conditioning, itwould appear that the cue was capable of influencing(dampening) motivation to drink following repeatedchronic ethanol exposure and withdrawal (conditioning)experience. A more direct assessment of the motivationalproperties of the conditioned cue might be required tomore fully address this question.

Similarly, since presentation of an odor cue previouslypaired with protracted periods of withdrawal did not sig-nificantly alter intake compared to the no-odor condition, itis difficult to draw firm conclusions regarding the hedonicvalence of this conditioned cue. It was hypothesized thatpresentation of this cue might result in further enhance-ment of ethanol drinking since it was paired with “recov-ery” from ethanol withdrawal. However, since animals werereturned to the inhalation chambers for their next 16 hr

bout of ethanol vapor exposure soon after each condition-ing trial (16 hr later), the odor cue may have inadvertentlybeen associated with re-exposure to ethanol inhalation.Inasmuch as this forced exposure may be aversive, associ-ation with anticipated “aversive” chronic ethanol exposuremight have canceled out positive attributes associated with“recovery” from withdrawal. Again, more direct testing ofthe motivation properties of the cue acquired through con-ditioning would address this issue.

In summary, results from this study support our previousfindings demonstrating that once the rewarding propertiesof ethanol are established (as indicated by stablephysiologically-relevant intake), chronic ethanol exposure/withdrawal experience enhances subsequent voluntary eth-anol drinking. Presentation of an odor cue that was asso-ciated with withdrawal altered this effect, depending onwhether the cue was paired with acute (peak) or protractedperiods of withdrawal. Additional studies are required tofurther characterize the motivational properties of odorcues that are acquired through association with differentphases of ethanol withdrawal, and the subsequent modu-lating effects of these cues on ethanol drinking. Thesestudies may be of clinical relevance in providing informa-tion about conditions in which environmental cues associ-ated with different periods of abstinence may impact re-lapse vulnerability.

CONDITIONED REINSTATEMENT: SIGNIFICANCE OFHISTORY OF DEPENDENCE AND WITHDRAWAL

F. Weiss

An important factor implicated in the chronic relapsingnature of alcohol addiction is learned responses evoked byenvironmental stimuli that have become associated withthe subjective actions of ethanol through classical condi-tioning (O’Brien et al., 1990). Exposure to such cues canprovoke drinking urges and other responses relevant foraddictive behavior in detoxified alcoholics. A significantrole of alcohol cues in relapse has also been demonstratedin animals. In particular, studies using the extinction-reinstatement model show that alcohol-related contextualstimuli (i.e., environmental cues that are both predictive ofethanol availability and associated with the reinforcing ef-fects of ethanol) exert powerful and long-lasting controlover ethanol-seeking behavior. Such stimuli reliably rein-state extinguished ethanol-seeking behavior as measured bythe resumption of responding at a previously activeethanol-paired lever (Katner and Weiss, 1999; Katner etal., 1999; Liu and Weiss, 2002a; Liu and Weiss, 2002b;Ciccocioppo et al., 2001, 2002, 2003, 2004). This condi-tioned drug-seeking response is remarkably resistant toextinction in that the efficacy of alcohol cues to elicitresumption of ethanol-seeking behavior does not diminisheven when presented repeatedly under non-reinforced con-ditions (Ciccocioppo et al., 2001). Further underscoring theimportance of conditioned responses to ethanol cues in

ALCOHOL WITHDRAWAL AND CONDITIONING 457

alcohol addiction is the finding that when rats are subjectedto stress – another risk factor for relapse – the reinstate-ment of ethanol seeking by subsequent exposure to alcoholcues is exacerbated (Liu and Weiss, 2002a). Lastly, rein-statement induced by alcohol cues is dose-dependently re-versible by the nonselective opiate receptor antagonist nal-trexone as well as by mu and delta-selective opiateantagonists (Katner and Weiss 1999; Ciccocioppo et al.,2002; 2003). In alcoholics, naltrexone attenuates condi-tioned cue reactivity and cue-induced craving (Rohsenowet al., 2000; Monti et al., 1999). Thus, conditioned rein-statement of ethanol-seeking in animals appears to havegood predictive validity as a model of craving and relapserisk associated with alcohol cue exposure in human alcoholabuse.

The growing literature on alcohol cue effects in animalmodels of relapse complements the literature on condi-tioned cue reactivity or craving in alcoholics and supportsthe hypothesis that alcohol cue conditioning may be acritical factor in susceptibility to relapse. What must bekept in mind, however, is that these animal studies havebeen conducted largely in rats with a history of only 30–60min of daily access to ethanol during which typically onlymodest blood alcohol levels of 50–80 mg% are attained.The cue-induced reinstatement observed under these con-ditions is consistent with evidence that even light drinkerswho are not dependent show conditioned cue reactivity andmild craving in response to alcohol cue exposure (Greeleyet al., 1993; Streeter et al., 2002). However, cue-inducedethanol-seeking in nondependent animals is unlikely tomodel the learning history and motivational forces under-lying conditioned cue reactivity and craving in alcoholicswith long histories of heavy drinking and repeated with-drawal episodes. Indeed, in alcoholics the degree or sever-ity of craving induced by alcohol cues is highly correlatedwith the history and degree of dependence (Greeley et al.,1993; Streeter et al., 2002; Laberg, 1986). One possibleexplanation for these findings is that the availability andconsumption of ethanol during withdrawal allows for avoid-ance learning to occur (i.e., the reversal or avoidance ofwithdrawal distress by resumption of ethanol use), therebymodifying the individual’s ethanol reinforcement history toinclude learning about negative reinforcement as an impor-tant aspect of ethanol’s actions. As a result, ethanol maybecome a qualitatively different and presumably more po-tent reinforcer. A testable hypothesis then is that ethanol,when available and ingested during withdrawal, acquiresincreased incentive salience as a reinforcer and, that as aresult, the conditioned incentive salience of ethanol cuesincreases as well.

An earlier study that in some respects provides informa-tion relevant for a test of this hypothesis (Ciccocioppo etal., 2003) compared reinstatement produced by an ethanolcue in nondependent rats to the effects of the same cue inrats with a history of dependence that consisted of eithersingle or multiple ethanol vapor intoxication and with-

drawal. Thus, re-exposure to ethanol vapor in rats sub-jected to multiple withdrawal cycles provided an opportu-nity for associations to develop between ethanol vapor andalleviation of withdrawal, whereas this was not the case inrats experiencing only a single withdrawal episode. In thisstudy, ethanol was initially operantly self-administered in30 min sessions and the availability of ethanol was condi-tioned to the presence of a discriminative stimulus (SD).The rats then were subjected to single or multiple ethanolvapor intoxications, followed by seven days of full with-drawal from ethanol. At this time, responding at the leverproducing ethanol during earlier self-administration wasextinguished and the rats tested for reinstatement in thepresence of the previously ethanol-predictive SD only. Con-trary to the expectations, the effects of the ethanol-predictive cue on the number of reinstatement responsesdid not differ as a function of single versus repeated with-drawal experience, and the level of responding (i.e.,ethanol-seeking) in both “dependence groups” was identi-cal to that in nondependent rats. On closer examination ofthe contingencies that were in effect in this study, it be-comes apparent that two conditions had not been met thatmay be required for a valid test of the hypothesis. First, theethanol SD used to test for conditioned reinstatement hadbeen paired with ethanol availability only while rats stillwere in the nondependent state, and therefore associatedonly with the acute, positive reinforcing effects of ethanol.Second, no specific cue was paired with re-introduction toethanol vapor in rats undergoing repeated withdrawal thatcould have become associated with amelioration of with-drawal and tested for its motivational relevance. Finally,these animals had been subjected to ethanol withdrawalwithout being given the opportunity to associate an activebehavioral response (i.e., oral ethanol self-administration)with reversal of the aversive consequences of withdrawal.Two questions were therefore asked in a subsequent set ofexperiments: 1) Does learning about escape from the aver-sive effects of withdrawal by active ethanol self-administration alter the effects of alcohol cues that hadpreviously been associated only with the positive reinforc-ing effects of ethanol, and 2) to what extent do stimuli thatare associated specifically with ethanol self-administrationduring withdrawal promote reinstatement of ethanol-seeking behavior?

To address the first question, ethanol reinforced re-sponses in nondependent rats were response-contingentlypaired with a discrete light cue. Rats then were either madedependent by ethanol vapor intoxication or remained non-dependent. During the last 3 days of dependence induction,rats were removed daily from ethanol vapor and allowed tooperantly self-administer ethanol for 12 hr, followed byre-exposure to ethanol vapor for 12 hr. The rats then werefully withdrawn from ethanol, and previously ethanol-reinforced operant responding extinguished in daily ses-sions over a 3-week period. Animals then were tested forreinstatement by brief response-contingent presentation of

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the ethanol cue conditioned to the positive reinforcingeffects of ethanol during self-administration training. Un-der these conditions, rats that had about the same ofamount of exposure to the cue as the dependent animalshowed significantly greater conditioned reinstatementthan nondependent rats that had more or less the sameamount of exposure to the cue than the dependent animal.These observations suggest that learning about negativeethanol reinforcement during withdrawal enhances the ef-fects of cues that had previously been associated only withpositive reinforcement by ethanol.

A second experiment addressed the question as towhether stimuli conditioned specifically to the withdrawal-ameliorating actions of ethanol acquire motivational signif-icance in terms of eliciting reinstatement or relapse. Thesame general procedures as above were used, except that asecond and distinctly different stimulus was introduced,paired specifically and only with ethanol-reinforced re-sponses during the 12-hr self-administration sessions in the3-day withdrawal phase. The effects of this stimulus onreinstatement then were tested during acute ethanol with-drawal and 3 weeks following termination of ethanol vaporexposure. Under these conditions, both the stimulus thathad been paired only with positive reinforcement prior toinduction of dependence and the stimulus that had beenpaired only with negative reinforcement during withdrawalproduced substantial reinstatement during acute with-drawal. The same effect was obtained in rats tested follow-ing 3 weeks of abstinence. These observations suggest thatstimuli conditioned specifically to amelioration of with-drawal are of motivational significance in their own rightand may contribute in important respects to conditionedcue reactivity, alcohol craving, and relapse in alcoholicsubjects. Moreover, the findings of this series of studiesillustrate that without an appropriate history of negativereinforcement by ethanol, a history merely of dependencemay not be sufficient to document and study changes in themotivational impact of ethanol cues.

CONDITIONED AND UNCONDITIONED ALCOHOLWITHDRAWAL; DO THEY HAVE A ROLE IN ALCOHOL

DEPENDENCE?

C. Drummond, M. Peoples, and H. J. Little

Conditioning is considered to play an important role inmotivation to use drugs of abuse, but the situation is com-plex and has been the subject of various hypotheses. Bothalcohol ingestion, or withdrawal from alcohol, have beensuggested to serve as the unconditioned stimulus, whileenvironmental cues that have previously been associatedwith alcohol consumption act as conditioned stimuli. Ifalcohol ingestion is the unconditioned stimulus, then expo-sure to alcohol-related cues results in conditioned compen-satory responses that oppose the actions of the drug, thusproducing tolerance to the drug effects (Seigel, 1975). Inthe absence of drug actions, these opposing effects would

then induce subjective and physiological concomitants ofthe withdrawal syndrome. In a conditioned withdrawal sit-uation, in the absence of the drug, the alcohol-related cuescause aversive feelings similar to those experienced duringthe alcohol withdrawal syndrome (Drummond et al., 1990).

Reactivity to alcohol-related cues can be cognitive, phys-iological or behavioral. The former includes subjectivecraving for the drug and expectancies of drug effects. Phys-iological responses can take the form of physiologicalarousal including sweating and salivation, and can be mea-sured by changes in heart rate, skin temperature, skinconductance and salivary volume. Behavioral reactivity re-fers to alcohol seeking behavior and alcohol consumption,and has been measured by speed of consumption and la-tency to drink (Drummond, 2000). There is however, muchindividual variation, with some alcoholic study participantsshowing no reactivity to alcohol-related cues. A factors thatmay be involved in this variation is that some cues are moreclosely associated with alcohol than others, and thereforemay have greater salience (Drummond, 2000). Externalcues, such as sight or smell of alcohol, are thought to bemore influential than imaginal cues, for example. Expect-ancy is also important, as if subjects know there is nopossibility of consuming alcohol, cues may be less salient(Meyer, 2000). Negative affect also has considerable im-portance, and has also been observed to be the most fre-quent precipitating factor in relapse drinking (Marlatt andGordon, 1985).

A critical distinction with regard to craving for alcoholhas been made by Drummond (2000). Withdrawal cravingwas suggested to occur as a feature of alcohol withdrawal,and is thus likely to represent an unconditioned response tocessation of alcohol consumption. Such an effect wouldreach a peak shortly after alcohol use has stopped, thengradually decay over time. The acute withdrawal will usu-ally resolve within 7 days, but protracted withdrawal symp-toms may continue for several months. Cue-elicited crav-ing, in contrast, was said to be a conditioned response toalcohol-related cues occurring only in the presence of suchcues. This would be short lived, but could occur at any timeafter cessation of alcohol drinking when cues are encoun-tered. While the extent of both forms of reactivity arerelated to the degree of alcohol dependence, the condi-tioned response was hypothesized to be related to relapsedrinking, while the unconditioned response was not.

Study 1: Cue Reactivity and Alcohol Withdrawal in AlcoholDependent Drinkers. The present study aimed to examinethe differences between withdrawal craving and cue reac-tivity. A within-subjects, repeated measures, design wasused to study reactivity to alcohol-related cues in a sampleof patients admitted to the Inpatient Alcohol Assessmentand Treatment Unit at Springfield Hospital, London.Thirty-five severely dependent male patients undergoingalcohol detoxification were recruited, and demographicand clinical information gathered. Measurements weremade during the study of severity of dependence, using the

ALCOHOL WITHDRAWAL AND CONDITIONING 459

Severity of Alcohol Dependence Questionnaire (SADQ)and anxiety levels, using Speilberger’s State Trait AnxietyInventory (STAI). Urges to drink were examined using theAlcohol Urges Questionnaire (AUQ), which measuresthree aspects of craving, desire for a drink, expectation ofpositive effects from drinking and inability to avoid drink-ing if alcohol was available. Additionally a Value of Alco-hol scale was used to examine the strength of motivation todrink. Physiological reactivity was measured by change inskin conductance from baseline prior to cue exposure. Cueexposure was carried out on days 4 (Trial 1) and 12 (Trial2) after admission, with counterbalanced presentation ofalcohol-related and neutral cues. Unconditioned measureswere made on day 3, and prior to the cue exposures on days4 and 12.

The hypotheses tested were that the patients would dem-onstrate a higher level of reactivity to alcohol-related cuescompared with neutral cues, on both cue-exposure trials.Reactivity to the cues would be related to the backgroundlevel of withdrawal reactivity across time, and that a greaterincentive to drink, as measured by the Value of Alcoholscale, would be related to cue reactivity rather than with-drawal craving. Nonparametric statistical analysis was usedas the results were found not to be normally distributed.

Subjective reactivity to alcohol-related cues was signifi-cantly higher than reactivity to neutral cues, in both trials.Skin conductance level changes in response to alcohol re-lated cues were significantly higher than changes seen afterneutral cue presentation. The behavioral response patterns,however, were difficult to compare between alcohol andneutral cues, owing to the number of within-subject tiesacross repeated measures of the scale. There was thereforesubjective and physiological evidence of greater response tothe alcohol-related compared with neutral cues.

There were no significant differences between the twotrials for the subjective responses or the skin conductancechanges in response to the alcohol-related cues, when thepre-exposure levels were subtracted. The behavioral mea-sures were again complicated by the large number ofwithin-subject ties, suggesting that the behavioral reactivityremained stable over time. The responsivity to alcohol-related cues therefore did not appear to decrease signifi-cantly over the duration of the study.

The AUQ scores in the absence of cues showed a signif-icant decrease on day 12, compared with levels on days 3and 4, indicating a reduction by the end of the detoxifica-tion process. Logistic regression indicated that only thesubjective cue-elicited reactivity had a significant influenceon the motivation to drink. This is compatible with thehypothesis that relapse drinking is related to the subjectivereactivity to alcohol-related cues, but not to the physiolog-ical measures.

Study 2: Alcohol Withdrawal Conditioning in Mice. Theinfluence of conditioning on reactivity to alcohol-relatedcues was also studied in mice. Animals of the TO strainwere given daily intraperitoneal injections of either alcohol

or isotonic saline and repeatedly exposed to an elevatedplus maze immediately after the alcohol or saline adminis-tration (Cole et al., 1999). When the alcohol injections andmaze exposure had been repeated once daily for 9 days, thealcohol injections were replaced by saline on the 10th day.Under these conditions mice consistently exhibited a char-acteristic behavior pattern on the 10th day, with increased“stretched attend” postures and the proportion of timespent in the central square. These behaviors on the ele-vated plus maze are considered to represent “risk assess-ment.” This pattern of behavior was different from thatpreviously seen during withdrawal from alcohol, and wasnot observed when repeated injections of alcohol weregiven either without any maze exposure, or after repeatedexposure to the maze. Thus the characteristic behaviorpattern appeared to be contingent on the animals beingrepeatedly exposed to the maze environment while underthe influence of alcohol. In particular, the reduction instretched attend postures produced by acute alcohol, thetolerance to this behavior seen after repeated alcohol andthe increase in it after replacement of alcohol by saline, areconsistent with the pattern predicted for a behavioral re-sponse to the absence of alcohol, conditioned to the envi-ronment of the maze.

While subjective responses could clearly not be mea-sured in this preclinical study, the results clearly demon-strated an influence of conditioning on the pattern of be-havior of the mice when exposed to an alcohol-relatedenvironment. The mice showed a different pattern of be-havior when placed in a maze environment associated withthe experience of alcohol than on previous exposures to theenvironment under the influence of alcohol. However, thispattern of behavior was not the same as that seen duringalcohol withdrawal, showing that the conditioned responseto the alcohol-related cues was not identical to alcoholwithdrawal or to the effects of alcohol.

Conclusions from Cue-Elicited Withdrawal Studies. Thesestudies add to the evidence base that both conditioned andunconditioned withdrawal have a role in alcohol depen-dence. Unconditioned alcohol withdrawal is a feature ofthe Alcohol Dependence Syndrome and may be responsi-ble for other elements of dependence, including reliefdrinking, and hence the development of a compulsive pat-tern of behavior aimed at the avoidance of negative psy-chophysiological states in the dependent drinker. The pro-tracted withdrawal syndrome may also predispose to theexcess rate of relapse in the first few months followingalcohol cessation in dependent drinkers through a processof negative reinforcement. In the second study, miceshowed a different pattern of behavior when placed in amaze environment associated with the experience of alco-hol than on previous exposures to the environment underthe influence of alcohol. However, this pattern of behaviorwas not the same as that seen during alcohol withdrawal,showing that the conditioned response to the alcohol-

460 LITTLE ET AL.

related cues was not identical to alcohol withdrawal or tothe effects of alcohol.

This research also points to a relationship between con-ditioned and unconditioned withdrawal. The results pointto unconditioned alcohol withdrawal being related to anincrease in cue reactivity. It may be that the backgroundlevel of unconditioned alcohol withdrawal leads to a gen-erally heightened level of subjective and physiological re-activity, such that when an external stimulus is presented,the level of reactivity is increased. In the case of alcoholcues, since alcohol cue reactivity is compatible with awithdrawal-like response, it is likely that the backgroundlevel of unconditioned withdrawal and cue reactivity areadditive, leading to a heightened withdrawal-like state. Thisinteraction in turn could make alcohol cues particularlysalient during the immediate post withdrawal period. Thiscould also explain the heightened level of relapse duringthe early and protracted post withdrawal period, whichwarrants further research. It is possible that individualswith more severe and/or prolonged protracted withdrawaland have more marked cue reactivity, are more susceptibleto relapse though an interaction of these factors. Further ifone could develop methods of more effectively treatingprotracted withdrawal (e.g., through medications) and cuereactivity (e.g., through cue exposure treatment) it may bepossible to reduce the risk of relapse.

It may be that conditioned and unconditioned withdrawalshave a greater role in alcohol dependence than in stimulantdependence where positive reinforcement mechanisms andincentive sensitization are thought to have greater significance(Robinson and Berridge, 1993). This would be consistent withdifferences in drug action between stimulants (e.g., cocaineand amphetamines) and sedative drugs such as alcohol, whichhave very different withdrawal syndromes.

DISCUSSION

C. L. Cunningham

Research presented in this symposium nicely highlightsseveral of the important ways that withdrawal-related condi-tioning processes might alter the behavior of individuals whohave previously experienced or are currently undergoing eth-anol withdrawal. To organize the discussion of these findings,Fig. 1 offers a simplified overview of four possible ways inwhich such conditioning might occur. The triangular shapedareas outlined with solid lines are intended to represent thetime course of unconditioned behavioral, physiological andneurochemical responses that are produced by each exposureto ethanol. These effects might be produced by a brief periodof drug exposure such as occurs following a short drinkingbout (e.g., Weiss) or i.p. injection of ethanol (e.g., Drummondet al.). Alternatively, these responses might be induced by amore prolonged exposure as when ethanol is given in a liquiddiet for many days or weeks (e.g., Stephens et al.) or whenanimals are exposed to ethanol vapor in an inhalation cham-ber for several hours or days (e.g., Becker and Lopez; Weiss).

The triangular shaped area outlined with dashed lines is in-tended to represent the unconditioned withdrawal responses(“abstinence syndrome”) that are presumed to occur after aperiod of acute or chronic exposure to ethanol has ended(Crabbe and Cunningham, 1999). In both cases, a triangularshape is used to indicate that these phenomena increase overtime and reach a peak before declining back to baseline levels.

Within this figure, four different opportunities for con-ditioning are represented by the presence of four condi-tioned stimuli (CSs) distinguished by different subscripts.CS1 depicts a situation is which the CS is paired directlywith ethanol’s unconditioned effects. This type of condi-tioning is commonly studied in procedures that involvemeasurement of approach to or avoidance of taste or placecues that have been paired with ethanol (Cunningham etal., 2000). It has also been studied in procedures thatexamine changes in locomotor activity or in physiologicalresponses such as body temperature (Cunningham, 1998).Weiss describes this type of conditioning in his studies ofnondependent animals in which specific environmental

Fig. 1. This figure illustrates four different types of ethanol and withdrawal-related conditioning possibilities. CS1 depicts a conditioned stimulus (CS) that ispaired directly with unconditioned effects of ethanol. CS2 and CS3 represent cuesthat are paired with the early or late stages of ethanol withdrawal, respectively.CS4 shows a stimulus that is paired with alleviation of withdrawal by ethanol. Seetext (Discussion) for additional description.

ALCOHOL WITHDRAWAL AND CONDITIONING 461

cues were associated with ethanol availability and/or etha-nol reinforcement during operant self-administration. Asnoted by Weiss, cues established as CSs by such pairings areable to reinstate extinguished ethanol-seeking behavior andare highly resistant to extinction. A similar conditioningprocess was likely involved in producing changes in“stretched-attend” posture and other behaviors in micegiven paired exposures of ethanol with a plus maze (Drum-mond et al.). This type of conditioning is also usuallypresumed to have occurred, at least initially, in the drinkinghistory of human alcoholics and may contribute to thesubjective cue-related reactivity that influences motivationto drink (Drummond et al.).

The exact nature of the conditioning processes that un-derlie the behavioral and other changes produced by CSsthat have been directly paired with abused drugs has beena long-standing source of theoretical controversy (Wikler,1973; Cunningham, 1993, 1998). According to one view,CSs paired with such drugs acquire the ability to elicitdrug-like conditioned responses (CRs), including condi-tioned positive incentive motivational states (e.g., Stewartet al., 1984). Another popular approach has focused on theability of drug-paired CSs to elicit drug-opposite (compen-satory) CRs that are characterized as conditioned with-drawal responses (e.g., Hinson and Siegel, 1980). The lit-erature provides support for both points of view and,regardless of their direction, these CRs are thought to havemotivational consequences that can maintain or reinstatedrug-seeking behavior. Although the underlying CRs areunknown, data presented by Weiss and by Drummond et al.offer additional support for this functional role of drug-paired CSs.

Figure 1 also illustrates several possible types of condi-tioning that may be produced when CSs overlap the periodof drug withdrawal. CS2 and CS3 represent CSs that overlapthe period of peak withdrawal and the terminal (recovery)phase of withdrawal, respectively. Becker and Lopez stud-ied these two opportunities for withdrawal conditioning bypairing odor CSs with the early (8 hr) or late (32 hr) phasesof withdrawal in mice given repeated cycles of ethanolvapor exposure and withdrawal. The possibility that cuespaired with drug withdrawal might influence subsequentdrug seeking in the presence of those cues was a prominentfeature in Wikler’s (1965, 1973) conditioning-based basedtheory of drug dependence and relapse. However, contraryto predictions derived from Wikler’s theory, Becker andLopez did not find that ethanol self-administration wasenhanced by presentation of odor cues that had beenpaired with the early or late phases of withdrawal. Al-though repeated ethanol withdrawal cycles enhanced eth-anol self administration, presentation of the odor cue pre-viously paired with late stage (32 hr) withdrawal had noeffect compared to the effect of the odor cue in mice thathad undergone multiple withdrawals without odor pairings.Of interest, however, exposure to the odor cue previouslypaired with early stage (8 hr) withdrawal appeared to pre-

vent the enhancement of ethanol intake that was otherwiseproduced by experience with repeated ethanol withdrawalcycles. As noted by Becker and Lopez, this finding raisesthe possibility that CSs paired with peak ethanol with-drawal may acquire aversive properties, a possibility thatshould be pursued in future research.

The last type of withdrawal-related conditioning depicted inFig. 1 is the case represented by CS4 in which the cue is pairedwith alleviation of the withdrawal state by exposure to ethanol.Presumably, in addition to providing an opportunity for theconditioning of drug-like or drug-opposite CRs (as in the caseof CS1), this situation would also allow the conditioning ofresponses that might uniquely reflect a reduction in the aver-sive withdrawal state (“negative reinforcement”). In the stud-ies reported by Weiss, such conditioning enhanced the subse-quent ability of the CS to reinstate an extinguished self-administration response. Moreover, the ability of such CSs toreinstate self-administration did not depend on a history ofCS-ethanol pairings prior to the induction of dependence.That is, a novel CS that was paired with ethanol self-administration only during withdrawal nevertheless acquiredthe ability to reinstate an extinguished self-administration re-sponse, even after several weeks of ethanol abstinence.Weiss’s emphasis on the role of negative reinforcement inproducing the effects observed in his studies may have impli-cations for understanding why the odor CSs used by Beckerand Lopez, which were paired with withdrawal but not withalleviation of withdrawal, failed to enhance ethanol self-administration in their studies. The types of conditioning pro-cesses described by Weiss presumably also occurred duringthe development of dependence in the alcoholics tested byDrummond et al., perhaps contributing to their reported sub-jective reactivity to alcohol-related cues.

The issues addressed by Stephens and colleagues are notwell illustrated by Fig. 1. However, their studies may haveimportant but underappreciated implications for under-standing the types of conditioning shown in Fig. 1. Specif-ically, the studies of Stephens et al. suggest that a history ofrepeated ethanol withdrawal interferes with an organism’slater ability to learn fear-related associations, an effectthought to be mediated by changes in amygdala function.The broader, unanswered question raised by these studiesis whether or how repeated withdrawal might subsequentlyaffect the learning (or extinction) of associations based onthe type of conditioning depicted in Fig. 1. The data re-ported by Becker and Lopez (2004) suggest that repeatedwithdrawal does not preclude learning about the relation-ship between a CS and the early stage of withdrawal. How-ever, based on the findings of Stephens et al., it seems quitepossible that the strength and perhaps even the direction ofthe conditioning reported by Becker and Lopez was influ-enced by a history of repeated ethanol withdrawal. Thedata of Stephens et al. also raise the possibility that re-peated withdrawal could interfere with the extinction oflearned associations, a possibility with important implica-tions for extinction-based treatments (e.g., cue-exposure)

462 LITTLE ET AL.

for alcoholism. Given the current paucity of information onthe neurobiological systems underlying the various types ofwithdrawal-related conditioning depicted in Fig. 1, one canonly speculate as to whether the amygdala-specific deficitsidentified by Stephens et al. would impact those types ofconditioning. Future research must address this issue.

In summary, research described in this symposiumstrongly supports the view that CSs paired with ethanol orwith the period of withdrawal from ethanol can produceconditioned responses that may play an critical role in themaintenance of ethanol-seeking behavior or in the relapseto such behavior after a period of abstinence. This learningoccurs under a variety of conditions (Fig. 1) and the learn-ing process itself may be altered by a history of repeatedethanol withdrawal. Overall, these studies make an importantcontribution to our current understanding of withdrawal-related conditioning processes. At the same time, theystrongly encourage additional research on the relationshipbetween withdrawal, conditioning and ethanol-seeking behav-ior (Fanselow and LeDoux, 1999; Greeley, et al., 1993).

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