Clonidine Blocks Acquisition But not Expression of Conditioned Opiate Withdrawal in Rats Gery Schulteis, Ph.D., Luis Stinus, Ph.D., Victoria B. Risbrough, B.A., and George F. Koob, Ph.D. Previous studies in rodents have reported that clonidine, an conditioned place aversion; and (2) conditioned suppression ␣ 2-adrenergic receptor agonist, attenuated conditioned of operant responding for food (fixed ratio-15 schedule), in a aversions to naloxone-precipitated opiate withdrawal when paradigm wherein rats received four pairings of naloxone administered prior to each withdrawal conditioning with a distinct tone and odor stimulus. Clonidine dose- episode. The current study was designed to determine dependently blocked the acquisition of both conditioned whether clonidine could modify the expression of behaviors when administered prior to naloxone on each previously established conditioned place aversions conditioning trial, but was ineffective in blocking the and conditioned suppression of operant responding. expression of these conditioned withdrawal signs when Dose- and time-dependent effects of clonidine on activity administered prior to the test session. and suppression of operant responding for food identified [Neuropsychopharmacology 19:406–416, 1998] © 1998 appropriate treatment parameters for subsequent studies in American College of Neuropsychopharmacology. Published which rats rendered dependent on opiates through by Elsevier Science Inc. implantation of morphine pellets were tested for: (1) KEY WORDS: Clonidine; Opiate dependence; Opiate after periods of abstinence are conditioned associations withdrawal; Conditioning; Naloxone that are formed over a course of repeated drug experi- ence. Within the domain of opiate withdrawal symp- Addiction can be defined as a “behavioral pattern of tomatology, it is now recognized that somatic/auto- drug use, characterized by overwhelming involvement nomic signs and affective or emotional signs (e.g., with the use of a drug (compulsive use), the securing of anxiety, depression, dysphoria), each with their own its supply, and a high tendency to relapse after with- unique underlying neurophysiological substrates (re- drawal” (Jaffe 1990). Among the factors that may con- viewed by Maldonado et al. 1996; Schulteis and Koob tribute to loss of control over drug intake and relapse 1996), may differentially motivate continued drug use, with the affective signs hypothesized to be of greater motivational significance than the somatic signs. From the Department of Neuropharmacology (GS, VBR, GFK), A considerable body of both clinical and preclinical The Scripps Research Institute, La Jolla; Department of Anesthesiol- literature suggests that positive (drug reward) and neg- ogy (GS), U.C. San Diego School of Medicine, San Diego, California, ative (drug withdrawal) affective states can become as- USA; and Laboratoire de Neuropsychobiologie des Desadaptations (LS), Université de Bordeaux II, Bordeaux, Cedex, France. sociated with stimuli in the drug-taking environment Address correspondence to: G. Schulteis, Department of Anesthe- and that these conditioned stimuli themselves acquire siology, VAMC 125, U.C. San Diego School of Medicine, 3350 La motivational significance in maintaining compulsive use Jolla Village Drive, San Diego, CA 92161-5085, USA. Received November 21, 1997; revised February 9, 1998; accepted and in precipitating relapse after periods of abstention February 16, 1998. (Baldwin and Koob 1993; Childress et al. 1994; O’Brien NEUROPSYCHOPHARMACOLOGY 1998–VOL. 19, NO. 5 © 1998 American College of Neuropsychopharmacology Published by Elsevier Science Inc. 0893-133X/98/$–see front matter 655 Avenue of the Americas, New York, NY 10010 PII S0893-133X(98)00036-0 NEUROPSYCHOPHARMACOLOGY 1998–VOL. 19, NO. 5 Clonidine and Conditioned Opiate Withdrawal 407 et al. 1976, 1993; Ramsay and Woods 1997; Schulteis (emotional) domain. Accordingly, results indicating that and Koob 1996; Schulteis et al. 1997a; Wikler 1973). clonidine could prevent the acquisition of conditioned Successful implementation of treatment strategies place aversions were interpreted as suggesting that af- that will facilitate detoxification and reduce the proba- fective components of opiate withdrawal were sensitive to bility of relapse must recognize the individual elements clonidine, at least under some conditions (Kosten 1994). that contribute to the addiction process and the degree Untested, however, was whether clonidine adminis- to which a given treatment strategy is able to address tered once the conditioned aversion was established those individual elements, both unconditioned and could prevent the expression of conditioned with- conditioned. For example, clonidine, a noradrenergic drawal. This situation would more closely approximate alpha2 agonist, has been found in both clinical (Charney the clinical condition wherein any conditioned associa- et al. 1981; Cuthill et al. 1990; Dawe and Gray 1995; tions between opiate reinforcement or opiate with- Gold et al. 1978; Janiri et al. 1994; Jasinski et al. 1985; drawal and environmental stimuli would have been Kasvikis et al. 1990) and preclinical animal studies formed long before onset of clonidine therapy. Therefore, (Coupar 1992; Katz 1986; Kelsey et al. 1990; Sparber and the current set of studies was undertaken to examine Meyer 1978; Taylor et al. 1988) to ameliorate some of the the relative ability of clonidine to attenuate the acquisi- effects of opiate withdrawal. Treatment strategies based tion and expression of conditioned opiate withdrawal. upon clonidine therapy are aimed primarily at facilitat- In addition to employing conditioned place aversions ing opiate detoxification through suppression of so- as an index of conditioned affective opiate withdrawal, matic opiate withdrawal symptoms. However, in many we also included conditioned suppression of operant of these same studies, it was reported that subjective responding for food (Baldwin and Koob 1993). Sup- signs of such withdrawal discomfort as dysphoria, anx- pression of operant responding for food is a sensitive iety, irritability, restlessness, and drug craving were at- index of antagonist precipitated opiate withdrawal that tenuated only partially, or not at all, when clonidine is attenuated by clonidine pretreatment (Sparber and was substituted for opiates in addicts. Moreover, there Meyer 1978). Its validity as an animal model of affective are reports that addicts will relapse to drug intake even withdrawal again is supported by the ability to precipi- during the period of clonidine therapy (Cuthill et al. tate suppression of operant responding by direct appli- 1990). Therefore, based upon the existing clinical litera- cation of opiate antagonists to the nucleus accumbens ture, it seems apparent that there are potentially signifi- (Koob et al. 1989; see Schulteis et al. 1997a for further cant limitations to the efficacy of clonidine therapy to discussion). facilitate detoxification, to suppress withdrawal, and to decrease the probability of relapse to opiate use. Data from the preclinical literature may provide some clues to understanding these limitations. GENERAL METHODS Preclinical studies have verified the efficacy of cloni- dine in blocking a number of somatic and autonomic All procedures employed in the studies described signs produced by spontaneous or naloxone-precipi- herein were reviewed and approved by appropriate In- tated opiate withdrawal in rodents and monkeys (Brit- stitutional Animal Care and Use Committees, and were ton et al., 1984; Coupar 1992; Kantak and Miczek 1988; carried out in accordance with the guidelines estab- Katz 1986; Sparber and Meyer 1978; Taylor et al. 1988). lished in the Guide for the Care and Use of Laboratory In addition, recent studies with conditioned place aver- Animals (National Research Council and National Insti- sion, a behavioral paradigm that serves as a sensitive tutes of Health). animal model of affective opiate withdrawal (Hand et al. 1988; Schulteis et al. 1994), suggested that clonidine administered prior to each conditioning trial could Subjects block the acquisition of a conditioned aversion to a dis- tinct environment paired with naloxone-precipitated For studies conducted at INSERM Unit 259 in Bor- withdrawal (Kosten 1994; Nader and van der Kooy deaux, France (Experiments 1 and 4), male Sprague– 1996). Conditioned place aversions can be elicited by Dawley rats (IFFA CREDO, Lyon, France) weighing 280 administration of opiate antagonists directly into the to 300 g at the beginning of the experiment were used. nucleus accumbens and central nucleus of the amygdala For studies conducted at The Scripps Research Institute (Stinus et al. 1990), critical elements of the brain’s re- in La Jolla, California (Experiments 2 and 3), male Wistar ward circuitry that mediate the acute hedonic (reward- rats (Charles River, Kingston, NY) weighing 280 to 300 g ing) effects of opiates and other drugs of abuse (see at the start of each experiment were used. All rats were Schulteis and Koob 1996; Schulteis et al. 1997a). There- group housed (2–3/cage) in temperature- and humid- fore, conditioned place aversions seem to be a specific ity-controlled rooms with a 12-hour light/12-hour dark manifestation of neuroadaptation within the affective cycle. All rats except those trained to level press for 408 G. Schulteis et al. NEUROPSYCHOPHARMACOLOGY 1998–VOL. 19, NO. 5 food (Experiments 2 and 3) had ad libitum access to food, Conditioned Place Aversion. The apparatus and