Drugs for Relapse Prevention of Alcoholism (Milestones in Drug Therapy)
Editors: Spanagel, Rainer; Mann, Karl F.
Title: Drugs for Relapse Prevention of Alcoholism, 1st Edition
Copyright 2005 Springer
> Table of Contents > How to measure relapse in animals
How to measure relapse in animals
Rainer Spanagel
Department of Psychopharmacology, Central Institute of Mental Health, University of Heidelberg, J 5, 68159 Mannheim, Germany
Introduction
In this chapter, two animal models - the reinstatement model [1] and the alcohol deprivation effect model [2] - will be described in detail and the limitations of these models in mimicking craving and relapse as observed in human alcoholics will also be discussed. It would be careless, however, if other models would not be considered to measure these phenomena. For example, the conditioned place preference paradigm [3], second order schedules [4], or the escalation paradigm [5] could easily be adapted for this purpose. Although these and other paradigms are widely used in the drug abuse field to further our understanding on craving and relapse, there has only been little effort to adapt these paradigms to alcohol research. Moreover, the application of these models to alcohol research remains a difficult issue. Thus, alcohol administration to rodents does not usually produce a conditioned place preference [3, 6]. However, some specific experimental conditions have been described in order to obtain alcohol-induced conditioned place preference. One paradoxical experimental condition is the use of DBA/2 mice [7]. They exhibit conditioned place preference to alcohol, despite the fact that they avoid alcohol under free drinking conditions. In contrast, C57BL6/J mice, which show a high preference for alcohol in a two bottle free choice paradigm, exhibit conditioned place aversion following alcohol treatment [7]. Therefore, alcohol-induced conditioned place preference cannot be considered as a reliable and reproducible measure of alcohol craving. It is desirable to see that preclinical researchers put more effort into more elaborate animal models of alcohol craving and relapse in the future; however, currently we have to rely on the two aforementioned models to further our understanding on addictive behaviour.
The reinstatement model
The reinstatement model is currently being used in many laboratories to investigate mechanisms underlying relapse behaviour [1]. However, it should be noted that the reinstatement test is performed under drug-free conditions. In
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contrast, a typical relapse or lapse in alcoholic patients is defined as compulsive alcohol consumption following a period of abstinence; a relapse can therefore not happen under drug-free conditions. Thus, having this definition in mind, it remains unclear to the author, how the reinstatement model was put forward by many researchers as a model of relapse. This is per definition wrong but does not diminish the value of this model in measuring drug-seeking behaviour, which without a doubt, is one behavioural dimension of craving. In conclusion, the reinstatement model should be considered as a model of craving rather than relapse, even if it will be a long way to change the literature in this respect. Importantly, it is necessary to use semantics in a proper fashion, as it provides the basis for our common and highly specialized scientific language.In the following, the reinstatement procedure is briefly described: an animal (rat or mouse) is trained to self-administer a drug and is then subjected to extinction - that is, the animal is tested under conditions of non-reinforcement until operant responding appears to be extinguished. When the animal reaches some criterion of unresponsiveness, various stimuli are presented. A stimulus is said to reinstate the drug-seeking behaviour if it causes renewed responding, i.e., lever pressing, without any further response-contingent drug reward. At least three conditions can reinstate responding: (i) drug priming - that is the injection of a small dose of the drug, (ii) stress, and (iii) conditioned stimuli. The data derived from studies using the reinstatement model suggest that the neuronal events mediating drug-, stress-, and cue-induced reinstatement of drug-seeking are not identical [1].
Although reinstatement of intravenous self-administration of psychostimulants and opioids has been established for many years, only a few attempts have been undertaken to transfer this paradigm into the alcohol field. In 1995, the first alcohol reinstatement study in rats was reported by Chiamulera and co-workers [8]. In this study, rats acquired operant responding for alcohol over several months. After stable lever pressing was obtained between subsequent sessions, the rats were tested in extinction, meaning that animals received water instead of alcohol following lever pressing. After eight to ten extinction sessions, re-exposure to a small quantity of ethanol was able to reinstate previously extinguished alcohol-seeking behaviour. These results are consistent with the widely reported description of the first-drink phenomenon: ingestion of a small quantity of alcohol may induce in abstinent alcoholics a strong subjective state of craving and, then, relapse to drug-taking behaviour [9]. The priming effect due to alcohol preload may be evident even after years of abstinence from the drug [10] and a strong craving for alcohol and higher alcohol intake in social drinkers following alcohol priming was described [11]. Only very recently has the alcohol reinstatement paradigm been followed up by other research groups, and it could be demonstrated that intermittent foot-shock stress can also reinstate previously extinguished responding for alcohol [12]. Furthermore, it has been shown that alcohol-associated olfactory cues and other cues can reinstate extinguished alcohol-seeking behaviour [13].
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Foot-shock stress and response-contingent presentation of an alcohol-associated light cue, acting as a conditioned stimulus, also augment reinstated extinguished responding [14]. Thus, addictive effects of these stimuli on responding are observed, supporting the idea of different neuronal systems mediating stress- and cue-induced reinstatement [1, 14].The reinstatement model of drug-seeking behaviour is now a well-established model in rats, and it is only recently that it has become possible to transfer this model to mice [15]. However, some methodological transfer problems from rats to mice ought to be considered: operant tasks have to be achieved by the subject during the course of a reinstatement experiment and usually rats acquire goal-directed behaviour more easily than mice. The first goal to be achieved by the subject in the reinstatement procedure is selective responding on a reinforced lever. This is usually an easy task for a rat but certainly a more difficult one for mice, due to higher motor activity. Another confounding variable in mice is that lever pressing is reinforcing per se. The same problem might also relate to nose-poking. Thus, whether a reinforcer follows a lever press/nose-poke or not, it might not influence subsequent behaviour of the mouse. Despite the problematic factors of high motor activity and reinforcing effects of lever pressing/nose poking, mice tend to successfully acquire selective responding under a simple fixed ratio (FR1) for the drug. However, on the control lever (i.e., the non-reinforced lever), a higher number of responses is observed in mice. The next task to be achieved, is extinction of lever responding. Thus, lever responding is without any further consequence and the individual does not receive the drug anymore. Rats, on average, show a short burst of responding, with responding gradually declining over the days. Following 10 days, rats usually only show few spontaneous responses. Extinction in mice appears to be more difficult and thus more extinction days are needed as compared to rats and again much higher rates of spontaneous responding are observed. Regarding the third task, reinstatement of drug-seeking behaviour has to be elicited. A combination of a light cue and alcohol priming has been shown to reinstate alcohol-seeking behaviour in mice [15]. However, only a few preliminary studies, using the reinstatement paradigm with mice, have been reported and it will take more effort to work out the optimal conditions for reinstatement of drug-seeking behaviour in mice. This effort, however, will pay off as in the future, this paradigm will most likely be of frequent use in studying conditional knock-out mice so as to precisely pin down the genes and brain sites involved in alcohol craving.
In conclusion, reinstatement of alcohol-seeking behaviour can be used to study the neurobiological and molecular basis of craving, since there appears to be a good correspondence between the events that induce craving in laboratory animals and those that provoke it in humans. Furthermore, acamprosate and naltrexone are known to reduce craving in alcoholic patients and can also reduce or even block cue-induced reinstatement of alcohol-seeking behaviour [13, 16, 17]. Nevertheless, the usefulness of the reinstatement model in mimicking craving in humans experiences some limitations. First, the phenomenon
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of craving is complex. Thus, although the operational definition of craving as incentive motivation to drink alcohol has the advantage of making the phenomenon of craving measurable, such a definition neglects the fact that craving also has a subjective dimension that is difficult, if at all possible, to assess in laboratory animals [18]. Second, it appears that extinction of alcohol-seeking behaviour usually only plays a minor role in alcoholic patients trying to achieve and maintain abstinence. With the exception of patients undergoing focused extinction therapy, alcoholics generally try to avoid exposure to external alcohol cues during abstinence. In most cases, alcoholics stay abstinent for a while but then may experience craving and subsequent relapse, if they are reexposed to external cues (e.g., the sight of a bar or smell of alcohol), and in particular, if they are in a vulnerable internal state. Consequently, the animal reinstatement procedure may not accurately reflect the situation of abstinent alcoholics experiencing craving.
The alcohol deprivation effect model
The alcohol deprivation effect model is an animal model to study compulsive alcohol drinking and relapse-like drinking behaviour [2]. Alcohol-experienced animals show a transient increase in alcohol consumption and alcohol preference after a period of forced abstinence (alcohol deprivation), which is termed the alcohol deprivation effect . It can be seen in long-term alcohol-drinking rats, both under home cage drinking and under operant self-administration conditions. The effect is observed in monkeys [19] and man as well [20]. Interestingly, the alcohol deprivation effect is prolonged and enhanced in alcohol-preferring P- and HAD-rat lines after repeated deprivation phases [21, 22] and it changes its characteristics with repeated deprivation phases [23]. Thus, the alcohol deprivation effect in long-term alcohol self-administering rats, which had experienced repeated deprivation phases, shows some particularly interesting features: during an alcohol deprivation effect, these animals consume large amounts of highly concentrated alcohol solutions and even at unusual times. Pronounced changes in the diurnal rhythm of drinking activity were observed in long-term alcohol-drinking rats, which had repeated deprivation phases [23]. Tested in a fully automated electronic drinkometer device, age-matched control animals showed normal drinking activity. Thus, drinking activity during the active night phase was high, whereas drinking activity during the inactive light phase was very low, reaching zero for some hours. In contrast, in long-term alcohol-drinking rats during the alcohol deprivation effect, the pattern of drinking activity completely changed. In particular, during the inactive phase, most of the animals still showed high drinking activity. Moreover, some animals were found that even demonstrated level drinking, i.e., which implies that the alcohol deprivation effect can be associated with alterations in circadian rhythmicity. This is a finding which probably translates to humans. Thus, a new hypothesis suggests that chronic alcohol intake can
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influence the expression and function of clock genes and can thereby alter circadian rhythmicity and it has further been shown that clock gene activity can influence drinking behaviour in mice and man as well [24].Figure 1. (A) Cue-induced reinstatement of ethanol-seeking. During a phase of conditioning rats acquire stable lever pressing for ethanol in the presence of a distinct set of cues. After extinction, the animals are again exposed to the respective cues, formerly associated with ethanol, leading to renewed responding on the ethanol lever in the absence of the primary reinforcer (CTRL). Treatment with naltrexone (NAL; 0.25 mg/kg) or acamprosate (AC; 200 mg/kg) leads to a significant reduction of ethanol-seeking behavior. (Katner et al. (1999) Neuropsychopharmacology 20: 471-479; Bachteler et al. (2005) Neuropsychopharmacology; in press). (B) Reinstatement paradigm. Each lever press is followed by a 25-30 l drop of ethanol as primary reinforcer. |
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Figure 2. (A) Effects of acamprosate and naltrexone on the alcohol-deprivation effect. Rats had unlimited, voluntary access to water and three different alcohol solutions (5, 10, 20%) for eight months before alcohol was completely withdrawn for two weeks (alcohol deprivation). Intermittent treatment with acamprosate (200 mg/kg) and naltrexone (5 mg/kg) reduced alcohol intake compared to control animals after renewed access to ethanol. (B) Home cage drinking. Rats are exposed to the choice of water and three different alcohol solutions (5, 10, 20%) in their home cage. After few weeks, a stable ethanol-intake and -preference develops. Both intake and preference patterns change after an imposed phase of alcohol deprivation. |
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As already mentioned, the alcohol deprivation effect is observed across several species, including monkeys and human social drinkers. Salimov and Salimova [25] were the first who described this effect in mice. In this study, and in subsequent ones of the same group [26], many mice failed to exhibit an alcohol deprivation effect. However, it is important to note that only a short deprivation period of 3 days was introduced in these studies, which might not lead to an effect in most of the mice. The experience in our lab over the years has shown that a deprivation period of at least 2-3 weeks is needed, that would then lead to an alcohol deprivation effect in most mice. However, there will always be a number of mice which will consistently fail to show such an effect. We are now in the course of a selective breeding program, where we are breeding two lines of mice: one which shows a consistent alcohol deprivation effect vs one which consistently fails to show such an effect. These two lines will certainly help in identifying the genetic factors underlying the alcohol deprivation effect, and thereby alcohol relapse drinking behaviour. So far, only a few reports on transgenic mice in the context of the alcohol deprivation effect model and the involvement of a particular gene are available [27, 28]. However, the information from these studies has so far failed to have great influence on better treatment strategies regarding relapse behaviour. It is hoped that it has become clear to the reader that with the use of conditional knockout mice, we are about to enter a new research area and it is strongly believed that in the future many labs working on relapse will follow this line of research and will produce helpful information to guide us in new treatment strategies on relapse behaviour.
In summary, the alcohol deprivation effect is a useful model to study compulsive alcohol drinking behaviour and relapse-like drinking behaviour. However, it is important to note that measuring an alcohol deprivation effect only assesses a behavioural outcome and does not provide insight about a subjective state associated with compulsive drinking behaviour. Nevertheless, the fact that the clinically effective anti-relapse drugs acamprosate and naltrexone also reduce or even abolish the alcohol deprivation effect [29] lends predictive value to this animal model for the development of new and better drugs for the treatment of alcoholism. Furthermore, the alcohol deprivation effect model could also be applied as a high through-put pharmacological screen in the pharmaceutical industry in identifying novel compounds which interfere with alcohol relapse. In fact, the alcohol deprivation effect model is currently used as a high through-put screen test to study relapse drinking in a N-ethyl-N-nitros urea
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(ENU) mutagenesis program. ENU is a chemical mutagen that has been shown to produce a large number of mutations. The most important requirement for an effective ENU screen is a simple and reliable behavioural high through-put test. Finally, the successful application of the alcohol deprivation effect model in an ENU mutagenesis program [30] demonstrates that this test could also be used as a high through-put test for medication development.
References
1 Shaham Y, Shalev U, Lin L, de Wit H, Stewart J (2003) The reinstatement model of drug relapse: history, methodoloy and major findings. Psychopharmacology 168: 3-20
2 Spanagel R (2003) Alcohol addiction research: From animal models to clinics. Best Pract Res Cl GA 17: 507-518
3 Tzschentke T (2005) Measuring reward with conditioned place preference: an up-date of the literature. Addict Biol; in press
4 Everitt BJ, Robbins TW (2000) Second-order schedules of drug reinforcement in rats and monkeys: measurement of reinforcing efficacy and drug-seeking behaviour. Psychopharmacology 153: 17-30
5 Ahmed SH, Koob GF (1998) Transition from moderate to excessive drug intake: change in hedonic set point. Science 282: 298-300
6 van der Kooy D, O'Shaughnessy M, Mucha RF, Kalant H (1983) Motivational properties of ethanol in naive rats as studied by place conditioning. Pharmacol Biochem Behav 19: 441-445
7 Cunningham CL, Niehus DR, Malott DH, Prather LK (1992) Genetic differences in the rewarding and activating effects of morphine and ethanol. Psychopharmacology 107: 385-393
8 Chiamulera C, Valerio E, Tessari M (1995) Resumption of ethanol-seeking behaviour in rats. Behav Pharmacol 6: 32-39
9 Ludwig AM, Wikler A, Stark LH (1974) The first drink: psychobiological aspects of craving. Arch Gen Psychiatry 30: 539-547
10 Besancon F (1993) Time to alcohol dependence after abstinence and first drink. Addiction 88: 1647-1650
11 de Wit H, Chutuape MA (1993) Increased ethanol choice in social drinkers following ethanol preload. Behav Pharmacol 4: 29-36
12 L AD, Quan B, Juzytch W et al. (1998) Reinstatement of alcohol-seeking by priming injections of alcohol and exposure to stress in rats. Psychopharmacology 135: 169-174
13 Katner SN, Magalong JG, Weiss F (1999) Reinstatement of alcohol-seeking behavior by drug-associated discriminative stimuli after prolonged extinction in the rat. Neuropsychopharmacology 20: 471-479
14 Liu X, Weiss F (2002) Addictive effect of stress and drug cues on reinstatement of ethanol seeking: exacerbation by history of dependence and role of concurrent activation of corticotropin-releasing factor and opioid mechanisms. J Neurosci 22: 7856-7861
15 Spanagel R, Sanchis-Segura C (2003) The use of transgenic mice to study addictive behavior. Clin Neurosci Res 3: 325-331
16 Bachteler D, Economidou D, Danysz W, Ciccocioppo R, Spanagel R (2005) The effects of acamprosate and neramexane on cue-induced reinstatement of ethanol-seeking behaviour. Neuropsychopharmacology; in press
17 L AD, Poulos CX, Harding S, Watchus J, Juzytsch W, Shaham Y (1999) Effects of naltrexone and fluoxetine on alcohol self-administration and reinstatement of alcohol seeking induced by priming injections of alcohol and exposure to stress. Neuropsychopharmacology 21: 435-444
18 Spanagel R, H lter SM (2000) Controversial research areas: a critical review. In: G Zernig, A Saria, A Kurz (eds): Handbook of Alcoholism: Clinical and Theoretical Approaches. CRC Press, Boca Raton, Fl, 401-416
19 Sinclair JD (1997) The alcohol-deprivation effect in monkeys. Psychonom Sci 25: 21-25
P.21
20 Burish TG, Maisto SA, Cooper AM, Sobell MB (1981) Effects of voluntary short-term abstinence from alcohol on subsequent drinking patterns of college students. J Stud Alcohol 42: 1013-1020
21 Rodd-Henricks ZA, McKinzie DL, Murphy JM et al. (2000) The expression of an alcohol deprivation effect in the high-alcohol-drinking replicate rat lines is dependent on repeated deprivations. Alcohol Clin Exp Res 24: 747-753
22 Rodd-Henricks ZA, McKinzie DL, Shaikh SR et al. (2000) Alcohol deprivation effect is prolonged in the alcohol preferring (P) rat after repeated deprivations. Alcohol Clin Exp Res 24: 8-16
23 Spanagel R, H lter SM (1999) Long-term alcohol self-administration with repeated alcohol deprivation phases: an animal model of alcoholism? Alcohol Alcoholism 34: 231-243
24 Spanagel R, Pendyala G, Abarca C et al. (2004) The circadian clock gene period2 alters the glutamatergic system and thereby modulates alcohol consumption. Nature Med; in press
25 Salimov RM, Salimova NB (1993) The alcohol-deprivation effect in hybrid mice. Drug Alcohol Depend 32: 187-191
26 Salimov RM, Salimova NB, Shvets LN, Maisky AI (2000) Haloperidol administered subchronically reduces the alcohol-deprivation effect in mice. Alcohol 20: 61-68
27 Cowen MS, Schroff KC, Gass P, Sprengel R, Spanagel R (2003) Neurobehavioral effects of alcohol in AMPA receptor subunit (GluR1) deficient mice. Neuropharmacology 45: 325-333
28 Cowen M, Schumann G, Yagi, Spanagel R (2003) Role of Fyn tyrosine kinase in ethanol consumption by mice. Alcohol Clin Exp Res 27: 1213-1219
29 Spanagel R, H lter SM (2000) Pharmacological validation of a new animal model of alcoholism. J Neural Transm 107: 669-680
30 Spanagel R, Sanchis-Segura C (2005) Basic considerations for random ENU mutagenesis in combination with an alcohol screen test. Addict Biol; in press