Beer consumption in rats: the influence of ethanol content, food deprivation, and cocaine

Moderate Beer Consumption Modifies Tumoral Growth Parameters and Pyrrolidone Carboxypeptidase Type-I and Type-II Specific Activities in the Hypothalamus-Pituitary-Mammary Gland Axis in an Animal Model of Breast Cancer

AIMS

To determine the effect of moderate alcoholic and nonalcoholic beer consumption on tumoral growth parameters, the histopathology, pyrrolidone carboxypeptidase type I (Pcp I), and type II (Pcp II) specific activities in the hypothalamus-pituitary-mammary gland axis, and the circulating levels of estradiol (E₂) and progesterone (P₄) in rats with N-methyl-N-nitrosourea (NMU) induced mammary tumors.

MATERIAL AND METHODS

Food and drink intake, weight gain and tumor growth parameters were collected. The malignant phenotype of the tumor was performed using the Scarff-Bloom-Richardson grading method. Pcp specific activities were fluorometrically analyzed using pyroglutamyl-β-naphthylamide as substrate. Circulating steroid hormones were determined.

RESULTS

Differences were found in tumoral parameters, depending on the drink. Animals that were given alcohol-containing beer (A/C) beer to drink showed the lowest values of hypothalamic Pcp I, in association with the lowest levels of circulating E₂. The significant decrease in Pcp I activity in all NMU-treated groups suggest a clear role of the Pcp I in the tumoral process, and A/C beer interferes with it.

DISCUSSION

Moderate consumption of alcoholic beer would have beneficial effects against mammary tumors through the modification of the endocrine status mediated by GnRH due to changes on Pcp I and II activities at different levels.

From appetite setpoint to appetition: 50years of ingestive behavior research

I review the main themes of my 50-year research career in ingestive behavior as a graduate student at the University of Chicago and a professor at the City University of New York. A seminar course with my Ph.D. mentor, S. P. Grossman, sparked my interest in the hypothalamic obesity syndrome. I developed a wire knife to dissect the neuropathways and the functional disorder responsible for the syndrome. An elevated appetite setpoint that permitted the overconsumption of palatable foods appeared central to the hypothalamic syndrome. In brain-intact rats, providing an assortment of highly palatable foods (the cafeteria diet) stimulated diet-induced obesity that mimicked elements of hypothalamic obesity. Studies of the determinants of food palatability led to the discovery of a "new" carbohydrate taste (maltodextrin taste) and the confirmation of a fatty taste. In addition to oral taste receptors, gut nutrient sensors stimulated the intake/preference for carbohydrate- and fat-rich foods via an appetition process that stimulates brain reward systems. My research career greatly benefited from many diligent and creative students, collaborators and technicians and research support from my university and the National Institutes of Health.

Progressive ratio (PR) schedules and the sipometer: Do they measure wanting, liking, and/or reward? A tribute to Anthony Sclafani and Karen Ackroff

This paper honors the contributions made by Anthony (Tony) Sclafani and Karen Ackroff to both the Columbia University Seminar on Appetitive Behavior and to the field of ingestive behavior in general. We review their use of the progressive ratio (PR) licking paradigm, to determine whether the taste of sucrose, independent of its post-ingestive effects, is always positively reinforcing in animals. They demonstrated a monotonic increase in licking as concentration increased, and obtained results identical to those obtained with a lever-pressing paradigm, but licking was easier and more natural than lever pressing. The PR paradigm was translated to evaluate liquid food reward value in humans. An instrument (the sipometer) was devised that initially permitted a few seconds access to small amounts of a sweet beverage as the participants increased the time to obtain it in 3-5-sec increments. The device went through two refinements and currently delivers the reinforcer and measures the pressure exerted to obtain it. The sipometer is compared with other techniques for measuring motivation and reward. The use of the sipometer and the PR method are discussed in relation to the theoretical challenges inherent in measuring motivation and pleasure, from both psychological and behavioral economics perspectives, and why it is or is not important to separate these processes for both theoretical and practical applications.

The effects of ethanol on diverse components of choice in the rat: reward discrimination, preference and relative valuation

Alcohol consumption impairs judgment and choice. How alcohol alters these crucial processes is primarily unknown. Choice can be fractionated into different components including reward discrimination, preference and relative valuation that can function together or in isolation depending upon diverse factors including choice context. We examined the diverse components and contextual effects by analyzing the effects of alcohol drinking on choice behavior in a task with a reduced level of temporal and spatial constraints. Rats were trained to drink 10% ethanol during 6 weeks of behavior testing using a combined sucrose-fade and two-bottle free-choice procedure. Two different sucrose pellet outcomes (e.g., constant vs. variable) were presented each week to examine the impact of voluntary drinking on reward-based decision-making. Behavioral contexts of single option, free choice and extinction were examined for each outcome set. Comparisons were made between alcohol and control groups and within the alcohol group over time to inspect choice profiles. Between-group results showed alcohol drinking animals expressed altered place preference and modified sucrose reward approach latencies. The within-group profile showed that alcohol drinking animals can express adequate reward discrimination, preference and incentive contrast during free choice. All of these components were significantly reduced during the context of extinction. Control animals were also impacted by extinction but not as severely. The findings point to a need for a greater focus on the context and the diverse components of choice when examining external and internal factors influencing decision-making during alcohol or other substance of abuse exposure.

Gastric bypass in rats does not decrease appetitive behavior towards sweet or fatty fluids despite blunting preferential intake of sugar and fat

After Roux-en-Y gastric bypass surgery (RYGB), patients report consuming fewer fatty and dessert-like foods, and rats display blunted sugar and fat preferences. Here we used a progressive ratio task (PR) in our rat model to explicitly test whether RYGB decreases the willingness of rats to work for very small amounts of preferred sugar- and/or fat-containing fluids. In each of two studies, two groups of rats - one maintained on a high-fat diet (HFD) and standard chow (CHOW) and one given CHOW alone - were trained while water-deprived to work for water or either Ensure or 1.0 M sucrose on increasingly difficult operant schedules. When tested before surgery while nondeprived, HFD rats had lower PR breakpoints (number of operant responses in the last reinforced ratio) for sucrose, but not for Ensure, than CHOW rats. After surgery, at no time did rats given RYGB show lower breakpoints than SHAM rats for Ensure, sucrose, or when 5% Intralipid served postoperatively as the reinforcer. Nevertheless, RYGB rats showed blunted preferences for these caloric fluids versus water in 2-bottle preference tests. Importantly, although the Intralipid and sucrose preferences of RYGB rats decreased further over time, subsequent breakpoints for them were not significantly impacted. Collectively, these data suggest that the observed lower preferences for normally palatable fluids after RYGB in rats may reflect a learned adjustment to altered postingestive feedback rather than a dampening of the reinforcing taste characteristics of such stimuli as measured by the PR task in which postingestive stimulation is negligible.

Ethanol self-administration in rats responding under concurrent schedules for milk or ethanol plus milk

The relative reinforcing strength of drugs can be characterized by the distribution of operant behavior during the availability of other reinforcing stimuli. 'Choice' procedures are not widely used in rats, with the exception of ethanol self-administration in which there often is a choice between ethanol and water, which typically does not maintain much responding. A procedure was developed to evaluate the relative reinforcing strength of ethanol in rats when a similar appetitive reinforcer is concurrently available. Rats were trained to respond on two levers under concurrent fixed-ratio schedules of reinforcement with milk (1-50%) or ethanol+milk (4-32% ethanol+5-10% milk). Daily 60-min sessions began with a forced sample of each reinforcer, followed by the concurrent schedules. Under this schedule, rats preferentially allocated their responding to the ethanol-associated lever under conditions of ethanol+5% milk versus 5% milk, but neither preferred nor avoided ethanol when ethanol+10% milk versus 10% milk was available. When 8% ethanol+5% milk was available, 85±6% of responses were directed toward the ethanol-associated lever and the mean ethanol intake was 1.55±0.10 g/kg. The response rate decreased monotonically with the concentration of ethanol. Naltrexone injections did not affect the distribution of responding, but slightly decreased ethanol intake. It is concluded that stable behavior can be maintained under concurrent fixed-ratio schedules of ethanol and milk presentation in rats, resulting in intake of behaviorally active amounts of ethanol.

The selective serotonin reuptake inhibitor paroxetine decreases breakpoint of rats engaging in a progressive ratio licking task for sucrose and quinine solutions

Increased serotonergic activity has been shown to reduce motivation to ingest, which may involve, in part, gustatory processes. Here, we examined the effect of paroxetine, a selective serotonin reuptake inhibitor, on appetitive responding for a preferred and an avoided taste solution using a progressive ratio (PR) task in which licking was employed as the operant. Male Sprague-Dawley rats (n = 8/taste stimulus) were trained to respond for a concentration series of sucrose or quinine on fixed and PR schedules of reinforcement. Performance for sucrose was assessed while the rats were partially food- and water-restricted and nondeprived, and performance for water and quinine was assessed while the rats were water-deprived. Then, the rats were injected with vehicle (10% dimethyl sulfoxide, 1mL/kg intraperitoneal [ip], -1h) or paroxetine (5mg/kg), and their responding on a PR schedule for sucrose measured when the rats were nondeprived or for water and quinine when the rats were water-deprived. Paroxetine decreased breakpoint, which was defined as the number of operant (e.g., dry) licks in the final reinforced ratio, for water, quinine, and sucrose. This demonstrates that a general systemic increase in serotonergic activity decreases the appetitive-based responses to both preferred and nonpreferred fluids under different deprivation states.

Operant, oral alcoholic beer self-administration by C57BL/6J mice: effect of BHF177, a positive allosteric modulator of GABA(B) receptors

RATIONALE

With its high palatability, near-beer has been successfully used in rats as a vehicle to induce ethanol oral self-administration.

OBJECTIVES

The study aimed to develop an operant model of oral alcoholic beer self-administration promoting a stable intake of pharmacologically relevant amounts of ethanol in free-feeding C57BL/6J mice. It also aimed to assess the model's predictive validity by evaluating the influence of baclofen, a GABA(B) agonist, and BHF177, a GABA(B) positive allosteric modulator, on alcoholic beer self-administration.

METHODS

Mice were trained to self-administer, under a fixed ratio three schedule of reinforcement, 10 μl of beer containing increasing ethanol concentrations (0-18% v/v) in daily 30-min sessions. The effects on motor coordination (rotarod), locomotor activity (open field, automated cages) and anxiety-like behavior (elevated plus maze, EPM) were examined. Baclofen (1.25-5 mg/kg, intraperitoneal, i.p.) and BHF177 (3.75-30 mg/kg, i.p.) were used to see the effects on 9% alcoholic beer and near-beer self-administration.

RESULTS

Near-beer stably maintained operant oral self-administration in mice. Adding ethanol to near-beer reduced the number of active lever presses, while the corresponding amount of ethanol self-administration increased (0.8-1.0 g/kg/session). Motor impairment was observed when more than 1.3 g/kg/session of ethanol was self-administered with beer and slight but consistent hyperlocomotion with more than 0.9-1.0 g/kg/session. BHF177 (15 mg/kg) preferentially reduced 9% alcoholic beer self-administration, while the higher dose (30 mg/kg)-like baclofen 5 mg/kg-also reduced near-beer self-administration.

CONCLUSIONS

The operant model of oral alcoholic beer self-administration in C57BL/6J mice should prove useful for studying ethanol-reinforced behaviors and to identify candidate compounds for the pharmacological management of alcohol addiction.

Adolescent oxytocin exposure causes persistent reductions in anxiety and alcohol consumption and enhances sociability in rats

Previous studies have suggested that administration of oxytocin (OT) can have modulatory effects on social and anxiety-like behavior in mammals that may endure beyond the time of acute OT administration. The current study examined whether repeated administration of OT to male Wistar rats (n = 48) during a key developmental epoch (early adolescence) altered their physiology and behavior in later-life. Group housed rats were given intraperitoneal injections of either 1 mg/kg OT or vehicle during early adolescence (post natal-days [PND] 33–42). OT treatment caused a transient inhibition of body weight gain that recovered quickly after the cessation of treatment. At PND 50, the rats pre-treated with OT displayed less anxiety-like behavior on the emergence test, while at PND 55 they showed greater levels of social interaction. A subgroup of OT pre-treated rats examined at PND 63 showed a strong trend towards increased plasma OT levels, and also displayed significantly increased OT receptor mRNA in the hypothalamus. Rats pre-treated with OT and their controls showed similar induction of beer intake in daily 70 min test sessions (PND 63 onwards) in which the alcohol concentration of beer was gradually increased across days from 0.44% to 4.44%. However, when given ad libitum access to beer in their home cages from PND 72 onwards (early adulthood), consumption of beer but not water was significantly less in the OT pre-treated rats. A “booster” shot of OT (1 mg/kg) given after 25 days of ad libitum access to beer had a strong acute inhibitory effect on beer intake without affecting water intake. Overall these results suggest that exogenous OT administered during adolescence can have subtle yet enduring effects on anxiety, sociability and the motivation to consume alcohol. Such effects may reflect the inherent neuroplasticity of brain OT systems and a feed-forward effect whereby exogenous OT upregulates endogenous OT systems.

Beer promotes high levels of alcohol intake in adolescent and adult alcohol-preferring rats

Previous studies suggest that high levels of alcohol consumption can be obtained in laboratory rats by using beer as a test solution. The present study extended these observations to examine the intake of beer and equivalent dilute ethanol solutions with an inbred line of alcohol-preferring P rats. In Experiment 1, male adolescent P rats and age-matched Wistar rats had access to either beer or equivalent ethanol solutions for 1h daily in a custom-built lickometer apparatus. In subsequent experiments, adolescent (Experiment 2) and adult (Experiment 3) male P rats were given continuous 24-h home cage access to beer or dilute ethanol solutions, with concomitant access to lab chow and water. In each experiment, the alcohol content of the beer and dilute ethanol solutions was gradually increased from 0.4, 1.4, 2.4, 3.4, 4.4, 5 to 10% EtOH (vol/vol). All three experiments showed a major augmentation of alcohol intake when rats were given beer compared with equivalent ethanol solutions. In Experiment 1, the overall intake of beer was higher in P rats compared with Wistar rats, but no strain difference was found during the 1-h sessions with plain ethanol consumption. Experiment 1 also showed that an alcohol deprivation effect was more readily obtained in rats with a history of consuming beer rather than plain ethanol solutions. In Experiments 2 and 3, voluntary beer intake in P rats represented ethanol intake of 10-15 g/kg/day, among the highest reported in any study with rats. This excessive consumption was most apparent in adolescent rats. Beer consumption markedly exceeded plain ethanol intake in these experiments except at the highest alcohol concentration (10%) tested. The advantage of using beer rather than dilute ethanol solutions in both selected and nonselected rat strains is therefore confirmed. Our findings encourage the use of beer with alcohol-preferring rats in future research that seeks to obtain high levels of alcohol self-administration.

Reinforcing efficacy of fat, as assessed by progressive ratio responding, depends upon availability not amount consumed

Intermittent limited access to an optional source of dietary fat can induce binge-type behavior in rats. However, the ability of such access to alter the reinforcing efficacy of fat has not been clearly demonstrated. In this study, performance under progressive ratio one (PR1) and three (PR3) schedules of shortening (fat) reinforcement was assessed in non-food deprived rats (n=15/group). One group of rats had intermittent access to a dietary fat option (INT, 1-hour shortening access in the home cage each Monday, Wednesday, and Friday), whereas the other group had daily access to the fat option (D, 1-hour shortening access daily). Chow and water were continuously available. After five weeks, the INT group consumed more shortening during the 1-hour access period than did the D group. Rats were then trained to lever press for a solid shortening reinforcer (0.1 gm). INT rats earned significantly more reinforcers than did D rats under PR1, but not under PR3. Subgroups of INT and D rats (n=7 each) were matched on the amount of shortening consumed in the home cage during week five of the protocol and the PR data were reanalyzed. The INT subgroup earned significantly more reinforcers than the D subgroup did under PR1, but not PR3. These results demonstrate that: (1) intermittent access to shortening in the home cage, but not the amount consumed during the access period (i.e. bingeing), increases the reinforcing efficacy of solid shortening; and (2) the type of PR schedule is critical in delineating differences between the groups.

Intermittent access to beer promotes binge-like drinking in adolescent but not adult Wistar rats

Teenagers are more likely than adults to engage in binge drinking and could be more vulnerable to long-term brain changes following alcohol abuse. We investigated the possibility of excessive adolescent drinking in a rodent model in which beer (4.44% ethanol vol/vol) is presented to adult and adolescent male Wistar rats. Experiment 1 tracked ad libitum beer and water consumption in group-housed rats from postnatal day (PND) 28-96. Rats consumed an average of 7.8 g/kg/day of ethanol during adolescence (PND 34-55) and this gradually declined to a lower level of intake in adulthood (PND 56-93) of 3.9 g/kg/day. In Experiment 2, beer was made available to both adolescent (PND 29+) and adult (PND 57+) rats for 2h each day in a custom-built "lickometer" apparatus over 75 days. Access to beer was provided either 1 day out of every 3 ("intermittent" groups) or every day ("daily" groups). Relative to body weight, adolescent rats consumed more beer than adult rats in these limited access sessions. Adolescents with intermittent access consumed more than adolescents with daily access, a "binge"-like effect that was not observed in adult groups and that disappeared in adulthood. After 3 months of daily or intermittent alcohol consumption, the preference for beer versus sucrose was assessed. Rats previously kept under an intermittent schedule displayed a higher preference for beer relative to 3% sucrose, but only when testing occurred after 2 days of abstinence. In Experiment 3, adolescent (PND 30-37) and adult (PND 58-65) rats were given 20-min access to beer and their blood alcohol concentrations (BACs) were assessed. Adolescent groups consumed more alcohol than adults and showed higher BACS that were typical of human "binge" drinking (>80 mg/dL). Despite this, the correlation between BAC and beer intake was similar in both age groups. Together these results show that the intermittent presentation of alcohol itself appears to have subtle long-lasting effects on the motivation to consume alcohol. The findings support the use of beer solutions in modeling binge-like patterns of human alcohol consumption in adolescent rats.

The effect of food deprivation on cigarette smoking in females

Food deprivation is associated with increased self-administration of nicotine and other substances in laboratory animals, although little is known about the effects of food deprivation on substance use in humans. A within-subjects design was utilized to test the primary hypotheses that smoking rate and expired carbon monoxide (CO) levels would be greater among 15 female participants following a 24-hour fasting period than when participants were not food-deprived. Food-deprived participants were also expected to endorse greater negative mood, smoking urges, and pleasure from smoking, as well as less positive mood. Analyses indicated that CO levels were significantly greater in the food-deprived condition than in the non-deprived condition (p=.05), although no differences were found in the number of cigarettes smoked during the laboratory session. Participants reported significantly lower Vigor-Activity in the food-deprived condition (p=.02). No differences were found between conditions in urges to smoke or pleasure from smoking. Findings suggest that nicotine intake may increase among females during acute food deprivation.

Repeated exposure to alcoholic beer does not induce long-lasting changes in alcohol self-administration and intake in sardinian alcohol-preferring and sardinian non-preferring rats

AIMS

Rats avidly consume non-alcoholic beer, and addition of alcohol to non-alcoholic beer may function as a medium to induce intake of large amounts of alcohol in rats. The present study investigated whether Sardinian alcohol-preferring (sP) and Sardinian non-preferring (sNP) rats, initially exposed to non-alcoholic beer, and subsequently to non-alcoholic beer containing increasing concentrations of alcohol, would develop unusually high alcohol self-administration and drinking behaviours: (i) when alcohol was added to non-alcoholic beer, and (2) once beer was withdrawn and a plain alcohol solution was made available.

METHODS

In Experiment 1, rats were exposed to operant, 30-min/day self-administration sessions of non-alcoholic beer with increasing concentrations of alcohol [0, 2.5, 5, 7.5, and 10% (v/v)] for a total of 45 days. After a brief 'beer-fading' phase, the rats were exposed to self-administration sessions of a plain 10% (v/v) alcohol solution. In Experiment 2, the rats were exposed to non-alcoholic beer with increasing concentrations of alcohol [0, 2.5, 5, 7.5, and 10% (v/v)] and water under the 2-bottle choice regimen with unlimited access (24 h/day) for a total of 35 days. After a brief 'beer-fading' phase, the rats were exposed to the choice between a plain 10% (v/v) alcohol solution and water.

RESULTS

sP and sNP rats did not differ in self-administration (Experiment 1) and intake (Experiment 2) of non-alcoholic beer. In Experiment 1, as alcohol content increased, the amount of self-administered alcohol increased progressively in sP rats (up to 1-1.2 g/kg) and remained stable in sNP rats (approximately 0.65 g/kg). When the plain 10% alcohol solution was available, the amount of self-administered alcohol in sP rats initially dropped, and tended to increase-up to approximately 0.6 g/kg-on continuing exposure. In sNP rats, their lever-pressing behaviour was rapidly extinguished after beer withdrawal. In Experiment 2, as alcohol content was increased, daily alcohol intake increased progressively in sP rats (up to 8-9 g/kg) and averaged approximately 2.4 g/kg in sNP rats. When the plain alcohol solution was available, daily alcohol intake in sP rats was initially low, reaching control values on continuing exposure; conversely, daily alcohol intake was completely suppressed in sNP rats.

CONCLUSIONS

These results suggest that exposure to alcoholic beer resulted in unusually high intakes of alcohol in both sP and sNP rats for as long as non-alcoholic beer was added to alcohol; however, these high levels of alcohol self-administration and intake were not maintained once non-alcoholic beer was withdrawn.

Delayed access to alcohol accelerates self-administration of alcohol on a progressive ratio schedule

In a previous report, we found that a 5-min. delay in alcohol access increases ethanol intake in rats trained to self-administer 5% ethanol. To assess the effects of this delay on the motivation to self-administer ethanol, Wistar rats were trained on a progressive ratio schedule of reinforcement and presented with the 5-min. delay. There was no change in break point (6 presses/delivery), active (125 presses/30 min.) or inactive (10 presses/30 min.) lever presses after the 5-min. delay compared to baseline. However, response cessation occurred 10 min. earlier in this delay session compared to baseline indicating that consumption was accelerated by delayed access to alcohol.

Nutrient-conditioned flavor preference and incentive value measured by progressive ratio licking in rats

Rats develop strong preferences for flavors associated with the postingestive actions of glucose and other nutrients. This preference may involve changes in both the hedonic appeal and incentive salience of the nutrient-paired flavor. The present study used a progressive ratio (PR) operant licking task to evaluate the degree to which nutrient conditioning changes the incentive value of flavors. Food restricted rats were trained to associate one flavored saccharin solution (CS+) with intragastric glucose infusions and another flavored solution (CS-) with water infusions. The rats subsequently showed a strong preference for the CS+ in two-bottle tests and also licked more for the CS+ than CS- in PR tests. PR licking for the CS+ was similar to that for an 8% fructose solution. Together with earlier data indicating that the CS- is isopreferred to a 3% fructose solution, these findings indicate that IG glucose conditioning enhances the hedonic and incentive value of the CS+ solution so that the animal responds as if the solution had a sweeter taste.

Behavioural assessment of drug reinforcement and addictive features in rodents: an overview

Some psychoactive drugs are abused because of their ability to act as reinforcers. As a consequence behavioural patterns (such as drug-seeking/drug-taking behaviours) are promoted that ensure further drug consumption. After prolonged drug self-administration, some individuals lose control over their behaviour so that these drug-seeking/taking behaviours become compulsive, pervading almost all life activities and precipitating the loss of social compatibility. Thus, the syndrome of addictive behaviour is qualitatively different from controlled drug consumption. Drug-induced reinforcement can be assessed directly in laboratory animals by either operant or non-operant self-administration methods, by classical conditioning-based paradigms such as conditioned place preference or sign tracking, by facilitation of intracranial electric self-stimulation, or, alternatively by drug-induced memory enhancement. In contrast, addiction cannot be modelled in animals, at least as a whole, within the constraints of the laboratory. However, various procedures have been proposed as possible rodent analogues of addiction's major elements including compulsive drug seeking, relapse, loss of control/impulsivity, and continued drug consumption despite negative consequences. This review provides an extensive overview and a critical evaluation of the methods currently used for studying drug-induced reinforcement as well as specific features of addictive behaviour. In addition, comic strips that illustrate behavioural methods used in the drug abuse field are provided given for free download under http://www.zi-mannheim/psychopharmacology.de.

Δ9-THC REINSTATES BEER- AND SUCROSE-SEEKING BEHAVIOUR IN ABSTINENT RATS: COMPARISON WITH MIDAZOLAM, FOOD DEPRIVATION AND PREDATOR ODOUR

AIMS

Recent studies suggest that cannabinoid receptor agonists may promote relapse to drug-seeking behaviour after a period of abstinence. In this study, the ability of Delta(9)-tetrahydrocannabinol (THC) to reinstate previously reinforced responding for alcoholic and non-alcoholic beverages was assessed in rats using a novel lick-based paradigm.

METHODS

Rats were initially given free access to beer (containing 4.5% ethanol v/v), near-beer (a beverage that looks and tastes like beer but contains <0.5% ethanol v/v) or isocaloric sucrose in their home cages for 3 weeks. They were then trained to lick at a tube to self-administer the pre-exposed beverage in operant chambers under a VR10 schedule in 30-min sessions daily. After approximately 3 weeks of such access, the rats underwent an extinction procedure, so that licking at the tube produced no reward. Once responding had ceased, the rats were subjected to various reinstatement tests.

RESULTS

In Experiment 1, the cannabinoid receptor agonist Delta(9)-THC (1 mg/kg) significantly reinstated responding, previously reinforced with beer or near-beer. The effect was unlikely to be caused by increased appetite because 24 h food-deprivation had no such effect. Exposure to cat odour in the test chamber failed to reinstate responding for beer or near-beer and caused a complete inhibition of responding. In Experiment 2, Delta(9)-THC (0.3 and 1 but not 3 mg/kg) again reinstated beer-seeking behaviour while the 1 mg/kg dose also reinstated responding in sucrose trained animals. Midazolam (0.15 mg/kg but not 0.5 or 1.5 mg/kg) produced a modest reinstatement of beer-seeking but had no effect on sucrose-seeking behaviour.

CONCLUSIONS

The finding that Delta(9)-THC can reinstate alcohol-seeking provides the impetus for further research into the involvement of the cannabinoid system in alcohol craving. However, the reinstatement of near-beer and sucrose-seeking behaviour caused by Delta(9)-THC suggests a relatively non-specific effect. This may perhaps be related to the stressor-like effects of cannabinoids, and their ability to activate key neural circuitry in the amygdala and bed nucleus of the stria terminalis.

Rats on the grog: novel pharmacotherapies for alcohol craving

Current pharmacotherapies for alcohol dependence in humans (e.g., naltrexone, acamprosate) are meeting with only limited therapeutic success. The development of novel pharmacotherapies is urgently needed but is reliant upon the screening of large numbers of candidate "anticraving" drugs using appropriate animal models. The development of animal models is complex because (1) laboratory animals are often reluctant to consume large quantities of alcohol, (2) inducing a state of alcohol dependence, analogous to the human condition, may require many months of alcohol exposure, (3) concluding that a given drug selectively reduces alcohol craving requires very carefully controlled experiments, and (4) false positives and false negatives may result from the sometimes distinct physiology and psychology of the alcohol-addicted human and rat. To address some of these problems, our laboratory has recently developed the "beer model" of alcohol dependence and craving. Rats, like humans, have a prodigious appetite for beer and will drink much more beer than equivalent ethanol solutions in water. Beer consumption in rats leads to clear signs of intoxication, anxiety reduction, and signs of withdrawal when beer access is suddenly denied. We have found that beer craving in rats is selectively reduced by the cannabinoid receptor antagonist SR 141716 and the opioid receptor antagonist naltrexone. Combining these two drugs appears to have a synergistic anticraving effect. Other promising pharmacotherapies for the future are discussed.

Different pattern of brain c-Fos expression following re-exposure to ethanol or sucrose self-administration environment

Exposure of alcohol addicts to alcohol-related environmental cues may elicit alcohol-seeking behavior and lead to relapse to heavy drinking. The aim of the present study was to identify brain regions activated by alcohol (ethanol)-related stimuli in Wistar rats trained to lever press for 8% ethanol solution in operant self-administration cages. Ethanol self-administration was stabilized in a maintenance phase, which lasted for 30 days. c-Fos protein expression was used as a marker of neuronal activation.Re-exposure to ethanol self-administration environment after 30-day but not after 24-h abstinence increased the number of Fos-positive nuclei in the thalamic paraventricular nucleus, granular insular cortex and medial prefrontal cortex. In general, no differences were found in c-Fos protein expression between the rats allowed to self-administer alcohol and the subjects exposed only to alcohol-related stimuli. In contrast, no increase in c-Fos immunoreactivity was observed in rats trained to lever press for sucrose solution and exposed to sucrose-related environmental stimuli after 30-day abstinence. Taken together, these results suggest that at least some thalamo-cortical circuits become more responsive to ethanol-paired stimuli after prolonged abstinence and that ethanol- and sucrose-seeking behavior may be regulated by partially different neural mechanism(s).

Increased motivation for beer in rats following administration of a cannabinoid CB1 receptor agonist

A series of experiments examined the effects of the cannabinoid CB1 receptor agonist CP 55,940 ((-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hyd roxypropyl)cyclohexanol) on the motivation to consume beer, near-beer (a beer-like beverage containing <0.5% ethanol) and sucrose solutions in rats. The experiments employed a 'lick-based progressive ratio paradigm' in which an ever increasing number of licks had to be emitted at a tube for each successive fixed unit of beverage delivered. Break point, the lick requirement at which responding ceased, was used as an index of motivation. In the first experiment, CP 55,940 (10, 30 or 50 microg/kg) caused a dose-dependent increase in break points for beer (containing 4.5% ethanol v/v) and for near-beer. The highest (50 microg/kg) dose of CP 55,940 also significantly decreased locomotor activity. In the second experiment, CP 55,940 (10 or 30 microg/kg) dose-dependently increased break points in rats licking for 'light' beer (containing 2.7% ethanol v/v) or for a sucrose solution (8.6% w/v) containing the same number of calories as the beer. In the third experiment, the facilitatory effects of CP 55,940 (30 microg/kg) on responding for beer and near-beer were reversed by both the cannabinoid CB1 receptor antagonist SR 141716 (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1H-pyrazole-3-carboxamide hydrochloride) (1.5 mg/kg) and the opioid receptor antagonist naloxone (2.5 mg/kg). Naloxone had a proportionally greater effect on rats licking for beer compared to near-beer, consistent with previous reports of opioid receptor mediation of alcohol craving. These results show that cannabinoids modulate the motivation for beer via both cannabinoid CB1 receptors and opioid receptors. The similar effect of CP 55,940 on the motivation for beer, near-beer and sucrose suggests that the drug effect may reflect a general stimulatory effect on appetite for palatable beverages, although a more specific effect on the desire for alcohol cannot be ruled out.

Possible neural substrates of beer-craving in rats

Rats voluntarily consumed beer in a distinctive environment during 30 min daily sessions over 21 days, ingesting a daily average of 0.96 g/kg of ethanol. On a final test day, rats in a 'craving' condition were denied access to the beer in the drinking environment. The expression of c-fos in the brain of 'craving' rats was compared with that in rats given free access on the test day ('beer' condition), and to rats which had been repeatedly placed in the drinking environment without ever having access to beer ('control' condition). Rats in the 'craving' condition showed significantly higher c-fos counts than either the 'beer' or 'control' rats in a variety of corticolimbic and brainstem structures, indicating that activation of these regions occurs when a desirable alcoholic beverage is expected but not received.