Alcohol intake in prairie voles is influenced by the drinking level of a peer

Background: Peer interactions can have important effects on alcohol‐drinking levels, in some cases increasing use, and in other cases preventing it. In a previous study, we have established the prairie vole as a model animal for the effects of social relationships on alcohol intake and have observed a correlation of alcohol intake between individual voles housed together as pairs. Here, we investigated this correlated drinking behavior, hypothesizing that 1 animal alters its alcohol intake to match the drinking of its partner. Methods: Adult prairie voles were tested for baseline drinking levels with continuous access to 10% alcohol and water for 4 days. In Experiment 1, high alcohol drinkers (>9 g/kg/d) were paired with low alcohol drinkers (<5 g/kg/d) of the same sex on either side of a mesh divider for 4 days with continuous access to the same 2‐bottle choice test. In Experiment 2, high drinkers were paired with high drinkers and low drinkers paired with low drinkers. In both experiments, animals were again separated following pairing, and drinking was retested in isolation. In Experiment 3, alcohol‐naïve animals were tested for saccharin consumption (0.05%) first in isolation and then in high saccharin drinkers paired with low saccharin drinkers, and then in another isolation period. Results: In Experiment 1, high drinkers paired with low drinkers significantly decreased their alcohol intake and preference from baseline drinking in isolation, and drinking levels remained significantly lower during isolation following pairing. Interestingly, there was variability between pairs in whether the high drinker decreased or the low drinker increased intake. In Experiment 2, high drinkers paired with high drinkers did not significantly change their intake level or preference, nor did low drinkers paired with low drinkers, and no changes occurred during the subsequent isolation. In Experiment 3, there was no change in saccharin intake or preference when high drinkers were paired with high drinkers or low paired with low, or in the subsequent isolation. Conclusions: Alcohol drinking of prairie voles can be altered under social conditions, such that 1 animal changes its alcohol intake to more closely match the intake of the other animal, helping to explain previous findings of correlated alcohol drinking. The effect does not extend to saccharin, a naturally rewarding sweet substance. This behavior can be used to model the peer pressure that can often affect alcohol intake in humans.     

Motivation for Alcohol Becomes Resistant to Quinine Adulteration After 3 to 4 Months of Intermittent Alcohol Self‐Administration

Background: Continued consumption of alcohol despite deleterious consequences is a hallmark of alcoholism and represents a critical challenge to therapeutic intervention. Previous rat studies showed that enduring alcohol self‐administration despite pairing alcohol with normally aversive stimuli was only observed after very long‐term intake (>8 months). Aversion‐resistant alcohol intake has been previously interpreted to indicate pathological or compulsive motivation to consume alcohol. However, given the time required to model compulsive alcohol seeking in previous studies, there is considerable interest in developing more efficient and quantitative rodent models of aversion‐resistant alcohol self‐administration. Methods: Outbred Wistar rats underwent 3 to 4 months or approximately 1.5 months of intermittent, home‐cage, two‐bottle access (IAA) to 20% alcohol (v/v) or water. Then, after brief operant training, the effect of the bitter‐tasting quinine (0.1 g/l) on the motivation to seek alcohol was quantified via progressive ratio (PR). Motivation for quinine‐adulterated 2% sucrose under PR was assayed in a separate cohort of 3 to 4 months IAA rats. The effects of quinine on home‐cage alcohol consumption in IAA rats and rats with continuous access to alcohol were also examined. Finally, a dose–response for quinine taste preference in IAA and continuous‐access animals was determined. Results: Motivation for alcohol after 3 to 4 months IAA, measured using an operant PR procedure, was not altered by adulteration of alcohol with 0.1 g/l quinine. In contrast, after 3 to 4 months of IAA, motivation for sucrose under PR was significantly reduced by adulteration of sucrose with 0.1 g/l quinine. In addition, motivation for alcohol after only approximately 1.5 months IAA was significantly reduced by adulteration of alcohol with 0.1 g/l quinine. Furthermore, home‐cage alcohol intake by IAA rats was insensitive to quinine at concentrations (0.01, 0.03 g/l) that significantly reduced alcohol drinking in animals with continuous access to alcohol. Finally, no changes in quinine taste preference after 3 to 4 months IAA or continuous access to alcohol were observed. Conclusions: We have developed a novel and technically simple hybrid operant/IAA model in which quinine‐resistant motivation for alcohol is evident after an experimentally tractable period of time (3 to 4 months vs. 8 months). Quinine dramatically reduced sucrose and water intake by IAA rats, indicating that continued responding for alcohol in IAA rats despite adulteration with the normally aversive quinine might reflect maladaptive or compulsive motivation for alcohol. This model could facilitate identification of novel therapeutic interventions for pathological alcohol seeking in humans.     

Involvement of arginine vasopressin and V1b receptor in alcohol drinking in Sardinian alcohol-preferring rats

Background: Recent animal studies have shown that the level of stress‐responsive arginine vasopressin (AVP) gene expression in the amygdala is increased during early withdrawal from long‐term heroin or cocaine administration. The selective AVP V1b receptor antagonist SSR149415 (capable of exerting antidepressant‐like and anxiolytic effects in animal models) also blocked stress‐induced reinstatement of drug‐seeking behavior. This study was undertaken to investigate the effects of alcohol and to determine whether (i) there are genetically determined differences in basal AVP mRNA levels in the medial/central amygdala (Me/CeA) and medial hypothalamus (MH) between selectively bred Sardinian alcohol‐preferring (sP) and alcohol‐nonpreferring (sNP) rats; (ii) the AVP mRNA levels are altered by long‐term alcohol drinking in sP rats; and (iii) the V1b receptor antagonist SSR149415 alters alcohol drinking in sP rats. Methods: In Experiment 1, AVP mRNA levels were measured in the Me/CeA and MH of alcohol‐naïve sP and sNP rats, and sP rats exposed to the standard, homecage 2‐bottle “alcohol versus water” choice regimen 24 h/d for 17 days. In Experiment 2, SSR149415 (0, 3, 10, or 30 mg/kg; intraperitoneal) was acutely administered 30 minutes before lights off to alcohol‐experienced sP rats. Alcohol, water, and food intake were monitored 6 and 24 hours later. Results: We found higher basal AVP mRNA levels in both Me/CeA and MH of alcohol‐naïve sP than sNP rats; alcohol consumption decreased AVP mRNA levels in both brain regions of sP rats, suggesting genetically determined differences between the 2 rat lines and in the effects of alcohol drinking in sP rats. Acute treatment with SSR149415 significantly reduced alcohol intake of sP rats. Conclusion: The stress‐responsive AVP/V1b receptor system is 1 component of the neural circuitry underlying high alcohol drinking in sP rats.     

Intermittent access to 20% ethanol induces high ethanol consumption in Long-Evans and Wistar rats

Background: There has been some difficulty getting standard laboratory rats to voluntarily consume large amounts of ethanol without the use of initiation procedures. It has previously been shown that standard laboratory rats will voluntarily consume high levels of ethanol if given intermittent‐access to 20% ethanol in a 2‐bottle‐choice setting [ Wise, Psychopharmacologia 29 (1973), 203 ]. In this study, we have further characterized this drinking model. Methods: Ethanol‐naïve Long–Evans rats were given intermittent‐access to 20% ethanol (three 24‐hour sessions per week). No sucrose fading was needed and water was always available ad libitum. Ethanol consumption, preference, and long‐term drinking behaviors were investigated. Furthermore, to pharmacologically validate the intermittent‐access 20% ethanol drinking paradigm, the efficacy of acamprosate and naltrexone in decreasing ethanol consumption were compared with those of groups given continuous‐access to 10 or 20% ethanol, respectively. Additionally, ethanol consumption was investigated in Wistar and out‐bred alcohol preferring (P) rats following intermittent‐access to 20% ethanol. Results: The intermittent‐access 20% ethanol 2‐bottle‐choice drinking paradigm led standard laboratory rats to escalate their ethanol intake over the first 5 to 6 drinking sessions, reaching stable baseline consumption of high amounts of ethanol (Long–Evans: 5.1 ± 0.6; Wistar: 5.8 ± 0.8 g/kg/24 h, respectively). Furthermore, the cycles of excessive drinking and abstinence led to an increase in ethanol preference and increased efficacy of both acamprosate and naltrexone in Long–Evans rats. P‐rats initiate drinking at a higher level than both Long–Evans and Wistar rats using the intermittent‐access 20% ethanol paradigm and showed a trend toward a further escalation in ethanol intake over time (mean ethanol intake: 6.3 ± 0.8 g/kg/24 h). Conclusion: Standard laboratory rats will voluntarily consume ethanol using the intermittent‐access 20% ethanol drinking paradigm without the use of any initiation procedures. This model promises to be a valuable tool in the alcohol research field.     

Carisbamate, a Novel Antiepileptic Candidate Compound, Attenuates Alcohol Intake in Alcohol-Preferring Rats

Background: Since 1994, when naltrexone (Revia^®) was approved by the FDA for the treatment of alcoholism, only 2 other drugs (Campral^® and Topamax^®) have been approved for alcoholism treatment. However, various experimental drugs, including antiepileptic medications, have been tested in both animal models and in humans with some promising results. The purpose of this project was to study the effect of the novel neuromodulator carisbamate, which is in development for epilepsy treatment, on alcohol intake in selectively bred alcohol‐preferring rats. Methods: Male alcohol‐preferring inbred P rats were allowed to freely drink water or alcohol (10%, v/v) using a 2‐bottle choice procedure. After stable baselines for alcohol and water intakes were established, the acute effects of oral carisbamate (0, 10, 30, 45, 60, and 90 mg/kg) were assessed. Then, the chronic effect of the compound (60 mg/kg/day for 14 consecutive days) on alcohol intake was assessed in a separate group of male P rats. In another set of experiments, the effects of carisbamate and naltrexone on alcohol withdrawal‐induced elevated drinking of alcohol, an index of craving, were compared. Rats were withdrawn from alcohol for 24 hours and were given vehicle, 20 mg/kg naltrexone or 60 mg/kg carisbamate 30 minutes before re‐exposure to alcohol. Alcohol and water intake was measured 6 hours after alcohol re‐exposure. To determine the effects of carisbamate on saccharin preference, rats were put on a 2‐bottle choice of water versus a solution of 2% saccharin. Then, the effect of the highest dose of carisbamate (90 mg/kg) and naltrexone (20 mg/kg) and the vehicle on saccharin preference was determined. Results: Our results showed that there was a selective dose‐dependent reduction in alcohol intake and preference in the alcohol‐preferring P rat after an acute oral administration of carisbamate. There were no significant effects on food or water intake. Chronic administration of carisbamate significantly reduced alcohol intake and preference initially, but partial tolerance developed after the 10th treatment. The degree of tolerance development was less than that observed for naltrexone. Acute administration of carisbamate was more effective than naltrexone in reducing enhanced alcohol intake after a period of alcohol deprivation . Compared with control vehicle neither carisbamate nor naltrexone had a significant effect on saccharin intake and preference. Conclusion: The novel neuromodulator compound carisbamate has a favorable profile of effects on alcohol intake and related measures and should be considered for testing on human alcoholics.     

Dissociation of ethanol and saccharin preference in sP and sNP rats

BACKGROUND: It has been proposed that ethanol intake and consumption of sweet tasting solutions are positively correlated in rodents. Experiment 1 of the present study investigated whether selectively bred ethanol-preferring (sP) and -nonpreferring (sNP) rats differed, consistently with the above hypothesis, as to saccharin intake and preference. Experiment 2 evaluated whether saccharin addition to the ethanol solution, likely resulting in a highly palatable fluid, would result in an increase in voluntary ethanol intake in sP rats. METHODS: The saccharin solution was offered, in free choice with water, at a fixed concentration of 1 g/liter for 6 consecutive days in Experiment 1A or at ascending concentrations (0.002 to 16.4 g/liter, doubling the concentration every day) in Experiment 1B. In Experiment 2, 1 g/liter saccharin was added to the standard 10% ethanol solution and offered to sP rats in free choice with water for 7 consecutive days. RESULTS: In both Experiments 1A and 1B, sP and sNP rats showed avidity for the saccharin solution with marginal line difference in saccharin intake and preference. In Experiment 2, daily ethanol intake remained stable at baseline levels (6-7 g/kg), irrespective of the saccharin addition to the ethanol solution. CONCLUSIONS: The results of Experiments 1A and 1B suggest that saccharin drinking behavior in sNP rats deviates from the hypothesis that saccharin and ethanol intakes may co-vary; thus, at least in sNP rats, saccharin and ethanol intakes do not appear to be influenced by the same genetic factors. The results of Experiment 2 provide further support to the existence of a central set-point mechanism that regulates daily ethanol intake in sP rats, likely based on the pharmacological effects of ethanol.     

Effect of Calcitonin on the Alcohol Drinking of Rats

Previous work has shown that calcitonin inhibits eating by rats and that it affects several neurotransmitter systems suspected to play a role in alcohol consumption. The present study was an initial test of whether calcitonin does affect voluntary alcohol consumption by male Wistar rats with prolonged alcohol experience. Calcitonin (20 IU/kg) or saline was injected subcutaneously on 10 consecutive days when the rats (n = 20) had continual access to 10% (v/v) ethanol solution, and to food and water. Using a cross-over design, the effects of 40 IU/kg calcitonin vs. saline were then examined in a second 10-day treatment period. Similar patterns of effects were obtained with both calcitonin doses, but the patterns differed with alcohol, food, and water intake. Alcohol drinking showed biphasic changes with both doses, producing highly significant Treatment x Day interactions (p < 1E-10 and p = 6E-7): it was significantly reduced on the first day of calcitonin treatment and significantly increased on the last few days. Food intake was reduced on all calcitonin days although most markedly on the first. Water drinking was not altered on the first calcitonin day, but was greatly increased on the second, then gradually returned toward the baseline. In a second experiment, the animals were switched to 1 hr of alcohol access per day, and calcitonin (20 IU/kg) was administered periodically to one group 4 hr before the alcohol access. Alcohol drinking was significantly reduced in all cases when the calcitonin injection was preceded by at least 1 day without calcitonin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intermittent (every-other-day) drinking induces rapid escalation of ethanol intake and preference in adolescent and adult C57BL/6J mice

Background: Using adult C57BL/6J (B6) mice, we previously developed a procedure that causes a progressive increase in ethanol intake and preference (i.e., alcohol escalation effect) following weekly (intermittent) access to ethanol ( Melendez et al., 2006 ). A limitation of this procedure is that it requires many weeks of testing, which limits its use to study ethanol escalation (i.e., binge‐like drinking) during adolescence. Previous studies have shown that intermittent every‐other‐day (EOD) access to ethanol is sufficient to induce ethanol escalation in rats. The objective of this study was to verify whether EOD access is sufficient to induce escalated levels of ethanol intake and preference in adult and adolescent B6 mice. Methods: Male B6 mice received free‐choice 24‐hour access to 15% ethanol and water on an EOD or daily basis for 2 weeks. Food and water were available at all times. Using adult mice, Experiment 1 characterized the induction of ethanol escalation following EOD access at 6 (i.e., drinking in the dark) and 24‐hour intervals, whereas Experiment 2 determined whether daily drinking reverses escalation induced by EOD drinking. Experiment 3 compared ethanol‐drinking capacity following daily versus EOD drinking in adolescent (P30‐45) and adult (P70‐85) mice. Results: Experiment 1 revealed that EOD drinking leads to a significant (nearly 2‐fold) increase in ethanol intake and preference over mice given daily access. Experiment 2 demonstrated that EOD‐elicited escalation is blocked and subsequently reversed following daily drinking. Experiment 3 revealed that ethanol drinking was greater in adolescent mice compared with adults following daily drinking and EOD (escalated) drinking. Although the escalated levels of ethanol intake were greater in adolescent mice, the rate or onset of escalation was comparable between both age‐groups. Conclusions: This study is the first to demonstrate that EOD drinking leads to escalation of ethanol intake and preference in adolescent and adult mice. Moreover, our results indicate that daily ethanol reverses ethanol escalation induced by intermittent drinking. The study also revealed that adolescent mice have a greater capacity to drink ethanol under both daily (controlled) and EOD (escalated) conditions, which further supports the notion of adolescent’s susceptibility to heavy drinking.     

Modulation of Brain Endocannabinoid Levels by Voluntary Alcohol Consumption in Alcohol-Preferring AA Rats

Background: The central nervous system cannabinoid CB1 receptors have been implicated in regulation of alcohol consumption. Less data are available on the role of the endogenous ligands for these receptors, anandamide (AEA) and 2‐arachidonoylglycerol (2‐AG), in alcohol‐related behaviors. The purpose of this study was to assess the effects of voluntary alcohol consumption on the levels of these endocannabinoids in key brain areas mediating alcohol reinforcement. Methods: Female and male alcohol‐preferring AA (Alko, Alcohol) rats were trained to drink 10% (v/v) alcohol during 90‐min limited access sessions every second day. Following establishment of stable alcohol drinking, half of the subjects were killed immediately before the daily alcohol access (“pre‐session” group), while the other half was killed after the drinking session (“post‐session” group). A separate control group consisted of water‐drinking rats. AEA and 2‐AG levels were measured from prefrontal cortex (PFC), nucleus accumbens (NAc), caudate putamen (CPu), amygdala, and hippocampus using liquid chromatography–tandem mass spectrometry (LC/MS/MS). Results: Voluntary alcohol drinking caused widespread alterations in the levels of both AEA and 2‐AG. Compared to the water group, increased AEA levels were seen in the pre‐session group, but they were decreased immediately following limited access drinking in the female AA rats. Also 2‐AG levels were significantly elevated after long alcohol exposure, and an additional increase was found after limited access drinking in PFC. In males, however, the only alterations caused by alcohol drinking were significantly elevated AEA levels in NAc and CPu in the post‐session group. No changes were seen in the levels of 2‐AG. Conclusions: These results demonstrate that voluntary alcohol drinking modulates the levels of endocannabinoids in several brain areas implicated in alcohol reinforcement. AEA and 2‐AG were differentially affected, suggesting that they could have partially separate modulatory roles. Alterations were more widespread in females than males, possibly reflecting their higher alcohol intake. Taken together, alcohol‐induced release of endocannabinoids may have an important role in alcohol reinforcement and development of alcohol addiction.     

Genetic Selection for High and Low Alcohol Consumption in a Limited-Access Paradigm

BACKGROUND: Several rat lines have been bred for their differences in alcohol consumption based on a continuous-access paradigm in which alcohol solution is available 24 hr/day. The limited-access paradigm (LAP), in which access to alcohol solution is restricted to a short period per day, however, has been used extensively to investigate the neurochemical mechanisms underlying alcohol consumption. There is evidence of possible differences in genetic determination of alcohol drinking in a continuous- versus limited-access condition. For these reasons, selective breeding for high- and low-alcohol consumption (HARF and LARF, respectively) based on a LAP was conducted. METHODS: N/Nih rats were used as the breeding stock. A within-family breeding procedure was used to develop HARF and LARF lines with 10 families per line. Access to alcohol solution was restricted to 20 min/day. Alcohol was provided as 3%, 6% and 12% w/v solutions. Average intake of alcohol during the 12% phase was used as the selection criterion. Inbreeding began in the seventh generation. RESULTS: After the sixth generation of selection, rats from the HARF line consumed an average of 1.2 g/kg, whereas rats from the LARF line consumed an average of 0.6 g/kg of alcohol during the 20-min access period. Alcohol consumption remained stable over the next eight generations of inbreeding. In the continuous-access-drinking paradigm, the HARF and LARF rats consumed an average of 5.5 to 7.0 g/kg and 1.0 to 2.0 g/kg of alcohol per day respectively. An estimated heritability of 0.25 was obtained. CONCLUSIONS: These findings indicate that alcohol drinking in the LAP is influenced by genetic factors. Differences in alcohol drinking in the LAP also generalize to continuous access drinking. These rat lines will be very useful for investigations into the genetic and neurochemical mechanisms underlying alcohol drinking.     

Taste Reactivity in High Alcohol Drinking and Low Alcohol Drinking Rats

High alcohol drinking (HAD) and low alcohol drinking (LAD) rats were tested, in three exposures, for taste reactivity to five concentrations of alcohol (5%, 10%, 20%, 30%, and 40%, v/v), water, and one concentration each of sucrose and quinine. Of the three reactivity exposures, one was done before a 3-week period of continuous access to water and 10% alcohol, the second test was done immediately after the consumption period, and the final reactivity test was done after 1 month of alcohol abstinence. The results showed that the groups did not differ in reactivity on the initial test. After the consumption tests (when the HAD rats consumed significantly more alcohol than the LAD rats), differences in reactivity were found: HAD rats produced significantly more ingestive responses (which promote consumption) and significantly fewer aversive responses (which facilitate fluid rejection) than LAD rats. These differences were maintained even after 1 month of alcohol abstinence. The present data replicate an earlier experiment with alcohol-preferring (P) rats and alcohol-non-preferring (NP) rats, and indicate that the selective breeding process does not produce differences in the innate perception of the taste of alcohol. However, after experience with drinking alcohol, rats selectively bred for high alcohol consumption exhibit a palatability shift reflected by high ingestive responding and little or no aversive responding. Such a shift would clearly contribute to the maintenance of high levels of alcohol consumption.     

Thyrotropin Releasing Hormone Analog TA-0910 Suppresses Alcohol Intake in Alcohol Drinking African Green Monkeys

In previous studies, we found that single injections of the thyrotropin-releasing hormone analog TA-0910 dose-dependently reduced alcohol intake and preference in alcohol-preferring (P) and Fawn-Hooded (FH) rats over a 24-hr period of continuous access to alcohol and water. However, several consecutive daily injections of TA-0910 resulted in the development of tolerance to these effects. In the present study, we found that in a 5-hr limited-access schedule in which monkeys could select an aqueous alcohol solution (7.5% v/v) or tap water, single doses of TA-0910 (0.0625, 0.125, 0.25, 0.5, and 0.75 mg/kg), similar to those found effective in P and FH rats, reduced consumption of alcohol. In this protocol, tolerance to the attenuating effects of TA-0910 on alcohol intake was not evident after five consecutive once-daily doses of 0.5 mg/kg. Furthermore, it was shown that a single dose of 0.75 mg/kg TA-0910 did not significantly influence 24-hr water intake when water was the only available fluid, but did reduce the intake of a preferred solution of saccharin. These findings suggest that activation of brain thyrotropin-releasing hormone systems reduces alcohol intake in primates and that tolerance to this effect is not evident within 5 days under a limited access schedule.     

The α1-Adrenergic Receptor Antagonist, Prazosin, Reduces Alcohol Drinking in Alcohol-Preferring (P) Rats

Background:  Preliminary evidence suggest that noradrenergic signaling may play a role in mediating alcohol drinking behavior in both humans and rats. Accordingly, we tested the hypothesis that blockade of α₁-adrenergic receptors will suppress alcohol drinking in rats selectively bred for alcohol preference (P line).
Methods:  Adult male P rats were given 24-hour access to food and water and scheduled access to a 15% (v/v) alcohol solution for 2 hours daily. Rats were injected IP with the α₁-adrenergic receptor antagonist, prazosin (0, 0.5, 1.0, 1.5, or 2.0 mg/kg body weight), once a day at 15 minutes prior to onset of the daily 2-hour 2-bottle choice, alcohol versus water, access period for 2 consecutive days and then 3 weeks later for 5 consecutive days.
Results:  Prazosin significantly reduced ( p  < 0.01) alcohol intake during the initial 2 daily administrations, and this reduction of alcohol intake was maintained for 5 consecutive days by daily prazosin treatment in the subsequent more prolonged trial ( p  < 0.05). The prazosin-induced reduction of alcohol intake was not dependent upon drug-induced motor impairment since increases in water drinking ( p  < 0.05) were exhibited during the 2-hour access periods during both 2- and 5-day prazosin treatment.
Conclusions:  The results indicate that the noradrenergic system plays a role in mediating alcohol drinking in rats of the P line and suggest that prazosin—a safe, well-characterized, and well-tolerated drug—may be an effective pharmacotherapeutic agent for the treatment of alcohol use disorders.     

Alcohol drinking in MCH receptor-1-deficient mice

Background: Recently, we demonstrated that exogenous melanin‐concentrating hormone (MCH) increases alcohol drinking in rats when administered into the brain. However, because the physiological relevance of this finding is unclear, we tested the hypothesis that endogenous MCH signaling enhances alcohol consumption. Methods: Alcohol intake was assessed in male and female wildtype (WT), heterozygous (HET), and homozygous MCH receptor‐1‐deficient (KO) mice. Mice were given 24‐hour access to a series of alcohol‐containing solutions. Following this, the mice were given limited (1‐hour) access to 10% alcohol. Finally, mice were allowed 24‐hour access to sucrose/quinine as a caloric control and a means to assess taste preference. A naïve cohort of male WT and KO mice was tested for alcohol clearance following intraperitoneal administration of 3 g/kg alcohol. Another naïve cohort of female mice was utilized to confirm that intracerebroventricular administration of MCH (5 μg) would augment alcohol drinking in mice. Results: Exogenous MCH enhanced 10% alcohol consumption in mice (saline=0.45±0.08 g/kg, 5 μg MCH=0.94±0.20 g/kg). Male KO mice consumed more 10% alcohol (11.50±1.31 g/kg) than WT (6.26±1.23 g/kg) and HET mice (6.49±1.23 g/kg) during ad libitum access. However, alcohol intake was similar among genotypes during 1 hour daily access. Male KO mice tended to consume less 17.75% sucrose+1.3 mM quinine than controls (WT=10.5±3.6, HET=7.5±1.7, KO=4.4±0.9 g/kg). Alcohol metabolism was similar between WT and KO mice. Conclusions: The finding that male KO consume more alcohol than WT and HET mice, are reminiscent of the counterintuitive reports that KO mice are hyperphagic and yet eat more when administered exogenous MCH. Changes in taste preference or alcohol metabolism do not appear to be important for the increased alcohol drinking in KO mice.     

Proteomic Analysis Demonstrates Adolescent Vulnerability to Lasting Hippocampal Changes Following Chronic Alcohol Consumption

Background: Excessive teenage alcohol consumption is of great concern because alcohol may adversely alter the developmental trajectory of the brain. The aim of the present study was to assess whether chronic intermittent alcohol intake during the adolescent period alters hippocampal protein expression to a greater extent than during adulthood. Methods: Adolescent [postnatal day (PND) 27] and adult (PND 55) male Wistar rats were given 8 hours daily access to beer (4.44% ethanol v/v) in addition to ad libitum food and water for 4 weeks. From a large subject pool, subgroups of adolescent and adult rats were selected that displayed equivalent alcohol intake (average of 6.1 g/kg/day ethanol). The 4 weeks of alcohol access were followed by a 2‐week alcohol‐free washout period after which the hippocampus was analyzed using 2‐DE proteomics. Results: Beer consumption by the adult group resulted in modest hippocampal changes relative to alcohol naïve adult controls. The only changes observed were an up‐regulation of citrate synthase (a precursor to the Krebs cycle) and fatty acid binding protein (which facilitates fatty acid metabolism). In contrast, adolescent rats consuming alcohol showed more widespread hippocampal changes relative to adolescent controls. These included an increase in cytoskeletal protein T‐complex protein 1 subunit epsilon (TCP‐1) and a decrease in the expression of 10 other proteins, including glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH), triose phosphate isomerise, alpha‐enolase, and phosphoglycerate kinase 1 (all involved in glycolysis); glutamate dehydrogenase 1 (an important regulator of glutamate); methylmalonate‐semialdehyde dehydrogenase (involved in aldehyde detoxification); ubiquitin carboxyl‐terminal hydrolase isozyme L1 (a regulator of protein degradation); and synapsin 2 (involved in synaptogenesis and neurotransmitter release). Conclusions: These results suggest the adolescent hippocampus is more vulnerable to lasting proteomic changes following repeated alcohol exposure. The proteins most affected include those related to glycolysis, glutamate metabolism, neurodegeneration, synaptic function, and cytoskeletal structure.     

Effects of Taste Aversion Training on the Acquisition of Alcohol Drinking in Adolescent P and HAD Rat Lines

Early alcohol drinking has been hypothesized to cause alcohol-related problems in adulthood. In addition, a potential role for genetic factors exist in the etiology of some types of alcoholism. The objective of the present study was to determine if taste aversion training to ethanol during adolescence in previously ethanol-naive, alcohol-preferring P and high-alcohol drinking HAD-1 lines of rats would retard or prevent the onset of high alcohol drinking. Taste aversion training began at 30 days of age. Male and female rat pups were fluid-deprived for 24 hr before 30 min access to a 10% (v/v) ethanol solution, followed by an intraperitoneal injection of either saline or 0.15 M LiCl (10 ml/kg). A total of five training sessions were administered every other day with unrestricted access to water on intervening training days. Twenty-four hours after the last training trial, rats were given continuous free-choice between water and 10% ethanol for 4 weeks with food available ad libitum. There were no obvious gender or line differences to the effects of taste aversion training. All LiCl-treated subjects avoided the usually preferred ethanol solution for the entire 4-week test period, whereas saline-treated rats steadily increased their alcohol intake to over 6.0 g/kg/day by week 4. Rats in the saline and LiCl-treated groups gained weight at comparable rates, and the groups did not differ in total fluid intake. The findings demonstrate that early environmental intervention can prevent the onset of high alcohol drinking in the selectively bred alcohol-preferring P and high-alcohol drinking HAD-1 lines of rats.     

Effects of long-term episodic access to ethanol on the expression of an alcohol deprivation effect in low alcohol-consuming rats

Background: The alcohol‐preferring (P) and ‐nonpreferring (NP) and high alcohol–drinking (HAD) and low alcohol–drinking (LAD) rats have been selectively bred for divergent preference for ethanol over water. In addition, both P and HAD rats display an alcohol deprivation effect (ADE). This study was undertaken to test whether the NP, LAD‐1, and LAD‐2 lines of rats could display an ADE as well. Method: Adult female NP, LAD‐1, and LAD‐2 rats were given concurrent access to multiple concentrations of ethanol [5, 10, 15% (v/v)] and water in an ADE paradigm involving an initial 6 weeks of 24‐hr access to ethanol, followed by four cycles of 2 weeks of deprivation from and 2 weeks of re‐exposure to ethanol (5, 10, and 15%). A control group had continuous access to the ethanol concentrations (5, 10, and 15%) and water through the end of the fourth re‐exposure period. Results: For NP rats, a preference for the highest ethanol concentration (15%) was evident by the end of the fifth week of access (～60% of total ethanol fluid intake). Contrarily, LAD rats did not display a marked preference for any one concentration of ethanol. All three lines displayed an ADE after repeated cycles of re‐exposure to ethanol, with the general ranking of intake being LAD‐1 > NP > LAD‐2 (e.g., for the first day of reinstatement of the third re‐exposure cycle, intakes were 6.5, 2.9, and 2.4 g/kg/day compared with baseline values of 3.1, 2.0, and 1.3 g/kg/day for each line, respectively). By the 13th week, rats from all three lines, with a ranking of LAD‐1 > NP > LAD‐2, were drinking more ethanol (3.3, 2.2, and 2.0 g/kg/day, respectively) compared with their consumption during the first week of access (～1.1 g/kg/day for all three lines). Conclusion: These data indicate that access to multiple concentrations of ethanol and exposure to multiple deprivation cycles can partially overcome a genetic predisposition of NP, LAD‐1, and LAD‐2 rats for low alcohol consumption. In addition, the findings suggest that genetic control of low alcohol consumption in rats is not associated with the inability to display an ADE.     

Increase of Rat Alcohol Drinking Behavior Depends on the Age of Drinking Onset

Background Although alcohol drinking onset in younger people is associated with an increased risk of alcohol-related injuries, other factors, such as habituation and susceptibility to alcohol, in the process of aging have not been adequately examined in animal models. In the present study, we determined whether age of drinking onset affected alcohol drinking behavior and led to alcohol tolerance in experimental animals, and extrapolated some of the findings to human alcohol drinking patterns.
Methods In the first experiment, 18 rats that were naive to alcohol were tested at the age of 1, 4, and 10 months with 4 hr of access to 10% (v/v) alcohol. After the time access tests, these animals (1, 4, and 10 months of age) were housed individually and given free access to 10% alcohol solution and tap water. At 3 and 6 months later, all rats that had experienced alcohol drinking were studied for the voluntary consumption of the alcohol solution, alcohol preference, under the two-bottle method in a second experiment.
Results In the 4-hr alcohol-access test, alcohol intake (g/kg/hr) was significantly increased at 0.5 and 1 hr in 1- and 4-month-old naive rats compared with 10-month-old naive rats. The daily alcohol intake (g/kg/day) of rats with drinking onset at 1 month of age was significantly increased at 3 and 6 months after the voluntary alcohol consumption. The daily alcohol intake in the rats with drinking onset at 4 months of age was significantly increased at 6 months only. However, the daily alcohol intake did not change in the rats with drinking onset at 10 months of age through the alcohol preference test.
Conclusions Alcohol drinking behavior in experimental animals depends on the age of alcohol drinking onset.     

Carbohydrate-Deficient Transferrin as a Marker of Change in Alcohol Intake in Men Drinking 20 to 60 g of Alcohol Per Day

We evaluated carbohydrate-deficient transferrin (CDT) and γ-glutarnyltranspeptidase (γ-GT) as markers of alcohol intake and change in alcohol intake in white Australian men aged 20 to 63 years who regularly drank 20 to 60 g of alcohol/day (2 to 6 standard drinks), either as weekend (n = 14) or daily drinkers (n = 41). After 4 weeks of familiarization on usual alcohol intake, men were provided with low alcohol beer (24 times 375 ml cans, 0.9%, v/v, two-weekly), and, for 4 weeks, consumed as much or as little as they wished with no additional alcohol permitted. In an alternate 4-week period, the same amount of full-strength beer (4.9%, v/v) was provided, whereas subjects continued their usual amount and pattern of alcohol consumption. The order of experimental conditions was randomized. Retrospective 7-day diaries documented weekly alcohol intake during 4 weeks of familiarization and 8 weeks of intervention. Mean alcohol intake was 345 g/week of alcohol (SD 97) during familiarization. During the last 4 weeks of intervention (study weeks 8 to 12), mean alcohol intake either increased by 360 g/week (SD 138) with the switch from low to high alcohol or decreased by 328 g/week (SD 120) with the reverse. During familiarization (study weeks 1 to 4), alcohol intake was significantly related independently (R²= 0.21) to mean corpuscular volume (ρ= 0.008) and uric acid (ρ= 0.003), but not to γ-GT (ρ= 0.22) nor CDT (p = 0.94). Change in alcohol intake was predicted independently (R²= 0.60) by change in CDT (ρ < 0.0001) and γ-GT (ρ= 0.0003), but not by change in uric acid or mean corpuscular volume. A 10% change in CDT gave 70% sensitivity and 80% specificity to detect a change of at least 2 standard drinks/day; respective values were 68% and 0 for 10% change in γ-GT. Results were not related to drinking pattern, smoking, age, or weight CDT, particularly when used as a continuous variable, may have a place in monitoring alcohol consumption, even in men whose alcohol intake is in the 20 to 60 g/day range.