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.     

P rats develop physical dependence on alcohol via voluntary drinking: changes in seizure thresholds, anxiety, and patterns of alcohol drinking

BACKGROUND: It has been proposed that the alcohol-preferring P rat meets many of the criteria for an animal model of alcoholism. However, the development of alcohol dependence has not been explored in rats that self-administer ethanol for less than 15-20 weeks. The present study investigated the development of physical dependence upon alcohol after 2-6 weeks of voluntary alcohol intake. Changes in bicuculline-induced seizure thresholds, microstructure of alcohol drinking, and anxiety-related behavior were used as indices of alcohol dependence. In addition, we evaluated the microstructure of alcohol drinking associated with the development of physical dependence upon alcohol. METHODS: Alcohol (10% ethanol solution) was measured in graduated drinking tubes with both alcohol and water available continuously. Microstructure of alcohol intake was monitored by a computerized drinkometer. Physical dependence upon alcohol was determined by measuring bicuculline-induced seizure thresholds after alcohol withdrawal. Anxiety-related behavior of P rats after alcohol withdrawal was determined by the social interaction and elevated plus maze tests. RESULTS: Initial alcohol intake in the alcohol-preferring P rat was relatively modest (3.9 +/- 0.4 g/kg/day). Four days of forced alcohol exposure (initiation) followed by 6 weeks of voluntary drinking resulted in an increase of alcohol intake to 5.5 +/- 0.2 g/kg/day. Ethanol self-administration for 6 weeks, but not for 2 or 4 weeks, produced a significant reduction (30%; p < 0.05) in bicuculline-induced seizure thresholds during alcohol withdrawal. Alterations in the microstructure of alcohol intake (i.e., 90% increase in the size of alcohol drinking bouts compared to the baseline [p < 0.001] with no change in bout frequency) were associated with the development of alcohol dependence. Termination of alcohol intake after 6 weeks of voluntary alcohol consumption resulted in increased anxiety according to both the social interaction and elevated plus maze tests. CONCLUSIONS: The results of this study indicate that 6 weeks of voluntary alcohol intake are sufficient for the development of physical dependence upon alcohol in the alcohol-preferring P rats as measured by susceptibility to bicuculline-induced seizures. This time is much shorter than the 15-20 weeks reported earlier. Development of physical dependence to alcohol was associated with an increase in daily alcohol intake (40% over the baseline), an increase in alcohol intake during each drinking bout (90% over the baseline), and elevated anxiety during alcohol withdrawal.     

Drinking typography established by scheduled induction predicts chronic heavy drinking in a monkey model of ethanol self-administration

Background: We have developed an animal model of alcohol self‐administration that initially employs schedule‐induced polydipsia (SIP) to establish reliable ethanol consumption under open access (22 h/d) conditions with food and water concurrently available. SIP is an adjunctive behavior that is generated by constraining access to an important commodity (e.g., flavored food). The induction schedule and ethanol polydipsia generated under these conditions affords the opportunity to investigate the development of drinking typologies that lead to chronic, excessive alcohol consumption. Methods: Adult male cynomolgus monkeys (Macaca fascicularis) were induced to drink water and 4% (w/v in water) ethanol by a Fixed‐Time 300 seconds (FT‐300 seconds) schedule of banana‐flavored pellet delivery. The FT‐300 seconds schedule was in effect for 120 consecutive sessions, with daily induction doses increasing from 0.0 to 0.5 g/kg to 1.0 g/kg to 1.5 g/kg every 30 days. Following induction, the monkeys were allowed concurrent access to 4% (w/v) ethanol and water for 22 h/day for 12 months. Results: Drinking typographies during the induction of drinking 1.5 g/kg ethanol emerged that were highly predictive of the daily ethanol intake over the next 12 months. Specifically, the frequency in which monkeys ingested 1.5 g/kg ethanol without a 5‐minute lapse in drinking (defined as a bout of drinking) during induction strongly predicted (correlation 0.91) subsequent ethanol intake over the next 12 months of open access to ethanol. Blood ethanol during induction were highly correlated with intake and with drinking typography and ranged from 100 to 160 mg% when the monkeys drank their 1.5 g/kg dose in a single bout. Forty percent of the population became heavy drinkers (mean daily intakes >3.0 g/kg for 12 months) characterized by frequent “spree” drinking (intakes >4.0 g/kg/d). Conclusion: This model of ethanol self‐administration identifies early alcohol drinking typographies (gulping the equivalent of 6 drinks) that evolve into chronic heavy alcohol consumption in primates (drinking the equivalent of 16 to 20 drinks per day). The model may aid in identifying biological risks for establishing harmful alcohol drinking.     

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.     

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.     

Early ethanol consumption predicts relapse-like behavior in adolescent male rats

Background: Alcohol abuse disorders emerge over time with repeated consumption of ethanol, but not all ethanol drinkers develop these disorders. There are pre‐existing characteristics that indicate which drinkers are most likely to abuse alcohol. Adolescence, novelty seeking, and high stress reactivity are among the characteristics of the most vulnerable individuals. In addition, an individual’s response to his or her first exposure to the drug influences future consumption. We assessed an array of behavioral and hormonal characteristics in adolescent (28‐day‐old) male rats before exposure to ethanol, and then determined which rats were most prone to high levels of alcohol drinking. Methods: The assessments consisted of measures of anxiety (elevated plus maze), response to novelty (open field locomotion, novel object exploration), and circulating corticosterone levels after mild restraint and after the elevated plus maze task. After this test battery, the rats were placed in lickometer cages nightly (5 pm to 9 am ) for evaluation of fluid consumption. Rats were first habituated to the cages with water in the lickometer bottles, and then given 10% (v/v) ethanol for 3 nights as the only available fluid. After this forced ethanol exposure, the rats were allowed to choose between 8% ethanol and water for 10 consecutive nights. After 2 nights of abstinence, the rats were again placed in the lickometer cages and given a choice between 8% ethanol and water to assess ethanol consumption in response to alcohol deprivation, a measure of relapse‐like behavior. Results: Ethanol consumption on the third day of forced consumption was significantly correlated with ethanol consumption on days 8 to 10 of the choice phase, which in turn was significantly correlated to relapse‐like consumption. Preference for ethanol was also significantly correlated with early consumption. Novel object exploration, open field activity, open arm time in the elevated plus maze, initial water consumption, and circulating corticosterone levels did not significantly predict deprivation‐stimulated consumption. Conclusions: These results suggest that consumption during early exposure to ethanol establishes a pattern leading to development of increased alcohol consumption and preference in adolescent male rats. In addition, they represent an animal model of the well‐described observation that humans who consume large quantities of ethanol during early exposure are the most likely to repeat heave drinking behavior. Furthermore, early consumption is distinct from novelty seeking, anxiety, and stress hormone levels which are also thought to contribute to vulnerability to alcoholism.     

Limited Access Alcohol Drinking in High- and Low-Alcohol Preferring Selected Lines of Mice

BACKGROUND: Selection studies and genetic analyses of drinking behavior in rodents often involved unlimited access to alcohol over a period of weeks, with water and food freely available. Most studies investigating the pharmacology of alcohol drinking, on the other hand, use procedures in which access to alcohol is limited to a particular time each day. Reconciliation of findings between these two conditions likely depends on their sharing common genetic mechanisms as indicated, for example, by covariation in response to selection. To this end, high- and low-alcohol preferring (HAP and LAP, respectively) mice, selected for differences in 24-hr access alcohol drinking over a 4-week period, were subjected to a limited access alcohol drinking protocol. METHODS: During 2-hr sessions, mice had access to various concentrations of alcohol (7-15%, v/v) in the home cage for 2 hr a day, with ad libitum access to food and water. Additional sessions were conducted with no food present. RESULTS: Although both strains consumed alcohol and water during these sessions, HAP mice drank far more alcohol than did LAP mice. HAP but not LAP mice drank alcohol at a high rate early in the session compared with later in the session. Additionally, HAP mice responded to changes in alcohol concentration, whereas LAP mice did not. Removal of food did not influence alcohol drinking, although water drinking decreased following food removal. HAP mice reached appreciable blood alcohol concentrations after limited access. CONCLUSIONS: These findings indicate that in these selectively bred mice, alcohol drinking during limited and unlimited access may be genetically related, and that drinking during limited access sessions in HAP mice is likely for the pharmacological properties of alcohol.     

Effects of naltrexone on alcohol self-administration in heavy drinkers

The mechanisms underlying the suppressant effects of naltrexone (NTX) on ad libitum alcohol drinking in a bar/restaurant setting were investigated in heavy beer drinkers. Fifty-one male and female heavy drinkers (mean age = 22) received 50 mg of NTX or placebo (PBO), p.o., on two separate occasions in a randomized, double-blind crossover protocol. After 7 days of taking medication, subjects were provided with the opportunity to consume beer ad libitum during two, 90-min test sessions that were held 1 to 2 weeks apart. Blood samples were collected on test days to ensure medication compliance and to measure blood levels of NTX and the active beta-naltrexol. Less beer was consumed during NTX treatment. NTX decreased urges to consume alcohol. NTX-treated subjects also took significantly longer to finish each glass of beer and were more likely to terminate beer drinking early. Self-report stimulation and ratings of positive mood states were lower during NTX treatment. Negative side effects of NTX, such as nausea and headache, were reported more frequently with NTX. Not all of the subjects decreased their beer intake on NTX, and some subjects drank more beer. Nonresponders to NTX were not related to blood levels of the active metabolite beta-naltrexol or to a family history of alcoholism. Overall, the results of this study suggest that NTX affects a number of the components of alcohol drinking sequence, including lowering cravings, decreasing the positive reinforcing effects of alcohol, and increasing headache and nausea, each of which may contribute to reducing alcohol intake.     

Inhibition of 5alpha-reduced steroid biosynthesis impedes acquisition of ethanol drinking in male C57BL/6J mice

Background: Allopregnanolone (ALLO) is a physiologically relevant neurosteroid modulator of GABA_A receptors, and it exhibits a psychopharmacological profile that closely resembles the post‐ingestive effects of ethanol. The 5α‐reductase inhibitor finasteride (FIN), which inhibits biosynthesis of ALLO and structurally related neurosteroids, was previously demonstrated to reduce the maintenance of limited‐access ethanol consumption. The primary aim of the current work was to determine whether FIN would reduce the acquisition of drinking in ethanol‐naïve mice. Methods: Male C57BL/6J (B6) mice were acclimated to a reverse light/dark schedule, and were provided ad libitum access to chow and water. Following habituation to vehicle injections (VEH; 20% w/v β‐cyclodextrin; i.p.) administered 22‐hour prior to drinking sessions with water only, mice were divided into 3 treatment groups: vehicle control (VEH), 50 mg/kg FIN (FIN‐50), and 100 mg/kg FIN (FIN‐100). Twenty‐two hours after the first treatment, mice were permitted the inaugural 2‐hour limited access to a 10% v/v ethanol solution (10E) and water. The acquisition of 10E consumption and underlying drinking patterns were assessed during FIN treatment (7 days) and subsequent FIN withdrawal (13 days) phases. Results: FIN dose‐dependently blocked the acquisition of 10E drinking and prevented the development of ethanol preference, thereby suggesting that the GABAergic neurosteroids may be important in the establishment of stable drinking patterns. FIN‐elicited reductions in 10E intake were primarily attributable to selective and marked reductions in bout frequency, as no changes were observed in bout size, duration, or lick rates following FIN treatment. FIN‐treated mice continued to exhibit attenuated ethanol consumption after 2 weeks post‐treatment, despite a full recovery in brain ALLO levels. A second study confirmed the rightward and downward shift in the acquisition of ethanol intake following 7 daily FIN injections. While there were no significant group differences in brain ALLO levels following the seventh day of ethanol drinking, ALLO levels were decreased by 28% in the FIN‐50 group. Conclusions: Although the exact mechanism is unclear, FIN and other pharmacological interventions that modulate the GABAergic system may prove useful in curbing ethanol intake acquisition in at‐risk individuals.     

Increase in Alcohol Intake,Reduced Flexibility of Alcohol Drinking,and Evidence of Signs of Alcohol Intoxication in Sardinian Alcohol‐Preferring Rats Exposed to Intermittent Access to 20% Alcohol

Background: This study assessed in Sardinian alcohol‐preferring (sP) rats a procedure known to promote alcohol drinking and based on the intermittent (once every other day) access to 2 bottles containing alcohol (20%, v/v) and water, respectively (Wise, 1973). Methods: To this end, sP rats were exposed – under the 2‐bottle choice regimen – to: (i) 10% (v/v) alcohol with continuous access (CA10%; i.e., the procedure under which sP rats had been selectively bred); (ii) 10% (v/v) alcohol with intermittent access (IA10%); (iii) 20% (v/v) alcohol with continuous access (CA20%); (iv) 20% (v/v) alcohol with intermittent access (IA20%; the “Wise” condition) (Experiment 1). Additional experiments assessed the influence of (i) adulteration with quinine of the alcohol solution (Experiment 2) and (ii) concurrent presentation of a saccharin solution (Experiment 3) on alcohol drinking under the CA10% and IA20% conditions. Finally, it was assessed whether alcohol drinking under the CA10% and IA20% conditions resulted in motor incoordination at the Rota‐Rod task, as a possible sign of alcohol intoxication (Experiment 4). Results: Daily alcohol intake markedly escalated in rats exposed to the IA20% condition, averaging 9.0 g/kg (in comparison with the average intake of 6.5 g/kg in the CA10% rat group). CA20% and IA10% rats displayed intermediate values of daily alcohol intake between those of CA10% and IA20% rats. Alcohol intake was virtually abolished by addition of quinine or by concurrent presentation of the saccharin solution in CA10% rats; conversely, alcohol intake in IA20% rats was only partially affected by gustatory aversion or concurrent presentation of an alternative reinforcer. Finally, alcohol intake in IA20%, but not in CA10%, rats resulted in clear motor‐incoordinating effects. Conclusions: These data suggest that the “Wise” procedure is effective in inducing marked increases in alcohol intake in sP rats. These increases are associated with a reduced flexibility of alcohol drinking (suggesting the development of “behavioral” dependence) and produce signs of alcohol intoxication that are not detected when sP rats are exposed to the more conventional CA10% condition.     

Alteration of ethanol drinking in mice via modulation of the GABA(A) receptor with ganaxolone, finasteride, and gaboxadol

Background: Neurosteroids and other γ‐aminobutyric acid_A (GABA_A) receptor–modulating compounds have been shown to affect ethanol intake, although their mechanism remains unclear. This study examined how patterns of 24‐hour ethanol drinking in mice were altered with the synthetic GABAergic neurosteroid ganaxolone (GAN), with an inhibitor of neurosteroid synthesis (finasteride [FIN]), or a GABA_A receptor agonist with some selectivity at extrasynaptic receptors (gaboxadol HCL [THIP]). Methods: Male C57BL/6J mice had continuous access to a 10% v/v ethanol solution (10E) or water. Using lickometer chambers, drinking patterns were analyzed among mice treated in succession to GAN (0, 5, and 10 mg/kg), FIN (0 or 100 mg/kg), and THIP (0, 2, 4, 8, and 16 mg/kg). Results: GAN shifted drinking in a similar but extended manner to previous reports using low doses of the neurosteroid allopregnanolone (ALLO); drinking was increased in hour 1, decreased in hours 2 and 3, and increased in hours 4 and 5 postinjection. THIP (8 mg/kg) and FIN both decreased 10E drinking during the first 5 hours postinjection by 30 and 53%, respectively, while having no effect on or increasing water drinking, respectively. All 3 drugs altered the initiation of drinking sessions in a dose‐dependent fashion. FIN increased and GAN decreased time to first lick and first bout. THIP (8 mg/kg) decreased time to first lick but increased time to first bout and attenuated first bout size. Conclusions: The present findings support a role for the modulation of ethanol intake by neurosteroids and GABA_A receptor–acting compounds and provide hints as to how drinking patterns are shifted. The ability of THIP to alter 10E drinking suggests that extrasynaptic GABA_A receptors may be involved in the modulation of ethanol intake. Further, the consistent results with THIP to that seen previously with high doses of ALLO suggest that future studies should further examine the relationship between neurosteroids and extrasynaptic GABA_A receptors, which could provide a better understanding of the mechanism by which neurosteroids influence ethanol intake.     

Increased drinking during withdrawal from intermittent ethanol exposure is blocked by the CRF receptor antagonist D-Phe-CRF(12-41)

BACKGROUND: Studies in rodents have determined that intermittent exposure to alcohol vapor can increase subsequent ethanol self-administration, measured with operant and 2-bottle choice procedures. Two key procedural factors in demonstrating increased alcohol intake are the establishment of stable alcohol self-administration before alcohol vapor exposure and the number of bouts of intermittent vapor exposure. The present studies provide additional behavioral validation and initial pharmacological validation of this withdrawal-associated drinking procedure. METHODS: Studies at 2 different sites (Portland and Scripps) examined the effect of intermittent ethanol vapor exposure (3 cycles of 16 hours of ethanol vapor+8 hours air) on 2-hour limited access ethanol preference drinking in male C57BL/6 mice. Separate studies tested 10 or 15% (v/v) ethanol concentrations, and measured intake during the circadian dark. In one study, before measuring ethanol intake after the second bout of intermittent vapor exposure, mice were tested for handling-induced convulsions (HICs) indicative of physical dependence on ethanol. In a second study, the effect of bilateral infusions of the corticotropin-releasing factor (CRF) receptor antagonist D-Phe-CRF(12-41) (0.25 microg/0.5 microL) into the central nucleus of the amygdala (CeA) on ethanol intake was compared in vapor-exposed animals and air controls. RESULTS: Intermittent ethanol vapor exposure significantly increased ethanol intake by 30 to 40%, and the mice had higher blood ethanol concentrations than controls. Intra-amygdala infusions of D-Phe-CRF(12-41) significantly decreased the withdrawal-associated increase in ethanol intake without altering ethanol consumption in controls. Following the second bout of intermittent vapor exposure, mice exhibited an increase in HICs, when compared with their own baseline scores or the air controls. CONCLUSIONS: Intermittent alcohol vapor exposure significantly increased alcohol intake and produced signs of physical dependence. Initial pharmacological studies suggest that manipulation of the CRF system in the CeA can block this increased alcohol intake.     

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.     

The distribution of alcohol consumption and the prevention paradox in Brazil

Aims To examine the proportion of self‐reported alcohol consumed by different gender and age groups in Brazil over the past year, and to examine whether the ‘prevention paradox’ applies to Brazilian data on alcohol‐related problems. Design A multi‐stage cluster sample, representative of the Brazilian household population. Setting This study was conducted in Brazil between November 2005 and April 2006. Participants Respondents were aged ≥ 14 years (n = 3007). Measurements Measures included past year estimates of (i) number of standard drinks, (ii) frequency of binge drinking, and (iii) alcohol‐related problems. Findings The survey response rate was 66.4%. The top 2.5% of the drinkers by volume consume 14.9%, the top 5% consume 27.4% and the top 10% consume 44.2% of all alcohol consumed in Brazil. Men consume 77.8% of the total alcohol, and 18–29‐year‐olds consume 40.3%. Individuals below risky drinking guidelines for weekly volumetric intake account for 49–50% of all problem drinkers and 45–47% of all problem types reported. Individuals who do not binge or who binge infrequently (1–3 times/year) account for 50–51% of all problem drinkers and 45–46% of all reported problem types. Most binge drinkers are low‐volume drinkers. Conclusions Consistent with the prevention paradox literature, most drinking problems in Brazil are associated with low or moderate drinking. Binge drinking accounts more clearly for the distribution of alcohol problems than total volume consumed.     

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.     

Voluntary ethanol consumption differs in adolescent and adult male rats using a modified sucrose-fading paradigm

Background: Initiation of alcohol consumption during adolescence is high, which usually begins with consumption of highly concentrated sweetened alcoholic beverages in adolescent humans. Enhanced voluntary ethanol (EtOH) intake has been observed previously in adolescent relative to adult rats under continuous access conditions using sweetened EtOH solutions. The present set of experiments investigated patterns of voluntary EtOH intake in adolescent and adult rats using sweetened EtOH solutions in a limited access paradigm. Methods: Rats were trained with modified sucrose‐substitution protocols that ended at either 5% sucrose‐20% EtOH (5S/20E) (Exp. 1) or 5% sucrose‐10% EtOH (5S/10E) (Exp. 2). Results: Voluntary EtOH consumption differences between the 2 age groups were apparent at higher (i.e., 10 and 20%), but not lower (i.e., 2 and 5%) EtOH concentrations. Adolescent rats consumed more EtOH on a g/kg basis only at 20% EtOH (Exp. 1). Adolescent rats voluntarily consumed more EtOH than adults when maintained at 5S/10E (Exp. 2). To assess whether these age‐related differences in voluntary EtOH intake were concentration dependent, rats were trained with 5S/20E and subsequently trained with decreasing EtOH concentrations (i.e., 5S/10E and 5S/5E). Adolescents consumed more EtOH when initially presented with the 5S/10E and 5S/20E EtOH concentrations, and subsequently at the lower 5S/5E EtOH concentration (Exp. 3). There were no differences in preference for the sucrose‐only solution, however adolescents tended to consume more sucrose at the 5S sucrose concentration (Exp. 4). Given that adolescents consumed more EtOH at the 5S/10E and 5S/20E, but not at the 5S/5E EtOH concentrations, preference for sucrose does not solely explain the age differences in voluntary EtOH intake observed. Conclusions: Overall, results replicate previous work, demonstrating adolescent rats consume more EtOH relative to adults. However, the present results were observed using sweetened EtOH solutions in a limited access paradigm. The present modified sucrose‐substitution paradigm may serve as a valid model of human adolescent drinking behavior.     

Alcohol effects on cerebral blood flow in subjects with low and high responses to alcohol

Background: Although there are multiple indications that alcohol can alter many physiological brain functions, including cerebral blood flow (CBF), studies of the latter have generally used small‐ or modest‐sized samples. Few investigations have yet evaluated how CBF changes after alcohol relate to subsets of subjects with elevated alcoholism risks, such as those with lower levels of response (LR) to alcohol. This study used arterial spin labeling (ASL) after alcohol administration to evaluate a large sample of healthy young men and women with low and high alcohol responses, and, thus, varying risks for alcohol use disorders (AUD). Methods: Healthy young adult social drinkers with low and high LR (N = 88, 50% women) matched on demography and drinking histories were imaged with whole‐brain resting ASL ～1 hour after ingesting ～3 drinks of ethanol and after a placebo beverage (i.e., 178 ASL sessions). The relationships of CBF changes from placebo to alcohol for subjects with low and high LR were evaluated. Results: CBF increased after alcohol when compared to placebo in 5 frontal brain regions. Despite identical blood alcohol concentrations, these increases with alcohol were less prominent in individuals who required more drinks to experience alcohol‐related effects (i.e., had a lower LR to alcohol). The LR group differences remained significant after covarying for recent drinking quantities. Conclusions: The results confirm that alcohol intake is associated with acute increases in CBF, particularly in frontal regions. Less intense CBF changes were seen in subjects with a genetically influenced characteristic, a low LR to alcohol, that relates to the future risk of heavy drinking and alcohol problems.     

Thyrotropin-Releasing Hormone Analog TA-0910 Reduces Voluntary Alcohol Intake of P Rats Subchronically in a Limited Scheduled Access Paradigm

We previously reported that single intraperitoneal injections of the thyrotropin-releasing hormone analog TA-0910 dose-dependently reduce alcohol intake in alcohol-preferring (P) rats in a free-choice continuous access protocol. We later showed, using the same protocol, that a transient tolerance develops to this effect after several consecutive, once-daily injections. In the present study, P rats that had been accustomed to continuous access to alcohol were acclimated to a limited scheduled access protocol in which alcohol was available only between 10 and 11 AM. This resulted in an elevated rate of alcohol intake. Rats were then injected once daily with TA-0910 (0.75 mg/kg) or an equal volume of a saline vehicle at 9:45 AM for 12 consecutive days. After 11 days of scheduled access, rats were allowed continuous access to alcohol. Intake of alcohol and water was measured each day at 11:00 AM. Compared with vehicle, TA-0910 reduced alcohol intake on the 11 days of scheduled access and during the first hour of day 12 when continuous access was restored, but did not reduce total (24 hr) alcohol intake on day 12. Data from this experiment show that TA-0910 reduces alcohol intake over a long period of time in a limited scheduled access protocol.     

Effects of prazosin, an α1-adrenergic receptor antagonist, on the seeking and intake of alcohol and sucrose in alcohol-preferring (P) rats

Background: Previous studies show that prazosin, an α₁‐adrenergic receptor antagonist, decreases alcohol drinking in animal models of alcohol use and dependence [Rasmussen et al. (2009) Alcohol Clin Exp Res 3:264–272; Walker et al. (2008) Alcohol 42:91–97] and in alcohol‐dependent men [Simpson et al. (2009) Alcohol Clin Exp Res 33:255–263]. This study extended these findings by using a paradigm that allows for separate assessment of prazosin on motivation to seek versus consume alcohol or sucrose in selectively bred rats. Methods: Alcohol‐preferring (P) rats were trained to complete an operant response that resulted in access to either 2% sucrose or 10% alcohol. A 4‐week Seeking Test Phase examined responding in single, weekly extinction sessions when no reinforcer could be obtained. A 4‐week Drinking Test Phase consisted of rats lever‐pressing to “pay” a specified amount up front to gain access to unlimited alcohol (or sucrose) for a 20‐minute period. On Seeking and Drinking test days, prazosin (0.0, 0.5, 1.0, and 1.5 mg/kg) was administered intraperitoneally 30 minutes prior to behavioral sessions. Results: Rats were self‐administering an average of 0.9 (±0.09) g/kg alcohol on vehicle test day and had pharmacologically relevant blood ethanol concentrations. Prazosin significantly decreased alcohol seeking at all doses tested. The highest dose of prazosin also increased the latency to first response for alcohol and decreased alcohol intake. While sucrose‐seeking and intake were similarly affected by prazosin, the high dose of prazosin did not increase response latency. Conclusions: These findings are consistent with and extend previous research and suggest that prazosin decreases motivation to initiate and engage in alcohol consumption. The specificity of prazosin in attenuating the initiation of alcohol‐ but not sucrose‐seeking suggests that this effect is not because of prazosin‐induced motor‐impairment or malaise. Together with previous findings, these data suggest that prazosin may be an effective pharmacotherapy, with specific application in people that drink excessively or have a genetic predisposition to alcohol abuse.     

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.