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

Differential sensitivity of ethanol-elicited ERK phosphorylation in nucleus accumbens of Sardinian alcohol-preferring and -non preferring rats

Sardinian alcohol-preferring (sP) and -non preferring (sNP) rats have been selectively bred for opposite ethanol preference and consumption; sP rats represent a validated experimental tool to model several aspects of excessive ethanol drinking in humans. Phosphorylated Extracellular signal-Regulated Kinase (pERK) in dopamine-rich terminal areas plays a critical role in several psychopharmacological effects of addictive drugs, including ethanol. This study was aimed at investigating whether ethanol-elicited ERK activation may differ in key brain areas of ethanol-naïve sP and sNP rats. To this end, the effects of ethanol (0, 0.5, 1, and 2 g/kg, administered intra-gastrically [i.g.]) on ERK phosphorylation were assessed by pERK immunohistochemistry in the shell (AcbSh) and core (AcbC) of the nucleus accumbens (Acb) as well as in the prelimbic (PrL) and infralimbic (IL) prefrontal cortex (PFCx), in the bed nucleus of stria terminalis (BSTL) and in the central nucleus of the amygdala (CeA). Ethanol (1 g/kg) significantly increased pERK immunoreactivity in AcbSh and AcbC of sP but not sNP rats. Conversely, ethanol failed to affect pERK expression in PrL and IL PFCx as well as in BSTL and CeA of both sP and sNP rats. These results suggest that selective breeding of these rat lines results in differential effects of acute ethanol on ERK phosphorylation in brain regions critical for the psychopharmacological effects of ethanol.

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.

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.

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.

Conditioned cues and yohimbine induce reinstatement of beer and near-beer seeking in Long-Evans rats

Alcohol use disorders (AUDs) impact millions of individuals, yet there are few effective treatments. One major problem in treating AUDs is the high rate of relapse to drinking often induced by stress and/or anxiety states. Although beer accounts for over 81% of all alcohol consumed in hazardous amounts in the United States, the use of beer in pre-clinical research has been limited. It has been shown that rats will self-administer beer and near-beer using a standard operant self-administration paradigm; however, there have been few studies examining reinstatement of beer and near-beer seeking. We have determined that reward-associated cues and/or yohimbine will induce reinstatement of beer and near-beer seeking in a similar manner to that seen for 10% ethanol and sucrose seeking using standard operant self-administration and reinstatement paradigms. We show that rats will self-administer beer, near-beer and 4.5% ethanol using an operant self-administration paradigm and both conditioned cues, and yohimbine will induce reinstatement of beer, near-beer and 4.5% ethanol seeking in previously extinguished animals. This demonstrates that both environmental cues and yohimbine-stress will reinstate beer and near-beer seeking, as previously shown for both 10% ethanol and sucrose seeking.