Effects of Cagemate Gender and the Cagemate's access to ethanol on ethanol and water intake of the proximal male or the proximal female CD-1 mouse

Alcohol Binge Drinking and Anxiety-Like Behavior in Socialized Versus Isolated C57BL/6J Mice

BACKGROUND

Binge alcohol drinking has been characterized as a key feature of alcoholism. The drinking-in-the-dark (DID) preclinical model, a procedure that promotes high levels of ethanol (EtOH) intake in short periods of time, has been extensively used to investigate neuropharmacological and genetic determinants of binge-like EtOH consumption. Using DID methodology, alcohol-preferring strains of mice such as C57BL/6J (B6) mice consume enough EtOH to achieve blood concentrations (≥1.0 mg/ml) associated with behavioral intoxication (i.e., motor incoordination). DID procedures typically involve the use of socially isolated animals (single-housed prior to and during the experiment). Previous research indicates that stress associated with social isolation can induce anxiety-like behavior and promote increases in EtOH intake. The present study investigates the role of housing conditions in anxiety-like behavior and binge-like EtOH intake using a DID procedure.

METHODS

Male and female B6 mice were isolated or pair-housed for a period of 6 weeks prior to evaluation of anxiety-like (elevated plus maze, light and dark box, open field) and drinking (water, 10% sucrose, 10 to 30% EtOH) behavior. In order to measure intake, a variation of the standard DID procedure using a removable, transparent, and perforated plastic barrier strip (designed to temporarily divide the cage in 2) was introduced. This allowed for individual intake records (2-hour test) of isolated and socially housed animals.

RESULTS

Increased anxiety-like behavior and reduced sucrose consumption were found in isolated mice. The effects of housing conditions on EtOH intake were sex- and concentration-dependent. In male mice, isolation increased 20 and 30% EtOH intake. In females, however, an increased intake of EtOH (30%) was found in socialized animals. No effects of housing or sex were found at EtOH 10%.

CONCLUSIONS

Together with previous literature, the present study suggests that social isolation can promote anxiety-associated behavior and produce sex-dependent changes in binge-like EtOH consumption.

Social modulation of drug use and drug addiction

This review aims to demonstrate how social science and behavioral neurosciences have highlighted the influence of social interactions on drug use in animal models. In neurosciences, the effect of global social context that are distal from drug use has been widely studied. For human and other social animals such as monkeys and rodents, positive social interactions are rewarding, can overcome drug reward and, in all, protect from drug use. In contrast, as other types of stress, negative social experiences facilitate the development and maintenance of drug abuse. However, interest recently emerged in the effect of so-called "proximal" social factors, that is, social interactions during drug-taking. These recent studies have characterized the role of the drug considered, the sharing of drug experience and the familiarity of the peer which interaction are made with. We also examine the few studies regarding the sensorial mediator of social behaviors and critically review the neural mediation of social factors on drug use. However, despite considerable characterization of the factors modulating distal influences, the mechanisms for proximal influences on drug use remain largely unknown. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

Assessing Social Alcohol Drinking in Rodent Models: Are We There Yet?

Pathological and social consequences associated with excessive alcohol consumption and dependence constitute a serious concern for human well-being. The success of preventative and therapeutic strategies for alcohol use disorder depends on the development of appropriate animal models of alcohol consumption. Alcohol consumption in humans typically occurs in social settings. In contrast, the vast majority of animal models investigate alcohol drinking in socially isolated animals. A number of rodent model studies have attempted to assess drinking of individual animals within social setting. These studies identified varied directions of effects of social environment on alcohol consumption. However, the interpretation of these results is strongly hampered by technical issues associated with the existing approaches to assess drinking of individual animals within each group. This review analyzes the existing literature mostly focusing on the interpretation caveats of performed studies and highlights some of the new directions in these studies.

The glucagon-like peptide 1 receptor agonist Exendin-4 decreases relapse-like drinking in socially housed mice

Glucagon-like peptide-1 (GLP-1) is a gut peptide that regulates food intake and glucose metabolism. GLP-1 is also produced and released in the brain, and GLP-1 receptors are expressed in brain regions important for alcohol and drug reward, and for the development of addiction. GLP-1 receptor agonists can decrease alcohol intake acutely in rodents. However, alcohol use disorder is a chronic condition that requires treatments to be effective in promoting abstinence from excessive alcohol consumption over time. Here, we assessed the effect of daily treatment with the GLP-1 receptor agonist Exendin-4 in an assay of relapse-like drinking in socially housed mice. Male C57BL/6NTac mice were allowed continuous access to alcohol without tastant in the home cage for 37days. Then, alcohol bottles were removed and Exendin-4 (1.5μg/kg/day) or saline was administered subcutaneously for 8days during alcohol deprivation. Treatment continued for 8 additional days after reintroducing access to alcohol. A high-precision automated fluid consumption system was used to monitor intake of alcohol and water, drinking kinetics, and locomotor activity. Exendin-4 prevented the deprivation-induced increase in alcohol intake observed in control mice, without significantly affecting total fluid intake, body weight, or locomotor activity. The reduced alcohol intake was caused by a protracted latency to the first drink of alcohol and a reduced number of drinking bouts, while bout size and duration were not affected. The effect was maintained undiminished throughout the treatment period. These findings support the possible use of GLP-1 receptor agonists in the treatment of alcohol use disorder.

Animal models of social contact and drug self-administration

Social learning theories of drug abuse propose that individuals imitate drug use behaviors modeled by social peers, and that these behaviors are selectively reinforced and/or punished depending on group norms. Historically, animal models of social influence have focused on distal factors (i.e., those factors outside the drug-taking context) in drug self-administration studies. Recently, several investigators have developed novel models, or significantly modified existing models, to examine the role of proximal factors (i.e., those factors that are immediately present at the time of drug taking) on measures of drug self-administration. Studies using these newer models have revealed several important conclusions regarding the effects of social learning on drug abuse: 1) the presence of a social partner influences drug self-administration, 2) the behavior of a social partner determines whether social contact will increase or decrease drug intake, and 3) social partners can model and imitate specific patterns of drug self-administration. These findings are congruent with those obtained in the human laboratory, providing support for the cross-species generality and validity of these preclinical models. This mini-review describes in detail some of the preclinical animal models used to study social contact and drug self-administration to guide future research on social learning and drug abuse.

Effects of number of cagemates on home cage ethanol drinking during proximal cagemate drinking (PCD) procedures in male and female CD-1 mice

The present experiment evaluated the effects of the Number of Cagemates (0 vs 1 vs 2) on home cage ethanol drinking during Proximal Cagemate Drinking (PCD) procedures in Male and Female CD-1 mice. Continuous-access home cage 2-bottle (ethanol vs. water) free-choice procedures were employed. PCD procedures eliminate the distracting effects of direct physical contact between Drinkers and their Cagemates on ethanol drinking by imposing a translucent plastic barrier strip between them. If direct physical contact distracts from drinking, then one Cagemate would drink more ethanol and more water than two Cagemates housed together on the same side of the barrier. This would be the case even if two Cagemates stimulated more ethanol drinking in the Drinker housed on the other side of the barrier, due to the social stimulation effects of additional Cagemates. Results revealed that the ethanol intake of Female Drinkers was directly related to the number of Cagemates on the other side of the barrier strip, but this social stimulation effect was not observed in Male Drinkers. For Male Cagemates and Female Cagemates, the single Cagemate provided elevated ethanol intake and elevated water intake relative to the ethanol intake and water intake of each Cagemate in the two Cagemates condition. The data revealed that direct physical contact between Cagemates reduced their ethanol intake, even while stimulating ethanol intake of the Drinker on the other side of the barrier, indicating that the effects of social stimulation on ethanol drinking are not entirely due to effects of modeling or peer pressure. The PCD procedures allow the evaluation of effects of a broad range of social factors on home cage ethanol drinking in mice.