Acute effects of ethanol on social behavior of adolescent and adult rats: role of familiarity of the test situation.

Background Adolescence is a time when the risk for extensive alcohol use is elevated. At least two important qualities of alcohol may contribute to extensive alcohol use in adolescence: its ability to facilitate certain forms of social behavior, including interactions with peers, and its properties to alleviate anxiety. These issues may be addressed using sensitive animal tests of social behavior. Method A modified social interaction test was used to investigate acute effects of ethanol on different forms of social behavior (social investigation, contact behavior, and play fighting) and social motivation of adolescent and adult rats tested in a familiar (nonanxiogenic) or unfamiliar (anxiogenic) test situation. Testing in the familiar environment assessed age-related differences in sensitivity of social behavior to activating and/or suppressing effects of ethanol (ethanol-induced social facilitation or social inhibition), whereas testing in the unfamiliar environment provided information about age-related differences in ethanol anxiolytic effects (ethanol-induced reduction in the social inhibition provoked by the unfamiliar environment). Results Ethanol-induced social facilitation was observed only in adolescent animals: 0.5 g/kg of ethanol significantly increased social investigation and play fighting in adolescents tested in the familiar environment. Ethanol-induced reduction of social inhibition in the unfamiliar test situation was observed in both adolescents and adults, however, higher doses of ethanol were required to attenuate social inhibition in adolescents than in adults. Adolescent animals were also less sensitive than adults to the inhibition of social behavior evident at higher doses. Adolescents decreased contact behavior and play fighting (but not social investigation) following ethanol only in the familiar test situation and only at the highest dose, whereas adults showed inhibition of all forms of social activity in both contexts after the highest dose of ethanol, and in the familiar environment after the two highest doses. No age-related differences were found in blood alcohol concentrations assessed 30 min after ethanol administration. Conclusions Adolescent animals were more sensitive than adults to ethanol-induced social facilitation, but were less sensitive than adults to ethanol anxiolytic effects, as indexed by an ethanol-related reinstatement of social interactions in an unfamiliar, anxiogenic environment that typically decreases social activity. Adolescents were also less sensitive than adults to the suppression of social interactions seen at higher ethanol doses in both test situations. These adolescent-associated alterations in ethanol sensitivity are unlikely to be attributable to ontogenetic differences in ethanol pharmacokinetics, given that observed age-related changes included both suppressant and facilitatory effects, and that blood alcohol levels were similar in adolescent and adult animals. These findings demonstrate age-related differences in sensitivity to the effects of ethanol in a social milieu that vary dramatically with the context and particular ethanol consequences. The results suggest the importance of considering social and environmental factors as contributors to patterns of extensive alcohol use, particularly in adolescence.