Sensitization to social anxiolytic effects of ethanol in adolescent and adult Sprague-Dawley rats after repeated ethanol exposure

Ontogenetic studies using a social interaction paradigm have shown that adolescent rats are less sensitive to anxiolytic properties of acute ethanol than their adult counterparts. It is not known, however, whether adaptations to these anxiolytic effects on repeated experiences with ethanol would be similar in adolescents and adults. The present study investigated sensitivity to the anxiolytic effects of ethanol in adolescent and adult male and female Sprague-Dawley rats after 7 days of exposure (postnatal day [P] 27-33 for adolescents and P62-68 for adults) to 1 g/kg ethanol or saline (intraperitoneally]) and in animals left nonmanipulated during this time. Anxiolytic effects of ethanol (0, 0.75, 1.0, 1.25, and 1.5 g/kg for adolescents and 0, 0.25, 0.5, 0.75, 1.0, and 1.25 g/kg for adults in experiments 1 and 2, respectively) were examined 48 h after the last exposure using a modified social interaction test under unfamiliar test circumstances. At both ages, repeated ethanol exposure resulted in the development of apparent sensitization to anxiolytic effects of ethanol, indexed by enhancement of social investigation and transformation of social avoidance into social indifference or preference and expression of tolerance to the socially inhibiting effects induced by higher ethanol doses. Evidence for the emergence of sensitization in adults and tolerance at both ages was seen not only after chronic ethanol but also after chronic saline exposure, suggesting that chronic manipulation per se may be sufficient to alter the sensitivity of both adolescents and adults to socially relevant effects of ethanol.