DESCRIPTION (provided by applicant): While the exact cause of the increase in ethanol consumption during adolescence is not known, age differences in tolerance development and sensitivity to ethanol's rewarding effect may play a contributory role. The proposed research will examine age differences in tolerance to ethanol's effects on the autonomic system as well as several potential markers of ethanol's hedonic effects between adolescent and adult rats. Using a 2-hour limited access paradigm, tolerance to ethanol's autonomic effects as well as the effects of ethanol on markers of dopamine functioning within brain pathways implicated in reward will be measured in animals of both ages. This testing paradigm will provide a unique assessment of age differences in these factors as previous work in this area has used experimenter-administered ethanol but work in our laboratory has indicated that mode of ethanol administration may differentially impact adolescents and adults. Adolescents are expected to show less acute sensitivity to ethanol, faster tolerance development and less dopaminergic activity following chronic ethanol exposure than adults, supporting the hypothesis that younger animals consume more ethanol than adults in part because of their relative insensitivity to its effects.