Although adolescents respond less to alcohol's aversive effects, they are more sensitive to many positive and rewarding effects of alcohol. For instance, alcohol mediates appetitive second-order conditioning in adolescent but not adult rats, suggesting greater reinforcing properties of alcohol [19]. Adolescents, but not adults, will self-administer enough alcohol to induce tachycardia, an effect linked to alcohol's hedonic value [20,21]. Thus, the rewarding effects of alcohol may be greater in adolescents than adults, which may promote future alcohol seeking behavior [19-21]. This idea is supported by studies where alcohol exposure during adolescence enhanced novelty seeking and influenced conditioned place preference in adulthood, both of which are predictors of alcohol seeking behavior [22,23]. Adolescents are also more sensitive to the social facilitation effects of alcohol, an important factor in adolescent human expectancies about alcohol and adolescent drinking behavior [24]. A mere passive social interaction with an intoxicated rat increases alcohol self-administration [25], which supports that the enhanced positive effects of alcohol in adolescence can drive alcohol consumption in adulthood [22,23]. The underlying neurobiology responsible for the adolescent's enhanced sensitivities likely involves the mesocorticolimbic reward system, recent reports on which are discussed below.
