Adolescence has been conservatively defined as the period between postnatal day 28 and postnatal day 42 (P28 – P42; e.g., Spear, 2000), although some adolescent typical characteristics may last, particularly in males, until P60 or so (Smith, 2003; Spear, 2000). During adolescence animals exhibit enhanced levels of basal behavioral activation as well as greater expression of conspecific-directed behaviors, including play behavior (Panksepp, 1981; Spear & Brake, 1983). They also show age-specific patterns of response to several drugs, notably psychostimulants and ethanol (Adriani & Laviola, 2000; Spear, 2000; Spear & Varlinskaya, 2005). For instance, expression of amphetamine, nicotine, cocaine, and ethanol-mediated conditioned taste aversions has been reported to be not as strong in adolescent rats as in older animals (Infurna & Spear, 1979; Schramm-Sapyta et al., 2006; Varlinskaya et al., 2006). Conditioned aversion induced by lithium chloride, an emetic agent, is also reduced in adolescents relative to older subjects (Schramm-Sapyta et al., 2006). Taken together, these results suggest that adolescents may exhibit an increased threshold for the acquisition of aversive motivational learning.
