Female and male rats in late adolescence differ from adults in amphetamine-induced locomotor activity, but not in conditioned place preference for amphetamine

Abstract

Rodent models display differences in drug-induced behaviour between prepubertal/young adolescents and adults that parallel developmental differences in people; however, little is known as to when the transition to 'adultlike' behaviour occurs. We investigated the differences in locomotor and reward responses to amphetamines in male and female rats in late adolescence and compared them with corresponding adult responses. Long-Evans rats were tested for locomotor activity and conditioned place preference (CPP) for amphetamine (0.25, 0.5 or 1.0 mg/kg), beginning at 45 or 69 days of age. Adolescent female rats moved less to the first injection of amphetamine compared with adult female rats irrespective of dose, whereas adolescent male rats did not differ from adults. Adolescent female rats significantly increased locomotor activity in response to subsequent injections of amphetamine at all three doses, whereas such sensitization was only found at the highest dose for adult female and male rats. No effect of repeated injections at any dose was observed in adolescent male rats. No age differences were observed in CPP, but female rats showed greater CPP during the dioestrous than during the oestrous phase of the cycle. These data suggest that differences in neural systems underlying some behavioural responses to amphetamine continue to mature postpubertally into late adolescence in a sex-specific manner.