Does a rat's exposure to cocaine during adolescence affect its response to cocaine in adulthood?

Many contradictory responses to cocaine have been observed in adolescent rats as compared to adult rats including increased and decreased activity levels. Previous studies reported that adolescent exposure to cocaine affects adulthood response to cocaine. However, most studies compare age differences in cocaine response in separate groups of adolescents and adults. The present study assessed the acute and chronic dose effects of cocaine on the same rats during their adolescent period and again when they matured into young adults. Forty-eight female Sprague-Dawley rats were randomly divided into four treatment groups. Group 1 served as our control and received saline for 6 consecutive days, 3 days washout, and a day of rechallenge. Groups 2-4 received either 3.0, 7.5, or 15 mg/kg cocaine respectively for 6 consecutive days, 3 days washout, and a day of rechallenge. Adolescent rats did not show an acute or chronic response to 3.0 mg/kg cocaine whereas as adults they responded to the acute treatment and moreover became sensitized to this dose. The 7.5 and 15 mg/kg cocaine doses significantly increased the locomotor activity following the initial (acute) injection and therefore induced sensitization in adolescents, whereas as adults these doses elicited different responses. The same rats as adults developed tolerance to the 7.5 mg/kg cocaine and failed to respond significantly to the 15 mg/kg cocaine dose. The results of this study indicate that chronic cocaine exposure during adolescence alters the same rats' responses to cocaine during their adulthood.