Early adolescents show enhanced acute cocaine-induced locomotor activity in comparison to late adolescent and adult rats.

Initiation of drug use during adolescence is associated with an increased probability to develop a drug addiction. The present study examined dose-response effects of cocaine (0, 5, 10, or 20 mg/kg, i.p.) on locomotor activity in early adolescent (postnatal day (PND) 35), late adolescent (PND 45), and young adults (PND 60) by measuring total distance moved (TDM) and frequency of start-stops. In response to 20 mg/kg cocaine, early adolescents showed the greatest cocaine-induced increase in TDM in comparison to late adolescent and adult rats. At this same dose, early adolescents showed the greatest cocaine-induced attenuation of start-stops relative to older rats. Results suggest that early adolescents engage in more cocaine-induced locomotor activity and less stationary behavior indicating that early adolescents are more sensitive to locomotor activating effects of high dose cocaine than older rats. (c) 2008 Wiley Periodicals, Inc.