• Sprague–Dawley;
  • adolescent rat;
  • dopamine;
  • limbic system;
  • drug abuse


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. © 2008 Wiley Periodicals, Inc. Dev Psychobiol 50: 127–133, 2008.