Mean total distance traveled scores (+SEM) of preweanling rats (n = 8 per group) given a challenge injection of cocaine (20 mg/kg, ip) prior to placement in activity chambers on PD 20. These are the same rats as described in Figures 2 and 3. The cocaine-activity groups (dark gray bars) were pretreated with cocaine (10–40 mg/kg, ip) before being placed in the activity chamber on PD 19, while the cocaine-home groups (light gray bars) were injected with cocaine 30 min after being returned to the home cage. The home-restricted groups (open bars) were pretreated with cocaine (10–40 mg/kg, ip) while being maintained in the home cage on PD 19. *Significantly different from the other cocaine groups (Drug Dose main effect, p < .05). †Significantly different from the home-restricted condition (Condition main effect, p < .05).