Figure 4.

Cocaine re-exposure produces tolerance to the locomotor-activating effects of cocaine. A, Experimental timeline. Rats performed cocaine self-administration followed by a 60 d abstinence period before subsequent re-exposure to a cocaine challenge (15 mg/kg, i.p.). B, Rats with a history of cocaine self-administration show tolerance to the locomotor activating effects of cocaine, with no change in spontaneous locomotor activity. C, Area under the locomotor activity curve following the cocaine challenge is decreased in rats with a history of cocaine self-administration. *p < 0.05, **p < 0.01, ***p < 0.001 versus re-exposure group. Control, n = 5; re-exposure at Day 60, n = 6. Error bars indicate ± SEM.