Sensitization to cocaine's reinforcing effects produced by various cocaine pretreatment regimens in rats.

A number of studies have demonstrated sensitization to the behavioral effects of cocaine following pretreatment. In most cases, pretreatments have been administered in the test environment. The present study determined the effects of home-cage administrations of cocaine on the acquisition of cocaine self-administration. Initial groups established that the latency to acquisition of cocaine self-administration varied inversely with dose. The effect of cocaine pretreatment on latency to acquisition of cocaine self-administration (0.25 mg/kg/infusion) was then determined in other groups. On each of 5 pretreatment days, separate groups received home-cage administrations of cocaine as either a single injection (20.0 mg/kg), or two (20.0 mg/kg) or three (10.0 mg/kg) injections separated by 1 h. Testing commenced 3 days following the last of the pretreatments. Only the pretreatment consisting of two daily injections of 20.0 mg/kg cocaine decreased the latency to acquisition of self-administration. These data are consistent with a sensitized response to cocaine's reinforcing effects and provide minimum pretreatment conditions for its development.