Persistence of the ability of amphetamine preexposure to facilitate acquisition of cocaine self-administration.

This study assessed the enduring effects of amphetamine preexposure on the subsequent reinforcing effects of cocaine. Rats received nine daily injections of either d-amphetamine SO4 (2.0 mg/kg, IP) or vehicle 45 days prior to testing of the acquisition of cocaine (0.25 mg/kg/infusion) self-administration. The latency to acquire reliable cocaine self-administration was shorter (day 3) in the amphetamine-preexposed rats than in the vehicle-preexposed rats (day 6). These data are comparable to those observed when testing was carried out 1 day following the treatment. In previous studies, shorter latencies to acquisition also occurred when the training dose of cocaine was increased, suggesting that the treatment had sensitized rats to cocaine's reinforcing properties. These effects of amphetamine exposure persist for 45 days following treatment, which suggest a long-lasting phenomenon.