CONTEXT-DEPENDENT CROSS-SENSITIZATION BETWEEN COCAINE AND AMPHETAMINE

We investigated the effect of amphetamine pretreatment on the locomoto r response to subsequent cocaine challenge. Rats were administered eit her 0.75 mg/kg amphetamine in a testing environment and saline in thei r home cage, saline in the testing environment and 0.75 mg/kg amphetam ine in their home cage, or saline in both the testing environment and home cage. After 5 pairings of drug to environment, conditioning was t ested by administration of a saline injection. Both amphetamine treate d groups exhibited increased locomotion in response to saline injectio n. After the eighth session of the pairing regimen, all animals were a dministered 5 mg/kg cocaine in the test environment and their behavior measured for 30 min. Sensitization to cocaine was observed only in ra ts with previous amphetamine exposure in the testing environment. Ther e was no difference between groups in whole brain, striatal, or plasma levels of cocaine. The data support the hypothesis that sensitization is independent of brain cocaine levels.