Abstract

Rhesus monkeys were studied during daily three-hour sessions in which every 10th key press (response) produced an intravenous cocaine injection. Cocaine doses from 0.2 down to 0.05 mg/kg/injection maintained stable responding. When monkeys were maintained at the 0.05 mg/kg/injection cocaine dose, sessions were conducted during which responses produced either saline, d-amphetamine, imipramine, morphine or chlorpromazine injection (substitution sessions) rather than cocaine injections. Response rate over successive saline-substitution sessions gradually decreased. Stable responding, at rates higher than saline-substitution responding, was well maintained during successive substitution sessions, by injections of 0.01 to 0.05 mg/kg of d-amphetamine and by injections of 0.025 to 0.5 mg/kg of morphine. Imipramine, at injection doses of 0.05 to 0.5 mg/kg, failed to maintain rates of responding different from those during saline substitution. Response rates during and after chlorpromazine substitution (0.05-0.5 mg/kg/injection) were markedly suppressed, indicating that chlorpromazine has aversive or punishing properties.