Effects of Dopamine Reuptake Inhibitors on Food- and Cocaine-Maintained Responding: I. Dependence on Unit Dose of Cocaine

The effects of the high-affinity dopamine reuptake inhibitor, GBR 12909, were studied on responding maintained under multiple fixed ratio schedules of food and cocaine delivery in rhesus monkeys (Macaca mulatta). GBR 12909 decreased rates of responding maintained by both events in a dose-related manner, however large decreases in cocaine-maintained responding could be obtained with doses of GBR 12909 that had little effect on food-maintained responding. This behaviorally selective effect of GBR 12909 on cocaine-maintained responding was inversely related to the unit dose of cocaine. When responding was maintained by low doses of cocaine, GBR 12909 (1 mg/kg) decreased cocaine-maintained responding almost completely. When responding was maintained by the highest dose, the same dose of GBR 12909 had little effect on responding. To the extent that higher doses of cocaine may be expected to be more reinforcing, the current results suggest that the effect of GBR 12909 on cocaine-maintained responding was determined by the reinforcing efficacy of the unit dose of cocaine.