Evidence for cocaine dependence in monkeys following a prolonged period of exposure.

The behavioral consequences of prolonged continuous exposure to cocaine were examined in rhesus monkeys. Operant behavior was sampled for 0.5 h every 6 h, and cocaine was continuously infused through an intravenous catheter. Cocaine (4.0-32 mg/kg/day) initially caused reductions in the rate of responding for food and tolerance developed to this effect. When the infusion of cocaine was terminated following a period of exposure during which cocaine dose was escalated to 32 mg/kg/day, there was a marked suppression of operant behavior, lasting as long as 72 h, as well as observable changes in behavior (e.g., hyporesponsiveness). This is the first demonstration of behavioral disruptions following discontinuation of cocaine exposure and suggests that the preparation will be a useful animal model for further examining the possibility that exposure to cocaine can induce dependence.