Shock avoidance but not DRL history reverses the effects of cocaine on punished behavior of squirrel monkeys

Abstract

A history of responding maintained by a shock-avoidance procedure can alter the effect of psychomotor stimulant drugs on punished responding. This study was designed to evaluate whether another type of historical intervention could also alter the effects of cocaine on punished responding and, as a result, clarify certain variables contributing to this effect. Lever pressing of four squirrel monkeys was suppressed by a punishment procedure consisting of a fixed-interval 5-min schedule of food presentation in which every 30th response also produced a 200-ms 5-mA electric shock. Cocaine (0.03-1.0mg/kg) had no effect on or reduced punished responding. Conditions were then changed and responding was maintained for several sessions by a differential reinforcement of low rate (DRL) schedule in which food was delivered only when one response followed another by at least 25s. The punishment schedule was then reinstated and the effects of cocaine redetermined; the dose-response curve was similar to that initially obtained. The monkeys then responded on a shock-avoidance schedule in which each response postponed the next scheduled shock for 25s; shocks occurred every 5s in the absence of responding. Subsequently, the shock-avoidance schedule was replaced by the punishment schedule and the effects of cocaine were redetermined. In contrast to the initial determination of the effects of cocaine on punished responding, and the effects obtained following training on the DRL schedule, cocaine then produced response rate increases or no change in rate at several doses that formerly reduced responding. These results demonstrate that the rate-decreasing effects of cocaine on punished responding may be reversed by a history of responding on a shock-avoidance schedule and also indicate that a history of responding on a DRL schedule is not sufficient to reverse the effects of cocaine. These data suggest that a history of responding under schedules, such as the DRL, that engender responding that is typically increased by psychomotor stimulant drugs, is not sufficient to reverse the effects of these drugs on punished responding. The reversal of the effects of cocaine on punished responding resulting from a history of avoidance responding appears to be attributable to factors other than the rate-increasing effect of cocaine on responding maintained by avoidance.