Effects of phencyclidine, ketamine and MDMA on complex operant behavior in monkeys.

In one component of a multiple schedule, patas monkeys acquired a different four-response chain each session by responding sequentially on three levers in the presence of four numerals (acquisition). In the other component, the four-response chain was the same each session (performance). The response chain in each component was maintained by food presentation under a fixed-ratio schedule. After IM administration, phencyclidine, ketamine, and MDMA (3,4-methylenedioxymethamphetamine or "ecstasy") each produced dose-related decreases in overall response rate in both schedule components, though ketamine and MDMA were less potent (on a mg/kg basis) than phencyclidine. At high doses of each drug, the marked decrease in overall response rate was due primarily to a long initial pause. Ketamine was similar to phencyclidine in producing dose-related increases in percent errors in both schedule components, but the maximal error-increasing effect was considerably smaller with ketamine. This quantitative difference appeared to be related to the shorter duration of ketamine's effects on accuracy. Unlike phencyclidine and ketamine, MDMA had no effect on accuracy in either acquisition or performance. The results indicate that MDMA disrupts complex operant behavior to a lesser extent than phencyclidine-type drugs.