Phencyclidine in combination with d-amphetamine: differential effects on acquisition and performance of response chains in monkeys.

In one component of a multiple schedule, patas monkeys acquired a different four-response chain each session by responding sequentially on three keys in the presence of four geometric forms (learning). 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. Errors produced a brief timeout but did not reset the chain. When phencyclidine was administered alone, overall response rate decreased and percent errors increased in both components with increasing doses. d-Amphetamine alone generally decreased rate and increased errors in learning, but increased rate and had no effect on accuracy in performance. When phencyclidine was administered in combination with d-amphetamine, the phencyclidine dose-effect curves tended to shift to the left as the dose of d-amphetamine was increased. The extent to which the curves shifted, however, depended on both the schedule component and the behavioral measure. For example, with accuracy, the shift was more evident in learning than in performance. Combinations of phencyclidine with a high dose of d-amphetamine generally produced supra-additive effects: i.e., the effects on rate and accuracy were greater than expected from simple addition of the effects of each drug given alone.