Abstract

Cocaine was shown to serve as a reinforcer for the rat. The effects of different infusion doses and fixed-ratio schedules on cocaine self-administration were studied. Within the range of doses that maintained responding, the response rate was found to vary inversely as a function of drug dose per infusion (reinforcement magnitude) and directly as a function of size of the fixed ratio. Outside this range, low doses produced ragged performance and high doses caused responding to cease entirely. In general, ratio performance was somewhat dependent on reinforcement magnitude, with higher ratios being achieved by intermediate and higher drug doses. Food reinforcement under conditions resembling those used with cocaine also yielded an inverse relationship between reinforcement magnitude and response rate, reconciling what appeared to be a major difference between the reinforcers. The most striking characteristic of cocaine-reinforced behavior was long but regularly spaced pauses after reinforcement. Comparable pauses were obtained in food-reinforced fixed-ratio performance after cocaine infusion, suggesting the effect may be due at least in part to performance disruption produced by the drug.