The Role of Dopamine Receptor Subtypes in Reinforced Variability

Abstract

Variability in behavior can be measured and reinforced. However, the underlying neurological mechanisms of such variability are unknown. Dopamine is associated with reinforcement but its role in reinforced variability is also unclear. d Amphetamine has been proposed to induce both variability and stereotypy, so this drug was used as a probe to examine behavior under each of these components. The present study sought to examine how specific dopamine receptors, namely D1 and D2, may also influence variable responding. In Experiment 1, Long Evans rats were trained under a multiple VARY 8:4 FR 4 schedule. In the VARY 8:4 component, all four-response sequences that differed from previous 8 were reinforced. In the FR 4 component, all four-response sequences were reinforced. Discrimination between the two components was evidenced by high entropy (variability) in the VARY 8:4 component and low entropy in the FR 4 component. The effects of amphetamine on entropy depended on the baseline value of this measure of variability. When entropy was high (Vary 8:4 component) the effect was to reduce entropy, making behavior less variable. When variability was low and responding was more stereotyped, as during the FR 4 component, amphetamine increased variability. SKF 38393 administration decreased entropy only at doses that produced large reductions in response rate. There were dose-related increases in variability in the FR 4 component for the Quinpirole group. Entropy values in the FR 4 component approached those in the VARY 8:4 component for higher doses of Quinpirole. The present study suggests an association between dopamine and response variability as was evidenced by the effects of d amphetamine. It appears that these effects of amphetamine may have occurred because of its action on the dopamine D2 receptor. Experiment 2 used a variable interval schedule (VI 60”) to determine the effects of intermittent reinforcement on behavior in both the VARY 8:4 and FR 4 components. Discrimination between the two components disappeared and was evidenced by high entropy (variability) in the VARY 8:4 component and high entropy in the FR 4 component. Administration of d amphetamine had no effect on the behavior in either component.