Differential effects of chlordiazepoxide and d-amphetamine on responding maintained by a DRL schedule of reinforcement.

Abstract

Rats pressed a lever and obtained food pellets on a schedule of differential reinforcement of low rate (DRL) which required that responses were spaced at least 15 sec apart in order for them to produce reinforcement. When responding had stabilised at slow and steady rates the effects of d-amphetamine and chlordiazepoxide were assessed. Low doses of both drugs increased response rates while higher doses decreased them. Reinforcement frequency showed a dose related decrease after both drugs. When interresponse times (IRTs) were analysed it was found that both drugs shifted the peak of the distribution towards shorter IRTs but that chlordiazepoxide also produced a specific increase in the percentage of responses after very short IRTs (bursts). When IRTs were divided into those following a reinforced response (hit) and those following a non-reinforced response (miss) it was found that bursts normally followed only misses and chlordiazepoxide consistently increased the number of bursts following misses only. Amphetamine did not affect bursts in any consistent way.