Discrimination of response-contingent and response-independent shock by rats: effects of chlordiazepoxide HCl and sodium amylobarbitone.

Abstract

Rats, trained to press a lever for sucrose reward on a random interval (RI) schedule, were presented while lever-pressing with two stimuli, each associated with a different schedule of shock delivery: in the presence of one stimulus (Se), shock occurred on an RI schedule irrespective of the rat's behaviour; in the presence of the other (Sp) shocks were programmed by the same schedule but delivered only when the rat pressed the lever. Both stimuli suppressed lever-pressing. In addition, the rats developed significantly different response rates in the two stimuli, thus demonstrating a discrimination between response-contingent and response-independent shock. Group data showed faster responding in Se than in Sp, supporting the view that response-contingent shock produces greater suppression than response-independent shock. Individual animal analyses, however, demonstrated that this was the case in the majority of animals, but not in all. Response suppression was alleviated by amylobarbitone sodium (15 mg/kg) or chlordiazepoxide HCI (5 mg/kg); the latter drug alleviated suppression significantly more in Sp than Se and eliminated the difference between the response rates controlled by the two stimuli.