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 (S_e), shock occurred on an RI schedule irrespective of the rat's behaviour; in the presence of the other (S_p) 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 S_e than in S_p, 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 S_p than S_e and eliminated the difference between the response rates controlled by the two stimuli.