Discrimination of response-contingent and response-independent shock by rats: Effects of medial and lateral septal lesions and chlordiazepoxide

Abstract

Sprague-Dawley rats sustained electrolytic lesions to the medial septal or lateral septal areas. They were allocated to lesion conditions on the basis of electrophysiological criteria (loss or persistence of hippocampal theta rhythm) and subsequently checked histologically. They were trained to press a lever for sucrose reward on a random interval schedule and were presented while lever pressing with two stimuli, each associated with a different schedule of shock delivery: in the presence of one stimulus (conditioned suppression), shocks occurred on a random-interval schedule irrespective of the rat's behavior; in the presence of the other stimulus (discriminated punishment) shocks were programed 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 presence of the two stimuli, thus demonstrating a discrimination between response-contingent and response-independent shock. The majority responded more in conditioned suppression than in punishment. Medial but not lateral septal lesions significantly improved the rat's capacity to discriminate between response-contingent and response-independent shock. These behavioral effects were well correlated with the effects of medial and lateral septal lesions on hippocampal theta. Chlordiazepoxide hydrochloride impaired the discrimination of response-contingent and response-independent shock by alleviating response suppression more in punishment than conditioned suppression; this drug effect was not influenced by septal lesions.