Comparison of the effects of buspirone and chlordiazepoxide on successive discrimination

Buspirone is a novel anxiolytic which does not share the muscle relaxant, anticonvulsant and sedative properties of classical anxiolytics such as the benzodiazepines. It has variable effects in conflict tasks based on shock which normally show consistent effects with classical anxiolytics. The present experiment investigated the effects of buspirone on successive discrimination, a conflict task employing omission of reward rather than shock. Buspirone (3.3, 1.1 and 0.3 mg/kg, IP) and chlordiazepoxide (5 and 20 mg/kg, IP) were administered to separate groups of rats throughout acquisition of a visual successive discrimination. Chlordiazepoxide released nonrewarded responding in a dose-related fashion. The effects of buspirone were qualitatively similar in releasing response suppression but were both less in magnitude and less clearly related to dose. The experiment shows that the action of buspirone in successive discrimination tasks does not depend on the use of shock but, rather, appears to be a genuine failure to fully release behavioural inhibition.