Chlordiazepoxide and successive discrimination: different effects on acquisition and performance

Benzodiazepines have been reported to increase low rates of responding during a stimulus correlated with non-reinforcement while leaving prestimulus rates unaffected (successive discrimination). However, the results have been obtained by superimposition of the drug upon a discrimination which was learned in the absence of drug. The observed effects may therefore have been due to the sudden change in drug state (state-dependency) rather than to a specific action of the drug. The present experiments found that chronic administration of chlordiazepoxide (5 mg/kg, IP) impaired acquisition but not performance of successive discrimination. Intermittent administration of chlordiazepoxide impaired discrimination by increasing low rates of responding during the stimulus signalling non-reinforcement. This effect was obtained with saline-drug but not drug-saline state changes (asymmetric state-dependency). A final experiment showed that chronic administration of the drug did reduce well-learned inhibition resulting from signalled shock. It was concluded that chlordiazepoxide has not only pure anxiolytic but also state-dependent effects and that if successive discrimination depends on conditioned frustration it does so only while the discrimination is being learned.