Effects of scopolamine, amphetamine and benzodiazepines on conditioned suppression

Conditioned suppression of operant behavior was produced by preshock stimuli (i.e., stimuli that precede the noncontigent presentation of electric shock), or prereward stimuli (i.e., stimuli that precede the noncontingent presentation of food) in rats and squirrel monkeys responding on a variable interval schedule of food reinforcement. Benzodiazepine derivatives and amphetamine differentially affect conditioned reactions which are elicited by preshock and prereward stimuli. Conditioned suppression to prereward stimuli were unaffected by chlordiazepoxide, diazepam, scopolamine hydrobromide and scopolamine methyl nitrate but clearly reduced by amphetamine. On the other hand, chlordiazepoxide attenuated the conditioned suppression to preshock stimuli whereas amphetamine, scopolamine hydrobromide and scopolamine methyl nitrate had no significant effects in this paradigm. The results suggest that the effects of drugs on conditioned suppression cannot be interpreted, a priori, in terms of selective effects on mechanisms related to emotional behavior or inhibition.