Dissociation of the anti-punishment activities of chlordiazepoxide and atropine using two heterogeneous passive avoidance tasks

The effects of chlordiazepoxide and atropine on the acquisition of passive avoidance learning in rats were compared in two superficially similar but theoretically distinct forms of the step down task in an attempt to dissociate behaviourally the disinhibiting effects of these two classes of drug. In a discrete trial procedure both chlordiazepoxide and atropine significantly retarded acquisition; on retention testing under saline treatment alone, the initial chlordiazepoxide group showed no change in behaviour while the initial atropine group showed a facilitation. In a continuous trial procedure, however, atropine but not chlordiazepoxide produced an increase in the total number of step downs; despite this, these groups showed acquisition at similar rates, though learning was not shown on retention testing under saline alone. These results enabled the two classes of drug to be distinguished. The nature of the heterogeneity between the two test paradigms is discussed, and results interpreted in terms of possible differential drug effects on punishment and escape components of the tasks.