Effects of chlordiazepoxide on heart rate and behavioural suppression in pigs subjected to operant conditioning procedures

Two groups of four pigs were subjected to a punishment discrimination (conflict) or to a non-reinforcement procedure. Conflict behaviour was evidenced by the suppression of operant responding and the occurrence of a marked decrease in heart rate during the presentation of the conditioned stimulus. Pigs in the non-reinforcement procedure showed no consistent changes in heart rate although an important decrease occurred in response rate. Chlordiazepoxide was administered in order to establish whether it would attenuate the response suppression in either procedure. The drug produced a weak attenuation of conflict in terms of the operant and heart rate responses at the maximum dose used (20 mg/kg) and a small disinhibiting effect on the non-reinforced responding at 10 mg/kg. Such effects were less clear-cut than usually reported in other species.