Benzodiazepine effects on heart rate conditioning in the rabbit.

The present experiment was undertaken to assess the ways in which benzodiazepine administration alters heart rate responding during Pavlovian aversive conditioning in the rabbit. Each of three benzodiazepine compounds (chlordiazepoxide, flurazepam, diazepam) reliably attenuated the magnitude of the conditioned bradycardia response as compared to vehicle controls. Lower doses of two of these compounds significantly potentiated the conditioned bradycardia response. Benzodiazepine treatment did not significantly alter baseline heart rate, the expression and habituation of the heart rate orienting response, or heart rate responding during unpaired stimulus presentations. The effects of benzodiazepines under these conditions therefore appeared to be selective to those heart rate responses that were conditioned. These results are consistent with evidence suggesting the involvement of benzodiazepine-sensitive processes in the expression of emotional responses, including concomitant cardiovascular alterations.