Conditioned heart rate response: testing under anaesthesia in rats.

Classically conditioned heart rate response was studied in anaesthetized rats. Rats were conditioned with photic stimuli followed by electric tail shocks in a conscious state and tested under anaesthesia for conditioned heart rate change. Testing photic stimuli evoked a transient bradycardia in about one-third of testing trials. Magnitude of the bradycardia was significantly greater in conditioned rats than that in untrained or control rats trained with electric tail shocks followed by photic stimuli. The difference was found to be mainly due to the difference in amplitude of individual bradycardia response rather than that in frequency of occurrence of the response. Testing stimuli also evoked a slight and sustained tachycardia, but magnitude of the tachycardia in conditioned rats did not differ significantly from that in control or untrained rats. These results suggest that effects of classical conditioning on autonomic functions can be detected and studied under anaesthesia.