Learning of physiological responses .2. Classical conditioning of the baroreflex

The baroreflex can be classically conditioned. In neuromuscular blocked (NMB) rats, electrical stimulation of the aortic depressor nerve (ADN) and dopamine-produced blood pressure rise were effective unconditioned stimuli (UCS) for auditory discriminative classical conditioning. The conditioned response (CR) pattern (bradycardia, vasodilatation, and hypotension > 10 torr) closely resembled that of the unconditioned baroreflex. Conditioned stimulus (CS) specificity was demonstrated by discrimination of baroreflex-associated and nonassociated auditory stimuli, and also by elaborating depressor and presser CRs to auditory CSs, which respectively had been associated with either baro-afferent (depressor) or tail-shock (presser) UCSs. The conditioned-baroreflex-magnitude increased with trials. These findings support quantitative models in which CRs interact with and calibrate the gain and dynamic properties of natural reflexes.