HEART-RATE RESPONSES OF SPONTANEOUSLY HYPERTENSIVE RATS DURING AVERSIVE CLASSICAL-CONDITIONING

Heart rate (HR) responses of restrained spontaneously hypertensive (SHR) and normotensive (WKY) female rats were compared during aversive classical conditioning. Baseline HR of the SHR group was temporarily higher than that of the WKY group. For both groups, the directions of the HR-orienting response to the novel CS prior to conditioning as well as the HR-conditioned response during conditioning were decelerative. Although the magnitude of the orienting response was larger in the SHR group than in the WKY group, the conditioned responses of the two groups were nearly the same. It was suggested that the orienting response in both groups was due to inhibition of sympathetic activity in conjunction with increased vagal outflow. It was further suggested that the enhanced orienting response in the SHR group could be accounted for by the greater β-adrenergic tone in the resting HR of the SHR which, with inhibition of sympathetic tone, resulted in a relatively larger fall in HR. © 1979 Academic Press, Inc.