Cardiovascular Responses to Avoidance Conditioning in the Dog: Effects of Beta Adrenergic Blockade

Five laboratory dogs were trained to press a response panel to postpone shocks during 1-hr free-operant avoidance conditioning sessions. In addition, each dog was confined in the experimental environment for 1 hr immediately prior to each avoidance session. During these 2-hr sessions, blood pressure and heart rate were monitored continuously from indwelling catheters. After repeated exposure to the schedule, the onset of the avoidance contingency elicited acute increases in systolic and diastolic pressure and heart rate, which were maintained throughout the session. During the preavoidance interval, systolic and diastolic pressure increased gradually while heart rate decreased. Blockade of beta adrenergic receptor activity in these behaviorally-trained dogs by infusions of propranolol was associated with a significant attenuation of the tachycardia normally maintained during avoidance. Beta blockade did not prevent the rise in blood pressure or fall in heart rate during preavoidance. The results are consistent with the view that the cardiovascular pattern sustained during avoidance is mediated by activation of the sympathetic nervous system, but that the progressive change in cardiovascular activity during preavoidance intervals is mediated by other than sympathetic influences.