Pharmacological studies of behavioral influences on cardiovascular function

Squirrel monkeys, prepared with chronic arterial and venous catheters, responded (pressed a key) under fixed-ratio schedules of termination of a stimulus associated with electric shock or under fixed-ratio schedules of food presentation. Although there was no necessary correlation between schedule-controlled responding and cardiovascular changes, pronounced elevations in both heart rate and blood pressure occurred during and just after brief periods of fixed-ratio responding. These episodic increases in blood pressure and heart rate were as marked under schedules of food presentation as under schedules of stimulus-shock termination. Thus, these episodic changes appear to be more dependent upon the schedule-controlled behavior than upon the type of event maintaining the behavior. Pharmacological studies indicated that under the conditions of the behavioral experiments the squirrel monkey has a relatively high degree of cardiac sympathetic tone; however, blood pressure elevations produced by administration of 1-norepinephrine were associated with an increased parasympathetic tone and decreased heart rate. The reflex bradycardia induced by 1-norepinephrine was inhibited during periods of schedule-controlled responding, suggesting that environmental and behavioral factors can not only modulate the parameters of physiological variables but also modulate this basic cardiovascular control system.