Pituitary Neuropeptides, Emotional Behavior and Cardiac Responses

Abstract

Pituitary neuropeptides related to adrenocorticotropic hormone (ACTH) or vasopressin affects brain functions and modifies behavioral adaptation. The effect of these peptides on cardiac responses accompanying emotional behavior has been studied in the rat in a passive avoidance situation. Passive avoidance behavior is accompanied by tonic and phasic changes in cardiac rhythm. Tonic changes appear as a decrease in mean heart rate as a consequence of emotional experience. Phasic changes are related to approach-avoidance movements in the conflict situation and appear as an abrupt decrease in heart rate or arrhythmias. Pituitary peptides related to ACTH facilitates emotional behavior and tonic heart rate (HR) response appears as tachycardia. Analysis of R-R interval distribution histograms indicate increased arousal and consequent sympathetic activation. Neuropeptides related to vasopressin also facilitate passive avoidance behavior but a more pronounced deceleration of HR accompanies behavior and the irregularity of cardiac rhythm increases. Genetic absence of vasopressin in rats with hereditary hypothalamic diabetes insipidus leads to a deficit in behavioral expression of emotional experience; phasic heart rate changes are absent, but tonic response is present. Vasopressin and related peptides normalize behavioral and cardiac deficits.