Studies of the role of the central nucleus of the amygdala in controlling cardiovascular functions.

Studies on cats anesthetized with a mixture of chloralose and Nembutal addressed the effects of high-frequency stimulation (100 impulses/sec) of the central nucleus of the amygdala on bioelectrical activity in two postganglionic sympathetic nerves-the inferior cardiac nerve and the vertebral branch of the stellate ganglion, which innervate the coronary vessels and the vessels of the anterior thorax respectively. The central nucleus of the amygdala was found to have differential, selective effects, in most experiments producing increases in the amplitude of integrated activity in the inferior cardiac nerve and decreases in the amplitude of biopotentials in the vertebral nerve. In a few experiments, a second type of modulation of the activities of these two postganglionic nerves was seen, with selective inhibition of activity in the inferior cardiac nerve and an accompanying increase in activity in the vertebral nerve. Stimulation of the central nucleus of the amygdala induced significant increases in systemic arterial blood pressure. The role of the central nucleus of the amygdala in the development of experimental neurogenic hypertension was studied in a series of chronic experiments on rats; these established that rats subjected to bilateral electrolytic lesioning of the central nucleus of the amygdala prevented the development of neurogenic hypertension induced by daily imposition of stress for four weeks for induction of operant aversive conditioned reflexes, which was not the case in control rats. The role of the central nucleus of the amygdala in the regulation of vascular tone is discussed.