Effect of sound on the hypothalamic-pituitary-adrenal axis

¹ Departments of Medicine and Anatomy, School of Medicine, University of California, Los Angeles, and the Neurophysiology Laboratory, Veterans Administration Hospital, Sepulveda, California

In the rat, the stress of exposure to continuous, high intensity sound (130 db, 220 cycles/sec) evoked a pattern of adrenocortical response consisting of an initial, immediate high rate of hormone secretion (determined in adrenal venous blood by chromatographic techniques), a subsequent period of depression of corticosterone output to normal or subnormal levels, and eventual return of hormone secretion to high levels. The period of suppressed corticosterone secretion appeared dependent upon the continuous presence of the stressor for a period of 12 hr. The data suggest that the depression of corticosterone secretion is due to inhibition of secretion of ACTH. Bilateral surgical destruction of the middle ear of the animals abolished the response pattern. After placement of bilateral lesions in the posterior hypothalamus, the resting rate of corticosterone secretion was significantly greater than normal and the response pattern was markedly attenuated.