Hypothalamic involvement in the pituitary adreno-cortical response

Abstract

There is now general agreement that the central nervous system, or, more particularly, the hypothalamus, is capable of stimulating the anterior pituitary gland to secrete adrenocorticotrophic hormone (ACTH) whenever the individual is exposed to a stressing agent. This ACTH, by its effect on the adrenal cortical secretion, brings about the adaptation of the body (general adaptation syndrome). On the other hand, there is no agreement concerning the location of the specific region, if any, in the hypothalamus or diencephalon which brings about the secretion ofACTH. Also it is not known whether this response is brought about by direct or indirect activation. Anand, Raghunath, Dua & Mohindra (1954) localized the hypothalamic centres in the rat which control the nervous phase ofACTH secretion in response to stress. This was done by determining the eosinopenic response to stress stimuli before and after producing small electrolytic lesions in the hypothalamus. These areas are located in the medial part of the anterior hypothalamus and the area just caudal to it, i.e. antero-medial part of the median eminence. de Groot & Harris (1950) and Porter (1953), however, by experiments on rabbits and cats respectively, localized the effective areas in the posterior part of the tuber cinereum and mammillary body. Studies of Hume and Wittenstein, reported by Hume (1952), in dogs, on the other hand, located this area in the anterior portion of the median eminence, but did not localize it more precisely. The present investigation was undertaken to determine the localization of this area in the cat by stimulation of the ypothalamus with implanted electrodes. The results have tended to confirm the previous observations, made as a result of ablation studies in the rat (Anand et al. 1954).