Diffuse Hypothalamic System for the Regulation of ACTH Secretion1

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Abstract
A study has been carried out in the rat to determine the extent of the hypothalamic area which is concerned with the secretion of ACTH. The hypothalamus of the rat was divided into 4 zones extending from the optic chiasm to the mammillary bodies, and bilateral electrolytic lesions were placed in several combinations so that the effectiveness of small and large lesions in various regions of the hypothalamus could be compared. The peripheral plasma corticosterone response to ether stress was used to evaluate the deficit resulting from a particular lesion. It was found that a significant impairment of response occurred following placement of a small lesion in almost any region at the base of the hypothalamus between the optic chiasm and the mammillary bodies. Larger lesions produced greater impairment of response and extensive hypothalamic destruction resulted in a maximal deficit which was nonetheless compatible with a response to ether of the order of 25–30 % of normal. These results indicate that the entire region of the ventral hypothalamus extending from the optic chiasm to the mammillary bodies is involved in ACTH secretion and that a diffuse hypothalamic nucleus or network exists for the control of ACTH secretion rather than a localized discrete center. Since graded hypothalamic destruction resulted in graded pituitary ACTH response, a comparison was made between lesions placed in the hypothalamus and lesions placed directly in the pituitary gland. A small amount of pituitary tissue in circulatory contact with an intact hypothalamus secreted a greater amount of ACTH than did a larger pituitary gland which was in the vicinity of a damaged hypothalamus.