COMPLETE AND PERMANENT ELIMINATION OF THE HYPOTHALAMIC THERMOGENIC MECHANISM WITHOUT AFFECTING THE ADEQUACY OF THE HEAT LOSS MECHANISM

Abstract

The ability of normal and operated dogs to tolerate cold and hot environments was calibrated by subjecting them to several test environmental temps. for a standard 8-hr. interval. Unoperated long-haired dogs tolerated both cold and hot environments slightly more effectively than did the short-haired dogs. The animal''s ability to prevent a fall in rectal temp. when it was subjected to ordinary or cool environmental temps. was completely eliminated by any procedure that severed the caudal connections of the entire hypothalamic gray. If only a small amt. of the caudal portion of this gray remained undisturbed, considerable of this ability was retained. Evidence was encountered which indicated that at the hypothalamic level there are separate neutral elements for the shivering and non-shivering thermogenic functions. Certain "ahypothalamic and midbrain" dogs retained sufficient heat loss regulating ability to combat successfully an environmental temp. of 38[degree]C for an extended period of time. In these there was a complete elimination of all heat maintenance powers with retention of an adequate heat loss regulation. Heat loss powers were markedly impaired in certain dogs which retained considerable heat maintenance ability by virtue of intactness of the caudal extent of the hypothalamic gray.