The Hypothalamus and Heat Regulation

Abstract

Isenschmid and Schnitzler 1 localized the chief central mechanism for the control of body temperature in the hypothalamus by demonstrating that a hypothalamic rabbit heat regulated, whereas, a midbrain preparation did not. Would extirpation of the hypothalamus alone without injury to other parts of the brain-stem render the animal incapable of heat regulating? In a few isolated cases in high mid-brain preparations, typical panting and vaso-dilation was readily elicited and persisted at relatively low rectal temperatures 2 ; however, subsequent preparations were made in which this response could not be obtained under any condition. It therefore seemed probable to us that the “heat regulating center” was really in the cephalic mid-brain and was consistently spared functionally only by a transection passed ahead of the hypothalamus and rarely by a section passing nearer to it caudally. By the lateral approach (elevation of the temporal pole) the hypothalamus has been successfully sectioned free from its cephalic, dorsal, and caudal connections with the brain stem with no resultant hemorrhage, and without disturbing the blood supply to adjacent brain tissue.

The hypothalamus was sectioned free from its connection on one side (unilateral removal) without disturbing bilateral heat regulation so far as could be determined grossly. An incomplete section which crossed the mid-line to involve the opposite half of the stem, impaired the power of the animal to maintain body temperature. Thus a cat with approximately a three-quarter section maintained a rectal temperature of 36°C. housed in an unheated cage. However, when put in the ice box its rectal temperature fell slowly in spite of the presence of shivering. This condition supervened 3 months postoperative in the same state as the first week after operation. The animal panted typically and vigorously when heated.