Central Control of Heat Loss Mechanisms in the Gost.

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Abstract
Summary.: 1. In non‐anesthetized goats, the existence of a discrete “heat loss centre” has been demonstrated by electrical stimulation of the brain stem using modified Hess technique and the effects of electrical stimulation of this “centre” have been compared with those of exposing the goat to a hot environment.2. The “centre” occupies the dorsal half only of the area between the anterior commissure and the optic chiasma and extends laterally to the medial edge of the internal capsula. Posteriorly it probably does not extend into the hypothalamus proper.3. Stimulation of the “centre” with damped square wave stimuli at 50 cycles per second and 0.5 to 1.5 V causes vigorous polypneic panting and cutaneous vasodilatation in the ears. These effects are similar to those resulting from exposure to an environmental temperature of 50°C for 15–20 minutes.4. Exposure to cold or lowering of the body temperature by administration of cold water by stomach tube increases the voltage threshold for production of comparable effects and increases the latency of the responses, sometimes abolishing the ear vasodilatation response. The shivering of cold animals is inhibited promptly by stimulation of the same “centre” and the threshold for this effect likewise raised by a fall in body temperature. Repeated stimulation of the “centre” lowered body temperature especially in animals exposed to cold.5. The effects of stimulation show some latency and a pronounced “after effect”. Cold exposure increases the latencies and decreases the duration of “after effects”.6. Stimulation of the caudo‐ventral part only of the “heat loss centre” caused slight inhibition of water diuresis and milk ejection. Exposure to heat did not modify the course of water diuresis or electrolyte excretion significantly. Stimuli causing vigorous panting did not affect blood pressure, heart rate or blood sugar concentration and behavioural changes were slight or absent.7. The area defined is thought to be a true “heat loss centre” concerned with the coordinated activation of the animal's defenses against hyperthermia.Possible reasons for the long “after effects” of stimulating the “centre” are discussed.