THERMAL SIGNALS IN CONTROL OF SELECTIVE BRAIN COOLING

In species with a carotid rete, the arterial blood destined for the br ain can be cooled on its passage through the rete. The temperature dif ference between the blood before the rete and the brain is termed sele ctive brain cooling (SBC). The onset and degree of cooling depend on i nternal body temperature. The aim of this study was to determine the b rain sites where the temperature signals driving SBC are generated. Th irty-six experiments were performed in three conscious goats, which we re prepared with an arteriovenous shunt, carotid loops, and hypothalam ic thermodes to manipulate the temperatures of the trunk (T-tr), the h ypothalamus (T-hyp), the extrahypothalamic brain (T-exh), Or. the whol e brain (T-br). In all experiments, T-tr was clamped at 39.5 degrees C . The increase of SBC was 2.1 degrees C per 1 degrees C increase of T- br (gain = 2.1). The rise of T-hyp at constant T-exh yielded a gain of 1.6, whereas the gain of T-exh at constant T-hyp was 0.7. It is concl uded that onset and degree of SBC are predominantly determined by temp erature signals generated in the hypothalamus itself.