Neural Control of Homeothermy, Torpor, and Hibernation.

Homeothermy, the physiologic capacity to maintain a constant core body temperature, provided a critical survival advantage for mammalian and avian phyla, enabling the colonization of diverse habitats. However, the higher metabolic demands associated with homeothermy necessitate greater food intake. When challenged by food deprivation or harsh environmental conditions, many mammalian and avian species initiate adaptive energy-conserving survival strategies-including hibernation and daily torpor-during which their body temperature decreases far below its homeostatic range. Despite their biological significance and potential biomedical applications, the neural circuit mechanisms regulating entry into these hypometabolic states and their relationship to characterized thermoregulatory pathways remain to be fully elucidated. Here we review known thermoregulatory mechanisms and recent findings concerning the neural control of torpor and hibernation to identify points of convergence as well as important next steps in pursuit of an understanding of these regulatory pathways.