Neurons that regulate mouse torpor.

The advent of endothermy, which is achieved through the continuous homeostatic regulation of body temperature and metabolism, is a defining feature of mammalian and avian evolution. However, when challenged by food deprivation or harsh environmental conditions, many mammalian species initiate adaptive energy-conserving survival strategies-including torpor and hibernation-during which their body temperature decreases far below its homeostatic set-point. How homeothermic mammals initiate and regulate these hypothermic states remains largely unknown.