The hypothalamic peptide orexin A (also called hypocretin-1) was originally named so with the intend of emphasizing its role in promoting food intake. The aim of this brief review is to show that orexin A is an important neuropeptide that primarily controls body temperature through activation of the sympathetic nervous system. The modification of eating behavior due to orexin A could be only secondary to change in the thermoregulatory set-point. Activity of the sympathetic nerves system, brown adipose tissue and central body temperatures, heart rate and food intake were monitored to measure the modifications induced by an intracerebroventricular injection of orexin A on the thermoregulation and eating behavior in various experimental conditions in the rat. We report many experimental evidences derived from our laboratory to demonstrate that orexin A is a thermoregulatory peptide. Our viewpoint is compared with vision of other authors, finding possible agreement or disagreement.
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