Role of orexin system in coordinating ultradian rhythm

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The aim of the present project is to explore brain system that coordinates the ultradian rhythm, focusing orexin, a neuropeptide that is important to promote wakefulness. The project investigated ultradian pattern in genetically-modified mice that have a deficient of orexin or of orexin neurons. In the wild type, body temperature and heat rate increased episodically at every approximately 90 min, confirming the existence of the ultradian rhythm in mice as with rats. In orexin-related transgenic mice, the amplitude of ultradian increase in body temperature and locomotor activity was significantly reduced. The project also employed optogenetically-modified mice in which orexin neuronal activity can be controlled by focal light illumination. Long lasting activation of orexin neurons attenuated the amplitude of the ultradian rhythm. These data suggest that orexin system is important for coordinating ultradian rhythm in body temperature and locomotor activity.