Changes in CSF hypocretin-1 (orexin A) levels in rats across 24 hours and in response to food deprivation

Hypocretin-1 is consistently detectable in the CSF of healthy human subjects, but is absent in narcoleptics. However, functional roles of CSF hypocretin are largely unknown. We examined fluctuation of CSF hypocretin-1 across 24 h and in response to food restriction in rats. Hypocretin-1 levels were high during the dark period when animals were active, but decreased by 40% toward the end of the light (rest) period. After 72 h food deprivation hypocretin-1 levels during the rest phase increased to concentrations similar to those seen during the baseline active phase; however, no increase in response to food deprivation was observed during the,active phase. These results indicate an important link between circadian control of sleep and energy homeostasis via the hypocretin system. NeuroReport 12:993-997 (C) 2001 Lippincott Williams & Wilkins.