Brain glycogen decreases with increased periods of wakefulness: implications for homeostatic drive to sleep.

Sleep is thought to be restorative in function, but what is restored during sleep is unclear. Here we tested the hypothesis that increased periods of wakefulness will result in decreased levels of glycogen, the principal energy store in brain, and with recovery sleep levels of glycogen will be replenished, thus representing a homeostatic component of sleep drive. Using a high-energy focused microwave irradiation method to kill animals and thereby snap-inactivate glycogen-producing and -metabolizing enzymes, we determined, with accuracy and precision, levels of brain glycogen and showed these levels to decrease significantly by approximately 40% in brains of rats deprived of sleep for 12 or 24 hr.