title: The energy hypothesis of sleep revisited.
abstract: One of the proposed functions of sleep is to replenish energy stores in the brain that have been depleted during wakefulness. Benington and Heller formulated a version of the energy hypothesis of sleep in terms of the metabolites adenosine and glycogen. They postulated that during wakefulness, adenosine increases and astrocytic glycogen decreases reflecting the increased energetic demand of wakefulness. We review recent studies on adenosine and glycogen stimulated by this hypothesis. We also discuss other evidence that wakefulness is an energetic challenge to the brain including the unfolded protein response, the electron transport chain, NPAS2, AMP-activated protein kinase, the astrocyte-neuron lactate shuttle, production of reactive oxygen species and uncoupling proteins. We believe the available evidence supports the notion that wakefulness is an energetic challenge to the brain, and that sleep restores energy balance in the brain, although the mechanisms by which this is accomplished are considerably more complex than envisaged by Benington and Heller.
authors.affiliation: Center for Sleep and Respiratory Neurobiology, University of Pennsylvania School of Medicine, Translational Research Building, Suite 2100, 125 S. 31st Street, Philadelphia, PA 19104-3403, USA. mscharf@mail.med.upenn.edu
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Scharf
authors.forename: Nirinjini
authors.initials: N
authors.lastname: Naidoo
authors.forename: John E
authors.initials: JE
authors.lastname: Zimmerman
authors.forename: Allan I
authors.initials: AI
authors.lastname: Pack
mesh_terms: D000241:Adenosine / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D004734:Energy Metabolism / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D012890:Sleep / Q000502:physiology*
chemical_list: D006003:Glycogen; D000241:Adenosine