title: Ghrelin-immunopositive hypothalamic neurons tie the circadian clock and visual system to the lateral hypothalamic arousal center.
abstract: Ghrelin, a circulating gut-hormone, has emerged as an important regulator of growth hormone release and appetite. Ghrelin-immunopositive neurons have also been identified in the hypothalamus with a unique anatomical distribution. Here, we report that ghrelin-labeled neurons receive direct synaptic input from the suprachiasmatic nucleus, the central circadian timekeeper of the brain, and lateral geniculate nucleus, a visual center, and project synaptically to the lateral hypothalamic orexin/hypocretin system, a region of the brain critical for arousal. Hypothalamic ghrelin mRNA oscillates in a circadian pattern peaking in the dark phase prior to the switch from arousal to sleep. Ghrelin inhibits the electrophysiological activity of identified orexin/hypocretin neurons in hypothalamic slices. These observations indicate that the hypothalamic neurons identified by ghrelin immunolabeling may be a key mediator of circadian and visual cues for the hypothalamic arousal system.
authors.affiliation: Program in Cell Signaling and Neurobiology of Metabolism, Section of Comparative Medicine, Yale University School of Medicine, New Haven, CT 06520, USA ; Department of Neurobiology, Yale University School of Medicine, New Haven, CT 06520, USA.
authors.forename: Tamas L
authors.initials: TL
authors.lastname: Horvath
authors.forename: Alfonso
authors.initials: A
authors.lastname: Abizaid
authors.forename: Marcelo O
authors.initials: MO
authors.lastname: Dietrich
authors.forename: Ying
authors.initials: Y
authors.lastname: Li
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Takahashi
authors.forename: Joseph
authors.initials: J
authors.lastname: Bass
keywords: Arousal; Circadian rhythm; Ghrelin; Hypothalamus; Lateral hypothalamus
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