The hypocretin/orexin ligand-receptor system: implications for sleep and sleep disorders.

The molecules originally described as the hypocretins and subsequently as the orexins were initially implicated in the control of food intake. Recent observations implicate this newly-described neurotransmitter system in the sleep disorder narcolepsy and, potentially, in the regulation of normal sleep processes. This article reviews the research that led to the isolation of the hypocretin/orexin peptides, their receptors and the activity of these molecules as we currently understand them. A model is proposed in which the cells that make these peptides might be involved in arousal state control.