Input of orexin/hypocretin neurons revealed by a genetically encoded tracer in mice

Neuron. 2005 Apr 21;46(2):297-308. doi: 10.1016/j.neuron.2005.03.010.


The finding of orexin/hypocretin deficiency in narcolepsy patients suggests that this hypothalamic neuropeptide plays a crucial role in regulating sleep/wakefulness states. However, very little is known about the synaptic input of orexin/hypocretin-producing neurons (orexin neurons). We applied a transgenic method to map upstream neuronal populations that have synaptic connections to orexin neurons and revealed that orexin neurons receive input from several brain areas. These include the amygdala, basal forebrain cholinergic neurons, GABAergic neurons in the preoptic area, and serotonergic neurons in the median/paramedian raphe nuclei. Monoamine-containing groups that are innervated by orexin neurons do not receive reciprocal connections, while cholinergic neurons in the basal forebrain have reciprocal connections, which might be important for consolidating wakefulness. Electrophysiological study showed that carbachol excites almost one-third of orexin neurons and inhibits a small population of orexin neurons. These neuroanatomical findings provide important insights into the neural pathways that regulate sleep/wakefulness states.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain Stem / anatomy & histology
  • Brain Stem / drug effects
  • Brain Stem / ultrastructure
  • Carbachol / pharmacology
  • Cholinergic Agonists / pharmacology
  • Green Fluorescent Proteins / genetics
  • Humans
  • Hypothalamus / anatomy & histology*
  • Hypothalamus / drug effects
  • Hypothalamus / ultrastructure
  • Immunohistochemistry
  • In Situ Hybridization
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Mice
  • Mice, Transgenic
  • Neural Pathways / anatomy & histology*
  • Neural Pathways / drug effects
  • Neurons / cytology*
  • Neurons / physiology
  • Neuropeptides / metabolism*
  • Orexins
  • Patch-Clamp Techniques
  • Recombinant Fusion Proteins / genetics
  • Tetrodotoxin / genetics
  • Wakefulness / physiology


  • Cholinergic Agonists
  • Intracellular Signaling Peptides and Proteins
  • Neuropeptides
  • Orexins
  • Recombinant Fusion Proteins
  • Green Fluorescent Proteins
  • Tetrodotoxin
  • Carbachol