Distribution of orexin neurons in the adult rat brain

Brain Res. 1999 May 8;827(1-2):243-60. doi: 10.1016/s0006-8993(99)01336-0.


Orexin (ORX)-A and -B are recently identified neuropeptides, which are specifically localized in neurons within and around the lateral hypothalamic area (LHA) and dorsomedial hypothalamic nucleus (DMH), the regions classically implicated in feeding behavior. Here, we report a further study of the distribution of ORX-containing neurons in the adult rat brain to provide a general overview of the ORX neuronal system. Immunohistochemical study using anti-ORX antiserum showed ORX-immunoreactive (ir) neurons specifically localized within the hypothalamus, including the perifornical nucleus, LHA, DMH, and posterior hypothalamic area. ORX-ir axons and their varicose terminals showed a widespread distribution throughout the adult rat brain. ORX-ir nerve terminals were observed throughout the hypothalamus, including the arcuate nucleus and paraventricular hypothalamic nucleus, regions implicated in the regulation of feeding behavior. We also observed strong staining of ORX-ir varicose terminals in areas outside the hypothalamus, including the cerebral cortex, medial groups of the thalamus, circumventricular organs (subfornical organ and area postrema), limbic system (hippocampus, amygdala, and indusium griseum), and brain stem (locus coeruleus and raphe nuclei). These results indicate that the ORX system provides a link between the hypothalamus and other brain regions, and that ORX-containing LHA and DMH neurons play important roles in integrating the complex physiology underlying feeding behavior.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Age Factors
  • Amygdala / cytology
  • Amygdala / physiology
  • Animals
  • Antibody Specificity
  • Basal Ganglia / cytology
  • Basal Ganglia / physiology
  • Brain Chemistry / physiology*
  • Brain Stem / cytology
  • Brain Stem / physiology
  • Carrier Proteins / analysis*
  • Carrier Proteins / immunology
  • Cell Size / physiology
  • Cerebellum / cytology
  • Cerebellum / physiology
  • Dorsomedial Hypothalamic Nucleus / chemistry
  • Dorsomedial Hypothalamic Nucleus / physiology
  • Feeding Behavior / physiology
  • Hippocampus / chemistry
  • Hippocampus / physiology
  • Hypothalamic Area, Lateral / chemistry
  • Hypothalamic Area, Lateral / physiology
  • Intracellular Signaling Peptides and Proteins*
  • Male
  • Neurons / chemistry*
  • Neurons / cytology
  • Neurons / ultrastructure
  • Neuropeptides / analysis*
  • Neuropeptides / immunology
  • Olfactory Pathways / chemistry
  • Olfactory Pathways / physiology
  • Orexins
  • Pituitary Gland / cytology
  • Pituitary Gland / physiology
  • Presynaptic Terminals / chemistry
  • Rats
  • Rats, Wistar
  • Septal Nuclei / chemistry
  • Septal Nuclei / physiology


  • Carrier Proteins
  • Intracellular Signaling Peptides and Proteins
  • Neuropeptides
  • Orexins