Differential distribution of orexin-A and orexin-B immunoreactivity in therat brain and spinal cord

The orexins are recently identified appetite-stimulating hypothalamic pepti des. We used immunohistochemistry to map orexin-A and orexin-B immunoreacti vity in rat brain, spinal cord, and some peripheral tissues. Orexin-A- and orexin-B-immunoreactive cell bodies were confined to the lateral hypothalam ic area and perifornical nuclei. Orexin-A-immunoreactive fibers were densel y distributed in the hypothalamus, septum. thalamus, locus coeruleus, spina l cord, and near the ventricles, but absent from peripheral sites investiga ted. In contrast, orexin-B-immunoreactive fibers were distributed sparsely in the hypothalamus. Orexin cells are strategically sited to contribute to feeding regulation, but their widespread projections suggest that orexins h ave other physiological roles. (C) 1999 Elsevier Science Inc. All rights re served.