Distribution of orexin-A and orexin-B (hypocretins) in the rat spinal cord

Orexin-A and orexin-B (also known as hypocretin-1 and hypocretin-2) are hyp othalamic peptides that regulate feeding behavior, energy metabolism, and s leep-wake cycle. We determined the distribution of orexin-A and -B in the r at spinal cord, using sensitive radioimmunoassays and an immunohistochemica l technique with three antisera specific for these orexins. Orexins were di stributed throughout the spinal cord, and their contents were highest in th e cervical region. Orexin fibers were concentrated in lamina I of the dorsa l horn and area X surrounding the central canal of the spinal cord. Abundan t orexin fibers also were present in the preganglionic sympathetic and para sympathetic cell columns. These findings suggest that orexins in the spinal cord may be involved in the modulation of sensory informations and the aut onomic system as neurotransmitters or neuromodulators, both. (C) 2000 Elsev ier Science Ireland Ltd. All rights reserved.