Orexin-A immunoreactive neurons in the rat hypothalamus do not contain neuronal nitric oxide synthase (nNOS)

The lateral hypothalamic area (LHA), a key site involved in the central con trol of feeding and energy homeostasis, contains populations of neurons tha t produce the orexin peptides or nitric oxide, two chemical factors that in crease food intake. In this: study, we used immunohistochemistry to investi gate the possibility that rat LHA neurons co-express orexin-A and neuronal nitric oxide synthase (nNOS). The orexin-A and nNOS cell populations in the LHA showed extensive overlap without co-localization, and no evidence of d irect anatomic contact was found. The finding that LI-IA neurons do not co- localize orexin-A and nNOS may suggest that the actions of the orexins and nitric oxide on food intake are mediated via independent mechanisms, howeve r, nitric oxide is a diffusible molecule and could potentially affect the a ctivity of orexin neurons via a non-synaptic mechanism. (C) 2001 Elsevier S cience Inc. All rights reserved.