The role of neuropeptide Y in orexin-induced hypothalamic-pituitary-adrenal activation

The role of neuropeptide Y (NPY) in the mediation of orexin-induced hypotha lamic-pituitary-adrenal (HPA) activation was investigated in the rat. The H PA system was stimulated by intracerebroventricular (i.c.v.) administration of orexin-A or orexin-B (140 or 280 pmol, respectively) and the plasma con centration of corticosterone was used as an index of the degree of activati on. i.c.v. pretreatment with NPY antagonist or NPY antiserum (30 min or 24 h before orexin administration, respectively) inhibited the orexin-induced corticosterone release. The inhibitory actions of the antagonist and the an tiserum were revealed by the dose-response curve; the highest concentration s practically abolished the HPA activation evoked by the orexins. These dat a suggest that the HPA system-stimulating effect of the orexins may be medi ated by NPY.