Centrally administered orexin/hypocretin activates HPA axis in rats

The effects of i.c.v. administration of orexin/hypocretin on plasma ACTH, c orticosterone and c-fos mRNA in the paraventricular nucleus (PVN) of the ra t were examined. Plasma ACTH levels were markedly increased at 30 min after i.c.v. administration of orexin-A Plasma corticosterone fevers were signif icantly increased in a dose-related manner 30 min after i.c.v. administrati on of orexin-A and orexin-B. In situ hybridization histochemistry revealed that the induction of the c-fos mRNA in the parvocellular division of the P VN was increased in a dose-related manner 30 min after i.c.v. administratio n of orexin-A and orexin-B. These results suggest that central orexin/hypoc retin activates hypothalamo-pituitary-adrenal (HPA) axis and may be involve d in stress-induced activation of the HPA axis. NeuroReport 11:1977-1980 (C ) 2000 Lippincott Williams & Wilkins.