The effects of i.c.v. administration of orexin/hypocretin on plasma ACTH, corticosterone and c-fos mRNA in the paraventricular nucleus (PVN) of the rat were examined. Plasma ACTH levels were markedly increased at 30 min after i.c.v. administration of orexin-A. Plasma corticosterone levels were significantly increased in a dose-related manner 30 min after i.c.v. administration 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 PVN was increased in a dose-related manner 30 min after i.c.v. administration of orexin-A and orexin-B. These results suggest that central orexin/hypocretin activates hypothalamo-pituitary-adernal (HPA) axis and may be involved in stress-induced activation of the HPA axis.
1Department of Physiology, School of Medicine, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishiku, Kitakyushu 807-8555
2Third Department of Internal Medicine, Miyazaki Medical College, Kihara Kiyotake, Miyazaki 889-1692, Japan
3Present address: Clinical Laboratory, Kyurin Co., Kitakyushu 806-0046, Japan
4Corresponding Author: Yoichi Ueta
Acknowledgements: This work was supported by Grant-in Aid for Scientific Research (B) (2) No. 10218210 for H.Y. and (C) No. 11670078 for Y.U. from the Ministry of Education, Science, Sports and Culture, Japan and a research grant from the Ministry of Health and Welfare.
Received 28 February 2000; accepted 10 April 2000