Centrally Administered Neuromedin U Activates Neurosecretion and Induction of c-fosMessenger Ribonucleic Acid in the Paraventricular and Supraoptic Nuclei of Rat

We examined the effects of intracerebroventricular (icv) administration of neuromedin U (NMU) on plasma arginine vasopressin (AVP), oxytocin (OXT), and ACTH in rats, using RIA. The induction of c-fos protein (Fos) was examined by immunohistochemical study, and in situ hybridization histochemistry was used to detect c-fos gene expression in the paraventricular (PVN) and supraoptic nuclei (SON). Plasma AVP, OXT, and ACTH were increased in a dose-related manner 15 min after icv administration of NMU. The icv administration of NMU caused a marked induction of Fos-like immunoreactivity (LI) in the SON and the magnocellular and parvocellular divisions of the PVN. In the SON and the magnocellular divisions of the PVN, OXT-LI cells predominantly exhibited nuclear Fos-LI in comparison with AVP-LI cells. The marked induction of the expression of c-fos gene in the PVN and SON was observed 15, 30, and 60 min after icv administration of NMU. Neurosecretion and induction of c-fos gene expression after centrally administered NMU were significantly reduced by pretreatment with anti-NMU IgG. These results suggest that centrally administered NMU activates OXTergic cells in the PVN and SON predominantly as well as hypothalamo-pituitary adrenal axis.