Endogenous vasopressin induced by central salt loading principally increases vasopressin and oxytocin mRNA in the magnocellular parts but decreases the FLI in the parvocellular parts of the PVN in rats

Abstract

We showed that endogenous vasopressin increases the vasopressin (AVP) and oxytocin (OT) mRNA production in the paraventricular nucleus (PVN) of the hypothalamus after central salt loading in conscious rats. However, as compared to our previous results, there is a conflict between the expression of Fos-like immunoreactivity (FLI) and the mRNA (AVP and OT) in the PVN. That is, endogenous AVP decreases the FLI expression but increases the AVP and OT mRNA after central salt loading. In this study, we evaluated the FLI expression in the PVN after drawing a distinction between magnocellular and parvocellular parts using single and double immunohistochemical staining methods. Endogenous AVP prominently suppressed the FLI expression in the parvocellular parts, but no difference was observed in the magnocellular parts. However, the ratio of AVP- to FLI-positive neurons in the magnocellular parts of the PVN was decreased after pretreatment with AVP V₁ receptor antagonist, OPC-21268. We concluded that the distribution of the hybridization signal (AVP and OT) and FLI in the PVN might not conflict each other after central salt loading. [J Physiol Sci. 2007;57 Suppl:S143]