Abstract
Activation by angiontensin II (ANGII) of subfornical organ (SFO) neurons induces water intake and vasopressin release. On the other hand, central and peripheral administrations of galanin (GAL) have been reported to inhibit water intake and vasopressin release in recent in vivo studies. We anatomically, molecularbiologically and electrophysiologically investigated existences of GAL-receptors, and GAL-induced responses in SFO neurons of rats. Immuno-electron microscopic observation revealed existence of GAL-containing synaptic vesicles in the SFO. Conventional RT-PCR analysis demonstrated that there were present all mRNAs of three known GAL receptor subtypes, GALR1, GALR2 and GALR3, in the SFO tissues. In the extracellular recordings, application of GAL inhibited spontaneous firing rate in more than half of SFO neurons, even after synaptic blockade by a low [Ca2+] and high [Mg2+] solution. The inhibitory responses were dose-dependent. Seventy-two percent of GAL-sensitive neurons were also responsive to ANGII. ANGII increased the firing rate. These results suggest that GAL functions as an inhibitory neurotransmitter or neuromodulater in the SFO. Furthermore, the electrophysiological results offer a plausible explanation for the in vivo-observed opposite effects of ANGII and GAL on water intake and vasopressin release. [J Physiol Sci. 2006;56 Suppl:S141]
