Abstract
The anteroventral third ventricular region (AV3V), a pivotal area for autonomic functions, contains synaptic boutons with Glu and three subtypes of glutamate receptors (Glu-Rs). Although our previous data suggest involvements of NMDA- and metabotropic Rs in ADH release triggered by several stimuli, roles of AMPA/kinate (non NMDA)-Rs related to Na+ channels in hormone release and other functions have not been examined as yet. This study aimed to elucidate the issue through experiments in conscious rats with indwelling cerebral and vascular cannulae. Infusion sites in the brain were identified histologically after experiments. Topical AV3V infusion with a non NMDA-R agonist FWD augmented plasma ADH (pADH), glucose (Glc) and osmolality (Osm), and enhanced arterial pressure (AP) in a dose-dependent manner. All the responses of these variables were blocked by pre-administering NBQX, a selective non NMDA-R antagonist. When NBQX was applied to the AV3V structures such as the median preoptic nucleus, rises of pADH in response to systemic load of hypertonic saline or normo- or hypotensive bleeding were inhibited remarkably. The increases of AP, Osm or Na+ provoked by the osmotic load and the responses of plasma angiotensin II, Osm, Glc or AP caused by the bleeding were not affected significantly. These results suggest that AV3V non NMDA-Rs, as well as NMDA-Rs, may contribute to both the hyperosmotic and hypovolemic ADH secretion. [J Physiol Sci. 2006;56 Suppl:S99]
