Taurine selectively modulates the secretory activity of vasopressin neurons in conscious rats

Previous experiments have shown that a 10-min forced swimming session trigg ers the release of vasopressin from somata and dendrites, but not axon term inals, of neurons of the hypothalamic-neurohypophysial system. To further i nvestigate regulatory mechanisms underlying this dissociated release, we fo rced male Wistar rats to swim in warm (20 degreesC) water and monitored rel ease of the potentially inhibitory amino acids gamma amino butyric acid (GA BA) and taurine into the hypothalamic supraoptic nucleus using microdialysi s. Forced swimming caused a significant increase in the release of taurine (up to 350%; P < 0.05 vs. prestress release), but not GABA. To reveal the p hysiological significance of centrally released taurine, the specific tauri ne antagonist 6-aminomethyl-3-methyl-4H-1,2,4-benzothiadiazine-1,1-dioxide was administered into the supraoptic nucleus via retrodialysis. Administrat ion of this antagonist caused a significant increase in the release of vaso pressin within the supraoptic nucleus and into the blood both under basal c onditions and during stress (up to 800%; P < 0.05 vs. basal values), withou t affecting hypothalamic or plasma oxytocin. Local administration of the GA BAA receptor antagonist bicuculline, in contrast, failed to influence vasop ressin secretion at either time point. In a separate series of in vivo elec trophysiological experiments, administration of the same dosage of the taur ine antagonist into the supraoptic nucleus via microdialysis resulted in an increased electrical activity of identified vasopressinergic, but not oxyt ocinergic, neurons. Taken together our data demonstrate that taurine is rel eased within the supraoptic nucleus during physical/emotional stress. Furth ermore, at the level of the supraoptic nucleus, taurine inhibits not only t he electrical activity of vasopressin neurons but also acts as an inhibitor of both central and peripheral vasopressin secretion during different phys iological states.