Effect of glutamate and angiotensin II on whole cell currents and release of nitric oxide in the rat subfornical organ.

Blood-borne angiotensin II (AngII) is known to mediate water-intake by its excitatory effect on neurons in the subfornical organ (SFO). Conversely, nitric oxide (NO) has exclusively inhibitory effects on rat SFO-neurons and on SFO-mediated water-intake. Extracellular and patch-clamp recordings from freshly dissociated rat SFO-neurons showed that glutamate activates AngII-sensitive SFO-neurons by opening ligand-gated cation channels. An immunocytochemical study showed that activation of glutamate receptors increased the concentration of the inhibitory second messenger cGMP in the SFO. A model is proposed suggesting that NO protects SFO-neurons from overexcitability by excitatory neurotransmitters.