Effects of local application of SNP,l-arginine, and l-NNA on activity of vasopressin and oxytocin neurons. A–C, Retrodialysis of SNP onto the SON inhibited the electrical activity of oxytocin (A) and vasopressin (B) neurons, repeatedly and dose-dependently (SNP1, 10 mm; SNP2, 100 mm). C, A significant decrease in the activity quotient and the burst length of phasic vasopressin neurons was observed after retrodialysis of 100 mm SNP. *p < 0.05; n = 5 at 0 and 15 min and 4 at 45 min, respectively. D, Inhibition of a continuously firing putative vasopressin neuron during administration of l-arginine. E, l-NNA administered over 60 min induced an increase in the firing rate of this vasopressin neuron, identified by its inhibitory response to intravenous CCK.