Electrical stimulation in subfornical organ increases plasma vasopressin concentrations in the conscious rat

Electrical stimulation in the subfornical organ (SFO) of conscious freely moving rats was found to increase plasma vasopressin concentrations from control values of 1.43 +/- 0.32 to poststimulation values of 22.32 +/- 4.9 pg/ml (P less than 0.01). Similar stimulation in immediately adjacent brain regions including the medial septum and hippocampal commissure caused no significant changes in plasma concentrations of this peptide hormone. These data indicate that activation of SFO neurons in conscious rats causes increased release of vasopressin from the posterior pituitary. Such data corroborate previous electrophysiological findings demonstrating that in anesthetized animals electrical stimulation in SFO results in increased excitability of antidromically identified vasopressin-secreting neurons in the supraoptic and paraventricular nuclei of the hypothalamus.