Subfornical organ neurons act to enhance the activity of paraventricular vasopressin neurons in response to intravenous angiotensin II.

The effects of pretreatment of the angiotensin II (ANGII) antagonist, saralasin (Sar), in the subfornical organ (SFO) on intravenous ANGII-induced responses of the activity of phasically firing paraventricular nucleus (PVN) neurons (n = 23) antidromically identified as projecting to the posterior pituitary were examined in urethane-anesthetized rats. The activity of the majority (n = 18) of identified PVN neurons was excited by intravenously administered ANGII, whereas the remaining neurons (n = 5) were not affected. The excitatory responses (n = 13) to ANGII were prevented by pretreatment with Sar, but not by isotonic saline (n = 3), in the SFO. These results suggest that ANGII-sensitive SFO neurons may act to enhance the excitability of putative vasopressin (VP)-secreting neurons in the PVN in response to circulating ANGII.