Paraventricular nucleus neurons projecting to the dorsomedial medulla are influenced by systemic angiotensin.

Activation of subfornical organ (SFO) efferents has been reported to increase the excitability of paraventricular nucleus (PVN) neurons projecting to cardiovascular centres in the medulla. Such findings suggest a role for these neural projections in the cardiovascular effects of systemic angiotensin II (AII) acting at the SFO. The present studies examine the effects of peripheral AII (50-500 ng) on the activity of PVN neurons antidromically identified as projecting to the dorsomedial medulla (DM). A total of 68 neurons were tested, of which 25% were found to be specifically activated by AII, and 25% inhibited as a consequence the increased blood pressure accompanying administration of this peptide. The activity of the remaining neurons tested was unaffected by AII. These studies demonstrate that only a small proportion of PVN neurons projecting to the DM, which have been shown to be influenced by SFO efferents, are also activated by systemic AII. Such data do however, support a significant role for these neurons in the cardiovascular functions of SFO.