Arcuate nucleus inputs onto subfornical organ neurons that respond to plasma hypernatremia and angiotensin II

Experiments were done in urethane anesthetized rats to investigate the effect of electrical and glutamate stimulation of arcuate nucleus (Arc) on the discharge rate of subfornical organ (SFO) neurons that responded to either plasma hypernatremia or angiotensin II (ANG II). Extracellular recordings were made from 253 histologically verified single neurons in SFO. Of these, 40.3% (102/253) responded with excitation and 10% (25/253) with inhibition to Arc stimulation. Thirty-five (34.3%) of the units excited by Arc were also excited by intracarotid infusion of hypertonic (0.5 M) NaCl. In addition, 37 (36.3%) of the units excited by Arc were also excited by intracarotid infusion of ANG II. Furthermore, 10 (40.0%) of the units inhibited by Arc were found to be excited by ANG II. None of the units inhibited by Arc stimulation were responsive to plasma hypernatremia. These data indicate that inputs from Arc neurons converge onto SFO neurons that alter their discharge rate during changes in plasma concentration of Na+ or ANG II. These results suggest that Arc may be involved in body fluid balance and circulatory regulation by modulating the activity of SFO neurons that function in the detection of blood-borne signals from the depletion of intra- and extra-cellular fluid volumes.