Afferent renal inputs onto subfornical organ neurons responsive to angiotensin II.

Experiments were done in pentobarbital sodium-anesthetized rats to investigate the effect of electrical stimulation of afferent renal nerves (ARN) on the discharge rate of subfornical organ (SFO) neurons that responded to changes in plasma levels of angiotensin II (ANG II) and projected directly to the paraventricular nucleus of the hypothalamus (PVH). Extracellular recordings were made from 76 histologically verified single neurons in the SFO that were excited by intracarotid infusions of ANG II. Of these units, 54.8% (23 of 42) responded with excitation to ARN stimulation (mean onset latency, 125 +/- 35 ms). None of the SFO units excited by plasma ANG II were found to be inhibited by ARN stimulation. An additional 34 units in the SFO that were excited by plasma ANG II were also antidromically activated by stimulation of the PVH. Of these neurons, 17.8% (6 of 34) were also excited by stimulation of ARN. The results indicate that inputs from ARN converge onto SFO neurons that alter their discharge rate during changes in plasma concentration of ANG II and project directly to the PVH. These data suggest that ARN may play an important role in body fluid balance and circulatory regulation by modulating the activity of SFO neurons that function in the detection of blood-borne signals resulting from the decrease in extracellular fluid volume and arterial pressure and that influence the activity of hypothalamic nuclei that contain neurosecretory neurons.