Enhanced response of subfornical organ neurons projecting to the hypothalamic paraventricular nucleus to angiotensin II in spontaneously hypertensive rats

Thirty subfornical organ (SFO) neurons in normotensive Wistar-Kyoto (WKY) rats and 32 SFO neurons in spontaneously hypertensive rats (SHR) were antidromically activated by electrical stimulation of the hypothalamic paraventricular nucleus (PVN) under urethane anesthesia. The spontaneous firing rate was significantly higher in SHR than in WKY rats. No significant differences in the latency, conduction velocity, and threshold of antidromic response were observed between WKY and SHR. All the identified SFO units were tested for a response to intracarotid injection of angiotensin II (ANG II, 20-ng/kg b.w.t.). Injections of ANG II elicited an increase in the activity of 21 units in WKY and 20 units in SHR and a depression in the firing of one unit in WKY rats, but did not affect the remaining units. The magnitude of the excitatory response caused by the ANG II injection was much greater in SHR than in WKY rats. These results show that there are differences between WKY and SHR in the spontaneous discharge rate of SFO neurons projecting to the PVN and in their response to circulating ANG II.