Differences in Electrophysiological Properties of Angiotensinergic Pathways from the Subfornical Organ to the Median Preoptic Nucleus between Normotensive Wistar-Kyoto and Spontaneously Hypertensive Rats

Abstract

Electrophysiological properties of angiotensinergic pathways from the subfornical organ (SFO) to the median preoptic nucleus (MnPO) were investigated in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) under urethane anesthesia. The activity of SFO neurons that were antidromically activated by electrical stimulation of the MnPO was compared between WKY (n = 28) and SHR (n = 27). No significant differences were observed between WKY and SHR in the latency, conduction velocity, or threshold of antidromic activation. The firing rate was significantly higher and the refractory period was significantly shorter in SHR. The activity of MnPO neurons was tested for a response to microiontophoretic application of angiotensin II (ANG II) and electrical stimulation of the SFO. Sixteen of 46 MnPO neurons tested in WKY and 15 of 47 MnPO neurons tested in SHR were excited by both ANG II applied iontophoretically and SFO stimulation, and the excitatory responses were prevented by iontophoretically applied saralasin, a specific ANG II antagonist. In these MnPO neurons that demonstrated the excitation to both SFO stimulation and ANG II, the firing rate was significantly higher and the threshold current required to evoke the SFO stimulus-induced excitation was significantly lower in SHR. The sensitivity to SFO stimulation was much greater in SHR than in WKY. These results provide evidence that there are marked alterations in the physiological properties of the angiotensinergic circuit from the SFO to the MnPO between WKY and SHR and imply that a disorder in the neural circuit may contribute, in part, to hypertension.