Attenuated noradrenaline release in the paraventricular nucleus are induced by electrical and angiotensin II activation of the subfornical organ in estrogen‐treated rats

Previous studies have demonstrated that estrogen alters the responsiveness of subfornical organ (SFO) neurons projecting to the hypothalamic paraventricular nucleus (PVN) to angiotensin II (ANG II) and activation of the SFO facilitates noradrenaline (NA) release in the PVN area. The present study was carried out to investigate whether estrogen elicits alterations in the NA release in the PVN area induced by electrical and chemical activation of the SFO. Intracerebral microdialysis techniques were utilized to quantify the extracellular content of NA in the region of the PVN in ovariectomized (OVX) female rats that were treated with either propylene glycol (PG) vehicle or estradiol benzoate (EB). In both groups, electrical stimulation (5–20 Hz, 600 μA) of the SFO significantly increased the NA concentration in the PVN area. Injections of ANG II (10–8 M, 0.2 μl) into the stimulation site significantly enhanced the release of NA in the PVN area. The NA release to either electrical or chemical stimulation of the SFO was much greater in the PG-treated than in the EB-treated rats. These results suggest that estrogen may decrease the NA release in the PVN area caused by ANG II acting at the SFO.