Involvement of neurons sensitive to angiotensin II in the median preoptic nucleus in the drinking response induced by angiotensin II activation of the subfornical organ in rats.

The involvement of neurons sensitive to angiotensin II (ANG II) in the median preoptic nucleus (MnPO) in mediating the drinking response caused by administration of ANG II either directly into the subfornical organ (SFO) or intravenously was examined in the conscious rat. In all rats (n = 16) having correct injector placement in both of these brain sites, injections of ANG II (10(-12) M) into the SFO elicited drinking. Previous injections of saralasin (10(-10) M), a specific ANG II antagonist, but not saline vehicle, into the MnPO significantly attenuated the drinking response to ANG II administration directly into the SFO. Intravenous infusions of ANG II (75 ng/kg) produced a drinking response in 12 of the 16 rats, and the response was significantly reduced by pretreatment with saralasin (10(-10) M), but not by saline, in the SFO. These results show the importance of MnPO neurons responsible for ANG II in mediating the dipsogenic response to ANG II acting at the SFO and suggest that the response may be implicated in angiotensinergic neural circuits from the SFO to the MnPO.