Dipsogenic response induced by angiotensinergic pathways from the lateral hypothalamic area to the subfornical organ...

Experimental observations in several species have suggested that angiotensinergic neural circuits from the lateral hypothalamic area (LHA) to the subfornical organ (SFO) may participate in the control of drinking behavior in the rat. In an attempt to verify this possibility, experiments were undertaken to investigate whether activation of LHA neurons following microinjection of angiotensin II (ANG II) into the LHA elicits drinking. Injections of ANG II (10(-11) mol) into the LHA caused drinking in 25 out of 36 rats having the tips of cannulas in the LHA. The efficacy of ANG II was potentiated by increasing the dose of the drug. To clarify the contribution of angiotensinergic neurons in the LHA with efferent projections to the SFO to the drinking induced by ANG II, the effects of pretreatment with saralasin (Sar), a specific ANG II antagonist, in the SFO or its surrounding region on the drinking to ANG II were examined. Previous injections of Sar into the SFO significantly reduced the water intake caused by ANG II injected into the LHA, whereas treatment with Sar in the ventral hippocampal commissure (VHC) or third ventricle (3V) was without effect. These findings provide the evidence for the involvement of the angiotensinergic pathways from the LHA to the SFO in the dipsogenic action.