Specific angiotensin II receptive neurons in the cat subfornical organ

To test if neurons in the subfornical organ (SFO) are specifically sensitive to angiotensin II (AII) we have applied the AII analog sar1-ala8-AII (P113) directly on to cells in the SFO by microiontophoresis. Adult cats were anesthetized and the SFO exposed for penetration by a 5-barreled micropipette electrode. Of 22 units which responded positively to AII, 7 were also positive to acetylcholine. P113 alone produced either no effect or a decrease in unit firing. P113 plus AII produced antagonism in 17 of 18 units. P113 plus acetylcholine produced antagonistic effects in 5 of 14 cases. Only two units were completely antagonized and 5 units showed agonistic interaction. The most sensitive antagonism with respect to dose of P113 was on neurons responsive only to AII and not to both AII and acetylcholine. We conclude that there are specific AII neurons in the SFO.