EFFECT OF INTRAVENOUS ANGIOTENSIN-II ON FOS DISTRIBUTION AND DRINKINGBEHAVIOR IN RABBITS

We investigated the effect of intravenous infusion of angiotensin II ( ANG II, 40 ng.kg(-1).min(-1)) on the distribution of Fos in the subfor nical organ (SFO), organum vasculosum of the lamina terminalis (OVLT), and the medulla of the conscious rabbit. ANG II elicited significant increases in the number of Fos-positive cell nuclei in the SFO and OVL T (15- and 10-fold, respectively). Raising blood pressure with phenyle phrine did not elicit Fos in these nuclei. These nuclei are believed t o be responsible for the dipsogenic actions of ANG II; however, ANG II was not dipsogenic. When blood pressure was held at preinfusion level s by the coadministration of sodium nitroprusside and ANG II, the rabb its did not drink but Fos production in the lamina terminalis was elev ated. In the medulla, ANG II did not significantly increase Fos produc tion in the nucleus of the solitary tract (NTS) or ventrolateral medul la (VLM). However, with the coadministration of sodium nitroprusside, there were marked increases in the NTS and VLM. The results suggest th at neurons in the SFO and OVLT are either not involved in the dipsogen ic pathways or there is disruption further downstream in the central p athways that would normally mediate a drinking response to ANG II.