ACTIONS OF ANGIOTENSIN IN THE SUBFORNICAL ORGAN AND AREA POSTREMA - IMPLICATIONS FOR LONG-TERM CONTROL OF AUTONOMIC OUTPUT

1. Considerable physiological and anatomical evidence indicates that c irculating angiotensin II (AngII), plays important roles in the long-t erm regulation of autonomic output as a result of actions in two circu mventricular structures, the subfornical organ (SFO) and area postrema (AP). 2. Extracellular recordings have demonstrated excitatory action s of AngII on neurons from both of these structures which are AT(1) re ceptor mediated, maintained when cells are placed in synaptic isolatio n, and are dose dependent. Interestingly SFO neurons appear to be an o rder of magnitude more sensitive to AngII than those in AP. 3. Recent calcium imaging studies have demonstrated that AngII induces increases in intracellular calcium in bath SFO and AP neurons, Whole cell patch recordings have also begun to provide important information suggestin g that AngII actions may modulate voltage activated ion channels in th ese two o structures to elicit its observed actions on circumventricul ar organs (CVO) neurons at the blood-brain interface. 4. Through these actions circulating AngII is thus able to influence efferent projecti ons from these CVO which in turn influence the output of hypothalamic cells projecting to the posterior pituitary (vasopressin secretion), n ucleus tractus solitarius (NTS), and intermediolateral cell column of the spinal cord (to influence sympathetic preganglionics), and medulla ry neurons in the NTS.