Localization of the anterior hypothalamic angiotensin II pressor system

Previous studies by this laboratory have shown that an electrolytic lesion of tissue surrounding the anteroventral third cerebral ventricle (AV3V) produces pressor deficits to both intravenously (i.v.) and intracerebroventricularly (i.c.v.) administered angiotensin II (AII). These studies were designed to identify the neural substrates critical to the central AII pressor response. The AII pressor system was mapped employing a spectrum of overlapping electrolytic lesions within the medial preoptic-anterior hypothalamic area. The effect of each lesion on the pressor response to AII (i.c.v.) was tested in each animal, which was then grouped as a responder (R) or nonresponder (NR). The extent of damage produced by lesions that abolished the AII response was mapped. Bilateral destruction of tissue along the lamina terminalis (LT) either below or at the level of the anterior commissure eliminated the AII pressor response as did destruction of tissue near the margin of the preoptic and anterior hypothalamic nuclei. These data suggested that an AII pressor pathway originating in the ventral AV3V region ascends along the LT to the level of the anterior commissure and then descends through the anterior hypothalamus. The path of the descending projection through the anterior hypothalamus was ascertained by making a series of horizontal knife cuts. Transections were found that effectively eliminated the central AII pressor response without impinging upon the LT. It is concluded that the anterior hypothalamus contains an efferent pathway from the AV3V region associated with the central AII pressor response.