Regional Subdivisions Within Sensory Circumventricular Organs

Abstract

It is clear from several points of view that the subfornical organ is not a uniform structure. The subfornical organs of several mammalian species were described by Akert et al. (1961) and subdivided into three regions: a dorsal stalk, the body and ventral stalk. Dellmann and Simpson (1976) also recognised three divisions within the subfornical organ, and, more recently, Sposito and Gross (1987) and Shaver et al. (1990) subdivided the subfornical organ of the rat into a number of regions, largely on the basis of capillary morphology and distribution. These were rostral, transitional, central and caudal subregions, with dorsal, ventromedial and lateral zones of the latter three subregions. Other studies of neural connectivity, receptor binding, histo-chemical staining and functional neuroanatomy utilising c-fos expression are indicative of two major functional subdivisions of the rat subfornical organ: the first is a rostrodorsal ’outer shelP which includes the ventral and dorsal stalks of the original classification and dorsal and lateral zones of all regions specified by Sposito and Gross (1987); the second subdivision is a central Ventromedial core’ of the subfornical organ, corresponding to the ventromedial zone of Sposito and Gross (1987). A schematic diagram of the subdivisions of the rat subfornical organ is presented in Figure. 11.