The subfornical organ's neural connections and their role in water balance.

The subfornical organ (SFO) has projections to specific sets of nuclei within the preoptic area and hypothalamus which enable it to influence behavioral and physiological controls of water balance. It projects to the nuclei of the anteroventral third ventricular area, to vasopressinergic (heavily) and oxytocinergic (moderately) magnocellular neurons of the supraoptic and paraventricular nucleus. It also projects to the parvocellular areas of the paraventricular nucleus which project to the median eminence and to all the motor nuclei of the autonomic nervous system. In addition the SFO projects to regions of the lateral preoptic area, lateral hypothalamus and the dorsal perifornical region. Cutting the efferent projections from the SFO causes disturbances in behavioral and physiological controls of water balance. There is moderate polyuria and a concentrating defect in urine osmolality. The rats do not drink to intravenous angiotensin II but retain their ability to drink to angiotensin II given intracerebroventricularly. They appear to drink normally to overnight water deprivation but remain in negative water balance because of excessive urinary water loss during the deprivation period.