Influence of the subfornical organ on water intake induced by septal lesion.

Rats bearing lesions in the septal area (SA), or in the subfornical organ (SFO) or simultaneously in both regions were submitted to various thirst-eliciting procedures. The rats with hyperdipsia induced by lesion of the SA drank more water than either normal rats or SFO-lesioned animals under the same thirst-eliciting or angiotensin-liberating stimuli (polyethyleneglycol, isoproterenol, water deprivation and ligation of the inferior vena cava). The overdrinking elicited by SA lesions was blocked after SFO lesions. Neither hypovolemia, nor hypotension or water deprivation could elicit increased water intake in SFO-lesioned animals even after destruction of the SA. Animals with SFO lesions did not show increase of the water intake after cellular dehydration. The results obtained suggest that the SFO acts as the main structure in the regulation of water intake elicited by angiotensin with two opposite effects: one direct, facilitating water intake and the other indirect inhibiting the SA. The SA has an inhibitory effect on the SFO and on water intake.