Subfornical organ lesions in rats abolish hyperdipsic effects of isoproterenol and serotonin.

Isoproterenol (300 micrograms/ml/kg) and serotonin (2 mg/ml/kg) given SC to rats (n = 27) caused significant drinking (Fisher PLSD, Scheffe F test, Dunnett t) in the 1 and 2 hours after injection. Such drinking was completely prevented in rats later shown to have complete lesions of their subfornical organs (n = 7). In contrast a response not significantly different from the prelesion response was found in rats later given cortical lesions (n = 11) or other lesions which did not damage the subfornical organ (n = 7). We conclude that drinking evoked by SC injection of serotonin and isoproterenol is brought about by peripheral production of angiotensin II. Blood borne angiotensin II in turn stimulates neurons in subfornical organ which initiate the neural organization of a drinking response.