Studies on the subcommissural organ area in the rat: the effects aldosterone infused into the central nervous system

D-aldosterone (5 ng/μl/hr) was infused for six days into the area of the subcommissural organ (SCO) of conscious rats to test the hypothesis that the SCO and the adrenal zona glomerulosa are related functionally in a negative feedback manner. Aldosterone increased urinary sodium loss and the sodium/potassium ratio. These effects still occurred when cannulae were displaced caudally up to 1 mm from the targeted SCO area. Aldosterone decreased the cross-sectional area of the adrenal medulla without affecting chromaffin cell density. Adrenal content of corticosterone was increased. These effects were highly dependent upon proper cannula placement and were not observed when the tip of the cannula was not in contact with the cerebrospinal fluid of the pineal recess over the rostral two-thirds of the SCO. Aldosterone infused intracerebroventricularly (ivt) into a lateral ventricle had no effect on sodium excretion, adrenal corticosterone concentration or adrenal morphology. After the infusion of radiolabelled aldosterone into the SCO area, the majority of the radioactivity was restricted to an area about 1-2 mm in diameter from the SCO. Iron-dextran injected intraperiotoneally did not accumulate in the SCO; therefore, the blood-brain barrier is intact. It is concluded that the effects of aldosterone were dependent upon the area of the brain in which it was infused. Aldosterone increased sodium excretion by an action in the SCO and/or adjacent structures. A relationship between mineralocorticoids and the adrenal modulla mediated by the SCO is also postulated. With regard to the blood-brain and brain-CSF barriers, the SCO more closely resembles general brain tissue than other circumventricular organs