Glucose-6-phosphate Dehydrogenase Activity in the Subcommissural Organ of Rats. A Histochemical Study

The subcommissural organ (SCO) of rats shows a striking activity of glucose-6-phosphate dehydrogenase. The histochemical distribution pattern of this enzyme in the SCO was not appreciably altered by an increased sodium intake, by deprivation of drinking water or by Pitressin tannate injections. {Endocrinology 76: 996,1965) I THE adult rat the subcommissural organ (SCO) consists of tall columnar cells that line the antero-inferior surface of the posterior cerebral commissure. These elongated cells are continuous with the ependymal cells lining the third ventricle and cerebral aqueduct. Generally, they are considered to be modified ependymal cells. The SCO produces a periodic acid-Schiff (PAS) positive substance (1-4) that stains selectively deep purple with Gomori's chrome alum-hematoxylin-phloxine, a tinctorial property which is shared by the neurosecretory substance within the hypothalamus and neurohypophysis (1-5). Gilbert found that the PAS positive substance in the SCO has hormonal properties that are destroyed by dilute acetic acid or by shaking with ether (6). In a series of investigations Gilbert has shown that microcoagulation of the SCO in rats caused an immediate and persistent fall in water consumption, resulting in death within a few days. He has also demonstrated that saline extracts of SCO injected into normal rats cause a rapid fall in water consumption over the succeeding 24 hr, presumably due to increased conservation of fluid and electrolyte at the renal level (7). On the basis of Received December 9, 1964. This study was supported by Research Grant NB 04155-03 of the National Institute of Neurological Diseases and Blindness, USPHS. 1 Reprint requests should be addressed to Dr. K. Balogh, Massachusetts General Hospital, Boston 14, Mass. 2 Summer Trainee (1964) under National Institute of Health Training Grant 1 S01-FR5381-01. these findings, Gilbert has postulated that the SCO might participate in the regulation of body fluid volume. In a later experiment he showed that the amount of PAS positive material in the SCO varied with the state of hydration of the rats (8). Palkovits and Fbldvari have demonstrated that the SCO extracts produce a decrease in diuresis (9) and in the urinary Na/K ratio. More recently, they also found an increase in the intestinal resorption of Na and water following intravenous injection of SCO homogenates (10). The apparent hormonal function of this organ prompted us to investigate the effects of hydration and dehydration on the activity of certain enzymes in the SCO as demonstrated by histochemical techniques. The present communication reports the findings of this study on the SCO of normal and experimentally manipulated rats. Materials and Methods Twenty-four 3to 4-week old white male rats were used. All animals were allowed to feed on a standard laboratory diet. They were exposed daily to 12 hr of artificial light and 12 hr of darkness. In 4 rats dehydration was accomplished by replacing the drinking water with a 2.5 % saline solution for 13 days. Four other animals were dehydrated by depriving them of all drinking water for 6 days. Overhydration was achieved in 4 rats by injecting intramuscularly 1 ml of Pitressin tannate in oil (5 pressor units) every other day for 6 days. These, as well as 12 control animals, had free access to drinking water. The animals were decapitated under light ether 3 Parke, Davis & Co., Detroit 32, Michigan.