The effect of thiouracil, excess thyroxine and thyroidectomy on the ependymal cells with special reference to the subcommissural organ

Abstract

The effects of cxccss thyroxine, thiouracil and thyroidcctomy upon the ependymal cells of the subcommissural organ, the choroid plexus and the wall of the caudal part of the third cerebral ventricle in the adult male albino rats were studied. A total of 203 rats were used. Thiouracil and thyroxine werc administered orally, thyroidectomy was performed by means of radioiodine. Thiouracil was seen to diminish the ependymal nuclear volume especially in the subcommissural organ and in the wall of the third ventricle. Similar effects were observed by thyroidectomy, though the change was significant only in the ependyma covering the wall of the third ventricle. Excess thyroxine, again, increased nuclear volume of all ependymal cells studied. The changes could be observed over a period of 4-18 days. The signs of a return to normal after withdrawal of thyroxine arid thiouracil were perceived after four days. Visual estimation revealed no clear change in aldehyde-fuchsin-positive "secretory material" in the subcommissural organ of any test group. The functional significance o f the results is discussed.The ependymal cells cover the ~valls of the cerebral ventricles. There is also a layer of ependymal cells on the surface of the choroid plexus. In some regions the ependymal cell system is specialized. An example of this is in the subcornmissural organ (SCO), where the ependymal cells differ both structurally and presumably also functionally from other ependymal cells.The current concept is that the site of formation of cerebrospinal fluid is the choroid plexus (Fleischhauer, '65). The ependymal cells of the choroid plexuses maintain a characteristic electrolyte structure in the cerebrospinal fluid; in other words these cells actively regulate the transfer of ions and apparently also the other components of the liquor. The production of cerebrospinal fluid is, thus, labelled a process of "secretion." The physiological significance of the ependymal layer covering thP wall of the cerebral ventricle itself is still largely unclarified. It appears to play a role in the metabolism of the tissues of the central nervous system (Oksche, '61) and very possible also acts as a secretory cell system. A N A~. Rrrc., 159: 379-366.

Certain Observations on the Pineal Organ of Indian House Crow, Corvus splendens (Vieillot) during Annual Cycles

“…Nevertheless, variation in the nuclear volume of a secretory cell may apparently be considered as an index of a change in its secretory activity. Generally an increase in nuclear volume is associated with increased activity, while a decrease in volume corresponds to diminished activity (Benninghoff 1953, Szentagothai et al 1962Talanti 1967). Provided that the above concepts on the influence of functional activity upon nuclear volume are correct, it would seem that the present observations on the pineal cells presumably indicate considerable increase in pinealocyte activity during mid-August to November months (Figs.…”