SUBCOMMISSURAL ORGAN AND REISSNERS FIBRE OF TORTOISE UNDER CONDITIONS OF OSMOTIC STRESS

The subcommissural organ (SCO) and Reissner's fibre of three species of tortoises living under conditions of osmotic stress was investigated with the light microscope. Complementary to a study of the reptilian ependyma by Fleischhauer (1957) a particular rostral part of the SCO was found, situated in the recessus mesocoelicus just in front of the posterior commissure. This part differs from the surrounding ependyma by its subependymal layer of nerve cells and vacuoles, and by its flat, cuboidal ependymal cells. Under osmotic stress the structure of Reissner's fibre in the course of its passage through the 3rd ventricle is not that of a compact fibre, as it is well known, but it consists of a spongy network of many single filaments. There are obvious differences in the appearance of the clotted cerebrospinal fluid within and outside this network. At the end of the 3rd ventricle the fibers lie closely together and form a dorsal and basal dense layer. The spatial relation of the dorsal layer of this network to the sulcus medialis tecti includes ependymal and subependymal layers of the roof of the 3rd ventricle into this study. Location and extention of this subependymal layer of nerve cells with secretory activity and close relation to the capillaries suggest, that they have the same origin from nerve cells as the basal parts of the ependyma of the SCO. According to the high content of sialic acid and biogenic amines one can imagine, that Reissner's fibre has some importance as a cation-exchanger in the cerebrospinal fluid. The observed formation of a filamentous network by which its surface is largely increased, is in favour of this assumption. © 1969 Springer-Verlag Berlin Heidelberg.