Ultrastructural studies of subependymal extracellular spaces in adult and neonatal rat brain.

Ultrastructural studies of the subependymal neuropil of the lateral ventricular wall in the adult rat reveal two different types of enlarged extracellular spaces which appear to be due to the presence of glycosaminoglycans. Focal irregular enlargements are more numerous and are distinguished by the presence of fibrillar material. The other network is characterized by uniform width, branching processes, and an electron density identical to vascular basement membranes. The origin of the extracellular material is not revealed by these studies, but a relationship is suggested between the focal dilatation and subependymal cells. The distinction of these spaces is emphasized by the study of neonatal brain and by the use of ruthenium red (RR). Focal dilatations are very prominent in the 10 day old rat, but they do not contain fibrillar material. An adult type basement membrane-like network is present at this time. In the adult rat the focal dilatation has great affinity for RR, but the second network is very sparsely stained. The RR affinity is not present in the 10 day old rat; however, by the 26th day, the affinity is almost as great as that of an adult. These findings are considered to enhance the concept of a separate origin, composition, and probable function of these two networks.