The subependymal layer and neighboring region in the brain of the young rat

Abstract

The subependymal layer found below the ependyma of the lateral ventricle, as well as the border area separating the layer from corpus callosum and caudate nucleus, were investigated in the brain of 40‐ and 80‐gm rats with the help of the electron microscope. The subependymal layer is composed of cells packed under the ependymal epithelium. These cells undergo division frequently. They are characterized by an irregular nucleus with patches of ill defined chromatin and a scanty cytoplasm rich in free ribosomes. These features are suggestive of immaturity, although the presence of processes indicates some degree of differentiation. The border area is characterized by the presence of cells scattered among neuronal and glial processes. The cells in 40‐gm rats include a few neuroblasts and, in both 40‐ and 80‐gm rats, neurons and neuroglia, as well as numerous cells which resemble the cells of the subependymal layer or appear intermediate between them and oligodendrocytes or astrocytes. Such transitional cells are also found in corpus callosum and caudate nucleus. It is suggested that cells may leave the subependymal layer, cross the border area and enter white and gray matter while undergoing differentiation. Perhaps neuroblasts arise from these cells in the younger group studied (40‐gm rats). In both groups, most of these cells seem to differentiate into astrocytes and oligodendrocytes.