An electron microscopic study of the development of the ependyma of the central canal of the mouse spinal cord.

The central canal of the adult mouse spinal cord is lined for most of its extent by ependymal cells which are rich in microfilaments and whose apical surface is covered with matted, broad microvilli. The canal itself is filled with amorphous material containing glycogen granules. Two forms of this material are present, a dark form rich in glycogen, and a light form containing a few glycogen granules. Each type appears to be surrounded by a membrane. The upper cervical region, however, has a large empty lumen and the ependymal cells in this region have only scattered, narrow microvilli. During development, the floor and roof plates are at first composed largely of ependymoglial cells, unlike the lateral walls, where undifferentiated neuroepithelial cells predominate. By E15 few undifferentiated neuroepithelial cells remain. At E17 the morphology of the ependymal cells changes. Their apical surface becomes covered with matted, club-shaped microvilli and the central canal is filled with glycogen-containing material. By P5 microfibrils are present in large bundles in the ependymal cells. The piaglial surface opposite the roof and floor plates has finger-like projections unique to these regions and these persist at the surface of the dorsal median septum until myelination is well advanced after P5. The fibres forming the dorsal median septum are at first pale processes containing scattered glycogen granules and microtubules. By P5 microfibrils are present and at P150 the processes are packed with masses of microfibrils.