Relationship between glial organization and the establishment of nerve tracts in rat spinal cord.

Embryo and adult rat spinal cord sections immunostained for S-100 protein, vimentin, glial fibrillary acidic protein (GFAP), or phosphorylated 160 kDa neurofilament protein (NF), were used to study glial participation in nerve tissue assembly. Radial glial fibers (RGF) expressed vimentin since E12. In the peripheral ventral zone, RGF formed cephalocaudal plates (CP) within the white matter, ensheathing developing axonal tracts first expressing NF at E13. As axonal tracts increased, CP became denser and extended ventrolaterally. S-100 protein appeared at E17 in the midline and, at E18, it overlapped vimentin expression. Astrocytes expressed GFAP since E20. We conclude that the pattern found in the spinal cord results from interactions between developing axonal tracts and radial glia, and that it could set the structural basis for the organized assembly of the spinal cord found in adults.