The possibility of identification of oligodendrocyte-myelin sheath processes in the white matter of rats.

When myelination is completed it is no longer possible to see with the EM the continuity of myelin sheath with the oligodendroglial processes. An ultrastructural study has been therefore carried out of the unmyelinated of the white matter to see whether it might be possible to recognize the presence of such continuity. The following were considered: 1) unmyelinated fibres in bundles, 2) astroglial processes, 3) large oligodendroglial processes, 4) tongues, 5) "fibre-like" processes (including tubulus and filamentes which are partly identifiable as either unmyelinated fibres or thin oligondendroglial processes). In addition to morphology, quantitative aspects were also considered such as area of section of each process and number of tubules and filamentes present in each section. No substantial quantitative differences were found between "fibre-like" processes and unmyelinated fibres in bundles. These findings failed to show any morphological evidence of connections between myelin sheaths and oligodendroglial processes. This however still possible that the oligodendroglial processes are so few in number in comparison with the unmyelinated fibers that their statistical contribution is negligeable and that no substantial error is made in identifying all "fibre-like" processes as unmyelinated fibres.