Abnormalities expressed in long-term cultures of dorsal root ganglia from the dystrophic mouse

We have compared the development in long-term tissue culture of dorsal root ganglia taken from normal and dystrophic mice. Cultures were prepared from late fetal (15--20 days) or neonatal mice of either the C57BL/6 dy2j/dy2j dystrophic (dy) or C57BL/6J +/+ (control) strain and maintained until fully myelinated (5 weeks or more). Analysis by light and electron microscopy indicated that the substantial ensheathment failure present in certain dy nerve roots in vivo is not expressed in cultures; myelination and Schwann cell numbers are comparable to control cultures. On the other hand, many of the subtle abnormalities more recently described in distal parts of peripheral nerves of dystrophic mice are expressed in the dy cultures. These include: (a) discontinuity in the basal lamina surrounding both myelin-forming and non-myelinating Schwann cells: (b) elongated nodes of Ranvier occurring along otherwise well myelinated nerve fibers; (c) relatively short myelin internodes that are increased in thickness as well as irregularities of internode length along a nerve fiber; (d) Schwann cell nuclei substantially displaced from the central point of myelin internodes; and (e) occasional regions of incomplete ensheathment of unmyelinated nerve fibers. In discussing these observations, we present arguments that the dy nerve lesion may be explained by the presence of an abnormality in the extracellular matrix of the peripheral nerve tissues of the dy mouse.