ATYPICAL AXON‐SCHWANN CELL RELATIONSHIPS IN THE COMMON PERONEAL NERVE OF THE DYSTROPHIC MOUSE: AN ULTRASTRUCTURAL STUDY

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Abstract
Several atypical features of myelination of the peripheral nervous system are reported in the common peroneal nerve of dystrophic mice (129 ReJ dy/dy): CNS-like contact between myelin sheaths of adjacent nerve fibers; nodes and internodes of myelinated fibers enwrapped with cytoplasmic processes of Schwann cells from adjacent nerve fibers; Schwann cells of adjacent nerve fibers cooperating in formation of a single myelin sheath and a single Schwann cell myelinating 2 separate axons. In view of the presence of similar features of myelination in the CNS, where the myelin producing cells lack basement membrane, in the dystrophic peripheral nerves the development of these features can be attributed to the partial deficiency of the Schwann cell basement membrane. Two types of widened nodes of Ranvier are also identified: nodes with and without paranodal damage. Abnormal features of myelination are described which are likely to represent altered Schwann cell/axon relationships during demyelination and remyelination and/or decreased myelinating ability of Schwann cells. A metabolic disorder of Schwann cells is indicated. They provide an experimental model for the investigation of factors involved in the origin and maintenance of the structural organization of peripheral nerve.