Three-dimensional ultra-structures of myelin and the axons in the spinal cord: application of SEM with the osmium maceration method to the central nervous system in two mouse models.

Axonal injury and demyelination are observed in demyelinating diseases such as multiple sclerosis. However, pathological changes that underlie these morphologies are not fully understood. We examined in vivo morphological changes using a new histological technique, scanning electron microscopy (SEM) with osmium maceration method to observe three-dimensional structures such as myelin and axons in the spinal cord. Myelin basic protein-deficient shiverer mice and mice with experimental autoimmune encephalomyelitis (EAE) were used to visualize how morphological changes in myelin and axons are induced by dysmyelination and demyelination. SEM revealed following morphological changes during dysmyelination of shiverer mice. First, enriched mitochondria and well-developed sER in axons were observed in shiverer, but not in wild-type mice. Second, the processes from some perinodal glial cells ran parallel to internodes of axons in addition to the process that covered the nodal region of the axon in shiverer mice. Last, this technique left myelin and axonal structures undisturbed. Moreover, SEM images showed clear variations in the ultrastructural abnormalities of myelin and axons in the white matter of the EAE spinal cord. This technique will be a powerful tool for identifying the mechanisms underlying the pathogenesis in demyelination.