Return of axonal and glial membrane specializations during remyelination after tellurium-induced demyelination

Summary

We have studied remyelination of rat peripheral nerves after tellurium-induced demyelination using thin section and freeze-fracture techniques. In rats fed a 1% tellurium diet, regions of demyelination were readily identified by myelin debris and the presence of large denuded axons. Remyelination occurred despite continued tellurium ingestion. However, the demyelinated axons underwent a more rapid remyelination if tellurium was removed from the diet. Remyelination proceeded as described for myelination in the normal developing animal. Sites destined to become nodes of Ranvier were identified as patches of intramembranous particles in the axonal E-face. Early terminal loops of the remyelinating Schwann cell were found adjacent to these particle patches. As wrapping proceeded, terminal loops of myelin, along with associated rows of dimeric-particles characteristic of the axonal P-face, were wound into a paranodal location. This winding of the membrane specializations and associated terminal loops resulted in the reformation of morphologically normal paranodes. The size of the nodal E-face particle patch increased in concordance with increases in the number of paranodal loops until an annulus of particles was obtained as seen in the normal node. The thin section and freeze-fracture morphology of remyelinated fibres was indistinguishable from the morphology of control fibres. These observations are discussed with respect to proposed functions of membrane specializations in myelination and nerve conduction.