Some aspects of remyelination after demyelination produced by the intraneural injection of lysophosphatidyl choline

The morphology of remyelination following demyelination induced by the intraneural injection of lysophosphatidyl choline, LPC, has been examined in the mouse sciatic nerve, at periods up to 240 days post-injection. It was found that, in many fibres, the process resembled primary myelinogenesis. There was a moderate Schwann cell proliferation; those Schwann cells not involved in remyelination remained closely associated with the remyelinating Schwann cell/axon unit, within a common basal lamina tube. Numerous small axons, considered to be sprouts from the remyelinating axon, were observed lying in contact with the ‘supernumerary Schwann cells’. In a small population of fibres, however, atypical morphological features were consistently seen: (i) multiple mesaxons, indicating probable remyelination by tunication; (ii) paranodal reorganization in the junctional zone; (iii) the formation of internodal ‘pseudonodes’, which subsequently underwent transition into incisures of Schmidt-Lanterman. These structures are discussed in terms of the re-establishment of the Schwann cell/axon relationship.