CNS axons retain their competence for myelination throughout life.

An important question relevant to developing remyelination therapies is whether axons that remain without myelin sheaths after an episode of demyelination retain myelination competence. To resolve this, we have developed a model of transplantation into the nerve fibre layer of the adult rat retina, where the axons are unmyelinated. In the adult, these axons can be myelinated by transplantation of both the oligodendrocyte progenitor cells (OPCs) and an OPC line (CG4). The extent of myelination achieved following transplantation of OPCs is the same in young adult recipients (2 months old) as that which occurs in old adult recipients (12-18 months old), indicating that there are no changes in axons remaining unmyelinated for many months that would prevent effective remyelination. This finding suggests that chronically demyelinated regions of axons such as those in seen in multiple sclerosis are likely to remain competent to be remyelinated.