The myelinic channel in inflammatory disease

In the central nervous system (CNS) the majority of axons are surrounded by a myelin sheath, which is synthesised by oligodendrocytes. Oligodendrocytes do not only insulate axons, but they are also responsible for long term axonal function and integrity. The mechanism by which the oligodendrocyte supports the axon is not known, but there is good evidence to suggest that it involves the transfer of glycolytic products from the myelinating cell to the neuronal cell. Myelin consists of both compacted and non-compacted membrane. The myelinic channel (or non-compact myelin) comprises the inner and outer tongue processes of the oligodendrocyte and the paranodal loops. Electron micrographs show that the myelinic channel contains microtubules, vesicles and multivesicular bodies, suggesting that it acts as a transport route between the oligodendroglial soma and the glial-axonal junction.To date, very little is known about this channel, but we hypothesise that oligodendroglial mediated axonal support depends on its function and integrity. Further, we suggest that axonal injury in multiple sclerosis, which often precedes demyelination, reflects inflammation induced injury to the myelinic channel and impaired communication between the oligodendrocyte and the axon.