Primary demyelination in cat optic nerves associated with surgically induced axonal degeneration

Localized Wallerian degeneration was induced in cat optic nerves by the gentle scratching of the exposed retinas. At intervals ranging up to 103 days after operation, the cats were killed and microscopic examination of the optic nerves showed, in addition to axonal degeneration, the presence of both demyelinating and demyelinated normal axons. The tongues of oligodendroglial cytoplasm were still associated with these demyelinated axons. This phenomenon is considered to reflect a change in the homeostasis of the oligodendroglial cell imposed by degeneration of a few axons from a state of maintaining the myelin sheath to one of resorption from adjacent normal axons. No evidence for the involvement of microglia in this process was found. It is concluded also that oligodendrocytes alone can be responsible for the removal of myelin debris during Wallerian degeneragion. This observation may be important to the understanding of certain demyelinating diseases of the central nervous system.