OLIGODENDROCYTES FROM OPTIC NERVES SUBJECTED TO LONG-TERM WALLERIAN DEGENERATION RETAIN THE CAPACITY TO MYELINATE

It has previously been shown in the adult rat optic nerve that cells with many features of oligodendrocytes are capable of surviving for extended periods of time in the absence of axons. This is in contrast to the situation in the developing nervous system, where removal of axons leads to the failure of differentiation and to the death of oligodendrocytes. In the adult, these surviving oligodendrocytes were not typical in their appearance, and could only be identified with certainty using cell specific markers. In the present experiments, the functional capacity of these long-term quiescent cells to regenerate and myelinate was tested using the Shiverer mouse, a mutant lacking the gene for myelin basic protein (MBP), as a host animal. Fragments of optic nerve from adult rats which had been enucleated up to 2 years previously, were implanted into neonatal Shiverer mice. Four weeks later, the brains were removed and the formation of myelin investigated with antibodies to MBP, to ensure that this was of donor origin. Axons were demonstrated to have grown into the implants, and may have provided the stimulus for the production of MBP by the oligodendrocytes, which were stained positively within the implant. Myelin was demonstrated both within and adjacent to the implant This study indicates that in the adult central nervous system, cells can survive for extended periods of time in the absence of axons, albeit in an inactive state, and are then capable of functional regeneration when placed in contact with unmyelinated axons. The origin of these cells, either from surviving oligodendrocytes which had previously myelinated the axons, or from progenitors lying within the adult nerve is unclear. The implications of these results are of importance in the further investigation of the potential for central nervous system regeneration.