The demonstration by transplantation of the very restricted remyelinating potential of post-mitotic oligodendrocytes.

To examine the remyelinating ability of post-mitotic oligodendrocytes, we subjected cell preparations derived from neonatal and adult rats to 40 Grays of X-irradiation to remove mitotically active cells and injected them into areas of demyelination in which the inherent ability to generate remyelinating cells had been inhibited. The extensive remyelination seen following implantation of non-irradiated neonatal and adult cells was almost completely abolished when the transplanted cell suspension was exposed to 40 Grays of X-irradiation, demonstrating that effective remyelination requires the generation of cells by mitosis. Radiation-resistant and therefore non-dividing oligodendrocytes were detected in areas of demyelination following transplantation of neonatal cultures and oligodendrocyte preparations derived from the adult nervous system. However, the pattern of myelin formation associated with the radiation-resistant oligodendrocytes from the two sources was different. Following implantation of X-irradiated neonatal cultures, a small number of oligodendrocytes could be found within the area of demyelination, and although these cells formed sheets of myelin membrane, they did not form myelin sheaths. After implantation of X-irradiated adult cells, in addition to the aberrant myelin formation seen with the neonatal cells, some myelin sheaths were observed. Our findings confirm that effective remyelination requires cell division and suggest that there may be diverse populations of radiation-resistant oligodendrocytes in the adult nervous system, some of which can form myelin sheaths and others of which can only make myelin sheets. Important for the interpretation of our previous studies is the demonstration here that 40 Grays of X-irradiation per se does not inhibit oligodendrocytes from remyelinating axons.