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

To examine the remyelinating ability of post-mitotic oligodendrocytes, we s ubjected 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 remyelina ting cells had been inhibited. The extensive remyelination seen following i mplantation of non-irradiated neonatal and adult cells was almost completel y abolished when the transplanted cell suspension was exposed to 40 Grays o f X-irradiation, demonstrating that effective remyelination requires the ge neration of cells by mitosis. Radiation-resistant and therefore non-dividin g oligodendrocytes were detected in areas of demyelination following transp lantation of neonatal cultures and oligodendrocyte preparations derived fro m the adult nervous system. However, the pattern of myelin formation associ ated with the radiation-resistant oligodendrocytes from the two sources was different. Following implantation of X-irradiated neonatal cultures, a sma ll number of oligodendrocytes could be found within the area of demyelinati on, and although these cells formed sheets of myelin membrane, they did not form myelin sheaths. After implantation of X-irradiated adult cells, in ad dition to the aberrant myelin formation seen with the neonatal cells, some myelin sheaths were observed. Our findings confirm that effective remyelina tion requires cell division and suggest that there may be diverse populatio ns of radiation-resistant oligodendrocytes in the adult nervous system, som e 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 de monstration here that 40 Grays of X-irradiation per se does not inhibit oli godendrocytes from remyelinating axons.