The mitotic history and radiosensitivity of developing oligodendrocytes in vitro.

By use of pulse-chase exposure of dissociated cells of rat fetal spinal cord or brain to [3H]thymidine (TdR) and unlabeled TdR it has been shown that oligodendroglial precursors which do not express galactocerebroside (GalC) divide first and later differentiate to express GalC. The rate of proliferation of more mature GalC+ oligodendrocytes is considerably lower than that of their GalC- precursors. It has been found that oligodendrocyte precursor cells are extremely sensitive to [3H]TdR irradiation. Exposure to as little as 0.03 microCi/ml for 24 hr proved to be harmful, particularly during a critical period before birth. This critical period corresponded to the peak of division of oligodendrocyte precursor cells.