The caudal half of the spinal cords of 3 day old Sprague-Dawley rats were subjected to 2000 R x-irradiation. Morphological studies revealed that a considerable number of oligodendroglia were destroyed in the irradiated animals by 5 days post-irradiation, and that the proliferation of the surviving glia as well as myelination were inhibited. By 35 days post-irradiation there appeared to be a cephalo-caudal progression of glial proliferation and myelination within the irradiated area, which by 50 days post-irradiation had progressed into the upper lumbar segments; little further progression was noted after GS days post-irradiation. Although the lower lumbarand sacral segments remained unmyelinated, the animals displayed no permanent neurological abnormalities.The appearance of Schwann-like cells within the irradiated spinal cord was first noted at the dorsal aspect of the cord 25 days after irradiation. In later periods the cellular invasion was found to be more extensive and accompanied by the deposition of peripheral myelin within the cord. Histochemical evidence also suggested that these cells were Schwann cells.
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