Alterations in nerve cells and myelinated fibers in spinal cord injury.

The morphological alterations occurring in the primate spinal cord following acute nondisruptive trauma resulting in paraplegia were studied by light microscopy at intervals up to three months. Specimens were stained specifically for nerve cells, axon cylinders, myelin sheaths, and free fat. Hypoxic degenerative changes were observed in nerve cells. Initially these consisted of cytoplasmic vacuolation and dispersion of the Nissl substance followed by a progressive decrease in the size and the number of nerve cells seen. Simultaneously in the white matter traumatic degenerative changes were noted. At four and eight hours after injury, structures indicating the severance of axon cylinders and of myelin sheaths were observed. Although shearing of myelinated fibers by the mechanical impact of the injury is suggested, it is not possible in this study clearly to separate the development of alterations in the white matter from the changes occurring in the gray matter.