A comparison of histopathologic changes following X-irradiation of mid-thoracic and lumbosacral levels of neonatal rat spinal cord.

Light microscopic changes were studied in the dorsal funiculi of spinal cords from rats irradiated (4000 R) at 3 days of age and killed from 9-60 days postirradiation (P-I). The irradiated site was limited to a 5-mm length of mid-thoracic spinal cord (T only) in one group of rats, to a 5-mm length of lumbosacral spinal cord (L only) in a second group, and to 5-mm lengths of both mid-thoracic and lumbosacral spinal cord (T/L) in the third group. Changes in the lumbosacral regions were essentially the same in both L only and T/L irradiated groups. These changes included a decreased neuroglial population and a concurrent state of hypomyelination from 9-30 days P-I. In contrast, in the mid-thoracic regions of T only and T/L irradiated groups the decrease in the neuroglial population was obvious only through 13 days P-I, and by 30 days this population resembled that of the controls. The irradiated mid-thoracic areas were hypomyelinated, with the fasciculus gracilis showing a greater degree of hypomyelination than the fasciculus cuneatus. By 25 days P-I, myelination appeared to be normal in these areas. Scattered hemorrhages were noted in both lumbosacral and mid-thoracic regions, but necrotic areas occurred only at the lumbosacral level. In general, the mid-thoracic area appeared to be less sensitive to x-radiation at 3 days of age than the lumbosacral area. These data suggest that there may be marked differences in the developmental states of cells at these two levels at 3 days of age.