Identified central axons differ in their response to spinal cord transection.

The responses of two distinct populations of neurons to axotomy were examined in this study. Spinal cord transections were made in mice, and horseradish peroxidase was used to label the severed axons of dorsal root ganglion cells and corticospinal neurons at various times after injury. Corticospinal axons formed terminal bulbs near the site of injury, and exhibited little evidence of regrowth. Dorsal column axons, that lie adjacent to corticospinal axons in the dorsal funiculus, formed terminal enlargements that clearly resembled growth cones, and on occasion these axons were directed away from the site of injury. The axons proximal to these enlargements often took curved erratic courses, and were occasionally branched. These experiments show that the anterograde transport of HRP can be used to distinguish differences in the morphology of separate populations of severed axons. The results suggest a structural basis for the variability exhibited by different populations of axons in the spinal cord in regrowth after transection.