The histopathology of freezing injury to the rat spinal cord. A light and electron microscope study. II. Repair and regeneration.

We utilized a recently developed model of spinal cord injury in which freezing of the rat dorsal column produced axonal injury with sparing and proliferation of the supporting tissue. We examined the progress of the reparative and regenerative processes for 15, 30 and 60 days after the injury. In transverse and sagittal sections at the proximal middle, and distal injury zone and at the zone of Wallerian degeneration we have demonstrated an apparent outgrowth of axons which makes its appearance between 15 and 30 days following injury and increases in amount between 30 and 60 days. The myelination of these fibers is bimodal with Schwann cells predominating in the subpial region, and oligodendrocytes in the deeper regions. Growth into the Wallerian zone is significantly less but does occur at 30 days increasing only slightly at 60 days despite extensive clearing of the breakdown products. We believe that the conditions created by this method of injury provide a suitable model for the study of repair and regeneration of mammalian central nervous tissue.