Histological repair of damaged spinal cord tissue from chronic contusion injury of rat: A LM observation

Abstract

The spinal cord has an intrinsic, limited ability of spontaneous repair; the endogenous repair of damaged tissue starts a few days after spinal cord injury (SCI). To date, however, detailed observation in histology at the injury site has not been well documented. In the present study we analyzed the histological structure of the repaired tissue from injury site of rats 6 or 14 weeks after contusion injury (NYU impactor device, 25 mm height setting) on T10, and rats 8 weeks after transplantation of lamina propria (LP) or acellular lamina propria. We found that the initial repaired tissue can be histologically divided into three different zones, i.e., fibrotic, cellular and axonal. The fibrotic zone consists of invading connective tissue, while the cellular zone is composed of invading, densely compacted Schwann cells. Schwann cells migrate from dorsal roots laterally toward and merge underneath the fibrotic zone, forming the U-shape shell of the cellular zone. The major component of the axonal zone is regenerating axons. Schwann cells myelinate regenerating axons in all three zones. In rats with combination treatments including scar ablation and LP transplantation, both cellular and axonal zones significantly expand in size, resulting in the disappearance of the lesion cavity and the integration of repaired tissue with spared tissue. Olfactory ensheathing cells from transplanted LP may promote the expansion of the cellular and axonal zones through stimulating host Schwann cells, indirectly contributing to tissue repair and axonal regeneration. The ependyma-derived cells may be directly involved in tissue repair, but not contribute to the formation of myelin sheaths.