Relationship of Wallerian degeneration to regrowing axons

Because Wallerian degeneration constitutes a highly significant and unavoidable position in the sequence of nervous system regeneration we have extended our observations regarding this process as it occurs in our cryogenic model of spinal cord injury in the rat. In previous studies we have observed essentially no growth into the Wallerian zone despite a significant amount of axonal regrowth through the injured region. In the present study we have examined by electron microscopy the Wallerian degeneration and its interface with the axons from the injured region. In the Wallerian region our observations have not only confirmed those of many previous investigators but have suggested an orderly sequence of changes during the first 60 days post-injury, beginning with relative tissue preservation followed by depletion of degenerating axoplasm, extracellular deposition of myelin and the development of a cellular reaction. Associated with the cellular reaction is the development of large astrocytic cells which can be found adjacent to unmyelinated and thinly myelinated axons. With this limited evidence of support for axonal growth in the Wallerian zone it is suggested that further expansion of this cellular matrix should provide significant support to regrowing axons.