Spontaneous longitudinally orientated axonal regeneration is associated with the Schwann cell framework within the lesion site following spinal cord compression injury of the rat.

Spontaneous cellular reorganisation at the lesion site has been investigated following massive spinal cord compression injury in adult rats. By 2 days post operation (p.o.), haemorrhagic necrosis, widespread axonal degeneration, and infiltration by polymorphnuclear granulocytes and OX42-positive macrophages were observed in the lesion site. By 7 days p.o., low affinity nerve growth factor receptor-positive Schwann cells, from activated spinal roots, were identified as they migrated far into the lesion. Between 7 and 14 days p.o., the overlapping processes of Schwann cells within the macrophage-filled lesion formed a glial framework which was associated with extensive longitudinally orientated ingrowth by many neurofilament-positive axons. Relatively few of these axons were calcitonin gene-related peptide (CGRP)-, substance P (SP)-, or serotonin (5HT)-positive; however, many were glycinergic or gamma aminobutyric acid (GABA)ergic. At 21 and 28 days p.o. (the longest survival times studied), a reduced but still substantial amount of orientated Schwann cells and axons could be detected at distances of up to 5 mm within the lesion. Glial fibrillary acidic protein (GFAP) immunoreactivity demonstrated the slow formation of astrocytic scarring which only became apparent at the lesion interface between 21 and 28 days p.o. The current data suggest the possibility of developing future therapeutic strategies designed to maintain or even enhance these spontaneous and orientated regenerative events.