EFFECTS OF PRELESIONED PERIPHERAL-NERVE GRAFT ON NERVE REGENERATION IN THE RAT SPINAL-CORD

OBJECTIVE: The aim of this study was to examine the effects of prelesi oned peripheral nerve grafts on central nerve regeneration compared wi th the freshly transected peripheral nerve grafts in the dorsal funicu lus of the rat spinal cord. METHODS: The experimental paradigm consist ed of ligating the common peroneal nerve at the midthigh level for 7 d ays, while the adjacent tibial nerve was left intact. Numerous Schwann cells appeared accompanying regenerating axons in the proximal stump of the ligated nerve. The proximal stumps of the ligated (prelesioned) common peroneal nerve and the intact (untreated) tibial nerve were ex cised as one tissue block and autografted into the dorsal funiculi of the upper cervical cord. The graft was placed so that the prelesioned common peroneal nerve was positioned on the left dorsal funiculus and the untreated tibial nerve was positioned to the right of the midsagit tal plane. Nerve regeneration was examined by light and transmission e lectron microscopy 1 to 16 weeks after grafting, comparing the effecti veness of prelesioned and untreated nerve grafts. RESULTS: Numerous re generating axons were observed in the caudal border of both grafts 1 t o 2 weeks after grafting. Astrocyte proliferation was suppressed in th e prelesioned grafts compared to the untreated grafts. Four to 16 week s later, the number of regenerating axons was approximately 10-fold as large in the prelesioned grafts as in the untreated grafts. The regen erating axons were myelinated by Schwann cells. Astrocytic glial scar formation was inconspicuous in the prelesioned grafts, whereas it was prominent in the untreated grafts. Schwann cells were contiguous with astrocytes along regenerating axons, forming a continuous conduit from the central to peripheral nerve microenvironments for the outgrowth o f regenerating axons. CONCLUSION: The prelesioned peripheral nerve gra ft is more effective than the untreated graft in suppressing astrocyti c scar formation and in supporting the outgrowth of regenerating axons in the dorsal funiculus of rat spinal cord.