ARE SCHWANN-CELLS ESSENTIAL FOR AXONAL REGENERATION INTO MUSCLE AUTOGRAFTS

When axons regenerate through frozen-thawed (FT) muscle grafts, they a re accompanied by co-migrating Schwann cells derived from the nerve st umps. Although acellular, FT muscle grafts contain an internal scaffol d of basal laminae rich in components capable of supporting neurite ou tgrowth in vitro such as laminin and fibronectin: it is not known whet her Schwann cells are essential for axonal regrowth within these graft s. In this paper we test the hypothesis that sarcolemmal basal laminae will support axonal regeneration in the absence of Schwann cells. Two groups of 12 adult Wistar rats were used. All rats received a 0.5 cm FT muscle graft, and 12 rats also received a subperineurial injection of the anti-mitotic agent mitomycin C (400 mu g/ml in physiological sa line) prior to grafting. Previous studies have shown that this dose ef fectively depresses cell proliferation within the endoneurium for 3-4 weeks [17, 18, 28]. Rats were killed (n=3) 1, 2, 3 or 4 weeks later. T he spatio-temporal sequence of axonal regeneration into the grafts was assessed histologically, by immunofluorescence using antibodies again st GAP-43; S-100; RT97; laminin and macrophages (ED1), and by transmis sion electron microscopy. Outgrowth of almost all axons from the mitom ycin C-treated proximal stumps was delayed for up to 3 weeks, after wh ich time vigorous regeneration occurred into the persisting tubes of s arcolemmal basal lamina. All axons regenerating within the grafts (irr espective of mitomycin C-treatment) were accompanied by co-migrating S chwann cells. The results suggest that Schwann cells play an important role in axonal regeneration across FT muscle autografts and that sarc olemmal basal laminae alone are insufficient to support axonal regener ation.