An immunocytochemical analysis of growing axons in a silicone chamber prefilled with artificial sponge matrix

We have used antibodies against growth associated protein (GAP-43), phosphorylated neurofilament protein of 200 kDa molecular weight (RT-97) and substance P (SP) to analyze regrowing axons and their features in a silicone chamber filled with resorbable sponge matrix within the first two weeks after sciatic nerve transection in the rat. Growing axons identified with the GAP-43 antibody extended over a distance of about 7 mm from the proximal stump at 7 days and grew over a 10 mm gap within, 14 days. This is a markedly longer distance than in the case of the standard chamber model without artificial sponge matrix. The regrowing axons were labelled with RT-97 already on the 7th day up to a distance of 5 mm and they made up about 75% of all axons in the first segments. The number of RT-97-positive axons did not increase significantly over the next 7 days, although they could be identified over a longer distance. Some of the growing axons expressed SP-like immunoreactivity (LI) 14 days, but not 7 days after chamber application and constituted about 30% of all growing axons in the first segment. The SP-LI fibres also appeared to grow from the distal stump since they were found in larger numbers in the distal segments than in central ones. Those fibres accompanying blood vessels are probably sympathetic. Our findings demonstrate that axons are able to bridge a 10 mm gap within 14 days under appropriate substrate conditions, which are provided by the resorbable fibrin sponge.