Activation of non-neuronal cells in the rat sciatic nerve in response to inflammation caused by implanted silicone...

The presence of macrophages and the induction of c-jun protein and proliferation of non-neuronal cells were studied following implantation of silicone tubes with different diameters (i.e. 0.8 or 1.6 mm) around the rat sciatic nerve. Three days after implantation, numerous EDI and ED2 positive macrophages could be observed around the nerve beneath the 1.6 mm tubes. Some EDI and ED2 positive macrophages were also present in the endoneurium. In contrast, there were numerous EDI and ED2 positive macrophages in the endoneurium beneath the tube and distally in nerves surrounded by the 0.8 mm tube. In these experiments, there was also a massive induction of c-jun protein and DNA synthesis in non-neuronal cells, as visualised by c-jun and BrdU antibodies respectively (e.g. a response similar to that observed after a crush lesion). Such activated cells, albeit few, were also present in the endoneurium beneath the tube of nerves with a 1.6 mm tube, but not distal to the tube in the endoneurium. At 7 days, the responses were somewhat amplified but essentially the same as at 3 days. The results showed that the large diameter implants, which do not cause axonal damage, as does the small diameter tube, but result in conditioning of the nerve [4], induced invasion of macrophages around the nerve and activation of some cells in the endoneurium beneath the tube. We suggest that cell activation is caused by factors released from macrophages and that endoneurial cell activation is important for the conditioning of the nerve by the silicone tube implant.