Regeneration of the perineurium across a surgically induced gap in a nerve encased in a plastic tube.

Sciatic nerves of mice were cut and the early regenerative stages were studied after the stumps had been encased within plastic tubes and kept separate by a gap of 5 mm. Only isolated cells were seen inside the tube after 7 days; after 12 days active regeneration and myelination were seen proximally; more distally, cells with long processes formed large spaces filled with collagen and less numerous Schwann cells. Zonulae occludentes and segments of basal lamina became more evident at a later stage. One month after the operation an almost complete regeneration of the nerve had taken place and perineurial cells were lined by a continuous basal lamina. The regeneration of the perineurium seemed to take place from fibroblasts; their cytoplasm as well as that of Schwann cells contained fibrillary material at this stage, sometimes in relation to segments of basal lamina. The results of this study indicate that both types of cells take part in the formation of endoneurial structures and that the early arrangement of fibroblasts contributes to the orderly longitudinal alignment of collagen fibrils.