The influence of distal environment on peripheral nerve regeneration across a gap

Adult mice were divided into groups, all of which had the right sciatic nerve cut. In some groups, both the proximal and distal stumps were put into a plastic tube after various manipulations, while in other groups one or other stump was left out. Observations following survival periods of between 15 and 60 days showed that successful regeneration took place only in animals in which both proximal and distal stumps were present in the plastic tube and providing the cut ends of both stumps were facing each other. If the distal stumps were excluded from the tube or bent through 180 degrees, regeneration occurred initially, but was eventually ineffective. If the distal stump alone was inserted in the tube, a proliferation of Schwann cells, fibroblasts and regularly aligned collagen occurred. These findings support the hypothesis that the distal stump is essential for successful regeneration, but that in order to enhance it, the peripheral segment must be perfectly aligned with the proximal stump within the tube. Reasons for the necessity of such an alignment are discussed.