Conditioning effect induced by chronic nerve compression. An experimental study of the sciatic and tibial nerves of rats.

To find out if chronic nerve compression could affect the peripheral nerve by acting as a "conditioning lesion", silicone tubes (internal diameter 0.8-1.6 mm) were placed round the sciatic or tibial nerves of adult rats for different time periods. After the period of compression the tubes were removed and a test crush lesion was made on the sciatic nerve in the thigh. Regeneration distances of the sensory nerve fibres were analysed by the pinch reflex test after a further three or six days. Compression of sciatic or tibial nerves induced a significant increase in outgrowth length compared with nerves subjected to mobilisation and crush lesion alone. All the tubes tested had a conditioning effect, but only tubes with a small internal diameter seemed to induce nerve fibre degeneration as assessed by immunocytochemistry. The results showed that chronic compression induced a regenerative response in the peripheral nerve. The mechanism by which this was accomplished remains obscure but it may involve both the neurons and the non-neuronal cells.