Maximal regeneration distance. How far can a peripheral axon regenerate?

Peripheral nerves of the fore- and hindlimbs of 20 rats were induced to regenerate over double and triple of their original lengths through consecutive orthograde and retrograde (zigzag) anastomoses along parallel nerves of the same limb. Morphological changes were followed on longitudinal sections of the whole-mount composite nerves by several histological techniques. Regeneration regularly took place along this pathway. The regenerated axonal segments were intensively remyelinated, demonstrating the capacity of the spinal neurons to produce and maintain disproportionately long axonal processes. These observations may be relevant for reconstructive neurosurgery when very long peripheral nerve gaps have to be bridged.