An experimental study of peripheral nerve regeneration after x-irradiation.

The effects of x-irradiation on peripheral nerve regeneration in the mouse were examined using quantitative and ultrastructural techniques. One hind limb was exposed to 15 or 20 Gy one day before, or 20 Gy three days after the right sciatic nerve was crushed. The distal sciatic and posterior tibial nerves were examined up to 120 days after injury. Irradiation before injury initially reduced the proliferation of endoneurial cells although cell numbers reached control levels after a few weeks. Myelination was delayed but not prevented, and after exposure to 20 Gy the myelin sheaths remained abnormally thin. In nerves irradiated after injury endoneurial cellular proliferation was severely and persistently reduced, and many fibres showed segmental absence of myelin. Internodes abutting the nonmyelinated segments were abnormally long, suggesting that contact with adjacent internodes may limit elongation of internodes during normal regeneration.