Reinnervation of muscle in the mouse following nerve crush and X-irradiation.

The effects of X-irradiation on nerve regeneration were examined in adult mice. The right sciatic nerve was crushed focally and 3 d later the hind limb was exposed to 20 Gy X-rays. Compound muscle action potentials (m.a.p.s) were recorded in vivo from the posterior crural muscles. Stimulation of the sciatic nerve proximal to the crush injury evoked m.a.p.s of low amplitude with marked temporal dispersion. Stimulation at 20 or 50 Hz resulted in almost immediate intermittent failure of the longer latency m.a.p.s. In vitro physiological examination showed X-irradiation to have no effect on the timing of reinnervation. However, the latency of evoked end-plate potentials was prolonged and, on repetitive nerve stimulation, increased markedly until failure occurred. Nerves which regenerated after X-irradiation showed impaired conduction, particularly of trains of impulses.