RESUMO
The sciatic nerves of rabbit were frozen with different temperatures(-20℃,-60℃, -- 100℃, -140℃ and 180℃).The morphology and function of the frozen nerves were examined with light microscopy (HE stain and histochemical thiocholism method), electron microscopy, and short latency sematesthelic evoked potentials(SSEP), sensory conduction velocity(SCV), electromyo-gram(EMG) at various time intervals after freezing. It was showed that there were no changes in morphology and function of nerves after being frozen at -20C. The nerve fibers showed signs of frozen degeneration and lost their conduction function at -60℃. However, the nerves could recover in this group. About one half of the nerve fibres frozen with -100℃ showed Wallerian degeneration, and the time of repair was delayed. But still the regeneration of nerves was complete. Necrosis of nerve fibers occurred immediately after freezing with -140℃ and-180℃. There were destruction of the basement membrane and proliferation of collagen fibers. The results explained the mechanism of cryoanalgesia clinically. We believe that the temperatures lower than -140℃ are optimal for cryoanalgesia.