Objective To investigate an effect of differenttemperature cryopreservation of the two-step freezing method on the Schwann cell biological activity in the peripheral nerve of the rat. Methods Eighty femaleSD rats were randomly divided into 8 groups of 10 rats each. One was the control group and 7 were the experimental groups. Two 2-cm-long sciatic nerve segments were respectively taken from both legs of each rat. In the control group, the sciatic nerve segments did not undergo the treatment of cryopreservation; however, in the 7 experimental groups, the sciatic nerve segments respectively underwent the different temperature cryopreservation of the twostep freezing method at -20℃, -30℃, -40℃, -50℃, -60℃, -70℃ and -80℃. The sciatic nerve segments were cryopreserved for 2 hours，and then placed into the liquid nigrtrogen at -196℃. After 48 hours of storage，the nerve segments werethawed quickly in the 37℃ water bath box for 1 minute. Then, the sciatic nerve segments each group were harvested. The cells of the sciatic nerve were incubated with Calcein-AM for 15 minutes. The average fluorescence intensity of the cells was measured by the flow cytometry. The nerve fibers were also incubated with Calcein-AM for 15 minutes. The fluorescence intensity of the cells was analyzed by the confocal fluorescence microscope. The Schwann cell biological activity intensity was measured. Results The fluorescence intensity in the -40℃ group was the best and the Schwann cell biological activity in this group was thebest among all the groups（P＜0.01）. The fluorescence intensity in the 8 groups measured by the flow cytometry was as follows：242.522 0±9.568 4 in the control group，168.677 0±10.207 0 in the -20 ℃ group，214.992 0±8.329 1 in the -30 ℃ group，235.526 0±9.280 5 in the -40 ℃ group，222.434 0±8.515 5 in the -50 ℃ group，217.409 0±9.515 7 inthe -60 ℃ group，132.376 0±13.459 7 in the -70 ℃ group， and 108.132 0±16.033 1 in the -80 ℃ group. The fluorescence intensity detected by the confocal fluorescence microscope was as follows：143.700 0±5.567 8 in the control group，119.700 0±5.161 5 in the -20 ℃ group，121.300 0±4.347 4 in the -30 ℃ group，700 0±5.012 2 in the -40 ℃ group，121.000 0±4.546 1 in the -50 ℃ group，118.400 0±4.9261 in the -60 ℃ group，81.200 0±5.116 4in the -70 ℃ group，and 79. 000 0±5.716 4 in the -80 ℃ group. Conclusion The Schwann cell biological activity treated by the two-step freezing methodcan be preserved and the activity is cryopreserved best at -40 ℃.

Citation： XIAO Yuzhou,YAO Yunfeng,PAN Gongping,et al.. AN EFFECT OF THE TWO-STEP FREEZING METHOD ON THE SCHWANN CELL BIOLOGICAL ACTIVITY IN THE PERIPHERAL NERVE OF THE RAT. Chinese Journal of Reparative and Reconstructive Surgery, 2006, 20(8): 801-804. doi: Copy