| IntroductionPeripheral nerve injury is one of the most common clinical diseases. Serious nerve injury is always accompanied by Wallerian degeneration in the wound and distal regions of the nerve, apoptosis of some related neurons, wrong growth of motor and sensory neurites with each other in regeneration.More over, it will cause fibroplasias in nerve gap, and atrophy of axon terminals after a long period of denervation. So the treatment result is always dissatisfactory.Schwann cell is special glial cell in the peripheral nerve system. It plays an important role not only in the development, morphology and function of normal nerve, but also during the critical period of nerve injury, regeneration and healing. Hitherto, Schwann cell has become focus in clinical and basic research.As for the changes of Schwann cell during Wallerian degeneration in the peripheral nervous system, most scholars assume that being stimulated by numerous factors Schwann cell comes into mitogenic phase directly and proliferates massively,while a few researchers declare that Schwann cell has necrosis or apoptosis phase. The purpose of this study is to systematically investigate Schwann cell apoptosis in Wallerian degeneration, and evaluate itstime-related feature, by examining the morphologic changes, the different expression of apoptosis genes and TUNEL detection.Materials and MethodsThis study used a typical Wallerian degeneration model of adult female rat in response to sciatic nerve transection in vivo. Ninety-five SD rats were divided randomly into one normal group (8 rats) and eleven experimental groups (66 rats). Secondly, for experimental groups, the both hind legs of each rat were randomly divided into test leg (with sciatic nerve transected on upper 1/3 fraction) and control leg (nerve uninjured). So all test legs constitute a test group and ?11 control legs constitute a control group. After operation, all rats in experimental groups were respectively sacrificed at Ih, 6h, 12h, 24h, 2d, 3d, 4d, 8d, 14d, 21d and 30d. The specimens of mid distal sciatic nerve were collected. Then we examined the morphological changes of the nerve, the different expression level of S-100 protein and apoptosis genes yielding proteins such as Bcl-2, Bax, Fas in Schwann cell. We also use TUNEL method to detect Schwann cell positive rate.Results1. The test group showed Wallerian degeneration. The number of Schwann cell began to decrease at 24h, surprisingly rare at Day3 and Day4, then began to increase from Day8 and formed Bungner belt after 14 days. The control group merely showed slight changes in morphology in early trauma period.2. Schwann cell generally expressed S-100 at low level in all groups, which had significant difference from previous articles. The control group had no statistical significance (P>0.05), compared with the normal group; The S-100 positive rate of the test group began to elevate at Ih, and thendecreased obviously at 6h. Till Day4, it began to increase, arid reached the peak at Day21. It had statistical difference between the test group and the normal group at Ih and Day21 (PO.05).3. The normal group expressed Bcl-2 at low level, and the left legs had no statistical significance (P>0.05), compared with the right legs; Bcl-2 level in the control group apparently elevated at 6h, then slightly elevated at 24h, Day4 and Day21, it had significant difference (PO.01) compared with the normal group; Bcl-2 level in the test group was stepping up at 6h, 24h, 8d,14d and 30d, it had highly statistical significance (PO.01), compared with the normal group.4. The normal group expressed Bax at low level, and the left legs had no statistical significance (P>0.05) compared with the right legs;The control group continuously expressed Bax at high level at 6h, and from the 3rd to the 21st day. It had highly statistical significance (P<0.01) comoared with the normal group. Bax levels in the test group elevated progressively since Dayl4, and reached the top at Day30 . It had highly statistical sign...
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