BACKGROUND: Operation of spine does not involve in spinal cord; however, spinal cord injury occurs at post-operation induced by unclear factors. Meanwhile, after decompression of lumbar spinal canal, symptoms are severer and severer. In addition, during extirpation of cervical and lumbar intervertabral disc, spinal cord and its vessels are not damaged, but spinal cord injury is also suffered from patients with partial improvement. All statuses mentioned above are related to expressed changes of bcl -2 gene inhibiting apoptosis and bax gene accelerating apoptosis. OBJECTIVE: To observe motor function of hindlimbs of ischemia/reperfusion model in rabbits at various time points after reperfusion and expressions of apoptosis correlated protein Bcl-2 and Bax. DESIGN: Completely randomized grouping design and contrast study. SETTING: Department of Orthopedics, the First Affiliated Hospital of Medical School, Xi’an Jiao Tong University. MATERIALS: Forty-eight New Zealand white rabbits of both genders were randomly divided into sham operation group (n =24) and model group (n =24), and then, rabbits in each group were observed at four time points: 8, 24, 72 and 168 hours after reperfusion, with 6 in each time point. Rabbit-anti-rabbit Bcl-2 antibody and rabbit-anti-rabbit Bax antibody were provided by Boster Company. The procedures were accordant to the kit introduction. METHODS: The experiment was carried out at Laboratory of Orthopaedics of First Affiliated Hospital of Medical School, Xi’an Jiao Tong University from April to August 2005. ① Delayed paralysis models of spinal cord after ischemia/reperfusion were established based on method of Zivin et al. Animals in sham operation group underwent an exposure of abdominal aorta but the aorta was not occluded. ② Motor function of hindlimb was observed 8, 24, 72 and 168 hours after reperfusion. A grade of 0-5 was assigned to each animal (grade 0: no voluntary hind limb function; grade 5: normal hop; grades 0-3: paraplegia). ③ The lumbar segment of the spinal cord (L3 to L5) was used for morphological studies at 168 hours after reperfusion and cut into sections with the thickness of 4 μm; and then, the sections were stained with hematoxylin and eosin and observed under optic microscope. ④ After dewaxing, paraffin sections were used to detect expression of Bcl-2 and Bax proteins with Strept-Avidin-Biotin Complex, (SABC) kit (Wuhan Boster Company). The detailed operation was accordant to kit instruction. ⑤ Sections under the same staining condition but at various time points were measured with Image-Pro Plus Version 5.1 for Window TM (Median Cybernetics, Inc. USA.) to detect average integrated absorbency of positive cells of Bcl-2 and Bax protein. ⑥ Measurement data were compared with one-way analysis of variance and t test. MAIN OUTCOME MEASURES: ①Hind limb motor function deficit;②Histopathological examination; ③ Expression of Bcl-2 and Bax proteins at different reperfusion time points in spinal cord. RESULTS: All the 48 rabbits were involved in the analysis of results. ① Motor function of hindlimb: Rabbits did not have paralysis in sham operation group. Rabbits in model group did not have paralysis at 8 hours after reperfusion, but had delayed paralysis at 24, 72 and 168 hours after reperfusion. Grade of motor function was lower than that in sham operation group (t =15.65, 20.55, 29.00, P < 0.01), similar to that in sham operation group at 8 hours after reperfusion and decreased obviously at 24 hours after reperfusion. ② Pathological changes of spinal cord tissue: Spinal cord tissue was normal in sham operation group. With the reperfusion time passing by, necrosis of neurons in spinal cord tissue in model group was increased, inflammatory reaction was strengthened gradually and pathological changes were obvious at 72 hours after reperfusion. ③ Expressions of Bcl-2 and Bax protein: At 8 hours after reperfusion, expressions were similar in both sham operation group and model group (Bcl-2: 20.42±4.22, 19.63±2.72; Bax: 5.22±1.24, 4.82±1.52, P > 0.05); expression of Bcl-2 was decreased obviously at 24 hours after reperfusion (8.09±0.96, t =9.78, P < 0.05) and reached the lowest value at 72 hours after reperfusion (6.08±1.51, t =11.06, P < 0.05). However, expression of Bax was increased obviously at 24 hours after reperfusion (12.84±1.77, t =7.88, P < 0.05) and reached peak at 72 hours after reperfusion (15.84±5.19, t =4.42, P < 0.05). At 168 hours after reperfusion, structure of gray matter was damaged severely and only a few of neurons survived. However, numbers of positive glial cells in white matter were increased, and expression of Bax was higher than that in sham operation group (9.41±1.53, t =6.44, P < 0.05). CONCLUSION: Ischemia/reperfusion injury of spinal cord can induce decrease of motor function of experimental animals and cause apoptosis. Changes of both of them are general coincidence with changes of Bcl-2 and Bax expressions with the reperfusion time passing by. BACKGROUND: Operation of spine does not involve in spinal cord; however, spinal cord injury occurs at post-operation induced by unclear factors. Meanwhile, after decompression of lumbar spinal canal, symptoms are severer and severer. In addition, during extirpation of cervical and lumbar intervertabral disc, spinal cord and its vessels are not damaged, but spinal cord injury is also suffered from patients with partial improvement. All statuses mentioned above are related to expressed changes of bcl- 2 gene inhibiting apoptosis and bax gene accelerating apoptosis. OBJECTIVE: To observe motor function of hindlimbs of ischemia / reperfusion model in rabbits at various time points after reperfusion and expressions of apoptosis correlated protein Bcl-2 and Bax. DESIGN: Completely randomized grouping design and contrast study. SETTING: Department of Orthopedics, the First Affiliated Hospital of Medical School, Xi’an Jiao Tong University. MATERIALS: Forty-eight New Zealand white rabbits of both genders were randomly divided into sham operation groups (n = 24) and model groups (n = 24), and then, rabbits in each group were observed at four time points: 8, 24, 72 and 168 hours after reperfusion, with 6 in each time point. Rabbit-anti-rabbit Bcl-2 antibody and rabbit-anti-rabbit Bax antibody were provided by Boster Company. METHODS; The experiment was carried out at Laboratory of Orthopedics of First Affiliated Hospital of Medical School, Xi’an Jiao Tong University from April to August 2005. ① Delayed paralysis models of spinal cord after ischemia / reperfusion were established based on method of Zivin et al. Animals in sham operation group underwent an exposure of abdominal aorta but The motor function of hindlimb was observed 8, 24, 72 and 168 hours after reperfusion. A grade of 0-5 was assigned to each animal (grade 0: no voluntary hind limb function; grade 5: normal hop ; grades 0-3: paraplegia). ③ The lumbar segment of the spinal cord (L3 to L5) was used for morphological studies at 168 hours after reperfusion and cut into sections with the thickness of 4 μm; and then, the sections were stained with hematoxylin and eosin and observed under the optic microscope. ④ After dewaxing, paraffin sections were used to detect expression of Bcl-2 and Bax proteins with Strept-Avidin-Biotin Complex, (SABC) kit (Wuhan Boster Company). ⑤ Sections under the same staining condition but at various time points were measured with Image-Pro Plus Version 5.1 for Window ™ (Median Cybernetics, Inc. USA.) to detect average integrated absorbency of positive cells of Bcl-2 and Bax protein. one-way analysis of variance and t test. MAIN OUTCOME MEASURES: ①Hind limb motor function deficit; ②Histopathological examination; ③Expression of Bcl-2 and Bax proteins at different reperfusion time points in spinal c ord. RESULTS: All the 48 rabbits were involved in the analysis of results. ① Motor function of hindlimb: Rabbits did not have paralysis in sham operation group. Rabbits in model group did not have paralysis at 8 hours after reperfusion, but had delayed paralysis at 24, 72 and 168 hours after reperfusion. Grade of motor function was lower than that in sham operation group (t = 15.65, 20.55, 29.00, P <0.01) obviously at 24 hours after reperfusion. ② Pathological changes of spinal cord tissue: Spinal cord tissue was normal in sham operation group. With reperfusion time passing by, necrosis of neurons in spinal cord tissue in model group was increased, and pathological changes were observed at 72 hours after reperfusion. ③ Expressions of Bcl-2 and Bax protein: At 8 hours after reperfusion, expressions were similar in both sham operation group and mod el group (Bcl-2: 20.42 ± 4.22, 19.63 ± 2.72; Bax: 5.22 ± 1.24, 4.82 ± 1.52, P> 0.05); expression of Bcl-2 was decreased obviously at 24 hours after reperfusion (8.09 ± 0.96, t = 9.78, and reached the lowest value at 72 hours after reperfusion (6.08 ± 1.51, t = 11.06, P <0.05). However, the expression of Bax was increased obviously at 24 hours after reperfusion (12.84 ± 1.77, t = and reached peak at 72 hours after reperfusion (15.84 ± 5.19, t = 4.42, P <0.05). At 168 hours after reperfusion, the structure of gray matter was damaged severely and only a few of neurons survived. However, numbers of positive glial cells in white matter were increased, and the expression of Bax was higher than that in sham operation group (9.41 ± 1.53, t = 6.44, P <0.05). CONCLUSION: Ischemia / reperfusion injury of spinal cord can induce decrease of motor function of experimental animals and cause apoptosis. Changes of both of them are general coincidence with changes of Bcl-2 and Bax expressions with the reperfusion time p assing by.