| Objective A graded contusion spinal cord injury (SCI) model was made by weight drop technique (modified Allen's method). The contents of major element calcium (Ca), Magnesium (Mg) and trace elements Copper (Cu), Zinc (Zn) and Iron (Fe) were measured before SCI and at different time points after SCI, combined with examination of nervous function of rabbits hind legs, somatosensory evoked potential, to study the changes of serum elements after SCI, and the outcome of them during the course of functional recovery, discuss the mechanism and their role in secondary damage of spinal cord, provide experimental bases for clinical treatment of spinal cord injury.Method 26 health mature rabbits, weight 2.5-3.0kg, without distinction of sex, were randomized divided into three groups: group SCI A (group A, n=10). Group SCI B (group B, n=10) and sham operation control group (group C, n=6). The animals of group A and group B were anesthetized with ear venous injection of 3% Pentobarbital sodium solution (30mg/kg), pronated on the operating table. The twelfth thoracic vertebra (T12) leminectomy was performed, and about 0.6×0.6cm spinal cord was exposed. The spinal cord injury was produced with modified Allen's method. The impact energy of 100 gram cm force (gcf) and 60gram cm force were separately given to group A and group B. For the animals of group C, only leminectomy were made with same approach to group A and group B. The spinal cords were not subjected to impact trauma. Served as controls. 2ml venous blood was taken from the upper part of small saphenous vein of all the animals of three groups before surgery and at 30 minutes, 24 hours, 72 hours and 7 days after surgery. The blood samples were placed at room temperature for 30 minutes - 60 minutes after blood coagulation, centrifugalized at 3000r/min with electric ceatrifuger for ten minutes. The serum was extracted and stored at -80℃ hypothermia refrigerator for tater examination. Diluting 0.5 ml serum with double - distilled water, the elements were measured by SpectraSpan V. Three Electrodes Direct Current Plasma Atomic Emission Spectrometer (DCP-AES) made in Beck Man. U.S.A. All the test tubes used in the experiment were cleansed with distilled water. At the same time points of blood taking, the animals nervous function of group A and group B were observed. The move functions of hind legs were classified as six grades: grade 0, no move of hind legs and tails; grade I , slight move of hind legs and tails; grade II, hind legs and tails move obviously, even one leg can stand; grade III, stand with two legs, but can't walk, tails swing, grade IV, stand and walk with two legs, can't ran; gradeV, normal. The somatosensory evoked potential was introduced simultaneously with the functional examination. The apparatus used were Key point - portable Two Channel Evoked Potential Recorder and Magnetic Stimulus made in Denmark. The stimulus electrode of needle type was inserted into subcutaneous tissue of medial side of left calcaneal tendon. The record electrode (black) of needle type was placed subcutaneously between two ears. The reference electrode (red) was inserted to brow subcutaneous tissue. Stimulated the tibial nerve with voltage impulse mode, wave - width: 0.2ms, stimulus frequency: 2 Hz; stimulus intensity: 0.5-1mA; analysis time: 20 ms; number of stimulus: average 100-200 times. The latence and amplitude were separately examined and recorded.Results Remarkable changes were found in serum elements after spinal cord injury. These changes include that the contents of Ca, Cu increased and Mg, Zn and Fe decreased rapidly. The changes were obvious early at 24h, reached to the climax at 72h after SCI. For the control group (group C), the contents of serum elements before sham operation were: Ca 109.31 ±9.18, Mg 22.09+1.98, Cu 1.12 + 0.09, Zn 1.43 + 0.30, Fe 2.89 + 0.40. At 30minutes after surgery, Ca 110.50 + 8.97, Mg 21.85 + 2.89, Cu 1.14 + 0.12, Zn 1.45 + 0.29, Fe 2.78 + 0.40. At 24h, Ca 107.92 + 7.59, Mg 23.05± 2.01, Cu 1.10+0.14, Zn 1.41 ±0.17, Fe 2.64±0.48. At 72h, Ca 104.74± 10.10, Mg 20.59 ±2.57, Cu 1.08 ±0.13, Zn 1.39 ±0.18, Fe 2.90±0.73 c At 7d, Ca 112.08 ±9.19, Mg 21.47±7.98, Cu 1.20±0.16, Zn 1.35 + 0.31, Fe 2.94±0.65. There were no difference in element contents of every time point after surgery and before that. For the group A, the element contents before SCI were: Ca 105.83 ±9.89, Mg 22.51 + 2.31, Cu 1.10+0.12, Zn 1.39±0.30, Fe 2.90±0.69. At 30min after SCI, Ca 107.61 + 8.57, Mg 21.98±3.05, Cu 1.13+0.17, Zn 1.35±0.25, Fe 2.91 ±0.59. At 24h, Ca149.51 + 10.17, Mg 16.17 + 2.58, Cu 1.46±0.19, Zn 0.98+0.11, Fe 2.18+0.45. At 72h, Ca 161.85+9.49, Mg 15.83 + 2.19, Cu 1.56+0.18, Zn 0.91+0.09, Fe 2.08 + 0.34. At 7d Ca 158.47+11.54, Mg 16.53 + 3.01, Cu 1.51+0.21, Zn 1.01+0.17, Fe 2.51+0.30. There were no obvious differences between 30min after SCI and before SCI or the control group. But the contents of 24h to 7d after SCI had remarkably difference with that of before SCI and control group. For the group B, before SCI, the contents were: Ca 108.31+8.98, Mg 21.60 + 2.22, Cu 1.11 ±0.11, Zn 1.40 + 0.31, Fe 2.89+0.57, had no difference with that of group C. At 30min after SCI, Ca 107.92 + 10.91, Mg 21.83 + 2.19, Cu 1.14+0.09, Zn 1.40±0.29, Fe 2.81+0.49. had still no difference with that before SCI. At 24h, Ca 139.42 + 7.96, Mg 16.59 ±2.01, Cu 1.38 ±0.15, Zn 1.17±0.25, Fe 2.51 ±0.75. At 72h, Ca 149.81 ± 11.05, Mg 19.80 + 3.18, Cu 1.41 ±0.14, Zn 1.12±0.19, Fe2.78±0.64. At 7d, Ca 121.09±6.54, Mg 20.89± 3.51, Cu 1.20±0.15, Zn 1.18+0.18, Fe 2.98±0.83. The changes were similar to group A, but comparatively slight. All the elements measured in the time of 72h after SCI were significantly different between group A and group B. The results of functional examination to the hind legs were: group A, all the animals were graded as 0 at 30min after SCI; at 24h after SCI, nine of ten animals were grade 0, one was grade I ; at 72h, eight were grade 0, two were grade I ; at 7d, seven were grade 0, two were grade I, one was grade II. group B, at 30min after SCI. all ten animals were also grade 0; at 24h, eight were grade 0, two were grade I ; at 72h, two were grade 0, four were grade I , three were grade II, one was grade III; at 7d, only one was grade 0, four were grade I three were grade II, two were grade III. It was indicated that the function began to recover from the time of 24h after SCI. The difference of recovery degree between group A and group B from 24h - 7d after SCI were significant. The results of somatosensory evoked potential examination: SCI led to a series of alterations characterized as decline or disappearance of amplitude and lengthening of latence. In group A, the amplitudes were 5.89 ±0.28 u V before SCI, but at the time of 30min after SCI, they were complete disappeared, showing as a straight line; at 24h, they were 0.48±0.05 u V , at 72h, 0.78±0.08 u V; at 7d, 0.98± 0.11 u V. The changes were remarkably different between after and before SCI. In group B, the amplitudes were 5.85±0.18 u V before SCI; at the time of 30min after...
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