| Backgrounds:Spinal cord injury caused by catastrophic accidents, one of the intractable diseases at present,has a high morbidity, high cost and the victims are mainly young adults. Up to now, there isn't still effective measures to repair the injured spinal cord and restore its function after injury. The reason is that the regeneration of mature central nervous system is difficult, but to our encouragement, in recent years, the studies related to regeneration of spinal cord injury has acquired abundant results.Many new methods such as repetitive transcranial magnetic stimulation,nerve transplantation, including neural stem cell transplantation, fetal spinal cord transplantation, peripheral nerve transplantation, neurotrophic factors,and electrical stimulation can make adult animals recovery to some degree, of which,repetitive transcranial magnetic stimulation is a new non-invasive painless treatment.Transcranial magnetic stimulation (transcranial magnetic stimulate, TMS) was first invented by Barker in 1985 as a cortical stimulation, which is painless, non-invasive, safe,reliable and easy to operate, so it was quickly applicated in clinic. TMS is the use of time-varying magnetic field generated in the cerebral cortex induced current changes in the cortex of the action potential of nerve cells, thereby affecting brain metabolism and electrical activity of biological neural stimulation. The role of the principle of TMS is that induced by a time-varying magnetic field induced electric field, specifically a fast current pulse through the stimulating coil, producing a strong transient magnetic field through the skull,causing adjacent nerve tissue produces secondary currents, local neurons to the polarization, resulting in physiological effects.Transcranial magnetic stimulation for the treatment of spinal cord injury is mainly to improve the function of motoring spinal cord injury, and various complications of treatment. The mechanism may be related to the coil stimulates the motor cortex of the brain, motor area neurons to produce depolarization and enhance the role of corticospinal tract conduction, promoting axon growth, thereby improving motor function. Frequency is an important parameter for the repetitive transcranial magnetic stimulation, and high frequency or low frequency which improve the motor function better, will be taken further study.Objective:To explore the mechanisms and the effects of repetitive transcranial magnetic stimulation(rTMS)on spinal cord injured rats(SCI)。Methods:Weight drop spinal cord injury model was made at thoracic 10 segments with improvement impactor device, Fourty-eight rats were rademaley devided into four groups, high repetitive transcranial magnetic stimulated group(n=12),low repetitive transcranial magnetic stimulated group(n=12,spinal cord injury control group(n=12),normal control group(n=12).Stimulated group received daily upthreshold rTMS for 8 weeks. Magnetic stimulation group after the operation 24h began to give stimulation, high frequency group frequency of 10Hz, low frequency group frequency of 1Hz, were all suprathreshold stimulation,500 pulses,1 day for 8 weeks, spinal cord injury in the control group was given sham stimulation.Observe all rats neurological function score,test motor evoked potential (MEP),at 1 day,1 week,2 weeks,3 weeks,4 weeks,5 weeks,6 weeks,7 weeks,8 weeks, and at 2 weeks and 4 weeks in each group were sacrificed three rats, all rats were killed at 8 weeks, using HE staining of spinal cord tissue morphological changes and immunohistochemical detection of neurofilament protein (NF-200) expression change.Results:1,Neurological function scorescore of rat in normal group was 21 points. The repeated measures analysis of variance showed significant differences between groups (F=1618.988,P=0.000), the treatment group than in the no treatment group the BBB score was higher. Different time points were significantly different (F=624.690, P=0.000), BBB score of each group changed with time change.Between treatment and time interaction (F=72.598,P=0.000), suggested that different treatment increased with time, BBB score variation. Further analysis of single effect, the results showed that within each time point between the two groups were significantly different (P= 0.000), within each group between different time points were significantly different (P=0.000).Normal group and the other groups at any time, there were significant differences compared (P=0.000).1 day,1 week control group, high frequency group, low frequency between the two groups showed no significant (P>0.05).2 weeks, the control group and high frequency group difference was significant (P=0.000), the control group and low group difference was significant (P=0.034), high frequency group and low frequency group difference was significant (P=0.021).4 weeks, control group and high frequency group difference was significant (P= 0.000), the control group and low group difference was significant (P=0.000), high frequency group and low frequency group difference was significant (P=0.024).8 weeks, control group and high frequency group difference was significant (P= 0.000), the control group and low group difference was significant (P=0.026), high frequency group and low frequency group difference was significant (P=0.013).2,Spinal cord morphologyGeneral observation:each group spinal was completely,the spinal of normal spinal cord integrity of smooth, spinal cord injury can be seen at the surface of yellow dye, the spinal cord significantly narrow in the spinal cord injury group Light microscope observation(400 times):spinal cord organizational structure of normal group integrity was clear, no swelling of the changes in morphologically normal neurons was shown, nuclear circle, the organizational structure of spinal cord injury control group loose, showing cavity formation, a large number of necrotic neurons. Spinal cord injury in high frequency group, low frequency group can be seen more loose spinal cord tissue, glial cell proliferation, part of the nerve cells swelling.3,Expression of NF-200 (NF-200 expression in the percentage of the total area%) In the normal group, the most densely nerve fibers was observered, the most sparse nerve fibers;in the spinal cord injury control group, only the small and short nerve fibers was observered; the magnetic stimulation group showed intensity of nerve fibers between the normal group and the spinal cord injuryed control group, high frequency group and low frequency group nerve fibers were slightly densty.NF-200 positive fibers of the total area percentage by factorial analysis of variance showed:there was significant difference on time (F=11.409, P=0.000) there was significant difference on groups (F=172.941, P=0.000) there was interaction effects between group and time (F=4.736, P=0.001),suggested that different treatment increased with time variation. Further analysis from single effect, there was significant difference on groups at 2 weeks(F=151.415, P=0.000), compared the normal group with the other groups,there was ststistical difference (P =0.000), compared high frequency group with the control group, there was no ststistical difference (P=0.222), compared low frequency with the control group, there was no ststistical difference (P=0.764), compared high frequency group with the low frequency group,there was no ststistical difference (P= 0.141).there was significant difference on groups at 4 weeks (F=127.725,P=0.000),compared the normal group with the other groups, there was ststistical difference (P=0.000), compared high frequency group and the control group, there was ststistical difference (P=0.003),compared low frequency group with the control group, there was ststistical difference (P=0.020), compared high frequency group with low frequency group,there was no ststistical difference (P=0.194);there was significant difference on groups at 8 weeks (F=65.211,P=0.000), compared normal group with the other groups, there was ststistical difference (P=0.000), compared high frequency group with the control group,there was ststistical difference (P=0.000),compared low frequency group with the control group, there was ststistical difference (P=0.000), compared high frequency group with low frequency group, there was ststistical difference (P=0.013).There was showed that NF-200 expression increased treatment group compared with spinal cord injury in the control group at 4 weeks, compared high frequency with low frequency group NF-200 expression increased at 8 weeks.4,Motor evoked potentialIn normal group the motor evoked potential latency was the shortest,the amplitude was the largest; In spinal cord injury control group the motor evoked potential latency was longest and the amplitude was smallest, almost invisible; the motor evoked potential latency and amplitude of high frequency group and low frequency group wan beteewen the normal group and the spinal cord injury control group.the positive rate of motor evoked potentials in the same group at different time points detected,in addition to the normal group unchanged(100%), other groups at different time points were significant differences (P values were 0.001,0.001,and 0.042).The same time in different groups were compared,in addition eight weeks (P=0.143), within the various time points were statistically significant differences between groups (P all＜0.005).Conclusions:Repetitive transcranial magnetic stimulation can promote the recovery of motor function in rats,which may be related to the promotion of axon growth. High frequency stimulation can improve motor function than low frequency stimulation,which indicated that the excitement of the cerebral cortex.However the possible the other parameters such as intensity of treatment may also played a role.The study in the field need to be further explored.
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