Effects Of Epidural Spinal Cord Stimulation On Hindlimb Locomotor Generators In Rats

PARTⅠSpinal cord reflexes induced by epidurat spinal cord stimulationin normal adult ratsEXP.ⅠEffects of epidural spinal cord stimulation voltage alteration on spinal cordreflexes in normal adult ratsObjective Effects of epidural spinal cord stimulation voltage alterationon spinal cord reflexes in normal adult rats were investigated, expecting to find out whereand how the spinal cord reflexes were generated. Methods Ten adult femaleSprague-Dawley rats were anaesthetized, following with electrode placed at S1 spinal cordsegment. 400mV, 600mV, 1200mV epidural spinal cord stimulation were appliedrespectively, while EMG signal was recorded with concentric needle electrodes atsemitendinosus of the rats, to observe the characteristics of spinal cord reflexes. ResultsThe threshold for generating a hind limb muscle respond is 300mV. Three kinds ofepidural spinal cord stimulation could induce 2 kinds of spinal cord reflexes. Lowerstimulation voltages, including 400mV, 600mV, had induced the short latency spinal cordreflexes, which were 5.27±0.36 ms and 5.19±0.67ms respectively. The higher 1200mV stimulation voltage had induced the long latency spinal cord reflexes, which were 2.57±0.23ms. Conclusion Different voltages of epidural spinal cord stimulation could inducedifferent spinal cord reflexes generated differently. The long latency reflexes might bemonosynaptic responses mediated by dorsal root excitement, while the short latencyreflexes might be sarcous electric activity mediated by direct excitement of motor neuron ormotor fiber.EXP.ⅡEffects of epidural spinal cord stimulation frequency alteration on spinalcord reflexes in normal adult ratsObjective Effects of epidural spinal cord stimulation frequencyalteration on spinal cord reflexes in normal adult rats were investigated, expecting to findout where and how the spinal cord reflexes were generated. Methods Ten adult femaleSprague-Dawley rats were anaesthetized, following with electrode placed at S1 spinal cordsegment. 50Hz, 60Hz, 80Hz, 100Hz epidural spinal cord stimulations were appliedrespectively, while EMG signal was recorded with concentric needle electrodes atsemitendinosus of the rats, to observe the characteristic of spinal cord reflexes. ResultsSpinal cord reflexes could be generated by 50Hz, 60Hz, 80Hz, 100Hz epidural spinalcord stimulations, while the late stage of high frequency stimulations could induce spinalcord reflexes lost, and appeared irregularly. Some of the rats appeared with spinal cordvanishing totally at the late stage of the stimulations. Latency and duration of spinal cordreflexes induced by 50Hz epidural spinal cord stimulations, which were 4.46±1.07ms and7.33±1.00ms respectively, statistically differed from the ones initiated by 60Hz, 80Hz,100HzESCS. Conclusion Spinal cord reflexes induced by high frequency epiduralspinal cord stimulation might be some kind of monosynaptic responses. Irregularly appearances of spinal cord reflexes induced by high frequency stimulation might due to theinhibitory effect of the high frequency stimulation.EXP.ⅢEpidural stimulation on different spinal segments induced spinal cordreflexes recorded using a concentric needle electrode in normal adult ratsObjective Spinal cord reflexes induced by epidural spinal cordstimulation of L2/S1 spinal cord segments in normal adult rats were recorded, expecting tofind out how the spinal cord reflexes were generated. Methods EMG signals weredetected using a concentric needle electrode inserted into the tibia muscle. Reflexlatencies induced by different stimulation voltages (400 mV, 600 mV, 1200 mV) werecompared with magnetic transcranial stimulation-induced motion evoked potentials. Theeffects upon the spinal cord reflex under epidural spinal cord stimulation with variousfrequencies (50 Hz, 60 Hz, 80 Hz, and 100 Hz) were also investigated. ResultsElectrical stimulation of L2 segment with different voltages did not induce statisticallysignificant changes in the latency of spinal cord reflexes. However, different voltageelectrical stimulation of S1 segment induced different reflexes. Conclusion Low voltageelectrical stimulation of S1 segment induced reflexes with longer latencies, which may bedue to excitation of dorsal root neurons. High voltage electrical stimulation of S1segments induced short latency reflexes, which may be due to direct excitation of motorneurons or nerve fibers. We recorded wave shapes that were different to those describedin previous studies, which may be related to the more localized recording area of theconcentric needle electrode used in this study. This highlights the need for furtherresearch using different recording electrodes. We were unable to induce rhythmichindlimb movement with high frequency electrical stimulation, possibly due to suppressedsensory feedback in anesthetized rats. Therefore, further studies that record EMG signals in waking rats are necessary.PARTⅡEffects of epidural spinal cord stimulation combined withtreadmill training on stimulated spinal cord and cerebral motor cortexultrastructure after moderate spinal cord injury in ratsObjective Epidural spinal cord stimulation (ESCS) combined withtreadmill training has been proven to help spinal cord injury patients and rats regainwalking ability. We plan to investigate how this procedure affects the ultrastructure of thestimulated spinal cord and cerebral motor cortex after moderate spinal cord injury in rats.Methods Twelve adult female Sprague-Dawley rats were randomly distributed intofour groups: (1) spinal cord injury group (SI), (2) spinal cord injury plus ESCS group (SE),(3) spinal cord injury plus treadmill training group (TT), and (4) spinal cord injury plustreadmill training and ESCS group (TE). All rats received a moderate spinal cord injurysurgery. Four weeks after the surgery, SE and TE rats received an electrode implantationprocedure, with the electrode field covering spinal cord segments L2～S1. Four weeks afterelectrode implantation, the SE rats received subthreshold ESCS for 30 minutes per day. TTrats received 5cm/s treadmill training for 30 minutes per day. TE rats received ESCS whilecarrying out treadmill training, with parameters equal to those of the SE and TT rats. SI ratsreceived no intervention, thus functioning as a control group. All procedures in these fourgroups lasted four weeks. After four weeks intervention, tissues of stimulated spinal cordand cerebral motor cortex were cut off following standard protocols for electronmicroscopy. Results After four weeks of intervention, TT and TE animals improvedtheir open field locomotion score to 18 (there were no significant differences between thetwo groups). In contrast, no significant improvement was observed in groups SI and SE. The diameters of cortical blood vessels were significantly larger in the TT and TE groupswhen compared to the SI and SE groups. There were no significant differences between theTT and TE groups or between the SI and SE groups. Synapses and neurons of thestimulated spinal cord and cerebral motor cortex were similar regardless of whether ratsunderwent ESCS combined with treadmill training or not. Conclusion Localizedstimulation on the lumbar enlargement may play an important role in ESCS's effectiveness.Treadmill trained rats showed widened motor cortex blood vessels, which could be due tothe expression of angiogenesis-related proteins leading to an increase in the size of thecapillary reserve. ESCS and treadmill training might not contribute to changes in thestimulated spinal cord and cortical pathways underlying the recovery of walking ability,which still needs more investigation.