Research On The Regulation And Mechanism Of Exercise On Different Levels Of Central Nervous System BDNF In SCI Rats

Backgrond:A vast majority of studies mainly focused on the effects of a variety of therapeutic measures on the local axonal regeneration and repair after spinal cord injury.However,these studies have paid no attention on the impact of these treatments on cerebral cortical neurons and spinal cord motoneuron distal to injury site,and thus exert certain influence on the spinal cord injury.Our preliminary research results suggested that exercise training can promote spinal cord injury(SCI)motor recovery in rats,but the mechanism remains unclear.Objective:To observe the role of exercise on cortical neurons,spinal cord injury site neurons distal lumbar spinal cord injury motor neurons in severe incomplete spinal cord injury rat.Methods:Female Sprague-Dawley rats(45)were randomly divided into three groups,sham operation group(Sham group),spinal cord injury group(SCI group),and spinal cord injury with exercise training group(SCI-TT group),each group has 15 rats.SCI group and SCI-TT group were operated at T10 vertebral level to make SCI model,all rats were recovered for 1 week after surgery then SCI-TT rats exerted four weeks of exercise training.BBB score and inclined plane test were carried out prior to the injury,and 2,7,14,21,28,35 days post SCI operation.All rats were sacrificed at 35 days after SCI,Hind limb sensorimotor cortex,injured spinal cord,L3-L6 spinal segments were collected for further research.The retrograde tracer Flouro-gold(FG)was adopted to retrograde the position of cortex neurons,and the number of the hind limb sensorimotor cortex neurons were counted.The corticospinal tract in the spinal cord injury site was checked By using anterograde tracer BDA.Nissl staining was used to compare the quantity and morphology of motor neurons in lumbar spinal cord,Western-blot,immunofluorescence and QPCR were used to detect the BDNF and TrkB expression in hind limb sensorimotor cortex,injured spinal cord,and L3-L6 spinal segments.Results:(1)The motor function assessments(BBB score and Inclined plane test)demonstrated that exercise training promoted the movement function recovery in spinal cord injury rats.(2)Investigation of anterograde tracer BDA injection showed no extended corticospinal tract in distal end of injury in both SCI-TT group and SCI rats.(3)Observation of retrograde tracer Flouro-gold injection showed that exercise training to promote hindlimb motor neurons survival after spinal cord injury in rats.(4)Results of Nissl staining on lumbar spinal cord revealed that exercise alleviated the secondary injury after the thoracic spinal cord injury.(5)Exercise training increased the expression of BDNF in both protein and RNA level at rat brain cortex,the distal lumbar spinal cord,spinal cord injury site.Conclusion:Exercise training enhanced the recovery of the injured spinal cord,reduced the secondary damage in the Hind limb sensorimotor cortex,injured spinal cord,and distal lumbar spinal segments,and promoted the expression of BDNF at all these sites.Background:Previous studies have reveal that treadmill training decreases the secondary damage in distal spinal motor neurons,and enhances BDNF and TrkB expression in lumbar spinal cord,thus promotes locomotor recovery after SCI.However,it was still remain uncover on the impact of treadmill training on the distal spinal cord.Neuromuscular activity was involved in this training process,but further studies should be taken to investigate its biological function on distal spinal segments.Objective:To figure out whether treadmill training promotes the recovery of movement ability in SCI rat through the neuromuscular interaction or not,intramuscular botulinum toxin A(BTX-A)injection was adopted to paralyzed gastrocnemius to abolish the effects of niche formed by surrounding muscle,furthermore,the rehabilitation was checked.Methods:Female Sprague-Dawley rats(48)were randomly divided into four groups to generate incomplete spinal cord injury models at T10 vertebral level using a modified Allen's method at T10 Lamina,including control group with normal saline injection(Sed-NS group),exercise group with normal saline injection(TT-NS group),control group with BTX-A injection(Sed-BTX group),exercise group with BTX-A injection(TT-BTX group).BTX-A or saline were injected to the gastrocnemius.All rats were recovered for 1 week after surgery then Exercise training groups were trained for 4 weeks by body weight support treadmill training(BWSTT).The retrograde tracer Flouro-gold(FG)was injected 1 week before sacrifice.BBB score and inclined plane test were taken to compare the motor function,and the morphlogical characteristics of gastrocnemius,gene expression in distal spinal segments including BDNF,TrkB,NeuN and c-fos.Results:(1)The locomotor function assessments(Inclined plane test and DAS assay)demonstrated that BTX-A reduced the locomotor recovery that promoted by treadmill training.(2)Results of Nissl staining on lumbar spinal cord revealed that BTX-A injection block the function that exercise alleviated the secondary injury after the thoracic spinal cord injury.(3)The enhancement of the neuronal activity markers,such as BDNF,TrkB,NeuN,and c-fos,by treadmill training after SCI was inhibited by BTX-A injection in distal spinal cord.Similar decrease of the markers'expression were observed in FG positive motor neurons by immunofluorescence.Conclusion:The improvement in motor function after treadmill training was inhibited with BTX-A injection.Also,the protection effects against the secondary damage of the motor neurons were reduced.The expression of such neuronal markers as BDNF,TrkB,NeuN,and c-fos after treadmill training was also inhibited after BTX-A injection.It showed "skeletal muscle-motor-reverse spinal cord pathway" played an important role in the functional recovery of injured spinal cord,and maintain neuromuscular activity which was the fundamental role of exercise training to promote functional recovery of rats' motor activity after SCI.