Effects Of Exercise Training On Distal Lumbar Spinal Cord In Rats With Thoracic Spinal Cord Injury And Its Mechanism

Background:Current studies have confirmed that treadmill training leads to functional and morphologic changes in distal spinal segments after spinal cord injury, but it’s still unclear whether the changes in distal spinal segments promote locomotor recovery after treadmill training.Objective:To observe the role of lumbar spinal changes in locomotor recovery after incomplete thoracic spinal cord injury (iSCI) in rats.Methods:48 SD rats were randomly divided into 4 groups:control group with sham operation (Con-Sed group), exercise group with sham operation (Con-TT group),control group with SCI (SCI-Sed group), exercise group with SCI (SCI-TT group). Sham operations were made for the Con-Sed group and Con-TT group, ISCI (T10 vertebral level) were made for the SCI-Sed group and SCI-TT group. Treadmill training began at the 8th day post surgery and lasted for 4 weeks. The spinal cord transection (T10 vertebral level) was performed on the 5th week. Motor function assessments were BBB score and inclined plane test, and evaluation time points were before injury and on the 2nd,7th,14th,21st,28th,35th,37th day post iSCI. All rats were sacrificed 2 days after SCT and L3-L6 spinal segments were taken after sacrificed. Nissl staining was used to compare the quantity and morphology of motor neurons, Western-blot and immunofluorescence were used to detect the BDNF and TrkB expression in distal spinal segments.Results:1) The motor function assessments (BBB score and Inclined plane test) demonstrated that motor function has self-recovery capacity after iSCI in rats and BWSTT could increase the degree of recovery. Rats in SCI-TT group retained better motor function than untrained rats after SCT.2) Results of Nissl staining on L3-L6 sections showed that secondary lesions, such as motor neurons reduction and paramorphia, were occurred in distal spinal motor neurons after iSCI, while BWSTT reduced the secondary lesions.3) Western-blot and immunofluorescence of lumbar spinal cord showed that BDNF increased after thoracic iSCI and the increase amplified by BWSTT. TrkB expression was not significantly changed after iSCI but was significantly increased after BWSTT.Conclusion:Exercise training may alleviate the secondary degeneration in lumber spinal motor neurons and enhance the expression of BDNF/TrkB in spinal cord distal to injury level in rats, and exercise training promotes lumbar spinal cord changes leading to locomotor recovery after partial thoracic spinal cord in rats.Background:Previous studies have revealed that treadmill training decreases the secondary lesion in distal spinal motor neurons, promotes BDNF/TrkB expression in lumbar spinal cord and promotes locomotor recovery after SCI, but how did treadmill training impact the distal spinal cord remains unclear. Neuromuscular activity is part of the treadmill training process, but it is still unclear whether it related with changes in distal spinal segments.Objective:In this study, the gastrocnemius were paralyzed via intramuscular botulinum toxin A (BTX-A) injection to determine the effects of reducing the neuromuscular activity on the motor function and BDNF/TrkB expression in distal spinal segments after thoracic SCI.Methods:A total of 48 female rats were randomly divided into four groups: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). Animal model of incomplete SCI was created using a modified Allen’s method at T10 Lamina. After SCI, BTX-A or normal saline were injected to the gastrocnemius. Exercise training groups were trained for 4 weeks by body weight support treadmill training (BWSTT) 1 week after surgery. All rats were sacrificed 5 weeks after SCI and L3-L6 spinal segments were taken after sacrificed. We compared the motor function (Inclined plane test and digit abduction score), the morphlogical characteristics and EMG of gastrocnemius, BDNF/TrkB expression in distal spinal segments.Results:1) The locomotor function assessments (Inclined plane test and DAS assay) demonstrated that BTX-A reduced the locomotor recovery that promoted by BWSTT.2) Pathological analysis and EMG on gastrocnemius showed an obvious atrophy of gastrocnemius and lower neuromuscular activity after BTX-A injection. 3) Western-blot and immuno fluorescence of lumbar spinal cord showed that BDNF and TrkB expression were decreased after BTX-A injection. Fluorogold retrograde tracing showed that those proteins mainly reduced in motoneurons which domain gastrocnemius.Conclusion:The improvement in motor function after treadmill training was inhibited with BTX-A injection. The expression of BDNF and TrkB after treadmill training was also inhibited after BTX-A injection. Skeletal muscle may influence lumber segments through motor nerve, and play an important role in functional recovery after spinal cord injury. Neuromuscular activity is required to locomotor recovery in SCI rats following treadmill training.