| Spinal Cord Injury (SCI) is a common clinical orthopedic trauma. As people's increasingly wide range of social activities and the speed development of transportation industries, the spinal cord injury incidence is showing a rising trend. In recent years, with the development of molecular biology, cell biology and other disciplines, a large number of experiments confirmed that mature mammalian central nervous system injury can have different degrees of restoration, and some damaged neurons regenerated axons can have a certain and target cells with the formation of functional synaptic connections. Allow paralyzed patients to return to normal function, they must place the damaged spinal cord axon regeneration. To enable paralyzed patients to return to normal function, the damaged spinal cord axon must be regenerated. The regeneration and extension of the axon are the key. But axon regeneration requires a certain environment. The related research shows that structural damage to the nervous system and functional recovery depends on many factors, including nerve endogenous and exogenous factors. The internal factors include the regeneration ability of nerve, however the external facotors are affect by the environment of the damaged parts. Glial cells are activated and participate in scar formation and the dense scar tissue repair in the CNS is a difficult obstacle to overcome.Based on that, there is no effective clinical treatment for spinal cord injury. In another word, axonal regeneration and injury treatment of the spinal injury are not satisfactory, particularly complete spinal cord injury. What factors are primarily related to the regeneration environment for nerve axons? Neurotrophic factor is one of the factors, because CNS synapses have plasticity and external environment for the full neurotrophic factors can support their axons to the target cell bud growth, and the additional neurotrophic factors of the lesion in the CNS can increase the capability of regeneration. Glial cell line-derived neurotrophic factor (GDNF) is a kind of NTFs . Although research finds spinal cord injury& peripheral target tissues and damaged neurons can also produce a limited and small amount of NTFs. As the axon is damaged, Neurons lost contact with the effector,as well as NTFs damaged axons can not transfer to neurons.With the large number of neurons compete with each other NTFs, programmed cell death happened to the never cells which have no sufficient NTFs nutrition. Based on this, exogenous GDNF in spinal cord injury is possible.Because the normal tissue content of GDNF in very small, GDNF protein of high purity has been synthesized. With the further development of technology and genetic engineering, therefore, this sub-GDNF in animal experiments and clinical application of a solid material foundation, and then the application to the clinical treatment of spinal cord injury is possible. So far, it is discovered that GDNF has played the most powerful role of neurotrophic factors .In addition, how to bridge the regeneration of spinal cord nerve fibers through the holes and scars has become the key to the treatment of spinal cord injury. For this reason, in recent years, application of biological material of catheter induced spinal cord injury has gained attention. Because a large number of experimental studies have confirmed that nerve regeneration can not guarantee that the impact of the surrounding fibrous connective tissue so as to make new nerve fibers to grow into successful remote. Nerve tissue engineering scaffolds can serve as a guide nerve regeneration hollow pipe which can providethe regeneration of axons with a relatively closed micro-environment and avoid nerve neuroma false and the formation of long to enable neurons to reach the target organ and restore nerve function. PLA - poly trimethylene carbonate (PLA-PTMC) is an ideal scaffold of biodegradable absorbent ,which is newly discovered in recent years. It solved the shortcomings of time and hardness of polylactic acid (PLA) Degradation. It is more soft, more flexible. In addition, PLA retains the characteristics of excellent incompatibility, degradation mechanism is the diffusion type.The purpose of this experiment is to study the PLA-PTMC / GDNF complex catheter formed by PLA-PTMC catheter biomaterials combined GDNF, of which application can more effectively perform its biological activity to repair spinal cord injury in rats, and observe the recovery of rats' complete spinal cord tansecton lesion after treatment as well as explore the repair mechanisms. 1 The experimental study on appropriate GDNF content in PLA - Poly-TMC / GDNF composite catheterMethods: Female Wistar rats of 220 ~ 260g were randomly divided into three groups, which are normal control group, complete spinal cord transection group (Group A ) and treatment group. Composite catheter in accordance with PLA-PTMC/GDNF treatment, group differences in GDNF content was divided into 4 groups which are 100u group (Group B), 300u group (Group C), 500u group (Group D) and 700u group (Group E), in each group of nine rats. When 2 weeks, 4 weeks, 6 weeks, 8 weeks, through behavioral analysis, animals were sacrificed after 8 weeks, Spinal Cord Injury Zone line GAP-43 mmunohistochemistry, ultrastructural analysis .Results: After the treatment, the double hind limbs BBB scores of Group C, Group D & Group E versus Group A and Group B increased significantly at 4 weeeks,P<0.05. At 6 weeks, the scores of Group C and Group D versus those of Group A, Group B, Group E are higher.At 8 weeks, the growth rate of the scores of Group D and Group D slowed down,but compared with Group A, Group B and Group E, it was still higher,P<0.05. GAP-43 immunohistochemistry results:After 8 weeks, Group C, GroupD , the transplanted office GAP-43 positive cells was significantly greater than the determination of area A group, B group and E group, P <0.05. GAP-43 positive cell areas in the transplant area of Group C and Group D was significantly greater than which of Group B, Group D and Group E,P<0.05。8 weeks after surgery , electron microscope observation of spinal cord injury zone indicated the structure of Group C and Group D was better than Group A, Group B and Group E, showing a large number of myelinated nerve fibers formed more regular shape, thick myelin sheath.Conclusion: PLA-PTMC/GDNF composite catheter in the GDNF content of 300u and 500u groups get the best recovery of motor function, to wit, neural regeneration is the best. The GDNF content of 300 ~ 500 is appropriate.2 The experimental study of the mechanism and the protective effect of PLA - Poly-TMC joint GDNF on pinal cord injury of rats2.1 All of rats complete spinal cord injury model were established and ehavioral analysisMethods: Wistar female rats weighing 220 ~ 260 g, were randomly divided into: normal control group, complete spinal cord transection group (Group A ) and treatment group, treatment group was divided according to 3 different treatment groups, a single application GDNF group (Group B ), a single application of PLA-PTMC implantation group (Group C), application PLA-PTMC/GDNF composite catheter implantation group (Group D). Nine rats in each group, experiment, animal model of death, to analyze the reasons and correct promptly added, and the labeling is done according to experimental design delay the completion of the assessment of the indicators. The experiment, animal model of death, then promptly added, and the labeling is done according to experimental design delay the completion of the assessment of the indicators. After 2 weeks, 4 weeks, 6 weeks and 8 weeks BBB behavioral score.Results: BBB behavioral score results showed that when it was 2 weeks, the scores of each group have no significant difference . 4 weeks after surgery , the scores of Group C& Group D versus Group A & group B high were higher and there was significant difference, P <0.05. 6 weeks or 8 weeks after surgery, the scores of Group D versus Group A were higher and there was significant difference, P <0. 05.Conclusion: The functional Recovery in the composite catheter group (Group D) function is best , the repair of the recovery of Spinal Cord Injury is superior to a single application of PLA-PTMC catheter group (Group B) and a single application of GDNF group (Group C).2.2 Study on histology of spinal cord injuryMethods: Preparation of animal model and grouping with 2.1, 36 rats in each group, respectively, at 2 weeks, 4 weeks, 6 weeks and 8 weeks, the survival of rats in each group 6 rows HE, immunohistochemistry, and ultra- microstructure observation.Results: HE staining in 4-8 weeks after surgery Group A, GroupB and group C to stabilize the number of glial cells did not change significantly, Group A of glial scar formation. Group D of glial cells after 4 weeks still more, after 6-8 weeks, reduce the number of glial cells at 8 weeks and there was no glial scar formation, 6-8 weeks in nerve fibers in the catheter appears. GFAP immunohistochemistry results: 2 weeks, more GFAP immunoreactive cells appeared in the damaged zone of each group, comparing the the determination of the positive cell area, it was found that Group C ,Group D versus Group A, Group B had a significant difference, P <0.05. At 4 weeks, 6 weeks and 8 weeks, the number of positive cells gradually decreased and the size of the positive became smaller. The positive cell area in Group D versus that in Group A, Group B and Group C decreased with significant difference, P<0.05. NF200 immunohistochemistry Results: At 4 weeks, 6 weeks and 8 weeks, Group D OD values and Group A, Group B, Group C were higher, and there was significant difference, P <0.05. Electron microscope results: 2 weeks after operation, Group D showed a small number of myelinated nerve fibers and myelin sheath thick. At 4 weeks, compared with Group A, Group B &Group C, a small number of myelinated nerve fibersa had formed and myelin sheath had gotten thicker in Group D. 6 weeks after operation , the number of nerve fibers in Group D continues to grow , which is larger than that in Group A, Group B& Group C.Conclusion: The composite catheter implanted PLA-PTMC/GDNF reduce secondary spinal cord injury with the impact of glial cell proliferation and differentiation, and promote nerve fiber regeneration and myelin formation.2.3 Effects of PLA - Poly-TMC / GDNF catheter on the expression of spinal cord injury district GAP-43mRNAMethods: Preparation of animal model and the group with 2.1, respectively, in the first 2 weeks, 4 weeks, 6 weeks and 8 weeks each group were sacrificed three surviving rats underwent the spinal cord injury district GAP-43 mRNA of PT-PCR detection and analysis. Results: 2 weeks after operation, the GAP-43mRNA relative expression level of Group A, Group B, Group C and Group D was significantly higher, compared with the normal group, P <0.05; 4 weeks after operation, the GAP- 43 mRNA expression of Group Band Group D which was compared with the first 2 weeks were significantly higher, P <0.05, and it was significantly higher than that of Group A and Group C ,which has significant difference, P <0.05; 6 weeks, the expression of GAP-43mRNA in Group D still significantly increased which was significantly higher,compared with that in the first 4 weeks, P <0.05, and compared with Group A, Group B and Group C , Group D has significant differences, P <0.05; after 8 weeks mRNA expression of GAP-43 in each group decreased, but therelative expression level of GAP-43mRNA in Group Dwas still higher than that in Group A, Group B and Group C , P <0.05.2.4 Effects of PLA - Poly-TMC / GDNF catheter on the protein expression of spinal cord injury district GAP-43Methods: Preparation of animal model and the group with 2.1, respectively, in the first 2 weeks, 4 weeks, 6 weeks and 8 weeks, each group was sacrificed three surviving rats underwent the spinal cord injury district GAP-43 protein in Western Blot detection and analysis.Results: After 2 weeks, GAP-43 protein levels of Group B, Group C and Group D was higher than the normal group, P <0.05; 4 weeks after surgery, compared with the second weeks, GAP-43 protein expression in Group D significantly increased, P <0.05, and it was significantly increased more than Group A Group B and Group C.P <0.05. 6 weeks after surgery, the GAP-43 protein expression in Group C and Group D was significantly higher than that in the normal control group, Group A and Group B, P <0.05. 8 weeks after surgery, compared with that that of 6 weeks, the GAP43 expression of each group decreased , however, the GAP-43 protein expression in Group D was still higher than that in the normal control group, Group A , Group B and Group C, P <0.05.Conclusion: RT-PCR and Western Blot detection show that after surgery, GAP-43mRNA expression and GAP-43 protein expression of Composite catheter after injury have increased since 2 weeks. The first 4 weeks and 6 weeks increased significantly after operation, highest at 6 weeks, 8 weeks down. PLA-PTMC / GDNF complex catheter more conducive to axon regeneration of spinal cord repair connection and functional recovery.As stated previously, the positive correlation between GDNF catheter and the PLA-PTMC synergy can significantly promote the nerve regeneration of the central nervous system. Better than the simple application of PLA-PTMC catheter and a simple application of GDNF on spinal cord injury. GDNF content in the appropriate form of PLA-PTMC / GDNF complex catheter can promote the recovery of the functions and structures of the nerve with complete spinal cord injury, and the method presented in this paper proves to be a novel way to the treatment of spinal cord injury.
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