大鼠慢性颈脊髓压迫减压术后神经功能改变及其相关机制探讨

目的:观察大鼠慢性颈脊髓压迫减压术后神经功能的恢复情况,探讨其相关机制。方法:30只成年SD大鼠随机分为假手术组(A组,10只)、压迫组(B组,10只)和减压组(C组,10只)。压迫组和减压组在C6~C7椎板下置入聚乙烯醇丙烯酰胺互穿网络水凝胶制作慢性颈脊髓压迫模型,减压组于造模后4周行手术咬除椎板充分减压。三组均于造模后4周行运动诱发电位(MEP);12周先行MRI和MEP检测,再处死大鼠取出颈段脊髓,行大体形态观察和组织学切片,快蓝(LFB)染色观察三组大鼠脊髓组织髓鞘变化,免疫荧光染色观察神经元数目形态及脑源性神经营养因子(BDNF)和血管内皮生长因子(VEGF)表达的变化。结果:造模后4周时,B、C组MEP潜伏期与A组比较明显延长(P<0.05),波幅与A组比较明显降低(P<0.05),B组和C组比较潜伏期和波幅均无显著性差异(P>0.05)。造模后12周时MRI轴位和矢状位均显示B组大鼠椎管狭窄,颈脊髓明显受压,A组和C组大鼠椎管无明显狭窄,脊髓无明显受压;三组间MEP潜伏期和波幅两两比较差异有显著性(P<0.05),潜伏期A组C组>B组。大体形态观察示A组脊髓形态正常,B组脊髓受压节段压痕明显,C组压痕较B组轻。LFB染色示A组脊髓组织中髓鞘染色密集,B组轴突脱髓鞘明显,C组脱髓鞘现象较B组轻。免疫荧光染色示A组脊髓组织中可见大量形态正常的神经元;B组脊髓受压节段压迫侧神经元明显减少,胞体固缩;C组脊髓受压节段神经元数量比B组多,有轻微细胞固缩,三组神经元计数有显著性差异(P<0.05),A组>C组>B组。免疫荧光染色示A组大鼠脊髓组织有少量BDNF和VEGF的表达;B组大鼠BDNF表达水平较A组有所升高,且主要集中在脊髓受压部位附近的白质区域,VEGF表达无明显增加;C组BDNF和VEGF表达水平明显增加,主要集中在原受压部位白质周围,灰质部位有少量表达。C组BDNF和VEGF表达阳性细胞计数与A、B组比较有显著性差异(P<0.05);B组BDNF表达阳性细胞与A组比较有显著性差异(P<0.05),VEGF表达阳性细胞数与A组无显著性差异(P>0.05)。结论:大鼠慢性颈脊髓压迫减压术后神经功能有所恢复,其可能是通过减轻神经元损伤和轴突脱髓鞘改变、增加BDNF和VEGF的表达水平,从而促进受损脊髓组织的修复。

Neurofunctional change and its mechanism after decompression for chronic cervical myelopathy

Objectives: To observe the neurofunctional recovery after decompression for chronic cervical myelopathy,and to investigate its mechanism.Methods: The rats were randomly divided into three groups: sham group(group A,n=10);compressive group(group B,n=10);decompressive group(group C,n=10).The expanding compression sheet made of a water-absorbing material was inserted underneath the C6-C7 laminae in rats of the compressive and decompressive groups.Laminectomy was performed after 4 weeks of compression.Moter evoked potential(MEP) was performed after 4 weeks and 12 weeks,and MRI was performed after 12 weeks.Then the rats were sacrificed,and gross specimens were processed for histological study.Luxol Fast Blue staining(LFB) was used to assess the myelin change.Immunofluorescence was performed to observe the number of neurons and the expression of brain-derived neurotrophic factor(BDNF) and vascular endothelial growth factor(VEGF).Results: For MEP at 4 weeks after injury,the latency and amplitude in group B and C showed significant difference compared with group A(P<0.05).There was no significant difference between group B and group C(P>0.05).At 12 weeks after injury,axial and sagittal MRI showed significant spinal cord compression and severe spinal canal stenosis in group B,while which were not noted in group A and B.For the latency and amplitude of MEP,there were significant differences among the three groups.For the latency,group Agroup C>group B.Gross specimens showed normal morphology in group A and obvious identation in group B,while the identation improved significantly in group C after 8 weeks of decompression.Immunofluorescence for neurons showed that a great number of healthy neurons was found in group A,with the number of neurons of 68.4±2.5.The majority of neurons disappeared and shrinked markedly in compressed level in group B,with the number of neurons of 35.2±3.1.The neurons shrinked slightly and the number of neurons increased in compressed level in group C compared with group B,with the number of neurons of 58.4±1.7.It showed significant differences among three groups(P<0.05).LFB staining revealed dense axon in group A,axonal demyelination in group B and significant recovery of demyelination in group C.For the immunofluorescence,a small amount of BDNF and VEGF expression was found in group A,with the number of BDNF and VEGF of 18.4 ±1.9 and 19.2 ±1.4 respectively.The expression of BDNF in group B was significantly up-regulated compared with group A,mainly located in the white matter of the compressed site,with the number of BDNF and VEGF of 37.2±3.5 and 17.4±2.1 respectively.The number of BDNF(68.4 ±2.7) and VEGF(51.7 ±3.1) in the white matter region increased significantly in group C after 8 weeks of decompression compared with group A and B.The number of BDNF and VEGF in group C was statistically upregulated than group A and B(P<0.05).Conclusions: The neurofunction improves after decompression,which may be contributed to inhibit neuronal damage and axonal demyelination as well as to increase the expression of BDNF and VEGF in the cervical spinal cord compression model.