Demyelination and changes in chondrotin sulfate proteoglycan expression after spinal cord compression injury / 中华物理医学与康复杂志

ABSTRACT

Objective To investigate the role of demyelination and the alteration of chondrotin sulfate proteoglycan (CSPG,NG2) expression after compression injury of the spinal cord (CSCI).Methods Seventy-five adult Sprague-Dawley rats were randomly divided into a normal group,a sham-operation group,a CSCI 1 day group,a CSCI 3 day group,and a CSCI 7 day group.There were 15 rats in each group.The injuries in the CSCI groups were inflicted using a technique devised in our laboratory.Basso-Beattie-Bresnahan (BBB) neurological function assessment was used to assess the rats' motor function,osmic acid staining and transmission electronic microscopy (TEM)were used to observe any pathological changes of myelinated nerve fibers in the white matter at 1,3 and 7 days after CSCI.The amount of myelinated nerve fibers in the posterior funiculus of the spinal cord and the ratio of myelin sheath thickness to axon diameter (the G-ratio) were calculated.Any alteration in NG2 expression was observed by Western blotting.Results The average neurological function assessment scores in the CSCI groups were (1.23 ±0.45),(0.65 ± 0.35) and (0.00 ± 0.00) respectively.Compared with the normal group (21.00 ± 0.00) and the sham operation group (21.00 ± 0.00),the differences were all statistically significant.The rats' motor function deteriorated gradually with time after the CSCI.Osmic acid staining showed that the white matter was intact in the normal and sham groups.After being compressed the myelinated nerve fibers became swollen,degenerated and broke down.The amount of myelinated nerve fibers in the normal group,the sham operation group and the three CSCI groups was (2771 ± 108),(2675 ± 199),(2403 ± 161),(1708 ± 70) and (8 10 ± 95) respectively.The amount of myelinated nerve fibers decreased in the CSCI groups and reached a minimum on the 7th day.The difference was statistically significant.The TEM quantity analysis showed that the G-ratios in the normal,sham operation,and CSCI 1 day,3 day and7 day groups were (18.10±0.4),(17.70±1.0),(6.69 ±0.8),(5.73 ±0.4) and (4.95 ±0.5) respectively.Compared with the normal and sham operation groups,the G-ratios in the 3 CSCI groups were lower and reached their minimum on the 7th day after injury.The difference was statistically significant.TEM observation showed that the axons and myelin sheaths were intact in the normal and sham groups.After CSCI the axons became swollen and cell organelles in the axoplasm degenerated and decreased.The layers of myelin sheath shrank,folded and even wrinkled,which had an onion-like appearance.The oligodendrocytes exhibited chromatin condensation.Macrophages showed infiltration.Western blotting showed that the expression of NG2 in the CSCI groups reached a maximum on the 1st day after injury and then decreased with time.The expression of NG2 in the CSCI groups was higher than in the normal and sham groups,and the difference was statistically significant.Conclusion Demyelination occurs after CSCI-the amount of myelinated nerve fibers decreases and neurological deficits increase with time.The expression of NG2 was associated with changes in the myelin sheaths after CSCI and contributed to recovery of the myelin sheath through proliferation and differentiation to oligodendrocytes and perhaps other kinds of cells.