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Protective effects and anti-apoptotic role of nerve growth factor on spinal cord neurons in sciatic nerve-injured rats

Abstract Objectives: The purpose of this study is to demonstrate a dependence of spinal cord motoneurons on the communication with their targets, sciatic nerves, and investigate whether the effects of nerve growth factor (NGF) on the spinal cord neuron apoptosis and surviving through the regulation of nuclear factor-kappa B (NF-kappaB) in Schwann cells (SCs) in sciatic nerve injured rats. Methods: Ninety healthy adult Sprague–Dawley rats were divided randomly into normal control group, crushing group, and NGF-intervened group. When sciatic nerve crushed 1, 3, 7, 14, and 21 days, the expression of NF-kappaB in SCs and the apoptosis regulator Bcl-2 and Caspase-3 in spinal cord were examined by immunohistochemistry staining, Western blot analysis, and immunofluorescence double-labeling method, the motor neuron apoptosis were investigated by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), and the surviving neurons were tested by toluidine blue (Nissl) staining, respectively. All the data were further analyzed with SPSS10·0 application software. Results: The level of the expression of NF-kappaB in crushing group enhanced at 1 day after crushing, reached peak at 3 days, and reduced at least until 21 days, which was markedly higher than that in the normal control group. The expression of NF-kappaB in NGF-intervened group showed the same changes, reached peak at 7 days, and reduced until 21 days. However, when compared with crushing group, the expression of NF-kappaB in NGF-intervened group was down-regulated significantly until 3 days after injury, and up-regulated obviously with time going on. The same trend was observed in the time course on motor neuron apoptosis in crushing group and NGF-intervened group after sciatic nerves injury, while the reversing change was found in the surviving neurons. Moreover, the kinetics of Bcl-2 expression in spinal cord was consistent with that of NF-kappaB, while reversing with that of Caspase-3. Conclusion: The findings revealed that NGF may play a pivotal role of anti-apoptosis in spinal cord neurons through retrograde transport of NF-kappaB in SCs following sciatic nerve injury in rats.