封闭内源性NT-3在脊髓损伤后期神经元有髓神经纤维出芽中的作用

Function of endogenous NT-3 in the regeneration sprouting of large neuron at late-stage spinal cord injury

目的探讨成年猫脊髓损伤后期内源性Neurotrophin-3(NT-3)对脊髓背根节(DRG)大型感觉神经元功能修复的作用。方法切除猫L1-L5、L7-S2DRG,术后随机行NT-3抗体封闭处理,2个月后行形态学示踪和免疫组化、酶组化等比较分析。结果 NT-3阳性神经元在DRG和脊髓的分布和损伤后变化与既往研究一致,霍乱毒素B亚单位结合辣根过氧化物酶复合物(CB-HRP)示踪显示,手术组DRG感觉性大神经元中枢投射轴突终末集中分布在III、IV、V板层内侧,其有髓神经纤维终末再生出芽点密度高于对照组,NT-3抗体封闭组轴突再生较手术组显著降低。结论脊髓损伤后期修复中,内源性NT-3能促进损伤脊髓和感觉神经元的形态和功能修复,有利于脊髓后角III、IV、V板层有髓神经纤维轴突终末的再生、出芽生长,其机制可能在于上调DRG大型神经元NT-3的表达,进而参与脊髓可塑性修复。

Objective To explore the function of endogenous neurotrophin-3 （NT-3） in the regeneration sprouting of large neuron at late-stage spinal cord following dorsal root rhizotomy in adult cats. Methods The 1st to the 5th lumbar （L1 -L5 ）, and the 7th lumbar （L7 ） to the 2nd sacral （$2） dorsal root ganlia （DRG） were exposed and removed from their respective intervertebral foramina, leaving the L6 DRG untouched. Antibody of NT-3 was blocked. Two months later, CB-HRP transganglionic tracing, histochemistry and enzymohistochemistry analysis were performed to compare the spinal cord segments and the spared DRG. Results NT-3 positive immunity reaction （IR） mainly distributed in large-sized neurons of DRG and part of neurons in spinal lamina II. Two months after the operation, the number of NT- 3-IR neurons in DRG significantly increased （P 〈 0.05 ）, but in lamina II there was no difference compared to the con- trol group. After CB-HRP tetramethyl benzidine （TMB） enzymohistochemistry coloration, the densities of axon terminal sprouting derived from spared DRG were more markedly increased in the operation group than in the control group. However, after antibody blockade of NT-3, the densities decreased sharply compared to that of operation group. Conelusion The regeneration sprouting of large sensory neuron of DRG at late-stage distribute mainly in the deep lay- ers （Ⅲ, Ⅳ, Ⅴ layer） of spinal dorsal horn. Endogenous NT-3 may be involved in the spinal cord plasticity by up-reg- ulating the expression of NT-3, which promotes the long-term repair of injured spinal cord.