内源性神经营养因子-3对小鼠周围神经损伤后再生与髓化的影响

为了探讨内源性神经营养因子3(NT3)在小鼠周围神经损伤后再生与髓化中的作用,本研究建立小鼠坐骨神经压榨损伤模型,腹膜腔注射抗NT3血清为实验组,腹膜腔注射生理盐水(NS)和羊血清(NSS)为对照组。采用fastblue(FB)逆行束路追踪与电子显微镜相结合的方法观察周围神经损伤后再生与髓化的情况,并运用体视学方法测量单位面积髓化纤维的数密度、直径分布。结果显示(1)实验各组的脊髓前角运动神经元内均可观察到FB逆标细胞,但抗NT3组FB逆标细胞的数目明显少于NS组和NSS组(P<0.05);(2)半薄切片上观察到抗NT3组动物坐骨神经损伤远端,其再生纤维分布稀疏、直径小,但间质增多,有许多溃变细胞;NS组和NSS组损伤远端再生纤维数目多,分布均匀;(3)超薄切片上还可观察到抗NT3组损伤远端有髓纤维的数目明显减少,轴突内细胞器少,髓鞘薄;而NS组和NSS组损伤远端有髓纤维数目多,轴突内细胞器多,髓鞘板层结构清楚、呈致密有规律的排列。以上结果提示内源性NT3与损伤神经的再生有关,对不同直径神经纤维的髓化具有选择性作用,主要影响大直径神经纤维的髓化。

THE EFFECTS OF ENDOGENOUS NEUROTROPHIN-3 ON REGENERATION AND MYELINATION OF INJURED PERIPHERAL NERVE IN MICE

To investigate the effects of endogenous neurotrophin-3 (NT-3) on regeneration and myelination of injured peripheral nerve in mice, after building the model of sciatic nerve crush, the mice treated with anti-NT-3 serum intraperitoneally were experimental group, others respectively treated with normal saline (NS) and normal sheep serum (NSS), intraperitoneally were control groups. The regeneration and myelination of injured peripheral nerve in mice were detected by the fast blue(FB) retrogradely labeling motoneurons and electronmicroscope. The average number of regenerating fibers and the diameter distribution of axons were examined with stereology. The results showed: (1)Many neurons with FB-labelling were observed in the motoneurons of anterior horn of spinal cord in every group. But the number of motoneurons with FB-labelling were significantly smaller in anti-NT-3 group than in NS group or NSS group (P<0.05). (2)Observations on semi-sections revealed that the regenerating myelinated fibers, degenerated cells were rarely distributed with more intercellular substance in the distal sciatic nerve of the mice treated with anti-NT-3, with smaller-diameter axons compared with the control groups. On the other hand, many regenerating myelinated axons were homogenously distributed across the section in the mice treated with NS or NSS. (3)The ultrastructural examinations showed that there were less myelinated fibers which lacked normal organelles and became thinly ensheathed in anti-NT-3 group. But myelinated fibers were found with normal organelles in the distal ends of the lesioned sciatic nerve from the NS or NSS group. The laminal structure of myelin was clearly seen and the myelin sheath was densely packed and regularly arranged. The results suggest that endogenous NT-3 is related to regeneration of sciatic nerve and exert a selective role on myelination of sciatic nerve, mainly affected large diameter nerve fiber.