大鼠视神经部分损伤后视神经纤维再生的形态学观察

目的探讨大鼠视神经不同程度损伤后视网膜神经节细胞（RGC）和轴突的变化规律及神经再生能力。方法用夹持力为148g的反向镊夹持大鼠视神经3、6、12、30、60S建立不同程度视神经损伤的动物模型,计数视神经损伤后0．5、1、2、3、7个月RGC和损伤后1、2、3个月轴突随时间的变化规律,透射电镜观察损伤的再生反应,在银染的视神经纵切片上计数后计算视神经横断面上纤维数目,根据横断面的纤维数目计算损伤视神经的再生指数以衡量不同程度视神经损伤后的再生能力。再生指数的计算为（损伤点后0．5mm纤维数-损伤点后2．5唧纤维数）／（球后0．5唧纤维数-损伤点后2．5mm纤维数）。结果视神经部分损伤后RGC和轴突持续丢失,这种丢失可分为伤后2周内的急性丢失和其后的缓慢丢失两个时期,并呈指数形式下降。随着致伤程度的加重,RGC的丢失率上升而存活率降低,RGC和轴突的丢失率随致伤程度的加重而增高,轻度损伤时这种继发损伤具有自限性。视神经损伤后,有大量丛状聚集、区域化分布的无髓再生纤维。视神经夹持损伤3、6、12、30、60s后,再生指数分别为1．409、1．490、0．916、1．119、1．224（χ^2=281．2,P〈0．01）,不同程度损伤后神经的再生能力可能不同,轻度损伤的再生能力较强。结论不同程度视神经部分损伤后继发反应和再生能力不同,轻度损伤后的继发损伤具有自限性并具有更强的再生能力,在一定程度的损伤下修复与损伤可能达到某种平衡而导致成功再生。

Regeneration of optic nerve fibers following graded injuries in rats

OBJECTIVE: To investigate the changes of retinal ganglion cell (RGC) and their axons, and nerve regeneration ability following graded optic nerve injury (ONI) in rats. METHODS: A pair of cross-action forceps with 148.0 g clipping pressure was used to clip rat optic nerves for 3, 6, 12, 30 and 60 s to induce graded ONI animal model. The RGC was counted at 0.5, 1, 2, 3 and 7 months and the axons were observed 1, 2 and 3 months post-injury. The regeneration process was observed by transmission electron microscopy. The number of optic nerve fibers in transverse sections was calculated in silver-stained longitudinal sections, and a regeneration index (RI) was calculated based on these numbers. The RI, reflecting the regeneration ability of injured optic nerves, was calculated as follows: (number of nerve fibers 0.5 mm behind injury site-number of nerve fibers 2.5 mm behind injury site)/(number of nerve fibers 0.5 mm retrobulbarly-number of nerve fibers 2.5 mm behind injury site). RESULTS: RGC and axons lost continuously after partial ONI. The loss of RGC was fitted with exponential pattern consisted of two phases, acute losing phase within first two weeks post injury and followed by another phase characterized by slowly reducing of RGC. The loss ratio of RGC increased and the survival ratio decreased with the severity of injury intensity. The loss of RGC and axons was aggregated in severe injury and showed a self-limited trend in mild injury. A large amount of clustered, zonal unmyelinated regeneration fibers were present after injury. The RI was 1.409, 1.490, 0.916, 1.119 and 1.224 following 3, 6, 12, 30 and 60 s clipping injury (chi2 = 281.2, P < 0.01), respectively. Different RI was associated to different injury intensity, with a greater regeneration ability in mild injury. CONCLUSIONS: The secondary reaction and regeneration ability vary with graded intensity of optic nerve injury. A self-limited secondary reaction and a more powerful regeneration ability are associated with a mild injury. The repair behavior and the injury may reach a balance and result in a successful regeneration after a certain degree of injury.