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3 讨论
EGb 761主要含有黄酮苷（24%）和萜类内酯（6%）两种成分。黄酮类化合物主要有槲皮素、山奈黄素、异鼠李素。萜类内酯除银杏内酯外还有银杏苦内酯A、B、C和J。该制剂可抗脂质过氧化，对缺血和（或）缺氧损伤、机械损伤的神经元具有保护作用。它能减轻谷氨酸毒性，抑制血小板凝集，对抗凋亡，还能使眼动脉血流量增加。本研究结果证明EGb 761能抑制视神经横断后RGC凋亡，对RGC有保护作用，该结果与Hirooka等［11］的研究结果一致。
PERG是客观评价RGC功能的方法之一，其波形主要特征为一个正向的P50波和一个向下的N95波。根据各种疾病PERG的不同表现，Holder［12］认为两个波的起源不同。药理学分析也证明，N95波可被河豚毒素完全阻断，N95波依赖于RGC产生的动作电位。尽管P50波的确切起源还不清楚，并不能被河豚毒素阻断，但在青光眼患者和猴青光眼模型中P50波振幅均有所下降，因此推测它可能起源于RGC的胞体和（或）RGC的远端［13］。以往评价慢性高眼压引起的RGC数目减少常常采用闪光ERG［14］，然而闪光ERG只代表视网膜外层电反应，PERG才真正代表视网膜内层电反应［15, 16］。迄今，尽管对PERG的确切起源尚未完全清楚，但起源于视网膜内层是一致公认的，主要是RGC［17］。Berardi等［18］证实横断大鼠视神经后可引起RGC逆行性变性，导致PERG反应消失，而闪光ERG不受影响。目前PERG已被应用于临床评价高眼压症和青光眼患者的视功能，并认为青光眼对PERG的N95的影响比P50大［19, 20］。BenShlomo等［9］首次应用PERG评价大鼠高眼压后RGC功能，并研究N95振幅和RGC数目的相关性，结果发现两者呈正相关关系。我们的研究也证明豚鼠视神经横断后，随着RGC数目的减少N95振幅逐渐降低，且两者呈正相关关系（r=0.858 68，P=0.001 5），表明PERG的N95振幅可评价RGC数目丧失的程度。
总之，腹腔注射EGb 761可抑制视神经横断后RGC凋亡，从而保护RGC的结构和功能。PERG是评价视神经横断后RGC丧失程度的有效指标之一。
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