单眼形觉剥夺性弱视大鼠视皮层突触密度及功能的研究

目的：研究视觉发育关键期单眼形觉剥夺(MD)对弱视大鼠视皮层突触密度超微形态结构变化规律的影响，以及突触素(SYN)在视皮层的表达及意义，探讨弱视大鼠视皮层突触密度及功能的关系，为弱视的发病机制及临床治疗提供分子水平理论依据。

方法：选用正常新生Long Evans大鼠随机分为正常对照组与弱视模型组，每组16只，两组大鼠均在相同环境下饲养。正常对照组不做任何处理，弱视模型组在出生后第13d采用单眼缝合的方法建立单眼形觉剥夺性弱视经典模型。两组大鼠均于出生后51d进行闪光视觉诱发电位(F-VEP)的检测。检测结束后立即取材，用透射电镜及Image J图像分析软件观察并统计两组大鼠初级视皮层V1M区第Ⅳ～Ⅵ层大锥体细胞周围神经纤维网络的突触密度变化。利用漂染法对视皮层冰冻切片进行免疫荧光组织化学染色，在激光共聚焦显微镜及荧光显微镜下对SYN阳性神经元进行定位观察和定量统计分析。

结果：F-VEP检查结果显示与正常对照组相比，弱视模型组剥夺眼的P2潜伏期较正常眼明显延长，P2波振幅较正常眼明显降低(P<0.05)； 透射电镜结果显示，与正常对照组相比，弱视模型组双侧视皮层的突触密度显著降低(P<0.05)，其中弱视眼对侧视皮层下降更加明显(P<0.05)； 免疫荧光染色结果显示两组大鼠视皮层脑切片形态完整，镜下组织结构清晰，与正常对照组相比，弱视模型组SYN阳性神经元表达强度值明显降低(P<0.01)。

结论：视觉发育关键期存在着突触结构可塑性，单眼形觉剥夺可以造成大鼠初级视皮层突触密度的降低，SYN表达水平下降，视皮层功能下降。

Study on the cortical synaptic density and visual function in monocular form deprivation rats with amblyopia

AIM: To study the effect of monocular form deprivation(MD)on the synaptic density in the visual cortex of the amblyopic rats during the critical period of visual development, the visual cortical synaptophysin(SYN)expression and significance of its expression, as well as the relationship between the synaptic density and the visual function. This research will provide mechanisms underlying the pathogenesis and clinical treatment of amblyopia.

METHODS: Normal newborn Long Evans rats were randomly divided into normal control group and amblyopia model group, each with 16 rats. Both groups of rats were raised in the same environment. The normal control group did not receive any treatment. On the 13d after birth, the amblyopic model group received monocular suture to establish a classic monocular form deprived amblyopic model. Both groups of rats were received Visual evoked potential(F-VEP)detection on the 51d. Samples were taken immediately after the detection. The transmission electron microscope and Image J image analysis software were used to observe and analyse the synaptic density in the V1M of the primary visual cortex of the two groups of rats. Frozen sections of visual cortex were stained by immunofluorescence histochemical staining by bleaching method and the expression of SYN positive neurons was observed and quantitatively analyzed.

RESULTS: F-VEP examination showed that compared with the normal control group, the P2 latency of the deprived eyes in the amblyopic group was significantly long, and the amplitude of P2 wave was significantly lower than that of normal eyes(P<0.05); Transmission electron microscopy results showed that the synaptic density of the bilateral visual cortex of the amblyopic model group was significantly reduced compared with the normal control group(P<0.05), the contralateral visual cortex of the amblyopic eye decreased more significantly(P<0.05); immunofluorescence staining results showed that the brain slices in the visual cortex of the two groups were intact and the tissue structure was clear under the microscope. Compared with the normal control group, the expression intensity of SYN positive neurons in the amblyopic group was significantly reduced(P<0.01).

CONCLUSION: There is structural synaptic plasticity during the critical period of visual development. Monocular form deprivation can reduce the synaptic density, SYN expression and the visual function in the primary visual cortex of the amblyopic rats.