IGF-1介导的丰富环境对成年弱视小鼠视皮层可塑性的影响

目的:检测丰富环境干预对单眼剥夺成年弱视小鼠视皮质中IGF-1及其受体的表达变化,初步探讨其对成年弱视小鼠初级视皮质突触可塑性的影响及分子机制。方法:将正常新生昆明小鼠随机分为正常组(Nor),单眼剥夺+标准环境组(MD+SE),单眼剥夺+丰富环境组(MD+EE),单眼剥夺+氟西汀组(MD+FLX)。在小鼠21日龄时构建单眼剥夺模型,确定模型建立成功后,每组选取18只小鼠按照预先分组放置在标准环境或丰富环境中饲养4wk,单眼剥夺+氟西汀组小鼠饮水中加入氟西汀。通过前爪触地反射实验检测小鼠视敏度,闪光视觉诱发电位检测客观视功能;小鼠处死后取材,使用电镜检测视皮层神经元的突触间隙宽度、突触活性区长度及突触后致密物厚度,Western Blot法检测视皮层中IGF-1、IGF-1R及IGFBP5蛋白表达。结果:(1)视敏度检测结果:MD+SE组小鼠前爪触地成功率明显低于Nor组(P<0.001);MD+EE组及MD+FLX组小鼠前爪触地成功率明显高于MD+SE组(均P<0.001);与MD+FLX组比较,MD+EE组小鼠前爪触地成功率无差异(P=0.816)。(2)闪光视觉诱发电位检测结果:与Nor组比较,MD+SE组小鼠剥夺眼闪光视觉诱发电位P2波潜伏期延长、波幅降低(均P<0.01);丰富环境饲养后,MD+EE组较MD+SE组小鼠剥夺眼闪光视觉诱发电位P2波潜伏期缩短、波幅增加(均P<0.01);与MD+FLX组比较,MD+EE组小鼠剥夺眼闪光视觉诱发电位P2波的潜伏期和波幅变化无差异(P>0.05)。(3)电镜检测视皮层神经细胞突触超微结构:与N or组比较,M D+SE组小鼠剥夺眼对侧视皮层神经细胞突触间隙增宽(P <0.01),突触活性区长度缩短(P <0.01),突触后致密物厚度变薄(P <0.01);丰富环境饲养后,MD+EE组小鼠较MD+SE组突触间隙变窄(P=0.0035),突触活性区长度延长(P<0.01),突触后致密物厚度增加(P<0.01),MD+EE组突触超微结构各项指标较MD+FLX组比较无差异(P>0.05)。(4)Western blot检测视皮层中IGF-1、IGF-1R及IGFBP5蛋白表达:MD+SE组小鼠IGF-1及IGF-1R蛋白表达明显低于Nor组(均P<0.01);MD+EE组小鼠IGF-1及IGF蛋白的表达明显高于MD+SE组(均P<0.01),然而仍显著低于Nor组(均P<0.01)。各组间小鼠IGFBP5蛋白表达异常无差异(P>0.05)。结论:丰富环境能重新激活成年单眼剥夺弱视小鼠视皮质可塑性,改善弱视小鼠视觉功能,其机制可能与调控IGF-1及受体的表达有关。

Effects of IGF-1 mediated enrichment environment on visual cortex plasticity in adult amblyopic mice

AIM: To investigate the effect and possible mechanism of enriched environment on regulating the plasticity of visual cortex in adult monocular deprivation amblyopia mice.

METHODS: In this experimental study, a total of 72 Kunming mice were randomly divided into control group(Nor), monocular deprivation+ standard environment group(MD+SE), monocular deprivation + enriched environment group(MD+EE)and monocular deprivation+ fluoxetine group(MD+FLX). MD model of mice were established at postpartum 21d, and then fed the mice under SE or EE for 4wk. For the mice in MD+FLX group, they were fed by water with fluoxetine. The visual acuity and flash visual evoked potential of mice in each group were detected. Ultrastructral modifications of synaptic junctions in each group were detected using the electronic microscope. We also applied the molecular biology to study the role of enriched environment in visual cortex of adult amblyopic mice whether through regulating the expression of IGF-1, IGF-1R and IGFBP5.

RESULTS: 1)Visual acuity examination: the successful rate of forepaw-reaching reflex in MD+SE group mice is lower than that in Nor group(P<0.001). Compared to MD+SE group, the successful rate of forepaw-reaching reflex improved in MD+EE group(P<0.001)and MD+FLX group(P<0.001). The difference is not significant between the MD+EE group and MD+FLX group(P=0.816); 2)Flash-visual evoked potential examination: compare to the Nor group, the P2 latency was prolonged(P<0.01), and the P2 amplitude was decreased(P<0.01)of flash-visual evoked potential(F-VEP)in the deprived eye in MD+SE group mice; After raring in enriched environment, the P2 latency was shortened(P=0.003)and P2 amplitude was increased(P=0.000)in the deprivated eye detected with F-VEP, which is not significant in P2 latency and amplitude when compare to MD+FLX group(P>0.05); 3)The structural modifications of synaptic junctions examined by electromicrographs: Compare to the Nor group, the synaptic clefts increased(P<0.01), the synaptic active zone shortened(P<0.01), and the thickness of PSD decreased(P<0.01)in MD+SE group mice. After raring in enriched environment, the synaptic clefts decreased(P=0.0035), the synaptic active zone prolonged(P=0.000)and the thickness of PSD increased(P=0.000)in the visual cortex contralateral to the deprived eye, which is not significant in all of the structural parameters of the synaptic junction in visual cortex when compare to MD+FLX group(P>0.05); 4)IGF-1, IGF-1R and IGFBP5 expression detected by Western-blot: Compare to the Nor group, the IGF-1 and IGF-1R expression in visual cortex contralateral to deprivated eye are both down-regulated in MD+SE group(P<0.01; P<0.01). After raring in enriched environment, the expression of IGF-1 and IGF-1R in MD+EE group was significantly higher than that in MD+SE group(P=0.016; P=0.041), but still lower than that in Nor group(P=0.001; P=0.001). The different expression of IGFBP5 in each group is not significant(P>0.05).

CONCLUSION: Environmental enrichment can improve the visual function through reactivating the plasticity of monocular deprivation amblyopia mice. The mechanism is presumed to be related to the expression of IGF-1 and IGF-1R.