大鼠发育过程中视皮层神经元视觉依赖性突触反应的变化

Changes in experience-dependent synaptic responses of neurons in rat visual cortex during development

目的 :研究大鼠不同发育阶段视皮层各层次神经元的被动膜学特性和突触传递特性 ,探讨视觉经验在视皮层发育过程中对神经元突触的修饰作用。方法 :依年龄将 5 7只 4～ 2 8d龄SD大鼠分为两组 :睁眼前组 (即 1,2周龄组 ) ;睁眼后组 (即 3,4周龄组 ) ,应用脑片膜片钳全细胞记录技术获得视皮层神经元的全细胞记录 ,在电压钳下应用强度为 0 .1～ 1.0mA刺激来引起神经元的突触后电流 (postsynapticcurrents,PSCs)。 结果 :15 6个大鼠视皮层神经元的PSCs可分为无反应型、单突触反应型和多突触反应型三种类型。大鼠睁眼前无反应型细胞的百分率为 5 7.3% ,而睁眼后下降至 11.94 % (P <0 .0 0 1) ;多突触反应型细胞所占的百分率则由睁眼前的 12 .36 %上升至睁眼后的 31.34% (P <0 .0 5 )。出生后 1周内的细胞属于不成熟细胞 :阻抗高 (RN>1.0GΩ)、峰值低 (约 0 .87mA)、下降时间短 (约 0 .98ms)。 4周龄 (2 2～ 2 8d)的神经元则属于成熟型细胞 :阻抗低 (RN<310MΩ)、峰值高(约 6 6mA)、下降时间长 (约 2 2 5ms)。 1～ 3周龄神经元的电生理学特性则是介于上述两者之间。钳制电压为 -70mV时 ,随着刺激强度的增大 ,神经元PSCs的波幅也逐渐增大。与Ⅳ层组相比 ,Ⅱ～Ⅲ层组神经元PSCs的峰值明显增高 (约 34pA) 。

Objective:The membrane properties and synaptic transmission of neurons in rat visual cortex were examined to explore modification of these characteristics by visual experience during development. Methods:Whole cell patch clamp recording was used to record postsynaptic currents (PSCs) from neurons in the visual cortex of 57 Sprague Dawley rats (postnatal days 4 28). Results:There were three types of PSCs in 156 cells: silent response, monosynaptic response and polysynaptic response during the first developmental month. Before eye opened the number of the neurons with silent responses (57.3%) was significantly higher than that after the eye opened (11.9%) ( P< 0.001). However, the incidence of polysynaptic responses increased from 12.4% before eye opened to 31.3% after eye opened ( P< 0.05). During postnatal week 1, all cells were classified as immature. The immature cells had very high input resistances ( R N >1.0 GΩ), low peak amplitude (～0.87mA) and short decay time (～0.98 ms). During postnatal week 4, all cells were mature with lower input resistances ( R N <310 MΩ), higher peak amplitude (～66 mA), and longer decay time (～225 ms). From postnatal weeks 1 to 3, the cells had electrophysiological properties that were intermediate between the immature and mature cell types. In 60 neurons of all types at holding potential -70mV, the peak amplitude of PSCs was increased by increasing stimulus intensity. Comparing with neurons in layer Ⅳ, those of layer Ⅱ Ⅲ had higher peak amplitude (～34 pA), longer decay time (～69 ms), and longer latency(～5 ms). Conclusion:The convertion from silent synapse to functional synapse is activity dependent synaptic modification.The activity dependent synapses formed and distributed with visual stimulating. Visual experience plays a critical role in the modification of synaptic connection of neurons in the visual cortex.