发育对大鼠视皮层第2和3层锥体神经元AMPA受体介导的自发兴奋性突触后电流影响的研究

Developmental changes of spontaneous excitatory postsynaptic currents mediated by AMPA receptor in layer 2 and 3 pyramidal neurons of rat visual cortex

目的研究发育过程中大鼠视皮层第2、3层锥体神经元的自发兴奋性突触后电流（sEPSC）变化，探讨生后早期自发性突触活动情况，以及视觉经验在视皮层发育过程中对神经元突触的修饰作用。方法实验研究。应用红外微分干涉相差显微镜（IR—DIC）结合电耦合式摄像机（CCD—Camera）可视法膜片钳全细胞记录生后2～7d．8—14d、15～21d、22～28d各组sEPSC变化，同时于电极内液中加入0．3％荧光黄对所记录细胞进行染色观察形态学改变。计量资料以均数±标准误表示，经方差齐性检验后，多组样本比较采用单因素方差分析，并进行样本均数间的多重比较。结果4个组视皮层神经元sEPSC幅值分别为（14．13±0．73）、（15．01±0．62）、（19．87±0．75）、（22．09±1．14）pA，随发育逐渐升高（F=20．69，P〈0．01），但2—7d组与8～14d组差异无统计学意义（P〉0．05），而睁眼前8～14d组较睁眼后15～21d组幅值比较差异有统计学意义（P〈0．01）。4个组视皮层神经元sEPSC频率分别为（1．35±0．05）、（1．33±0．12）、（2．26±0．15）、（2．85±0．12）Hz，随发育逐渐提高（F=87．46，P〈0．01），同样睁眼前8～14d组较睁眼后15—21d组频率比较差异有统计学意义（P〈0．01）。视皮层第2、3层神经元胞体及突起以及生物电学特性随发育逐渐成熟。结论视觉经验对于视皮层第2、3层神经元及突触发育成熟起了关键性作用。发育早期视皮层第2、3层有一定的α-氨基-3-羟基-5-甲基-4-异皤唑丙酸（AMPA）受体功能表达，突触并非完全处于静息状态。

Objective To investigate the modification function of visual experience onto synapses by recording developmental changes of spontaneous excitatory postsynaptic currents （ sEPSC ） in layer 2 and 3 pyramidal neurons of rat visual cortex, and to observe the spontaneous synaptic activities during the earlier postnatal period. Methods This was an experimental study. By combining infrared differential interference contrast （IR-DIC） technique and a CCD-camera system with visual patch clamp whole-cell recording technique, spontaneous EPSCs of P2 - 7, P8 - 14, P15 - 21 and P22 - 28 groups were observed and analyzed. The neurons were stained by adding 0. 3% Lucifer yellow to the pipette solution simultaneously. Results The amplitude of sEPSC was enhanced when aging （ F = 20. 69, P 〈 0. 01 ）. The sEPSC frequency increased with age （ F = 87.46, P 〈 0. 01 ）. There was no significant difference between P2 - 7 groups and P8- 14 groups （P 〉 0. 05 ） . The electrophysiology and dendrite of neuron became mature whilst development. Conclusions During the early postnatal days neurons were relatively immature, and became mature during development. Visual experience played an important role in this process. In spite of most synapses were taken silent at early postnatal days, and NMDA receptor-mediated function was revealed exclusively, these results suggested that early AMPA receptor-mediated functional activities existed in layer 2 and 3 pyramidal neurons. Synapses were not completely silent, but had early spontaneous activities.