PATCH CLAMP ANALYSES ON DEVELOPMENTAL CHANGES IN GABA RECEPTOR FUNCTION

我们对出生后0 ~ 21天的大鼠脊髓、视觉皮质和丘脑神经元的gaba能IPSCs进行全细胞记录。我们还从脊髓神经元切除的斑块中进行了gaba门控Cl通道电流的外向-外向斑块记录。gaba门控通道具有脉冲内闪烁的特征。对开始时排列的脉冲进行集合平均，得到的电流与GABAergic IPSCs具有相似的时间过程，这表明脉冲持续时间可能决定GABAergic IPSCs的衰减时间过程。在脊髓中，1日龄和16日龄动物间IPSCs的衰变时间无显著差异。从视觉皮质神经元中记录的IPSCs也是如此。最近有报道称，在大鼠丘脑神经元中，GABA受体亚基在出生后2-3周内从未成熟亚型alpha2转变为成熟亚型alpha1。然而，我们没有发现新生儿和3周龄动物之间IPSCs的时间过程有显著差异。这些结果有些出乎意料，因为在甘氨酸能多能干细胞和胆碱能终板电流中观察到突触电流的发育时间明显缩短，在这两种情况下，亚基都从未成熟的形式转变为成熟的形式。由此可见，GABA受体α亚单位的亚单位转换可能不会对抑制性突触反应的时间过程产生显著变化。

We made whole cell recordings of GABAergic IPSCs from spinal, visual cortical and thalamic neurons of rats at the postnatal period ranging from 0 day to 21 days. We also made outside-out patch recordings of GABA-gated Cl channel currents from patches excised from spinal neurons. The GABA-gated channels were characterized with flickerings within a burst. Ensemble averaging of the bursts aligned at the onset gave currents having similar time course with the GABAergic IPSCs, suggesting that the burst duration might determine the decay time course of GABAergic IPSCs. In the spinal cord, no significant difference was observed for the decay time courses of the IPSCs between one-day old and 16 day old animals. This was also the case for the IPSCs recorded from visual cortical neurons. It has been reported recently that GABA receptor subunit switches from immature subtype alpha2 to mature alpha1 subunit within 2-3 weeks after birth prominently in rat thalamic neurons. However, we could not find a marked difference in the time course of IPSCs between neonatal and 3 week old animals. These results were somewhat unexpected because a clear developmental shortening in the time course of synaptic currents has been observed for glycinergic IPSCs and also for cholinergic end-plate currents, in both cases subunits being switched from immatre to mature forms. It is concluded that subunit switching of GABA receptor alphasubunit may not produce a significant changes in the time course of inhibitory synaptic responses.