PATCH CLAMP ANALYSES ON DEVELOPMENTAL CHANGES IN GABA RECEPTOR FUNCTION

我们对出生后0d至21d的大鼠脊髓、视皮层和丘脑神经元进行了GABA能IPSCs的全细胞记录。我们还从外向外记录了从脊髓神经元摘除的斑块中的GABA门控氯通道电流。GABA门控通道的特征是突发性闪烁。对起始点对齐的爆发的集合平均得到的电流与GABA能IPSCs具有相似的时间进程，这表明爆发持续时间可能决定GABA能IPSCs的衰减时间进程。在脊髓中，1日龄和16日龄动物IPSCs的衰变时间进程没有显著差异。从视觉皮质神经元记录的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周内显著地从未成熟的α2亚型转变为成熟的α1亚基。但新生动物和3周龄动物的IPSCs时程未见明显差异。这些结果有些出乎意料，因为在甘氨酸能ipscs和胆碱能终板电流中观察到了突触电流的明显发育缩短，在这两种情况下，亚单位都从未成熟的形式切换到成熟的形式。结论：GABA受体α亚基的亚基转换不会对抑制性突触反应的时程产生明显的影响。

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.