PATCH CLAMP ANALYSES ON DEVELOPMENTAL CHANGES IN GABA RECEPTOR FUNCTION

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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.