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首页> 外文期刊>Journal of Neurophysiology >Characterization of spontaneous inhibitory synaptic currents in salamander retinal ganglion cells.
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Characterization of spontaneous inhibitory synaptic currents in salamander retinal ganglion cells.

机译：sal视网膜神经节细胞中自发抑制突触电流的特征。

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摘要

Spontaneous and light-evoked postsynaptic currents (sPSCs and lePSCs, respectively) in retinal ganglion cells of the larval tiger salamander were recorded under voltage-clamp conditions from living retinal slices. The focus of this study is to characterize the spontaneous inhibitory PSCs (sIPSCs) and their contribution to the light-evoked inhibitory PSCs (leIPSCs) in ON-OFF ganglion cells. sIPSCs were isolated from spontaneous excitatory PSCs (sEPSCs) by application of 10 microM 6,7-dinitroquinoxaline-2,3-dione (DNQX) + 50 microM 2-amino-5-phosphonopentanoic acid (AP5). In approximately 70% of ON-OFF ganglion cells, bicuculline (or picrotoxin) completely blocks sIPSCs, suggesting all sIPSCs in these cells are mediated by GABAergic synaptic vesicles and gamma-aminobutyric acid-A (GABAA) receptors (GABAergic sIPSCs, or GABAsIPSCs). In the remaining 30% of - ganglion cells, bicuculline (or picrotoxin) blocks 70-98% of the sIPSCs, and the remaining 2-30% are blocked by strychnine (glycinergic sIPSCs, or GLYsIPSCs). GABAsIPSCs occur randomly with an exponentially distributed interval probability density function, and they persist without noticeable rundown over time. The GABAsIPSC frequency is greatly reduced by cobalt, consistent with the idea that they are largely mediated by calcium-dependent vesicular release. GABAsIPSCs in DNQX + AP5 are tetrodotoxin (TTX) insensitive, suggesting that amacrine cells that release GABA under these conditions do not generate spontaneous action potentials. The average GABAsIPSCs exhibited linear current-voltage relation with a reversal potential near the chloride equilibrium potential, and an average peak conductance of 319.67 +/- 252.83 (SD) pS. For GLYsIPSCs, the average peak conductance increase is 301.68 +/- 94.34 pS. These parameters are of the same order of magnitude as those measured in inhibitory miniature postsynaptic currents (mIPSCs) associated with single synaptic vesicles in the CNS. The amplitude histograms of GABAsIPSCs did not exhibit multiple peaks, suggesting that the larger events are not discrete multiples of elementary events (or quanta). We propose that each GABAsIPSC or GLYsIPSC in retinal ganglion cells is mediated by a single or synchronized multiple of synaptic vesicles with variable neurotransmitter contents. In a sample of 16 ON-OFF ganglion cells, the average peak leIPSC (held at 0 mV) at the light onset is 509.0 +/- 233.85 pA and that at the light offset is 529.0 +/- 339.88 pA. The approximate number of GABAsIPSCs and GLYsIPSCs required to generate the average light responses, calculated by the ratio of the charge (area under current traces) of the leIPSCs to that of the average single sIPSCs, is 118 +/- 52 for the light onset, and 132 +/- 76 for the light offset.
机译：在电压钳制条件下，从活体视网膜切片中记录幼虫虎sal视网膜神经节细胞中的自发和轻度诱发的突触后电流（分别为sPSCs和lePSCs）。这项研究的重点是表征自发性抑制性PSC（sIPSCs）及其对开关神经节细胞中的光诱发性抑制性PSC（leIPSCs）的贡献。通过应用10 microM 6,7-dinitroquinoxaline-2,3-dione（DNQX）+ 50 microM 2-amino-5-phosphonopentanoic acid（AP5）从自发性兴奋性PSC（sEPSCs）中分离出sIPSC。在大约70％的开-关神经节细胞中，双小分子（或微毒素）完全阻断sIPSC，表明这些细胞中的所有sIPSC均由GABA能突触小泡和γ-氨基丁酸-A（GABAA）受体（GABA能sIPSC或GABAsIPSC）介导。 。在剩余的30％的神经节细胞中，双小分子（或微毒素）阻断了70-98％的sIPSC，而其余的2-30％被士力宁（甘氨酸sIPSC或GLYsIPSC）阻断。 GABAsIPSC随机发生，具有指数分布的间隔概率密度函数，并且随着时间的推移它们持续存在而没有明显的减少。钴大大降低了GABAsIPSC的频率，这与它们主要由钙依赖性水泡释放介导的想法一致。 DNQX + AP5中的GABAsIPSC对河豚毒素（TTX）不敏感，表明在这些条件下释放GABA的无长突细胞不会产生自发的动作电位。平均GABAsIPSCs具有线性电流-电压关系，其反向电位接近氯化物平衡电位，平均峰值电导为319.67 +/- 252.83（SD）pS。对于GLYsIPSC，平均峰值电导增加为301.68 +/- 94.34 pS。这些参数与在与CNS中单个突触小泡相关的抑制性微型突触后电流（mIPSC）中测得的量级相同。 GABAsIPSC的振幅直方图未显示多个峰，这表明较大的事件不是基本事件（或量子）的离散倍数。我们建议，视网膜神经节细胞中的每个GABAsIPSC或GLYsIPSC都是由单个或同步多个具有可变神经递质含量的突触小泡介导的。在16个ON-OFF神经节细胞的样本中，leIPSC的平均峰值（保持在0 mV）在光开始时为509.0 +/- 233.85 pA，在光偏移时为529.0 +/- 339.88 pA。产生平均光响应所需的GABAsIPSC和GLYsIPSC的近似数量，是通过leIPSC的电荷（电流迹线下的面积）与平均单个sIPSC的电荷之比计算得出的，光开始时约为118 +/- 52，和132 +/- 76的光偏移量。

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