Characterization of spontaneous inhibitory synaptic currents in salamander retinal ganglion cells
Characterization of spontaneous inhibitory synaptic currents in salamander retinal ganglion cells
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DOI：
10.1152/jn.1998.80.4.1752
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发表时间：
1998-10-01
影响因子：
2.5
通讯作者：
Wu, SM
中科院分区：
文献类型：
--
作者：
Gao, F;Wu, SM
在电压箝位条件下，记录了虎蝾螈幼体视网膜神经节细胞的自发和光诱发突触后电流（sPSCs和光诱发突触后电流）。本研究的重点是表征自发抑制性PSCs （sIPSCs）及其对光诱发抑制性PSCs （leIPSCs）在ON-OFF神经节细胞中的作用，通过应用10 μ M 6,7-二硝基喹啉-2,3-二酮(DNQX) + 50 μ M 2-氨基-5-磷酸戊酸（AP5）从自发兴奋性PSCs （sEPSCs）中分离出sIPSCs。与70%的ON-OFF神经节细胞类似，双管碱（或微毒素）完全阻断了sIPSCs，这表明这些细胞中的所有sIPSCs都是由GABA能突触囊泡和γ -氨基丁酸-a （GABA）受体（GABA能sIPSCs或GABAsIPSCs）介导的。在其余30%的ON-OFF神经节细胞中，双管碱（或微毒素）阻断70-98%的sIPSCs，其余2-30%被士的宁（甘氨酸能sIPSCs，或GLYsIPSCs）阻断。GABAsIPSCs以指数分布的间隔概率密度函数随机发生，并且随着时间的推移不会出现明显的减少。钴大大降低了GABAsIPSC频率，这与它们主要由钙依赖性囊泡释放介导的观点一致。DNQX + AP5中的GABAsIPSCs对河豚毒素（TTX）不敏感，这表明在这些条件下释放GABA的无毛细胞不会产生自发动作电位。GABAsIPSCs的平均峰值电导率为319.67 +/- 252.83 (SD) pS， GLYsIPSCs的平均峰值电导率为301.68 +/- 94.34 pS，这些参数与CNS中单个突触囊泡相关的抑制微型突触后电流（mIPSCs）的测量值相同。GABAsIPSCs的振幅直方图没有出现多个峰，这表明较大的事件不是基本事件（或量子）的离散倍数。我们认为视网膜神经节细胞中的每一个GABAsIPSC或GLYsIPSC都是由单个或同步的多个突触囊泡介导的，这些囊泡具有可变的神经递质含量。在16个ON-OFF神经节细胞的样品中，光启动时leIPSC（保持在0 mV）的平均峰值为509.0 +/- 233.85 pA，光偏移时leIPSC的平均峰值为529.0 +/- 339.88 pA。产生平均光响应所需的GABAsIPSCs和GLYsIPSCs的大约数量，由leIPSCs的电荷（电流迹线下的面积）与平均单个sIPSCs的电荷之比计算，光开始时为118 +/- 52，光偏移时为132 +/- 76。
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 mu M 6,7-dinitroquinoxaline-2,3-dione (DNQX) + 50 mu M 2-amino-5-phosphonopentanoic acid (AP5). In similar to 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 (GABA,) receptors (GABAergic sIPSCs, or GABAsIPSCs). In the remaining 30% of ON-OFF 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.