Sr2+ and quantal events at excitatory synapses between mouse hippocampal neurons in culture
Sr2+ and quantal events at excitatory synapses between mouse hippocampal neurons in culture
复制标题
DOI：
10.1113/jphysiol.1996.sp021578
复制
发表时间：
1996-08-15
影响因子：
5.5
通讯作者：
Pennefather, PS
中科院分区：
文献类型：
--
作者：
AbdulGhani, MA;Valiante, TA;Pennefather, PS
1. 本研究利用培养的相邻小鼠海马神经元对的全细胞记录，研究了动作电位诱发的兴奋性突触传递的量子特性，并证明了Sr2+在量化这些特性方面的应用。在细胞外Sr2+存在的情况下，激发性突触后电流（EPSCs）之后是持续1 ~ 2 s的微型兴奋性突触后电流（mEPSCs）后放电，该电流是由突触前量子的异步释放引起的。与EPSC一样，后放电被认为是神经末梢Sr2+内流的调节过程。2 .增加细胞外[Mg2+]可减少放电后mEPSCs的数量，增加细胞外[Sr2+]或增加引起放电后动作电位的数量可增加mEPSCs的数量。在含有1mm Ca2+或6mm Sr2+的培养基中记录的EPSCs振幅相似。在低ca2 +介质中添加Sr2+使EPSC振幅增加，在高ca2 +介质中添加Sr2+使EPSC振幅降低。这些结果表明细胞外Sr2+在支持定量释放方面不如Ca2+有效。调节细胞外Ca2+、Mg2+和Sr2+的水平，使大多数放电后的mEPSCs是离散的，在数量上与导致相应epsc的量子事件相当。在一系列25对神经元中，在-80 mV下记录的mEPSCs的平均振幅为35 +/- 10 pA，平均变异系数为0.50 +/- 0.10（范围为0.26-0.62）。mEPSC振幅直方图呈正偏态。在10对神经元中，从100多个诱发事件的样本（在含有（mM）： 0.5 Ca2+， 2 Sr2+和10 Mg2+的超融合溶液中）中测定EPSC和mEPSC的均值和方差以及量子含量，并从EPSC和mEPSC均值振幅的比值中测定平均量子含量。二项量子分析得出N-app（独立突触的表观数量）的值为2-12，p(app)（在其中一个突触释放量子的表观概率）的值为0.25-0.75。这些参数预测了观察到的故障的数量。当考虑放电后mepsscs的量子幅值变异系数时，观测到的量子含量变异系数可以预测EPSC幅值的变异系数。在6对神经元中，记录了250多个诱发事件，EPSCs的振幅直方图可以用估计的二项参数产生的预测振幅分布和描述放电后mepsscs振幅分布的经验函数来近似。放电后产生Sr2+的mEPSCs的参数可以预测EPSC振幅分布的形状以及与观察到的故障率和EPSC振幅方差一致的量子含量，这表明该mEPSCs子集与相应EPSC峰值前后释放的量子事件具有相同的性质。使用Sr2+来唤起mepsscs放电后，应该可以明确地确定突触强度的改变在突触前或突触后的程度。
1. Whole-cell recording from pairs of adjacent mouse hippocampal neurons in culture was used to study the quantal properties of action potential-evoked excitatory synaptic transmission and to demonstrate the use of Sr2+ in quantifying those properties.2. In the presence of extracellular Sr2+, excitatoray postsynaptic currents (EPSCs) were followed by an after-discharge of miniature excitatory postsynaptic currents (mEPSCs) lasting 1-2 s and generated by evoked asynchronous release of presynaptic quanta of transmitter. Like the EPSC of which it is thought to be an extension, the after-discharge was modulated by procedures expected to modulate Sr2+ influx into the nerve terminal. The number of mEPSCs in the after-discharge was decreased by increasing extracellular [Mg2+], and increased by increasing extracellular [Sr2+] Or increasing the number of action potentials used to evoke the after-discharge.3. EPSCs recorded in media containing either 1 mM Ca2+ or 6 mM Sr2+ were of similar amplitude. Adding Sr2+ to low-Ca2+ media increased EPSC amplitude, while adding Sr2+ to high-Ca2+ media lowered EPSC amplitude. These results suggest that extracellular Sr2+ is less effective than Ca2+ in supporting quantal release.4. The levels of extracellular Ca2+, Mg2+ and Sr2+ were adjusted so that most after-discharge mEPSCs were discrete and comparable in numbers to the quantal events that contributed to the corresponding evoked EPSCs. In a series of twenty-five pairs of neurons, the mean amplitude of mEPSCs recorded at -80 mV was 35 +/- 10 pA and the mean coefficient of variation was 0.50 +/- 0.10 (range, 0.26-0.62). The mEPSC amplitude histogram was positively skewed.5. In ten pairs of neurons, the mean and variance of EPSCs and mEPSCs and quantal content were determined from samples of more than 100 evoked events (in superfusion solutions containing (mM): 0.5 Ca2+, 2 Sr2+ and 10 Mg2+) and mean quantal content was determined from the ratio of amplitudes of the mean EPSC and mEPSC. A binomial quantal analysis produced values of 2-12 for N-app (apparent number of independent synapses) and 0.25-0.75 for p(app) (apparent probability of releasing a quantum at one of those synapses). These parameters predicted the number of observed failures. The observed coefficient of variation for quantal content predicted the observed coefficient of variation of the EPSC amplitude when the coefficient of variability of quantal amplitude of after-discharge mEPSCs was taken into account.6. In six pairs of neurons, where more than 250 evoked events were recorded, the observed amplitude histogram for EPSCs could be approximated by a predicted amplitude distribution generated from the estimated binomial parameters and an empirical function describing the amplitude distribution of after-discharge mEPSCs.7. The observation that parameters derived from mEPSCs that contribute to the Sr2+-generated after-discharge can predict the shape of the EPSC amplitude distribution and a quantal content consistent with the observed failure rate and EPSC amplitude variance, suggests that this subset of mEPSCs has the same properties as the quantal events released around the time of the peak of the corresponding EPSCs. The use of Sr2+ to evoke after-discharges of mEPSCs should allow unambiguous determination of the extent to which modification of synaptic strength is pre- or postsynaptic.