Thomson A M, West D C
Department of Physiology, Royal Free Hospital School of Medicine, London, U.K.
Neuroscience. 1993 May;54(2):329-46. doi: 10.1016/0306-4522(93)90256-f.
Single axon excitatory connections between pairs of neocortical pyramidal neurons were studied using paired intracellular recordings in layers II/III and IV of coronal slices of adult rat somatosensory/motor cortex. Excitatory postsynaptic potentials evoked with different presynaptic firing patterns and at different postsynaptic membrane potentials were compared. Two methods of statistical analysis were used in attempts to determine whether changes in mean excitatory postsynaptic potential amplitude were due to presynaptic or postsynaptic modifications. Analysis of the decrease in mean excitatory postsynaptic potential amplitude associated with increases in presynaptic firing rate were consistent with a change in probability of transmitter release. Paired pulse depression appeared to exhibit both presynaptic and postsynaptic components when the interspike interval was < 10 ms, but could be explained simply by a decrease in probability of release with interspike intervals between 10 and 80 ms. Previous studies had demonstrated that these excitatory postsynaptic potentials are partially mediated by N-methyl-D-aspartate receptors. In contrast to the apparently presynaptic effects of firing pattern, postsynaptic membrane depolarization appeared to produce an increase in quantal amplitude. In addition to this increase at low frequencies, a form of frequency-dependent, self-potentiation involving the recruitment of an additional, longer-latency postsynaptic component occurred at higher presynaptic firing rates. The possibility is discussed that two different mechanisms are involved in the replacement of vesicles at release sites. Over a few tens of milliseconds (paired-pulse depression) availability of releasable transmitter may be determined by the rate of replacement of discharged vesicles from a readily releasable pool of vesicles. Over longer periods of firing at 0.33-2 Hz, the readily releasable pool may become exhausted and require replenishment. Postsynaptic depolarization increases the duration of these excitatory postsynaptic potentials, facilitating summation and enables two components of excitatory postsynaptic potential enhancement at N-methyl-D-aspartate receptor-mediated synapses; one that is present at all firing rates and relates simply to voltage dependent events and one that occurs at higher firing rates and involves a gradual, time dependent event. These data also indicate that the optimal pyramidal firing pattern if another pyramid is to be activated is a tonic, or brief burst pattern at relatively low repetition rates. Long bursts of many presynaptic spikes recruit little that is not activated by pairs of spikes. This situation is in stark contrast to the results obtained in the following paper in which excitatory inputs from pyramids to non-pyramids are described.
利用成年大鼠体感/运动皮层冠状切片II/III层和IV层中的细胞内配对记录，研究了成对的新皮层锥体神经元之间的单轴突兴奋性连接。比较了不同突触前放电模式和不同突触后膜电位诱发的兴奋性突触后电位。使用了两种统计分析方法，试图确定平均兴奋性突触后电位幅度的变化是由于突触前还是突触后修饰引起的。与突触前放电频率增加相关的平均兴奋性突触后电位幅度的降低分析，与递质释放概率的变化一致。当峰间期<10毫秒时，双脉冲抑制似乎表现出突触前和突触后成分，但在峰间期为10至80毫秒时，可简单地用释放概率的降低来解释。先前的研究表明，这些兴奋性突触后电位部分由N-甲基-D-天冬氨酸受体介导。与放电模式明显的突触前效应相反，突触后膜去极化似乎会使量子幅度增加。除了在低频时的这种增加外，在较高的突触前放电频率下，还会出现一种频率依赖性的自增强形式，涉及额外的、潜伏期更长的突触后成分的募集。讨论了在释放位点囊泡替换可能涉及两种不同机制的可能性。在几十毫秒内（双脉冲抑制），可释放递质的可用性可能由从易于释放的囊泡池中排出的囊泡的替换速率决定。在0.33 - 2 Hz的较长时间放电过程中，易于释放的囊泡池可能会耗尽并需要补充。突触后去极化增加了这些兴奋性突触后电位的持续时间，促进了总和，并在N-甲基-D-天冬氨酸受体介导的突触处实现了兴奋性突触后电位增强的两个成分；一个在所有放电频率下都存在，仅与电压依赖性事件有关，另一个在较高放电频率下出现，涉及一个逐渐的、时间依赖性事件。这些数据还表明，如果要激活另一个锥体神经元，最佳的锥体神经元放电模式是相对低重复率的强直或短暂爆发模式。许多突触前尖峰的长爆发募集的很少，而双尖峰不能激活的部分。这种情况与以下论文中描述的从锥体神经元到非锥体神经元的兴奋性输入的结果形成了鲜明对比。
