Yim C C, Krnjević K, Dalkara T
J Neurophysiol. 1986 Jul;56(1):99-122. doi: 10.1152/jn.1986.56.1.99.
Passive (ephaptic) transmembrane currents generated by antidromically evoked electrical fields were studied in CA1 hippocampal neurons of urethan-anesthetized rats. Recording was mostly from the stratum pyramidale where the fields have a maximum (negative) amplitude. The antidromic population spike was consistently smaller when recorded inside a noninvaded neuron rather than extracellularly. This indicated a substantial transmembrane potential (Vm), which was revealed and quantified by subtracting from the intracellular record a just-extracellular one. In neurons that have spikes greater than or equal to 40 mV (mean 60 mV), the average Vm was 41.1% of the extracellular field (Ve; mean 6.7 mV). Typically, Vm was very brief (mean duration 1.1 ms), predominantly monophasic, and in a depolarizing direction. Though almost synchronous with Ve, the peak of Vm was most often delayed slightly. Its amplitude varied with the intensity of antidromic stimulation, bearing an approximately constant relation to Ve, and it was not markedly sensitive to large changes in membrane potential. Most of these features confirm its ephaptic nature. By contrast, no consistent Vm was recorded from unresponsive cells, presumed to be glia. When combined with subthreshold depolarizing pulses, antidromic fields increased the firing probability of cells not activated by the antidromic stimulus. The ephaptic nature of this excitation was indicated by its very short latency, too early to be of synaptic origin, a much greater jitter of spike latency than was seen with antidromic spikes, and its inability to follow repetitive stimulation at frequencies as low as 2 Hz. In addition, juxta-threshold ephaptic excitations showed the random patterns of firing and very steep relation to intensity of stimulation expected of single-unit responses to electrical stimulation. In general, much larger excitatory effects could be demonstrated in neurons that had a high threshold for antidromic activation. The correlation between Vm and the increase in firing probability (r = 0.85) was strongly positive. A significant excitatory effect was detectable with antidromic fields as small as 1 mV. These ephaptically generated transmembrane potentials are probably of functional significance, even under physiological conditions, particularly in promoting synchronized firing of CA1 neurons. In the APPENDIX, the predictions of a simple neuronal model as a lumped resistance and capacitance circuit are shown to agree quite well with the observations.(ABSTRACT TRUNCATED AT 400 WORDS)
在经乌拉坦麻醉的大鼠海马CA1神经元中，研究了由逆向诱发电场产生的被动（电突触）跨膜电流。记录主要来自场强（负向）最大的锥体层。在未被侵入的神经元内记录到的逆向群体峰电位始终比细胞外记录时小。这表明存在显著的跨膜电位（Vm），通过从细胞内记录中减去刚好在细胞外的记录来揭示和量化该电位。在峰电位大于或等于40 mV（平均60 mV）的神经元中，平均Vm为细胞外场（Ve；平均6.7 mV）的41.1%。通常，Vm非常短暂（平均持续时间1.1 ms），主要为单相，且方向为去极化。尽管Vm几乎与Ve同步，但Vm的峰值最常稍有延迟。其幅度随逆向刺激强度而变化，与Ve保持大致恒定的关系，并且对膜电位的大幅变化不敏感。这些特征大多证实了其电突触性质。相比之下，从未反应细胞（推测为神经胶质细胞）记录到一致的Vm。当与阈下去极化脉冲结合时，逆向场增加了未被逆向刺激激活的细胞的放电概率。这种兴奋的电突触性质表现为其潜伏期非常短，早于突触起源，峰电位潜伏期的抖动比逆向峰电位大得多，并且在低至2 Hz的频率下无法跟随重复刺激。此外，阈下电突触兴奋表现出随机的放电模式以及与电刺激的单单位反应预期的刺激强度非常陡峭的关系。一般来说，在逆向激活阈值较高的神经元中可以证明更大的兴奋效应。Vm与放电概率增加之间的相关性（r = 0.85）呈强正相关。在小至1 mV的逆向场中可检测到显著的兴奋效应。即使在生理条件下，这些电突触产生的跨膜电位可能也具有功能意义，特别是在促进CA1神经元的同步放电方面。在附录中，一个作为集总电阻和电容电路的简单神经元模型的预测结果与观察结果相当吻合。（摘要截取自400字）
