Auerbach A A, Bennett M V
J Gen Physiol. 1969 Feb;53(2):211-37. doi: 10.1085/jgp.53.2.211.
The adductor muscles of the pectoral fins of the hatchetfish Gasteropelecus are innervated by bilateral pools of about 40 motoneurons which lie primarily in the first spinal segment. A pair of giant fibers on each side of the medulla send processes ventroposteriorly to the motoneuron pools. Electrophysiological evidence indicates that giant fibers are presynaptic to ipsilateral motoneurons, but not to contralateral ones. Transmission across the giant fiber, motoneuron synapse is electrically mediated as is indicated by direct measurement of electrotonic spread in either direction across the synapse, and by the extremely short latency of the giant fiber postsynaptic potentials (PSP's) in the motoneuron. The coupling resistance across the synapse was calculated from measurements of input and transfer resistance. The coupling resistance rectifies in such a way as to facilitate spread of depolarization from giant fiber to motoneuron, and to oppose transmission in the opposite direction. As a consequence of rectification, the giant fiber PSP in a motoneuron is augmented by hyperpolarization of the motoneuron. The coupling resistance calculated on the basis of this effect is in good agreement with calculations from input and transfer resistance data. Rectification at the electrotonic synapses may permit the motoneurons to act in small swimming movements as well as to fire synchronously in an extremely fast escape reflex mediated by Mauthner and giant fibers.
胸斧鱼胸鳍的内收肌由约40个运动神经元的双侧神经元池支配，这些神经元池主要位于第一脊髓节段。延髓两侧各有一对巨纤维向后腹侧发出突起至运动神经元池。电生理证据表明，巨纤维对同侧运动神经元是突触前的，但对 contralateral ones 不是。通过直接测量突触两侧电紧张扩布以及运动神经元中巨纤维突触后电位（PSP）的极短潜伏期表明，跨巨纤维 - 运动神经元突触的传递是电介导的。根据输入电阻和转移电阻的测量计算出突触的耦合电阻。耦合电阻以这样一种方式整流，即促进去极化从巨纤维向运动神经元的扩布，并阻止相反方向的传递。整流的结果是，运动神经元中的巨纤维PSP因运动神经元的超极化而增强。基于这种效应计算出的耦合电阻与根据输入电阻和转移电阻数据计算的结果非常吻合。电紧张性突触的整流可能使运动神经元在小的游泳运动中发挥作用，以及在由Mauthner细胞和巨纤维介导的极快逃避反射中同步放电。
