Davis R E, Stretton A O
Neurosciences Training Program, University of Wisconsin-Madison 53706.
J Neurosci. 1989 Feb;9(2):415-25. doi: 10.1523/JNEUROSCI.09-02-00415.1989.
The commissural motorneurons of the nematode Ascaris are capable of transmitting signals passively over long distances with little decrement. This ability is due to the high resistivities of their membranes (Davis and Stretton, 1989). Although these cells rely on their passive properties for long-distance signaling, voltage-sensitive channels are present in commissural membranes. These channels underlie the graded active responses that can be elicited at the offset of abrupt hyperpolarizing and depolarizing intracellular current pulses. The inhibitory motorneurons generate membrane potential oscillations when they are strongly depolarized. All-or-none action potentials have never been observed to occur spontaneously, nor has it been possible to evoke them even when the cells have been strongly hyperpolarized to remove any possible channel inactivation. Our findings indicate that the typical all-or-none action potentials so commonly used in nerve cells throughout the animal kingdom do not occur in these cells. Synaptic transmission is therefore mediated without spikes and is graded. The resting potentials of Ascaris motorneurons lie where the synaptic input-output curves are steepest, above the threshold for release of neurotransmitter. Tonic transmitter release from commissural motorneurons may be the neural mechanism underlying the hydrostatic skeleton of Ascaris.
线虫蛔虫的连合运动神经元能够被动地远距离传递信号，且信号衰减很小。这种能力归因于其细胞膜的高电阻率（戴维斯和斯特雷顿，1989年）。尽管这些细胞依靠其被动特性进行远距离信号传递，但连合细胞膜中存在电压敏感通道。这些通道是在突然的超极化和去极化细胞内电流脉冲结束时可引发的分级主动反应的基础。抑制性运动神经元在强烈去极化时会产生膜电位振荡。从未观察到全或无动作电位自发出现，即使在细胞被强烈超极化以消除任何可能的通道失活时，也无法诱发它们。我们的研究结果表明，动物界神经细胞中常用的典型全或无动作电位在这些细胞中不会出现。因此，突触传递是无峰介导的且是分级的。蛔虫运动神经元的静息电位位于突触输入 - 输出曲线最陡峭的位置，高于神经递质释放阈值。连合运动神经元的持续性递质释放可能是蛔虫流体静力骨骼的神经机制基础。
