AN INVESTIGATION OF THRESHOLD PROPERTIES AMONG CAT SPINAL ALPHA-MOTONEURONES
AN INVESTIGATION OF THRESHOLD PROPERTIES AMONG CAT SPINAL ALPHA-MOTONEURONES
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DOI：
10.1113/jphysiol.1984.sp015511
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发表时间：
1984-01-01
影响因子：
5.5
通讯作者：
PINTER, MJ
中科院分区：
文献类型：
--
作者：
GUSTAFSSON, B;PINTER, MJ
在麻醉猫，阈值长（基强度）和短持续时间的电流脉冲从脊髓运动神经元，并与其他细胞参数和膜特性进行比较。基强度表现出只有弱的整体关系与传导速度和细胞大小，估计为总电容的个人运动神经元等效圆柱体。Rheobase表现出明显的趋势，与后超极化（a. h. p.）持续时间，并与输入电导和与膜时间常数的倒数密切相关。然而，基强度电流的范围超过输入电导的几乎2倍。出现这种范围差异的部分原因是阈值去极化倾向于随基强度电流增加。因此，在根据基强度分组的运动神经元（3组）中，最低基强度组内的运动神经元具有阈值去极化。平均比最高基强度组低6 mV。尽管这种差异与组间静息电位差异无直接关系，但进一步分析表明，其可能继发于穿刺诱导的去极化。实验估计的阈值去极化在个别运动神经元的发现，一般大于输入电阻和基强度的产品预测表明，阈下整流过程也有助于基强度的范围。低基强度组的差异最大，高基强度组的差异最小。由于这些差异成比例的不同的运动神经元组之间的输入电阻的差异，有人建议，整流过程中的电流的大小并没有系统地不同的运动神经元。根据基强度或a. h. p.持续时间分类的运动神经元组内，基强度电流和输入电导之间存在显著相关性。方差分析表明，即使在这样的功能亚组的运动神经元，基强度明显更好地与膜时间常数比估计的细胞大小相关。虽然显示了一个范围. apprx.其瞬时电流阈值与细胞总电容、a. h. p.时程及膜时间常数的倒数的关系与基强度相似。利用房室模型的个别运动神经元的分析表明，可以解释的基础上的神经元表面积，树突的几何形状和实验观察到的阈值去极化的变化的范围内的脉冲阈值。基强度/脉冲阈值比的变化符合相当接近预期的膜时间常数。然而，这在某种程度上是偶然的，亚阈值整流的效果部分地被电压阈值的时间依赖性变化所抵消。运动神经元池和功能亚组内兴奋性的变化显然主要受特定膜电阻率和与电阻率共变的其他膜特性的变化所支配。细胞大小本身，以及与之共变的因素，似乎起着更有限的作用。
In anesthetized cats, thresholds for long (rheobase) and brief duration current pulses were obtained from spinal motoneurons and compared with other cell parameters and membrane properties. Rheobase showed only weak over-all relationships with conduction velocity and with cell size, estimated as the total capacitance of individual motoneuronal equivalent cylinders. Rheobase showed a clear tendency to vary inversely with after-hyperpolarization (a.h.p.) duration and was strongly correlated with the input conductance and with the inverse of the membrane time constant. However, the range of rheobase current exceeded that of input conductance by almost a factor of 2. Part of this range discrepancy arose because threshold depolarization tended to increase with rheobase current. Thus, among motoneurons grouped according to rheobase magnitude (3 groups), those within the lowest rheobase group had threshold depolarizations .apprx. 6 mV on average lower than those within the highest rheobase group. Even though this difference was not directly related to resting potential differences between the groups, further analysis suggested that it may have arisen secondarily to impalement-induced depolarization. The finding that experimentally estimated threshold depolarizations in individual motoneurons were generally larger than those predicted by the product of input resistance and rheobase indicated that a subthreshold rectification process also contributed to the range of rheobase. The difference was largest in the low-rheobase group and smallest in the high-rheobase group. Because these differences were proportional to the differences in input resistance between the separate motoneuron groups, it was suggested that the magnitude of the current underlying the rectification process does not differ systematically among motoneurons. Within groups of motoneurons classified on the basis of rheobase or a.h.p. duration, significant correlations existed between rheobase current and input conductance. An analysis of variance indicated that even within such functional subgroups of motoneurons, rheobase was appreciably better correlated with membrane time constant than with estimated cell size. Although showing a range .apprx. 1/2 that of rheobase, the brief current threshold was similar to rheobase in its relations with total cell capacitance, a.h.p. duration and the inverse of membrane time constant. An analysis utilizing compartmental models of individual motoneurons showed that the range of brief-pulse threshold could be explained on the basis of variations in neuronal surface area, dendritic geometry and experimentally observed threshold depolarizations. The variation of the rheobase/brief-pulse threshold ratio conformed rather closely to that expected from the membrane time constant. However, this was to some extent fortuitous, the effect of subthreshold rectification being in part cancelled by a time-dependent change in voltage threshold. The variation of excitability both across the motoneuron pool and within functional subgroups evidently is governed chiefly by the variation in specific membrane resistivity and other membrane properties that co-vary with resistivity. Cell size itself, and factors co-varying with it, appear to play a more limited role.