Bistability in spinal motoneurons in vivo: Systematic variations in persistent inward currents
Bistability in spinal motoneurons in vivo: Systematic variations in persistent inward currents
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DOI：
10.1152/jn.1998.80.2.583
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发表时间：
1998-08-01
影响因子：
2.5
通讯作者：
Heckman, CJ
中科院分区：
文献类型：
--
作者：
Lee, RH;Heckman, CJ
脊髓运动神经元的双稳态行为包括由短时间输入引起的自我持续放电。然而，并不是所有的运动神经元都具有相同的双稳态行为能力。在这篇论文中，我们发现只有在低流变基和慢轴突传导速度的运动神经元中，自我持续放电才会持续很长时间。高流变碱、传导速度快的运动神经元在自持放电最多持续1-2秒时，往往只有部分双稳态。在给予去甲肾上腺素能α(1)激动剂甲氧胺后，通过测量其电流电压（I-V）关系，研究了完全和部分双稳态运动神经元之间这些差异的机制。采用不连续的单电极电压箝位技术，施加缓慢（8 mV/s）的三角形电压命令。完全和部分双稳态细胞都表现出一个负的I-V斜率区域，这是由于一个强大的、持续的内向电流的激活。在完全和部分双稳态细胞中，总持续向内电流（I-PIC）的峰值幅度同样大，但在I-PIC的激活和失活方式上存在实质性差异。在完全双稳态电池中，I-PIC在三角形电压命令下降阶段的偏移发生在一个远高于其在上升阶段开始的超极化电压。因此，完全双稳态细胞的I-V功能表现出明显的滞后性。部分双稳态细胞的迟滞明显减小。部分双稳态细胞缺乏迟滞是由于I-PIC随时间的衰减比完全双稳态细胞更大。此外，IPIC的激活和失活范围在部分双稳态细胞中比在完全双稳态细胞中更多地去极化。将I-V函数与来自同一细胞的频率-电流（F-I）函数进行了比较，其特征在后续论文中给出。在完全双稳态细胞中，I-PIC的强烈发病偏移差异对应于其F-I功能阈值的类似大滞后。在部分双稳态细胞中，I-PIC的发病偏移差异减少，与F-l阈值缺乏迟滞相对应。因此，IPIC的特性解释了完全和部分双稳态细胞之间F-I行为的主要差异。
Bistable behavior in spinal motoneurons consists of self-sustained firing evoked by a brief period of input. However, not all motoneurons possess an equal capacity for bistable behavior. In the companion paper, we found that self-sustained firing was persistent for long periods only in motoneurons with low rheobases and slow axonal conduction velocities. High rheobase, fast conduction velocity motoneurons tend to be only partially bistable in that self-sustained firing lasts at most 1-2 s. The mechanisms underlying these differences between fully and partially bistable motoneurons were investigated by measuring their current voltage (I-V) relationships in the decerebrate cat preparation after administration of the noradrenergic alpha(1) agonist methoxamine. Slow (8 mV/s) triangular voltage commands were applied using the discontinuous single-electrode voltage-clamp technique. Both fully and partially bistable cells exhibited a region of negative I-V slope due to activation of a strong, persistent inward current. The peak amplitude of the total persistent inward current (I-PIC) was equally large in fully and partially bistable cells, but there were substantial differences in how I-PIC was activated and deactivated. In fully bistable cells, the offset of I-PIC on the descending phase of the triangular voltage command occurred at a substantially more hyperpolarized voltage then its onset on the rising phase. Thus the I-V function of fully bistable cells exhibited marked hysteresis. Partially bistable cells had significantly less hysteresis. The lack of hysteresis in partially bistable cells was due to a greater decay of I-PIC With time than that seen in fully bistable cells. Furthermore, the range over which activation and deactivation of IPIC occurred was more depolarized in partially than in fully bistable cells. The I-V functions were compared with frequency-current (F-I) functions from the same cells, the characteristics of which were presented in the companion paper. The strong onset-offset difference in I-PIC in fully bistable cells corresponded to a similarly large hysteresis for the thresholds of their F-I functions. The reduced onset-offset difference for I-PIC in partially bistable cells corresponded to a lack of hysteresis in F-l thresholds. Thus the properties of IPIC accounted for the main differences in the F-I behavior seen between fully and partially bistable cells.