McDonagh J C, Gorman R B, Gilliam E E, Hornby T G, Reinking R M, Stuart D G
Department of Physiology, University of Arizona, College of Medicine, Tucson 85724-5051, USA.
J Physiol Paris. 1999 Jan-Apr;93(1-2):3-16. doi: 10.1016/s0928-4257(99)80131-4.
In this report, we present recent findings on the electrophysiological and morphological properties of spinal motoneurons (MNs) and interneurons (INs) of the adult turtle which were studied in slices of the spinal cord. The range of values for the measured electrophysiological parameters in 96 tested cells included: resting potential, -57 to -83 mV; input resistance, 2.5-344 M omega; time constant, 2.5-63 ms; rheobase current, 0.04-5.3 nA; after-hyperpolarization (AHP) duration, 72-426 ms; AHP half-decay time; 11-212 ms; and, slope of the stimulus current-spike frequency relationship, 3.4-235 Hz/nA. For another 20 cells, we made both morphological and electrophysiological measurements (the latter values within the above ranges). Their ranges in morphological properties included: soma diameter, 20-54 microm; soma surface area, 299-2045 microm2; soma volume, 2.3-45 microm3 x 10(4); rostro-caudal dendritic projection distance, 150-1200 microm; and, sum of dendritic lengths, 1.5-16 microm x 10(3). The emphasized findings include: 1) the quality and robustness of the intracellular recordings, which enabled accurate measurement of the action potential's shape parameters (spike, afterhyperpolarization [AHP]); 2) the substantial AHP of the INs' AP; 3) no single action-potential shape parameter (nor combination of parameters) being cardinal for its (or their combined) changes matching the profile of the initial and later phases of spike-frequency adaptation; 4) the utility and flexibility of a cluster analysis (using varying combinations of passive, transitional and active cell properties) for providing a provisional classification of low (like cat S) and high (like cat F) threshold MNs, and groups of INs with non-spontaneous versus spontaneous discharge; 5) the clear-cut morphological confirmation of the provisional classification strategy; 6) the basis for testing the possibility that one of the provisionally classified MN types innervates non-twitch muscle fibers; and 7) the heuristic value of comparing the properties of MNs versus INs across vertebrate species, with an emphasis on the lamprey, turtle, and cat.
在本报告中，我们展示了对成年海龟脊髓切片中脊髓运动神经元（MNs）和中间神经元（INs）的电生理及形态学特性的最新研究结果。在96个受试细胞中测得的电生理参数值范围包括：静息电位，-57至-83 mV；输入电阻，2.5 - 344 MΩ；时间常数，2.5 - 63 ms；基强度电流，0.04 - 5.3 nA；超极化后电位（AHP）持续时间，72 - 426 ms；AHP半衰时间，11 - 212 ms；以及刺激电流-动作电位频率关系的斜率，3.4 - 235 Hz/nA。对于另外20个细胞，我们进行了形态学和电生理测量（后者的值在上述范围内）。它们的形态学特性范围包括：胞体直径，20 - 54 μm；胞体表面积，299 - 2045 μm²；胞体体积，2.3 - 45×10⁴μm³；前后树突投射距离，150 - 1200 μm；以及树突总长度，1.5 - 16×10³μm。重点研究结果包括：1）细胞内记录的质量和稳定性，这使得能够准确测量动作电位的形状参数（峰电位、超极化后电位[AHP]）；2）中间神经元动作电位的显著超极化后电位；3）没有单一的动作电位形状参数（或参数组合）对于其（或它们的组合）变化与峰电位频率适应的初始和后期阶段的特征相匹配是至关重要的；4）聚类分析（使用被动、过渡和主动细胞特性的不同组合）在对低阈值（如猫的S型）和高阈值（如猫的F型）运动神经元以及具有非自发性与自发性放电的中间神经元群体进行初步分类方面的实用性和灵活性；5）对初步分类策略的明确形态学确认；6）测试初步分类的运动神经元类型之一支配非抽搐性肌纤维可能性的基础；7）比较脊椎动物物种间运动神经元与中间神经元特性的启发价值，重点是七鳃鳗、海龟和猫。
