Saint Mleux B, Moore L E
Laboratoire de Neurobiologie des Reseaux Sensorimoteurs, Centre National de la Recherche Scientifique-Unité Propre de Recherche de l'Enseignement Supérieur Associée-7060, 75270 Paris Cedex 06, France.
J Neurophysiol. 2000 Mar;83(3):1366-80. doi: 10.1152/jn.2000.83.3.1366.
Whole cell voltage- and current-clamp measurements were done on intact Xenopus laevis larval spinal neurons at developmental stages 42-47. Firing patterns and electrotonic properties of putative interneurons from the dorsal and ventral medial regions of the spinal cord at myotome levels 4-6 were measured in isolated spinal cord preparations. Passive electrotonic parameters were determined with internal cesium sulfate solutions as well as in the presence of active potassium conductances. Step-clamp stimuli were combined with white-noise frequency domain measurements to determine both linear and nonlinear responses at different membrane potential levels. Comparison of analytic and compartmental dendritic models provided a way to determine the number of compartments needed to describe the dendritic structure. The electrotonic structure of putative interneurons was correlated with their firing behavior such that highly accommodating neurons (Type B) had relatively larger dendritic areas and lower electrotonic lengths compared with neurons that showed sustained action potential firing in response to a constant current (Type A). Type A neurons had a wide range of dendritic areas and potassium conductances that were activated at membrane potentials more negative than observed in Type B neurons. The differences in the potassium conductances were in part responsible for a much greater rectification in the steady-state current voltage (I-V curve) of the strongly accommodating neurons compared with repetitively firing cells. The average values of the passive electrotonic parameters found for Rall Type A and B neurons were c(soma) = 3.3 and 2.6 pF, g(soma) = 187 and 38 pS, L = 0.36 and 0.21, and A = 3.3 and 6.5 for soma capacitance, soma conductance, electrotonic length, and the ratio of the dendritic to somatic areas, respectively. Thus these experiments suggest that there is a correlation between the electrotonic structure and the excitability properties elicited from the somatic region.
在发育阶段42 - 47的非洲爪蟾幼体完整脊髓神经元上进行了全细胞电压钳和电流钳测量。在分离的脊髓标本中，测量了脊髓4 - 6肌节水平背侧和腹侧内侧区域假定中间神经元的放电模式和电紧张特性。使用内部硫酸铯溶液以及在存在活性钾电导的情况下测定被动电紧张参数。阶跃钳刺激与白噪声频域测量相结合，以确定不同膜电位水平下的线性和非线性响应。分析性和房室性树突模型的比较提供了一种确定描述树突结构所需房室数量的方法。假定中间神经元的电紧张结构与其放电行为相关，因此与对恒定电流表现出持续动作电位发放的神经元（A型）相比，高度适应性神经元（B型）具有相对更大的树突面积和更低的电紧张长度。A型神经元具有广泛的树突面积和钾电导，其在比B型神经元更负的膜电位下被激活。钾电导的差异部分导致了与重复放电细胞相比，强适应性神经元的稳态电流 - 电压（I - V曲线）有更大的整流。对于拉伊尔A型和B型神经元，被动电紧张参数的平均值分别为：胞体电容c(soma) = 3.3和2.6 pF，胞体电导g(soma) = 187和38 pS，电紧张长度L = 0.36和0.21，以及树突与胞体面积之比A = 3.3和6.5。因此，这些实验表明电紧张结构与从胞体区域引发的兴奋性特性之间存在相关性。
