Armstrong W E, Smith B N
Department of Anatomy and Neurobiology, University of Tennessee, Memphis 38163.
Neuroscience. 1990;38(2):485-94. doi: 10.1016/0306-4522(90)90044-5.
The electrotonic properties of tuberal supraoptic neurons were studied from conventional intracellular recordings made in the hypothalamo-neurohypophysial explant in vitro. The cable parameters electrotonic dendritic length, and the dendritic to somatic conductance ratio, were estimated using the slopes and intercepts of the first two peeled exponentials of the voltage transients generated by current steps. The estimations were made assuming an equivalent cylinder model consisting of a soma and an attached, lumped dendrite of finite length. An equalizing time constant was resolved in 12 of 17 neurons, allowing calculation of both cable parameters. In only one of these 12 was it necessary to assume a somatic shunt to account for the data. The average value of the dendritic electrotonic length was 1.02, and that of the dendritic to somatic conductance ratio, 4.11. In the remaining five neurons, an equalizing time constant could not be peeled and consequently the dendritic cable parameters could not be estimated. The average input resistance of these 12 neurons was 162 M omega and the average membrane time constant was 11.86 ms. Principal Components Analysis revealed that the variance of input resistance and time constant was largely explained by one factor, while that of dendritic electrotonic length and the dendritic to somatic conductance ratio was explained by a separate, independent factor, suggesting a separation of electrical and morphological parameters, respectively. In addition, the variability of the data indicates that considerable differences in the morphology and specific membrane resistivity exist across supraoptic neurons. An analysis of spontaneously occurring postsynaptic potentials revealed that the shapes of these potentials could not be explained simply by assuming that they were determined by their passive decay from some point along the equivalent cable to the soma. In conclusion, dendrites make a significant and previously unappreciated contribution to the electrotonic behavior of supraoptic neurons. These electrotonic properties are similar to those of many other, morphologically diverse, central nervous system neurons.
通过在体外下丘脑 - 神经垂体离体组织中进行的传统细胞内记录，研究了结节 - 视上核神经元的电紧张特性。利用电流阶跃产生的电压瞬变的前两个剥离指数的斜率和截距，估计电缆参数电紧张树突长度和树突与体细胞电导比。这些估计是在假设一个等效圆柱体模型的基础上进行的，该模型由一个胞体和一个附着的、有限长度的集中树突组成。在17个神经元中的12个中解析出了一个均衡时间常数，从而可以计算两个电缆参数。在这12个神经元中只有一个需要假设存在体细胞分流来解释数据。树突电紧张长度的平均值为1.02，树突与体细胞电导比的平均值为4.11。在其余5个神经元中，无法剥离出均衡时间常数，因此无法估计树突电缆参数。这12个神经元的平均输入电阻为162 MΩ，平均膜时间常数为11.86 ms。主成分分析表明，输入电阻和时间常数的方差在很大程度上由一个因素解释，而树突电紧张长度和树突与体细胞电导比的方差由一个单独的、独立的因素解释，这分别表明了电参数和形态参数的分离。此外，数据的变异性表明，视上核神经元在形态和比膜电阻率方面存在相当大的差异。对自发产生的突触后电位的分析表明，这些电位的形状不能简单地通过假设它们由沿着等效电缆从某个点到胞体的被动衰减所决定来解释。总之，树突对视上核神经元的电紧张行为做出了重大且以前未被认识到的贡献。这些电紧张特性与许多其他形态多样的中枢神经系统神经元的特性相似。
