Schierwagen Andreas, Alpár Alán, Gärtner Ulrich
Institute for Computer Science, University of Leipzig, 04109 Leipzig, Germany.
Math Biosci. 2007 Jun;207(2):352-64. doi: 10.1016/j.mbs.2006.08.019. Epub 2006 Sep 5.
Dendritic morphology is the structural correlate for receiving and processing inputs to a neuron. An interesting question then is what the design principles and the functional consequences of enlarged or shrinked dendritic trees might be. As yet, only a few studies have examined the effects of neuron size changes. Two theoretical scaling modes have been analyzed, conservative (isoelectrotonic) scaling (preserves the passive and active response properties) and isometric scaling (steps up low pass-filtering of inputs). It has been suggested that both scaling modes were verified in neuroanatomical studies. To overcome obvious limitations of these studies like small size of analyzed samples and restricted validity of utilized scaling measures, we considered the scaling problem of neurons on the basis of large sample data and by employing a more general method of scaling analysis. This method consists in computing the morphoelectrotonic transform (MET) of neurons. The MET maps the neuron from anatomical space into electrotonic space using the logarithm of voltage attenuation as the distance metric. The theory underlying this approach is described and then applied to two samples of morphologically reconstructed pyramidal neurons (cells from neocortex of wildtype and synRas transgenic mice) using the NEURON simulator. In a previous study, we could verify a striking increase of dendritic tree size in synRas pyramidal neurons. Surprisingly, in this study the statistical analysis of the sample MET dendrograms revealed that the electrotonic architecture of these neurons scaled roughly in a MET-conserving mode. In conclusion, our results suggest only a minor impact of the Ras protein on dendritic electroanatomy, with non-significant changes of most regions of the corresponding METs.
树突形态是神经元接收和处理输入信息的结构基础。那么一个有趣的问题是，树突树增大或缩小的设计原则及功能后果可能是什么。到目前为止，仅有少数研究考察了神经元大小变化的影响。已经分析了两种理论缩放模式，保守（等电紧张）缩放（保留被动和主动反应特性）和等距缩放（增强输入的低通滤波）。有人提出这两种缩放模式在神经解剖学研究中都得到了验证。为了克服这些研究的明显局限性，如分析样本量小以及所用缩放测量方法的有效性受限，我们基于大样本数据并采用更通用的缩放分析方法来考虑神经元缩放问题。该方法包括计算神经元的形态电紧张变换（MET）。MET使用电压衰减的对数作为距离度量，将神经元从解剖空间映射到电紧张空间。描述了该方法的理论基础，然后使用NEURON模拟器将其应用于两个形态重建的锥体神经元样本（来自野生型和synRas转基因小鼠新皮层的细胞）。在先前的一项研究中，我们证实了synRas锥体神经元的树突树大小显著增加。令人惊讶的是，在本研究中，对样本MET树状图的统计分析表明，这些神经元的电紧张结构大致以MET保守模式缩放。总之，我们的结果表明Ras蛋白对树突电解剖学的影响较小，相应MET的大多数区域变化不显著。
