2012年9月20日 讯 /生物谷BIOON/ --人类大脑可能是宇宙上最为复杂的物体，但是它的生长依赖于一种东西：神经元的形状。
不同类型的神经元在与哪些其他的神经元相连接在一起以及与它们在何处附着是有选择性的。人们认为特异性的信号分子在指导这种过程中发挥着至关重要的作用。
来自瑞士联邦理工学院的Henry Markram和同事们构建了大鼠躯体感觉皮质(somatosensory cortex)的三维计算机模型，并且每个模型含有在大鼠大脑中发现的细胞类型的随机组合，但不含有信号分子。然而，只需允许这些神经元产生它们正确的形状，就可以使得74%的神经元连接最终都在正确的地方形成。
这些研究结果提示着科学家们可能在不需要信号分子的存在下绘制出大脑大部分结构。对于努力绘制大脑中令人眼花缭乱的神经元连接网络的神经科学家们而言，这是一个好消息。Markram说，“它将需要花费数十年的时间来绘制大脑中的每个突触。”
人们通常认为精神分裂症是由于大脑连接存在的缺陷而导致的。这项研究可能也有助于揭示诸如精神分裂症之类疾病的病因。如果Markram的这项研究证明是对的，那么不能正确形成连接的有缺陷的神经元可能是这类疾病的一个影响因素。(生物谷Bioon.com)
doi: 10.1073/pnas.1202128109
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Statistical connectivity provides a sufficient foundation for specific functional connectivity in neocortical neural microcircuits
Sean L. Hilla,1,2, Yun Wangb,c,1, Imad Riachia,1, Felix Schürmanna, and Henry Markram
It is well-established that synapse formation involves highly selective chemospecific mechanisms, but how neuron arbors are positioned before synapse formation remains unclear. Using 3D reconstructions of 298 neocortical cells of different types (including nest basket, small basket, large basket, bitufted, pyramidal, and Martinotti cells), we constructed a structural model of a cortical microcircuit, in which cells of different types were independently and randomly placed. We compared the positions of physical appositions resulting from the incidental overlap of axonal and dendritic arbors in the model (statistical structural connectivity) with the positions of putative functional synapses (functional synaptic connectivity) in 90 synaptic connections reconstructed from cortical slice preparations. Overall, we found that statistical connectivity predicted an average of 74 ± 2.7% (mean ± SEM) synapse location distributions for nine types of cortical connections. This finding suggests that chemospecific attractive and repulsive mechanisms generally do not result in pairwise-specific connectivity. In some cases, however, the predicted distributions do not match precisely, indicating that chemospecific steering and aligning of the arbors may occur for some types of connections. This finding suggests that random alignment of axonal and dendritic arbors provides a sufficient foundation for specific functional connectivity to emerge in local neural microcircuits
