2012年9月20日 訊 /生物谷BIOON/ --人類大腦可能是宇宙上最為復(fù)雜的物體，但是它的生長(zhǎng)依賴于一種東西：神經(jīng)元的形狀。
不同類型的神經(jīng)元在與哪些其他的神經(jīng)元相連接在一起以及與它們?cè)诤翁幐街怯羞x擇性的,。人們認(rèn)為特異性的信號(hào)分子在指導(dǎo)這種過(guò)程中發(fā)揮著至關(guān)重要的作用。
來(lái)自瑞士聯(lián)邦理工學(xué)院的Henry Markram和同事們構(gòu)建了大鼠軀體感覺(jué)皮質(zhì)(somatosensory cortex)的三維計(jì)算機(jī)模型，并且每個(gè)模型含有在大鼠大腦中發(fā)現(xiàn)的細(xì)胞類型的隨機(jī)組合，但不含有信號(hào)分子,。然而，只需允許這些神經(jīng)元產(chǎn)生它們正確的形狀,，就可以使得74%的神經(jīng)元連接最終都在正確的地方形成,。
這些研究結(jié)果提示著科學(xué)家們可能在不需要信號(hào)分子的存在下繪制出大腦大部分結(jié)構(gòu)。對(duì)于努力繪制大腦中令人眼花繚亂的神經(jīng)元連接網(wǎng)絡(luò)的神經(jīng)科學(xué)家們而言,，這是一個(gè)好消息,。Markram說(shuō),，“它將需要花費(fèi)數(shù)十年的時(shí)間來(lái)繪制大腦中的每個(gè)突觸。”
人們通常認(rèn)為精神分裂癥是由于大腦連接存在的缺陷而導(dǎo)致的,。這項(xiàng)研究可能也有助于揭示諸如精神分裂癥之類疾病的病因。如果Markram的這項(xiàng)研究證明是對(duì)的,，那么不能正確形成連接的有缺陷的神經(jīng)元可能是這類疾病的一個(gè)影響因素,。(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
