Price David J, Kennedy Henry, Dehay Colette, Zhou Libing, Mercier Marjorie, Jossin Yves, Goffinet André M, Tissir Fadel, Blakey Daniel, Molnár Zoltán
Centre for Integrative Physiology, Hugh Robson Building, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK.
Eur J Neurosci. 2006 Feb;23(4):910-20. doi: 10.1111/j.1460-9568.2006.04620.x.
The cortex receives its major sensory input from the thalamus via thalamocortical axons, and cortical neurons are interconnected in complex networks by corticocortical and callosal axons. Our understanding of the mechanisms generating the circuitry that confers functional properties on cortical neurons and networks, although poor, has been advanced significantly by recent research on the molecular mechanisms of thalamocortical axonal guidance and ordering. Here we review recent advances in knowledge of how thalamocortical axons are guided and how they maintain order during that process. Several studies have shown the importance in this process of guidance molecules including Eph receptors and ephrins, members of the Wnt signalling pathway and members of a novel planar cell polarity pathway. Signalling molecules and transcription factors expressed with graded concentrations across the cortex are important in establishing cortical maps of the topography of sensory surfaces. Neural activity, both spontaneous and evoked, plays a role in refining thalamocortical connections but recent work has indicated that neural activity is less important than was previously thought for the development of some early maps. A strategy used widely in the development of corticocortical and callosal connections is the early overproduction of projections followed by selection after contact with the target structure. Here we discuss recent work in primates indicating that elimination of juvenile projections is not a major mechanism in the development of pathways feeding information forward to higher levels of cortical processing, although its use is common to developing feedback pathways.
皮层通过丘脑皮质轴突从丘脑接收主要的感觉输入，并且皮层神经元通过皮质皮质轴突和胼胝体轴突在复杂的网络中相互连接。尽管我们对赋予皮层神经元和网络功能特性的电路生成机制的理解还很有限，但最近关于丘脑皮质轴突导向和排序分子机制的研究已使其取得了显著进展。在此，我们综述了关于丘脑皮质轴突如何被导向以及它们在这一过程中如何保持有序的最新知识进展。多项研究表明，包括Eph受体和ephrin、Wnt信号通路成员以及一种新型平面细胞极性通路成员在内的导向分子在这一过程中具有重要意义。在整个皮层中以梯度浓度表达的信号分子和转录因子对于建立感觉表面地形的皮层图谱很重要。自发和诱发的神经活动在细化丘脑皮质连接中发挥作用，但最近的研究表明，神经活动对于某些早期图谱的发育而言，其重要性不如之前认为的那样。在皮质皮质和胼胝体连接发育中广泛使用的一种策略是早期过度产生投射，随后在与靶结构接触后进行选择。在此我们讨论最近在灵长类动物中的研究工作，这些研究表明，消除幼年投射并非将信息向前传递到更高皮层处理水平的通路发育中的主要机制，尽管其在发育中的反馈通路中很常见。
