Department of Cell Biology, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, California 92037, USA.
Nature. 2011 Apr 14;472(7342):217-20. doi: 10.1038/nature09945. Epub 2011 Mar 30.
Sensory information may be represented in the brain by stereotyped mapping of axonal inputs or by patterning that varies between individuals. In olfaction, a stereotyped map is evident in the first sensory processing centre, the olfactory bulb (OB), where different odours elicit activity in unique combinatorial patterns of spatially invariant glomeruli. Activation of each glomerulus is relayed to higher cortical processing centres by a set of ∼20-50 'homotypic' mitral and tufted (MT) neurons. In the cortex, target neurons integrate information from multiple glomeruli to detect distinct features of chemically diverse odours. How this is accomplished remains unclear, perhaps because the cortical mapping of glomerular information by individual MT neurons has not been described. Here we use new viral tracing and three-dimensional brain reconstruction methods to compare the cortical projections of defined sets of MT neurons. We show that the gross-scale organization of the OB is preserved in the patterns of axonal projections to one processing centre yet reordered in another, suggesting that distinct coding strategies may operate in different targets. However, at the level of individual neurons neither glomerular order nor stereotypy is preserved in either region. Rather, homotypic MT neurons from the same glomerulus innervate broad regions that differ between individuals. Strikingly, even in the same animal, MT neurons exhibit extensive diversity in wiring; axons of homotypic MT pairs diverge from each other, emit primary branches at distinct locations and 70-90% of branches of homotypic and heterotypic pairs are non-overlapping. This pronounced reorganization of sensory maps in the cortex offers an anatomic substrate for expanded combinatorial integration of information from spatially distinct glomeruli and predicts an unanticipated role for diversification of otherwise similar output neurons.
感觉信息可能通过轴突输入的刻板映射或个体之间的模式来在大脑中表示。在嗅觉中，在第一个感觉处理中心——嗅球（OB）中存在刻板的图谱，不同的气味以独特的组合模式在空间不变的神经球中引起活动。每个神经球的激活通过一组约 20-50 个“同型”僧帽和丛状（MT）神经元传递到更高的皮质处理中心。在皮质中，靶神经元整合来自多个神经球的信息，以检测化学多样气味的独特特征。这是如何完成的仍然不清楚，也许是因为单个 MT 神经元对神经球信息的皮质映射尚未被描述。在这里，我们使用新的病毒追踪和三维大脑重建方法来比较定义的 MT 神经元集合的皮质投射。我们表明，OB 的总体规模组织在向一个处理中心的轴突投射模式中得以保留，但在另一个处理中心中被重新排列，这表明不同的编码策略可能在不同的靶标中起作用。然而，在个体神经元水平上，无论是在哪个区域，神经球的顺序或刻板性都没有得到保留。相反，来自同一神经球的同型 MT 神经元支配着个体之间不同的广泛区域。引人注目的是，即使在同一动物中，MT 神经元在布线方面也表现出广泛的多样性；同型 MT 神经元的轴突彼此发散，在不同的位置发出初级分支，同型和异型神经元的 70-90%的分支是不重叠的。这种皮质感觉图谱的显著重构为从空间上不同的神经球中扩展组合信息的综合提供了一个解剖学基础，并预测了otherwise similar output neurons （其他相似输出神经元）多样化的预期作用。
