Chehrehasa Fatemeh, St John James A, Key Brian
Brain Growth and Regeneration Lab, Discipline of Anatomy and Developmental Biology, School of Biomedical Sciences, The University of Queensland, Brisbane 4072, Australia.
Brain Res. 2006 Nov 13;1119(1):58-64. doi: 10.1016/j.brainres.2006.08.060. Epub 2006 Sep 25.
Primary olfactory axons expressing different odorant receptors are interspersed within the olfactory nerve. However, upon reaching the outer nerve fiber layer of the olfactory bulb they defasciculate, sort out, and refasciculate prior to targeting glomeruli in fixed topographic positions. While odorant receptors are crucial for the final targeting of axons to glomeruli, it is unclear what directs the formation of the nerve fiber and glomerular layers of the olfactory bulb. While the olfactory bulb itself may provide instructive cues for the development of these layers, it is also possible that the incoming axons may simply require the presence of a physical scaffold to establish the outer laminar cytoarchitecture. In order to begin to understand the underlying role of the olfactory bulb in development of the outer layers of the olfactory bulb, we physically ablated the olfactory bulbs in OMP-IRES-LacZ and P2-IRES-tau-LacZ neonatal mice and replaced them with artificial biological scaffolds molded into the shape of an olfactory bulb. Regenerating axons projected around the edge of the cranial cavity at the periphery of the artificial scaffold and were able to form an olfactory nerve fiber layer and, to some extent, a glomerular layer. Our results reveal that olfactory axons are able to form rudimentary cytoarchitectonic layers if they are provided with an appropriately shaped biological scaffold. Thus, the olfactory bulb does not appear to provide any tropic substance that either attracts regenerating olfactory axons into the cranial cavity or induces these axons to form a plexus around its outer surface.
表达不同气味受体的初级嗅觉轴突散布在嗅神经内。然而，到达嗅球的外神经纤维层时，它们会散开、分选并重新成束，然后在固定的地形位置靶向肾小球。虽然气味受体对于轴突最终靶向肾小球至关重要，但尚不清楚是什么指导了嗅球神经纤维层和肾小球层的形成。虽然嗅球本身可能为这些层的发育提供指导性线索，但也有可能传入的轴突可能仅仅需要一个物理支架的存在来建立外层细胞结构。为了开始理解嗅球在嗅球外层发育中的潜在作用，我们在OMP-IRES-LacZ和P2-IRES-tau-LacZ新生小鼠中物理切除嗅球，并用模制成嗅球形状的人工生物支架替代它们。再生轴突在人工支架周边围绕颅腔边缘投射，并能够形成嗅神经纤维层，在一定程度上还能形成肾小球层。我们的结果表明，如果为嗅觉轴突提供形状合适的生物支架，它们能够形成基本的细胞结构层。因此，嗅球似乎并未提供任何吸引再生嗅觉轴突进入颅腔或诱导这些轴突在其外表面形成神经丛的促生长物质。
