Key B, Akeson R A
Department of Anatomy and Cell Biology, University of Melbourne, Vic, Australia.
J Comp Neurol. 1993 Sep 15;335(3):355-68. doi: 10.1002/cne.903350306.
The axons of the primary sensory olfactory neurons project from the olfactory neuroepithelium lining the nasal cavity, onto glomeruli covering the surface of the olfactory bulb. Neuroanatomical studies have shown previously that individual olfactory glomeruli are innervated by neurons that are dispersed widely within the nasal cavity. The aim of the present study was to test the hypothesis that phenotypically unique subsets of primary sensory olfactory neurons, scattered throughout the nasal cavity, project to a subset of glomeruli in specific olfactory bulb loci. Immunochemical and histochemical analyses in neonatal mice revealed that the plant lectin, Dolichos biflorus agglutinin, bound to a subset of mature primary sensory olfactory neurons which express the olfactory marker protein. This subset of neurons was principally located in the rostromedial and dorsal portions of the nasal cavity and projected specifically to a subset of glomeruli in the rostromedial and caudodorsal portions of the olfactory bulb. Analysis of Dolichos biflorus-reactive axons revealed that these axons coursed randomly, with no evidence of their selective fasciculation, within the olfactory nerve. It was only at the level of the rostral olfactory bulb that a significant reorganisation of their trajectory was observed. Within the outer fibre layer of the bulb, discrete bundles of lectin-reactive axons began to coalesce selectively into fascicles which preferentially oriented toward the medial side of the olfactory bulb. These data demonstrated that a phenotypically distinct subset of primary sensory olfactory neurons exhibits a topographical projection from the olfactory epithelium to the olfactory bulb, and suggests that these, and other subsets, may form the basis of the mosaic nature of this pathway. Moreover, it appears that the outer nerve fibre layer in the rostral olfactory bulb plays an important instructive role in the guidance and fasciculation of olfactory sensory axons.
初级感觉嗅觉神经元的轴突从鼻腔内衬的嗅觉神经上皮伸出，投射到覆盖嗅球表面的肾小球上。神经解剖学研究先前表明，单个嗅觉肾小球由广泛分布在鼻腔内的神经元支配。本研究的目的是检验以下假设：分散在整个鼻腔内的表型独特的初级感觉嗅觉神经元亚群投射到嗅球特定位点的肾小球亚群。对新生小鼠的免疫化学和组织化学分析表明，植物凝集素双花扁豆凝集素与表达嗅觉标记蛋白的成熟初级感觉嗅觉神经元亚群结合。这一神经元亚群主要位于鼻腔的吻内侧和背侧部分，并特异性地投射到嗅球吻内侧和尾背侧部分的肾小球亚群。对双花扁豆反应性轴突的分析表明，这些轴突在嗅神经内随机走行，没有选择性成束的证据。只有在嗅球前端水平才观察到它们的轨迹有明显的重新组织。在嗅球的外纤维层内，离散的凝集素反应性轴突束开始选择性地聚集成束，优先朝向嗅球内侧。这些数据表明，表型不同的初级感觉嗅觉神经元亚群表现出从嗅觉上皮到嗅球的拓扑投射，并表明这些亚群和其他亚群可能构成该通路镶嵌性质的基础。此外，嗅球前端的外神经纤维层似乎在嗅觉感觉轴突的引导和成束中起重要的指导作用。
