Malun D, Brunjes P C
Department of Psychology, University of Virginia, Charlottesville 22903, USA.
J Comp Neurol. 1996 Apr 22;368(1):1-16. doi: 10.1002/(SICI)1096-9861(19960422)368:1<1::AID-CNE1>3.0.CO;2-7.
Mitral cells are the primary output neurons of the vertebrate olfactory bulb and are major recipients of sensory input from the periphery. The morphogenesis of mitral cell dendrites was followed to elucidate their early spatial and temporal interactions with olfactory receptor neurons and glia during the construction of olfactory glomeruli. Monodelphis domestica, a marsupial born at an extremely immature stage, and rats were examined. Mitral cells were retrogradely labeled by application of the lipophilic dye 1,1' dihexadecyl-3,3,3'3'-tetramethylin-docarbocyanine perchlorate (DiI) to the lateral olfactory tract. In double-labeling experiments, olfactory receptor neurons were stained with 3,3' dihexadecyloxacarbocyanine perchlorate (DiO), or olfactory nerve Schwann cells were visualized using S-100 protein immunohistochemistry. Tissue was examined with a confocal laser scanning microscope. Some preparations were subsequently investigated with an electron microscope. In Monodelphis, differentiation of mitral cells starts with an outgrowth of numerous, uniform, and widespread dendrites. As soon as terminals of olfactory receptor axons coalesce into glomerular knots within the presumptive glomerular layer, dendrites of individual mitral cells innervate several adjacent glomeruli where they receive sensory synaptic input. With maturation, supernumerary mitral cell dendrites retract, leaving one primary dendrite bearing a terminal glomerular tuft. Simultaneously, secondary dendrites begin to arise. The formation of glomeruli begins earlier and progresses faster in the rat compared to Monodelphis. Nevertheless, mitral cell differentiation in both species follows a common sequence: overproduction of dendrites, selection of usually one primary apical dendrite, and elimination of supernumerary processes. Since olfactory receptor neurons form synaptic contacts with the widespread mitral cell dendrites, considerable synaptic rearrangement must occur within the olfactory glomeruli during maturation.
二尖瓣细胞是脊椎动物嗅球的主要输出神经元，也是来自外周的感觉输入的主要接受者。追踪二尖瓣细胞树突的形态发生，以阐明它们在嗅觉小球构建过程中与嗅觉受体神经元和神经胶质细胞的早期空间和时间相互作用。研究了有袋动物短尾负鼠（Monodelphis domestica），其出生时极度不成熟，同时也对大鼠进行了研究。通过将亲脂性染料1,1'-二十六烷基-3,3,3',3'-四甲基吲哚羰花青高氯酸盐（DiI）应用于外侧嗅束，对二尖瓣细胞进行逆行标记。在双标记实验中，用3,3'-二十六烷氧基羰花青高氯酸盐（DiO）对嗅觉受体神经元进行染色，或使用S-100蛋白免疫组织化学观察嗅神经雪旺细胞。用共聚焦激光扫描显微镜检查组织。随后对一些标本进行电子显微镜检查。在短尾负鼠中，二尖瓣细胞的分化始于大量、均匀且广泛的树突生长。一旦嗅觉受体轴突的终末在假定的小球层内聚集成小球结，单个二尖瓣细胞的树突就会支配几个相邻的小球，在那里它们接受感觉突触输入。随着成熟，多余的二尖瓣细胞树突回缩，只留下一个带有终末小球簇的初级树突。同时，次级树突开始出现。与短尾负鼠相比，大鼠中小球的形成开始得更早且进展更快。然而，两个物种中二尖瓣细胞的分化遵循共同的顺序：树突过度产生，通常选择一个初级顶端树突，以及消除多余的突起。由于嗅觉受体神经元与广泛分布的二尖瓣细胞树突形成突触联系，因此在成熟过程中，嗅觉小球内必然会发生相当大的突触重排。
