Oland L A, Orr G, Tolbert L P
Arizona Research Laboratories, University of Arizona, Tucson 85721.
J Neurosci. 1990 Jul;10(7):2096-112. doi: 10.1523/JNEUROSCI.10-07-02096.1990.
Olfactory glomeruli in insects share many features of organization with their vertebrate counterparts, and yet offer distinct advantages for study of neuronal development. Previous studies have revealed that the olfactory lobes of the brain of the moth Manduca sexta arise postembryonically and that glomeruli in the lobe are induced by olfactory afferent axons (Hildebrand et al., 1979; Oland and Tolbert, 1987). In the present study, we have used the Golgi method, intracellular labeling of neurons with Lucifer yellow, and electron microscopy to follow neuronal development in the antennal lobe through the period when glomeruli develop. Our results, taken together with other results from our laboratory, suggest that olfactory sensory axons have the intrinsic ability to form protoglomeruli, and that an interaction between these axons and glial cells (but not the majority of the neurons of the antennal lobe) causes the glial cells to surround the protoglomeruli. Ingrowth of the neurites of most antennal-lobe neurons into the protoglomeruli occurs after a small delay and appears to be constrained to glomerular units by the presence of the glial boundaries. Synapses, initially not detected in the protoglomeruli, begin to appear as soon as the neurites of antennal-lobe neurons appear in the glomeruli. Thus, antennal axons, instead of immediately seeking out postsynaptic targets, first form the template for organization of future glomeruli. The neurites of most of the neurons of the antennal lobe grow outward to meet the olfactory sensory axons, and in doing so, join with these axons to form glomeruli. Preliminary results concerning the development of a second class of neuron in the lobe, the projection neurons, indicate that at least some of these neurons may arborize in the region of the protoglomeruli very early and therefore participate with the afferent axons in laying the foundation for glomeruli.
昆虫的嗅觉小球与脊椎动物的嗅觉小球在组织上有许多共同特征，但在神经元发育研究方面具有独特优势。先前的研究表明，烟草天蛾大脑的嗅觉叶在胚胎后期形成，叶中的小球由嗅觉传入轴突诱导形成（希尔德布兰德等人，1979年；奥兰德和托尔伯特，1987年）。在本研究中，我们使用了高尔基方法、用荧光黄对神经元进行细胞内标记以及电子显微镜技术，来追踪触角叶在小球发育期间的神经元发育过程。我们的研究结果与我们实验室的其他结果共同表明，嗅觉感觉轴突具有形成原小球的内在能力，并且这些轴突与神经胶质细胞（而非触角叶的大多数神经元）之间的相互作用会导致神经胶质细胞围绕原小球。大多数触角叶神经元的神经突在稍有延迟后长入原小球，并且似乎由于神经胶质边界的存在而被限制在小球单元内。原小球中最初未检测到突触，一旦触角叶神经元的神经突出现在小球中，突触就开始出现。因此，触角轴突不是立即寻找突触后靶点，而是首先形成未来小球组织的模板。触角叶大多数神经元的神经突向外生长以与嗅觉感觉轴突相遇，并在此过程中与这些轴突结合形成小球。关于叶中第二类神经元即投射神经元发育的初步结果表明，这些神经元中的至少一些可能很早就会在原小球区域形成分支，因此与传入轴突一起为小球的形成奠定基础。
