舌内机械感受器的解剖学特征

摘要(中文译文)

口腔的机械感觉神经支配使我们能够检测所摄入食物的质地和位置。我们的目标是寻找一种机械感受亚型的遗传标识。为实现这一目标，我们检查了表达神经营养因子受体TrkC（TrkC-tdTomato）、小清蛋白（Pvalb）或谷氨酸转运体Vglut3的神经元。我们发现，支配舌的大部分Pvalb谱系、Vglut3谱系和TrkC-tdTomato神经元是彼此独立的 trigeminal 神经元群体。由于不同乳头类型以不同方式参与食物检测，我们检查了这些神经元亚型的支配模式。我们发现Pvalb谱系和Vglut3谱系神经元为菌状乳头特异性，而TrkC+纤维则支配两种乳头类型。我们发现所有Pvalb谱系神经纤维均标记有神经丝重链（NFH），其轴突被髓鞘碱性蛋白包围，且缺乏降钙素基因相关肽。这表明它们均为有髓神经元。相比之下，Vglut3谱系和TrkC-tdTomato神经纤维是NFH+神经纤维与NFH-神经纤维以及有髓与无髓神经纤维的混合群体。当我们检查这三个遗传群体的轴突末梢形态时，我们发现Pvalb谱系神经元一致显示围绕味蕾的“篮状”轴突末梢。虽然TrkC+和Vglut3谱系神经元有时也显示这种“篮状”轴突末梢，但其他轴突末梢缺乏此结构。跨组比较时，Vglut3谱系轴突末梢表现出最大程度的形态变异性。总体而言，这些数据表明Pvalb谱系可能是支配菌状乳头的单一有髓机械感受器的遗传标识。

Abstract

Mechanosensory innervation of the oral cavity enables us to detect the texture and location of the foods we consume. Our goal was to find a genetic identifier for a mechanoreceptive subtype. Toward this goal, we examined neurons expressing the neurotrophin receptor TrkC (TrkC-tdTomato), parvalbumin (Pvalb), or glutamate transporter, Vglut3. We found that the majority of Pvalb-lineage, Vglut3-lineage, and TrkC-tdTomato neurons innervating the tongue are separate trigeminal neuron populations. Because different papilla types contribute to food detection in different ways, we examined the innervation patterns of these neuron subtypes. We found that Pvalb-lineage and Vglut3-lineage neurons were fungiform papilla-specific, whereas TrkC+ fibers innervated both papilla types. We found that all Pvalb-lineage nerve fibers are labeled with neurofilament heavy chain (NFH), have axons that are surrounded by myelin basic protein, and lack calcitonin gene-related peptide. This indicates that these are all myelinated neurons. In contrast, Vglut3-lineage and TrkC-tdTomato nerve fibers were a mixed population of NFH+ nerve fibers and NFH- nerve fibers, as well as myelinated and unmyelinated nerve fibers. When we examined the axonal ending morphologies of the three genetic populations, we found that the Pvalb-lineage neurons consistently displayed a "basket-like" axonal ending that surrounded the taste bud. While TrkC+ and Vglut3-lineage neurons sometimes displayed this "basket-like" axonal ending, other axonal endings lacked this structure. When compared across groups, the Vglut3-lineage axonal endings displayed the greatest degree of morphological variability. Collectively, these data show that Pvalb-lineage may be a genetic identifier for a single myelinated mechanoreceptor innervating fungiform papillae.

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