Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, CU Anschutz Medical Campus, Aurora, Colorado 80045.
Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, CU Anschutz Medical Campus, Aurora, Colorado 80045
J Neurosci. 2022 Feb 2;42(5):804-816. doi: 10.1523/JNEUROSCI.0838-21.2021. Epub 2021 Dec 7.
Taste buds contain multiple cell types, two of which mediate transduction of specific taste qualities: Type III cells transduce sour while Type II cells transduce either sweet, or bitter or umami. In order to discern the degree of interaction between different cell types and specificity of connectivity with the afferent nerve fibers (NFs), we employed serial blockface scanning electron microscopy (sbfSEM) through five circumvallate mouse taste buds. Points of contact between Type II and Type III cells are rare and lack morphologically identifiable synapses, suggesting that interaction between these cell types does not occur via synapses. Of the 127 NFs that make synaptic contacts with taste cells in the sampling volume, ∼70% ( = 91) synapse with only one taste cell while 32 fibers synapse exclusively with multiple Type II cells or multiple Type III cells. Our data do not rule out multimodal fibers innervating Type II cells of separate taste qualities. Notably, four fibers (∼3%) synapse with both Type II and Type III cells, forming both mitochondrial and vesicular synapses on the different cell types. Since Type II and Type III cells transduce different taste qualities, these dual connected fibers are not consistent with a absolute labeled-line encoding system. Further, our data reveal considerable variation in both the number of synapses per cell/nerve pair and the number of innervating NFs per taste cell, both of which likely have consequences for encoding taste quality and concentration. Finally, we identify a subset of Type II cells which may represent an immature stage. Taste buds, the sensory end organs for the sense of taste, contain multiple types of sensory cells, with each responding to one of the primary tastes: salt, sweet, sour, bitter, and umami. In order to determine the degree of interaction between cell types and specificity of connectivity to afferent nerves, we employed serial blockface electron microscopy (EM) of mouse circumvallate taste buds. We find no synapses between cell types within the taste bud suggesting that any interactions are indirect. While the majority of nerve fibers (NFs) connect to a single type of taste cell, 3.1% of the fibers branch to receive input from taste cells of different specificities. Thus, taste cannot entirely be carried along NFs dedicated to single taste qualities.
味蕾包含多种细胞类型，其中两种介导特定味觉的转导：III 型细胞转导酸味，而 II 型细胞转导甜味、苦味或鲜味。为了辨别不同细胞类型之间的相互作用程度和与传入神经纤维 (NF) 的连接特异性，我们采用了连续块面扫描电子显微镜 (sbfSEM) 对五个环状鼠味蕾进行了研究。II 型和 III 型细胞之间的接触点很少，缺乏形态上可识别的突触，表明这些细胞类型之间的相互作用不是通过突触发生的。在采样体积中与味觉细胞形成突触的 127 个 NF 中，约 70%（=91）仅与一个味觉细胞形成突触，而 32 个纤维仅与多个 II 型细胞或多个 III 型细胞形成突触。我们的数据不排除多模态纤维支配不同味觉品质的 II 型细胞。值得注意的是，有 4 个纤维（约 3%）与 II 型和 III 型细胞形成突触，在不同的细胞类型上形成线粒体和囊泡突触。由于 II 型和 III 型细胞转导不同的味觉品质，这些双重连接的纤维与绝对标记线编码系统不一致。此外，我们的数据显示每个细胞/神经对的突触数和每个味觉细胞的支配 NF 数都存在相当大的变化，这两者都可能对味觉品质和浓度的编码产生影响。最后，我们确定了一部分 II 型细胞可能代表不成熟阶段。味蕾是味觉感觉器官，包含多种类型的感觉细胞，每种细胞对一种主要味觉：盐、甜、酸、苦和鲜味做出反应。为了确定细胞类型之间的相互作用程度和与传入神经的连接特异性，我们采用了连续块面电子显微镜 (EM) 对环状鼠味蕾进行了研究。我们在味蕾内没有发现细胞类型之间的突触，这表明任何相互作用都是间接的。虽然大多数神经纤维 (NF) 连接到单一类型的味觉细胞，但 3.1%的纤维分支以接收来自不同特异性的味觉细胞的输入。因此，味觉不能完全沿着专门传递单一味觉品质的 NF 进行。
