Witt M, Reutter K
Department of Anatomy, Technical University Dresden, Germany.
Anat Rec. 1996 Dec;246(4):507-23. doi: 10.1002/(SICI)1097-0185(199612)246:4<507::AID-AR10>3.0.CO;2-S.
Taste buds are assemblies of slender epithelial cells that receive chemical stimuli from the outer (oral) environment. In contrast to the large and well documented information on the morphology of taste buds in adult humans and animals, there are only a few reports on fetal ones, and ultrastructural studies of prenatal human taste buds are lacking completely. Therefore, the present investigation has been carried out to study the taste bud primordium, its morphological changes including synaptogenesis, cell differentiation, and taste pore formation from the time of the onset of taste bud formation around the 8th week until the 15th postovulatory week.
Taste bud primordia of 42 human embryonic/fetal tongues have been examined by means of transmission electron microscopy.
Nerve fibers approach the lingual epithelium between the 6th and 7th postovulatory week. They penetrate the basal lamina during the 8th week and form synapses with poorly differentiated, elongated, epithelial cells. By the 12th week, more differentiated cell types are seen: 1) electron-dense cells resembling type III cells of the adult taste bud containing large numbers of dense-cored vesicles (80-150 nm in diameter); 2) electron-dark cells with well developed endoplasmic reticulum and many apical mitochondria, being candidates for type II cells. Basally, these cells have foot-like processes containing dense-cored vesicles (120-200 nm in diameter), but they do not synapse to nerve fibers. Type I cells, characterized by apically located dense secretory granules, are not observed. First shallow grooves above the taste bud primordium are found around the 10th week. Untypically differentiated apical cellular processes extend onto the surface. Most of the taste pores develop around the 14th to 15th week. In the taste pit, mucous material is not present during the first 15 weeks of gestation. Synapses between cells and afferent nerve fibers were found by the 8th week, reaching a maximum around the 12th to 13th week.
The early presence of taste bud cells containing dense-cored vesicles suggests an at least dual function of embryonic/ fetal taste buds: First, from the 8th until the 14th week, non-gustatory, paracrine functions should be considered. After the 14th week of gestation, when typical taste pores are present, the taste buds possibly start their gustatory function. Differentiated marginal cells are possibly involved in the formation of the taste pore. The lack of type I cells producing the mucous material in the taste pit indicates that the taste bud has not achieved a fully developed function until the 15th week of gestation.
味蕾是细长上皮细胞的集合体，可接收来自外部（口腔）环境的化学刺激。与关于成年人类和动物味蕾形态的大量且详尽记录的信息相比，关于胎儿味蕾的报道较少，产前人类味蕾的超微结构研究则完全缺失。因此，本研究旨在从大约第8周味蕾形成开始直至排卵后第15周，研究味蕾原基及其形态变化，包括突触形成、细胞分化和味孔形成。
通过透射电子显微镜检查了42个人类胚胎/胎儿舌头的味蕾原基。
在排卵后第6至7周，神经纤维靠近舌上皮。它们在第8周穿透基膜，并与分化程度低、细长的上皮细胞形成突触。到第12周时，可以看到更多分化的细胞类型：1）电子致密细胞，类似于成年味蕾的III型细胞，含有大量致密核心小泡（直径80 - 150纳米）；2）电子透亮细胞，内质网发达，顶端有许多线粒体，可能是II型细胞的候选者。在基部，这些细胞有含致密核心小泡（直径120 - 200纳米）的足状突起，但它们不与神经纤维形成突触。未观察到以顶端有致密分泌颗粒为特征的I型细胞。在第10周左右，在味蕾原基上方发现了最初浅的沟。异常分化的顶端细胞突起延伸到表面。大多数味孔在第14至15周左右形成。在味窝中，妊娠前15周期间不存在粘液物质。细胞与传入神经纤维之间的突触在第8周时发现，在第12至13周左右达到最大值。
含有致密核心小泡的味蕾细胞的早期出现表明胚胎/胎儿味蕾至少具有双重功能：首先，从第8周到第14周应考虑非味觉的旁分泌功能。妊娠第14周后，当典型味孔出现时，味蕾可能开始其味觉功能。分化的边缘细胞可能参与味孔的形成。味窝中缺乏产生粘液物质的I型细胞表明，直到妊娠第15周味蕾才实现完全发育的功能。
