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At least 19 recordsLinked to original sources
PubMed2003

Bovine circumvallate taste buds: taste cell structure and immunoreactivity to alpha-gustducin.

The taste buds of bovine circumvallate papillae were investigated under light and electron microscopy both by histological and immunohistochemical methods. Taste buds existed in the inner epithelium of the trench of the papillae. Under electron microscopy, two types of taste cells, type I and type II, could be classified according to the existence of dense-cored vesicles and cytoplasmic density. Type I had electron-lucent cytoplasm and possessed many electron-dense cored vesicles in the apical cytoplasm. It was considered that the electron-dense materials of the vesicles were released and constituted the pore substance. This type of cell possessed long and thick apical processes in the taste pore. Type II had denser electron cytoplasm compared with that of type I and possessed many electron-lucent vesicles in the apical cytoplasm. This type of cell possessed microvilli in the taste pore. To know the immunoreactivity to alpha-gustducin in bovine circumvallate taste buds, we used the immunoblotting method and the immunohistochemical method. The alpha-gustducin reaction band at 40 kDa was displayed in the specimen of Western blots. The immunohistochemical property of the antiserum to alpha-gustducin was investigated by using the avidin-biotin complex (ABC) method and the 1.4-nm gold and silver enhancement methods. A subset of taste cells showed the immunoreactivity under light microscopy. The electron microscopic specimens with the 1.4-nm gold and silver enhancement method revealed that only type II cells exhibited the alpha-gustducin immunoreactivity.

Animals↗
PubMed1987

A sensitive period for the neural induction of taste buds.

Taste buds mature postnatally in the vallate papilla of the rat and reach a mean number of 610 by day 90. Although taste buds are neurotrophically dependent, the presence of widespread bilateral innervation permits more than 80% of the 610 vallate taste buds to survive after one IXth nerve is removed in adults. However, after a IXth nerve is removed at 0-3 d postpartum, about two-thirds of the vallate taste buds fail to develop. In the present investigation, the timing of the neural induction of taste buds was examined by unilaterally removing the IXth nerve at 12 different postnatal ages, from 0 to 75 d. Unilateral denervation revealed the existence of a sensitive period that is maximal from 0 to 10 d, when unilateral or bilateral interruption of the IXth nerve profoundly impairs the formation of taste buds. The number of taste buds that form is nonlinearly dependent upon the number of axons; at low levels of innervation, a doubling of the number of myelinated axons quintuples the number of taste buds. Thus, taste axons interact synergistically. In studying regeneration, we found that axons of both neonatal and adult IXth nerves elongate approximately 1.8 mm/d. Taste buds were re-formed more rapidly and a higher proportion were bilaterally innervated when regenerating axons and the sites of former taste buds were numerous. The proportion of bilaterally innervated taste buds could be approximated from the likelihood of random overlap of axons from the right and left IXth nerves. The greater ease with which taste buds are re-formed than developed suggests that taste bud regeneration does not recapitulate taste bud development.

Animals↗
PubMed2002

Analysis of cell lineage relationships in taste buds.

Taste buds are a heterogeneous population of cells exhibiting diverse morphological and biochemical characteristics. Because taste buds arise from multiple progenitors, the different types of taste cells may represent distinct lineages. The present study was undertaken to determine the following: (1) how many progenitors contribute to a taste bud, and (2) whether the specific subpopulation of serotonin-immunoreactive (IR) taste cells are related by lineage to a restricted set of progenitor cells. These questions were addressed using cell lineage analysis of taste buds from H253 X-inactivation mosaic mice. After random X-inactivation of the lacZ transgene, the tongue of hemizygous female mice displays discrete patches of epithelial cells, which are either beta-galactosidase (beta-gal) positive or beta-gal negative. By analyzing the proportion of the two differently stained cell populations in taste buds located at the boundary between positive and negative epithelial patches, we can determine the minimum number of progenitors that may contribute to the formation of a taste bud. The presence of taste buds containing only 6-12% labeled cells indicates that at least eight progenitors contribute to an average taste bud of 55 cells, assuming progenitors contribute equally to the cell population. Cell lineage analysis of serotonin-IR taste cells in such mixed taste buds suggests that this subpopulation likely arises from only one to two progenitors and often is related by lineage. Thus, at least some of the cell types in a taste bud represent distinct lineages of cells and are not merely phenotypic stages as a cell progresses from a young to a mature state.

Animals↗
PubMed2005

[Development and cell dynamics of PLCbeta2 positive cells in mouse taste buds].

Taste buds, the sensory end organs for the sense of taste, consist of taste sensing cells, supportive cells and basel cells. Taste bud cells are heterogeneous in terms of morphology as well as functional profiles. Although the lineage of mammalian taste bud cells is largely unknown, it is generally accepted that undifferentiated epithelial basal cells surrounding taste buds enter the taste buds to form and maintain this specialized corpuscle. To analyze taste bud formation during development, we conducted morphological observations and examined differentiation marker expression. Thickening of epithelia starts at 13 dpc foetus and immunohistochemistry against a neural marker, PGP 9.5, revealed that the change of epithelial morphology precedes neural projection observed at 14 dpc foetus. Taste sensing cells appear 6 days after birth indicated by expression of the single transduction component phospholipase Cbeta2 (PLCbeta2) as differentiation marker. To further investigate the maintenance and cell lineage in the taste buds in adults, we injected 5'bromo-2'deoxyuridine (BrdU) solution to young growing mice for a week. BrdU label retaining cells (LRCs) could be observed even 8 weeks after injection. LRCs were examined the differentiation by PLCbeta2 and proliferative activity by Ki-67. The results suggested two possibilities. (1) Part of PLCbeta2 positive cells retain proliferative activity and multipotentiality, or (2) precursor cells (stem cells) stay in the taste buds and produce at least part of the taste sensing cells through proliferation and differentiation processes.

Animals↗
PubMed1993

Immunolocalization of different forms of neural cell adhesion molecule (NCAM) in rat taste buds.

Taste buds consist of approximately 100 taste cells, including three morphological types of short receptor cells which synapse on the peripheral gustatory nerves. Some of the receptor cells produce neural cell adhesion molecule (NCAM), which may play a role in formation of specific connections in this system. Antibodies directed against different forms of NCAM were utilized in an attempt to define not only the distribution, but also the type of NCAM within taste buds. Within each taste bud approximately 10% of the taste cells exhibit abundant immunoreactivity for 180 kD (ld) or 140 kD (sd) forms of NCAM (i.e., those with an intracellular domain) along virtually the entire surface of the cell. Ultrastructural analysis reveals that these abundantly immunoreactive taste cells are of the intermediate morphological type, although not all of the intermediate taste cells within any bud are immunoreactive. In addition, the ultrastructural studies show that punctate (ld/sd) NCAM-immunoreactivity occurs on the membranes of taste cells and nerve fibers throughout each taste bud. The embryonic form of NCAM (E-NCAM), rich in polysialic acid residues, is present only in association with nerve fibers and other unidentified elongate, thin profiles of a few taste buds. The nerve plexus beneath the gustatory epithelium is also rich in NCAM-immunoreactivity. These fibers occasionally reveal immunoreactivity indicative of only the 120 kD (ssd) form of NCAM, typical of glial cells.

Animals↗
PubMed1999

Distribution of cytokeratin filaments and vimentin in developing human taste buds.

Taste buds in humans originate from approximately the 8th postovulatory week under the influence of ingrowing nerve fibers. Since they develop from local epithelium, it is of interest whether or not prospective taste cells maintain or develop characteristics of epithelial cells that are different from those of the adjacent epithelium during differentiation. The aim of this study was to monitor changes of the distribution of the cytokeratin filaments (CKs) 8, 18, 19 and 20 ("gastrointestinal" type), CK 7 ("ductal" type), and CK 13 (maturation "mucosa type"), as well as vimentin in developing human taste buds and adjacent squamous epithelium. With the exception of CK13, which remains negative in taste bud anlagen and adult taste buds, all cytokeratins tested were present in taste cells. With the progress of development, the distribution of CKs becomes more and more restricted to taste cells and salivatory ducts as well as Ebner gland cells. Only CK20 is exclusively specific to taste bud anlagen and sometimes to individual bipolar cells occurring in early stages (week 8-9). Vimentin was located mainly in mesodermal derivatives but also in perigemmal epithelial cells during all stages of development. The occurrence of vimentin in "borderline" epithelia that interface with underlying connective tissue, i.e., in a region of discontinuity, may be associated with particular events in development, cell migration or even dedifferentiation.

Adult↗
PubMed2002

The neural differentiation gene Mash-1 has a distinct pattern of expression from the taste reception-related genes gustducin and T1R2 in the taste buds.

Taste bud cells have a limited lifespan and are continuously replaced just like other epithelial cells. Although there is some evidence that taste buds may arise from the local epithelium, taste receptor cells have neuronal properties. This implies that there must be a critical stage at which the epithelial precursor cells for taste receptor cells start to exhibit neural properties during the differentiation of the taste receptor cells. The expression of the neural-specific transcription factors Mash-1 and Prox-1 in the nervous system is transient and precedes neuronal differentiation. Therefore, we examined the expression of Mash-1 and Prox-1 in the epithelium of circumvallate papillae of the tongue in order to clarify the localization of the precursor cells with neural properties and observed that both expressions are restricted to the taste buds. Two-colour in situ hybridization showed that the signals for Mash-1 did not overlap those for taste receptor cell-specific genes such as gustducin and T1R2. In the process of development and regeneration of the taste buds, the expression of Mash-1 preceded that of gustducin and T1R2. These observations suggest that Mash-1 could be a candidate for a marker of immature taste receptor cells, including the cells that express gustducin and/or T1R2 at a later stage.

Animals↗
PubMed2006

Separate populations of receptor cells and presynaptic cells in mouse taste buds.

Taste buds are aggregates of 50-100 cells, only a fraction of which express genes for taste receptors and intracellular signaling proteins. We combined functional calcium imaging with single-cell molecular profiling to demonstrate the existence of two distinct cell types in mouse taste buds. Calcium imaging revealed that isolated taste cells responded with a transient elevation of cytoplasmic Ca2+ to either tastants or depolarization with KCl, but never both. Using single-cell reverse transcription (RT)-PCR, we show that individual taste cells express either phospholipase C beta2 (PLCbeta2) (an essential taste transduction effector) or synaptosomal-associated protein 25 (SNAP25) (a key component of calcium-triggered transmitter exocytosis). The two functional classes revealed by calcium imaging mapped onto the two gene expression classes determined by single-cell RT-PCR. Specifically, cells responding to tastants expressed PLCbeta2, whereas cells responding to KCl depolarization expressed SNAP25. We demonstrate this by two methods: first, through sequential calcium imaging and single-cell RT-PCR; second, by performing calcium imaging on taste buds in slices from transgenic mice in which PLCbeta2-expressing taste cells are labeled with green fluorescent protein. To evaluate the significance of the SNAP25-expressing cells, we used RNA amplification from single cells, followed by RT-PCR. We show that SNAP25-positive cells also express typical presynaptic proteins, including a voltage-gated calcium channel (alpha1A), neural cell adhesion molecule, synapsin-II, and the neurotransmitter-synthesizing enzymes glutamic acid decarboxylase and aromatic amino acid decarboxylase. No synaptic markers were detected in PLCbeta2 cells by either amplified RNA profiling or by immunocytochemistry. These data demonstrate the existence of at least two molecularly distinct functional classes of taste cells: receptor cells and synapse-forming cells.

Animals↗
PubMed2005

Using biosensors to detect the release of serotonin from taste buds during taste stimulation.

CHO cells transfected with high-affinity 5HT receptors were used to detect and identify the release of serotonin from taste buds. Taste cells release 5HT when depolarized or when stimulated with bitter, sweet, or sour tastants. Sour- and depolarization-evoked release of 5HT from taste buds is triggered by Ca2+ influx from the extracellular fluid. In contrast, bitter- and sweet-evoked release of 5HT is triggered by Ca2+ derived from intracellular stores.

Adenosine Triphosphate↗
PubMed2006

The bHLH transcription factors, Hes6 and Mash1, are expressed in distinct subsets of cells within adult mouse taste buds.

Taste buds are multicellular receptor organs embedded in the lingual epithelium of vertebrates. Taste cells within these buds are modified epithelial cells as they lack axons and turnover rapidly throughout life, yet have neuronal properties enabling them to transduce taste stimuli and transmit this information to the nervous system. Taste cells are heterogeneous, comprising types I, II, III and basal cells, and are continually replaced during adult life, raising the question of how these different cells are generated. The molecular mechanisms governing taste cell differentiation are unknown, but the Notch signaling system has been implicated in this process based upon recent gene expression data. Here we investigate the expression in mature taste buds of Notch related transcription factors, Hes6 and Mash1, which are among the first genes expressed in embryonic taste buds. We further compare these patterns with those of immunocytochemical markers of discrete taste cell types. We find that Hes6 is expressed in a subset of basally located, possibly progenitor cells, yet is rarely coexpressed with taste cell markers. In contrast, Mash1 is detected in some basal cells and in the majority of differentiated type III taste cells, but never in type II cells. These data suggest a role for Notch signaling in taste cell differentiation in adult taste buds.

Animals↗
PubMed2006

Cell communication in taste buds.

Taste bud cells communicate with sensory afferent fibers and may also exchange information with adjacent cells. Indeed, communication between taste cells via conventional and/or novel synaptic interactions may occur prior to signal output to primary afferent fibers. This review discusses synaptic processing in taste buds and summarizes results showing that it is now possible to measure real-time release of synaptic transmitters during taste stimulation using cellular biosensors. There is strong evidence that serotonin and ATP play a role in cell-to-cell signaling and sensory output in the gustatory end organs.

Adenosine Triphosphate↗
PubMed1985

Ultrastructure of mouse vallate taste buds. I. Taste cells and their associated synapses.

The ultrastructural features of murine vallate taste bud cells and their associated synapses have been examined in thin and thick sections with conventional transmission electron microscopy and high-voltage electron microscopy. Computer-assisted reconstructions from serial sections were utilized to aid in visualization of taste bud cell-nerve fiber synapses. We have classified taste bud cells on the basis of previously established criteria-namely, size of the nucleus, shape and density of chromatin, density of cytoplasm, and presence or absence of dense-cored or clear vesicles, other cytoplasmic organelles, and synaptic foci. Both dark cells and light cells are present, as well as cells with intermediate morphological characteristics. Synapses were observed from taste bud cells onto nerve fiber processes. In virtually all instances, synapses are associated with the nuclear region of the taste cell. These synapses are characterized by the presence of 40-70 nm clear vesicles embedded in a thickened presynaptic membrane separated from the postsynaptic membrane by a 16-30 nm cleft. Synapses are not unique to any particular cell type. Dark, intermediate, and light cells all synapse onto nerve fibers. Two general types of synapses exist: spot (or macular) and fingerlike. In the latter, the postsynaptic region of the neuronal process protrudes into an invagination of the taste cell membrane. Differences in synaptic morphology are not correlated with taste cell type. In some cases a single taste cell was observed to possess both macular and fingerlike synapses adjacent to one another, forming a synaptic complex onto a single neuronal process. On the basis of the presence of synaptic contacts, we conclude that both "dark" and "light" cells are gustatory receptors.

Animals↗
PubMedDate not supplied

Desquamation on taste buds.

Taste bud surface cells suffer from a desquamation process that modifies the pores' shape and size and the amount of amorphous substance in the pits region. We have studied this phenomenon-which probably plays an important functional role-by light, electron and scanning microscopy.

Animals↗
PubMed1990

Variations in human taste bud density and taste intensity perception.

Some variations in human taste sensitivity may be due to different numbers of taste buds among subjects. Taste pores were counted on the tongue tips of 16 people with videomicroscopy, and the subjects were divided into two groups (N = 8) by the rank order of their taste bud densities. The "higher" density group averaged 374 +/- 134 taste pores/cm2, while the "lower" density group averaged 135 +/- 43 tp/cm2. The higher density group had an average fungiform papilla density which was 1.8 times greater than the lower density group and an average of 1.5 times more taste pores/papilla. The subjects also rated the intensity for 4 suprathreshold concentrations of 5 taste stimuli placed on the same region of the tongue where taste pores were counted. The group with higher taste bud densities gave significantly higher average intensity ratings for sucrose (196%), NaCl (135%) and PROP (142%), but not for citric acid (118%) and quinine HCl (110%) than the lower density group. Thus, the subjects with higher fungiform taste bud densities also reported some tastes as more intense than subjects with fewer fungiform taste buds.

Arousal↗
PubMed2000

Fingerprinting taste buds: intermediate filaments and their implication for taste bud formation.

Intermediate filaments in taste organs of terrestrial (human and chick) as well as aquatic (Xenopus laevis) species were detected using immunohistochemistry and electron microscopy. During development, the potential importance of the interface between the taste bud primordium and non-gustatory adjacent tissues is evidenced by the distinct immunoreactivity of a subpopulation of taste bud cells for cytokeratins and vimentin. In human foetuses, the selective molecular marker for taste bud primordia, cytokeratin 20, is not detectable prior to the ingrowth of nerve fibres into the epithelium, which supports the hypothesis that nerve fibres are necessary for initiating taste bud development. Another intermediate filament protein, vimentin, occurs in derivatives of mesoderm, but usually not in epithelium. In humans, vimentin immunoreactivity is expressed mainly in border (marginal) epithelial cells of taste bud primordia, while in chick, vimentin expression occurs in most taste bud cells, whereas non-gustatory epithelium is vimentin immunonegative. Our chick data suggest a relationship between the degree of vimentin expression and taste bud cell proliferation especially during the perihatching period. It is suggested that surrounding epithelial cells (human) and mesenchymal cells (chick) may be contributing sources of developing taste buds. The dense perinuclear network of intermediate filaments especially in dark (i.e. non-sensory) taste disc cells of Xenopus indicates that vimentin filaments also might be associated with cells of non-gustatory function. These results indicate that the mechanisms of taste bud differentiation from source tissues may differ among vertebrates of different taxa.

Animals↗
PubMed1978

Location of taste buds in intact taste papillae by a selective staining method.

Taste buds were found to stain strongly and selectively in intact papillae with highly acidic dyes such as ponceau S. In intact tongues the taste buds in the fungiform, circumvallate and foliate papillae of the cynomolgus monkey and in the fungiform papillae of the rat as well as the taste discs in the fungiform papillae of the frog could be visualized. This method enables a rapid location and counting of taste buds in taste papillae without preparing histological sections. In cynomolgus tongue material fixed in formalin, the dyes penetrate into the buds. In fresh tongues only the taste pore region of the buds stains, which suggests that in vivo taste buds are impenetrable underneath the pore.

Animals↗