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PubMed1996

Phagocytic cells in the taste buds of rat circumvallate papillae after denervation.

Phagocytic cells in the taste buds of rat circumvallate papillae after the sectioning of bilateral glossopharyngeal nerves were examined by electron microscopy and immunohistochemistry. Electron micrographs taken 1 day after denervation revealed that flat-shaped cells were present just beneath the taste buds and that their cellular processes extended toward the debris from the degenerating taste buds. At 2-6 days after denervation, long and thin processes of the flat cells surrounded the debris and appeared to have taken them up into the cytoplasm as small vesicles. Evidence for phagocytosis by the flat cells was seen up to 9 days after denervation and again at 24 and 40 days, in correlation to the degeneration and regeneration of the taste buds. Pre-embedding immunohistochemistry using anti-vimentin antibody showed that flat cells strongly reacted with vimentin. Light microscopic immunohistochemistry using anti-macrophage antibodies (ED1, ED2) showed that throughout the post-operative days macrophages were not present underneath or within the taste buds. Most of the ED2-immunoreactive resident macrophages were located in the deep layer of connective tissue, and a few were found in the nerve bundle. ED1-immunoreactive cells were seen in the duct cells of von Ebner's glands and a few were in the trench wall of circumvallate papillae; however, they were also immunoreactive for anti-OX62 antibody, which recognizes dendritic cells. The results indicate that the phagocytic cells of the taste buds are fibroblasts, not macrophages. Moreover, resident macrophages participate in phagocytosis of degenerated nerves together with Schwann cells.

Animals↗

PubMed1978

The taste buds of Suncus murinus (Indian musk shrew).

Taste buds were generally found on the posterior side of the tongue. Neural elements (nerve fibres, mainly thick myelinated, and ganglia arranged in a chain-like fashion) participated in the innervation of the taste buds. Cholinesterase activity was much marked in the bottom of the taste buds, while the marginal surface showed no such activity.

Animals↗

PubMed1990

Taste bud density in circumvallate and fungiform papillae of the bovine tongue.

Taste bud quantitation may provide useful parameters for interspecies comparisons of the gustatory system. The present study is a morphometric analysis of bovine taste papillae. Circumvallate and fungiform papillae from six bovine tongues were serially sectioned and, following staining, analyzed. Circumvallate papillae were found to have a mean volume of 3.66 +/- 2.82 mm3, a mean number of taste buds per papilla of 445 +/- 279, and a mean taste bud density of 155 +/- 112 buds/mm3. Values for lateral fungiform papillae for the same three parameters were 0.384 +/- 0.184 mm3, 13.2 +/- 13.4, and 40.8 +/- 46.6 buds/mm3, respectively. Values for dorsal fungiform papillae were 0.438 +/- 0.246 mm3, 4.39 +/- 4.78, and 14.0 +/- 17.1 buds/mm3, respectively. Circumvallate papillae were found to have a significantly greater volume, number of taste buds per papilla, and taste bud density than either type of fungiform papilla. These data should serve as background for biochemical, endocrinological, or neurological studies involving the bovine tongue.

Animals↗

PubMed1999

The effects of beta-bungarotoxin on the morphogenesis of taste papillae and taste buds in the mouse.

Although it has been long accepted that innervation by a taste nerve is essential for maintenance of taste buds, it is not clear what role, if any, innervation plays in the morphogenesis of taste papillae and taste bud development. The following study was undertaken to determine what effects lack of sensory innervation have on the development of taste papillae and the formation of taste buds in the mouse. Timed-pregnant female mice (n = 3) at gestational day 12 (gd12) were anesthetized and a 1 microl solution (1 microg/microl) of beta-bungarotoxin (beta-BTX), a neurotoxin that disrupts sensory and motor neuron development, was injected into the amniotic cavity of two embryos per dam. Two shams were injected with PBS. Fetuses were harvested at gd18, 1 day before birth, and four beta-BTX-injected embryos, two shams and two controls were fixed in buffered paraformaldehyde. Serial sections were examined for the presence and morphology of taste papillae and taste buds. No nerve profiles were observed in beta-BTX-injected tongues. Although circumvallate papillae were present on beta-BTX tongues, only five fungiform papillae could be identified. Taste buds were present on a large percentage of fungiform papillae profiles (24%) and on circumvallate papillae in sham and control fetuses; in contrast, no taste buds were associated with taste papillae in beta-BTX fetuses. These results implicate a significant role for innervation in taste papillae and taste bud morphogenesis.

Animals↗

PubMed1988

Proliferation of taste buds in the foliate and vallate papillae of postnatal hamsters.

The growth of the taste system in the hamster is considered in comparison to the postnatal development of other organ systems and the entire animal. No taste buds are present in vallate or foliate papillae of the hamster at birth, but they attain both the appearance and numbers of adult taste buds within 5 weeks of age. The most rapid increase in the number of taste buds occurs within the first 10 days of life, and this proliferation anticipates the weaning of hamsters which occurs by about three weeks of age. Foliate taste buds reach a maximal number within two months, but vallate taste buds continue to increase in number through 4 months of age. Taste bud proliferation and development occur earlier and more rapidly than in other organ systems. This early development of taste buds may protect the weanling hamster against accidental poisoning by noxious plants, and it may also reinforce the food intake which is required for normal growth.

Animals↗

PubMed1993

Keratin expression in taste bud cells of the circumvallate and foliate papillae of adult mice.

The patterns of keratin expression of taste buds in murine oral mucosa were examined using a panel of antibodies with various specificities for cytokeratins. The patterns for taste buds differed markedly from those of the surrounding epithelium but no regional differences in the staining patterns of the taste buds themselves were detected. The taste buds and the ducts of von Ebner's glands were strongly stained by monoclonal antibodies (mAbs) against cytokeratins (K) 8, 18 and 19, those typically expressed by simple epithelia. Merkel cells, which are also present in the oral epithelium and may correspond to the type III cells in taste buds, stained for K8 and K18 but not K19. None of the mAbs against simple epithelial keratins stained the stratifying epithelium of the trench wall or of the oral mucosa. Antibodies with specificity for keratins that are expressed as differentiation products of the mucosal epithelium did not stain taste buds. The staining pattern of the epithelium of the trench wall indicated that it expressed some keratins typical of stratifying epithelia but lacked the full pattern of differentiation of the adjacent mucosal epithelia. Staining within the taste buds was not homogeneous but no clear differences of keratin staining could be directly related to the subtypes of cells constituting them. The markedly differing patterns of keratin expression between taste buds and the adjacent epithelium raises questions about the type of inductive signals that produce and maintain these patterns.

Animals↗

PubMed2004

Taste buds and nerve fibers in the rat larynx: an ultrastructural and immunohistochemical study.

We investigated the rat laryngeal taste buds and their innervation by electron microscopy and immunohistochemical methods. Taste buds were densely arranged in the surface facing the laryngeal cavity of the epiglottis, the aryepiglottic fold, and the cuneiform process of the arytenoid cartilages. The cells of the buds were classified into types I, II, III, and basal cells, the ultrastucture of which was almost the same as that previously reported in lingual taste buds. The type III cells that had synaptic contacts with nerve fibers were considered to be sensory cells. Immunohistochemical analysis revealed thick calbindin D28k-immunoreactive fibers and thin varicose fibers immunoreactive for calcitonin gene-related peptide or substance P in and around the taste bud. Serotonin-immunoreactive cells were also observed here. The results revealed the innervation pattern of laryngeal taste buds to be the same as that in lingual taste buds. Carbonic anhydrase (CA) is known to catalyze the hydration of CO2 and dehydration of H2CO3, and seems to be essential in CO2 reception. Immunoreactivity for CAI was detected in slender cells and that for CAIII was observed in barrel-like cells in the laryngeal taste buds. The pH-sensitive inward rectifier K+ (Kir) channel in the cell membrane may be involved in CO2 reception as well. CAII-reactive cells were also reactive to Kir4.1, PGP 9.5 and serotonin. Our results indicated that CAII and Kir4.1 are located in type III cells of the laryngeal taste buds, and supported the idea that the buds may be involved in the recognition of CO2.

Animals↗

PubMed1987

Dye-coupling in taste buds in the mudpuppy, Necturus maculosus.

Electrical coupling in taste buds and in non-taste lingual epithelium in the mudpuppy was examined by injecting cells with a fluorescent dye, Lucifer yellow. Lucifer yellow coupling has been shown to indicate the presence of electrical junctions between cells. Lucifer yellow-filled taste cells usually have an elongate shape. Cells were an average of 111 microns long and were 13 microns in diameter at the widest region (nucleus). In taste buds, from a sample of 105 impalements we detected Lucifer yellow coupling in 21 cases: dye-coupled pairs of cells were observed in 17 cases, and trios of cells in 4 cases. Larger subsets of coupled cells (greater than 3) were not observed. Dye-coupled cells were usually equally intensely stained. In non-taste epithelium, we examined dye-coupling in the superficial and basal layers. Extensive Lucifer yellow coupling was found in the basal layer (15/15 cases). The number of cells coupled to the dye-injected cell varied from 3 to 5. In the superficial epithelium, dye-coupling was rare (1/45 cases). No dye-coupling was observed between epithelial cells and taste cells at the taste pore region. We conclude that strong electrical coupling in groups of 2-3 cells occurs in the mudpuppy taste buds. Coupling may occur selectively between identical types of taste cells (dark, light, etc.), but this remains to be determined. Electrical coupling also exists among basal epithelial cells but not in the superficial epithelial layers.

Animals↗

PubMed1996

Differential localization of putative amino acid receptors in taste buds of the channel catfish, Ictalurus punctatus.

The taste system of catfish, having distinct taste receptor sites for L-alanine and L-arginine, is highly sensitive to amino acids. A previously described monoclonal antibody (G-10), which inhibits L-alanine binding to a partial membrane fraction (P2) derived from catfish (Ictalurus punctatus) taste epithelium, was found in Western blots to recognize a single band, at apparent MW of 113,000 D. This MW differs from the apparent MW for the presumed arginine receptor identified previously by PHA-E lectin affinity. In order to test whether PHA-E lectin actually reacts with the arginine-receptor, reconstituted membrane proteins partially purified by PHA-E affinity were used in artificial lipid bilayers. These reconstituted channels exhibited L-arginine-activated activity similar to that found in taste cell membranes. Accordingly, we utilized the PHA-E lectin and G-10 antibody as probes to differentially localize the L-alanine and L-arginine binding sites on the apical surface of catfish taste buds. Each probe labels numerous, small (0.5-1.0 micron) patches within the taste pore of each taste bud. This observation suggests that each bud is not tuned to a single taste substance, but contains putative receptor sites for both L-arginine and L-alanine. Further, analysis of double-labeled tissue reveals that the PHA-E and G-10 sites tend to be separate within each taste pore. These findings imply that in catfish, individual taste cells preferentially express receptors to either L-arginine or L-alanine. In addition, PHA-E binds to the apices of solitary chemoreceptor cells in the epithelium, indicating that this independent chemoreceptor system may utilize some receptor sites similar to those in taste buds.

Alanine↗

PubMed1995

Innervation in human taste buds and its decrease in Alzheimer's disease patients.

The innervation in human taste buds of the foliate and circumvallate papillae was studied immunohistochemically using several neuronal markers in patients with Alzheimer's disease (AD) and their control (ADC) patients. Antisera to protein gene product 9.5 (PGP 9.5), neuron-specific enolase (NSE), tyrosine hydroxylase (TH), dopamine-beta hydroxylase (DbetaH) and calcitonin gene-related peptide (CGRP) were used in immunofluorescence and streptavidin-biotin-peroxidase complex studies. The antiserum to PGP 9.5 stained a greater number of intragemmal nerve fibers in taste buds than that of other antisera. PGP 9.5 immunoreactivity was strictly localized in the nerve fibers, whereas NSE immunoreactivity was observed not only in the nerve fibers, but also in taste bud cells. Intragemmal TH- and DbetaH-immunoreactive nerve fibers were not identified in taste buds. Only a few intragemmal nerve fibers immunoreactive for anti-CGRP antiserum were observe in a small number of taste buds. Furthermore, quantitive analysis in AD and ADC patients demonstrated that the mean number of PGP 9.5-immunoreactive intragemmal nerve fibers in taste buds of the foliate and circumvallate papillae decreased significantly in AD patients. These results indicated that PGP 9.5 is a most suitable molecular marker for the demonstration of the extrinsic innervation in human taste buds, and that the decreased innervation may account partially for the decrement in chemosensory capacity in AD patients.

Aged↗

PubMed1976

Apical secretion from taste bud and other epithelial cells in amphibians.

Taste buds of the axolotl, Ambystoma mexicanum, contain cells, previously undescribed in this species, which have a long apical process, and are similar to the Type III cells of mammalian taste buds, and to the gustatory cells in fish. In the supporting cells, there is evidence of periodic decapitation, in addition to secretion by exocytosis. Bilaminar fragments, which are leaf-shaped bodies formed of two dense laminae separated by a lucent gap, protrude from the apical microvilli of the supporting cells and are found detached in the extracellular secreted layer. Their form and dimensions suggest that they represent secreted lipo-protein material. Similar bilaminar fragments have been seen, in much smaller numbers, on some other epithelial cells in amphibians, and in fish. A unique case, in which rough endoplasmic reticulum was found in the extracellular layer of the axolotl oral epithelium, is reported; it had apparently been ejected from the cell. It is suggested that the axolotl produces a copious secretion at the taste bud pore, in order to wash the surface, and that the bilaminar fragments represent material aiding this cleansing process. The condition in the axolotl is compared with that in some other species, particularly Rana temporaria.

Ambystoma↗

PubMed1983

A quantitative study of cat epiglottal taste buds during development.

To quantify the development of upper airway chemoreceptors, epiglottal taste buds were counted in cat fetuses, kittens and adults. Taste buds with structural characteristics similar to those in the adult were observed in all fetuses close to term and in kittens from birth. During the first postnatal week a mean of 76 taste buds was present on the kitten epiglottis and by adulthood 800 were observed. The number of taste buds increased as a logarithmic function of both age and weight, but the correlation with weight is better than that with age. The presence of epiglottal taste buds from very early developmental stages suggests that these receptors may mediate the reflex apnoea and swallowing that occur in response to chemical stimulation of the larynx in newborns.

Aging↗

PubMed2006

Chronic hypoxia alters calbindin D-28k immunoreactivity in lingual and laryngeal taste buds in the rat.

The distribution and abundance of the calcium binding protein, calbindin D-28k (CB) immunoreactivity in the taste buds of the circumvallate papillae and larynx were compared between normoxic and chronically hypoxic rats (10% O2 for 8 weeks). In the normoxic rats, CB immunoreactivity was observed in some cells and fibers of the intragemmal region of the taste buds in the circumvallate papillae. In contrast, in the subgemmal region of the laryngeal taste buds, fibers but not cells were immunoreactive for CB. In chronically hypoxic rats, CB immunoreactive cells and fibers in the taste buds were decreased in the circumvallate papillae. In the laryngeal taste buds, the density of the subgemmal CB immunoreactive fibers in chronically hypoxic rats was greater than in normoxic rats. It is considered that function of the laryngeal taste buds is different from that of the lingual taste buds, so that laryngeal taste buds may be involved in chemosensation other than taste. The altered density of CB immunoreactive cells and fibers in the lingual and laryngeal taste buds is a predominant feature of hypoxic adaptation, and chronic hypoxic exposure might change the chemical sensitivity of the circumvallate papillae and larynx through the regulation of intracellular Ca2+.

Adaptation, Physiological↗

PubMed1977

Regeneration of fungiform taste buds: temporal and spatial characteristics.

The gross morphology of the tongue of the Mongolian gerbil Meriones unguiculatus), the location of papillae and taste buds, and the normal innervation pattern of the tongue and taste buds were determined. The chorda tympani nerve was interrupted to produce degeneration of fungiform taste buds. Regenerating chorda tympani axons followed the original nerve pathways in the tongue en route to the fungiform papillae in the epithelium where they initiated the regeneration of taste buds. The spatial distribution of reinnervated fungiform papillae and reformed taste buds was examined 7 to 19 days following surgery. Beginning at eight days following chorda tympani interruption there was a progressive increase, first, in the proportion of fungiform papillae that were reinnervated, and later in the number of reformed taste buds. On the basis of these measures it was concluded that a taste bud is reformed one to two days after reinnervation of its papilla. From the time course of reinnervation of the fungiform papillae it was calculated that some fibers regenerated at rates in excess of 2 mm/day. Regeneration was precise and systematic. The regenerating chorda tympani fibers accurately returned to the fungiform papillae; they did not follow the pathways of lingual nerve axons. In the initial stages of recovery both reinnervated papillae and reformed taste buds were preferentially located toward the front of the tongue; the reinnervation of posterior fungiform papillae was delayed.

Animals↗

PubMed1996

Whole-cell recording from non-dissociated taste cells in mouse taste bud.

A method for the whole-cell recording from non-dissociated taste cells within mouse taste bud is described. The lingual epithelial sheet containing the taste buds was peeled free from the tongue by injecting a proteolytic enzyme, elastase, under the lingual epithelium and by incubating it in normal Tyrode solution at 30 degrees C. The preparation consisting of a taste bud and a small piece of the lingual epithelium was obtained by further the incubation in divalent cation-free Tyrode solution. After holding the small piece of the epithelium by a holding pipette loaded with continuous negative pressure for keeping the orientation of the taste bud, whole-cell configuration was established in a non-dissociated taste cell within the taste bud with a patch pipette containing Lucifer Yellow. Taste stimuli or blockers were applied from the third pipette placed near the taste pore under the continuous flow of bathing solution. Under this condition, we could simultaneously accomplish patch-clamping, visualization of taste cell morphology, localized taste stimulation and maintenance of microenvironment around the taste organ. Rapid responses to a relatively high concentration of salt stimuli were also obtained.

Amiloride↗

PubMed1997

Taste buds develop autonomously from endoderm without induction by cephalic neural crest or paraxial mesoderm.

Although it had long been believed that embryonic taste buds in vertebrates were induced to differentiate by ingrowing nerve fibers, we and others have recently shown that embryonic taste buds can develop normally in the complete absence of innervation. This leads to the question of which tissues, if any, induce the formation of taste buds in oropharyngeal endoderm. We proposed that taste buds, like many specialized epithelial cells, might arise via an inductive interaction between the endodermal epithelial cells that line the oropharynx and the adjacent mesenchyme that is derived from both cephalic neural crest and paraxial mesoderm. Using complementary grafting and explant culture techniques, however, we have now found that well-differentiated taste buds will develop in tissue completely devoid of neural crest and paraxial mesoderm derivatives. When the presumptive oropharyngeal region was removed from salamander embryos prior to the onset of cephalic neural crest migration, taste buds developed in grafts and explants coincident with their appearance in intact control embryos. Similarly, explants from neurulae in which movement of paraxial mesoderm had not yet begun also developed taste buds after 9-12 days in vitro. We conclude that neither cranial neural crest nor paraxial mesoderm is responsible for the induction of embryonic taste buds. Surprisingly, the ability to develop taste buds late in embryonic development seems to be an intrinsic feature of the oropharyngeal endoderm that is determined by the completion of gastrulation.

Ambystoma↗

PubMed1997

Light and dark cells of rat vallate taste buds are morphologically distinct cell types.

Cells of mammalian taste buds have been classified into morphological types based on ultrastructural criteria, but investigators have disagreed as to whether these are distinct cell types or the extremes of a continuum. To address this issue, we examined taste buds from rat vallate papillae that had been sectioned transversely, rather than longitudinally, to their longest axis. In these transverse sections, dark (Type I) and light (Type II) cells were easily distinguished by their relative electron density, shape and topological relationships. Cells with electron-lucent cytoplasm (light cells) were circular or oval in outline, while those with electron-dense cytoplasm (dark cells) had an irregular outline with sheetlike cytoplasmic projections that separated adjacent light cells. A hierarchical cluster analysis of 314 cells across five morphological parameters (cell shape and area, and nuclear ellipticity, electron density and invagination) revealed two distinct groups of cells, which largely corresponded to the dark and light cells identified visually. These cells were not continuously distributed within a principal components factor solution. Differences in the means for dark and light cells were highly significant for each morphological parameter, but within either cell type, changes in one parameter correlated little with changes in any other. These analyses all failed to reveal cells with a consistent set of intermediate characteristics, suggesting that dark and light cells of rat vallate taste buds are distinct cell types rather than extremes of a continuum. Sections of taste buds were stained with antibodies to several carbohydrates, then observed by indirect immunofluorescence. Optical sections taken with a confocal laser-scanning microscope showed that the Lewis antigen was present only on spindle-shaped cells with circular or oval outlines and lacking transverse projections; these characteristic shapes matched those of light cells seen by electron microscopy. The H blood group antigen and the 2B8 epitope appeared at most cell-cell interfaces in the bud and are present on dark cells and possibly on some light cells. These findings relate molecular markers to morphological phenotypes and should facilitate future studies of taste cell turnover, development and regeneration.

Animals↗

PubMed1998

The innervation of taste buds in the soft palate and circumvallate papilla of the rat as revealed by the zinc iodide-osmium tetroxide technique.

The taste buds in the soft palate and the circumvallate papillae of the rat were investigated by the zinc iodide-osmium tetroxide technique. In addition, electron micrographs of taste buds stained with this method were presented for the first time. Differences in taste bud structures were found between the examined regions. The taste buds of the soft palate showed a complicated plexus of intragemmal nerve fibers. Some fibers exhibited terminal polymorphic swellings. Single branches could be traced close to the space of the taste pore. In the soft palate, the taste bud cells remained unstained, whereas in the circumvallate papillae of the tongue, a subpopulation of taste bud cells could be selectively stained and the intragemmal nerve fibers were characterized by large varicosities. The morphological dissimilarities between the taste buds of the investigated regions might be explained by their functional characteristics, or possibly their varying affinities to the taste qualities. Electron microscopic investigation of the stained circumvallate papillae revealed that the electron-dense reaction product had primarily accumulated in a subpopulation of light cells. Dark cells exhibited only a slight labelling. In detail, the precipitate was found loosely distributed in the cytoplasm as well as the nuclei of the cells, and particularly concentrated at the membranes of light vacuoles, this probably being profiles of dilated endoplasmic reticulum. A few roundish accumulations of precipitate were seen in the cytoplasm of taste bud cells, which showed no intensive light microscopic staining. Labelled material was also found within the taste pores outside the apical processes of the cells. The present findings indicate that the zinc iodide-osmium tetroxide technique is applicable to neuroanatomical studies of taste buds.

Animals↗