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PubMed1980

Further observations on the occurrence of taste buds in the papilla palatina of primates.

1. Taste buds occur in the epithelium of the papilla of Galago crassicaudatus and demidovi, Perodicticus potto and Microcebus murinus. The taste buds are found single or in groups of 2 or 3. A taste area ocurs in Galago crassicaudatus and Perodicticus potto. 2. The pattern of the distribution of the taste buds in the species studied is basically the same as found previously in Nycticebus and Tupaia. The taste buds are found in the oral part of the papilla palatina exclusively, far oral to the orifices of the ductus nasopalatinus and vomeronasalis. 3. From the orientation of the taste buds it can be concluded that they taste substances entering the sulcus papillae palatinae, because the buds point at the entrances and at the lumen of that sulcus. Since substances may approach the anterior part of the papilla from the oral direction the taste buds in this area point rostrally. In Galago the anteriormost taste buds are situated in the median plane pointing at the slit between the epithelial laminae of the labial folds. 4. Many taste buds were found in the process of disintegration.

Animals↗
PubMed1987

Persistence of taste buds in denervated fungiform papillae.

Taste buds in hamster fungiform papillae persist in an atrophic state for as long as 330 days after chorda tympani denervation or 50 days after combined chorda tympani-lingual nerve resection. Although taste bud structure depends on innervation, there is no absolute neural requirement for taste bud survival.

Animals↗
PubMed2007

Qualitative and quantitative differences between taste buds of the rat and mouse.

BACKGROUND: Numerous electrophysiological, ultrastructural, and immunocytochemical studies on rodent taste buds have been carried out on rat taste buds. In recent years, however, the mouse has become the species of choice for molecular and other studies on sensory transduction in taste buds. Do rat and mouse taste buds have the same cell types, sensory transduction markers and synaptic proteins? In the present study we have used antisera directed against PLCbeta2, alpha-gustducin, serotonin (5-HT), PGP 9.5 and synaptobrevin-2 to determine the percentages of taste cells expressing these markers in taste buds in both rodent species. We also determined the numbers of taste cells in the taste buds as well as taste bud volume. RESULTS: There are significant differences (p < 0.05) between mouse and rat taste buds in the percentages of taste cells displaying immunoreactivity for all five markers. Rat taste buds display significantly more immunoreactivity than mice for PLCbeta2 (31.8% vs 19.6%), alpha-gustducin (18% vs 14.6%), and synaptobrevin-2 (31.2% vs 26.3%). Mice, however, have more cells that display immunoreactivity to 5-HT (15.9% vs 13.7%) and PGP 9.5 (14.3% vs 9.4%). Mouse taste buds contain an average of 85.8 taste cells vs 68.4 taste cells in rat taste buds. The average volume of a mouse taste bud (42,000 microm3) is smaller than a rat taste bud (64,200 microm3). The numerical density of taste cells in mouse circumvallate taste buds (2.1 cells/1000 microm3) is significantly higher than that in the rat (1.2 cells/1000 microm3). CONCLUSION: These results suggest that rats and mice differ significantly in the percentages of taste cells expressing signaling molecules. We speculate that these observed dissimilarities may reflect differences in their gustatory processing.

Animals↗
PubMed1987

Neural induction of taste buds.

Bilateral innervation allows more than 80% of the 610 vallate taste buds to survive removal of one IXth nerve in adult rats. Removal of both IXth nerves in neonatal or adult rats results in the absence of taste buds. In studying development, we found that removing or crushing one IXth nerve in three-day-old neonates profoundly decreased the number of vallate taste buds that subsequently developed. Specifically, after removal of one IXth nerve at 3 days, only 228 taste buds formed, compared with 496 taste buds that one nerve would maintain in adults. Thus, during normal development, the right and left IXth nerves interact synergistically, as at least 150 more taste buds develop than predicted by the sum of the independent action of each IXth nerve. This suggests that vallate taste buds are induced by the IXth nerve. A second example of synergism, representing evidence for the neural induction of taste buds, came from experiments in which we crushed the left IXth nerve 3 days after birth and found that these regenerated IXth nerve axons induced 4 times as many taste buds in the presence of the normal right IXth nerve (118 taste buds) as in its early absence (30 taste buds). We conclude that taste buds are neurally induced and that axons of the IXth nerve interact synergistically in inducing them, rather than competing for targets. We propose that in development innervated progenitor cells form stem cells which lead to taste bud cells.

Animals↗
PubMed1998

Quantitative relationships between taste bud development and gustatory ganglion cells.

To determine whether patterns of taste bud innervation change during postnatal rat development, the number of geniculate ganglion cells that innervate single taste buds were quantified in adult and developing rats. While there was a large variation in numbers of ganglion cells that innervate individual taste buds, there was a high degree of organization in the system. Namely, the number of labeled geniculate ganglion cells innervating a taste bud was highly correlated with the size of the taste bud. This relationship between taste bud size and number of innervating ganglion cells develops over a prolonged postnatal period and is not established until postnatal day 40 (P40), when taste buds reach their adult size. In a second series of experiments, we sought to determine whether neural rearrangement of chorda tympani neurons is responsible for the development of this relationship by double-labeling single taste buds at different ages. We found that the number of ganglion cells innervating individual taste buds on P10 predicts the size that taste buds become by P40. This finding suggests that neural rearrangement is not responsible for establishing the relationship between taste bud size and the number of innervating ganglion cells during development. More importantly, it strongly suggests that the 'neural template' for the mature innervation pattern is determined during early postnatal development.

Animals↗
PubMed2006

Effects of streptozotocin-induced diabetes on taste buds in rat vallate papillae.

Some studies have documented taste changes in patients with diabetes mellitus (DM). In order to understand the relationships between taste disorders caused by DM and the innervation and morphologic changes in the taste buds, we studied the vallate papillae and their taste buds in rats with DM. DM was induced in these rats with streptozotocin (STZ), which causes the death of beta cells of the pancreas. The rats were sacrificed and the vallate papillae were dissected for morphometric and quantitative immunohistochemical analyses. The innervations of the vallate papillae and taste buds in diabetic and control rats were detected using immunohistochemistry employing antibodies directed against protein gene product 9.5 (PGP 9.5) and calcitonin gene-related peptide (CGRP). The results showed that PGP 9.5- and CGRP-immunoreactive nerve fibers in the trench wall of diabetic vallate papillae, as well as taste cells in the taste buds, gradually decreased both intragemmally and intergemmally. The morphometry revealed no significant difference in papilla size between the control and diabetic groups, but there were fewer taste buds per papilla (per animal). The quantification of innervation in taste buds of the diabetic rats supported the visual assessment of immunohistochemical labeling, that the innervation of taste cells was significantly reduced in diabetic animals. These findings suggest that taste impairment in diabetic subjects may be caused by neuropathy defects and/or morphological changes in the taste buds.

Animals↗
PubMed1994

Development of fungiform papillae, taste buds, and their innervation in the hamster.

Fungiform taste buds in mature hamsters are less subject to neurotrophic influences than those of other species. This study evaluates taste-bud neurotrophism during development in hamsters by examining the relation between growing nerves and differentiating fungiform papillae. Chorda tympani (CT) or lingual (trigeminal) nerve (LN) fibers were labelled with Lucifer Yellow as they grew into (CT fibers) or around (LN fibers) developing taste buds. Developing fungiform papillae and taste pores were counted with the aid of a topical tongue stain. The tongue forms on embryonic days (E) 10.5-11 and contains deeply placed CT and LN fibers but no papillae. By E12, the tongue epithelium develops scattered elevations. These "eminences" selectively become innervated by LN fibers that grow to the epithelium earlier and in larger numbers than CT fibers. Definitive fungiform papillae form rapidly during E13-14 and become heavily innervated by LN fibers. Intraepithelial CT fibers, rare at E13, invariably innervate fungiform papillae containing nascent taste buds at E14. During E14-15 (birth = E15-16), most papillae contain taste buds with pores, extensive perigemmal LN innervation, and extensive intragemmal CT innervation. At birth, numbers of fungiform papillae and taste pores are adultlike. The results show that fungiform eminences begin forming in the absence of innervation. The subsequent differentiation of definitive fungiform papillae and their innervation by LN fibers occur synchronously, prior to the differentiation of taste buds and their CT innervation. The hamster is precocious (e.g., compared to rat) in terms of LN development and the structural maturity of the anterior tongue at birth.

Animals↗
PubMed1976

An electron microscopic study on the innervation in the taste buds of the mouse circumvallate papillae.

Taste buds of the mouse circumvallate papillae were studied by electron microscopy to elucidate the innervation involving the adrenergic nerve supply. Typical afferent synaptic contacts, with increased density of the membranes and aggregations of synaptic vesicles in the cytoplasm adjacent to the nerve endings, were demonstrated between the type III cells and the nerve endings. Along the regions of contact between the type II cells and the nerve endings, cisternae of endoplasmic reticulum were often seen beneath the cell membrane, and the nerve endings contained relatively many synaptic-sized vesicles. Such an innervation seems to be efferent in nature. For the detection of the adrenergic nerve supply, 5-hydroxydopamine (5-OH-DA) was injected after pretreatment with L-DOPA and nialamide. The mice showed numerous adrenergic nerve fibers in the connective tissue underlying the taste buds. On very few occasions, the adrenergic nerves penetrated the basal lamina of the taste buds and came into contact with the bud cells. Some adrenergic nerves were distributed among the epithelial cells around the taste buds. The reaction product from acetylcholine esterase activity was found around the adrenergic nerve fibers labeled with 5-OH-DA.

Acetylcholinesterase↗
PubMed2002

Expression of the metabotropic glutamate receptor, mGluR4a, in the taste hairs of taste buds in rat gustatory papillae.

Taste-mGluR4, cloned from taste tissues, is a truncated variant of brain-expressed mGluR4a (brain-mGluR4), and is known to be a candidate for the receptor involved in the umami taste sense. Although the expression patterns of taste- and brain-mGluR4 mRNAs have been demonstrated, no mention has so far been made of the expression of these two mGluR4 proteins in taste tissues. The present study examined the expression of taste-mGluR4 and brain-mGluR4 proteins in rat taste tissues by using a specific antibody for mGluR4a which shared a C-terminus of both taste- and brain-mGluR4, for immunoblot analysis and immunohistochemistry. Immunoblot analysis showed that both brain-mGluR4 and taste-mGluR4 were expressed in the taste tissues. Taste-mGluR4 was not detected in the cerebellum. The immunoreactive band for brain-mGluR4 protein was much stronger than that for taste-mGluR4 protein. In the cryosections of fungiform, foliate and circumvallate papillae, the antibody against taste-mGluR4 exhibited intense labeling of the taste pores and taste hairs in all the taste buds of gustatory papillae examined; the immunoreaction to the antibody against brain-mGluR4 was more intense at the same sites of the taste buds. The portions of the taste bud cells below the taste pore and surrounding keratinocytes did not show any immunoreactivities. The results of the present study strongly suggest that, in addition to taste-mGluR4, brain-mGluR4 may function even more importantly than the former as a receptor for glutamate, i.e. the umami taste sensation.

Animals↗
PubMed2005

Are there efferent synapses in fish taste buds?

In fish, nerve fibers of taste buds are organized within the bud's nerve fiber plexus. It is located between the sensory epithelium consisting of light and dark elongated cells and the basal cells. It comprises the basal parts and processes of light and dark cells that intermingle with nerve fibers, which are the dendritic endings of the taste sensory neurons belonging to the cranial nerves VII, IX or X. Most of the synapses at the plexus are afferent; they have synaptic vesicles on the light (or dark) cells side, which is presynaptic. In contrast, the presumed efferent synapses may be rich in synaptic vesicles on the nerve fibers (presynaptic) side, whereas the cells (postsynaptic) side may contain a subsynaptic cistern; a flat compartment of the smooth endoplasmic reticulum. This structure is regarded as a prerequisite of a typical efferent synapse, as occurring in cochlear and vestibular hair cells. In fish taste buds, efferent synapses are rare and were found only in a few species that belong to different taxa. The significance of efferent synapses in fish taste buds is not well understood, because efferent connections between the gustatory nuclei of the medulla with taste buds are not yet proved.

Animals↗
PubMed2000

Heterogeneity of fish taste bud ultrastructure as demonstrated in the holosteans Amia calva and Lepisosteus oculatus.

Taste buds are the peripheral sensory organs of the gustatory system. They occur in all taxa of vertebrates and are pear-shaped intra-epithelial organs of about 80 microm height and 50 microm width. Taste buds mainly consist of specialized epithelial cells, which synapse at their bases and therefore are secondary sensory cells. Taste buds have been described based on studies of teleostean species, but it turned out that the ultrastructure of teleostean taste buds may differ between distinct systematic groups and that this description is not representative of those taste buds in other main taxa of fishes, such as selachians, holosteans and dipnoans. Furthermore, it is not known how variable the micromorphologies of non-teleostean taste buds are. For this reason the taste buds of two holosteans, Lepisosteus oculatus and Amia calva, were investigated and compared. While in both species the taste buds are of the same shapes and sizes, the cellular components of their sensory epithelia differ: in Lepisosteus taste buds comprise two types of elongated light cells and one type of dark cells. In contrast, Amia taste buds contain only one type of light, but two types of dark elongated cells. Afferent synapses are common in the buds of both species, efferent synapses occur only in Lepisosteus taste buds. These differences show that even in the small group of holostean fishes the taste buds are differently organized. Consequently, a representative type of fish taste buds does not exist.

Animals↗
PubMed2001

Age-related alteration of taste bud distribution in the common marmoset.

Alteration in the number of taste buds on the soft palate (SP), fungiform (FF), foliate (FL) and circumvallate (CV) papillae in the common marmoset at different postnatal ages was examined histologically. After paraffin embedding, complete serial sections at 10 microm thickness were made and stained by HE. Digitized images for each section were examined carefully. The number of FF taste buds at day 1 was 334. While only 20% of all the taste buds at birth possessed a taste pore, 39% of 174 SP taste buds at day 1 possessed a taste pore. The number of taste buds with pores at day 1 was small for the center CV (19 of 59), one side CV (7 of 25), and one side FL (2 of 16). These results suggest that the functional maturation of SP taste buds may precede maturation in other areas of the tongue. The total number of taste buds increased with increasing age, reached a maximum at 2 months of age: FF, 1069; SP, 609; CV-center, 530; CV-side, 390; FL, 201, and decreased thereafter. Almost all taste buds possessed a taste pore after 2 months of age. The decrease in the number of taste buds in the oral cavity with increase in age may change taste sensitivity.

Aging↗
PubMed1999

Cellular expression of alpha-gustducin and the A blood group antigen in rat fungiform taste buds cross-reinnervated by the IXth nerve.

Although taste buds are trophically dependent on their innervation, cross-reinnervation experiments have shown that their gustatory sensitivities are determined by the local epithelium. Both the gustatory G-protein, alpha-gustducin, and the cell-surface carbohydrate, the A blood group antigen, are expressed by significantly fewer fungiform than vallate taste cells in the rat. In these experiments, one side of the anterior portion of the tongue was cross-reinnervated by the IXth nerve in order to determine whether the molecular expression of taste bud cells is determined by the epithelium from which they arise or by the nerve on which they are trophically dependent. The proximal portion of the IXth nerve was anastomosed to the distal portion of the chorda tympani (CT) nerve using fibrin glue (IX-CT rats). Control animals had the CT cut and reanastomosed using the same technique (CT-CT rats), or had the CT avulsed from the bulla and resected to prevent regeneration (CTX rats). The animals survived for 12 weeks postoperatively, and the tongues were removed, stained with methylene blue, and the fungiform taste pores counted on both sides. Tissue from the anterior 5 mm of the tongue was cut into 50-microm sections, which were incubated with antibodies against alpha-gustducin and the human blood group A antigen. In both CT-CT and IX-CT rats, there was regeneration of fungiform taste buds, although in both groups there were significantly fewer taste buds on the operated side of the tongue. The normal vallate papilla had a mean of 8.37 alpha-gustducin-expressing cells and 5.22 A-expressing cells per taste bud, whereas the fungiform papillae contained 3.06 and 0.23 cells per taste bud, respectively. In both CT-CT and IX-CT rats there was a normal number of cells expressing alpha-gustducin or the A antigen in regenerated taste buds; in the CTX animals there was a significant decrease in the expression of these markers. These results demonstrate that the molecular phenotype of taste bud cells is determined by the local epithelium from which they arise and not by properties of the innervating nerve.

ABO Blood-Group System↗
PubMed1993

Morphometric and immunocytochemical assessment of fungiform taste buds after interruption of the chorda-lingual nerve.

Unilateral interruption of the chorda-lingual nerve led to a loss of most epithelial axons and to the deterioration of fungiform taste buds in the anterior portion of the tongue of albino rats, mongolian gerbils, and golden hamsters. By three weeks after surgery the following percentages of fungiform taste buds had completely disappeared: 71% in gerbils, 28% in rats, and 26% in hamsters. Residual taste buds were classified into two groups: atrophic taste buds and taste bud remnants. Atrophic taste buds were smaller than normal and typically had no visible taste pore, although they retained the characteristic oval shape of a taste bud and numerous elongated cells. Taste bud remnants were non-oval fragments of taste buds with few elongated cells. Specific markers for elongated taste cells (monoclonal antibodies to keratin 19) confirmed that atrophic taste buds, as well as some taste bud remnants, had elongated taste cells. By 180 days after chorda-lingual nerve transection, 44% of rat fungiform taste buds had disappeared; morphometric analysis of the 311 residual taste buds established that 241 atrophic taste buds and 69 taste bud remnants were, respectively, 50% and 75% smaller than the average volume of 480 normal taste buds. The aggregate loss of gustatory tissue, calculated from the shrinkage of residual taste buds and the volume lost by the outright disappearance of many taste buds, was 88% for gerbils, 72% for rats, and 65% for hamsters. Evaluation in gerbils of the co-occurrence of taste buds and axons suggests residual taste buds were neurotrophically supported. Every gerbil fungiform papilla that lacked axons lacked a taste bud.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

Neuron/target matching between chorda tympani neurons and taste buds during postnatal rat development.

During postnatal development, a relationship is established between the size of individual taste buds and number of innervating neurons. To determine whether rearrangement of neurons that innervate taste buds establishes this relationship, we labeled single taste buds at postnatal day 10 (P10) and again at either P15, P20, or P40 with retrograde fluorescent neuronal tracers. The number of single- and double-labeled geniculate ganglion cells was counted, and the respective taste bud volumes were measured for the three groups of rats. The current study replicates findings from an earlier report demonstrating that the larger the taste bud, the more geniculate ganglion cells that innervate it. This relationship between taste bud size and number of innervating neurons is not apparent until P40, when taste bud size reaches maturity. These findings are extended here by demonstrating that the number of neurons that innervate taste buds at P10, when taste bud size is small and relatively homogeneous, predicts the size that the respective taste bud will become at maturity. Moreover, while there is some neural rearrangement of taste bud innervation from P10 to P40, rearrangement does not impact the relationship between taste bud size and innervating neurons. That is, the neurons that maintain contact with taste buds from P10 through P40 accurately predict the mature taste bud size. Therefore, the size of the mature taste bud is determined by P10 and relates to the number of sensory neurons that innervate it at that age and the number of neurons that maintain contact with it throughout the first 40 days of postnatal development.

Age Factors↗
PubMed1995

Embryonic origin of amphibian taste buds.

Despite numerous descriptive studies, the embryonic origin of vertebrate taste buds has never been experimentally determined. A number of different alternatives have been suggested for taste bud origins, including epibranchial placodes, the neural crest, and the local epithelium of the oropharyngeal cavity. The role of a series of epibranchial placodes and the cephalic neural crest, which together give rise to the cranial nerves innervating taste buds, was examined with regard to the development of oropharyngeal taste buds in an ambystomatid salamander, the axolotl. When pigmented placodal ectoderm or neural folds were grafted isotopically and isochronically into nonpigmented host embryos, known derivatives of each tissue contained pigmented cells, but labeled taste buds were never encountered. Thus, neither epibranchial placodes nor neural crest contribute cells to taste buds during embryogenesis. The majority of the oropharyngeal cavity of ambystomatid salamanders is lined by an endodermal epithelium. In order to demonstrate conclusively that taste buds arise from this local epithelium, the presumptive cephalic endoderm of early axolotl gastrulae was microinjected with the lipophilic dye, DiI. In the oropharyngeal epithelium of all larvae examined, both taste buds and general epithelial cells were labeled with DiI, indicating their common endodermal origin. Our findings are novel in that this is the first experimental demonstration of the endodermal origin of a vertebrate sensory receptor cell class.

Ambystoma↗
PubMed2003

Postnatal development of the mouse volatile papilla taste bud cells.

In the present study, we examined specific markers for taste bud cells in the mouse and the postnatal development of volatile papilla taste bud cells in ddY mice. We examined the immunoreactivity of 4 types of carbonic anhydrase isoenzymes, CA I, CA II, CA III and CA VI, as specific markers for taste bud cells, and K8.13 cytokeratin antibody as a specific marker for the lingual epithelial cells. Of the carbonic anhydrase isoenzymes, only CA III immunoreactivity was clearly detected in the spindle shaped gustatory cells. CA VI immunoreactivity was detectable in suspentacular cells. CA I and CA II antibodies did not recognize any taste bud cell specifically. K8.13 cytokeratin immunoreactivity was detected in the lingual epithelial cells, but not in taste bud cells. At 7 days after birth, the suckling phase, very small taste buds developed from the anaplastic gustatory cells. At 14 days after birth, the taste buds showed larger size than those at 7 days after birth. At 21 days birth, after the weaning phase, taste bud structure approximated the mature structure. These results demonstrate the specificity of anti-CA III and anti-CA VI for gustatory cells and suspentacular cells, respectively. These markers should be useful for an analysis of taste bud development in mice.

Animals↗
PubMed1997

Differential expression of alpha-gustducin in taste bud populations of the rat and hamster.

The G-protein subunit alpha-gustducin, which is similar to rod transducin, has been implicated in the transduction of both sweet- and bitter-tasting substances. In rodents, there are differences in sensitivity to sweet and bitter stimuli in different populations of taste buds. Rat fungiform taste buds are more responsive to salts than to sweet stimuli, whereas those on the palate respond predominantly to sweet substances. In contrast, hamster fungiform taste buds are more sensitive to sweet-tasting stimuli. Taste buds in the vallate and foliate papillae of both species are sensitive to bitter compounds. These differences in sensitivity should be reflected in the numbers of gustducin-containing cells in different taste bud populations. We examined taste buds in the rat and hamster for immunoreactivity to an antibody against alpha-gustducin. Immunofluorescence of labeled taste cells was examined by confocal microscopy, and the cells were counted. Gustducin-positive cells were seen in all taste bud regions; they were spindle-shaped, with circular cross-sections and apical processes that extended to the taste pore. Cells with this characteristic shape in rat vallate taste buds are Type II (light) cells. In the rat, taste buds of the fungiform papillae had fewer gustducin-positive cells (3.1/taste bud) than those of other regions, including the posterior tongue and palate (>8.9/taste bud). Hamster fungiform taste buds contained twice as many gustducin-expressing cells (6.8/taste bud) as those of the rat. These data support the hypothesis that alpha-gustducin is involved in the transduction of both sweet- and bitter-tasting stimuli by mammalian taste receptor cells.

Animals↗