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PubMed2001

Glutamate-induced cobalt uptake reveals non-NMDA receptors in developing rat taste buds.

Non-NMDA type glutamate receptors are present in rat taste buds. However, the function of those receptors is not yet known. Developmental changes in the glutamate receptors in taste cells may provide clues to their functional role. We used a cobalt staining technique to determine at which stage in development functional non-NMDA glutamate receptors first appeared. Cobalt-stained taste bud cells first appeared in 20-day-old rats. The number of cobalt-stained cells increased with age and reached a maximum at 45 days. The shape of stained cells looked similar at all age groups. Cobalt-labeled cells appeared to be correlated with synaptic, not taste, glutamate receptors.

Aging↗
PubMed1987

A histochemical study of APUD ability in the taste buds of experimentally induced zinc-deficient mice.

To explore the relationship between taste acuity and zinc deficiency, a histochemical investigation was made into the taste buds of mice fed a zinc-deficient diet. Nine weeks after the start of the diet, the average serum zinc level of the mice was 45% lower than that of a control group of mice. Moreover, growth was arrested significantly. Two-bottle preference tests revealed that the intake ratio of 10(-5) M quinine hydrochloride solutions had increased markedly in the zinc-deficient mice compared with the controls. The circumvallate taste buds showed no morphological changes. Fluorescent histochemical examination showed an uptake of a monoamine precursor (5-HTP) by the gustatory cells in the zinc-deficient mice after the 5-HTP treatment. Upon immunohistological examination, however, no serotonin immunoreactivity appeared in the gustatory cells of the zinc-deficient mice after the 5-HTP treatment. These results suggest that zinc-deficiency may induce hypogeusia and decrease the ability to transform a monoamine precursor to monoamine in the gustatory cells, albeit the monoamine precursor uptake ability is not affected.

APUD Cells↗
PubMed1987

Papilla palatina, nasopalatine duct and taste buds of young and adult rats.

The morphology of the papilla palatina, the nasopalatine ducts and the taste buds situated within these ducts was studied in pups and adult rats using light and electron microscopy. During development, the papilla palatina grew in width and depth, becoming a protuberance in weanlings and adults. The nasopalatine ducts enlarged and two folds of the lateral walls of the ducts differentiated, reducing the width of the tubes in the region of the oral openings. Taste buds appeared postnatally. Light, dark, and perigemmal cells were found in all stages studied, but light cells were scarce up to 8 days of age. The taste pore appeared between 11 and 13 days of age; it lacked electron-dense material of cellular origin. Synaptic-like images could be found only in relation to dark cells. The papilla palatina, the nasopalatine ducts and the taste buds were fully developed by the 3rd week of life.

Animals↗
PubMed1987

Modified smooth endoplasmic reticulum in type II cells of rabbit taste buds.

Type II cells of taste buds from rabbit foliate papillae are characterized by a widespread system of smooth endoplasmic reticulum (SER), usually in the form of a loose network. In some cells, the SER is tightly compacted into a juxtanuclear aggregate that is continuous with the perinuclear space and that appears to merge with the Golgi complex. In other type II cells, the SER is in a honeycomb arrangement. Where type II cells confront nerves, they may have extensive smooth-membraned subsurface cisternae. The presence of manifold forms of SER in type II cells suggests that these cells may have a variety of secretory functions.

Animals↗
PubMed2006

Nucleoside triphosphate diphosphohydrolase-2 is the ecto-ATPase of type I cells in taste buds.

The presence of one or more calcium-dependent ecto-ATPases (enzymes that hydrolyze extracellular 5'-triphosphates) in mammalian taste buds was first shown histochemically. Recent studies have established that dominant ecto-ATPases consist of enzymes now called nucleoside triphosphate diphosphohydrolases (NTPDases). Massively parallel signature sequencing (MPSS) from murine taste epithelium provided molecular evidence suggesting that NTPDase2 is the most likely member present in mouse taste papillae. Immunocytochemical and enzyme histochemical staining verified the presence of NTPDase2 associated with plasma membranes in a large number of cells within all mouse taste buds. To determine which of the three taste cell types expresses this enzyme, double-label assays were performed with antisera directed against the glial glutamate/aspartate transporter (GLAST), the transduction pathway proteins phospholipase Cbeta2 (PLCbeta2) or the G-protein subunit alpha-gustducin, and serotonin (5HT) as markers of type I, II, and III taste cells, respectively. Analysis of the double-labeled sections indicates that NTPDase2 immunoreactivity is found on cell processes that often envelop other taste cells, reminiscent of type I cells. In agreement with this observation, NTPDase2 was located to the same membrane as GLAST, indicating that this enzyme is present in type I cells. The presence of ecto-ATPase in taste buds likely reflects the importance of ATP as an intercellular signaling molecule in this system.

Adenosine Triphosphatases↗
PubMed1995

Salt discriminability is related to number of regenerated taste buds after chorda tympani nerve section in rats.

Transection of the chorda tympani nerve (CTX) impairs taste-guided discrimination of NaCl from KCl in rats. We wanted to determine whether this discrimination recovers after chorda tympani regeneration. Experiment 1 showed that few taste buds regenerated 14 days after CTX, whereas substantial regeneration occurred 42 days after surgery. Experiment 2 demonstrated that rats trained before CTX could clearly discriminate the two salts when tested starting 49 days after surgery, whereas rats tested starting 8 days after surgery were severely impaired in this task. Rats tested starting 28 days after CTX were unimpaired, moderately impaired, or severely impaired on the discrimination task. Overall, discrimination performance was significantly related to the number of regenerated taste buds. Unilaterally transected rats tested shortly after surgery were nearly as competent as controls. These results indicate that rats can recover the ability to discriminate NaCl from KCl after regeneration of anterior tongue taste buds.

Animals↗
PubMed1991

Taste Buds and Neuromasts of Astyanax jordani: Distribution and Immunochemical Demonstration of Co-localized Substance P and Enkephalins.

The distribution and some immunohistochemical aspects of the taste buds and free neuromasts of the blind cave fish Astyanax jordani were investigated using serial sections of whole fish. Taste buds are restricted to the skin of the lips and the lower jaw. Neuromasts are widely distributed over the whole epidermis except the lips and are particularly numerous in the opercular region and the caudal fin; they are absent from all other fins. The histological structure of the taste buds and the free neuromasts is similar to that described in other fish. The former are composed of two types of cells. The free neuromast, as seen under the electron microscope, is also constituted by two types of cell: dark supporting cells and clear sensory cells whose basal cytoplasm contains presynaptic bodies. Immunohistochemical results obtained with the peroxidase antiperoxidase method revealed the presence of different peptides in the taste buds and the free neuromasts. The former contain substance P (SP) and enkephalins (leu- and metenkephalin); the latter contain SP and leuenkephalin, but no metenkephalin. These peptides are localized in the cytoplasm of the accessory and sensory cells but not in the nervous fibres. None of these peptides occur in the olfactory epithelium of A.jordani. These immunohistochemical results raise the question of whether SP, leuenkephalin or metenkephalin play a role in transmission between the sensory cells and the afferent fibre.

Journal Article↗
PubMed2001

Immunocytochemistry of glutathione S-transferase in taste bud cells of rat circumvallate and foliate papillae.

Immunocytochemistry was used to investigate the distribution of cells reacting with specific antibodies against glutathione S-transferase (GST) mu and pi in rat circumvallate and foliate taste buds; the findings were confirmed by Western blotting. Double immunofluorescence staining for protein gene product (PGP) 9.5 and GST subunits allowed the classification of taste bud cells of both papillae into: (i) cells immunoreactive to either PGP 9.5 or GST subunit antibody; (ii) cells immunoreactive to both antibodies; and (iii) cells that did not react with either of these antibodies. Immunoelectron microscopy revealed that most GST subunit-immunoreactive cells seemed to be either type II or type III cells based on their ultrastructure. Since PGP 9.5 is now widely used as a marker for type III cells in mammalian taste buds, it seems reasonable to believe that most GST subunit-immunoreactive cells are type II cells. Whether cells immunoreactive for both PGP 9.5 and GST subunits constitute a small subpopulation of type III cells or whether they are intermediate forms between type II and III cells is under investigation. No type I cells reacted with antibodies against GST subunits in the present study. GST subunits in taste bud cells may participate in xenobiotic metabolism of certain substances exposed to taste pits, as already shown for olfactory epithelium.

Animals↗
PubMed2004

Histogenesis of the oropharyngeal cavity taste buds and the relevant nerves and brain centers in substrate-brooding and mouth-brooding cichlid fish (Cichlidae, Teleostei).

This study follows the histogenesis of the oropharyngeal cavity taste buds, along with the development of the relevant neural centers and gustatory nerves, in two cichlid species: the substrate-brooding Cichlasoma cyanoguttatum and the mouth-brooding Astatotilapia flavijosephi, from fertilization to 20-day-old juveniles, grown at a temperature of 26 degrees C. Significant differences in pace of development were shown between the two social types: Substrate-brooders complete embryogenesis and hatch 48 h after fertilization (HAF) and begin to swim 120 HAF, with the yolk sac disappearing 160 HAF, whereas mouth-brooders hatch 84 HAF and begin to swim 196 HAF, with the yolk sac disappearing 360 HAF. Histogenesis of primordial taste buds occurs 75 HAF and 160 HAF in C. cyanoguttatum and A. flavijosephi, respectively. Accordingly, the related sensory ganglia and nerves (VII, IX, and X) develop much earlier in the substrate-brooded larvae and postlarvae. Nerve and brain development in juvenile A. flavijosephi of 13 mm total length (TL) closely resemble those of 8-mm-TL C. cyanoguttatum. These differences in development continue throughout the early stages of growth. Similar differences are observed in the ripening and increase in number of taste buds and dentition on the jaws and pharyngeal bones. The possible triggers and causes of such differences in development, as well as the inductors of taste bud development, are discussed.

Afferent Pathways↗
PubMed1996

Immunohistochemical, electrophysiological, and electron microscopical study of rat fungiform taste buds after regeneration of chorda tympani through the non-gustatory lingual nerve.

The sensory innervation of fungiform papillae on the rat dorsal tongue is derived from branches of two cranial nerves: the lingual branch of the trigeminal nerve which provides somatosensory innervation and the chorda tympani (CT) branch of the facial nerve, which provides innervation to the taste buds. Removal of the CT results in degeneration of the taste buds. Removal of both nerves results in reduction in size of fungiform papillae and an altered pattern of keratinization in its epithelium. Regeneration of nerves to the epithelium restores the pre-operative condition. Thus, in addition to their sensory functions, both the CT and lingual seem to exert trophic effects on the phenotypic expression of epithelial cells in the fungiform papillae. We severed both the CT and lingual nerves in rats and sutured the proximal stump of the CT to the distal stump of the lingual to promote regeneration of the CT along the lingual nerve pathway. At the same time, we prevented the proximal stump of the lingual from regenerating into the tongue. Our purpose was to determine whether and how the innervation pattern of the regenerated taste bud might be different from normal under these experimental conditions. We found that reinnervation by the CT through the lingual nerve occurs, that this restores the anatomical and functional integrity of the fungiform taste buds and papillae, and that some papillae, but not all, were richly innervated with subgemmal, extragemmal, and perigemmal neuron-specific enolase, calcitonin gene-related peptide, substance P, and neurokinin A-positive fibers. Moreover, responses to taste stimuli were recorded electrophysiologically from the CT.

Animals↗
PubMed2002

Changes in cell morphology and cell-to-cell adhesion induced by extracellular Ca2+ in cultured taste bud cells.

Cell morphology and cell-to-cell adhesion of taste bud cells were significantly altered by extracellular Ca2+ during in vitro culture. Under high Ca2+ condition (above 0.5 mM), the cells were tightly associated with each other and formed packed aggregates. Under low Ca2+ condition (below 0.1 mM), the cells were dispersed and had an elongated shape. These two forms were reversible and specifically dependent on Ca2+. The results indicate that extracellular Ca2+ regulates cell shape and cell-to-cell adhesion of taste bud cells.

Animals↗
PubMed1977

Effect of vincristine on the histological structure of taste buds.

10 adult rabbits were arranged in five batches, 2 animals of nearly the same body weight in each group. 1 animal in each group was injected with vincristine sulfate whereas the other animal was similarly injected with the dissolving medium and used as a control. The animals were sacrificed 2 days after the last injection, and the areas containing the circumvallate and foliate papillae were examined. Injection of vincristine was followed by a decrease in number and in cell contents of vallate and foliate taste buds. Most of the taste buds which persisted after vincristine injection were full of necrotic debris which represented the remnants of degenerated cells. Possible reasons for degeneration of taste buds after vincristine injections were put forewards.

Animals↗
PubMed1958

Electron microscopic observations on the taste buds of the rabbit.

An examination of the fine structure of the taste buds in the rabbit was undertaken. Gustatory epithelium was fixed in OsO(4) or 1 per cent KMnO(4) solution, containing polyvinylpyrrolidone (PVP). Thick sections were examined in the phase microscope and contiguous sections prepared for the electron microscope. The bud contains two types of cells, gustatory receptors and sustentacular cells. The receptors are characterized by a dark nucleus and densely granular cytoplasm. The apical processes bear numerous microvilli which extend into the taste pore. Imbedded between the microvilli there is a dense substance, which is also present in the apical cytoplasm of the receptors. The sustentacular cells contain a large pale nucleus and less dense cytoplasm. Their basal surfaces rest upon a basement membrane. The subepithelial nerve plexuses comprise the fibers which innervate the gustatory receptors. The nerve fibers vary in diameter from 500 A to 0.3 micro, and are ensheathed by Schwann cells. The intragemmal fibers enter the taste bud between adjacent cells, and are ensheathed by the plasma membranes of the supporting cell until they synapse upon the gustatory cell. The synaptic terminals contain synaptic vesicles, which at this junction reside in the postsynaptic element. This observation is discussed with reference to synapses described elsewhere in the nervous system.

Animals↗
PubMed1991

Ultrastructure of palatal taste buds in the perihatching chick.

Palatal taste buds of perihatching chicks were examined by electron microscopy. Four intragemmal cell types were characterized. 1) Light: with voluminous, electron-lucent cytoplasm containing scattered free ribosomes, rough and smooth endoplasmic reticulum, plump mitochondria, sparse perinuclear filaments, occasional Golgi bodies, and numerous clear and dense-cored vesicles. Clear vesicles sometimes aggregate in a presynaptic-like configuration apposed to an axonal profile. These cells contained large, spherical, uniformly granular nuclei with one nucleolus. 2) Dark: with dense cytoplasm containing filamentous bundles surrounding the nucleus, occasional clear vesicles, centrioles, rough endoplasmic reticulum, and compact mitochrondria. The apical cytoplasm noticeably lacks dense secretory granules. Irregular to lobulated nuclei are densely granular, and contain scattered clumps of chromatin, adhering especially to the inner leaflet of the nuclear membrane, and at least one nucleolus. Cytoplasmic extensions of dark cells envelop other intragemmal cell types and nerve fibers. Light and dark cells project microvilli into the taste pore. 3) Intermediate: contain gradations of features of light and dark cells. 4) Basal: darker than the other intragemmal cell types and confined to the ventral bud region. Putative afferent synapses in relation to light cells, and axo-axonal contacts are described. While the appearance of axo-axonal contacts may be a transient developmental event, other bud features are consonant with observations in adult chickens and suggest that the peripheral gustatory apparatus is mature at hatching in this precocial avian species.

Animals↗
PubMed1999

Three-dimensional architecture of the keratin filaments in epithelial cells surrounding taste buds in the rat circumvallate papilla.

The three-dimensional architectures of the perigemmal cells and their keratin bundles in the rat circumvallate papillae were studied by transmission and scanning electron microscopy. The perigemmal cells were classified into three layers: basal, middle and upper. The basal layer consisted of polygonal cells located close to the basal lamina, the middle layer comprised longitudinally elongated cells fitting the lateral convexity of the taste bud, and the upper layer was imbricating flat cells along the upper portion of the taste bud. When fresh specimens were jointly treated with Triton X-100 and sonication, the taste buds were often detached and the cytoplasmic matrices of the perigemmal cells were effectively removed. Consequently, we were able to demonstrate an extensive network of the subplasmalemmal keratin bundles of the perigemmal cells. The framework appeared either as a thin lacework, a thick fence-like structure, or a lattice work in the basal, middle, and upper layers, respectively. The thin lacework in the basal layer was considered to be a developing process of the framework. The thick fence-like structure in the middle layer probably plays a primary role in supporting the taste bud. The latticework in the upper layer is believed to reflect a remodeling in reducing the keratin framework.

Animals↗
PubMed2003

Brain-derived neurotrophic factor-, neurotrophin-3-, and tyrosine kinase receptor-like immunoreactivity in lingual taste bud fields of mature hamster.

The neurotrophins brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), as well as their respective tyrosine kinase (Trk) receptors, TrkB and TrkC, influence peripheral target cell innervation, survival, and proliferation. In the mature taste system the role of neurotrophins and their receptors is not known. The mature hamster is an intriguing model because anterior lingual fungiform, unlike posterior lingual foliate and circumvallate, taste buds survive denervation. In light of this difference, we examined whether the degree of neurotrophin- or neurotrophin receptor-like immunoreactivity (IR) normally differs among lingual gemmal fields. In single- and double-labeled immunofluorescent experiments, 3,209 taste bud sections (profiles) from 13 hamsters were examined for immunopositive gemmal cells or nerve fibers using antibodies to BDNF and NT-3, their respective receptors TrkB and TrkC, and the neural marker ubiquitin c-terminal hydrolase L-1 [protein gene product (PGP) 9.5]. In each gemmal field, more than 75% of taste bud profiles showed immunopositivity to BDNF, NT-3, and TrkB. Across bud fields, BDNF-, TrkB-, and BDNF/TrkB-like IR, as well as PGP 9.5 and PGP 9.5/BDNF-like IR in centrally located, fungiform bud cells was greater (P < 0.0001 to P < 0.002) than in circumvallate or foliate buds. Within bud fields, the number of BDNF-like, labeled bud cells/bud profile was greater than that for NT-3-like IR in fungiform (P < 0.0002) and foliate (P < 0.0001) buds. TrkC was immunonegative in gemmal cells. The average density of TrkB- and TrkC-like fiber IR was more pronounced in fungiform than posterior gemmal-bearing papillae. Thus, fungiform papillae, whose taste buds are least affected by denervation, exhibit specific neurotrophin and receptor enrichment.

Animals↗
PubMed1988

Changes in soft palate taste buds of rats due to aging and zinc deficiency--scanning electron microscopic observation.

The effects of aging and zinc deficiencies on taste were studied. The soft palate of zinc-deficient old rats, prepared by feeding with a zinc-deficient diet, were studied by a light microscope and a scanning electron microscope, and comparative examination was made on the morphological changes in soft palate papillae and taste buds of young normal rats and control old rats. In the case of young normal rats, papillae similar to lingual fungiform papillae were observed on the soft palate; one taste bud per one papilla was observed. The papillae were concentrated in the central area of the soft palate continuing from the hard palate. In the case of old rats, decrease in the number of papillae, flattening of papillae, exfoliation and atrophy of mucosal epithelium and leveling of microplicae were observed. In the case of zinc-deficient old rats, the above-mentioned tendencies were more significant. While dense substance and microvilli were observed in taste pores of taste buds of young normal rats, these were found to decrease or disappear in the zinc-deficient old rats.

Aging↗
PubMed2005

Glutamate-induced cobalt uptake elicited by kainate receptors in rat taste bud cells.

Glutamate-induced cobalt uptake reveals non-N-methyl-D-aspartate (non-NMDA) glutamate receptors (GluRs) in rat taste bud cells. However, it is not known which type of non-NMDA glutamate receptors is involved. We used a cobalt staining technique combined with pharmacological tests for kainate or alpha-amino-3-hydroxy-5-methyl-isoxazole-propionic acid (AMPA) receptors and/or immunohistochemistry against subunits of GluRs to examine the presence of non-NMDA receptors in rat foliate tastebud cells. Cobalt uptake into taste cells was elicited by treating taste buds with glutamate, kainate or SYM 2081, a kainate receptor agonist. Treating taste buds with AMPA or fluorowillardiine did not stimulate significant cobalt uptake. Moreover, 6-cyano-7-nitro-quinoxaline-2, 3-dione significantly reduced cobalt staining elicited by glutamate or kainate receptor agonists, but SYM 2206, an AMPA receptor antagonist, did not. Immunohistochemistry against subunits of GluRs reveals GluR6 and KA1-like immunoreactivity. Moreover, most glutamate-induced cobalt-stained cells showed GluR6 and KA1-like immunoreactivity. These results suggest that glutamate-induced cobalt uptake in taste cells occurs mainly via kainate type GluRs.

6-Cyano-7-nitroquinoxaline-2,3-dione↗