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PubMed2004

Immunohistochemical localization of monoamine oxidase type B in the taste bud of the rat.

We have used immunohistochemistry to examine the subcellular localization of monoamine oxidase type B (MAO-B) in the taste bud of the rat circumvallate papilla. Electron microscopy showed that MAO-B was localized to the outer membranes of mitochondria in nerve terminals of afferent and efferent fibers, as well as in taste bud cells. MAO-B also existed on the mitochondrial outer membranes within myelinated and unmyelinated axons in the lamina propria beneath the taste bud. It is suggested that MAO-B-containing mitochondria are localized in peripheral branches and their terminals of sensory neurons for taste. The present study is the first to reveal the localization of MAO-B in sensory organs.

Animals↗
PubMed1999

NT4/5 mutant mice have deficiency in gustatory papillae and taste bud formation.

Neurotrophins are key determinants for controlling the survival of peripheral neurons during development. Brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT4/5) exert their action through a common trkB receptor but independently support gustatory sensory neurons. To assess the role of NT4/5 during development, we examined the postnatal development and maintenance of fungiform taste buds in mice carrying a deletion of NT4/5. The absence of NT4/5 results in embryonic deficits in gustatory innervation and a reduced number of fungiform papillae at birth. No degenerative deficits of fungiform papillae were observed for the first 3 weeks of postnatal development. However, these remaining fungiform papillae were smaller in appearance and many did not contain taste pores. By postnatal day 60, there was 63% decrease in the number of fungiform papillae, and remaining papillae were smaller in size or modified into filiform-like spines. These papillae had either no taste bud or a taste bud with a reduced number of taste cells compared to controls. These findings demonstrate that the NT4/5 gene functions in the maintenance of fungiform gustatory papillae and raises the possibility for an earlier role in development.

Animals↗
PubMed1993

Ultrastructural evidence for a binding substance to the sweet-tasting protein thaumatin inside taste bud pores of rhesus monkey foliate papillae.

Thaumatin is a protein that tastes intensely sweet only to Old World monkeys and to higher primates, including man. Here we used pre-embedding ultrastructural methods to study the distribution of thaumatin in apical regions of Rhesus monkey foliate papillae, using thaumatin conjugated to 5 nm gold particles. With freeze-substitution we saw that gold-labeled thaumatin bound to an electron-opaque, sponge-like secretory substance inside the taste bud pores. Labeled thaumatin was found at the surface of the secretory substance even deep inside the pore, where other, unlabeled cellular structures surrounded the substance. With freeze-fracture deep-etching the secretory substance that bound the thaumatin-gold particles appeared coarsely granular. There was no labeling of any other taste bud pore structure, including microvilli and small membrane-lined vesicles. Pre-incubation with an excess of unlabeled thaumatin inhibited binding with gold-labeled thaumatin. The results suggest that the secretory substance had the greatest affinity of all taste pore structures to the sweet-tasting compound under our experimental conditions. Therefore, gustatory reception probably involves various taste compound binding structures, microvilli, and also secretory substances like the one described here which bound thaumatin. We speculate that the secretory substance may bind taste stimuli and serve as an intermediate between stimuli and receptors. It could be involved in stimulus removal or delivery or both.

Animals↗
PubMed1999

Transduction for sweet taste of saccharin may involve both inositol 1,4,5-trisphosphate and cAMP pathways in the fungiform taste buds in C57BL mice.

The transduction pathways for sweet and bitter tastes were investigated with assays of inositol 1,4,5-trisphosphate (IP3) and cyclic adenosine monophosphate (cAMP) levels in mouse fungiform taste buds. Recordings of taste responses were also made in the chorda tympani nerve. Stimulation of the tongue with saccharin elicited a significant increase in IP3 levels in the fungiform papilla only at 20 mM but in cAMP levels at 3 and 20 mM, without affecting those of the nonsensory epithelial tissue. Formation of both IP3 and cAMP induced by 20 mM saccharin was suppressed by pretreatment of the tongue with pronase, a proteolytic enzyme which specifically inhibits sweet responses. Quinine and denatonium elicited both significant increases in IP3 levels at a concentration of 20 mM and slight decreases in cAMP levels at concentrations of 1-20 mM in the fungiform papilla. Recording of the chorda tympani nerve showed good responses by saccharin, quinine, and denatonium at concentrations of 1 mM and higher. These results suggest that the fungiform taste cells in C57BL mice have pronase-sensitive receptors for saccharin, coupled to both the IP3 and the cAMP pathways; the former participates only at high concentration, while the latter acts from low to high concentrations. The results also do not rule out the possibility that a phosphodiesterase-mediated cAMP decrease may be involved in bitter transduction for quinine and denatonium.

Animals↗
PubMed1993

Merkel-like basal cells in Necturus taste buds contain serotonin.

Several types of cells have been identified in vertebrate taste buds, including dark cells, light cells, intermediate cells, type III cells, and basal cells. The physiological roles of these cell types are not well understood, especially those of basal cells. In this paper we show that there are two types of basal cells in taste buds from Necturus maculosus. One type of basal cell is an undifferentiated cell, presumably a stem cell. By combining light microscopic immunocytochemistry with electron microscopy, we show that the other type of basal cell is positive for serotonin-like immunoreactivity and that these cells have ultrastructural features similar to those found in cutaneous Merkel cells. Based on these findings, and the fact that the Merkel-like taste cells have been shown to make synaptic contacts with adjacent taste cells and with innervating nerve fibers, we conclude that these Merkel-like basal taste cells are serotonergic interneurons.

Animals↗
PubMed1978

[Modulating effect of the salivary glands upon differentiation and maturation of taste bud cells in the rat (author's transl)].

It is currently considered that the sensitive nerves of the papillary plexus are solely responsible for the normal differentiation of taste bud cells in the circumvallate papillae of the rat. The effect of syallectomy on taste bud cells was studied. Evaluation of results was performed through cell counts. The results demonstrate that the major salivary glands are quite important in both differentiation and maturation of taste bud cells.

Cell Count↗
PubMed1994

Ontogenesis and taste bud cell turnover in the chicken. I. Gemmal cell renewal in the hatchling.

Taste bud cell turnover rate was examined in oral epithelium of the precocial chick, which at hatching contains the adult complement of taste buds. Forty newly hatched chicks received single or double pulse injections of tritiated thymidine (specific activity was 6.7 Curies/millimole; dosage was 0.5 microCuries/g body weight, intraperitoneally). Anterior mandibular epithelium was processed for light microscopic autoradiography at 2 and 16 hours, as well as 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18, and 20 days after the initial pulse. In a coded and randomized procedure, the section (7 microns) through the bud's center was selected for counting > or = 6 silver grains over round-clear and gracile-dense gemmal cell nuclei. The mean number of labelled cells/bud varied significantly (P < or = 0.01) during the first four posthatch days, yielding the fastest gemmal cell turnover rates (3.4-4.4 days) yet reported in vertebrates. Average bud diameter also significantly changed during the first four posthatch days, and was reflected in shifts of the distribution of 40-69 microns and > or = 70 microns diameter buds. Both an increase in labelled bud cells and bud diameter during the first two posthatch days may reflect high proliferation rates in initially maturing buds. Subsequent decrease in bud diameter between 2 and 3 days postinjection may indicate splitting of large-diameter (> or = 70 microns) buds and/or normal bud cell death due to failure of sensory afferentation. Bud-splitting alone, however, cannot account for significant decreases in bud cell label which did not occur before 4-6 days postinjection.

Animals↗
PubMed2002

The 'goatee' of goatfish: innervation of taste buds in the barbels and their representation in the brain.

Goatfish use a pair of large chin barbels to probe the sea bottom to detect buried prey. The barbels are studded with taste buds but little else is known about the neural organization of this system. We found that the taste buds of the barbel are innervated in a strict orthogonal fashion. The barbel is innervated by a main nerve trunk running in the core of the barbel. A longitudinal nerve bundle originates from the main trunk and, after running a short distance distally, divides into two circumferential nerve bundles (CNB) extending respectively, medially and laterally around the barbel. Approximately 15 CNBs innervate each 1 mm length of barbel. At each transverse level, the CNB innervates two clusters of taste buds, each containing 14 end-organs. The primary taste centre in the brain is similarly extraordinary. The sensory inputs from the barbel terminate in a derived dorsal facial lobe, which has a highly convoluted surface forming a multitude of tubercles. Electrophysiological mapping experiments show that the entire barbel is somatotopically represented in a recurved elongate tubular fashion within the dorsal facial lobe.

Animals↗
PubMed1983

New details of the ultrastructure (TEM, SEM) of taste buds in fishes.

Quantitative distribution of the taste buds (TB) in different parts of the body and the fine structure of the TB components are described in Cobitis taenia L. No evidence of synaptic contacts between any cellular components in the TB has been found. The afferent synapses have been recognized only at the gustatory cells and at the basal cell. The microvillar processes on the upper side of the basal cell are demonstrated for the first time in fishes. These processes resemble those at the basal cells in the TB of tetrapods and at the Merkel cells, scattered in the epidermis of all vertebrates. Since the basal cells of fish TB correspond also to other criteria of the Merkel cells, its mechanoreceptive function in the TB is discussed. A relatively large number of atypical gustatory cells has been found in the studied material. As the examined specimens of C. taenia lived for a long time in aquarium conditions, it may be supposed that these gustatory cells are damaged by pollutants introduced mainly with food such as Tubifex. For purposes of comparison, a related species, Misgurnus fossilis L., was used in the study.

Animals↗
PubMed1989

Olfactory and nasal respiratory epithelia, and foliate taste buds visualized with rapid-freeze freeze-substitution and Lowicryl K11M embedding. Ultrastructural and initial cytochemical studies.

Rat olfactory and respiratory epithelia and Rhesus monkey taste buds were studied with rapid-freeze, acetone/0.1% uranyl acetate freeze-substitution and low-temperature Lowicryl K11M embedding, usually in the absence of other chemical fixation and cryoprotection procedures. Ultrastructural features of mucus, cytoplasm, including cytoskeletons, and membranes were better retained than with conventional methods. Some major examples: The mucus of the olfactory epithelium consisted of a single layer; that of the respiratory epithelium had an electron-opaque sol layer surrounding cilia and microvilli below a thin laminated electron-lucent gel layer. Taste-bud pores displayed a foam-like opaque secretory product, resembling the contents of secretory granules within Type I taste-bud cells. The electron-opacity of cytoplasmic matrices sometimes obscured features such as radial spokes of respiratory cilia. Membranes had smooth outlines; those of olfactory receptor cell cilia were more electron-opaque than those of olfactory supporting cell microvilli and respiratory cilia. Membranous monolayers of many respiratory cilia across large arrays often partially split apart, all in the same direction. The space between those monolayers contained an electron-lucent substance. Preliminary cytochemistry on olfactory and nasal respiratory epithelial samples with the lectin Concanavalin A (Con A) and antibodies against olfactory marker- and odorant-binding proteins and, in taste only, the sweet-tasting protein thaumatin, were sufficiently successful to warrant further endeavors.

Acrylic Resins↗
PubMed1976

An ultrastructural study on the development of vallate taste buds of the golden Syrian hamster.

An ultrastructural developmental study of hamster vallate taste buds was undertaken to demonstrate the sequential morphodifferentiation of their various cellular components. Under the neurogenic influence of the glossopharyngeal nerve, the undifferentiated epithelial cells of the vallate papilla first acquired fine structure features similar to those seen in the perigemmal adult peripheral cells and the gemmal basal cells. As the development progressed, the relatively undifferentiated basal cells appeared to differentiate into dark and light cell precursors. Mature light cells were frequently noted chronologically before any fully mature dark cells were observed. Transition from light to dark cells, or vice versa, was not noted at any time throughout the investigation, suggesting that light and dark cells originate as separate cell lines from the basal cells of the taste bud proper.

Age Factors↗
PubMed1971

Do unique proteins exist in taste buds?

Proteins in papillae on the bovine tongue were analyzed by semi-micro, polyacrylamide gel electrophoresis. All the proteins in the papillae with taste buds were observed to be common to proteins in the surrounding epithelium without taste buds. The protein band which was reported to form a weak complex with compounds called sweet by man was also found in all parts of the tongue epithelium. The receptor molecules for chemical stimuli may be distributed in all the cells of the tongue epithelium or the content of receptor molecules in taste bud papillae may be extremely low.

Animals↗
PubMed1979

[Taste buds in the epithelium of the plica sublingualis of New World monkeys (author's transl)].

The Plica sublingualis of new world monkeys was studied microscopically. In Ateles there are approximately 1700 taste buds in the epithelium of the Plica sublingualis, they are fewer in number in Alouatta, Lagothrix, Aotus and are absent in Saimiri and Cebus. The taste buds are situated consistently at the tip of the Plica sublingualis and near the orifices of the submandibular and sublingual salivary glands. From this topographical coincidence it is inferred that the function of the taste buds at the Plica sublingualis might permit a comparison between the fresh saliva with the general saliva in the cavum oris along a gradient.

Animals↗
PubMed1983

On the presence, structure and probable functional role of taste buds located on the laryngeal surface of the epiglottis in some domestic animals.

The authors have performed a systematic investigation on the epiglottis to determine the number and topography of taste buds possibly present. These chemoreceptors are constantly present in the ruminants studied (goat, cattle), while their finding is always negative in the pig, horse and ass and varying in the other animal species examined. Taste buds are, in the main, fairly numerous and show typical structure in very young kids and calves. On the contrary, in adult subjects degenerated taste buds can be found and their number usually increases with age. Sometimes such pictures can be observed also in young animals. The probable functional role of chemoreceptors located on the laryngeal surface of the epiglottis has been examined.

Animals↗
PubMed1979

Freeze-fracture study of taste bud pores in the foliate papillae of the rabbit.

In freeze-fractured specimens of taste buds from the foliate papillae of rabbits, the intercellular spaces are separated from the pore of the taste bud by zonulae occludentes of the "tight-type". Below these tight junctions numerous desmosomes are found at irregular intervals. The epithelial cells adjacent to the pore are also joined by single strands of fusion. The microvilli arising from the neck of the type I cells have a high particle density. The microvilli of type II cells and especially the short microvilli of peripherally situated cells have a lower intramembranous particle density. The single microvillus of type III cells has a very large diameter and is longer than the other microvilli. It contains a few larger intramembranous particles and vesicle-like protrusions of the membrane facing the cytoplasm. Transverse fracturing reveals a filamentous fine structure in all microvilli. The physiological implications of these observations are discussed.

Animals↗
PubMed1986

Immunohistochemical localization of keratin in the taste buds of rat vallate papillae.

Keratin detected with anti-human whole keratin serum, raised in rabbits by injection of the isolated human whole keratin, was used as a histologic marker to study the origin of the cells in taste buds. Rat vallate papillae, including surrounding tissue, were processed for indirect immunofluorescent staining of ketatin. In the taste buds, most basal cells and some of the elongated cells were immunoreactive with anti-keratin serum, showing that most taste-bud cells, if not all, originate from cells of epithelial origin.

Animals↗
PubMedDate not supplied

[Microelectrode study of the cellular reactions of the taste bud in the frog Rana temporaria].

Microelectrophysiological studies reveal two types of cells in the taste bud of frog which differ by the level of their membrane potential. During vertical implantation of microelectrode through the apical part of the taste bud, the potential difference in the upper layer amounts to 15 mV. Further implantation of the electrode results in a stepwise decrease of the potential difference up to 27 mV. Cells of the deeper layer are located 12-24 micron lower from the apical surface. Stimulation of cells by solutions of chemical substances is accompanied by cell depolarization, its amplitude being proportional to stimulus concentration. The steepness of depolarization depends on the modality of the stimulus, being maximum for salts. The data obtained suggest that cells of the second layer, with a higher resting membrane potential level, are taste ones.

Animals↗
PubMed2006

Heterogeneous distribution of taste cells in facial and vagal nerve-innervated taste buds.

Input from the three gustatory nerves of vertebrates is used to evaluate the nutritional quality of food. In some species, these cranial nerves are modified to accomplish additional specific functions. For example, the facial nerve innervated taste buds distributed over the body surface of catfish aid food search. Physiological studies indicate that this extra-oral taste pathway is more sensitive to amino acids than either the glossopharyngeal or vagal systems of the oral cavity. The current investigation seeks to determine if differences in taste cell subtypes might contribute to the observed differences in sensitivity. The distributions of five low molecular weight metabolites, L-alanine, L-aspartate, L-glutamate, GABA, taurine and the tripeptide glutathione, were examined in 2118 individual taste cells innervated by either the facial or vagal nerve of the channel catfish, Ictalurus punctatus. The metabolite profiles of these cells were determined immunocytochemically and subjected to a k-means clustering algorithm. Fifteen cell classes with quantitatively different patterns of metabolite co-localization were identified. All but one small class of two cells were found in both facial and vagal nerve-innervated taste buds. Four classes (9% of the total cells) had high, two classes (17%) had intermediate and the remaining nine classes (74%) had low levels of GABA immunoreactivity. While the functional significance of differences in metabolite profile remains to be determined, taste cell classes were not uniformly distributed across vagal and facial nerve innervated taste buds and may provide an anatomical basis for previously reported differences in gustatory sensitivity.

Algorithms↗