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PubMed2004

Laryngeal chemosensory clusters.

The expression of molecules involved in the transductory cascade of the sense of taste (TRs, alpha-gustducin, PLCbeta2, IP3R3) has been described in lingual taste buds or in solitary chemoreceptor cells located in different organs. At the laryngeal inlet, immunocytochemical staining at the light and electron microscope levels revealed that alpha-gustducin and PLCbeta2 are mainly localized in chemosensory clusters (CCs), which are multicellular organizations differing from taste buds, being generally composed of two or three chemoreceptor cells. Compared with lingual taste buds, CCs are lower in height and smaller in diameter. In laryngeal CCs, immunocytochemistry using the two antibodies identified a similar cell type which appears rather unlike the alpha-gustducin-immunoreactive (IR) and PLCbeta2-IR cells visible in lingual taste buds. The laryngeal IR cells are shorter than the lingual ones, with poorly developed basal processes and their apical process is shorter and thicker. Some cells show a flask-like shape due to the presence of a large body and the absence of basal processes. CCs lack pores and their delimitation from the surrounding epithelium is poorly evident. The demonstration of the existence of CCs strengthens the hypothesis of a phylogenetic link between gustatory and solitary chemosensory cells.

Animals↗
PubMed2004

Rat gustatory neurons in the geniculate ganglion express glutamate receptor subunits.

Taste receptor cells are innervated by primary gustatory neurons that relay sensory information to the central nervous system. The transmitter(s) at synapses between taste receptor cells and primary afferent fibers is (are) not yet known. By analogy with other sensory organs, glutamate might a transmitter in taste buds. We examined the presence of AMPA and NMDA receptor subunits in rat gustatory primary neurons in the ganglion that innervates the anterior tongue (geniculate ganglion). AMPA and NMDA type subunits were immunohistochemically detected with antibodies against GluR1, GluR2, GluR2/3, GluR4 and NR1 subunits. Gustatory neurons were specifically identified by retrograde tracing with fluorogold from injections made into the anterior portion of the tongue. Most gustatory neurons in the geniculate ganglion were strongly immunoreactive for GluR2/3 (68%), GluR4 (78%) or NR1 (71%). GluR1 was seen in few cells (16%). We further examined if glutamate receptors were present in the peripheral terminals of primary gustatory neurons in taste buds. Many axonal varicosities in fungiform and vallate taste buds were immunoreactive for GluR2/3 but not for NR1. We conclude that gustatory neurons express glutamate receptors and that glutamate receptors of the AMPA type are likely targeted to synapses within taste buds.

Animals↗
PubMed1990

Specificity of amiloride inhibition of hamster taste responses.

Amiloride, a blocker of epithelial sodium channels, was found to have significant effects on electrophysiological and behavioral taste responses in the golden hamster (Mesocricetus auratus). Recordings from the whole chorda tympani nerve showed that amiloride rapidly, reversibly, and competitively inhibited responses to NaCl applied to the anterior tongue. The apparent dissociation constant for amiloride binding, extrapolated to zero NaCl concentration, was 10 nM, a value comparable to estimates for various transporting tight epithelia. Recordings from single chorda tympani nerve fibers showed that 10 microM amiloride completely inhibited responses of Na-selective N fibers but had minimal effect on responses of electrolyte-sensitive H fibers, even though both types of fibers responded well to 0.1 M NaCl. Sucrose responses were not affected by amiloride. Addition of 100 microM amiloride to 0.1 M NaCl consistently increased consumption of NaCl in two-bottle drinking tests. These data suggest that one mechanism by which the taste of NaCl is sensed, which does not require adsorption or a second messenger, involves entry of Na+ into taste bud cells through an amiloride-blockable sodium channel. Taste bud cells utilizing this mechanism exclusively activate N fibers, which are involved in the control of NaCl intake. A different mechanism for the detection of NaCl and other electrolytes is utilized by taste bud cells that activate H fibers.

Action Potentials↗
PubMed1984

Intracellular taste cell responses of mouse.

Intracellular recordings of membrane potentials of taste cells in mouse taste bud were made using a glass microelectrode filled with procion yellow dye solution. The recorded taste cell was injected with procion yellow dye solution. Each taste bud preparation was observed under a fluorescence microscope and if a stained taste cell was not found in the taste bud preparation, the responses were negated. Sucrose produced a depolarization response and the response was accompanied by resistance increase, whereas NaCl produced a depolarization, hyperpolarization or null response and the response was accompanied by resistance decrease in all cases. Most mouse taste cells showed a multiple sensitivity to four fundamental taste stimuli.

Animals↗
PubMed2003

Expression of metabotropic glutamate receptor group I in rat gustatory papillae.

Taste-metabotropic glutamate receptor 4 (taste-mGluR4) and the heteromers of T1R1 and T1R3 are candidate receptors involved in the sense of umami (monosodium glutamate) taste. Although the expression of group III mGluRs (taste-mGluR4) has been demonstrated in taste tissues, no mention has been made of the expression of group I mGluRs (mGluR1 and mGluR5) in taste tissues. We examined the expression of mGluR1 and mGluR5 in rat gustatory tissues by using reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, immunohistochemistry and immunoelectron microscopy. RT-PCR assay showed that mGluR1 alpha and mGluR1 beta mRNAs were expressed in circumvallate papillae, but mGluR5 mRNA was not expressed. The positive signals of mGluR1 mRNA were detected only in circumvallate taste buds by in situ hybridization analysis. In cryosections of fungiform, foliate and circumvallate papillae, the antibody against mGluR1 alpha gave intense labeling on the taste hairs in all taste pores examined. In the developing taste buds, the positive signals of mGluR1alpha in taste hairs gradually increased with the increase in number of taste bud cells. These results show that, in addition to taste-mGluR4 and the heteromer of T1R1 and T1R3, mGluR1 alpha may function as a receptor for glutamate (umami) taste sensation.

Animals↗
PubMed2001

Amiloride-sensitive sodium currents in identified taste cells of the frog.

Sodium ions occurring in food are thought to be detected, at least in part, through specific amiloride-sensitive, sodium channels (ASSCs) localized in taste receptor cells. Cells within taste buds are morphologically heterogeneous, and include taste receptor cells and other cells that could perform a support or even transduction role. It is not known whether subsets of the taste bud cells express ASSCs, and whether the properties of these channels are similar. By applying the patch-clamp technique to morphologically distinct cells, the supporting wing cells, isolated from the frog taste disk, I have found functional ASSCs that are moderately sensitive to amiloride (Ki 3-4 microM) and which are distinctly lower in affinity for amiloride than reported frog taste receptor cells (Ki 0.2 microM). These results support the hypotheses of the existence of distinct, functional ASSCs in different cell morphotypes, at least in frog taste organs.

Amiloride↗
PubMed1975

Spatial distribution of rat fungiform papillae.

The objective of this study was to determine the spatial distribution of fungiform papillae on the rat's tongue. Since each fungiform papilla in the rat has a single taste bud, the spatial distribution of fungiform papillae is equivalent to the location of taste buds on the anterior tongue. A mean total number of 187 fungiform papillae per tongue were found which were about equally divided between the two lateral halves of the tongue. Over 50% of the total number of fungiform papillae were located on the tongue tip for an average density of 3.4 papillae/mm2,while the dorsal surface of the tongue had an average density of 1.3 papillae/mm2 of tongue surface. Papillae were absent on the dorsal midline, but a paracentral line of papillae running from anterior to posterior was a consistent finding. Though not identical, the distribution of papillae was essentially the same on different tongues. The functional significance of the papilla distribution is not understood, but electrophysiological experiments show evidence of neural interaction of papillae which are clustered together. The distribution of papillae and the distribution of nerve fibers which innervate them must be evaluated together in order to appreciate the significance of the distribution of fungiform papillae and their associated taste buds.

Animals↗
PubMed2002

Sensitive periods for the effect of dietary sodium restriction on intact and denervated taste receptor cells.

Unilateral chorda tympani nerve (CT) section combined with dietary sodium restriction leads to striking alterations in sodium taste function. The regenerated rat CT exhibits deficits in sodium sensitivity, and surprisingly, there are also functional alterations in the intact, contralateral nerve. The studies presented here describe the functional "sensitive periods" for these aberrations and the number of taste buds present during corresponding stages. The regenerated CT is sensitive to dietary sodium restriction during the first 2 wk after denervation, whereas the intact CT is sensitive to dietary manipulation during the first week postsection. Therefore, distinct mechanisms are responsible for the effects of sodium restriction combined with denervation, because separate sensitive periods exist for the regenerated and intact CT nerves. Identification of mature taste buds with an antibody directed at anti-keratin 19 revealed that there is a loss of ~85% of taste buds on the denervated side of the tongue under control and low-sodium diets within the first week postsection. Thus, sodium restriction does not differentially affect the loss of taste buds following denervation.

Animals↗
PubMed2000

Taste cells with synapses in rat circumvallate papillae display SNAP-25-like immunoreactivity.

SNAP-25 is a 25 kDa protein believed to be involved in the processes of membrane fusion and exocytosis associated with neurotransmitter release. In the present study we present evidence that SNAP-25-like immunoreactivity can be used as a marker for taste cells with synapses in rat circumvallate papillae. SNAP-25 immunoreactivity is present in most intragemmal nerve processes and a small subset of taste cells. Intense immunoreactivity is associated with the nerve plexus located below the base of the taste bud. Of a total of 87 taste cells with synapses onto nerve processes, 80 of the presynaptic taste cells had SNAP-25 immunoreactivity. The association of SNAP-25 immunoreactivity with taste cells possessing synapses suggests that these cells may be gustatory receptor cells. Because this SNAP-25 antibody can label taste cells with synapses, it may also serve as a useful tool for future studies correlating structure with function in the taste bud.

Animals↗
PubMed1996

Localization of substance P NK-1 receptors in rat tongue.

In rat tongue, neurons containing substance P terminate in connective tissue, in taste buds, and in lingual epithelium surrounding taste buds in fungiform, foliate and circumvallate papillae. Although many functions have been attributed to these neurons, virtually nothing is known about their physiological function. As a step towards this end, immunocytochemical methods were used to identify the NK-1 receptors (SPR) in rat tongue. SPR-IR was found in the basolateral membranes of taste cells in fungiform, circumvallate and foliate papillae. SPR-IR was not found in the dorsal epithelium or in any structure that could be clearly identified as a neuron. SPR-IR was also found in von Ebner's glands in circumvallate and foliate papillae and in blood vessels in connective tissue in all three papillae. These data suggest that substance P may play a role in taste and/or in oral pain.

Amino Acid Sequence↗
PubMed1977

Adenylate cyclase in paraneurons. A histochemical study.

Adenylate cyclase activity in the taste buds of the papilla vallata of the tongue, in the EC cells of the duodenal mucosa and in the chromaffin cells of the adrenal medulla of the hamster was histochemically examined using the method invented by Wagner and co-workers (1972). Two types of taste bud cells were distinguished. The dark cell was characterized by a dark cytoplasm: the light cell, by a clear-looking cytoplasm. When AMP-PNP was used as a substrate, and intense activity was demonstrated along the microvilli of all cells in the taste bud. Much weaker activity was demonstrated on the lateral cell membrane. After the use of ATP, the reaction products were found rather evenly distributed over the surface of the taste bud cell. The synaptic area on the surface of the light cell, however, was devoid of reaction products. Among the several kinds of basal-granulated gut cells examined, the EC cell of the duodenal mucosa was one. An intense activity was demonstrated along the microvilli after the use of AMP-PNP. When ATP was used as a substrate, a positive reaction was demonstrated on the lateral cell membranes as well as on the luminal microvilli; the reaction on the microvilli was much stronger than that on the lateral cell membrane. The chromaffin cells of the adrenal medulla showed almost no activity with AMP-PNP. However, when ATP was used, the plasma membrane of Schwann cells and axons showed an intense reaction. The cell membrane of the adrenaline and noradrenaline-storing cells showed a slightly positive reaction. The synaptic area of chromaffin cell was always negative in the reaction. The positive adenylate cyclase activity in the gustatory cells and gut endocrine cells may have some relation to the stimulus reception. This is in keeping with the observation that adrenal medulla chromaffin cells, which were embedded in the internal milieu, did not react to adenylate cyclase.

Adenosine Monophosphate↗
PubMed2000

In situ Ca2+ imaging reveals neurotransmitter receptors for glutamate in taste receptor cells.

The neurotransmitters at synapses in taste buds are not yet known with confidence. Here we report a new calcium-imaging technique for taste buds that allowed us to test for the presence of glutamate receptors (GluRs) in living isolated tissue preparations. Taste cells of rat foliate papillae were loaded with calcium green dextran (CaGD). Lingual slices containing CaGD-labeled taste cells were imaged with a scanning confocal microscope and superfused with glutamate (30 micromter to 1 mm), kainate (30 and 100 micrometer), AMPA (30 and 100 micrometer), or NMDA (100 micrometer). Responses were observed in 26% of the cells that were tested with 300 micrometer glutamate. Responses to glutamate were localized to the basal processes and cell bodies, which are synaptic regions of taste cells. Glutamate responses were dose-dependent and were induced by concentrations as low as 30 microm. The non-NMDA receptor antagonists CNQX and GYKI 52466 reversibly blocked responses to glutamate. Kainate, but not AMPA, also elicited Ca(2+) responses. NMDA stimulated increases in [Ca(2+)](i) when the bath medium was modified to optimize for NMDA receptor activation. The subset of cells that responded to glutamate was either NMDA-unresponsive (54%) or NMDA-responsive (46%), suggesting that there are presumably two populations of glutamate-sensitive taste cells-one with NMDA receptors and the other without NMDA receptors. The function of GluRs in taste buds is not yet known, but the data suggest that glutamate is a neurotransmitter there. GluRs in taste cells might be presynaptic autoreceptors or postsynaptic receptors at afferent or efferent synapses.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1999

Ultrastructure of taste receptor cells in active and hibernating ground squirrels.

Differences in taste bud ultrastructure between active and low-temperature hibernation states were investigated in the Siberian ground squirrel, Citellus undulatus. Compared to active summer animals, taste bud volume and the morphology of the taste pore showed little change while an animal was hibernating. However, impressive differences were observed in nuclei and cytoplasmic organelles of all cells within taste buds. In low-temperature hibernation the nucleoli of elongated, non-dark cells had few, but large, fibrillar centres, a sign of inactivity. In the cytoplasm, the number of free polyribosomes (polysomes) was sharply decreased; ribosomes were seen mainly as (non-synthesizing) monosomes and more seldom as membrane-associated ribosomes. Profiles of endoplasmic reticulum (ER) were reduced, to the extent that only separate and rare cisternae of smooth and rough ER remained. The large vacuoles, which are typically found in many taste cells of active animals, were absent during hibernation, and the Golgi apparatus appeared to be disassembled into numerous vesicles. Of these, many had small diameters near 60 nm, while a few had larger diameters near 300 nm. Secretory organelles (dense granules in dark cells and dense-cored vesicles in type III cells) were rare during hibernation, the lateral plasma membrane was smooth, and signs of exocytosis were not found. These changes suggest reduced protein synthesis and reduced sensory function during hibernation.

Animals↗
PubMed1998

Somatostatin administration alters taste preferences in the rat.

The effects of long-term and relatively constant concentrations of somatostatin (SRIF) were tested in rats to investigate its influence on taste preferences, fluid intake, and taste bud topography of the tongue. In SRIF-treated rats, intake of 3 x 10(-2) M NaCl and 6 x 10(-2) M sucrose solution decreased, whereas that of 3 x 10(-5) M quinine-HCl and 10(-3) M HCl (pH = 3) solutions increased significantly; distilled water intake and total fluid consumption remained almost unchanged. The light/dark cycle of consumption of NaCl solution was modified in a dose-dependent manner, but that of dwater, total fluids, and other solutions was not. Histologic exam by light microscopy showed that taste bud distribution on the tongue appeared to be altered, but the results only approached statistical significance. Given that it is possible to remove virtually all taste buds in the oral cavity and have only modest effects on preferences and aversion, it seems very unlikely that the small changes in taste bud distribution are related to the intake of sapid solutions. Since SRIF treatment influenced all sapid stimuli, it seems more likely that the changes are based on a blunted responsiveness in the gustatory system as a whole.

Acids↗
PubMed1977

Circumvallate papilla of dog following suture of the hypoglossal and glossopharyngeal nerves.

20 adult dogs were classified into five groups; in two animals of each group hypoglossa-glossopharyngeal suturing was done. In the other two animals glossopharyngeal nerve transection with concomitant central segment avulsion was done and these two animals were used as controls. The animals of the five groups were sacrified at 4-week intervals starting by the first group on the 4th post-operative week and ending by the fifth group on the 20th week; the circumvallate papillae were studied. On the 4th week following either operative procedure, few taste buds persisted on the circumvallate papillae. Invasion of the papillae by regenerating hypoglossal fibres from the 8th week onwards was not followed by any appreciable increase in the number of taste buds. The difference in number of taste buds between hypoglossal-glossopharyngeal suture and glossopharyngeal avulsion procedures was not statistically significant. from the 8th weeks following cross-innervation the reaction for acetylcholinesterase was more intense than in denervated papillae which showed a persistent weakly positive reaction up to the 20th post-operative week.

Acetylcholinesterase↗
PubMed2005

Lingual deficits in neurotrophin double knockout mice.

Brain-derived neurotrophic factor (BDNF) and Neurotrophin 3 (NT-3) are members of the neurotrophin family and are expressed in the developing and adult tongue papillae. BDNF null-mutated mice exhibit specific impairments related to innervation and development of the gustatory system while NT-3 null mice have deficits in their lingual somatosensory innervation. To further evaluate the functional specificity of these neurotrophins in the peripheral gustatory system, we generated double BDNF/NT-3 knockout mice and compared the phenotype to BDNF(-/-) and wild-type mice. Taste papillae morphology was severely distorted in BDNF(-/-) xNT-3(-/-) mice compared to single BDNF(-/-) and wild-type mice. The deficits were found throughout the tongue and all gustatory papillae. There was a significant loss of fungiform papillae and the papillae were smaller in size compared to BDNF(-/-) and wild-type mice. Circumvallate papillae in the double knockouts were smaller and did not contain any intraepithelial nerve fibers. BDNF(-/-) xNT-3(-/-) mice exhibited additive losses in both somatosensory and gustatory innervation indicating that BDNF and NT-3 exert specific roles in the innervation of the tongue. However, the additional loss of fungiform papillae and taste buds in BDNF(-/-) xNT-3(-/-) mice compared to single BDNF knockout mice indicate a synergistic functional role for both BDNF-dependent gustatory and NT-3-dependent somatosensory innervations in taste bud and taste papillae innervation and development.

Animals↗
PubMed1990

Neural control of ectopic filiform spines in adult tongue.

The tongue surface directly above a fungiform taste bud is flat, thinly keratinized, and free of filiform spines. We examined fungiform papillae in serial sections of rat and gerbil tongues after unilateral transection of the chorda-lingual nerve had caused many fungiform taste buds to degenerate. Such empty fungiform papillae often formed a solitary keratinized outgrowth that closely resembled the spine of an ordinary filiform papilla. By six months an ectopic spine was found on 61% of empty fungiform papillae, but never on fungiform papillae that contained a taste bud. Experimental innervation of the tongue reduced the incidence of ectopic filiform spines in proportion to the cross-sectional area of the trigeminal nerve branches tested (the mylohyoid nerve, the lingual nerve, lingual + mylohyoid or lingual + auriculotemporal nerves). The chorda tympani nerve was 60 times more effective than trigeminal nerves in preventing ectopic filiform spines. We suggest that positive and negative trophic actions are normal characteristics of taste axons, for they promote the formation of taste buds and prevent the expression of ectopic filiform spines. By preventing the outgrowth of ectopic spines on fungiform papillae, taste axons maintain a thinly keratinized apical surface that can be breached by the taste receptor cells.

Animals↗
PubMed1982

Scanning electron microscopic and histochemical studies of foliate papillae in the rabbit, rat and mouse.

The foliate papillae of the rabbit, rat and mouse were studied by scanning electron microscopy and histochemistry. The papillae consisted of folds and grooves located on the posterolateral margin of the tongue in front of the circumvallate papillae. The numbers of folds and taste buds varied among the three animals species. Scanning electron microscopy showed that in longitudinal sections the taste buds were oval in shape and their pores were surrounded by microvilli. The reaction product of alkaline phosphatase could only be demonstrated in the superficial epithelium of the rabbit as well as in the mouse foliate papillae, but it also diffused into the taste buds in the rat. The intensity and distribution of the reactions of adenosine triphosphatase, acetylcholinesterase and butyrylcholinesterase were identical to those reported by other investigators in spite of differences in animal species and histochemical techniques employed.

Adenosine Triphosphatases↗