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Results for “Taste Receptors, Type 2”

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PubMed1999

Baclofen alters ethanol-stimulated activity but not conditioned place preference or taste aversion in mice.

The present experiments examined the effects of the GABA(B) receptor agonist, baclofen, on the acquisition of ethanol-induced conditioned place preference (CPP) and conditioned taste aversion (CTA) in male DBA/2J mice. Mice in the CPP experiment received four pairings of ethanol (2g/kg) with a distinctive floor stimulus for a 5-min conditioning session (CS+ sessions). On intervening days (CS- sessions), mice received saline injections paired with a different floor type. On CS+ days, mice also received one of four doses of baclofen (0.0. 2.5, 5.0, or 7.5 mg/kg) 15 min before an injection of ethanol. For the preference test, all mice received saline injections, and were placed on a half-grid and half-hole floor for a 60-min session. Baclofen dose dependently reduced ethanol-stimulated activity, but did not alter the magnitude of ethanol-induced CPP at any dose. For the CTA experiment, mice were adapted to a 2-h per day water restriction regimen followed by five conditioning trials every 48 h. During conditioning trials, subjects received an injection of saline or baclofen (2.0 and 6.0 mg/kg) 15 min before injection of 2 g/kg ethanol or saline following 1-h access to a saccharin solution. Baclofen did not alter the magnitude of ethanol-induced CTA at any dose. In addition, baclofen alone did not produce a CTA. Overall, these studies show that activation of GABA(B) receptors with baclofen reduces ethanol-induced locomotor activation, but does not alter ethanol's rewarding or aversive effects in the CPP and CTA paradigms in DBA/2J mice.

Animals↗

PubMed2006

Group IIA phospholipase A(2) is coexpressed with SNAP-25 in mature taste receptor cells of rat circumvallate papillae.

The taste buds are composed of heterogeneous cell populations with diverse properties and at different stages of maturity. It is important to define the relationships between cell properties and cell maturity to understand the molecular events involved in intracellular taste signaling. In the present study, in situ hybridization analysis indicated that group IIA phospholipase A(2) (PLA(2)-IIA) is expressed in a subset of taste bud cells. Immunohistochemical studies showed that PLA(2)-IIA was expressed in a subset of cells expressing phospholipase Cbeta2, a molecule essential for taste signaling in taste receptor cells, and also that some PLA(2)-IIA-positive cells expressed gustducin (Ggust), a bitter-taste-signaling molecule. Although PLA(2)-IIA and Ggust were expressed at similar frequencies in taste buds, bromodeoxyuridine (BrdU) chase experiments indicated that the expression of Ggust began 2 days after BrdU injection, whereas the expression of PLA(2)-IIA commenced after 4 days. In addition, PLA(2)-IIA was coexpressed with SNAP-25, a synaptosomal-associated protein. These results indicated that PLA(2)-IIA is expressed in mature taste receptor cells that possess exocytotic machinery.

Animals↗

PubMedDate not supplied

The mammalian taste bud type III cell: a critical analysis.

Rabbit foliate tissue fixed in 2% paraformaldehyde and 2% glutaraldehyde, postfixed in OsO4, was embedded in Epon and sectioned and stained with uranyl acetate and lead citrate for ultrastructural analysis. Favorable serial sections contained an entire type III cell, demonstrating for the first time in a single preparation its most characteristic features. These are cytoplasm containing specific dense-cored vesicles concentrated in the base, masses of synaptic vesicles near typical chemical synapses with nerves, and the upper part of the cell ending in a blunt extension beyond the dense substance. It is emphasized in particular that specific dense-cored vesicles denote type III cells and larger dark granules denote type I cells. It is postulated that the type III cell is a special, but is not necessarily the only, gustatory receptor cell. Previous evidence from this and other laboratories is systematically reviewed to substantiate the validity of the cell type.

Animals↗

PubMed2006

Detection of NaCl and KCl in TRPV1 knockout mice.

Both amiloride-sensitive and -insensitive mechanisms contribute to NaCl taste transduction. The amiloride-sensitive mechanism relies on the epithelial Na(+) channel ENaC, which is widely expressed on the apical membrane of fungiform taste cells. The amiloride-insensitive mechanism, which predominates in circumvallate and foliate taste buds, was recently reported to involve a variant of the nonselective cation channel TRPV1. We performed 2-bottle preference and threshold experiments with TRPV1 knockout mice and wild-type (C57BL/6J) controls to test for NaCl preference and detection thresholds in the presence and absence of amiloride. Surprisingly, TRPV1 knockout mice not only detected NaCl in the presence of amiloride but they preferred NaCl over water at concentrations avoided by the wild-type mice. NaCl detection thresholds were between 2 and 3 mM for both genotypes. Amiloride increased the detection thresholds of wild-type mice but not knockout mice. The knockout mice also preferred 100 mM KCl compared with wild-type controls, suggesting that TRPV1 receptors may mediate a general aversive response to salts. Analyses of consumption data also revealed that TRPV1 knockout mice ingested more of the NaCl, with and without amiloride, and KCl solutions than the wild-type mice. However, comparisons of preference ratios and consumption volumes indicated that both wild-type and TRPV1 knockout mice avoided citric acid in quite a similar manner, suggesting that TRPV1 receptors do not mediate the detection of citric acid. These data, taken together, suggest that additional mechanisms must contribute to the amiloride-insensitive NaCl response.

Amiloride↗

PubMedDate not supplied

[Dysgeusias].

This is a review of multiple pathologic conditions associated with altered taste perception and identification. We stated the steps and the molecular basis of this sense. This paper includes two cases that exemplify two distinct types of dysgeusia; case, 1 a 48 year old man who had clinical manifestations of hypogeusia and dysgeusia for one year, probably secondary to air pollutants. Case 2, a 37 year old man who worked in the same factory and also had dysgeusia; we concluded that it was secondary to thermal and chemical agression of the oropharynx; his plasma and urinary levels of zinc were normal. Many medications and contaminants of air and water are related with changes in serum and urine levels of zinc, which is a determinant at several levels for the correct integration of the taste system. Namely it is important for synthesis of the metalloprotein, gustin, a parotid gland protein secreted into saliva, which in turns is very important to make union of the sapid substance (SS) with its receptor in the surface of the gustatory epithelium a the taste buds. Zinc is also related with neurotransmission of the electrical stimulus generated in the bud cell and ending in the central nervous system. There is an acute zinc loss syndrome, seen in patients treated with histidine, which simulates the steps in which taste sensation is integrated. A clinical approach for diagnosis of hypogeusic or dysgeusic patients must include a careful evaluation of the diat elements, an assesment of hereditary disorders, the type of work and contact with pollutants known to be related with dysgeusia. A special care regarding physical examination must be considered in particular a meticulous review of the oropharynx in order to diagnose inflammatory, neoplastic or neurological disorders. The levels of perception an identification of flavors: sweet, bitter, sour and salt, must be determined using the forced scale triple choice technic. Serum and urinary levels of zinc should be determined in each patient using a flameless atomic absorption spectrophotometer. A quantification of the activity of leucocyte alkaline phosphatase, a zinc metalloenzyme, is a useful aid, liver function tests. 13 and 14 determinations and serum protein electrophoresis are mandatory because many pathologic states of these organ systems are known to be related with disorders of taste. We wish to remark the important function of zinc in the taste system, the role of essential trace elements is receiving increased atention and these alterations are good examples of their clinical importance.

Adult↗

PubMed1998

Tonic GABAergic inhibition of taste-responsive neurons in the nucleus of the solitary tract.

The effects of gamma-aminobutyric acid (GABA) and the GABAA receptor antagonist bicuculline methiodide (BICM) on the activity of taste-responsive neurons in the nucleus of the solitary tract (NST) were examined electrophysiologically in urethane-anesthetized hamsters. Single neurons in the NST were recorded extracellularly and drugs (21 nl) were microinjected into the vicinity of the cell via a multibarrel pipette. The response of each cell was recorded to lingual stimulation with 0.032 M NaCl, 0.032 M sucrose, 0.0032 M citric acid and 0.032 M quinine hydrochloride (QHCl). Forty-six neurons were tested for the effects of GABA; the activity of 29 cells (63%) was inhibited by 5 mM GABA. Whether activity was elicited in these cells by repetitive anodal current stimulation (25 microA, 0.5 s, 0.1 Hz) of the tongue (n = 13 cells) or the cells were spontaneously active (n = 13 cells), GABA produced a dose-dependent (1, 2 and 5 mM) decrement in activity. Forty-seven NST neurons were tested for the effects of BICM on their responses to chemical stimulation of the tongue; the responses of 28 cells (60%) were enhanced by 10 mM BICM. The gustatory responses of 26 of these cells were tested with three concentrations (0.2, 2 and 10 mM) of BICM, which produced a dose-dependent increase in both spontaneous activity and taste-evoked responses. Nine of these neurons were sucrose-best, seven were NaCl-best, eight were acid-best and two responded best to QHCl. The responses to all four tastants were enhanced, with no difference among neuron types. For 18 cells that were tested with two or more gustatory stimuli, BICM increased their breadth of responsiveness to their two most effective stimuli. These data show that approximately 60% of the taste-responsive neurons in the rostral NST are inhibited by GABA and/or subject to a tonic inhibitory influence, which is mediated by GABAA receptors. The modulation of these cells by GABA provides a mechanism by which the breadth of tuning of the cell can be sharpened. Modulation of gustatory activity following a number of physiological changes could be mediated by such a GABAergic circuit.

Animals↗

PubMed2003

Human urocortin II, a selective agonist for the type 2 corticotropin-releasing factor receptor, decreases feeding and drinking in the rat.

Corticotropin-releasing factor (CRF) has been hypothesized to modulate consummatory behavior through the Type 2 CRF (CRF(2)) receptor. However, behavioral functions subserved by the CRF(2) receptor remain poorly understood. Recently, human urocortin II (hUcn II), a selective CRF(2) receptor agonist, was identified. To study the effects of this neuropeptide on ingestive behavior, we examined the effects of centrally infused hUcn II (i.c.v. 0, 0.01, 0.1, 1.0, 10.0 micro g) on the microstructure of nose-poke responding for food and water in nondeprived, male rats. Malaise-inducing properties of the peptide were monitored using conditioned taste aversion (CTA) testing. To identify potential sites of action, central induction of Fos protein expression was examined. hUcn II dose dependently reduced the quantity and duration of responding for food and water at doses lower (0.01-1.0 micro g) than that forming a CTA (10 micro g). Effects were most evident during hours 4 to 6 of the dark cycle. Meal pattern analysis showed that hUcn II potently (0.1 micro g) increased the satiating value of food. Rats ate and drank smaller and shorter meals without changing meal frequency. Rats also ate more slowly. hUcn II induced Fos in regions involved in visceral sensory processing and autonomic/neuroendocrine regulation and resembling those activated by appetite suppressants. hUcn II is a promising neuropeptide for investigating the role of the CRF(2) receptor in ingestive behavior.

Animals↗

PubMed2002

Inositol 1,4,5-trisphosphate transduction cascade in taste reception of the fleshfly, Boettcherisca peregrina.

The role of an inositol 1,4,5-trisphosphate (IP3)-mediated transduction cascade in the response of taste receptor cells of the fleshfly Boettcherisca peregrina was investigated by using the following reagents: neomycin (an inhibitor of IP3 production), U73122 (an inhibitor of phospholipase C), adenophostin A (an agonist of the IP3-gated channel), IP3, ruthenium red (a blocker of the IP3-gated channel), and 2-aminoethoxydiphenylborate (2-APB; an antagonist of the IP3-gated channel). For introduction into the receptor cell, the reagents were mixed with a detergent, deoxycholate (DOC). After treatment with neomycin + DOC or U73122 + DOC, the response of the sugar receptor cell to sugars was depressed compared with responses after treatment with DOC alone. During the treatment of adenophostin A + DOC, the response of the sugar receptor cell was elicited. After treatment with IP3 + DOC, the response of the sugar receptor cell to sugars and to amino acids was apparently enhanced. When taste stimuli were administered in the presence of ruthenium red or 2-APB, the response of the sugar receptor cell to glucose were inhibited. The expression of genes for substances involved in the IP3 transduction cascade, such as G protein alpha subunit (dGqalpha), phospholipase C (norpA), and IP3 receptor (itpr), were examined in the taste receptor cell of the fruitfly Drosophila melanogaster by using the pox-neuro70 mutant (poxn70), which lacks taste receptor cells. The expressed levels of dGqalpha and itpr in the tarsus of poxn70 mutant flies were reduced compared with those of wild-type flies. These results suggest that the IP3 transduction cascade is involved in the response of the sugar receptor cell of the fly.

Adenosine↗

PubMed2003

Ethanol consumption in mice with a targeted disruption of the dopamine-3 receptor gene.

Considerable evidence suggests that the mesolimbic dopaminergic system is an important substrate for the rewarding effects of ethanol consumption. Previous data have demonstrated that pharmacological agents that alter dopamine signaling also influence the self-administration of ethanol. The present experiments were designed to assess the role of the dopamine-3 receptor (D3-R) on voluntary ethanol consumption in C57BL/6 mice. Mice with targeted disruption of the D3-R gene (D3-R - /-) were compared to wild-type controls in an ethanol intake paradigm. In Experiment 1, mice had 24-hour access to ethanol each day in a two-bottle choice paradigm for a period of 7 days per concentration. The concentrations tested were 3, 6, 10 and 15%. In Experiment 2, mice had I hour of access to ethanol each day in a two-bottle paradigm for a period of 7 days per concentration. The same concentrations in Experiment I were compared in Experiment 2. In Experiment 3 we sought to test the development of a conditioned taste aversion (CTA) after receiving an intraperitoneal (ip.) injection of 2.0 g/kg ethanol. In Experiment 4, blood ethanol levels where assessed following a 2.0 g/kg ip.injection of ethanol. Experiment 5 assessed taste preference for saccharine and quinine in wild-type and D3-R -/- mice. Contrary to our predictions, both D3-R -/- and wild-types on a CS57BL/6 background had similar intakes of ethanol, at all concentrations tested, in the 24-hour and 1-hour intake paradigms. Wild-type and D3-R -/- mice respond to injected ethanol similarly by developing a conditioned taste aversion. Metabolic analysis revealed mutant mice are slower in metabolizing a bolus injection of ethanol. Lastly, wild-type and D3-R -/- mice showed similar consumption to increasing concentration of both sweet and bitter tastes. These data suggest that deletion of the D3-R gene does not increase ethanol consumption above that found on the C57BL/6 genetic background. Furthermore, the D3-R -/- mice adequately learn a CTA to ethanol and do not ham differing taste reactivity to saccharin or quinine. However, D3-R -/- mice do appear to have a slower rate of ethanol metabolism.

Alcohol Drinking↗

PubMed1981

Taste response in the facial nerve of the carp, Cyprinus carpio L.

The stimulating effect of taste substances on the external chemoreceptors of the carp, Cyprinus carpio L., was studied by recording the electrical activity from the facial taste fibers innervating the facial skin surface. The integrated responses from each whole nerve bundle of the trigemino-facial complex nerve revealed that gustatory receptors on the snout of the carp were extremely sensitive to salts, acids and the extract of silk worm pupae. Quinine-HCl and sucrose elicited relatively small responses. Responses occurred to several amino acids, and especially to betaine. The threshold concentration for both mono- and di-valent salts was estimated to be about 5 X 10-3 M and that for acids about 10-4 M. Single fiber analysis was performed on 77 preparations. According to responsiveness to the 4 basic chemicals, the fibers were classified into 5 types: type I, activated by one stimulus (22 fibers out of 77); type II by two (29); type III by three (11); type IV by four (13); and type V showing inhibition by quinine-HCl (2) as their notable feature. Single fibers responsive to several amino acids, and the worm extract were found, among which the last was the most effective stimulus as shown in the whole nerve experiments.

Animals↗

PubMed1995

The frog taste disc: a prototype of the vertebrate gustatory organ.

The frog taste disc (TD) is apparently the largest gustatory organ found in vertebrates and seems to differentiate into a specialized variety of the prototypic scheme of the taste bud. An explanation for this unusual organization is lacking although it is possible to speculate the existence of environmental and nutritional requirements. Up to the present time, the most common model of the TD was based on two main cell types (sensory and sustentacular). This model may oversimplify the morphology of this structure since more numerous cell types have been described. We now propose a new model of the TD, based on comprehensive data on the ultrastructure of the organ obtained in the last 20 years. The main conclusions are the following: (1) the TD is a pluristratified epithelium with a general organization similar to that of the olfactory and vomeronasal epithelium; (2) it has skeleton composed of three different types of epithelial cells; (3) the chemoreceptorial surface is covered by different microenvironments; (4) three different types of neuro-epithelial systems are present; the type II is an 'open' sensory cell with axonal contacts devoid of vesicles; the type III is an 'open' sensory cell with synaptic-like junctions; the type i.v. is a 'closed' sensory cell with a 'Merkel-neurite complex'; (5) the nerve fibers in the basal plexus are mostly cholinergic while the peridiscal nerve fibers are mostly peptidergic. The presence of several cell types in the TD must be considered using these large receptors in electrophysiological studies or as a source of isolated cells, and their complexity must induce caution in the interpretation of the data. Text books of histology usually describe the peripheral structures associated with taste as very simple: an idea that probably must be revised. A taste organ is a highly complex structure composed of several sensory systems and a comparative approach can aid comprehension of its general organization. The study of the 'large taste organs' present in some species of amphibians can provide useful data for knowledge of the gustatory system of vertebrates.

Animals↗

PubMed1982

Three Drosophila mutations that block associative learning also affect habituation and sensitization.

Drosophila melanogaster has been cultured with shock to avoid various odors. Mutants that failed to learn this task have been isolated. Here we report tests on these mutants for more elementary types of behavioral plasticity--habituation and sensitization of a reflex. Fruit flies have taste receptors on their feet. When a starved, water-satiated fly has sucrose applied to one foot, it usually responds by extending its proboscis. In normal flies this feeding reflex shows habituation: application of sugar to one foot depresses responsiveness through the contralateral leg for at least 10 min. The reflex also shows brief sensitization application of concentrated sucrose solution to the proboscis increases subsequent responsiveness to tarsal stimulation for 2-5 min. In three associative learning mutants , the proboscis-extension reflex is present with a normal threshold but behavioral modulation of the response is altered. The dunce, turnip, and rutabaga mutants all habituate less than normal flies. In addition, sensitization wanes unusually rapidly in dunce and rutabaga flies, lasting less than a minute in the case of dunce.

Animals↗

PubMed2005

[Effect of sour TCM compound recipe on insulin resistance in experimental rats with diabetes mellitus type 2].

OBJECTIVE: To study the effect of sour TCM compound Recipe (SCCR) on insulin resistance in experimental rats with diabetes mellitus type 2 (DM2), under the guidance of TCM doctrine of "sour restrains sweet". METHODS: Model rats of DM2 were established by 8 weeks' feeding with high calorie forage combined with intraperitoneal injection of small dose of streptozotocin, and treated with SCCR (15 g/kg of crude drug/day). Levels of fasting blood glucose (FBG), serum insulin, free fatty acids (FFA), tumor necrosis factor a (TNF-alpha), combining capacity and constant of insulin receptor in liver were determined before treatment and 4, 8 and 12 weeks after treatment, and the insulin sensitive index was calculated. The data were compared with those in the model group (untreated), sweet TCM compound recipe group and bitter TCM compound group (treated with sweet and bitter Chinese drugs respectively) and the control group (treated with dimethyldiguanide). RESULTS: SCCR could markedly reduce the FBG, serum FFA and TNF-alpha levels in rat model of DM2, stimulate the secretion of insulin, raise the combining capacity and constant of insulin receptor in liver and improve the insulin sensitivity, as compared with the effect of sweet or bitter Chinese compound recipe, the difference was significant (P < 0.05). CONCLUSION: SCCR could improve the glucose metabolic disorder and ameliorate the degree of insulin resistance in DM2 model rats, with the effect superior to those with sweet or bitter taste, which illustrates primarily that the therapeutic principle of "sour restrains sweet" of TCM is true of science in a certain degree and having its guiding significance in clinical practice.

Animals↗

PubMed2004

Immunolocalization of Alk8 during replacement tooth development in zebrafish.

The novel type I transforming growth factor-beta (TGF-beta) family member receptor Alk8 was previously identified in a degenerate RT-PCR screen for zebrafish type I and II TGF-beta family member receptors. Functional analyses revealed that Alk8 acts through Bmp signaling pathways in early embryonic dorsoventral patterning, in neural crest cell specification, and in patterning and differentiation of neural crest cell-derived pharyngeal arch cartilages. In addition, Alk8 forms active signaling complexes with TGF-beta1 and the TGF-beta RII receptor, suggesting that Alk8 mediates cross talk between Bmp and TGF-beta subfamily members. In this study, immunohistochemical analysis was performed on zebrafish aged 2 days postfertilization to 1 year, revealing immunolocalization of Alk8 to tissues of the tooth-bearing ceratobranchial 5 (cb5) arch including dental epithelial and mesenchymal tooth tissues of developing primary and replacement teeth, mucous-producing crypt epithelium, keratinized bite plate, and developing taste buds. These results suggest roles for Alk8 in patterning tooth-bearing pharyngeal epithelium, in the initiation of tooth development, in odontoblast and ameloblast differentiation, and in osteoblast maturation. The ability for zebrafish to continuously form teeth throughout their lives allows for the comparison of Alk8 expression in both primary and replacement tooth development, revealing identical Alk8 expression profiles. This study advances our current understanding of the functions of Alk8, particularly with respect to primary and replacement tooth formation, reveals additional roles for Alk8 in dental epithelial patterning and in odontoblast, ameloblast and osteoblast differentiation, and demonstrates the utility of the zebrafish as a model for primary and replacement tooth development.

Activin Receptors, Type I↗

PubMed1999

GABA(A) receptors modulate ethanol-induced conditioned place preference and taste aversion in mice.

RATIONALE: GABA(A) receptor antagonists have been shown to reduce ethanol self-administration and ethanol-induced conditioned taste aversion (CTA) in rats, suggesting a role for the GABA(A) receptor in modulating ethanol's motivational effects. OBJECTIVES: The present experiments examined the effects of the GABA(A) receptor antagonists, bicuculline and picrotoxin, on the acquisition of ethanol-induced conditioned place preference (CPP) and CTA in male DBA/2J mice. METHODS: Mice in the CPP experiments received four pairings of ethanol (2 g/kg) with a distinctive floor stimulus for a 5-min conditioning session (CS+ sessions). During CS+ sessions, mice also received bicuculline (0, 1.0, 3.0, or 5.0 mg/kg) or picrotoxin (2.0 mg/kg) before an injection of ethanol. On intervening days (CS- sessions), the pretreatment injection was always vehicle followed by saline injections that were paired with a different floor type. For the preference test, all mice received saline injections and were placed on a half grid and half hole floor for a 60-min session. For the CTA experiments, mice were adapted to a 2-h per day water restriction regimen followed by five conditioning trials every 48 h. During conditioning trials, subjects received an injection of vehicle, bicuculline (0.5 and 2.0 mg/kg), or picrotoxin (0.75 and 2.5 mg/kg) before injection of 2 g/kg ethanol or saline following 1-h access to a saccharin solution. RESULTS: Both picrotoxin and the lowest dose of bicuculline (1.0 mg/kg) significantly increased the magnitude of CPP relative to vehicle-treated controls. Picrotoxin alone did not produce place conditioning. Ethanol-stimulated locomotor activity was significantly reduced during conditioning trials with picrotoxin and the higher doses of bicuculline (3.0 and 5.0 mg/kg). Bicuculline did not alter ethanol-induced CTA; however, picrotoxin dose-dependently increased the magnitude of ethanol-induced CTA. Bicuculline and picrotoxin did not produce CTA when administered alone. CONCLUSIONS: Overall, these results suggest that blockade of GABA(A) receptors with bicuculline and picrotoxin enhances ethanol's motivational effects in the CPP paradigm; however, only picrotoxin enhances ethanol's motivational effects in the CTA paradigm.

Animals↗

PubMed2006

Taste bud contains both short-lived and long-lived cell populations.

Taste bud cells undergo continual turnover even in adulthood, and their average lifespan has been estimated as approximately 10 days. However, it is not clear whether this figure can be applied to all the different cell types contained in a taste bud. Here, we describe the age and life cycle of taste bud cells in rat circumvallate papillae, and indicate that the lifespan is heterogeneous, ranging from 2 days to over 3 weeks. Taste bud cells were incorporated from the basal proliferative layer in 1-2 days after birth. After incorporation, approximately half of the cells were eliminated within 2-3 days, and the remaining half were maintained with gradual decrease, suggesting that there are at least two types of cells; short-lived cells and long-lived cells. Moreover, above 10% of the incorporated cells were maintained at 3 weeks. In order to gain information about the relationship between the cell functions and the cell age, we carried out double-labeling experiments using 5-bromo-2'-deoxyuridine and each of two markers for in situ hybridization: mammalian achaete-scute homolog 1 (Mash1) and phospholipase C beta 2 (PLCbeta2) as markers of early differentiation and functional taste signaling, respectively. Mash1 expression began immediately after the incorporation and reached a maximum at 5-6 days after birth. Fewer but distinct Mash1-positive cells were still observed after 3 weeks. PLCbeta2 expression was observed from day 5, reached a maximum at day 12, and continued over 3 weeks. Taken together, a taste bud contains both short-lived and long-lived cells: the short-lived cells are eliminated in a time course similar to the surrounding epithelial cells, and the long-lived cells including taste receptor cells have a lifespan longer than the previous estimation.

Analysis of Variance↗

PubMed1997

Taste sensilla of flies: function, central neuronal projections, and development.

Taste sensilla of flies are composed of only a few cells, all of which have different functions. Depending on the species and on the sensillum type, there are from 2-5 neurons, each of which has its own stimulus specificity, and each of which makes a different contribution to the fly's behavior. In addition, taste sensilla include several nonneuronal cells that are important both for the development of the sensillum and for its functioning. The component cells of a sensillum derive from a single epidermal precursor according to a stereotyped sequence of mitoses. This review focuses on the different phenotypes of the component cells of taste sensilla, particularly the stimulus sensitivity and central neuronal anatomy of the receptor neurons, and on the development of this multicellular organ from a single precursor cell.

Animals↗

PubMed2004

Molecular mechanisms of ligand binding, signaling, and regulation within the superfamily of G-protein-coupled receptors: molecular modeling and mutagenesis approaches to receptor structure and function.

The superfamily of G-protein-coupled receptors (GPCRs) could be subclassified into 7 families (A, B, large N-terminal family B-7 transmembrane helix, C, Frizzled/Smoothened, taste 2, and vomeronasal 1 receptors) among mammalian species. Cloning and functional studies of GPCRs have revealed that the superfamily of GPCRs comprises receptors for chemically diverse native ligands including (1) endogenous compounds like amines, peptides, and Wnt proteins (i.e., secreted proteins activating Frizzled receptors); (2) endogenous cell surface adhesion molecules; and (3) photons and exogenous compounds like odorants. The combined use of site-directed mutagenesis and molecular modeling approaches have provided detailed insight into molecular mechanisms of ligand binding, receptor folding, receptor activation, G-protein coupling, and regulation of GPCRs. The vast majority of family A, B, C, vomeronasal 1, and taste 2 receptors are able to transduce signals into cells through G-protein coupling. However, G-protein-independent signaling mechanisms have also been reported for many GPCRs. Specific interaction motifs in the intracellular parts of these receptors allow them to interact with scaffold proteins. Protein engineering techniques have provided information on molecular mechanisms of GPCR-accessory protein, GPCR-GPCR, and GPCR-scaffold protein interactions. Site-directed mutagenesis and molecular dynamics simulations have revealed that the inactive state conformations are stabilized by specific interhelical and intrahelical salt bridge interactions and hydrophobic-type interactions. Constitutively activating mutations or agonist binding disrupts such constraining interactions leading to receptor conformations that associates with and activate G-proteins.

Amino Acid Sequence↗