Publishing type：Research paper (scientific journal)   Publisher：Society for Neuroscience  

Drug-induced taste disorders reduce quality of life, but little is known about the molecular mechanisms by which drugs induce taste disturbances. In this study, we investigated the short- and long-term effects of the antiarrhythmic drug flecainide, which is known to cause taste dysfunction. Analyses of behavioral responses (licking tests) revealed that mice given a single intraperitoneal injection of flecainide exhibited a significant reduction in preference for a sour tastant (HCl) but not for other taste solutions (NaCl, quinine, sucrose, KCl and monopotassium glutamate) when compared with controls. Mice administered a single dose of flecainide also had significantly higher taste nerve responses to HCl but not to other taste solutions. Compared with controls, mice administered flecainide once-daily for 30 days showed a reduced preference for HCl without any changes in the behavioral responses to other taste solutions. The electrophysiological experiments using HEK293T cells transiently expressing otopetrin-1 (Otop1, the mouse sour taste receptor) showed that flecainide rarely altered the responses to HCl. Taken together, our results suggest that flecainide specifically enhances the response to HCl in mice during short- and long- term administration. Although further studies will be needed to elucidate the molecular mechanisms, these findings provide new insights into the pathophysiology of drug-induced taste disorders.

Significance Statement

Drug-induced taste disorders reduce quality of life and can lead to nutritional disturbances. However, little is known about its molecular mechanisms. We focused on the antiarrhythmic drug flecainide inducing “unpleasant or bad taste” in human patients. Mice administered a single dose of flecainide exhibited a reduced preference for and higher taste nerve responses to HCl, sour tastants specifically. Flecainide had little change in response to HCl in HEK293T cells expressing the sour taste receptor, proton channel otopetrin-1 (Otop1). Our results suggest that flecainide enhances the responses of sour-sensing taste cells to HCl. Although further studies will be needed to elucidate the molecular mechanisms, these findings provide new insights into the pathophysiology of drug-induced taste disorders.

DOI： 10.1523/eneuro.0048-23.2023

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Purpose of Review

This review aims to discuss and summarize the peripheral sensory mechanisms involved in the induction of the early phase of insulin release, known as cephalic phase insulin release (CPIR), triggered by stimuli related to food, particularly sugars.

Recent Findings

At least, two distinct systems on the tongue are responsible for detecting oral sugars. The first system involves the G-protein-coupled receptor Tas1r2/Tas1r3, which can detect not only sugars but also artificial sweeteners and sweet proteins. The second system relies on glucose transporters, specifically recognize and transport monosaccharides. The Tas1r2/Tas1r3 receptor utilizes a signal transduction pathway involving gustducin, phospholipase β2, and transient receptor potential channel M5 to depolarize taste cells. On the other hand, glucose transporters facilitate the transport of monosaccharides into cells, where their degradation produces ATP. This ATP inhibits the metabolic sensor K_ATP channel, ultimately leading to cell depolarization. Recent studies in mice have demonstrated that glucose transporters and K_ATP channels, rather than the Tas1r2/Tas1r3 receptor, are essential for the induction of CPIR.

Summary

The detection of sugars in the oral cavity relies on two essential mechanisms: the Tas1r2/Tas1r3 receptor and glucose transporters. Notably, oral glucose transporters are likely to play a significant role in the induction of sugar-induced CPIR. As a result, these two sugar detection systems may have distinct roles in maintaining energy homeostasis within the body.

DOI： 10.1007/s40496-023-00347-y

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Other Link： https://link.springer.com/article/10.1007/s40496-023-00347-y/fulltext.html

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Cephalic-phase insulin release (CPIR) occurs before blood glucose increases after a meal. Although glucose is the most plausible cue to induce CPIR, peripheral sensory systems involved are not fully elucidated. We therefore examined roles of sweet sensing by a T1R3-dependent taste receptor and sugar sensing by oral glucose transporters in the oropharyngeal region in inducing CPIR. Spontaneous oral ingestion of glucose significantly increased plasma insulin 5 min later in wild-type (C57BL/6) and T1R3-knockout mice, but intragastric infusion did not. Oral treatment of glucose transporter inhibitors phlorizin and phloretin significantly reduced CPIR after spontaneous oral ingestion. In addition, a rapid increase in plasma insulin was significantly smaller in WT mice with spontaneous oral ingestion of nonmetabolizable glucose analog than in WT mice with spontaneous oral ingestion of glucose. Taken together, the T1R3-dependent receptor is not required for CPIR, but oral glucose transporters greatly contribute to induction of CPIR by sugars.

DOI： 10.1186/s12576-023-00875-3

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Other Link： https://link.springer.com/article/10.1186/s12576-023-00875-3/fulltext.html

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

On the tongue, the T1R-independent pathway (comprising glucose transporters, including sodium–glucose cotransporter (SGLT1) and the KATP channel) detects only sugars, whereas the T1R-dependent (T1R2/T1R3) pathway can broadly sense various sweeteners. Cephalic-phase insulin release, a rapid release of insulin induced by sensory signals in the head after food-related stimuli, reportedly depends on the T1R-independent pathway, and the competitive sweet taste modulators leptin and endocannabinoids may function on these two different sweet taste pathways independently, suggesting independent roles of two oral sugar-detecting pathways in food intake. Here, we examined the effect of adrenomedullin (ADM), a multifunctional regulatory peptide, on sugar sensing in mice since it affects the expression of SGLT1 in rat enterocytes. We found that ADM receptor components were expressed in T1R3-positive taste cells. Analyses of chorda tympani (CT) nerve responses revealed that ADM enhanced responses to sugars but not to artificial sweeteners and other tastants. Moreover, ADM increased the apical uptake of a fluorescent D-glucose derivative into taste cells and SGLT1 mRNA expression in taste buds. These results suggest that the T1R-independent sweet taste pathway in mouse taste cells is a peripheral target of ADM, and the specific enhancement of gustatory nerve responses to sugars by ADM may contribute to caloric sensing and food intake.

DOI： 10.3390/nu15132941

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/foods12061150

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

OBJECTIVE: This study aimed to determine changes in saliva secretion and subjective taste intensity during a sustained period with continuous gustatory stimulation. DESIGN: Twenty-two healthy adults participated in this study. The selected taste solutions were aspartame, sucralose, and acesulfame potassium, which are nonnutritive sweeteners. The concentrations of sucralose1 and acesulfame potassium were set to show the same sweetness intensity as aspartame. Sucralose2 was twice the concentration of sucralose1. The solution was continuously fed into the oral cavity at a flow rate of 0.04 mL / min through a neck-worn precise infusion system. The salivary flow rate (g/min) after 10 min of intraoral water supply from the device was used as the baseline. Salivary flow rate, subjective taste intensity evaluated by the visual analog scale (VAS), and salivary flow rate relative to the baseline were recorded at 10, 30, 60, and 120 min after the start of the test. RESULTS: In the aspartame, sucralose1, and sucralose2 groups, the salivary flow rate increased significantly from 10 min to 120 min after the start of the test when compared to the rate at baseline (p < 0.05). The relative salivary flow rate increased and the VAS value decreased significantly over time and were affected by the time factor (p < 0.001, p = 0.013, respectively) but not by the sweetener-group factor and the interaction effects. CONCLUSIONS: Continuous gustatory stimulation may maintain increased salivary production for a sustained period.

DOI： 10.1016/j.archoralbio.2022.105590

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Language：Japanese   Publisher：岡山歯学会  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.cophys.2021.01.009

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Orexin (OX), which regulates sleep and wakefulness and feeding behaviors has 2 isoforms, orexin-A and -B (OXA and OXB). In this study, the distribution of OXA and OXB was examined in the rat superior salivatory nucleus (SSN) using retrograde tracing and immunohistochemical and methods. OXA- and OXB-immunoreactive (-ir) nerve fibers were seen throughout the SSN. These nerve fibers surrounded SSN neurons retrogradely labeled with Fast blue (FB) from the corda-lingual nerve. FB-positive neurons had pericellular OXA- (47.5%) and OXB-ir (49.0%) nerve fibers. Immunohistochemistry for OX receptors also demonstrated the presence of OX1R and OX2R in FB-positive SSN neurons. The majority of FB-positive SSN neurons contained OX1R- (69.7%) or OX2R-immunoreactivity (57.8%). These neurons had small and medium-sized cell bodies. In addition, half of FB-positive SSN neurons which were immunoreactive for OX1R (47.0%) and OX2R (52.2%) had pericellular OXA- and OXB-ir nerve fibers, respectively. Co-expression of OX1R- and OX2R was common in FB-positive SSN neurons. The present study suggests a possibility that OXs regulate the activity of SSN neurons through OX receptors.

DOI： 10.1016/j.autneu.2020.102712

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

AIM: We investigated potential neuron types that code sugar information and how sodium-glucose cotransporters (SGLTs) and T1Rs are involved. METHODS: Whole-nerve recordings in the chorda tympani (CT) and the glossopharyngeal (GL) nerves and single-fibre recordings in the CT were performed in T1R3-KO and wild-type (WT) mice. Behavioural response measurements were conducted in T1R3-KO mice using phlorizin (Phl), a competitive inhibitor of SGLTs. RESULTS: Results indicated that significant enhancement occurred in responses to sucrose and glucose (Glc) by adding 10 mmol/L NaCl but not in responses to KCl, monopotassium glutamate, citric acid, quinine sulphate, SC45647(SC) or polycose in both CT and GL nerves. These enhancements were abolished by lingual application of Phl. In single-fibre recording, fibres showing maximal response to sucrose could be classified according to responses to SC and Glc with or without 10 mmol/L NaCl in the CT of WT mice, namely, Phl-insensitive type, Phl-sensitive Glc-type and Mixed (Glc and SC responding)-type fibres. In T1R3-KO mice, Phl-insensitive-type fibres disappeared. Results from behavioural experiments showed that the number of licks and amount of intake for Glc with or without 10 mmol/L NaCl were significantly suppressed by Phl. CONCLUSION: We found evidence for the contribution of SGLTs in sugar sensing in taste cells of mouse tongue. Moreover, we found T1R-dependent (Phl-insensitive) type, Glc-type and Mixed (SGLTs and T1Rs)-type fibres. SGLT1 may be involved in the latter two types and may play important roles in the glucose-specific cephalic phase of digestion and palatable food intake.

DOI： 10.1111/apha.13529

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1111/apha.13529

Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

(1) Background: Our previous studies revealed that orexin-A, an appetite-increasing peptide, suppressed reflex swallowing via the commissural part of the nucleus tractus solitarius (cNTS), and that glucagon-like peptide-1 (GLP-1), an appetite-reducing peptide, also suppressed reflex swallowing via the medial nucleus of the NTS (mNTS). In this study, we examined the mutual interaction between orexin-A and GLP-1 in reflex swallowing. (2) Methods: Sprague–Dawley rats under urethane–chloralose anesthesia were used. Swallowing was induced by electrical stimulation of the superior laryngeal nerve (SLN) and was identified by the electromyographic (EMG) signals obtained from the mylohyoid muscle. (3) Results: The injection of GLP-1 (20 pmol) into the mNTS reduced the swallowing frequency and extended the latency of the first swallow. These suppressive effects of GLP-1 were not observed after the fourth ventricular administration of orexin-A. After the injection of an orexin-1 receptor antagonist (SB334867) into the cNTS, an ineffective dose of GLP-1 (6 pmol) into the mNTS suppressed reflex swallowing. Similarly, the suppressive effects of orexin-A (1 nmol) were not observed after the injection of GLP-1 (6 pmol) into the mNTS. After the administration of a GLP-1 receptor antagonist (exendin-4(5-39)), an ineffective dose of orexin-A (0.3 nmol) suppressed reflex swallowing. (4) Conclusions: The presence of reciprocal inhibitory connections between GLP-1 receptive neurons and orexin-A receptive neurons in the NTS was strongly suggested.

DOI： 10.3390/ijms21124422

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Bitter taste receptors TAS2Rs detect noxious compounds in the oral cavity. Recent heterologous expression studies reported that some compounds function as antagonists for human TAS2Rs. For examples, amino acid derivatives such as γ-aminobutyric acid (GABA) and Nα,Nα-bis(carboxymethyl)-L-Lysine (BCML) blocked responses to quinine mediated by human TAS2R4. Probenecid inhibited responses to phenylthiocarbamide mediated by human TAS2R38. In this study, we investigated the effects of these human bitter receptor antagonists on behavioral lick responses of mice to elucidate whether these compounds also function as bitter taste blockers. In short-term (10 s) lick tests, concentration-dependent lick responses to bitter compounds (quinine-HCl, denatonium and phenylthiourea) were not affected by the addition of GABA or BCML. Probenecid reduced aversive lick responses to denatonium and phenylthiourea but not to quinine-HCl. In addition, taste cell responses to phenylthiourea were inhibited by probenecid. These results suggest some bitter antagonists of human TAS2Rs can work for bitter sense of mouse.

DOI： 10.1016/j.neulet.2020.135041

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Language：English   Publishing type：Research paper (scientific journal)  

The systemic renin-angiotensin system (RAS) is an important regulator of body fluid and sodium homeostasis. Angiotensin II (AngII) is a key active product of the RAS. We previously revealed that circulating AngII suppresses amiloride-sensitive salt taste responses and enhances the responses to sweet compounds via the AngII type 1 receptor (AT1) expressed in taste cells. However, the molecular mechanisms underlying the modulation of taste function by AngII remain uncharacterized. Here we examined the expression of three RAS components, namely renin, angiotensinogen, and angiotensin-converting enzyme-1 (ACE1), in mouse taste tissues. We found that all three RAS components were present in the taste buds of fungiform and circumvallate papillae and co-expressed with αENaC (epithelial sodium channel α-subunit, a salt taste receptor) or T1R3 (taste receptor type 1 member 3, a sweet taste receptor component). Water-deprived mice exhibited significantly increased levels of renin expression in taste cells (p < 0.05). These results indicate the existence of a local RAS in the taste organ and suggest that taste function may be regulated by both locally-produced and circulating AngII. Such integrated modulation of peripheral taste sensitivity by AngII may play an important role in sodium/calorie homeostasis.

DOI： 10.3390/nu11092251

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：日本味と匂学会  

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Language：Japanese   Publisher：日本味と匂学会  

視床下部に存在する10種類の摂食亢進ペプチドについて、ラット顎下腺・舌下腺支配の上唾液核(SSN)ニューロンを興奮させるかどうか検討した。Wistar系ラット(6〜14日齢)を用いて、標識ニューロンからホールセルパッチクランプ法により膜電位や膜電流を記録し、摂食亢進ペプチドをバス投与したときの影響を調べた。膜電位に対する応答では、orexin(OX)-Aに対する応答は他のペプチドと比較して有意に大きく、活動電位を伴うものがあった。また過分極応答を誘発するものはなかった。膜の入力抵抗に対する影響では、コントロールと比較してOX-A存在下では、同じ通電量60pAで発火頻度が増加した。また、通電ごとの平均の静止膜電位はコントロールでは-66mVであったのに対して、OX-A存在下では-59mVへと浅くなった。また、300nM OX-Aにより、多くのSSNニューロンが内向き電流を誘発していた。

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Language：Japanese   Publisher：日本味と匂学会  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/chemse/bjz013

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Language：English   Publishing type：Research paper (scientific journal)  

Expression of insulin and its receptor (IR) in rodent taste cells has been proposed, but exactly which types of taste cells express IR and the function of insulin signaling in taste organ have yet to be determined. In this study, we analyzed expression of IR mRNA and protein in mouse taste bud cells in vivo and explored its function ex vivo in organoids, using RT-PCR, immunohistochemistry, and quantitative PCR. In mouse taste tissue, IR was expressed broadly in taste buds, including in type II and III taste cells. With using 3-D taste bud organoids, we found insulin in the culture medium significantly decreased the number of taste cell and mRNA expression levels of many taste cell genes, including nucleoside triphosphate diphosphohydrolase-2 (NTPDase2), Tas1R3 (T1R3), gustducin, carbonic anhydrase 4 (CA4), glucose transporter-8 (GLUT8), and sodium-glucose cotransporter-1 (SGLT1) in a concentration-dependent manner. Rapamycin, an inhibitor of mechanistic target of rapamycin (mTOR) signaling, diminished insulin's effects and increase taste cell generation. Altogether, circulating insulin might be an important regulator of taste cell growth and/or proliferation via activation of the mTOR pathway.

DOI： 10.1371/journal.pone.0225190

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Bitter taste serves as an important signal for potentially poisonous compounds in foods to avoid their ingestion. Thousands of compounds are estimated to taste bitter and presumed to activate taste receptor cells expressing bitter taste receptors (Tas2rs) and coupled transduction components including gustducin, phospholipase Cβ2 (PLCβ2) and transient receptor potential channel M5 (TRPM5). Indeed, some gustducin-positive taste cells have been shown to respond to bitter compounds. However, there has been no systematic characterization of their response properties to multiple bitter compounds and the role of transduction molecules in these cells. In this study, we investigated bitter taste responses of gustducin-positive taste cells in situ in mouse fungiform (anterior tongue) and circumvallate (posterior tongue) papillae using transgenic mice expressing green fluorescent protein in gustducin-positive cells. The overall response profile of gustducin-positive taste cells to multiple bitter compounds (quinine, denatonium, cyclohexamide, caffeine, sucrose octaacetate, tetraethylammonium, phenylthiourea, L-phenylalanine, MgSO4, and high concentration of saccharin) was not significantly different between fungiform and circumvallate papillae. These bitter-sensitive taste cells were classified into several groups according to their responsiveness to multiple bitter compounds. Bitter responses of gustducin-positive taste cells were significantly suppressed by inhibitors of TRPM5 or PLCβ2. In contrast, several bitter inhibitors did not show any effect on bitter responses of taste cells. These results indicate that bitter-sensitive taste cells display heterogeneous responses and that TRPM5 and PLCβ2 are indispensable for eliciting bitter taste responses of gustducin-positive taste cells.

DOI： 10.1016/j.neuroscience.2017.10.047

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：FRONTIERS MEDIA SA  

Cholecystokinin (CCK) is a gut hormone released from enteroendocrine cells. CCK functions as an anorexigenic factor by acting on CCK receptors expressed on the vagal afferent nerve and hypothalamus with a synergistic interaction between leptin. In the gut, tastants such as amino acids and bitter compounds stimulate CCK release from enteroendocrine cells via activation of taste transduction pathways. CCK is also expressed in taste buds, suggesting potential roles of CCK in taste signaling in the peripheral taste organ. In the present study, we focused on the function of CCK in the initial responses to taste stimulation. CCK was coexpressed with type II taste cellmarkers such as G alpha-gustducin, phospholipase C beta 2, and transient receptor potential channel M5. Furthermore, a small subset (similar to 30%) of CCK-expressing taste cells expressed a sweet/umami taste receptor component, taste receptor type 1 member 3, in taste buds. Because type II taste cells are sweet, umami or bitter taste cells, the majority of CCK-expressing taste cells may be bitter taste cells. CCK-A and -B receptors were expressed in both taste cells and gustatory neurons. CCK receptor knockout mice showed reduced neural responses to bitter compounds compared with wild-type mice. Consistently, intravenous injection of CCK-Ar antagonist lorglumide selectively suppressed gustatory nerve responses to bitter compounds. Intravenous injection of CCK-8 transiently increased gustatory nerve activities in a dose-dependent manner whereas administration of CCK-8 did not affect activities of bitter-sensitive taste cells. Collectively, CCK may be a functionally important neurotransmitter or neuromodulator to activate bitter nerve fibers in peripheral taste tissues.

DOI： 10.3389/fphys.2017.00866

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Leptin is an important hormone that regulates food intake and energy homeostasis by acting on central and peripheral targets. In the gustatory system, leptin is known to selectively suppress sweet responses by inhibiting the activation of sweet sensitive taste cells. Sweet taste receptor (T1R2 + T1R3) is also expressed in gut enteroendocrine cells and contributes to nutrient sensing, hormone release and glucose absorption. Because of the similarities in expression patterns between enteroendocrine and taste receptor cells, we hypothesized that they may also share similar mechanisms used to modify/regulate the sweet responsiveness of these cells by leptin. Here, we used mouse enteroendocrine cell line STC-1 and examined potential effect of leptin on Ca2+ responses of STC-1 cells to various taste compounds. Ca2+ responses to sweet compounds in STC-1 cells were suppressed by a rodent T1R3 inhibitor gurmarin, suggesting the involvement of T1R3-dependent receptors in detection of sweet compounds. Responses to sweet substances were suppressed by &gt;= 1 ng/ml leptin without affecting responses to bitter, umami and salty compounds. This effect was inhibited by a leptin antagonist (mutant L39A/D40A/F41A) and by ATP gated K+ (K-ATP) channel closer glibenclamide, suggesting that leptin affects sweet taste responses of enteroendocrine cells via activation of leptin receptor and KATP channel expressed in these cells. Moreover, leptin selectively inhibited sweet-induced but not bitter-induced glucagon-like peptide-1 (GLP-1) secretion from STC-1 cells. These results suggest that leptin modulates sweet taste responses of enteroendocrine cells to regulate nutrient sensing, hormone release and glucose absorption in the gut. (C) 2016 IBRO. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.neuroscience.2016.06.036

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Authorship：Lead author   Language：English   Publisher：PORTLAND PRESS LTD  

The taste system of animals is used to detect valuable nutrients and harmful compounds in foods. In humans and mice, sweet, bitter, salty, sour and umami tastes are considered the five basic taste qualities. Sweet and umami tastes aremediated by G-protein-coupled receptors, belonging to the T1R (taste receptor type 1) family. This family consists of three members (T1R1, T1R2 and T1R3). They function as sweet or umami taste receptors by forming heterodimeric complexes, T1R1+T1R3 (umami) or T1R2+T1R3 (sweet). Receptors for each of the basic tastes are thought to be expressed exclusively in taste bud cells. Sweet (T1R2+T1R3-expressing) taste cells were thought to be segregated from umami (T1R1+T1R3-expressing) taste cells in taste buds. However, recent studies have revealed that a significant portion of taste cells in mice expressed all T1R subunits and responded to both sweet and umami compounds. This suggests that sweet and umami taste cells may not be segregated. Mice are able to discriminate between sweet and umami tastes, and both tastes contribute to behavioural preferences for sweet or umami compounds. There is growing evidence that T1R3 is also involved in behavioural avoidance of calcium tastes in mice, which implies that there may be a further population of T1R-expressing taste cells that mediate aversion to calcium taste. Therefore the simple view of detection and segregation of sweet and umami tastes by T1R-expressing taste cells, in mice, is now open to re-examination.

DOI： 10.1042/BJ20151015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Acidification of the glycoprotein, miraculin (MCL), induces sweet taste in humans, but not in mice. The sweet taste induced by MCL is more intense when acidification occurs with weak acids as opposed to strong acids. MCL interacts with the human sweet receptor subunit hTAS1R2, but the mechanisms by which the acidification of MCL activates the sweet taste receptor remain largely unexplored. The work reported here speaks directly to this activation by utilizing a sweet receptor TAS1R2 + TAS1R3 assay. In accordance with previous data, MCL-applied cells displayed a pH dependence with citric acid (weak acid) being right shifted to that with hydrochloric acid (strong acid). When histidine residues in both the intracellular and extracellular region of hTAS1R2 were exchanged for alanine, taste-modifying effect of MCL was reduced or abolished. Stronger intracellular acidification of HEK293 cells was induced by citric acid than by HCl and taste-modifying effect of MCL was proportional to intracellular pH regardless of types of acids. These results suggest that intracellular acidity is required for full activation of the sweet taste receptor by MCL.

DOI： 10.1038/srep22807

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Publishing type：Part of collection (book)  

© 2016 Elsevier Inc. All rights reserved. Taste receptor cells sense various chemical compounds in foods and transmit these signals through gustatory nerve fibers to the central nervous system. These sensory signals are vitally important for life; they provide information about which prospective foods are nutritious and warnings as to those that are noxious. Recent studies have revealed the involvement of multifarious bioactive peptides, many of which are primarily identified organs such as the gastrointestinal tract, in the modulation of taste responses. These peptides affect peripheral taste responsiveness of animals and play important roles in the regulation of feeding behavior and the maintenance of homeostasis. In this chapter, we discuss the various functions of peptide signaling in the peripheral taste system.

DOI： 10.1016/B978-0-12-801694-7.00017-2

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DOI： 10.1016/j.job.2015.09.002

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER DIABETES ASSOC  

Leptin is known to selectively suppress neural and behavioral responses to sweet-tasting compounds. However, the molecular basis for the effect of leptin on sweet taste is not known. Here, we report that leptin suppresses sweet taste via leptin receptors (Ob-Rb) and K-ATP channels expressed selectively in sweet-sensitive taste cells. Ob-Rb was more often expressed in taste cells that expressed T1R3 (a sweet receptor component) than in those that expressed glutamate-aspartate transporter (a marker for Type I taste cells) or GAD67 (a marker for Type III taste cells). Systemically administered leptin suppressed taste cell responses to sweet but not to bitter or sour compounds. This effect was blocked by a leptin antagonist and was absent in leptin receptor deficient db/db mice and mice with diet-induced obesity. Blocking the K-ATP channel subunit sulfonylurea receptor 1, which was frequently coexpressed with Ob-Rb in T1R3-expressing taste cells, eliminated the effect of leptin on sweet taste. In contrast, activating the K-ATP channel with diazoxide mimicked the sweet-suppressing effect of leptin. These results indicate that leptin acts via Ob-Rb and K-ATP channels that are present in T1R3-expressing taste cells to selectively suppress their responses to sweet compounds.

DOI： 10.2337/db14-1462

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FEDERATION AMER SOC EXP BIOL  

Five fundamental taste qualities (sweet, bitter, salty, sour, umami) are sensed by dedicated taste cells (TCs) that relay quality information to gustatory nerve fibers. In peripheral taste signaling pathways, ATP has been identified as a functional neurotransmitter, but it remains to be determined how specificity of different taste qualities is maintained across synapses. Recent studies demonstrated that some gut peptides are released from taste buds by prolonged application of particular taste stimuli, suggesting their potential involvement in taste information coding. In this study, we focused on the function of glucagon-like peptide-1 (GLP-1) in initial responses to taste stimulation. GLP-1 receptor (GLP-1R) null mice had reduced neural and behavioral responses specifically to sweet compounds compared to wild-type (WT) mice. Some sweet responsive TCs expressed GLP-1 and its receptors were expressed in gustatory neurons. GLP-1 was released immediately from taste bud cells in response to sweet compounds but not to other taste stimuli. Intravenous administration of GLP-1 elicited transient responses in a subset of sweet-sensitive gustatory nerve fibers but did not affect other types of fibers, and this response was suppressed by pre-administration of the GLP-1R antagonist Exendin-4(3-39). Thus GLP-1 may be involved in normal sweet taste signal transmission in mice.

DOI： 10.1096/fj.14-265355

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Potential roles of endogenous leptin and endocannabinoids in sweet taste were examined by using pharmacological antagonists and mouse models including leptin receptor deficient (db/db) and diet-induced obese (DIO) mice. Chorda tympani (CT) nerve responses of lean mice to sweet compounds were increased after administration of leptin antagonist (LA) but not affected by administration of cannabinoid receptor antagonist (AM251).db/db mice showed clear suppression of CT responses to sweet compounds after AM251, increased endocannabinoid levels in the taste organ, and enhanced expression of a biosynthesizing enzyme of endocannabinoids in taste cells. The effect of LA was gradually decreased and that of AM251 was increased during the course of obesity in DIO mice. These findings suggest that circulating leptin, but not local endocannabinoids, is a dominant modulator for sweet taste in lean mice and endocannabinoids become more effective modulators of sweet taste under conditions of deficient leptin signalling.
AbstractLeptin is an anorexigenic mediator that reduces food intake by acting on hypothalamic receptor Ob-Rb. In contrast, endocannabinoids are orexigenic mediators that act via cannabinoid CB1 receptors in hypothalamus, limbic forebrain, and brainstem. In the peripheral taste system, leptin administration selectively inhibits behavioural, taste nerve and taste cell responses to sweet compounds. Opposing the action of leptin, endocannabinoids enhance sweet taste responses. However, potential roles of endogenous leptin and endocannabinoids in sweet taste remain unclear. Here, we used pharmacological antagonists (Ob-Rb: L39A/D40A/F41A (LA), CB1: AM251) and examined the effects of their blocking activation of endogenous leptin and endocannabinoid signalling on taste responses in lean control, leptin receptor deficient db/db, and diet-induced obese (DIO) mice. Lean mice exhibited significant increases in chorda tympani (CT) nerve responses to sweet compounds after LA administration, while they showed no significant changes in CT responses after AM251. In contrast, db/db mice showed clear suppression of CT responses to sweet compounds after AM251, increased endocannabinoid (2-arachidonoyl-sn-glycerol (2-AG)) levels in the taste organ, and enhanced expression of a biosynthesizing enzyme (diacylglycerol lipase (DAGL)) of 2-AG in taste cells. In DIO mice, the LA effect was gradually decreased and the AM251 effect was increased during the course of obesity. Taken together, our results suggest that circulating leptin, but not local endocannabinoids, may be a dominant modulator for sweet taste in lean mice; however, endocannabinoids may become more effective modulators of sweet taste under conditions of deficient leptin signalling, possibly due to increased production of endocannabinoids in taste tissue.

DOI： 10.1113/JP270295

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

The taste receptor T1R1+T1R3 heterodimer and metabotropic glutamate receptors (mGluR) may function as umami taste receptors. Here, we used mGluR4 knockout (mGluR4-KO) mice and examined the function of mGluR4 in peripheral taste responses of mice. The mGluR4-KO mice showed reduced responses to glutamate and l-AP4 (mGluR4 agonist) in the chorda tympani and glossopharyngeal nerves without affecting responses to other taste stimuli. Residual glutamate responses in mGluR4-KO mice were suppressed by gurmarin (T1R3 blocker) and AIDA (group I mGluR antagonist). The present study not only provided functional evidence for the involvement of mGluR4 in umami taste responses, but also suggested contributions of T1R1+T1R3 and mGluR1 receptors in glutamate responses.
AbstractUmami taste is elicited by l-glutamate and some other amino acids and is thought to be initiated by G-protein-coupled receptors. Proposed umami receptors include heterodimers of taste receptor type 1, members 1 and 3 (T1R1+T1R3), and metabotropic glutamate receptors 1 and 4 (mGluR1 and mGluR4). Accumulated evidences support the involvement of T1R1+T1R3 in umami responses in mice. However, little is known about the in vivo function of mGluR in umami taste. Here, we examined taste responses of the chorda tympani (CT) and the glossopharyngeal (GL) nerves in wild-type mice and mice genetically lacking mGluR4 (mGluR4-KO). Our results indicated that compared to wild-type mice, mGluR4-KO mice showed significantly smaller gustatory nerve responses to glutamate and l-(+)-2-amino-4-phosphonobutyrate (an agonist for group III mGluR) in both the CT and GL nerves without affecting responses to other taste stimuli. Residual glutamate responses in mGluR4-KO mice were not affected by (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (an antagonist for group III mGluR), but were suppressed by gurmarin (a T1R3 blocker) in the CT and (RS)-1-aminoindan-1,5-dicarboxylic acid (an antagonist for group I mGluR) in the CT and GL nerve. In wild-type mice, both quisqualic acid (an agonist for group I mGluR) and l-(+)-2-amino-4-phosphonobutyrate elicited gustatory nerve responses and these responses were suppressed by addition of (RS)-1-aminoindan-1,5-dicarboxylic acid and (RS)-alpha-cyclopropyl-4-phosphonophenylglycine, respectively. Collectively, the present study provided functional evidences for the involvement of mGluR4 in umami taste responses in mice. The results also suggest that T1R1+T1R3 and mGluR1 are involved in umami taste responses in mice. Thus, umami taste would be mediated by multiple receptors.

DOI： 10.1113/jphysiol.2014.284703

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Language：Japanese   Publisher：日本味と匂学会  

アンジオテンシンII(Ang II)は血圧や体内Na+濃度を調節するホルモンであるが、近年著者らはAng IIが末梢の味覚器にもAng II type I受容体(AT1)を介して作用し、塩味感受性を修飾するのみならず、甘味感受性を増強することを発見した。この甘味増強作用は、摂食促進因子エンドカンナビノイド(eCB)の受容体(CB1)欠損マウスではみられなかったことから、Ang IIを介した甘味増強作用にはeCB系が関与する可能性が示唆されたが、その詳細はほとんど不明であった。今回、この点を明らかにするため、マウスを用いて様々な実験を行った。その結果、Ang IIによる甘味感受性の増強は、AT1シグナル下流で産生されるDiacylglycerolがDiacylglycerol lipaseの作用によって2-Arachidonoylglycerolに変換され、これが甘味細胞に発現するCB1を活性化することで生じる可能性が示唆された。

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Other Link： https://search.jamas.or.jp/index.php?module=Default&action=Link&pub_year=2014&ichushi_jid=J04102&link_issn=&doc_id=20150212090011&doc_link_id=%2Fcw7jasts%2F2014%2F002103%2F014%2F0259-0262%26dl%3D0&url=http%3A%2F%2Fwww.medicalonline.jp%2Fjamas.php%3FGoodsID%3D%2Fcw7jasts%2F2014%2F002103%2F014%2F0259-0262%26dl%3D0&type=MedicalOnline&icon=https%3A%2F%2Fjk04.jamas.or.jp%2Ficon%2F00004_2.gif

Language：English   Publishing type：Research paper (scientific journal)   Publisher：BENTHAM SCIENCE PUBL LTD  

In the oral cavity, taste receptor cells dedicate to detecting chemical compounds in foodstuffs and transmitting their signals to gustatory nerve fibers. Heretofore, five taste qualities (sweet, umami, bitter, salty and sour) are generally accepted as basic tastes. Each of these may have a specific role in the detection of nutritious and poisonous substances; sweet for carbohydrate sources of calories, umami for protein and amino acid contents, bitter for harmful compounds, salty for minerals and sour for ripeness of fruits and spoiled foods. Recent studies have revealed molecular mechanisms for reception and transduction of these five basic tastes. Sweet, umami and bitter tastes are mediated by G-protein coupled receptors (GPCRs) and second-messenger signaling cascades. Salty and sour tastes are mediated by channel-type receptors. In addition to five basic tastes, taste receptor cells may have the ability to detect fat taste, which is elicited by fatty acids, and calcium taste, which is elicited by calcium. Taste compounds eliciting either fat taste or calcium taste may be detected by specific GPCRs expressed in taste receptor cells. This review will focus on transduction mechanisms and cellular characteristics responsible for each of basic tastes, fat taste and calcium taste.

DOI： 10.2174/13816128113199990575

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BENTHAM SCIENCE PUBL LTD  

Detection of tastes is critical for animals. Sweet, umami and bitter taste are mediated by G-protein-coupled receptors that are expressed in the taste receptor cells. TAS1Rs which belong to class C G-protein-coupled receptors form heterodimeric complexes to function as sweet (TAS1R2 + TAS1R3) or umami (TAS1R1 + TAS1R3) taste receptors. Umami taste is also considered to be mediated by mGluRs. TAS2Rs belong to class A G-protein-coupled receptors and are responsible for bitter taste. After activation of these receptors, their second messenger pathways lead to depolarization and intracellular calcium increase in taste receptor cells. Then, transmitter is released from taste receptor cells leading to activation of taste nerve fibers and taste information is sent to the central nervous system. Recent studies on heterologous expression system and molecular modeling lead to better understanding of binding site of TAS1Rs and TAS2Rs and molecular mechanisms for interaction between taste substances and these receptors. TAS1Rs and TAS2Rs have multiple and single binding sites for structurally diverse ligands, respectively. Sensitivities of these receptors are known to differ among individuals, strains, and species. In addition, some species abolish these receptors and signaling molecules. Here we focus on structure, function, signaling, polymorphism, and molecular evolution of the taste G-protein-coupled receptors.

DOI： 10.2174/1389201015666140922105911

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Association for the Study of Taste and Smell  

CiNii Article

CiNii Books

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Other Link： http://search.jamas.or.jp/link/ui/2016009974

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC NEUROSCIENCE  

Understanding the mechanisms underlying gustatory detection of dietary sodium is important for the prevention and treatment of hypertension. Here, we show that Angiotensin II (AngII), a major mediator of body fluid and sodium homeostasis, modulates salty and sweet taste sensitivities, and that this modulation critically influences ingestive behaviors in mice. Gustatory nerve recording demonstrated that AngII suppressed amiloride-sensitive taste responses to NaCl. Surprisingly, AngII also enhanced nerve responses to sweeteners, but had no effect on responses to KCl, sour, bitter, or umamitastants. These effects of AngII on nerve responses were blocked by the angiotensin II type 1 receptor (AT1) antagonist CV11974. In behavioral tests, CV11974 treatment reduced the stimulated high licking rate to NaCl and sweeteners in water-restricted mice with elevated plasma AngII levels. In taste cells AT1 proteins were coexpressed with alpha ENaC (epithelial sodium channel alpha-subunit, an amiloride-sensitive salt taste receptor) or T1r3 (a sweet taste receptor component). These results suggest that the taste organ is a peripheral target of AngII. The specific reduction of amiloride-sensitive salt taste sensitivity by AngII may contribute to increased sodium intake. Furthermore, AngII may contribute to increased energy intake by enhancing sweet responses. The linkage between salty and sweet preferences via AngII signaling may optimize sodium and calorie intakes.

DOI： 10.1523/JNEUROSCI.5599-12.2013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

The T1R1 receptor subunit acts as an umami taste receptor in combination with its partner, T1R3. In addition, metabotropic glutamate receptors (brain and taste variants of mGluR1 and mGluR4) are thought to function as umami taste receptors. To elucidate the function of T1R1 and the contribution of mGluRs to umami taste detection in vivo, we used newly developed knock-out (T1R1/) mice, which lack the entire coding region of the Tas1r1 gene and express mCherry in T1R1-expressing cells. Gustatory nerve recordings demonstrated that T1R1/ mice exhibited a serious deficit in inosine monophosphate-elicited synergy but substantial residual responses to glutamate alone in both chorda tympani and glossopharyngeal nerves. Interestingly, chorda tympani nerve responses to sweeteners were smaller in T1R1/ mice. Taste cell recordings demonstrated that many mCherry-expressing taste cells in T1R1+/ mice responded to sweet and umami compounds, whereas those in T1R1/ mice responded to sweet stimuli. The proportion of sweet-responsive cells was smaller in T1R1/ than in T1R1+/ mice. Single-cell RT-PCR demonstrated that some single mCherry-expressing cells expressed all three T1R subunits. Chorda tympani and glossopharyngeal nerve responses to glutamate were significantly inhibited by addition of mGluR antagonists in both T1R1/ and T1R1+/ mice. Conditioned taste aversion tests demonstrated that both T1R1/ and T1R1+/ mice were equally capable of discriminating glutamate from other basic taste stimuli. Avoidance conditioned to glutamate was significantly reduced by addition of mGluR antagonists. These results suggest that T1R1-expressing cells mainly contribute to umami taste synergism and partly to sweet sensitivity and that mGluRs are involved in the detection of umami compounds.

DOI： 10.1113/jphysiol.2012.236604

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Language：English   Publisher：ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD  

Taste receptor cells play a major role in detection of chemical compounds in the oral cavity. Information derived from taste receptor cells, such as sweet, bitter, salty, sour and umami is important for evaluating the quality of food components. Among five basic taste qualities, sweet taste is very attractive for animals and influences food intake. Recent studies have demonstrated that sweet taste sensitivity in taste receptor cells would be affected by leptin and endocannabinoids. Leptin is an anorexigenic mediator that reduces food intake by acting on leptin receptor Ob-Rb in the hypothalamus. Endocannabinoids such as anandamide [N-arachidonoylethanolamine (AEA)] and 2-arachidonoyl glycerol (2-AG) are known as orexigenic mediators that act via cannabinoid receptor 1 (CB1) in the hypothalamus and limbic forebrain to induce appetite and stimulate food intake. At the peripheral gustatory organs, leptin selectively suppresses and endocannabinoids selectively enhance sweet taste sensitivity via Ob-Rb and CB1 expressed in sweet sensitive taste cells. Thus leptin and endocannabinoids not only regulate food intake via central nervous systems but also modulate palatability of foods by altering peripheral sweet taste responses. Such reciprocal modulation of leptin and endocannabinoids on peripheral sweet sensitivity may play an important role in regulating energy homeostasis. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.semcdb.2012.08.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

The distinctive umami taste elicited by L-glutamate and some other amino acids is thought to be initiated by G-protein-coupled receptors. Proposed umami receptors include heteromers of taste receptor type 1, members 1 and 3 (T1R1+ T1R3), andmetabotropic glutamate receptors 1 and 4 (mGluR1 and mGluR4). Multiple lines of evidence support the involvement of T1R1+ T1R3 in umami responses of mice. Although several studies suggest the involvement of receptors other than T1R1+ T1R3 in umami, the identity of those receptors remains unclear. Here, we examined taste responsiveness of umami-sensitive chorda tympani nerve fibres fromwild-type mice andmice genetically lacking T1R3 or its downstream transduction molecule, the ion channel TRPM5. Our results indicate that single umami-sensitive fibres in wild-type mice fall into two major groups: sucrose-best (S-type) andmonopotassium glutamate (MPG)-best (M-type). Each fibre type has two subtypes; one shows synergism between MPG and inosine monophosphate (S1, M1) and the other shows no synergism (S2, M2). In both T1R3 and TRPM5 null mice, S1-type fibres were absent, whereas S2-, M1-and M2-types remained. Lingual application of mGluR antagonists selectively suppressedMPG responses of M1-andM2-type fibres. These data suggest the existence of multiple receptors and transduction pathways for umami responses in mice. Information initiated from T1R3-containing receptors may be mediated by a transduction pathway including TRPM5 and conveyed by sweet-best fibres, whereas umami information from mGluRs may be mediated by TRPM5-independent pathway(s) and conveyed by glutamate-best fibres.

DOI： 10.1113/jphysiol.2011.211920

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

In taste bud cells, glutamate may elicit two types of responses, as an umami tastant and as a neurotransmitter. Glutamate applied to apical membrane of taste cells would elicit taste responses whereas glutamate applied to basolateral membrane may act as a neurotransmitter. Using restricted stimulation to apical or basolateral membrane of taste cells, we examined responses of taste cells to glutamate stimulation, separately. Apical application of monosodium glutamate (MSG, 0.3 M) increased firing frequency in some of mouse fungiform taste cells that evoked action potentials. These cells were tested with other basic taste compounds, NaCl (salty), saccharin (sweet), HCl (sour), and quinine (bitter). MSG-sensitive taste cells could be classified into sweet-best (S-type), MSG-best (M-type), and NaCl or other electrolytes-best (N- or E/H-type) cells. Furthermore, S- and M-type could be classified into two sub-types according to the synergistic effect between MSG and inosine-5&apos;-monophosphate (S1, M1 with synergism; S2, M2 without synergism). Basolateral application of glutamate (100 mu M) had almost no effect on the mean spontaneous firing rates in taste cells. However, about 10% of taste cells tested showed transient increases in spontaneous firing rates (&gt; mean + 2 standard deviation) after basolateral application of glutamate. These results suggest the existence of multiple types of umami-sensitive taste cells and the existence of glutamate receptor(s) on the basolateral membrane of a subset of taste cells.

DOI： 10.1007/s10571-011-9702-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PUBLIC LIBRARY SCIENCE  

Background: The polycystic kidney disease-like ion channel PKD2L1 and its associated partner PKD1L3 are potential candidates for sour taste receptors. PKD2L1 is expressed in type III taste cells that respond to sour stimuli and genetic elimination of cells expressing PKD2L1 substantially reduces chorda tympani nerve responses to sour taste stimuli. However, the contribution of PKD2L1 and PKD1L3 to sour taste responses remains unclear.
Methodology/Principal Findings: We made mice lacking PKD2L1 and/or PKD1L3 gene and investigated whole nerve responses to taste stimuli in the chorda tympani or the glossopharyngeal nerve and taste responses in type III taste cells. In mice lacking PKD2L1 gene, chorda tympani nerve responses to sour, but not sweet, salty, bitter, and umami tastants were reduced by 25-45% compared with those in wild type mice. In contrast, chorda tympani nerve responses in PKD1L3 knockout mice and glossopharyngeal nerve responses in single-and double-knock-out mice were similar to those in wild type mice. Sour taste responses of type III fungiform taste cells (GAD67-expressing taste cells) were also reduced by 25-45% by elimination of PKD2L1.
Conclusions/Significance: These findings suggest that PKD2L1 partly contributes to sour taste responses in mice and that receptors other than PKDs would be involved in sour detection.

DOI： 10.1371/journal.pone.0020007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHARMACEUTICAL SOC JAPAN  

Gustatory signaling begins with taste receptor cells that express taste receptors. Recent molecular biological studies have identified taste receptors and transduction components for basic tastes (sweet, salty, sour, bitter, and umami). Activation of these receptor systems leads to depolarization and an increase in [Ca2+](i), in taste receptor cells. Then transmitters are released from taste cells and activate gustatory nerve fibers. The connection between taste cells and gustatory nerve fibers would be specific because there may be only limited divergence of taste information at the peripheral transmission. Recent studies have demonstrated that sweet taste information can be modulated by hormones or other endogenous factors that could act on their receptors in a specific group of taste cells. These peripheral modulations of taste information may influence preference behavior and food intake. This paper summarizes data on molecular mechanisms for detection and transduction of taste signals in taste bud cells, information transmission from taste cells to gustatory nerve fibers, and modulation of taste signals at peripheral taste organs, in particular for sweet taste, which may play important roles in regulating energy homeostasis.

DOI： 10.1248/bpb.33.1772

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSIOLOGICAL SOC  

Murata Y, Yasuo T, Yoshida R, Obata K, Yanagawa Y, Margolskee RF, Ninomiya Y. Action potential-enhanced ATP release from taste cells through hemichannels. J Neurophysiol 104: 896-901, 2010. First published June 2, 2010; doi: 10.1152/jn.00414.2010. Only some taste cells fire action potentials in response to sapid stimuli. Type II taste cells express many taste transduction molecules but lack well-elaborated synapses, bringing into question the functional significance of action potentials in these cells. We examined the dependence of adenosine triphosphate (ATP) transmitter release from taste cells on action potentials. To identify type II taste cells we used mice expressing a green fluorescence protein (GFP) transgene from the alpha-gustducin promoter. Action potentials were recorded by an electrode basolaterally attached to a single GFP-positive taste cell. We monitored ATP release from gustducin-expressing taste cells by collecting the electrode solution immediately after tastant-stimulated action potentials and using a luciferase assay to quantify ATP. Stimulation of gustducin-expressing taste cells with saccharin, quinine, or glutamate on the apical membrane increased ATP levels in the electrode solution; the amount of ATP depended on the firing rate. Increased spontaneous firing rates also induced ATP release from gustducin-expressing taste cells. ATP release from gustducin-expressing taste cells was depressed by tetrodotoxin and inhibited below the detection limit by carbenoxolone. Our data support the hypothesis that action potentials in taste cells responsive to sweet, bitter, or umami tastants enhance ATP release through pannexin 1, not connexin-based hemichannels.

DOI： 10.1152/jn.00414.2010

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Language：English   Publisher：日本神経化学会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC NEUROSCIENCE  

The oral perception of fat has traditionally been considered to rely mainly on texture and olfaction, but recent findings suggest that taste may also play a role in the detection of long chain fatty acids. The two G-protein coupled receptors GPR40 (Ffar1) and GPR120 are activated by medium and long chain fatty acids. Here we show that GPR120 and GPR40 are expressed in the taste buds, mainly in type II and type I cells, respectively. Compared with wild-type mice, male and female GPR120 knock-out and GPR40 knock-out mice show a diminished preference for linoleic acid and oleic acid, and diminished taste nerve responses to several fatty acids. These results show that GPR40 and GPR120 mediate the taste of fatty acids.

DOI： 10.1523/JNEUROSCI.0496-10.2010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL ACAD SCIENCES  

Endocannabinoids such as anandamide [N-arachidonoylethanolamine (AEA)] and 2-arachidonoyl glycerol (2-AG) are known orexigenic mediators that act via CB(1) receptors in hypothalamus and limbic forebrain to induce appetite and stimulate food intake. Circulating endocannabinoid levels inversely correlate with plasma levels of leptin, an anorexigenic mediator that reduces food intake by acting on hypothalamic receptors. Recently, taste has been found to be a peripheral target of leptin. Leptin selectively suppresses sweet taste responses in wild-type mice but not in leptin receptor-deficient db/db mice. Here, we show that endocannabinoids oppose the action of leptin to act as enhancers of sweet taste. We found that administration of AEA or 2-AG increases gustatory nerve responses to sweeteners in a concentration-dependent manner without affecting responses to salty, sour, bitter, and umami compounds. The cannabinoids increase behavioral responses to sweet-bitter mixtures and electrophysiological responses of taste receptor cells to sweet compounds. Mice genetically lacking CB(1) receptors show no enhancement by endocannnabinoids of sweet taste responses at cellular, nerve, or behavioral levels. In addition, the effects of endocannabinoids on sweet taste responses of taste cells are diminished by AM251, a CB(1) receptor antagonist, but not by AM630, a CB(2) receptor antagonist. Immunohistochemistry shows that CB(1) receptors are expressed in type II taste cells that also express the T1r3 sweet taste receptor component. Taken together, these observations suggest that the taste organ is a peripheral target of endocannabinoids. Reciprocal regulation of peripheral sweet taste reception by endocannabinoids and leptin may contribute to their opposing actions on food intake and play an important role in regulating energy homeostasis.

DOI： 10.1073/pnas.0912048107

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Language：English   Publisher：JAPANESE PHARMACOLOGICAL SOC  

The ability to perceive sweet compounds is important for animals to detect an external carbohydrate source of calories and has a critical role in the nutritional status of animals. In mice, a subset of sweet-sensitive taste cells possesses leptin receptors. Increase of plasma leptin with increasing internal energy storage in the adipose tissue suppresses sweet taste responses via this receptor. The data from recent studies indicate that leptin may also act as a modulator of sweet taste sensation in humans with a diurnal variation in sweet sensitivity. The plasma leptin level and sweet taste sensitivity are proposed to link with post-ingestive plasma glucose level. This leptin modulation of sweet taste sensitivity may influence an individual's preference, ingestive behavior, and absorption of nutrients, thereby playing important roles in regulation of energy homeostasis.

DOI： 10.1254/jphs.09R07FM

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PubMed

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Language：English   Publisher：Japanese Association for Oral Biology  

Gustatory information processing begins with taste bud cells,astr which are activated by sapid molecules via specific taste receptors and transmit their signals to gustatory afferent fibers. Taste bud cells are morphologically classified into 4 groups (Type I -IV cells), two of which are involved in gustatory sig-naling. Type II cells express sweet, bitter, and umami taste receptors and transduction components and respond best to sweet, bitter, or umami stimuli, suggesting that sweet, bitter, and umami tastes are detected by different sets of Type II cells. Type m cells express putative sour taste receptors and respond to sour or multiple taste stimuli, indicating that sour tastes are mediated by Typem cells. These data suggest that each taste quality could be discriminated among taste bud cells. Type II cells do not possess a conventional synaptic structure but they release ATP in response to taste stimuli. Typem cells have a synaptic structure and they release serotonin and norepinephrine but not ATP. Therefore, each taste cell may use distinct mechanisms and transmitters for signal transmission to gustatory nerve fibers.

DOI： 10.2330/joralbiosci.52.358

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Language：English   Publishing type：Research paper (scientific journal)  

Sweet taste perception is important for animals to detect carbohydrate source of calories and has a critical role in the nutritional status of animals. Recent studies demonstrated that sweet taste responses can be modulated by leptin and endocannabinoids [anandamide (N-arachidonoylethanolamine) and 2-arachidonoyl glycerol]. Leptin is an anorexigenic mediator that reduces food intake by acting on hypothalamic receptor, Ob-Rb. Leptin is shown to selectively suppress sweet taste responses in wild-type mice but not in leptin receptor-deficient db/db mice. In marked contrast, endocannabinoids are orexigenic mediators that act via CB1 receptors in hypothalamus and limbic forebrain to induce appetite and stimulate food intake. In the peripheral taste system, endocannabinoids also oppose the action of leptin and enhance sweet taste sensitivities in wild-type mice but not in mice genetically lacking CB1 receptors. These findings indicate that leptin and endocannabinoids not only regulate food intake via central nervous systems but also may modulate palatability of foods by altering peripheral sweet taste responses via their cognate receptors. © 2011 Springer Berlin Heidelberg.

DOI： 10.1007/978-3-642-14426-4_9

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Language：English   Publishing type：Part of collection (book)   Publisher：ELSEVIER ACADEMIC PRESS INC  

Taste receptor cells detect chemical compounds in the oral cavity and transfer their messages to gustatory afferent nerve fibers. Considering the coding of taste information, the sensitivity of taste cells and the connection between taste cells and gustatory fibers may be critical in this process. Broadly tuned taste cells and random connections between taste cells and fibers would produce gustatory fibers that have broad sensitivity to multiple taste qualities. Narrowly tuned taste cells and selective connections would yield gustatory nerve fibers that respond to specific taste quality. This review summarizes results showing molecular and morphological aspects of taste bud cells, physiological responses of taste cells, possible connections between taste cells and gustatory fibers, and transmitter release from taste cells, and discusses how taste qualities are encoded among taste bud cells and how taste information is transmitted from taste cells to gustatory nerve fibers.

DOI： 10.1016/S1937-6448(10)79004-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL PUBLISHING, INC  

Multiple lines of evidence from molecular studies indicate that individual taste qualities are encoded by distinct taste receptor cells. In contrast, many physiological studies have found that a significant proportion of taste cells respond to multiple taste qualities. To reconcile this apparent discrepancy and to identify taste cells that underlie each taste quality, we investigated taste responses of individual mouse fungiform taste cells that express gustducin or GAD67, markers for specific types of taste cells. Type II taste cells respond to sweet, bitter or umami tastants, express taste receptors, gustducin and other transduction components. Type III cells possess putative sour taste receptors, and have well elaborated conventional synapses. Consistent with these findings we found that gustducin-expressing Type II taste cells responded best to sweet (25/49), bitter (20/49) or umami (4/49) stimuli, while all GAD67 (Type III) taste cells examined (44/44) responded to sour stimuli and a portion of them showed multiple taste sensitivities, suggesting discrimination of each taste quality among taste bud cells. These results were largely consistent with those previously reported with circumvallate papillae taste cells. Bitter-best taste cells responded to multiple bitter compounds such as quinine, denatonium and cyclohexamide. Three sour compounds, HCl, acetic acid and citric acid, elicited responses in sour-best taste cells. These results suggest that taste cells may be capable of recognizing multiple taste compounds that elicit similar taste sensation. We did not find any NaCl-best cells among the gustducin and GAD67 taste cells, raising the possibility that salt sensitive taste cells comprise a different population.

DOI： 10.1113/jphysiol.2009.175075

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC NUTRITION-ASN  

L-Glutamate is known to elicit a unique taste, umami, that is distinct from the tastes of sweet, salty, sour, and bitter. Recent molecular studies have identified several candidate receptors for umami in taste cells, such as the heterodimer T1R1/T1R3 and brain-expressed and taste-expressed type 1 and 4 metabotropic glutamate receptors (brain-mGluR1, brain-mGluR4, taste-mGluR1, and taste-mGluR4). However, the relative contributions of these receptors to umami taste reception remain to be elucidated. We critically discuss data from recent studies in which mouse taste cell, nerve fiber, and behavioral responses to umami stimuli were measured to evaluate whether receptors other than T1R1/T1R3 are involved in umami responses. We particularly emphasized studies of umami responses in T1R3 knockout (KO) mice and studies of potential effects of mGluR antagonists on taste responses. The results of these studies indicate the existence of substantial residual responses to umami compounds in the T1R3-KO model and a significant reduction of umami responsiveness after administration of mGluR antagonists. These findings thus provide evidence of the involvement of mGluRs in addition to T1R1/T1R3 in umami detection in mice and suggest that umami responses, at least in mice, may be mediated by multiple receptors. Am J Clin Nutr 2009; 90(suppl): 747S-52S.

DOI： 10.3945/ajcn.2009.27462J

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC NUTRITION-ASN  

The unique taste induced by monosodium glutamate is referred to as umami taste. The umami taste is also elicited by the purine nucleotides inosine 5'-monophosphate and guanosine 5'-monophosphate. There is evidence that a heterodimeric G protein-coupled receptor, which consists of the T1R1 ( taste receptor type 1, member 1, Tas1r1) and the T1R3 ( taste receptor type 1, member 3, Tas1r3) proteins, functions as an umami taste receptor for rodents and humans. Splice variants of metabotropic glutamate receptors, mGluR1 ( glutamate receptor, metabotropic 1, Grm1) and mGluR4 ( glutamate receptor, metabotropic 4, Grm4), also have been proposed as taste receptors for glutamate. The taste sensitivity to umami substances varies in inbred mouse strains and in individual humans. However, little is known about the relation of umami taste sensitivity to variations in candidate umami receptor genes in rodents or in humans. In this article, we summarize current knowledge of the diversity of umami perception in mice and humans. Furthermore, we combine previously published data and new information from the single nucleotide polymorphism databases regarding variation in the mouse and human candidate umami receptor genes: mouse Tas1r1 (TAS1R1 for human), mouse Tas1r3 (TAS1R3 for human), mouse Grm1 (GRM1 for human), and mouse Grm4 (GRM4 for human). Finally, we discuss prospective associations between variation of these genes and umami taste perception in both species. Am J Clin Nutr 2009; 90( suppl): 764S-9S.

DOI： 10.3945/ajcn.2009.27462M

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PUBLIC LIBRARY SCIENCE  

Umami taste (corresponds to savory in English) is elicited by L-glutamate, typically as its Na salt (monosodium glutamate: MSG), and is one of five basic taste qualities that plays a key role in intake of amino acids. A particular property of umami is the synergistic potentiation of glutamate by purine nucleotide monophosphates (IMP, GMP). A heterodimer of a G protein coupled receptor, TAS1R1 and TAS1R3, is proposed to function as its receptor. However, little is known about genetic variation of TAS1R1 and TAS1R3 and its potential links with individual differences in umami sensitivity. Here we investigated the association between recognition thresholds for umami substances and genetic variations in human TAS1R1 and TAS1R3, and the functions of TAS1R1/TAS1R3 variants using a heterologous expression system. Our study demonstrated that the TAS1R1-372T creates a more sensitive umami receptor than -372A, while TAS1R3-757C creates a less sensitive one than - 757R for MSG and MSG plus IMP, and showed a strong correlation between the recognition thresholds and in vitro dose - response relationships. These results in human studies support the propositions that a TAS1R1/TAS1R3 heterodimer acts as an umami receptor, and that genetic variation in this heterodimer directly affects umami taste sensitivity.

DOI： 10.1371/journal.pone.0006717

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Previous studies have demonstrated that rodents&apos; chorda tympani (CT) nerve fibers responding to NaCl can be classified according to their sensitivities to the epithelial sodium channel (ENaC) blocker amiloride into two groups: amiloride-sensitive (AS) and -insensitive (Al). The AS fibers were shown to respond specifically to NaCl, whereas Al fibers broadly respond to various electrolytes, including NaCl. These data suggest that salt taste transduction in taste cells may be composed of at least two different systems; AS and Al ones. To further address this issue, we investigated the responses to NaCl, KCl and HCl and the amiloride sensitivity of mouse fungiform papilla taste bud cells which are innervated by the CT nerve. Comparable with the CT data, the results indicated that 56 NaCl-responsive cells tested were classified into two groups; 25 cells (similar to 44%) narrowly responded to NaCl and their NaCl response were inhibited by amiloride (AS cells), whereas the remaining 31 cells (similar to 56%) responded not only to NaCl, but to KCl and/or HCl and showed no amiloride inhibition of NaCl responses (Al cells). Amiloride applied to the basolateral side of taste cells had no effect on NaCl responses in the AS and Al cells. Single cell reverse transcription-polymerase chain reaction (RT-PCR) experiments indicated that ENaC subunit mRNA was expressed in a subset of AS cells. These findings suggest that the mouse fungiform taste bud is composed of AS and Al cells that can transmit taste information differently to their corresponding types of CT fibers, and apical ENaCs may be involved in the NaCl responses of AS cells. (C) 2009 IBRO. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.neuroscience.2008.12.052

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Perception of sweet taste is important for animals to detect external energy source of calories. In mice, sweet-sensitive cells possess a leptin receptor. Increase of plasma leptin with increasing internal energy storage in the adipose tissue suppresses sweet taste responses via this receptor. Data from our recent studies indicate that leptin may also modulate sweet taste sensation in humans with a diurnal variation in sweet sensitivity. This leptin modulation of sweet taste information to the brain may influence individuals' preference and ingestive behavior, thereby playing important roles in regulation of energy homeostasis.

DOI： 10.1111/j.1749-6632.2009.03893.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL PUBLISHING  

Recent molecular studies proposed that the T2r1/T1r3 heterodimer, mGluR1 and mGluR4 might function as umami taste receptors in mice. However, the roles of each of these receptors in umami taste are not yet clear. In this paper, we summarize recent data for T1r3, mGluR1, and mGluR4 as umami taste receptors and discuss receptor systems responsible for umami detection in mice.

DOI： 10.1111/j.1749-6632.2009.03902.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FEDERATION AMER SOC EXP BIOL  

Ordinary gustatory experiences, which are usually evoked by taste mixtures, are determined by multiple interactions between different taste stimuli. The most studied model for these gustatory interactions is the suppression of the responses to sweeteners by the prototype bitter compound quinine. Here we report that TRPM5, a cation channel involved in sweet taste transduction, is inhibited by quinine (EC50=50 mu M at -50 mV) owing to a decrease in the maximal whole-cell TRPM5 conductance and an acceleration of channel closure. Notably, quinine inhibits the gustatory responses of sweet-sensitive gustatory nerves in wildtype (EC50=similar to 1.6 mM) but not in Trpm5 knockout mice. Quinine induces a dose- and time-dependent inhibition of TRPM5-dependent responses of single sweet-sensitive fibers to sucrose, according to the restricted diffusion of the drug into the taste tissue. Quinidine, the stereoisomer of quinine, has similar effects on TRPM5 currents and on sweet-induced gustatory responses. In contrast, the chemically unrelated bitter compound denatonium benzoate has an similar to 100-fold weaker effect on TRPM5 currents and, accordingly, at 10 mM it does not alter gustatory responses to sucrose. The inhibition of TRPM5 by bitter compounds constitutes the molecular basis of a novel mechanism of taste interactions, whereby the bitter tastant inhibits directly the sweet transduction pathway.

DOI： 10.1096/fj.07-9591com

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSIOLOGICAL SOC  

An epithelial Na+ channel (ENaC) is expressed in taste cells and may be involved in the salt taste transduction. ENaC activity is blocked by amiloride, which in several mammalian species also inhibits taste responses to NaCl. In mice, lingual application of amiloride inhibits NaCl responses in the chorda tympani (CT) gustatory nerve much stronger in the C57BL/6 (B6) strain than in the 129P3/J (129) strain. We examined whether this strain difference is related to gene sequence variation or mRNA expression of three ENaC subunits (alpha, beta, gamma). Real-time RT-PCR and in situ hybridization detected no significant strain differences in expression of all three ENaC subunits in fungiform papillae. Sequences of the beta- and gamma ENaC subunit genes were also similar in the B6 and 129 strains, but alpha ENaC gene had three single nucleotide polymorphisms (SNPs). One of these SNPs resulted in a substitution of arginine in the B6 strain to tryptophan in the 129 strain (R616W) in the alpha ENaC protein. To examine association of this SNP with amiloride sensitivity of CT responses to NaCl, we produced F2 hybrids between B6 and 129 strains. Amiloride inhibited CT responses to NaCl in F-2 hybrids with B6/129 and B6/B6 alpha ENaC R616W genotypes stronger than in F-2 hybrids with 129/129 genotype. This suggests that the R616W variation in the alpha ENaC subunit affects amiloride sensitivity of the ENaC channel and provides evidence that ENaC is involved in amiloride-sensitive salt taste responses in mice.

DOI： 10.1152/ajpregu.00420.2007

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Language：English   Publisher：The Biophysical Society of Japan General Incorporated Association  

DOI： 10.2142/biophys.48.S58_5

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Language：English   Publisher：The Biophysical Society of Japan General Incorporated Association  

DOI： 10.2142/biophys.48.S58_2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC  

Inositol 1,4,5-trisphosphate receptor (IP3R) is one of the important calcium channels expressed in the endoplasmic reticulum and has been shown to play crucial roles in various physiological phenomena. Type 3 IP3R is expressed in taste cells, but the physiological relevance of this receptor in taste perception in vivo is still unknown. Here, we show that mice lacking IP(3)R3 show abnormal behavioral and electrophysiological responses to sweet, umami, and bitter substances that trigger G-protein-coupled receptor activation. In contrast, responses to salty and acid tastes are largely normal in the mutant mice. We conclude that IP3R3 is a principal mediator of sweet, bitter, and umami taste perception and would be a missing molecule linking phospholipase C beta 2 to TRPM5 activation.

DOI： 10.1074/jbc.M705641200

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Language：English   Publisher：ELSEVIER IRELAND LTD  

DOI： 10.1016/j.neures.2007.06.1001

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DOI： 10.1016/j.neures.2007.06.1002

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Language：English   Publisher：INT SOC HISTOLOGY & CYTOLOGY  

Taste signals are first detected by the taste receptor cells, which are located in taste buds existing in the tongue, soft palate, larynx and epiglottis. Taste receptor cells contact with the chemical compounds in oral cavity through the apical processes which protrude into the taste pore. Interaction between chemical compounds and the taste receptor produces activation of taste receptor cells directly or indirectly. Then the signals are transmitted to gustatory nerve fibers and higher order neurons. A recent study demonstrated many similarities between response properties of taste receptor cells with action potentials and those of the gustatory nerve fibers innervating them, suggesting information derived from receptor cells generating action potentials may form a major component of taste information that is transmitted to gustatory nerve fibers. These findings may also indicate that there is no major modification of taste information sampled by taste receptor cells in synaptic transmission from taste cells to nerve fibers although there is indirect evidence. In the peripheral taste system, gustatory nerve fibers may selectively contact with taste receptor cells that have similar response properties and convey constant taste information to the higher order neurons.

DOI： 10.1679/aohc.69.233

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSIOLOGICAL SOC  

It is known that a subset of taste cells generate action potentials in response to taste stimuli. However, responsiveness of these cells to particular tastants remains unknown. In the present study, by using a newly developed extracellular recording technique, we recorded action potentials from the basolateral membrane of single receptor cells in response to taste stimuli applied apically to taste buds isolated from mouse fungiform papillae. By this method, we examined taste-cell responses to stimuli representing the four basic taste qualities (NaCl, Na saccharin, HCl, and quinine-HCl). Of 72 cells responding to taste stimuli, 48 (67%) responded to one, 22 (30%) to two, and 2 (3%) to three of four taste stimuli. The entropy value presenting the breadth of responsiveness was 0.158 +/- 0.234 (mean +/- SD), which was close to that for the nerve fibers (0.183 +/- 0.262). In addition, the proportion of taste cells predominantly sensitive to each of the four taste stimuli, and the grouping of taste cells based on hierarchical cluster analysis, were comparable with those of chorda tympani (CT) fibers. The occurrence of each class of taste cells with different taste responsiveness to the four taste stimuli was not significantly different from that of CT fibers except for classes with broad taste responsiveness. These results suggest that information derived from taste cells generating action potentials may provide the major component of taste information that is transmitted to gustatory nerve fibers.

DOI： 10.1152/jn.00409.2006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Amiloride, a sodium channel blocker, is known to suppress NaCl responses of the chorda tympani (CT) nerve in various mammalian species. In mice, the NaCl suppressing effect of amiloride is reported to differ among strains. In C57BL mice, amiloride inhibits NaCl responses to about 50% of control, whereas no such clear suppression was evident in prior studies with 129 mice. However, evidence from behavioral studies is not entirely consistent with this. Recently, it has been found that genetic backgrounds of 129 mice differ within substrains. 129X1/SvJ (formerly 129/SvJ) mice differ from the 129P3/J (formerly 129/J) strain by 25% of sequence length polymorphisms. Therefore, we examined possible substrain difference between 129P3/J and 129X1/SvJ mice in the amiloride sensitivity of electrophysiologically. recorded NaCl responses. Amiloride significantly suppressed CT responses to NaCl without affecting responses to KCl both in 129P3/J and 129X1/SvJ mice. However, the magnitude of the amiloride inhibition was significantly larger (similar to 50% of control in response to 0.01-1.0 M NaCl by 100 mu M amiloride) in 129X1/SvJ than in 129P3/J mice (similar to 20% of control in response to 0.03-0.3 M NaCl by 100 mu M amiloride). Threshold amiloride concentration for suppression of responses to 0.3 M NaCl was 30 mu M in 129P3/J mice, which was higher than that in 129X1/SvJ mice (10 mu M). In 129X1/SvJ mice, the threshold amiloride concentration eliciting inhibition of NaCl responses and the magnitude of the inhibition were comparable with those in C57BL/6 mice. These results suggest that amiloride sensitivity of NaCl responses differs even among the 129 substrains, 129P3/J and 129 X1/SvJ, and the substrain difference of 129 mice in amiloride sensitivity is as large as that between two inbred strains (129P3/J and C57BL/6).

DOI： 10.1093/chemse/bjj061

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Trpm5 is a calcium-activated cation channel expressed selectively in taste receptor cells. A previous study reported that mice with an internal deletion of Trpm5, lacking exons 15-19 encoding transmembrane segments 1-5, showed no taste-mediated responses to bitter, sweet, and umami compounds. We independently generated knockout mice null for Trpm5 protein expression due to deletion of Trpm5's promoter region and exons 1-4 (including the translation start site). We examined the taste-mediated responses of Trpm5 null mice and wild-type (WT) mice using three procedures: gustatory nerve recording [chorda tympani (CT) and glossopharyngeal (NG) nerves], initial lick responses, and 24-h two-bottle preference tests. With bitter compounds, the Trpm5 null mice showed reduced, but not abolished, avoidance (as indicated by licking responses and preference ratios higher than those of WT), a normal CT response, and a greatly diminished NG response. With sweet compounds, Trpm5 null mice showed no licking response, a diminished preference ratio, and absent or greatly reduced nerve responses. With umami compounds, Trpm5 null mice showed no licking response, a diminished preference ratio, a normal NG response, and a greatly diminished CT response. Our results demonstrate that the consequences of eliminating Trmp5 expression vary depending upon the taste quality and the lingual taste field examined. Thus, while Trpm5 is an important factor in many taste responses, its absence does not eliminate all taste responses. We conclude that Trpm5-dependent and Trpm5-independent pathways underlie bitter, sweet, and umami tastes.

DOI： 10.1093/chemse/bjj027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Gurmarin (Gur) is a peptide that selectively inhibits responses of the chorda tympani (CT) nerve to sweet compounds in rodents. In mice, the sweet-suppressing effect of Gur differs among strains. The inhibitory effect of Gur is clearly observed in C57BL/6 mice, but only slightly, if at all, in BALB/c mice. These two mouse strains possess different alleles of the sweet receptor gene, Sac (Tas1r3) (taster genotype for C57BL/6 and non-taster genotype for BALB/c mice), suggesting that polymorphisms in the gene may account for differential sensitivity to Gur. To investigate this possibility, we examined the effect of Gur in another Tas1r3 non-taster strain, 129X1/Sv mice. The results indicated that unlike non-taster BALB/c mice but similar to taster C57BL/6 mice, 129X1/Sv mice exhibited significant inhibition of CT responses to various sweet compounds by Gur. This suggests that the mouse strain difference in the Gur inhibition of sweet responses of the CT nerve may not be associated with polymorphisms of Tas1r3.

DOI： 10.1093/chemse/bji041

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Our previous electrophysiological study demonstrated that amiloride-sensitive (AS) and -insensitive (AI) components of NaCl responses recovered differentially after the mouse chorda tympani (CT) was crushed. AI responses reappeared earlier (at 3 weeks after the nerve crush) than did AS ones (at 4 weeks). This and other results suggested that two salt-responsive systems were differentially and independently reformed after nerve crush. To investigate the molecular mechanisms of formation of the salt responsive systems, we examined expression patterns of three subunits (alpha, beta and gamma) of the amiloride-sensitive epithelial Na+ channel (ENaC) in mouse taste cells after CT nerve crush by using in situ hybridization (ISH) analysis. The results showed that all three ENaC subunits, as well as alpha-gustducin, a marker of differentiated taste cells, were expressed in a subset of taste bud cells from an early stage (1-2 weeks) after nerve crush, although these taste buds were smaller and fewer in number than for control mice. At 3 weeks, the mean number of each ENaC subunit and alpha-gustducin mRNA-positive cells per taste bud reached the control level. Also, the size of taste buds became similar to those of the control mice at this time. Our previous electrophysiological study demonstrated that at 2 weeks no significant response of the nerve to chemical stimuli was observed. Thus ENaC subunits appear to be expressed prior to the reappearance of AI and AS neural responses after CT nerve crush. These results support the view that differentiation of taste cells into AS or AI cells is initiated prior to synapse formation.

DOI： 10.1093/chemse/bji046

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

DOI： 10.1093/chemse/bjh125

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DOI： 10.1093/chemse/bjh092

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DOI： 10.1093/chemse/bjh114

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS INC  

The calcium imaging method can detect the spike activities of many neurons simultaneously. In the present experiments, this method was used to search for unique neurons contributing to feeding behavior in the cerebral ganglia of Aplysia kurodai. We mainly explored the neurons whose cell bodies were located in the G cluster and the neuropile region posterior to this cluster on the ventral surface of the cerebral ganglia. When the extract of the food seaweed Ulva was applied to the tentacle-lip region, many neurons stained with a calcium-sensitive dye, Calcium Green-1, showed changes in fluorescence. Some neurons showed rhythmic responses and others showed transient responses, suggesting that these neurons may be partly involved in the feeding circuits. We also identified three motor neurons among these neurons that showed rhythmic fluorescence responses to the taste stimulation. One of them was a motor neuron shortening the anterior tentacle (ATS), and the other two were motor neurons producing lip opening-like (LOG) and closing-like (LCG) movements, respectively. Application of the Ulva extract to the tentacle-lip region induced phase-locked rhythmic firing activity in these motor neurons, suggesting that these neurons may contribute to the rhythmic patterned movements of the anterior tentacles and lips during the ingestion of seaweed. (C) 2003 Wiley Periodicals, Inc.

DOI： 10.1002/neu.10207

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Language：Japanese   Publisher：The Biophysical Society of Japan General Incorporated Association  

The conventional electrophysiological method revealed some aspects of neural network for animal behavior. But it was inappropriate for recording activities of many neurons simultaneously. For the purpose of the multi-cell recording from Aplysia central nervous system, we used the calcium imaging method. Spike activities could be recorded from-30 neurons simultaneously. We also demonstrated that the firing properties of individual neurons, such as frequency or period, and the phase-locked firing patterns of these neurons could be easily detected. Moreover, combining this method with the electrophysiological method, we could identify several motor neurons concerned with the feeding behavior of this animal.

DOI： 10.2142/biophys.43.15

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Other Link： https://jlc.jst.go.jp/DN/JALC/00160735934?from=CiNii

Language：Japanese   Publisher：(株)学研メディカル秀潤社  

味を受容する味蕾は,味細胞が数十個集まってできている.味細胞の寿命は短く,約10日のサイクルで,新しく置き換わっている(ターンオーバー).味神経は味蕾の基底部にsonic hedgehog(Shh)を誘導し味細胞を増殖し,味蕾を維持するものと推定される.味神経線維は各々適合する特定の味細胞或いはその前駆細胞を選択し,シナプスを作り,ターンオーバーに際しても味の情報を変えることなく脳に伝える

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Language：Japanese   Publisher：The Biophysical Society of Japan General Incorporated Association  

DOI： 10.2142/biophys.42.S21_3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ZOOLOGICAL SOC JAPAN  

We explored whether the calcium imaging can be applicable to detection of spike activity of Aplysia wide-spread neurons. Well-used procedures, the membrane permeable acetoxymethyl (AM) types and the retrograde labeling could not be used for loading the calcium sensitive dye into many neurons, however, impalement of each cell body with a microelectrode containing high concentration of the dye solution in turn could load the dye iontophoretically into many large neurons in a relatively short time and into several small neurons in a very short time. Spike activity just induced a fluorescent increase in the cell body while depolarization without spikes induced it in the axon hillock. In the cell body the slope of the fluorescent increase was almost relative to the spike frequency while the period of it almost corresponded to the firing duration. Therefore, the phase relationship of the rhythmic firing responses in plural neurons could be precisely detected. Moreover stable responses could be repeatedly obtained for a long time from small neurons unsuitable for a long time recording with microelectrodes. Removal of the extracellular Ca2+ completely suppressed the spike-induced increase in fluorescence in the cell body and application of nifedipine partly reduced it, suggesting contribution of L-type channels distributing in Aplysia wide-spread neurons.

DOI： 10.2108/zsj.18.631

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Language：Japanese   Publisher：The Biophysical Society of Japan General Incorporated Association  

DOI： 10.2142/biophys.39.S52_1

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：OXFORD UNIV PRESS  

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Language：Japanese   Publisher：(公社)日本薬学会  

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Publishing type：Book review, literature introduction, etc.  

© 2015 Japanese Association for Oral Biology. Published by Elsevier B.V. All rights reserved. Background Several studies have demonstrated that some gut peptides known to be important in energy metabolism are expressed in mouse taste bud cells. However, the functions of these peptides in taste cells are still largely unknown. In the gut, one of these peptides, glucagon-like peptide-1 (GLP-1), which is known as the insulinotropic gut peptide, is secreted from enteroendocrine L-cells, which express as many taste molecules as those on the tongue. These taste transduction molecules are suggested to be involved in GLP-1 secretion from L-cells in response to various nutrient stimuli. GLP-1 is reported to function as a neurotransmitter via activation of its receptors expressed on the vagus nerve, thereby regulating insulin secretion. Highlight Consistent with this evidence from the gastrointestinal tract, recent studies have demonstrated that GLP-1 is secreted from mouse taste cells in response to taste compounds such as sugars, artificial sweeteners, and long-chain fatty acids. GLP-1 secreted from taste cells may activate particular types of gustatory nerve fibers because they express GLP-1 receptors and respond to GLP-1 administered via the femoral vein. Conclusion GLP-1 released from taste cells may be involved in transmission of sweet and lipid signals, thereby impacting animalsfeeding behavior in response to these important nutrient factors.

DOI： 10.1016/j.job.2015.09.002

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Language：Japanese   Publisher：日本食品機械研究会  

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Language：Japanese   Publisher：(公社)日本生物工学会  

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Language：Japanese   Publisher：(一社)歯科基礎医学会  

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DOI： 10.18965/tasteandsmell.21.1_49

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：SPRINGER JAPAN KK  

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Language：Japanese   Publisher：The Japanese Association for the Study of Taste and Smell  

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Other Link： http://search.jamas.or.jp/link/ui/2012174177

Language：English   Publishing type：Research paper, summary (international conference)   Publisher：OXFORD UNIV PRESS  

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DOI： 10.1016/j.neures.2011.07.703

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DOI： 10.1016/j.neures.2011.07.1569

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DOI： 10.1016/j.neures.2011.07.179

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DOI： 10.1016/j.neures.2011.07.665

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Language：Japanese   Publisher：The Japanese Association for the Study of Taste and Smell  

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Other Link： http://search.jamas.or.jp/link/ui/2011206881

Language：Japanese   Publisher：日本味と匂学会  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：SPRINGER TOKYO  

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DOI： 10.1016/j.neures.2010.07.1726

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DOI： 10.1016/j.neures.2010.07.1702

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DOI： 10.1016/j.neures.2010.07.1703

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Language：Japanese   Publisher：日本味と匂学会  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：OXFORD UNIV PRESS  

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Language：Japanese   Publisher：The Japanese Association for the Study of Taste and Smell  

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Other Link： http://search.jamas.or.jp/link/ui/2010076314

Language：English   Publishing type：Research paper, summary (international conference)   Publisher：OXFORD UNIV PRESS  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：ELSEVIER IRELAND LTD  

DOI： 10.1016/j.neures.2009.09.934

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DOI： 10.1016/j.neures.2009.09.926

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：SPRINGER TOKYO  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：JAPANESE PHARMACOLOGICAL SOC  

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：OXFORD UNIV PRESS  

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Language：Japanese   Publisher：日本味と匂学会  

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Publisher：一般社団法人 日本生理学会  

Taste signals are transmitted from taste cells to gustatory nerve fibers through chemical synapses. Taste cells are morphologically classified into four types: I, II, III and basal cells. Among them, chemical synapses are observed only in type III cells with putative sour receptors. However, sweet, bitter and umami receptors are expressed in type II cells, and the mechanisms have not been elucidated. Recent reports have highlighted the role of ATP as a key neurotransmitter. Here we tried to detect ATP release from single taste cells with action potentials in mouse fungiform papillae. The action potentials were recorded with the electrode basolaterally attached to a cell. When an increase in the firing rate was observed in response to a tastant, the electrode solution was applied for luciferase assay to determine the ATP. Type II and III cells express gustducin and glutamic acid decarboxylase (GAD67), respectively. We identified these cell types with transgenic mice expressing GFP in gustducin- or GAD67-positive cells. When Type II cells responded to saccharin or quinine, ATP was detected in a firing rate-dependent manner. When Type III cells increased the firing rate by application of HCl, ATP was below the detection limit. The results suggest that the amount of ATP released from taste cells differ with the response properties, or that type III cells release another neurotransmitter. &lt;b&gt;[J Physiol Sci. 2008;58 Suppl:S167]&lt;/b&gt;

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Language：Japanese   Publisher：日本味と匂学会  

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Language：Japanese   Publisher：The Japanese Association for the Study of Taste and Smell  

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Other Link： http://search.jamas.or.jp/link/ui/2008133744

Language：Japanese   Publisher：The Japanese Association for the Study of Taste and Smell  

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Other Link： http://search.jamas.or.jp/link/ui/2008133742

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J-GLOBAL

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J-GLOBAL

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Other Link： http://search.jamas.or.jp/link/ui/2008064681

Language：Japanese   Publisher：Japanese Society for Cryobiology and Cryotechnology  

Trpm5, calcium-activated cation channel of the TRP superfamily, is highly expressed in taste buds of the tongue, where it has a key role in the perception of sweet, umami and bitter tastes. Activation of Trpm5 occurs downstream of the activation of G-protein-coupled taste receptors and is proposed to generate a depolarizing potential in the taste receptor cells. Factors that modulate Trpm5 activity are therefore expected to influence taste. Here we show that Trpm5 is a highly temperature-sensitive, heat-activated channel: inward Trpm5 currents increase steeply at temperatures between 15 and 35 degrees C. Heat activation is due to a temperature-dependent shift of the activation curve, in analogy to other thermosensitive TRP channels. Moreover, we show that increasing temperature between 15 and 35 degrees C markedly enhances the gustatory nerve response to sweet compounds in wild-type but not in Trpm5 knockout mice. The strong temperature sensitivity of Trpm5 may underlie known effects of temperature on perceived taste in humans, including enhanced sweetness perception at high temperatures and 'thermal taste`, the phenomenon whereby heating or cooling of the tongue evoke sensations of taste in the absence of tastants.

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Other Link： http://search.jamas.or.jp/link/ui/2008081022

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Language：Japanese   Publisher：日本味と匂学会  

味細胞の応答とそれに伴うATP放出の関係を明らかにした。マウス(C57BL/6N)の舌を摘出した。味細胞の応答記録はルーズパッチ記録法で行った。サッカリン刺激で応答する味細胞に当てた記録電極の内液にはATPが検出され、ATPは味細胞が放出したもと考えられた。サッカリン刺激によるATP放出は、味細胞が発する活動電位の頻度が上昇することで生じ、その放出量はスパイク頻度が上昇する程度に依存した。このことは、味刺激で誘発される味細胞の活動電位がATP放出に重要な役割を担っていることが示唆された。味細胞が発する活動電位はパネキシン1の開口に関与する可能性が考えられた。

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Other Link： https://search.jamas.or.jp/index.php?module=Default&action=Link&pub_year=2007&ichushi_jid=J04102&link_issn=&doc_id=20071228200037&doc_link_id=%2Fcw7jasts%2F2007%2F001403%2F047%2F0391-0394%26dl%3D0&url=https%3A%2F%2Fwww.medicalonline.jp%2Fjamas.php%3FGoodsID%3D%2Fcw7jasts%2F2007%2F001403%2F047%2F0391-0394%26dl%3D0&type=MedicalOnline&icon=https%3A%2F%2Fjk04.jamas.or.jp%2Ficon%2F00004_2.gif

Language：Japanese   Publisher：日本味と匂学会  

単一味蕾中に存在する複数の味細胞の基本味刺激(NaCl、HCl、サッカリン、キニーネ、MSG)に対する応答をルーズパッチ法にて記録し、それらを比較することで、個々の味蕾がどのような味覚情報を味神経へ伝達しているのかについて解析した。C57BL/6Nマウスの舌を摘出した。14個の味蕾から2個の異なる味細胞の応答を同時に、もしくは別々に記録することができた。6個の味蕾では2つの味細胞が同じ刺激で最大応答を示し、残りの8個の味蕾では2つの異なる味細胞は異なる刺激により最大応答を示した。28個の味細胞に対するエントロピー値は0.156±0.269、14個の味蕾のエントロピー値は0.378±0.310となり、両者の間には有意差が見られた。

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Other Link： https://search.jamas.or.jp/index.php?module=Default&action=Link&pub_year=2007&ichushi_jid=J04102&link_issn=&doc_id=20071228200038&doc_link_id=%2Fcw7jasts%2F2007%2F001403%2F048%2F0395-0398%26dl%3D0&url=https%3A%2F%2Fwww.medicalonline.jp%2Fjamas.php%3FGoodsID%3D%2Fcw7jasts%2F2007%2F001403%2F048%2F0395-0398%26dl%3D0&type=MedicalOnline&icon=https%3A%2F%2Fjk04.jamas.or.jp%2Ficon%2F00004_2.gif

Language：English   Publisher：一般社団法人 日本生物物理学会  

DOI： 10.2142/biophys.47.S68_2

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Language：English   Publisher：一般社団法人 日本生物物理学会  

DOI： 10.2142/biophys.47.S68_3

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Other Link： http://search.jamas.or.jp/link/ui/2007133450

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Other Link： http://search.jamas.or.jp/link/ui/2007133448

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Other Link： http://search.jamas.or.jp/link/ui/2007133447

Language：English   Publishing type：Research paper, summary (international conference)   Publisher：OXFORD UNIV PRESS  

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Other Link： http://search.jamas.or.jp/link/ui/2007008750

Language：English   Publishing type：Research paper, summary (international conference)   Publisher：OXFORD UNIV PRESS  

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Other Link： http://search.jamas.or.jp/link/ui/2006092876

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Other Link： http://search.jamas.or.jp/link/ui/2006081417

Language：Japanese   Publisher：金原一郎記念医学医療振興財団  

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Other Link： http://search.jamas.or.jp/link/ui/2005161594

Language：English   Publisher：ELSEVIER SCI IRELAND LTD  

DOI： 10.1016/j.neures.2004.12.003

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Language：Japanese   Publisher：歯科基礎医学会  

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Language：Japanese   Publisher：ソルト・サイエンス研究財団  

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Language：Japanese   Publisher：「日本味と匂学会」事務局  

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Other Link： http://search.jamas.or.jp/link/ui/2004268785

Language：Japanese   Publisher：歯科基礎医学会  

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Language：Japanese   Publisher：秀潤社  

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Other Link： http://search.jamas.or.jp/link/ui/2003145795

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Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

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