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Doyle ME, Premathilake HU, Yao Q, Mazucanti CH, Egan JM. Physiology of the tongue with emphasis on taste transduction. Physiol Rev 2023; 103:1193-1246. [PMID: 36422992 PMCID: PMC9942923 DOI: 10.1152/physrev.00012.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The tongue is a complex multifunctional organ that interacts and senses both interoceptively and exteroceptively. Although it is easily visible to almost all of us, it is relatively understudied and what is in the literature is often contradictory or is not comprehensively reported. The tongue is both a motor and a sensory organ: motor in that it is required for speech and mastication, and sensory in that it receives information to be relayed to the central nervous system pertaining to the safety and quality of the contents of the oral cavity. Additionally, the tongue and its taste apparatus form part of an innate immune surveillance system. For example, loss or alteration in taste perception can be an early indication of infection as became evident during the present global SARS-CoV-2 pandemic. Here, we particularly emphasize the latest updates in the mechanisms of taste perception, taste bud formation and adult taste bud renewal, and the presence and effects of hormones on taste perception, review the understudied lingual immune system with specific reference to SARS-CoV-2, discuss nascent work on tongue microbiome, as well as address the effect of systemic disease on tongue structure and function, especially in relation to taste.
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Affiliation(s)
- Máire E Doyle
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Hasitha U Premathilake
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Qin Yao
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Caio H Mazucanti
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Josephine M Egan
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
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Oral Sensory Neurons of the Geniculate Ganglion That Express Tyrosine Hydroxylase Comprise a Subpopulation That Contacts Type II and Type III Taste Bud Cells. eNeuro 2022; 9:ENEURO.0523-21.2022. [PMID: 36216506 PMCID: PMC9581578 DOI: 10.1523/eneuro.0523-21.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 07/30/2022] [Accepted: 08/22/2022] [Indexed: 01/26/2023] Open
Abstract
Oral sensory neurons of the geniculate ganglion (GG) innervate taste papillae and buds on the tongue and soft palate. Electrophysiological recordings of these neurons and fibers revealed complexity in the number of unique response profiles observed, suggesting there are several distinct neuronal subtypes. Molecular descriptions of these subpopulations are incomplete. We report here the identification of a subpopulation of GG oral sensory neurons in mice by expression of tyrosine hydroxylase (TH). TH-expressing geniculate neurons represent 10-20% of oral sensory neurons and these neurons innervate taste buds in fungiform and anterior foliate taste papillae on the surface of the tongue, as well as taste buds in the soft palate. While 35-50% of taste buds on the tongue are innervated by these TH+ neurons, 100% of soft palate taste buds are innervated. These neurons did not have extragemmal processes outside of taste buds and did not express the mechanosensory neuron-associated gene Ret, suggesting they are chemosensory and not somatosensory neurons. Within taste buds, TH-expressing fibers contacted both Type II and Type III cells, raising the possibility that they are responsive to more than one taste quality. During this analysis we also identified a rare TH+ taste receptor cell type that was found in only 12-25% of taste buds and co-expressed TRPM5, suggesting it was a Type II cell. Taken together, TH-expressing GG oral sensory neurons innervate taste buds preferentially in the soft palate and contact Type II and Type III taste bud receptor cells.
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Tian Y, Wang P, Du L, Wu C. Advances in gustatory biomimetic biosensing technologies: In vitro and in vivo bioelectronic tongue. Trends Analyt Chem 2022. [DOI: 10.1016/j.trac.2022.116778] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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4
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Cherkashin AP, Rogachevskaja OA, Kabanova NV, Kotova PD, Bystrova MF, Kolesnikov SS. Taste Cells of the Type III Employ CASR to Maintain Steady Serotonin Exocytosis at Variable Ca 2+ in the Extracellular Medium. Cells 2022; 11:cells11081369. [PMID: 35456048 PMCID: PMC9030112 DOI: 10.3390/cells11081369] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Revised: 04/07/2022] [Accepted: 04/11/2022] [Indexed: 12/17/2022] Open
Abstract
Type III taste cells are the only taste bud cells which express voltage-gated (VG) Ca2+ channels and employ Ca2+-dependent exocytosis to release neurotransmitters, particularly serotonin. The taste bud is a tightly packed cell population, wherein extracellular Ca2+ is expected to fluctuate markedly due to the electrical activity of taste cells. It is currently unclear whether the Ca2+ entry-driven synapse in type III cells could be reliable enough at unsteady extracellular Ca2. Here we assayed depolarization-induced Ca2+ signals and associated serotonin release in isolated type III cells at varied extracellular Ca2+. It turned out that the same depolarizing stimulus elicited invariant Ca2+ signals in type III cells irrespective of bath Ca2+ varied within 0.5–5 mM. The serotonin release from type III cells was assayed with the biosensor approach by using HEK-293 cells co-expressing the recombinant 5-HT4 receptor and genetically encoded cAMP sensor Pink Flamindo. Consistently with the weak Ca2+ dependence of intracellular Ca2+ transients produced by VG Ca2+ entry, depolarization-triggered serotonin secretion varied negligibly with bath Ca2+. The evidence implicated the extracellular Ca2+-sensing receptor in mediating the negative feedback mechanism that regulates VG Ca2+ entry and levels off serotonin release in type III cells at deviating Ca2+ in the extracellular medium.
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Abstract
This review summarizes our understanding of ATP signaling in taste and describes new directions for research. ATP meets all requisite criteria to be considered a neurotransmitter: (1) presence in taste cells, as in all cells; (2) release upon appropriate taste stimulation; (3) binding to cognate purinergic receptors P2X2 and P2X3 on gustatory afferent neurons, and (4) after release, enzymatic degradation to adenosine and other nucleotides by the ectonucleotidase, NTPDase2, expressed on the Type I, glial-like cells in the taste bud. Importantly, double knockout of P2X2 and P2X3 or pharmacological inhibition of P2X3 abolishes transmission of all taste qualities. In Type II taste cells (those that respond to sweet, bitter, or umami stimuli), ATP is released non-vesicularly by a large conductance ion channel composed of CALHM1 and CALHM3, which form a so-called channel synapse at areas of contact with afferent taste nerve fibers. Although ATP release has been detected only from Type II cells, it is also required for the transmission of salty and sour stimuli, which are mediated primarily by the Type III taste cells. The source of the ATP required for Type III cell signaling to afferent fibers is still unclear and is a focus for future experiments. The ionotropic purinergic receptor, P2X3, is widely expressed on many sensory afferents and has been a therapeutic target for treating chronic cough and pain. However, its requirement for taste signaling has complicated efforts at treatment since patients given P2X3 antagonists report substantial disturbances of taste and become non-compliant.
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Affiliation(s)
- Sue Kinnamon
- Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, USA.
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO, USA.
| | - Thomas Finger
- Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, USA.
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO, USA.
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6
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Joseph PV, Nolden A, Kober KM, Paul SM, Cooper BA, Conley YP, Hammer MJ, Wright F, Levine JD, Miaskowski C. Fatigue, Stress, and Functional Status are Associated With Taste Changes in Oncology Patients Receiving Chemotherapy. J Pain Symptom Manage 2021; 62:373-382.e2. [PMID: 33259906 PMCID: PMC8160023 DOI: 10.1016/j.jpainsymman.2020.11.029] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 11/18/2020] [Accepted: 11/21/2020] [Indexed: 02/07/2023]
Abstract
CONTEXT A common complaint among oncology patients receiving chemotherapy is altered taste perception. OBJECTIVE The purpose of this study was to evaluate for differences in common symptoms and stress levels in patients who reported taste changes. METHODS Patients were receiving chemotherapy for breast, gastrointestinal, gynecological, or lung cancer. Change in the way food tastes (CFT) was assessed using the Memorial Symptom Assessment Scale before the patients' second or third cycle of chemotherapy. Valid and reliable instruments were used to assess for depressive symptoms, state and trait of anxiety, cognitive impairment, diurnal variations in fatigue and energy, sleep disturbance, and pain. Stress was assessed using the Perceived Stress Scale and the Impact of Events Scale-Revised. Multiple logistic regression was used to evaluate for risk factors associated with CFT. RESULTS Of the 1329 patients, 49.4% reported CFT. Patients in the CFT group reported higher levels of depression, anxiety, fatigue, and sleep disturbance as well as higher levels of general and disease specific stress. Factors associated with CFT group included being non-White; receiving an antiemetic regimen that contained a neurokinin-1 receptor antagonist with two other antiemetics; having a lower functional status; higher levels of morning fatigue; and reporting higher scores on the hyperarousal subscale of the Impact of Event Scale-Revised. CONCLUSIONS This study provides new evidence on associations between taste changes and common co-occurring symptoms and stress in oncology patients receiving chemotherapy. Clinicians need to evaluate for taste changes in these patients because this symptom can effect patients' nutritional intake and quality of life.
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Affiliation(s)
- Paule V Joseph
- Sensory Science & Metabolism Unit, Biobehavioral Branch, Division of Intramural Research, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA
| | - Alissa Nolden
- Department of Food Science, College of Natural Sciences, University of Massachusetts, Amherst, Massachusetts, USA
| | - Kord M Kober
- Department of Physiological Nursing, School of Nursing, University of California, San Francisco, California, USA
| | - Steven M Paul
- Department of Physiological Nursing, School of Nursing, University of California, San Francisco, California, USA
| | - Bruce A Cooper
- Department of Physiological Nursing, School of Nursing, University of California, San Francisco, California, USA
| | - Yvette P Conley
- School of Nursing, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | | | - Fay Wright
- Rory Meyers College of Nursing, New York University, New York, New York, USA
| | - Jon D Levine
- Department of Medicine, School of Medicine, University of California, San Francisco, California, USA
| | - Christine Miaskowski
- Department of Physiological Nursing, School of Nursing, University of California, San Francisco, California, USA; Department of Medicine, School of Medicine, University of California, San Francisco, California, USA.
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Guarascio DM, Gonzalez-Velandia KY, Hernandez-Clavijo A, Menini A, Pifferi S. Functional expression of TMEM16A in taste bud cells. J Physiol 2021; 599:3697-3714. [PMID: 34089532 PMCID: PMC8361675 DOI: 10.1113/jp281645] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2021] [Accepted: 06/04/2021] [Indexed: 12/14/2022] Open
Abstract
Key points Taste transduction occurs in taste buds in the tongue epithelium. The Ca2+‐activated Cl– channels TMEM16A and TMEM16B play relevant physiological roles in several sensory systems. Here, we report that TMEM16A, but not TMEM16B, is expressed in the apical part of taste buds. Large Ca2+‐activated Cl− currents blocked by Ani‐9, a selective inhibitor of TMEM16A, are measured in type I taste cells but not in type II or III taste cells. ATP indirectly activates Ca2+‐activated Cl– currents in type I cells through TMEM16A channels. These results indicate that TMEM16A is functional in type I taste cells and contribute to understanding the largely unknown physiological roles of these cells.
Abstract The Ca2+‐activated Cl– channels TMEM16A and TMEM16B have relevant roles in many physiological processes including neuronal excitability and regulation of Cl– homeostasis. Here, we examined the presence of Ca2+‐activated Cl– channels in taste cells of mouse vallate papillae by using immunohistochemistry and electrophysiological recordings. By using immunohistochemistry we showed that only TMEM16A, and not TMEM16B, was expressed in taste bud cells where it largely co‐localized with the inwardly rectifying K+ channel KNCJ1 in the apical part of type I cells. By using whole‐cell patch‐clamp recordings in isolated cells from taste buds, we measured an average current of −1083 pA at −100 mV in 1.5 μm Ca2+ and symmetrical Cl– in type I cells. Ion substitution experiments and blockage by Ani‐9, a specific TMEM16A channel blocker, indicated that Ca2+ activated anionic currents through TMEM16A channels. We did not detect any Ca2+‐activated Cl– currents in type II or III taste cells. ATP is released by type II cells in response to various tastants and reaches type I cells where it is hydrolysed by ecto‐ATPases. Type I cells also express P2Y purinergic receptors and stimulation of type I cells with extracellular ATP produced large Ca2+‐activated Cl− currents blocked by Ani‐9, indicating a possible role of TMEM16A in ATP‐mediated signalling. These results provide a definitive demonstration that TMEM16A‐mediated currents are functional in type I taste cells and provide a foundation for future studies investigating physiological roles for these often‐neglected taste cells. Taste transduction occurs in taste buds in the tongue epithelium. The Ca2+‐activated Cl– channels TMEM16A and TMEM16B play relevant physiological roles in several sensory systems. Here, we report that TMEM16A, but not TMEM16B, is expressed in the apical part of taste buds. Large Ca2+‐activated Cl− currents blocked by Ani‐9, a selective inhibitor of TMEM16A, are measured in type I taste cells but not in type II or III taste cells. ATP indirectly activates Ca2+‐activated Cl– currents in type I cells through TMEM16A channels. These results indicate that TMEM16A is functional in type I taste cells and contribute to understanding the largely unknown physiological roles of these cells.
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Affiliation(s)
- Domenico M Guarascio
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, 34136, Italy
| | | | - Andres Hernandez-Clavijo
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, 34136, Italy
| | - Anna Menini
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, 34136, Italy
| | - Simone Pifferi
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, 34136, Italy.,Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, 60126, Italy
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8
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Zhang J, Lee H, Macpherson LJ. Mechanisms for the Sour Taste. Handb Exp Pharmacol 2021; 275:229-245. [PMID: 34117536 DOI: 10.1007/164_2021_476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Sour, the taste of acids, provides important sensory information to prevent the ingestion of unripe, spoiled, or fermented foods. In mammals, acids elicit disgust and pain by simultaneously activating taste and somatosensory neurons innervating the oral cavity. Early researchers detected electrical activity in taste nerves upon presenting acids to the tongue, establishing this as the bona fide sour taste. Recent studies have made significant contributions to our understanding of the mechanisms underlying acid sensing in the taste receptor cells at the periphery and the neural circuitry that convey this information to the brain. In this chapter, we discuss the characterization of sour taste receptor cells, the twists and turns eventually leading to the identification of Otopetrin1 (OTOP1) as the sour taste receptor, the pathway of sour taste signaling from the tongue to the brainstem, and other roles sour taste receptor cells play in the taste bud.
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Affiliation(s)
- Jin Zhang
- Mortimer B. Zukerman Mind Brain and Behavior Institute, Columbia University, New York, NY, USA.
| | - Hojoon Lee
- Department of Neurobiology, Northwestern University, Evanston, IL, USA.
| | - Lindsey J Macpherson
- Department of Biology, The University of Texas at San Antonio, San Antonio, TX, USA.
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Jang JH, Kwon O, Moon SJ, Jeong YT. Recent Advances in Understanding Peripheral Taste Decoding I: 2010 to 2020. Endocrinol Metab (Seoul) 2021; 36:469-477. [PMID: 34139798 PMCID: PMC8258330 DOI: 10.3803/enm.2021.302] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Accepted: 05/20/2021] [Indexed: 01/03/2023] Open
Abstract
Taste sensation is the gatekeeper for direct decisions on feeding behavior and evaluating the quality of food. Nutritious and beneficial substances such as sugars and amino acids are represented by sweet and umami tastes, respectively, whereas noxious substances and toxins by bitter or sour tastes. Essential electrolytes including Na+ and other ions are recognized by the salty taste. Gustatory information is initially generated by taste buds in the oral cavity, projected into the central nervous system, and finally processed to provide input signals for food recognition, regulation of metabolism and physiology, and higher-order brain functions such as learning and memory, emotion, and reward. Therefore, understanding the peripheral taste system is fundamental for the development of technologies to regulate the endocrine system and improve whole-body metabolism. In this review article, we introduce previous widely-accepted views on the physiology and genetics of peripheral taste cells and primary gustatory neurons, and discuss key findings from the past decade that have raised novel questions or solved previously raised questions.
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Affiliation(s)
- Jea Hwa Jang
- BK21 Graduate Program, Department of Biomedical Sciences, Yonsei University College of Dentistry, Seoul,
Korea
- Department of Pharmacology, Korea University College of Medicine, Yonsei University College of Dentistry, Seoul,
Korea
| | - Obin Kwon
- Departments of Biochemistry and Molecular Biology, Yonsei University College of Dentistry, Seoul,
Korea
- Biomedical Sciences, Seoul National University College of Medicine, Yonsei University College of Dentistry, Seoul,
Korea
| | - Seok Jun Moon
- Department of Oral Biology, BK21 FOUR Project, Yonsei University College of Dentistry, Seoul,
Korea
| | - Yong Taek Jeong
- BK21 Graduate Program, Department of Biomedical Sciences, Yonsei University College of Dentistry, Seoul,
Korea
- Department of Pharmacology, Korea University College of Medicine, Yonsei University College of Dentistry, Seoul,
Korea
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10
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Roper SD. Chemical and electrical synaptic interactions among taste bud cells. CURRENT OPINION IN PHYSIOLOGY 2021; 20:118-125. [PMID: 33521414 DOI: 10.1016/j.cophys.2020.12.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Chemical synapses between taste cells were first proposed based on electron microscopy of fish taste buds. Subsequently, researchers found considerable evidence for electrical coupling in fish, amphibian, and possibly mammalian taste buds. The development lingual slice and isolated cell preparations allowed detailed investigations of cell-cell interactions, both chemical and electrical, in taste buds. The identification of serotonin and ATP as taste neurotransmitters focused attention onto chemical synaptic interactions between taste cells and research on electrical coupling faded. Findings from Ca2+ imaging, electrophysiology, and molecular biology indicate that several neurotransmitters, including ATP, serotonin, GABA, acetylcholine, and norepinephrine, are secreted by taste cells and exert paracrine interactions in taste buds. Most work has been done on interactions between Type II and Type III taste cells. This brief review follows the trail of studies on cell-cell interactions in taste buds, from the initial ultrastructural observations to the most recent optogenetic manipulations.
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Affiliation(s)
- Stephen D Roper
- Department of Physiology & Biophysics and Department of Otolaryngology, Miller School of Medicine, University of Miami, FL 33136
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11
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Sensing Senses: Optical Biosensors to Study Gustation. SENSORS 2020; 20:s20071811. [PMID: 32218129 PMCID: PMC7180777 DOI: 10.3390/s20071811] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Revised: 03/19/2020] [Accepted: 03/21/2020] [Indexed: 12/11/2022]
Abstract
The five basic taste modalities, sweet, bitter, umami, salty and sour induce changes of Ca2+ levels, pH and/or membrane potential in taste cells of the tongue and/or in neurons that convey and decode gustatory signals to the brain. Optical biosensors, which can be either synthetic dyes or genetically encoded proteins whose fluorescence spectra depend on levels of Ca2+, pH or membrane potential, have been used in primary cells/tissues or in recombinant systems to study taste-related intra- and intercellular signaling mechanisms or to discover new ligands. Taste-evoked responses were measured by microscopy achieving high spatial and temporal resolution, while plate readers were employed for higher throughput screening. Here, these approaches making use of fluorescent optical biosensors to investigate specific taste-related questions or to screen new agonists/antagonists for the different taste modalities were reviewed systematically. Furthermore, in the context of recent developments in genetically encoded sensors, 3D cultures and imaging technologies, we propose new feasible approaches for studying taste physiology and for compound screening.
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12
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Huang AY. Immune Responses Alter Taste Perceptions: Immunomodulatory Drugs Shape Taste Signals during Treatments. J Pharmacol Exp Ther 2019; 371:684-691. [PMID: 31611237 DOI: 10.1124/jpet.119.261297] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Accepted: 10/08/2019] [Indexed: 01/01/2023] Open
Abstract
Considering that nutrients are required in health and diseases, the detection and ingestion of food to meet the requirements is attributable to the sense of taste. Altered taste sensations lead to a decreased appetite, which is usually one of the frequent causes of malnutrition in patients with diseases. Ongoing taste research has identified a variety of drug pathways that cause changes in taste perceptions in cancer, increasing our understanding of taste disturbances attributable to aberrant mechanisms of taste sensation. The evidence discussed in this review, which addresses the implications of innate immune responses in the modulation of taste functions, focuses on the adverse effects on taste transmission from taste buds by immune modulators responsible for alterations in the perceived intensity of some taste modalities. Another factor, damage to taste progenitor cells that directly results in local effects on taste buds, must also be considered in relation to taste disturbances in patients with cancer. Recent discoveries discussed have provided new insights into the pathophysiology of taste dysfunctions associated with the specific treatments. SIGNIFICANCE STATEMENT: The paradigm that taste signals transmitted to the brain are determined only by tastant-mediated activation via taste receptors has been challenged by the immune modification of taste transmission through drugs during the processing of gustatory information in taste buds. This article reports the findings in a model system (mouse taste buds) that explain the basis for the taste dysfunctions in patients with cancer that has long been observed but never understood.
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Affiliation(s)
- Anthony Y Huang
- Department of Anatomy and Center for Integrated Research in Cognitive and Neural Science, Southern Illinois University School of Medicine, Carbondale, Illinois
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Abstract
The study of taste has been guided throughout much of its history by the conceptual framework of psychophysics, where the focus was on quantification of the subjective experience of the taste sensations. By the mid-20th century, data from physiologic studies had accumulated sufficiently to assemble a model for the function of receptors that must mediate the initial stimulus of tastant molecules in contact with the tongue. But the study of taste as a receptor-mediated event did not gain momentum until decades later when the actual receptor proteins and attendant signaling mechanisms were identified and localized to the highly specialized taste-responsive cells of the tongue. With those discoveries a new opportunity to examine taste as a function of receptor activity has come into focus. Pharmacology is the science designed specifically for the experimental interrogation and quantitative characterization of receptor function at all levels of inquiry from molecules to behavior. This review covers the history of some of the major concepts that have shaped thinking and experimental approaches to taste, the seminal discoveries that have led to elucidation of receptors for taste, and how applying principles of receptor pharmacology can enhance understanding of the mechanisms of taste physiology and perception.
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Affiliation(s)
- R Kyle Palmer
- Opertech Bio, Inc., Pennovation Center, Philadelphia, Pennsylvania
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14
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Huang AY, Wu SY. Substance P as a putative efferent transmitter mediates GABAergic inhibition in mouse taste buds. Br J Pharmacol 2018; 175:1039-1053. [PMID: 29328505 DOI: 10.1111/bph.14142] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Revised: 11/21/2017] [Accepted: 12/23/2017] [Indexed: 01/02/2023] Open
Abstract
BACKGROUND AND PURPOSE Capsaicin-mediated modulation of taste nerve responses is thought to be produced indirectly by the actions of neuropeptides, for example, CGRP and substance P (SP), on taste cells implying they play a role in taste sensitivity. During the processing of gustatory information in taste buds, CGRP shapes peripheral taste signals via serotonergic signalling. The underlying assumption has been that SP exerts its effects on taste transmitter secretion in taste buds of mice. EXPERIMENTAL APPROACH To test this assumption, we investigated the net effect of SP on taste-evoked ATP secretion from mouse taste buds, using functional calcium imaging with CHO cells expressing high-affinity transmitter receptors as cellular biosensors. KEY RESULTS Our results showed that SP elicited PLC activation-dependent intracellular Ca2+ transients in taste cells via neurokinin 1 receptors, most likely on glutamate-aspartate transporter-expressing Type I cells. Furthermore, SP caused Type I cells to secrete GABA. CONCLUSION AND IMPLICATIONS Combined with the recent findings that GABA depresses taste-evoked ATP secretion, the current results indicate that SP elicited secretion of GABA, which provided negative feedback onto Type II (receptor) cells to reduce taste-evoked ATP secretion. These findings are consistent with a role for SP as an inhibitory transmitter that shapes the peripheral taste signals, via GABAergic signalling, during the processing of gustatory information in taste buds. Notably, the results suggest that SP is intimately associated with GABA in mammalian taste signal processing and demonstrate an unanticipated route for sensory information flow within the taste bud.
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Affiliation(s)
- Anthony Y Huang
- Department of Anatomy, Southern Illinois University School of Medicine, Carbondale, IL, USA.,Center for Integrated Research in Cognitive and Neural Science, Southern Illinois University School of Medicine, Carbondale, IL, USA
| | - Sandy Y Wu
- Department of Anatomy, Southern Illinois University School of Medicine, Carbondale, IL, USA
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15
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Wilson CE, Finger TE, Kinnamon SC. Type III Cells in Anterior Taste Fields Are More Immunohistochemically Diverse Than Those of Posterior Taste Fields in Mice. Chem Senses 2017; 42:759-767. [PMID: 28968659 DOI: 10.1093/chemse/bjx055] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Activation of Type III cells in mammalian taste buds is implicated in the transduction of acids (sour) and salty stimuli. Several lines of evidence suggest that function of Type III cells in the anterior taste fields may differ from that of Type III cells in posterior taste fields. Underlying anatomy to support this observation is, however, scant. Most existing immunohistochemical data characterizing this cell type focus on circumvallate taste buds in the posterior tongue. Equivalent data from anterior taste fields-fungiform papillae and soft palate-are lacking. Here, we compare Type III cells in four taste fields: fungiform, soft palate, circumvallate, and foliate in terms of reactivity to four canonical markers of Type III cells: polycystic kidney disease 2-like 1 (PKD2L1), synaptosomal associated protein 25 (SNAP25), serotonin (5-HT), and glutamate decarboxylase 67 (GAD67). Our findings indicate that while PKD2L1, 5-HT, and SNAP25 are highly coincident in posterior taste fields, they diverge in anterior taste fields. In particular, a subset of taste cells expresses PKD2L1 without the synaptic markers, and a subset of SNAP25 cells lacks expression of PKD2L1. In posterior taste fields, GAD67-positive cells are a subset of PKD2L1 expressing taste cells, but anterior taste fields also contain a significant population of GAD67-only expressing cells. These differences in expression patterns may underlie the observed functional differences between anterior and posterior taste fields.
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Affiliation(s)
- Courtney E Wilson
- Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, CO 80045, USA.,Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO 80045, USA.,Neuroscience Graduate Program, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Thomas E Finger
- Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, CO 80045, USA.,Neuroscience Graduate Program, University of Colorado School of Medicine, Aurora, CO 80045, USA.,Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Sue C Kinnamon
- Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, CO 80045, USA.,Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO 80045, USA.,Neuroscience Graduate Program, University of Colorado School of Medicine, Aurora, CO 80045, USA
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Sukumaran SK, Lewandowski BC, Qin Y, Kotha R, Bachmanov AA, Margolskee RF. Whole transcriptome profiling of taste bud cells. Sci Rep 2017; 7:7595. [PMID: 28790351 PMCID: PMC5548921 DOI: 10.1038/s41598-017-07746-z] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Accepted: 07/03/2017] [Indexed: 12/15/2022] Open
Abstract
Analysis of single-cell RNA-Seq data can provide insights into the specific functions of individual cell types that compose complex tissues. Here, we examined gene expression in two distinct subpopulations of mouse taste cells: Tas1r3-expressing type II cells and physiologically identified type III cells. Our RNA-Seq libraries met high quality control standards and accurately captured differential expression of marker genes for type II (e.g. the Tas1r genes, Plcb2, Trpm5) and type III (e.g. Pkd2l1, Ncam, Snap25) taste cells. Bioinformatics analysis showed that genes regulating responses to stimuli were up-regulated in type II cells, while pathways related to neuronal function were up-regulated in type III cells. We also identified highly expressed genes and pathways associated with chemotaxis and axon guidance, providing new insights into the mechanisms underlying integration of new taste cells into the taste bud. We validated our results by immunohistochemically confirming expression of selected genes encoding synaptic (Cplx2 and Pclo) and semaphorin signalling pathway (Crmp2, PlexinB1, Fes and Sema4a) components. The approach described here could provide a comprehensive map of gene expression for all taste cell subpopulations and will be particularly relevant for cell types in taste buds and other tissues that can be identified only by physiological methods.
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Affiliation(s)
- Sunil K Sukumaran
- Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA, 19104, USA
| | - Brian C Lewandowski
- Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA, 19104, USA
| | - Yumei Qin
- Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA, 19104, USA.,College of Food & Biology Engineering, Zhejiang Gongshang University, Hangzhou, 310018, P.R. China
| | - Ramana Kotha
- Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA, 19104, USA
| | | | - Robert F Margolskee
- Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA, 19104, USA.
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Chamoun E, Mutch DM, Allen-Vercoe E, Buchholz AC, Duncan AM, Spriet LL, Haines J, Ma DWL. A review of the associations between single nucleotide polymorphisms in taste receptors, eating behaviors, and health. Crit Rev Food Sci Nutr 2017; 58:194-207. [DOI: 10.1080/10408398.2016.1152229] [Citation(s) in RCA: 74] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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18
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Abstract
The past decade has witnessed a consolidation and refinement of the extraordinary progress made in taste research. This Review describes recent advances in our understanding of taste receptors, taste buds, and the connections between taste buds and sensory afferent fibres. The article discusses new findings regarding the cellular mechanisms for detecting tastes, new data on the transmitters involved in taste processing and new studies that address longstanding arguments about taste coding.
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Stratford JM, Larson ED, Yang R, Salcedo E, Finger TE. 5-HT 3A -driven green fluorescent protein delineates gustatory fibers innervating sour-responsive taste cells: A labeled line for sour taste? J Comp Neurol 2017; 525:2358-2375. [PMID: 28316078 DOI: 10.1002/cne.24209] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Revised: 03/03/2017] [Accepted: 03/10/2017] [Indexed: 12/29/2022]
Abstract
Taste buds contain multiple cell types with each type expressing receptors and transduction components for a subset of taste qualities. The sour sensing cells, Type III cells, release serotonin (5-HT) in response to the presence of sour (acidic) tastants and this released 5-HT activates 5-HT3 receptors on the gustatory nerves. We show here, using 5-HT3A GFP mice, that 5-HT3 -expressing nerve fibers preferentially contact and receive synaptic contact from Type III taste cells. Further, these 5-HT3 -expressing nerve fibers terminate in a restricted central-lateral portion of the nucleus of the solitary tract (nTS)-the same area that shows increased c-Fos expression upon presentation of a sour tastant (30 mM citric acid). This acid stimulation also evokes c-Fos in the laterally adjacent mediodorsal spinal trigeminal nucleus (DMSp5), but this trigeminal activation is not associated with the presence of 5-HT3 -expressing nerve fibers as it is in the nTS. Rather, the neuronal activation in the trigeminal complex likely is attributable to direct depolarization of acid-sensitive trigeminal nerve fibers, for example, polymodal nociceptors, rather than through taste buds. Taken together, these findings suggest that transmission of sour taste information involves communication between Type III taste cells and 5-HT3 -expressing afferent nerve fibers that project to a restricted portion of the nTS consistent with a crude mapping of taste quality information in the primary gustatory nucleus.
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Affiliation(s)
- J M Stratford
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, Colorado.,Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, Colorado
| | - E D Larson
- Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, Colorado.,Department of Otolaryngology, University of Colorado School of Medicine, Aurora, Colorado
| | - R Yang
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, Colorado.,Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, Colorado
| | - E Salcedo
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, Colorado.,Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, Colorado
| | - T E Finger
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, Colorado.,Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, Colorado
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20
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Liu D, Archer N, Duesing K, Hannan G, Keast R. Mechanism of fat taste perception: Association with diet and obesity. Prog Lipid Res 2016; 63:41-9. [DOI: 10.1016/j.plipres.2016.03.002] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Revised: 02/22/2016] [Accepted: 03/09/2016] [Indexed: 12/11/2022]
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21
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Recent Advances in Molecular Mechanisms of Taste Signaling and Modifying. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 323:71-106. [PMID: 26944619 DOI: 10.1016/bs.ircmb.2015.12.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The sense of taste conveys crucial information about the quality and nutritional value of foods before it is ingested. Taste signaling begins with taste cells via taste receptors in oral cavity. Activation of these receptors drives the transduction systems in taste receptor cells. Then particular transmitters are released from the taste cells and activate corresponding afferent gustatory nerve fibers. Recent studies have revealed that taste sensitivities are defined by distinct taste receptors and modulated by endogenous humoral factors in a specific group of taste cells. Such peripheral taste generations and modifications would directly influence intake of nutritive substances. This review will highlight current understanding of molecular mechanisms for taste reception, signal transduction in taste bud cells, transmission between taste cells and nerves, regeneration from taste stem cells, and modification by humoral factors at peripheral taste organs.
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Loper HB, La Sala M, Dotson C, Steinle N. Taste perception, associated hormonal modulation, and nutrient intake. Nutr Rev 2016; 73:83-91. [PMID: 26024495 DOI: 10.1093/nutrit/nuu009] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
It is well known that taste perception influences food intake. After ingestion, gustatory receptors relay sensory signals to the brain, which segregates, evaluates, and distinguishes the stimuli, leading to the experience known as "flavor." It is well accepted that five taste qualities – sweet, salty, bitter, sour, and umami – can be perceived by animals. In this review, the anatomy and physiology of human taste buds, the hormonal modulation of taste function, the importance of genetic chemosensory variation, and the influence of gustatory functioning on macronutrient selection and eating behavior are discussed. Individual genotypic variation results in specific phenotypes of food preference and nutrient intake. Understanding the role of taste in food selection and ingestive behavior is important for expanding our understanding of the factors involved in body weight maintenance and the risk of chronic diseases including obesity, atherosclerosis, cancer, diabetes, liver disease, and hypertension.
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Affiliation(s)
- Hillary B Loper
- H.B. Loper is with the Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA. M. La Sala and C. Dotson are with the Division of Addiction Medicine, Center for Smell and Taste, Department of Neuroscience and Psychiatry, University of Florida College of Medicine, Gainesville, FL, USA. N Steinle is with the Baltimore Veterans Administration Medical Center and University of Maryland School of Medicine, Baltimore, MD, USA
| | - Michael La Sala
- H.B. Loper is with the Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA. M. La Sala and C. Dotson are with the Division of Addiction Medicine, Center for Smell and Taste, Department of Neuroscience and Psychiatry, University of Florida College of Medicine, Gainesville, FL, USA. N Steinle is with the Baltimore Veterans Administration Medical Center and University of Maryland School of Medicine, Baltimore, MD, USA
| | - Cedrick Dotson
- H.B. Loper is with the Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA. M. La Sala and C. Dotson are with the Division of Addiction Medicine, Center for Smell and Taste, Department of Neuroscience and Psychiatry, University of Florida College of Medicine, Gainesville, FL, USA. N Steinle is with the Baltimore Veterans Administration Medical Center and University of Maryland School of Medicine, Baltimore, MD, USA
| | - Nanette Steinle
- H.B. Loper is with the Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA. M. La Sala and C. Dotson are with the Division of Addiction Medicine, Center for Smell and Taste, Department of Neuroscience and Psychiatry, University of Florida College of Medicine, Gainesville, FL, USA. N Steinle is with the Baltimore Veterans Administration Medical Center and University of Maryland School of Medicine, Baltimore, MD, USA
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Calcitonin Gene-Related Peptide Reduces Taste-Evoked ATP Secretion from Mouse Taste Buds. J Neurosci 2016; 35:12714-24. [PMID: 26377461 DOI: 10.1523/jneurosci.0100-15.2015] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
UNLABELLED Immunoelectron microscopy revealed that peripheral afferent nerve fibers innervating taste buds contain calcitonin gene-related peptide (CGRP), which may be as an efferent transmitter released from peripheral axon terminals. In this report, we determined the targets of CGRP within taste buds and studied what effect CGRP exerts on taste bud function. We isolated mouse taste buds and taste cells, conducted functional imaging using Fura-2, and used cellular biosensors to monitor taste-evoked transmitter release. The findings showed that a subset of Presynaptic (Type III) taste cells (53%) responded to 0.1 μm CGRP with an increase in intracellular Ca(2+). In contrast, Receptor (Type II) taste cells rarely (4%) responded to 0.1 μm CGRP. Using pharmacological tools, the actions of CGRP were probed and elucidated by the CGRP receptor antagonist CGRP(8-37). We demonstrated that this effect of CGRP was dependent on phospholipase C activation and was prevented by the inhibitor U73122. Moreover, applying CGRP caused taste buds to secrete serotonin (5-HT), a Presynaptic (Type III) cell transmitter, but not ATP, a Receptor (Type II) cell transmitter. Further, our previous studies showed that 5-HT released from Presynaptic (Type III) cells provides negative paracrine feedback onto Receptor (Type II) cells by activating 5-HT1A receptors, and reducing ATP secretion. Our data showed that CGRP-evoked 5-HT release reduced taste-evoked ATP secretion. The findings are consistent with a role for CGRP as an inhibitory transmitter that shapes peripheral taste signals via serotonergic signaling during processing gustatory information in taste buds. SIGNIFICANCE STATEMENT The taste sensation is initiated with a highly complex set of interactions between a variety of cells located within the taste buds before signal propagation to the brain. Afferent signals from the oral cavity are carried to the brain in chemosensory fibers that contribute to chemesthesis, the general chemical sensitivity of the mucus membranes in the oronasal cavities and being perceived as pungency, irritation, or heat. This is a study of a fundamental question in neurobiology: how are signals processed in sensory end organs, taste buds? More specifically, taste-modifying interactions, via transmitters, between gustatory and chemosensory afferents inside taste buds will help explain how a coherent output is formed before being transmitted to the brain.
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Vandenbeuch A, Larson ED, Anderson CB, Smith SA, Ford AP, Finger TE, Kinnamon SC. Postsynaptic P2X3-containing receptors in gustatory nerve fibres mediate responses to all taste qualities in mice. J Physiol 2015; 593:1113-25. [PMID: 25524179 DOI: 10.1113/jphysiol.2014.281014] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2014] [Accepted: 12/12/2014] [Indexed: 12/15/2022] Open
Abstract
Taste buds release ATP to activate ionotropic purinoceptors composed of P2X2 and P2X3 subunits, present on the taste nerves. Mice with genetic deletion of P2X2 and P2X3 receptors (double knockout mice) lack responses to all taste stimuli presumably due to the absence of ATP-gated receptors on the afferent nerves. Recent experiments on the double knockout mice showed, however, that their taste buds fail to release ATP, suggesting the possibility of pleiotropic deficits in these global knockouts. To test further the role of postsynaptic P2X receptors in afferent signalling, we used AF-353, a selective antagonist of P2X3-containing receptors to inhibit the receptors acutely during taste nerve recording and behaviour. The specificity of AF-353 for P2X3-containing receptors was tested by recording Ca(2+) transients to exogenously applied ATP in fura-2 loaded isolated geniculate ganglion neurons from wild-type and P2X3 knockout mice. ATP responses were completely inhibited by 10 μm or 100 μm AF-353, but neither concentration blocked responses in P2X3 single knockout mice wherein the ganglion cells express only P2X2-containing receptors. Furthermore, AF-353 had no effect on taste-evoked ATP release from taste buds. In wild-type mice, i.p. injection of AF-353 or simple application of the drug directly to the tongue, inhibited taste nerve responses to all taste qualities in a dose-dependent fashion. A brief access behavioural assay confirmed the electrophysiological results and showed that preference for a synthetic sweetener, SC-45647, was abolished following i.p. injection of AF-353. These data indicate that activation of P2X3-containing receptors is required for transmission of all taste qualities.
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Affiliation(s)
- Aurelie Vandenbeuch
- Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, USA; Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, CO, USA
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25
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Kinnamon SC, Finger TE. A taste for ATP: neurotransmission in taste buds. Front Cell Neurosci 2013; 7:264. [PMID: 24385952 PMCID: PMC3866518 DOI: 10.3389/fncel.2013.00264] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Accepted: 12/03/2013] [Indexed: 11/13/2022] Open
Abstract
Not only is ATP a ubiquitous source of energy but it is also used widely as an intercellular signal. For example, keratinocytes release ATP in response to numerous external stimuli including pressure, heat, and chemical insult. The released ATP activates purinergic receptors on nerve fibers to generate nociceptive signals. The importance of an ATP signal in epithelial-to-neuronal signaling is nowhere more evident than in the taste system. The receptor cells of taste buds release ATP in response to appropriate stimulation by tastants and the released ATP then activates P2X2 and P2X3 receptors on the taste nerves. Genetic ablation of the relevant P2X receptors leaves an animal without the ability to taste any primary taste quality. Of interest is that release of ATP by taste receptor cells occurs in a non-vesicular fashion, apparently via gated membrane channels. Further, in keeping with the crucial role of ATP as a neurotransmitter in this system, a subset of taste cells expresses a specific ectoATPase, NTPDase2, necessary to clear extracellular ATP which otherwise will desensitize the P2X receptors on the taste nerves. The unique utilization of ATP as a key neurotransmitter in the taste system may reflect the epithelial rather than neuronal origins of the receptor cells.
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Affiliation(s)
- Sue C Kinnamon
- Department of Otolaryngology, Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine Aurora, CO, USA
| | - Thomas E Finger
- Department Cell and Developmental Biology, Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine Aurora, CO, USA
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26
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Rebello MR, Maliphol AB, Medler KF. Ryanodine Receptors Selectively Interact with L Type Calcium Channels in Mouse Taste Cells. PLoS One 2013; 8:e68174. [PMID: 23826376 PMCID: PMC3694925 DOI: 10.1371/journal.pone.0068174] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Accepted: 05/27/2013] [Indexed: 12/04/2022] Open
Abstract
Introduction We reported that ryanodine receptors are expressed in two different types of mammalian peripheral taste receptor cells: Type II and Type III cells. Type II cells lack voltage-gated calcium channels (VGCCs) and chemical synapses. In these cells, ryanodine receptors contribute to the taste-evoked calcium signals that are initiated by opening inositol trisphosphate receptors located on internal calcium stores. In Type III cells that do have VGCCs and chemical synapses, ryanodine receptors contribute to the depolarization-dependent calcium influx. Methodology/Principal Findings The goal of this study was to establish if there was selectivity in the type of VGCC that is associated with the ryanodine receptor in the Type III taste cells or if the ryanodine receptor opens irrespective of the calcium channels involved. We also wished to determine if the ryanodine receptors and VGCCs require a physical linkage to interact or are simply functionally associated with each other. Using calcium imaging and pharmacological inhibitors, we found that ryanodine receptors are selectively associated with L type VGCCs but likely not through a physical linkage. Conclusions/Significance Taste cells are able to undergo calcium induced calcium release through ryanodine receptors to increase the initial calcium influx signal and provide a larger calcium response than would otherwise occur when L type channels are activated in Type III taste cells.
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Affiliation(s)
- Michelle R. Rebello
- Department of Biological Sciences, University at Buffalo, The State University of New York, Buffalo, New York, United States of America
| | - Amanda B. Maliphol
- Department of Biological Sciences, University at Buffalo, The State University of New York, Buffalo, New York, United States of America
| | - Kathryn F. Medler
- Department of Biological Sciences, University at Buffalo, The State University of New York, Buffalo, New York, United States of America
- * E-mail:
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Boucher Y, Felizardo R, Klein AH, Carstens MI, Carstens E. Gustatory modulation of the responses of trigeminal subnucleus caudalis neurons to noxious stimulation of the tongue in rats. Eur J Neurosci 2013; 38:2812-22. [PMID: 23802589 DOI: 10.1111/ejn.12282] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 05/15/2013] [Accepted: 05/22/2013] [Indexed: 11/30/2022]
Abstract
Certain tastants inhibit oral irritation by capsaicin, whereas anesthesia of the chorda tympani (CT) enhances oral capsaicin burn. We tested the hypothesis that tastants activate the CT to suppress responses of trigeminal subnucleus caudalis (Vc) neurons to noxious oral stimuli. In anesthetized rats, we recorded Vc unit responses to noxious electrical, chemical (pentanoic acid, 200 μm) and thermal (55 °C) stimulation of the tongue. Electrically evoked responses were significantly reduced by a tastant mix and individually applied NaCl, monosodium glutamate (MSG), and monopotassium glutamate. Sucrose, citric acid, quinine and water (control) had no effect. Pentanoic acid-evoked responses were similarly attenuated by NaCl and MSG, but not by other tastants. Responses to noxious heat were not affected by any tastant. Transection and/or anesthesia of the CT bilaterally affected neither Vc neuronal responses to electrical or pentanoic acid stimulation, nor the depressant effect of NaCl and MSG on electrically evoked responses. Calcium imaging showed that neither NaCl nor MSG directly excited any trigeminal ganglion cells or affected their responses to pentanoic acid. GABA also had no effect, arguing against peripheral effects of GABA, NaCl or MSG on lingual nocicepive nerve endings. The data also rule out a central mechanism, as the effects of NaCl and MSG were intact following CT transection. We speculate that the effect is mediated peripherally by the release from taste receptor cells (type III) of some mediator(s) other than GABA to indirectly inhibit trigeminal nociceptors. The results also indicate that the CT does not exert a tonic inhibitory effect on nociceptive Vc neurons.
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Affiliation(s)
- Yves Boucher
- UFR Odontologie, Université Diderot Paris, Paris, France
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28
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Dotson CD, Geraedts MCP, Munger SD. Peptide regulators of peripheral taste function. Semin Cell Dev Biol 2013; 24:232-9. [PMID: 23348523 DOI: 10.1016/j.semcdb.2013.01.004] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Accepted: 01/10/2013] [Indexed: 12/25/2022]
Abstract
The peripheral sensory organ of the gustatory system, the taste bud, contains a heterogeneous collection of sensory cells. These taste cells can differ in the stimuli to which they respond and the receptors and other signaling molecules they employ to transduce and encode those stimuli. This molecular diversity extends to the expression of a varied repertoire of bioactive peptides that appear to play important functional roles in signaling taste information between the taste cells and afferent sensory nerves and/or in processing sensory signals within the taste bud itself. Here, we review studies that examine the expression of bioactive peptides in the taste bud and the impact of those peptides on taste functions. Many of these peptides produced in taste buds are known to affect appetite, satiety or metabolism through their actions in the brain, pancreas and other organs, suggesting a functional link between the gustatory system and the neural and endocrine systems that regulate feeding and nutrient utilization.
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Affiliation(s)
- Cedrick D Dotson
- Department of Neuroscience, University of Florida College of Medicine, McKnight Brain Institute, Gainesville, FL 32611, USA
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Abstract
Taste buds are peripheral chemosensory organs situated in the oral cavity. Each taste bud consists of a community of 50-100 cells that interact synaptically during gustatory stimulation. At least three distinct cell types are found in mammalian taste buds - Type I cells, Receptor (Type II) cells, and Presynaptic (Type III) cells. Type I cells appear to be glial-like cells. Receptor cells express G protein-coupled taste receptors for sweet, bitter, or umami compounds. Presynaptic cells transduce acid stimuli (sour taste). Cells that sense salt (NaCl) taste have not yet been confidently identified in terms of these cell types. During gustatory stimulation, taste bud cells secrete synaptic, autocrine, and paracrine transmitters. These transmitters include ATP, acetylcholine (ACh), serotonin (5-HT), norepinephrine (NE), and GABA. Glutamate is an efferent transmitter that stimulates Presynaptic cells to release 5-HT. This chapter discusses these transmitters, which cells release them, the postsynaptic targets for the transmitters, and how cell-cell communication shapes taste bud signaling via these transmitters.
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Affiliation(s)
- Stephen D Roper
- Department of Physiology and Biophysics, and Program in Neuroscience, Miller School of Medicine, University of Miami, 1600 NW 10th Ave., Miami, FL 33136, USA.
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Desimone JA, Phan THT, Ren Z, Mummalaneni S, Lyall V. Changes in taste receptor cell [Ca2+]i modulate chorda tympani responses to bitter, sweet, and umami taste stimuli. J Neurophysiol 2012; 108:3221-32. [PMID: 22993258 DOI: 10.1152/jn.00129.2012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The relationship between taste receptor cell (TRC) intracellular Ca(2+) ([Ca(2+)](i)) and rat chorda tympani (CT) nerve responses to bitter (quinine and denatonium), sweet (sucrose, glycine, and erythritol), and umami [monosodium glutamate (MSG) and MSG + inosine 5'-monophosphate (IMP)] taste stimuli was investigated before and after lingual application of ionomycin (Ca(2+) ionophore) + Ca(2+), 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM; Ca(2+) chelator), U73122 (phospholipase C blocker), thapsigargin (Ca(2+)-ATPase blocker), and diC8-PIP(2) (synthetic phosphatidylinositol 4,5-bisphosphate). The phasic CT response to quinine was indifferent to changes in [Ca(2+)](i). However, a decrease in [Ca(2+)](i) inhibited the tonic part of the CT response to quinine. The CT responses to sweet and umami stimuli were indifferent to changes in TRC [Ca(2+)](i). However, a decrease in [Ca(2+)](i) attenuated the synergistic effects of ethanol on the CT response to sweet stimuli and of IMP on the glutamate CT response. U73122 and thapsigargin inhibited the phasic and tonic CT responses to bitter, sweet, and umami stimuli. Although diC8-PIP(2) increased the CT response to bitter and sweet stimuli, it did not alter the CT response to glutamate but did inhibit the synergistic effect of IMP on the glutamate response. The results suggest that bitter, sweet, and umami taste qualities are transduced by [Ca(2+)](i)-dependent and [Ca(2+)](i)-independent mechanisms. Changes in TRC [Ca(2+)](i) in the BAPTA-sensitive cytosolic compartment regulate quality-specific taste receptors and ion channels that are involved in the neural adaptation and mixture interactions. Changes in TRC [Ca(2+)](i) in a separate subcompartment, sensitive to inositol trisphosphate and thapsigargin but inaccessible to BAPTA and ionomycin + Ca(2+), are associated with neurotransmitter release.
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Affiliation(s)
- John A Desimone
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, USA
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31
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Desimone JA, Ren Z, Phan THT, Heck GL, Mummalaneni S, Lyall V. Changes in taste receptor cell [Ca2+]i modulate chorda tympani responses to salty and sour taste stimuli. J Neurophysiol 2012; 108:3206-20. [PMID: 22956787 DOI: 10.1152/jn.00916.2011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The relationship between taste receptor cell (TRC) Ca(2+) concentration ([Ca(2+)](i)) and rat chorda tympani (CT) nerve responses to salty [NaCl and NaCl+benzamil (Bz)] and sour (HCl, CO(2), and acetic acid) taste stimuli was investigated before and after lingual application of ionomycin+Ca(2+), 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM), U73122 (phospholipase C blocker), and thapsigargin (Ca(2+)-ATPase inhibitor) under open-circuit or lingual voltage-clamp conditions. An increase in TRC [Ca(2+)](i) attenuated the tonic Bz-sensitive NaCl CT response and the apical membrane Na(+) conductance. A decrease in TRC [Ca(2+)](i) enhanced the tonic Bz-sensitive and Bz-insensitive NaCl CT responses and apical membrane Na(+) conductance but did not affect CT responses to KCl or NH(4)Cl. An increase in TRC [Ca(2+)](i) did not alter the phasic response but attenuated the tonic CT response to acidic stimuli. A decrease in [Ca(2+)](i) did not alter the phasic response but attenuated the tonic CT response to acidic stimuli. In a subset of TRCs, a positive relationship between [H(+)](i) and [Ca(2+)](i) was obtained using in vitro imaging techniques. U73122 inhibited the tonic CT responses to NaCl, and thapsigargin inhibited the tonic CT responses to salty and sour stimuli. The results suggest that salty and sour taste qualities are transduced by [Ca(2+)](i)-dependent and [Ca(2+)](i)-independent mechanisms. Changes in TRC [Ca(2+)](i) in a BAPTA-sensitive cytosolic compartment regulate ion channels and cotransporters involved in the salty and sour taste transduction mechanisms and in neural adaptation. Changes in TRC [Ca(2+)](i) in a separate subcompartment, sensitive to inositol trisphosphate and thapsigargin but inaccessible to BAPTA, are associated with neurotransmitter release.
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Affiliation(s)
- John A Desimone
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, USA
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Romanov RA, Rogachevskaja OA, Bystrova MF, Kolesnikov SS. Electrical excitability of taste cells. Mechanisms and possible physiological significance. BIOCHEMISTRY MOSCOW SUPPLEMENT SERIES A-MEMBRANE AND CELL BIOLOGY 2012. [DOI: 10.1134/s1990747812010126] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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Immunocytochemical analysis of P2X2 in rat circumvallate taste buds. BMC Neurosci 2012; 13:51. [PMID: 22621423 PMCID: PMC3507709 DOI: 10.1186/1471-2202-13-51] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Accepted: 04/20/2012] [Indexed: 11/23/2022] Open
Abstract
Background Our laboratory has shown that classical synapses and synaptic proteins are associated with Type III cells. Yet it is generally accepted that Type II cells transduce bitter, sweet and umami stimuli. No classical synapses, however, have been found associated with Type II cells. Recent studies indicate that the ionotropic purinergic receptors P2X2/P2X3 are present in rodent taste buds. Taste nerve processes express the ionotropic purinergic receptors (P2X2/P2X3). P2X2/P2X3Dbl−/− mice are not responsive to sweet, umami and bitter stimuli, and it has been proposed that ATP acts as a neurotransmitter in taste buds. The goal of the present study is to learn more about the nature of purinergic contacts in rat circumvallate taste buds by examining immunoreactivity to antisera directed against the purinergic receptor P2X2. Results P2X2-like immunoreactivity is present in intragemmal nerve processes in rat circumvallate taste buds. Intense immunoreactivity can also be seen in the subgemmal nerve plexuses located below the basal lamina. The P2X2 immunoreactive nerve processes also display syntaxin-1-LIR. The immunoreactive nerves are in close contact with the IP3R3-LIR Type II cells and syntaxin-1-LIR and/or 5-HT-LIR Type III cells. Taste cell synapses are observed only from Type III taste cells onto P2X2-LIR nerve processes. Unusually large, “atypical” mitochondria in the Type II taste cells are found only at close appositions with P2X2-LIR nerve processes. P2X2 immunogold particles are concentrated at the membranes of nerve processes at close appositions with taste cells. Conclusions Based on our immunofluorescence and immunoelectron microscopical studies we believe that both perigemmal and most all intragemmal nerve processes display P2X2-LIR. Moreover, colloidal gold immunoelectron microscopy indicates that P2X2-LIR in nerve processes is concentrated at sites of close apposition with Type II cells. This supports the hypothesis that ATP may be a key neurotransmitter in taste transduction and that Type II cells release ATP, activating P2X2 receptors in nerve processes.
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Dando R, Roper SD. Acetylcholine is released from taste cells, enhancing taste signalling. J Physiol 2012; 590:3009-17. [PMID: 22570381 DOI: 10.1113/jphysiol.2012.232009] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Acetylcholine (ACh), a candidate neurotransmitter that has been implicated in taste buds, elicits calcium mobilization in Receptor (Type II) taste cells. Using RT-PCR analysis and pharmacological interventions, we demonstrate that the muscarinic acetylcholine receptor M3 mediates these actions. Applying ACh enhanced both taste-evoked Ca2+ responses and taste-evoked afferent neurotransmitter (ATP) secretion from taste Receptor cells. Blocking muscarinic receptors depressed taste-evoked responses in Receptor cells, suggesting that ACh is normally released from taste cells during taste stimulation. ACh biosensors confirmed that, indeed, taste Receptor cells secrete acetylcholine during gustatory stimulation. Genetic deletion of muscarinic receptors resulted in significantly diminished ATP secretion from taste buds. The data demonstrate a new role for acetylcholine as a taste bud transmitter. Our results imply specifically that ACh is an autocrine transmitter secreted by taste Receptor cells during gustatory stimulation, enhancing taste-evoked responses and afferent transmitter secretion.
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Affiliation(s)
- Robin Dando
- Department of Physiology and Biophysics, University of Miami Leonard M. Miller School of Medicine, PO Box 016430, Miami, FL 33101, USA.
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Rodriguez-Diaz R, Dando R, Huang YA, Berggren PO, Roper SD, Caicedo A. Real-time detection of acetylcholine release from the human endocrine pancreas. Nat Protoc 2012; 7:1015-23. [PMID: 22555241 DOI: 10.1038/nprot.2012.040] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Neurons, sensory cells and endocrine cells secrete neurotransmitters and hormones to communicate with other cells and to coordinate organ and system function. Validation that a substance is used as an extracellular signaling molecule by a given cell requires a direct demonstration of its secretion. In this protocol we describe the use of biosensor cells to detect neurotransmitter release from endocrine cells in real-time. Chinese hamster ovary cells expressing the muscarinic acetylcholine (ACh) receptor M3 were used as ACh biosensors to record ACh release from human pancreatic islets. We show how ACh biosensors loaded with the Ca(2+) indicator Fura-2 and pressed against isolated human pancreatic islets allow the detection of ACh release. The biosensor approach is simple; the Ca(2+) signal generated in the biosensor cell reflects the presence (release) of a neurotransmitter. The technique is versatile because biosensor cells expressing a variety of receptors can be used in many applications. The protocol takes ∼3 h.
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Affiliation(s)
- Rayner Rodriguez-Diaz
- Diabetes Research Institute, Miller School of Medicine, University of Miami, Miami, Florida, USA
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Grant J. Tachykinins stimulate a subset of mouse taste cells. PLoS One 2012; 7:e31697. [PMID: 22363709 PMCID: PMC3283679 DOI: 10.1371/journal.pone.0031697] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2011] [Accepted: 01/18/2012] [Indexed: 01/07/2023] Open
Abstract
The tachykinins substance P (SP) and neurokinin A (NKA) are present in nociceptive sensory fibers expressing transient receptor potential cation channel, subfamily V, member 1 (TRPV1). These fibers are found extensively in and around the taste buds of several species. Tachykinins are released from nociceptive fibers by irritants such as capsaicin, the active compound found in chili peppers commonly associated with the sensation of spiciness. Using real-time Ca2+-imaging on isolated taste cells, it was observed that SP induces Ca2+ -responses in a subset of taste cells at concentrations in the low nanomolar range. These responses were reversibly inhibited by blocking the SP receptor NK-1R. NKA also induced Ca2+-responses in a subset of taste cells, but only at concentrations in the high nanomolar range. These responses were only partially inhibited by blocking the NKA receptor NK-2R, and were also inhibited by blocking NK-1R indicating that NKA is only active in taste cells at concentrations that activate both receptors. In addition, it was determined that tachykinin signaling in taste cells requires Ca2+-release from endoplasmic reticulum stores. RT-PCR analysis further confirmed that mouse taste buds express NK-1R and NK-2R. Using Ca2+-imaging and single cell RT-PCR, it was determined that the majority of tachykinin-responsive taste cells were Type I (Glial-like) and umami-responsive Type II (Receptor) cells. Importantly, stimulating NK-1R had an additive effect on Ca2+ responses evoked by umami stimuli in Type II (Receptor) cells. This data indicates that tachykinin release from nociceptive sensory fibers in and around taste buds may enhance umami and other taste modalities, providing a possible mechanism for the increased palatability of spicy foods.
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Affiliation(s)
- Jeff Grant
- Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida, United States of America.
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Abstract
Taste buds are the transducing endorgans of gustation. Each taste bud comprises 50-100 elongated cells, which extend from the basal lamina to the surface of the tongue, where their apical microvilli encounter taste stimuli in the oral cavity. Salts and acids utilize apically located ion channels for transduction, while bitter, sweet and umami (glutamate) stimuli utilize G-protein-coupled receptors (GPCRs) and second-messenger signalling mechanisms. This review will focus on GPCR signalling mechanisms. Two classes of taste GPCRs have been identified, the T1Rs for sweet and umami (glutamate) stimuli and the T2Rs for bitter stimuli. These low affinity GPCRs all couple to the same downstream signalling effectors that include Gβγ activation of phospholipase Cβ2, 1,4,5-inositol trisphosphate mediated release of Ca(2+) from intracellular stores and Ca(2+) -dependent activation of the monovalent selective cation channel, TrpM5. These events lead to membrane depolarization, action potentials and release of ATP as a transmitter to activate gustatory afferents. The Gα subunit, α-gustducin, activates a phosphodiesterase to decrease intracellular cAMP levels, although the precise targets of cAMP have not been identified. With the molecular identification of the taste GPCRs, it has become clear that taste signalling is not limited to taste buds, but occurs in many cell types of the airways. These include solitary chemosensory cells, ciliated epithelial cells and smooth muscle cells. Bitter receptors are most abundantly expressed in the airways, where they respond to irritating chemicals and promote protective airway reflexes, utilizing the same downstream signalling effectors as taste cells.
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Affiliation(s)
- S C Kinnamon
- Department of Otolaryngology, School of Medicine, University of Colorado Denver, Aurora, 80534, USA.
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Abstract
PURPOSE OF REVIEW The purpose of this review is to discuss the presence and possible roles of peripheral taste/nutrient sensors, particularly taste receptors. RECENT FINDINGS Recent studies have demonstrated that taste signaling molecules are distributed not only in the gustatory epithelium, but also in other tissues, including the gastrointestinal tract, airways, testes and brain. Taste signaling mechanisms in the gastrointestinal tract were reported to participate in detecting sweet, umami and bitter compounds. Several research groups have suggested that tastant/nutrient detection by other systems contributes to the behavioral responses to food intake. SUMMARY Taste-like cells expressing taste signaling components are distributed in multiple tissues. Investigation of their potential roles in chemosensing has just begun. Researchers have identified at least two chemosensory pathways in the gastrointestinal tract for detecting tastants/nutrients. One is the taste receptor signaling pathway and the other is the currently unknown nutrient-sensing pathway that elicits postingestive effects. The former system utilizes a mechanism similar to taste sensing in the oral cavity. By understanding how tastants/nutrients are sensed and regulated through both systems, we may be able to more effectively control food intake in the future.
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Affiliation(s)
- Ken Iwatsuki
- Institute for Innovation, Ajinomoto Co. Inc., Kawasaki-ku, Kawasaki, Japan
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Huang YA, Grant J, Roper S. Glutamate may be an efferent transmitter that elicits inhibition in mouse taste buds. PLoS One 2012; 7:e30662. [PMID: 22292013 PMCID: PMC3266908 DOI: 10.1371/journal.pone.0030662] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 12/22/2011] [Indexed: 11/19/2022] Open
Abstract
Recent studies suggest that l-glutamate may be an efferent transmitter released from axons innervating taste buds. In this report, we determined the types of ionotropic synaptic glutamate receptors present on taste cells and that underlie this postulated efferent transmission. We also studied what effect glutamate exerts on taste bud function. We isolated mouse taste buds and taste cells, conducted functional imaging using Fura 2, and used cellular biosensors to monitor taste-evoked transmitter release. The findings show that a large fraction of Presynaptic (Type III) taste bud cells (∼50%) respond to 100 µM glutamate, NMDA, or kainic acid (KA) with an increase in intracellular Ca(2+). In contrast, Receptor (Type II) taste cells rarely (4%) responded to 100 µM glutamate. At this concentration and with these compounds, these agonists activate glutamatergic synaptic receptors, not glutamate taste (umami) receptors. Moreover, applying glutamate, NMDA, or KA caused taste buds to secrete 5-HT, a Presynaptic taste cell transmitter, but not ATP, a Receptor cell transmitter. Indeed, glutamate-evoked 5-HT release inhibited taste-evoked ATP secretion. The findings are consistent with a role for glutamate in taste buds as an inhibitory efferent transmitter that acts via ionotropic synaptic glutamate receptors.
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MESH Headings
- Animals
- CHO Cells
- Cricetinae
- Cricetulus
- Glutamic Acid/metabolism
- Glutamic Acid/pharmacology
- Green Fluorescent Proteins/genetics
- Green Fluorescent Proteins/metabolism
- Mice
- Mice, Inbred C57BL
- Mice, Transgenic
- Neural Inhibition/drug effects
- Neural Inhibition/genetics
- Neural Inhibition/physiology
- Neurons, Efferent/drug effects
- Neurons, Efferent/metabolism
- Neurons, Efferent/physiology
- Neurotransmitter Agents/metabolism
- Neurotransmitter Agents/pharmacology
- Phospholipase C beta/genetics
- Receptor, Serotonin, 5-HT2C/genetics
- Receptor, Serotonin, 5-HT2C/metabolism
- Receptors, Purinergic P2X2/genetics
- Receptors, Purinergic P2X2/metabolism
- Receptors, Purinergic P2X3/genetics
- Receptors, Purinergic P2X3/metabolism
- Synaptic Transmission/drug effects
- Synaptic Transmission/genetics
- Taste Buds/drug effects
- Taste Buds/metabolism
- Taste Buds/physiology
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Affiliation(s)
- Yijen A Huang
- Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida, United States of America.
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41
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Abstract
In response to gustatory stimulation, taste bud cells release a transmitter, ATP, that activates P2X2 and P2X3 receptors on gustatory afferent fibers. Taste behavior and gustatory neural responses are largely abolished in mice lacking P2X2 and P2X3 receptors [P2X2 and P2X3 double knock-out (DKO) mice]. The assumption has been that eliminating P2X2 and P2X3 receptors only removes postsynaptic targets but that transmitter secretion in mice is normal. Using functional imaging, ATP biosensor cells, and a cell-free assay for ATP, we tested this assumption. Surprisingly, although gustatory stimulation mobilizes Ca(2+) in taste Receptor (Type II) cells from DKO mice, as from wild-type (WT) mice, taste cells from DKO mice fail to release ATP when stimulated with tastants. ATP release could be elicited by depolarizing DKO Receptor cells with KCl, suggesting that ATP-release machinery remains functional in DKO taste buds. To explore the difference in ATP release across genotypes, we used reverse transcriptase (RT)-PCR, immunostaining, and histochemistry for key proteins underlying ATP secretion and degradation: Pannexin1, TRPM5, and NTPDase2 (ecto-ATPase) are indistinguishable between WT and DKO mice. The ultrastructure of contacts between taste cells and nerve fibers is also normal in the DKO mice. Finally, quantitative RT-PCR show that P2X4 and P2X7, potential modulators of ATP secretion, are similarly expressed in taste buds in WT and DKO taste buds. Importantly, we find that P2X2 is expressed in WT taste buds and appears to function as an autocrine, positive feedback signal to amplify taste-evoked ATP secretion.
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Huang YA, Pereira E, Roper SD. Acid stimulation (sour taste) elicits GABA and serotonin release from mouse taste cells. PLoS One 2011; 6:e25471. [PMID: 22028776 PMCID: PMC3197584 DOI: 10.1371/journal.pone.0025471] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2011] [Accepted: 09/05/2011] [Indexed: 11/19/2022] Open
Abstract
Several transmitter candidates including serotonin (5-HT), ATP, and norepinephrine (NE) have been identified in taste buds. Recently, γ-aminobutyric acid (GABA) as well as the associated synthetic enzymes and receptors have also been identified in taste cells. GABA reduces taste-evoked ATP secretion from Receptor cells and is considered to be an inhibitory transmitter in taste buds. However, to date, the identity of GABAergic taste cells and the specific stimulus for GABA release are not well understood. In the present study, we used genetically-engineered Chinese hamster ovary (CHO) cells stably co-expressing GABA(B) receptors and Gαqo5 proteins to measure GABA release from isolated taste buds. We recorded robust responses from GABA biosensors when they were positioned against taste buds isolated from mouse circumvallate papillae and the buds were depolarized with KCl or a stimulated with an acid (sour) taste. In contrast, a mixture of sweet and bitter taste stimuli did not trigger GABA release. KCl- or acid-evoked GABA secretion from taste buds was Ca(2+)-dependent; removing Ca(2+) from the bathing medium eliminated GABA secretion. Finally, we isolated individual taste cells to identify the origin of GABA secretion. GABA was released only from Presynaptic (Type III) cells and not from Receptor (Type II) cells. Previously, we reported that 5-HT released from Presynaptic cells inhibits taste-evoked ATP secretion. Combined with the recent findings that GABA depresses taste-evoked ATP secretion, the present results indicate that GABA and 5-HT are inhibitory transmitters in mouse taste buds and both likely play an important role in modulating taste responses.
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Affiliation(s)
- Yijen A. Huang
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Elizabeth Pereira
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Stephen D. Roper
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
- Program in Neuroscience, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
- * E-mail:
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Iguchi N, Ohkuri T, Slack JP, Zhong P, Huang L. Sarco/Endoplasmic reticulum Ca2+-ATPases (SERCA) contribute to GPCR-mediated taste perception. PLoS One 2011; 6:e23165. [PMID: 21829714 PMCID: PMC3149081 DOI: 10.1371/journal.pone.0023165] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2011] [Accepted: 07/13/2011] [Indexed: 02/01/2023] Open
Abstract
The sense of taste is important for providing animals with valuable information about the qualities of food, such as nutritional or harmful nature. Mammals, including humans, can recognize at least five primary taste qualities: sweet, umami (savory), bitter, sour, and salty. Recent studies have identified molecules and mechanisms underlying the initial steps of tastant-triggered molecular events in taste bud cells, particularly the requirement of increased cytosolic free Ca(2+) concentration ([Ca(2+)](c)) for normal taste signal transduction and transmission. Little, however, is known about the mechanisms controlling the removal of elevated [Ca(2+)](c) from the cytosol of taste receptor cells (TRCs) and how the disruption of these mechanisms affects taste perception. To investigate the molecular mechanism of Ca(2+) clearance in TRCs, we sought the molecules involved in [Ca(2+)](c) regulation using a single-taste-cell transcriptome approach. We found that Serca3, a member of the sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) family that sequesters cytosolic Ca(2+) into endoplasmic reticulum, is exclusively expressed in sweet/umami/bitter TRCs, which rely on intracellular Ca(2+) release for signaling. Serca3-knockout (KO) mice displayed significantly increased aversive behavioral responses and greater gustatory nerve responses to bitter taste substances but not to sweet or umami taste substances. Further studies showed that Serca2 was mainly expressed in the T1R3-expressing sweet and umami TRCs, suggesting that the loss of function of Serca3 was possibly compensated by Serca2 in these TRCs in the mutant mice. Our data demonstrate that the SERCA family members play an important role in the Ca(2+) clearance in TRCs and that mutation of these proteins may alter bitter and perhaps sweet and umami taste perception.
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Affiliation(s)
- Naoko Iguchi
- Monell Chemical Senses Center, Philadelphia, Pennsylvania, United States of America
| | - Tadahiro Ohkuri
- Monell Chemical Senses Center, Philadelphia, Pennsylvania, United States of America
| | - Jay P. Slack
- Givaudan Flavors Corporation, Cincinnati, Ohio, United States of America
| | - Ping Zhong
- Givaudan Flavors Corporation, Cincinnati, Ohio, United States of America
| | - Liquan Huang
- Monell Chemical Senses Center, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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Abstract
Taste buds consist of at least three principal cell types that have different functions in processing gustatory signals: glial-like (type I) cells, receptor (type II) cells, and presynaptic (type III) cells. Using a combination of Ca2+ imaging, single-cell reverse transcriptase-PCR and immunostaining, we show that GABA is an inhibitory transmitter in mouse taste buds, acting on GABA(A) and GABA(B) receptors to suppress transmitter (ATP) secretion from receptor cells during taste stimulation. Specifically, receptor cells express GABA(A) receptor subunits β2, δ, and π, as well as GABA(B) receptors. In contrast, presynaptic cells express the GABA(A) β3 subunit and only occasionally GABA(B) receptors. In keeping with the distinct expression pattern of GABA receptors in presynaptic cells, we detected no GABAergic suppression of transmitter release from presynaptic cells. We suggest that GABA may serve function(s) in taste buds in addition to synaptic inhibition. Finally, we also defined the source of GABA in taste buds: GABA is synthesized by GAD65 in type I taste cells as well as by GAD67 in presynaptic (type III) taste cells and is stored in both those two cell types. We conclude that GABA is an inhibitory transmitter released during taste stimulation and possibly also during growth and differentiation of taste buds.
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Affiliation(s)
- Albertino Bigiani
- Dipartimento di Scienze Biomediche, Sezione di Fisiologia; Università di Modena e Reggio Emilia; Modena, via G. Campi 287; 41125; Modena; Italy
| | - Simone Prandi
- Dipartimento di Scienze Biomediche, Sezione di Fisiologia; Università di Modena e Reggio Emilia; Modena, via G. Campi 287; 41125; Modena; Italy
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Behrens M, Meyerhof W, Hellfritsch C, Hofmann T. Moleküle und biologische Mechanismen des Süß- und Umamigeschmacks. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201002094] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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47
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Behrens M, Meyerhof W, Hellfritsch C, Hofmann T. Sweet and Umami Taste: Natural Products, Their Chemosensory Targets, and Beyond. Angew Chem Int Ed Engl 2011; 50:2220-42. [DOI: 10.1002/anie.201002094] [Citation(s) in RCA: 134] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2010] [Indexed: 11/11/2022]
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Oliveira-Maia AJ, Roberts CD, Simon SA, Nicolelis MAL. Gustatory and reward brain circuits in the control of food intake. Adv Tech Stand Neurosurg 2011; 36:31-59. [PMID: 21197607 DOI: 10.1007/978-3-7091-0179-7_3] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Gustation is a multisensory process allowing for the selection of nutrients and the rejection of irritating and/or toxic compounds. Since obesity is a highly prevalent condition that is critically dependent on food intake and energy expenditure, a deeper understanding of gustatory processing is an important objective in biomedical research. Recent findings have provided evidence that central gustatory processes are distributed across several cortical and subcortical brain areas. Furthermore, these gustatory sensory circuits are closely related to the circuits that process reward. Here, we present an overview of the activation and connectivity between central gustatory and reward areas. Moreover, and given the limitations in number and effectiveness of treatments currently available for overweight patients, we discuss the possibility of modulating neuronal activity in these circuits as an alternative in the treatment of obesity.
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Affiliation(s)
- A J Oliveira-Maia
- Department of Neurobiology, Duke University Medical Center, Durham, NC, USA,
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Abstract
Exocytosis, consisting of the merger of vesicle and plasma membrane, is a common mechanism used by different types of nucleated cells to release their vesicular contents. Taste cells possess vesicles containing various neurotransmitters to communicate with adjacent taste cells and afferent nerve fibers. However, whether these vesicles engage in exocytosis on a stimulus is not known. Since vesicle membrane merger with the plasma membrane is reflected in plasma membrane area fluctuations, we measured membrane capacitance (C(m)), a parameter linearly related to membrane surface area. To investigate whether taste cells undergo regulated exocytosis, we used the compensated tight-seal whole-cell recording technique to monitor depolarization-induced changes in C(m) in the different types of taste cells. To identify taste cell types, mice expressing green fluorescent protein from the TRPM5 promoter or from the GAD67 promoter were used to discriminate type II and type III taste cells, respectively. Moreover, the cell types were also identified by monitoring their voltage-current properties. The results demonstrate that only type III taste cells show significant depolarization-induced increases in C(m), which were correlated to the voltage-activated calcium currents. The results suggest that type III, but neither type II nor type I cells exhibit depolarization-induced regulated exocytosis to release transmitter and activate gustatory afferent nerve fibers.
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50
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Abstract
Taste buds are aggregates of 50–100 polarized neuroepithelial cells that detect nutrients and other compounds. Combined analyses of gene expression and cellular function reveal an elegant cellular organization within the taste bud. This review discusses the functional classes of taste cells, their cell biology, and current thinking on how taste information is transmitted to the brain.
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Affiliation(s)
- Nirupa Chaudhari
- Department of Physiology and Biophysics, and Program in Neurosciences, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
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