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Mikami A, Huang H, Hyodo A, Horie K, Yasumatsu K, Ninomiya Y, Mitoh Y, Iida S, Yoshida R. The role of GABA in modulation of taste signaling within the taste bud. Pflugers Arch 2024:10.1007/s00424-024-03007-x. [PMID: 39210062 DOI: 10.1007/s00424-024-03007-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Revised: 08/03/2024] [Accepted: 08/07/2024] [Indexed: 09/04/2024]
Abstract
Taste buds contain 2 types of GABA-producing cells: sour-responsive Type III cells and glial-like Type I cells. The physiological role of GABA, released by Type III cells is not fully understood. Here, we investigated the role of GABA released from Type III cells using transgenic mice lacking the expression of GAD67 in taste bud cells (Gad67-cKO mice). Immunohistochemical experiments confirmed the absence of GAD67 in Type III cells of Gad67-cKO mice. Furthermore, no difference was observed in the expression and localization of cell type markers, ectonucleoside triphosphate diphosphohydrolase 2 (ENTPD2), gustducin, and carbonic anhydrase 4 (CA4) in taste buds between wild-type (WT) and Gad67-cKO mice. Short-term lick tests demonstrated that both WT and Gad67-cKO mice exhibited normal licking behaviors to each of the five basic tastants. Gustatory nerve recordings from the chorda tympani nerve demonstrated that both WT and Gad67-cKO mice similarly responded to five basic tastants when they were applied individually. However, gustatory nerve responses to sweet-sour mixtures were significantly smaller than the sum of responses to each tastant in WT mice but not in Gad67-cKO mice. In summary, elimination of GABA signalling by sour-responsive Type III taste cells eliminates the inhibitory cell-cell interactions seen with application of sour-sweet mixtures.
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Affiliation(s)
- Ayaka Mikami
- Department of Oral Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
- Department of Oral and Maxillofacial Reconstructive Surgery, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Hai Huang
- Department of Oral Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Aiko Hyodo
- Department of Oral Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
- Department of Oral and Maxillofacial Reconstructive Surgery, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Kengo Horie
- Department of Oral Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
- Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1, Shikata-Cho, Kita-Ku, Okayama, 700-8525, Japan
| | | | - Yuzo Ninomiya
- Department of Oral Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
- Graduate School of Dental Science, Kyushu University, Fukuoka, Japan
- Monell Chemical Senses Center, Philadelphia, PA, USA
| | - Yoshihiro Mitoh
- Department of Oral Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
- Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1, Shikata-Cho, Kita-Ku, Okayama, 700-8525, Japan
| | - Seiji Iida
- Department of Oral and Maxillofacial Reconstructive Surgery, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
- Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1, Shikata-Cho, Kita-Ku, Okayama, 700-8525, Japan
| | - Ryusuke Yoshida
- Department of Oral Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan.
- Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1, Shikata-Cho, Kita-Ku, Okayama, 700-8525, Japan.
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Yu H, Song L, Duan X, Zhu D, Li N, Pan R, Xu R, Yu X, Ye F, Jiang X, Ye H, Pan Z, Wei S, Jiang Z. Optogenetics in taste research: A decade of enlightenment. Oral Dis 2024; 30:903-913. [PMID: 36620868 DOI: 10.1111/odi.14498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 12/03/2022] [Accepted: 01/05/2023] [Indexed: 01/10/2023]
Abstract
The electrophysiological function of the tongue involves complicated activities in taste sense, producing the perceptions of salty, sweet, bitter, and sour. However, therapies and prevention of taste loss arising from dysfunction in electrophysiological activity require further fundamental research. Optogenetics has revolutionized neuroscience and brought the study of sensory system to a higher level in taste. The year 2022 marks a decade of developments of optogenetics in taste since this technology was adopted from neuroscience and applied to the taste research. This review summarizes a decade of advances that define near-term translation with optogenetic tools, and newly-discovered mechanisms with the applications of these tools. The main limitations and opportunities for optogenetics in taste research are also discussed.
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Affiliation(s)
- Hanshu Yu
- Zhejiang University School of Medicine, Hangzhou, China
| | - Luyao Song
- Zhejiang University School of Medicine, Hangzhou, China
| | - Xiangyao Duan
- Zhejiang University School of Medicine, Hangzhou, China
| | - Danji Zhu
- Key Laboratory of Oral Biomedical Research of Zhejiang Province, School of Stomatology, Zhejiang Provincial Clinical Research Centre for Oral Diseases, Cancer Centre of Zhejiang University, Stomatology Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Na Li
- Key Laboratory of Oral Biomedical Research of Zhejiang Province, School of Stomatology, Zhejiang Provincial Clinical Research Centre for Oral Diseases, Cancer Centre of Zhejiang University, Stomatology Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Runxin Pan
- Zhejiang University School of Medicine, Hangzhou, China
| | - Rui Xu
- Zhejiang University School of Medicine, Hangzhou, China
| | - Xinying Yu
- Zhejiang University School of Medicine, Hangzhou, China
| | - Fengkai Ye
- Zhejiang University School of Medicine, Hangzhou, China
| | - Xinrui Jiang
- Zhejiang University School of Medicine, Hangzhou, China
| | - Han Ye
- Zhejiang University School of Medicine, Hangzhou, China
| | - Zikang Pan
- Zhejiang University School of Medicine, Hangzhou, China
| | - Sixing Wei
- Zhejiang University School of Medicine, Hangzhou, China
| | - Zhiwei Jiang
- Key Laboratory of Oral Biomedical Research of Zhejiang Province, School of Stomatology, Zhejiang Provincial Clinical Research Centre for Oral Diseases, Cancer Centre of Zhejiang University, Stomatology Hospital, Zhejiang University School of Medicine, Hangzhou, China
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Landon SM, Baker K, Macpherson LJ. Give-and-take of gustation: the interplay between gustatory neurons and taste buds. Chem Senses 2024; 49:bjae029. [PMID: 39078723 PMCID: PMC11315769 DOI: 10.1093/chemse/bjae029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/11/2024] Open
Abstract
Mammalian taste buds are highly regenerative and can restore themselves after normal wear and tear of the lingual epithelium or following physical and chemical insults, including burns, chemotherapy, and nerve injury. This is due to the continual proliferation, differentiation, and maturation of taste progenitor cells, which then must reconnect with peripheral gustatory neurons to relay taste signals to the brain. The turnover and re-establishment of peripheral taste synapses are vital to maintain this complex sensory system. Over the past several decades, the signal transduction and neurotransmitter release mechanisms within taste cells have been well delineated. However, the complex dynamics between synaptic partners in the tongue (taste cell and gustatory neuron) are only partially understood. In this review, we highlight recent findings that have improved our understanding of the mechanisms governing connectivity and signaling within the taste bud and the still-unresolved questions regarding the complex interactions between taste cells and gustatory neurons.
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Affiliation(s)
- Shannon M Landon
- Department of Neuroscience, Developmental and Regenerative Biology, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, United States
| | - Kimberly Baker
- Department of Neuroscience, Developmental and Regenerative Biology, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, United States
- 59th Medical Wing: Surgical and Technological Advancements for Traumatic Injuries in Combat: 204 Wagner Ave, San Antonio, TX 78211, United States
| | - Lindsey J Macpherson
- Department of Neuroscience, Developmental and Regenerative Biology, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, United States
- Brain Health Consortium, The University of Texas at San Antonio, San Antonio, TX, United States
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Travers SP, Kalyanasundar B, Breza J, Houser G, Klimovich C, Travers J. Characteristics and Impact of the rNST GABA Network on Neural and Behavioral Taste Responses. eNeuro 2022; 9:ENEURO.0262-22.2022. [PMID: 36104278 PMCID: PMC9536858 DOI: 10.1523/eneuro.0262-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 09/06/2022] [Accepted: 09/09/2022] [Indexed: 12/15/2022] Open
Abstract
The rostral nucleus of the solitary tract (rNST), the initial CNS site for processing gustatory information, is comprised of two major cell types, glutamatergic excitatory and GABAergic inhibitory neurons. Although many investigators have described taste responses of rNST neurons, the phenotypes of these cells were unknown. To directly compare the response characteristics of both inhibitory and noninhibitory neurons, we recorded from mice expressing Channelrhodopsin-2 (ChR2) under the control of GAD65, a synthetic enzyme for GABA. We observed that chemosensitive profiles of GABAergic taste neurons (G+TASTE) were similar to non-GABA taste neurons (G-TASTE) but had much lower response rates. We further observed a novel subpopulation of GABA cells located more ventrally in the nucleus that were unresponsive to taste stimulation (G+UNR), suggesting pathways for inhibition initiated by centrifugal sources. This preparation also allowed us to determine how optogenetic activation of the rNST GABA network impacted the taste responses of G-TASTE neurons. Activating rNST inhibitory circuitry suppressed gustatory responses of G-TASTE neurons across all qualities and chemosensitive types of neurons. Although the tuning curves of identified G-TASTE were modestly sharpened, the overall shape of response profiles and the ensemble pattern remained highly stable. These neurophysiological effects were consistent with the behavioral consequences of activating GAD65-expressing inhibitory neurons using DREADDs. In a brief-access licking task, concentration-response curves to both palatable (sucrose, maltrin) and unpalatable (quinine) stimuli were shifted to the right when GABA neurons were activated. Thus, the rNST GABAergic network is poised to modulate taste intensity across the qualitative and hedonic spectrum.
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Affiliation(s)
| | | | - Joseph Breza
- Division of Biosciences, College of Dentistry, Ohio State University, Columbus, OH 43210
| | - Grace Houser
- Division of Biosciences, College of Dentistry, Ohio State University, Columbus, OH 43210
| | - Charlotte Klimovich
- Division of Biosciences, College of Dentistry, Ohio State University, Columbus, OH 43210
| | - Joseph Travers
- Division of Biosciences, College of Dentistry, Ohio State University, Columbus, OH 43210
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METTL3-mediated m 6A RNA methylation regulates dorsal lingual epithelium homeostasis. Int J Oral Sci 2022; 14:26. [PMID: 35581183 PMCID: PMC9114113 DOI: 10.1038/s41368-022-00176-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2022] [Revised: 04/15/2022] [Accepted: 04/21/2022] [Indexed: 02/05/2023] Open
Abstract
The dorsal lingual epithelium, which is composed of taste buds and keratinocytes differentiated from K14+ basal cells, discriminates taste compounds and maintains the epithelial barrier. N6-methyladenosine (m6A) is the most abundant mRNA modification in eukaryotic cells. How METTL3-mediated m6A modification regulates K14+ basal cell fate during dorsal lingual epithelium formation and regeneration remains unclear. Here we show knockout of Mettl3 in K14+ cells reduced the taste buds and enhanced keratinocytes. Deletion of Mettl3 led to increased basal cell proliferation and decreased cell division in taste buds. Conditional Mettl3 knock-in mice showed little impact on taste buds or keratinization, but displayed increased proliferation of cells around taste buds in a protective manner during post-irradiation recovery. Mechanically, we revealed that the most frequent m6A modifications were enriched in Hippo and Wnt signaling, and specific peaks were observed near the stop codons of Lats1 and FZD7. Our study elucidates that METTL3 is essential for taste bud formation and could promote the quantity recovery of taste bud after radiation.
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"Tripartite Synapses" in Taste Buds: A Role for Type I Glial-like Taste Cells. J Neurosci 2021; 41:9860-9871. [PMID: 34697094 DOI: 10.1523/jneurosci.1444-21.2021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 09/29/2021] [Accepted: 10/17/2021] [Indexed: 11/21/2022] Open
Abstract
In mammalian taste buds, Type I cells comprise half of all cells. These are termed "glial-like" based on morphologic and molecular features, but there are limited studies describing their function. We tested whether Type I cells sense chemosensory activation of adjacent chemosensory (i.e., Types II and III) taste bud cells, similar to synaptic glia. Using Gad2;;GCaMP3 mice of both sexes, we confirmed by immunostaining that, within taste buds, GCaMP expression is predominantly in Type I cells (with no Type II and ≈28% Type III cells expressing weakly). In dissociated taste buds, GCaMP+ Type I cells responded to bath-applied ATP (10-100 μm) but not to 5-HT (transmitters released by Type II or III cells, respectively). Type I cells also did not respond to taste stimuli (5 μm cycloheximide, 1 mm denatonium). In lingual slice preparations also, Type I cells responded to bath-applied ATP (10-100 μm). However, when taste buds in the slice were stimulated with bitter tastants (cycloheximide, denatonium, quinine), Type I cells responded robustly. Taste-evoked responses of Type I cells in the slice preparation were significantly reduced by desensitizing purinoceptors or by purinoceptor antagonists (suramin, PPADS), and were essentially eliminated by blocking synaptic ATP release (carbenoxolone) or degrading extracellular ATP (apyrase). Thus, taste-evoked release of afferent ATP from type II chemosensory cells, in addition to exciting gustatory afferent fibers, also activates glial-like Type I taste cells. We speculate that Type I cells sense chemosensory activation and that they participate in synaptic signaling, similarly to glial cells at CNS tripartite synapses.SIGNIFICANCE STATEMENT Most studies of taste buds view the chemosensitive excitable cells that express taste receptors as the sole mediators of taste detection and transmission to the CNS. Type I "glial-like" cells, with their ensheathing morphology, are mostly viewed as responsible for clearing neurotransmitters and as the "glue" holding the taste bud together. In the present study, we demonstrate that, when intact taste buds respond to their natural stimuli, Type I cells sense the activation of the chemosensory cells by detecting the afferent transmitter. Because Type I cells synthesize GABA, a known gliotransmitter, and cognate receptors are present on both presynaptic and postsynaptic elements, Type I cells may participate in GABAergic synaptic transmission in the manner of astrocytes at tripartite synapses.
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