We thank Kavisca Kuruparanantha for her contributions to tissue staining and the imaging of circumvallate taste buds, Jennifer Xu for staining and imaging of innervation to the papilla, Kaytee Horn for animal care and genotyping, and Liqun Ma for her tissue staining of the soft-palate taste buds. This project was supported by R21 DC014857 and R01 DC007176 to R.F.K and F31 DC017660 to L.O.

The authors have nothing to disclose.

The development of an approach to consistently collect and stain whole taste buds from three oral cavity taste regions (fungiform, circumvallate, and the palate) provides significant improvements for analyzing taste-transducing cells, tracking newly incorporated cells, innervation, and relationships between these structures. In addition, it facilitates the localization of a potential secondary neuron marker both within or outside of a labeled population50. This is particularly relevant given that ...

Taste buds are collections of 50-100 specialized epithelial cells that bind subsets of chemical-taste stimuli present in the oral cavity. Taste-transducing cells are generally thought to exist as types1,2,3,4,5,6,7,8,9, initially based on electron microscopy criteria that were later correlated with molecular markers. Type II cells express phospholipase C-beta 2 (PLC&#946;2)2 and transient receptor potential cation channel, subfamily M member 51 and include cells that transduce sweet, bitter, and umami1,10. Type III cells express carbonic anhydrase 4 (Car4)11 and synaptosomal-associated protein 258 and denote cells that primarily respond to sour taste11. The cells that transduce saltiness have not been as clearly delineated12,13,14, but could potentially include Type I, Type II&#160;and Type III cells15,16,17,18,19.The taste-bud environment is complex and dynamic, given that taste-transducing cells continuously turn over throughout adulthood and are replaced by basal progenitors3,20,21. These taste-transducing cells connect to pseudo-unipolar nerve fibers from the geniculate and petrosal ganglia, which pass taste information to the brainstem. These neurons have primarily been categorized based on the kind of taste information they carry22,23 because information about their morphology has been elusive until recently24. Type II cells communicate with nerve fibers via calcium homeostasis modulator protein 1 ion channels25, whereas Type III cells communicate via classical synapses8,26. Further characterization of taste bud cells-including transducing cell type lineages, factors that influence their differentiation, and the structures of connecting arbors are all areas of active investigation.
Taste-bud studies have been hindered by several technical challenges. The heterogenous and dense tissues that make up the tongue significantly reduce antibody permeability for immunohistochemistry27,28,29. These obstacles have necessitated sectioning protocols that result in the splitting of taste buds across sections so that measurements are either approximated based on representative sections or summed across sections. Previously, representative thin sections have been used to approximate both volume values and transducing-cell counts30. Thicker serial sectioning allows for the imaging of all taste-bud sections and the summing of measurements from each section31. Cutting such thick sections and selecting only whole taste buds biases sampling towards smaller taste buds32,33,34. Nerve innervation estimates from sectioned taste buds have been based on analyses of pixel numbers13,35, if quantified at all36,37,38. These measurements completely ignore the structure and number of individual nerve arbors, because arbors are split (and usually poorly labeled). Lastly, although peeling away the epithelium does permit entire taste buds to be stained39,40, it also removes taste-bud nerve fibers and could disrupt the normal relationships between cells. Therefore, investigations of the structural relationships within taste buds have been limited because of this disruption caused by staining approaches.
Whole-structure collection eliminates the need for representative sections and allows the determination of absolute-value measurements of volumes, cell counts, and structure morphologies41. This approach also increases accuracy, limits bias, and reduces technical variability. This last element is important because taste buds show considerable biological variability both within34,42 and across regions43,44, and whole taste-bud analyses allow absolute cell numbers to be compared between control and experimental conditions. Furthermore, the ability to collect intact taste buds permits the analysis of the physical relationships between different transducing cells and their associated nerve fibers. Because taste-transducing cells may communicate with each other45 and do communicate with nerve fibers46, these relationships are important for normal function. Thus, loss-of-function conditions may not be due to a loss of cells, but instead to changes in cell relationships. Provided here is a method for collecting whole taste buds to achieve the benefits of absolute measurements for refining volume analyses for both taste buds and their innervations, taste-cell counts and shapes, and for facilitating analyses of transducing-cell relationships and nerve-arbor morphologies. Two workflows are also presented downstream of this novel whole-mount method for tissue preparation: 1) for analyzing taste bud volume and total innervation and 2) for sparse-cell genetic labeling of taste neurons (with subsets of taste-transducing cells labeled) and subsequent analyses of taste-nerve arbor morphology, numbers of taste-cell types and their shapes, and the use of image analysis software to analyze the physical relationships between transducing cells and those between transducing cells and their nerve arbors. Together, these workflows provide a novel approach to tissue preparation and for the analyses of whole taste buds and the complete morphology of their innervating arbors.

<table><tbody><tr><td>2,2,2-Tribromoethanol</td><td>ACROS Organics</td><td>AC421430100</td><td></td></tr><tr><td>2-Methylbutane</td><td>ACROS</td><td>126470025</td><td></td></tr><tr><td>AffiniPure Fab Fragment Donkey Anti-Rabbit IgG</td><td>Jackson ImmunoResearch</td><td>711-007-003</td><td>15.5&amp;mu;L/mL</td></tr><tr><td>Alexa Fluor&amp;reg; 647 AffiniPure Donkey Anti-Rat IgG</td><td>Jackson Immuno Research</td><td>712-605-150</td><td>(1:500)</td></tr><tr><td>AutoQuant X3 software</td><td>&amp;nbsp;Media Cybernetics</td><td></td><td></td></tr><tr><td>Blunt End Forceps</td><td>Fine Science Tools&amp;nbsp;</td><td>FST 91100-12</td><td></td></tr><tr><td>Click-iT&amp;trade; Plus EdU Cell Proliferation Kit</td><td>Molecular Probes</td><td>C10637</td><td>Follow kit instructions&amp;nbsp;</td></tr><tr><td>Coverglass</td><td>Marienfeld</td><td>107242</td><td></td></tr><tr><td>Cytokeratin-8</td><td>Developmental Studies Hybridoma Bank (DSHB), (RRID: AB_531826)&amp;nbsp;</td><td>Troma1 supernatant</td><td>(1:50, store at 4&amp;deg;C)</td></tr><tr><td>Dissection Scissors (coarse)</td><td>Roboz</td><td>RS-5619</td><td></td></tr><tr><td>Dissection Scissors (fine)</td><td>Moria</td><td>MC19B</td><td></td></tr><tr><td>Donkey anti-Rabbit IgG (H+L) Highly Cross-Adsorbed Secondary Antibody, Alexa Fluor 488</td><td>ThermoFisher Scientific</td><td>A21206</td><td>(1:500)</td></tr><tr><td>Donkey anti-Rabbit, Alexa Fluor&amp;reg; 555</td><td>ThermoFisher Scientific</td><td>A31572</td><td>(1:500)</td></tr><tr><td>DyLight&amp;trade; 405 AffiniPure Fab Fragment Bovine Anti-Goat IgG</td><td>Jackson Immuno Research</td><td>805-477-008</td><td>(1:500)</td></tr><tr><td>Fluoromount G</td><td>Southern Biotech</td><td>0100-01</td><td></td></tr><tr><td>Glass slides</td><td>Fisher Scientific (Superfrost Plus Miscroscope Slides)</td><td>12-550-15</td><td></td></tr><tr><td>Goat anti-Car4</td><td>R&amp;amp;D Systems&amp;nbsp;</td><td>AF2414</td><td>(1:500)</td></tr><tr><td>Imaris&amp;nbsp;</td><td>Bitplane&amp;nbsp;</td><td>pixel-based image analysis software</td><td></td></tr><tr><td>Neurolucida 360 + Explorer</td><td>MBF Biosciences</td><td>3D vector based image analysis software</td><td></td></tr><tr><td>Normal Donkey Serum</td><td>Jackson Immuno Research</td><td>017-000-121</td><td></td></tr><tr><td>Normal Rabbit Serum&amp;nbsp;</td><td>Equitech-Bio, Inc</td><td>SR30</td><td></td></tr><tr><td>Olympus FV1000</td><td></td><td>(multi-Argon laser with wavelengths 458, 488, 515 and additional HeNe lasers emitting 543 and 633)</td><td></td></tr><tr><td>Paraformaldehyde</td><td>EMD</td><td>PX0055-3</td><td>4% in 0.1M PB</td></tr><tr><td>Rabbit anti-dsRed</td><td>Living Colors DsRed Polyclonal Antibody; Clontech Clontech Laboratories, Inc. (632496)</td><td>632496</td><td>(1:500)</td></tr><tr><td>Rabbit anti-PLC&amp;beta;2&amp;nbsp;</td><td>Santa Cruz Biotechnology</td><td>Cat# sc-206</td><td>(1:500)</td></tr><tr><td>Sodium Phosphate Dibasic Anhydrous</td><td>Fisher Scientific</td><td>BP332-500</td><td></td></tr><tr><td>Sodium Phosphate Monobasic</td><td>Fisher Scientific</td><td>BP330-500</td><td></td></tr><tr><td>tert-Amyl alcohol</td><td>Aldrich Chemical Company</td><td>8.06193</td><td></td></tr><tr><td>Tissue Molds</td><td>Electron Microscopy Sciences</td><td>70180</td><td></td></tr><tr><td>Tissue-Tek&amp;reg;&amp;nbsp;O.C.T. Compound</td><td>Sakura</td><td>4583</td><td></td></tr><tr><td>Triton X-100</td><td>BIO-RAD</td><td>#161-0407</td><td></td></tr><tr><td>Zenon&amp;trade; Alexa Fluor&amp;trade; 555 Rabbit IgG Labeling Kit</td><td>ThermoFisher Scientific</td><td>Z25305</td><td>Follow kit instructions&amp;nbsp;</td></tr></tbody></table>

whole-mount staining, visualization, and analysis of fungiform, circumvallate, and palate taste buds

Taste buds are collections of taste-transducing cells specialized to detect subsets of chemical stimuli in the oral cavity. These transducing cells communicate with nerve fibers that carry this information to the brain. Because taste-transducing cells continuously die and are replaced throughout adulthood, the taste-bud environment is both complex and dynamic, requiring detailed analyses of its cell types, their locations, and any physical relationships between them. Detailed analyses have been limited by tongue-tissue heterogeneity and density that have significantly reduced antibody permeability. These obstacles require sectioning protocols that result in splitting taste buds across sections so that measurements are only approximated, and cell relationships are lost. To overcome these challenges, the methods described herein involve collecting, imaging, and analyzing whole taste buds and individual terminal arbors from three taste regions: fungiform papillae, circumvallate papillae, and the palate. Collecting whole taste buds reduces bias and technical variability and can be used to report absolute numbers for features including taste-bud volume, total taste-bud innervation, transducing-cell counts, and the morphology of individual terminal arbors. To demonstrate the advantages of this method, this paper provides comparisons of taste bud and innervation volumes between fungiform and circumvallate taste buds using a general taste-bud marker and a label for all taste fibers. A workflow for the use of sparse-cell genetic labeling of taste neurons (with labeled subsets of taste-transducing cells) is also provided. This workflow analyzes the structures of individual taste-nerve arbors, cell type numbers, and the physical relationships between cells using image analysis software. Together, these workflows provide a novel approach for tissue preparation and analysis of both whole taste buds and the complete morphology of their innervating arbors.

Staining of the lingual epithelium with antibodies to dsRed and keratin-8 (a general taste-bud marker) labeled both whole taste buds and all taste-bud innervation in Phox2b-Cre:tdTomato mice50,51 (Figure 3A). Imaging these taste buds from their pores to their bases gave the highest resolution x-y plane images (Figure 3A,B). The contour function of the pixel-based imaging program was used...

Watch this Scientific Journal Video about Whole-Mount Staining, Visualization, and Analysis of Fungiform, Circumvallate, and Palate Taste Buds at JoVE.com

Whole-Mount Staining, Visualization, and Analysis of Fungiform, Circumvallate, and Palate Taste Buds

This paper describes methods for tissue preparation, staining, and analysis of whole fungiform, circumvallate, and palate taste buds that consistently yield whole and intact taste buds (including the nerve fibers that innervate them) and maintain the relationships between structures within taste buds and the surrounding papilla.

Taste buds are collections of taste-transducing cells specialized to detect subsets of chemical stimuli in the oral cavity. These transducing cells ...

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3.4K Views.  University of Louisville. Deze hele ontlekings- en analyseworkflow biedt een nieuwe benadering om de volledige morfologie van individuele smaakzenuwprieels, transducerende celtypenummers en de fysieke relaties tussen cellen te analyseren. Het verzamelen van het volledige linguale epitheel stelt ons in staat om het absolute aantal cellen en het volume van innervatie in de hele smaakpapillen te meten. Deze benadering is nauwkeuriger dan schattingen van de celstructuur op basis van bemonstering uit secties, wat de techni...

Video: Whole-Mount Staining, Visualization, and Analysis of Fungiform, Circumvallate, and Palate Taste Buds

Technique to Collect Fungiform (Taste) Papillae from Human Tongue

The sense of taste is critical for human life. It informs the body about the quality of food that will be potentially ingested and stimulates metabolic processes that prepare the alimentary canal for digestion. Steady progress is being made towards understanding the early biochemical and molecular events underlying taste transduction (for a review, Breslin and Spector, 20081). However, progress to date has largely resulted from animal models. Yet, since marked differences in receptor specificity and receptor density vary among species, human taste transduction will only be understood by using human taste tissue. Here we describe a biopsy technique to collect human fungiform papillae, visible as rounded pink anterior structures, about 0.5 mm in diameter that contain taste buds. These biopsied papillae are used for several purposes including the isolation of viable taste bud cells, in situ hybridization, immunohistochemistry and, through techniques of molecular biology, the identification of taste-specific novel proteins.

Technique to Collect Fungiform Taste Papillae from Human Tongue

Knowledge of molecular mechanisms underlying gustatory transduction has recently enjoyed significant advances, largely due to using animal models. However, the wide diversity in taste sensitivity and specificity among mammals warrants studies in human tissue. We describe a biopsy technique to collect living taste cells from the papillae on human tongue.

The sense of taste is critical for human life. It informs the body about the quality of food that will be potentially ingested and stimulates metabolic ...

Medicine

Visualization of the Embryonic Nervous System in Whole-mount Drosophila Embryos

The Drosophila embryo is an attractive model system for investigating the cellular and molecular basis of neuronal development. Here we describe the procedure for the visualization of Drosophila embryonic nervous system using antibodies to neuronal proteins. Since the entire embryonic peripheral nervous and central nervous systems are well characterized at the level of individual cells (Dambly-Chaudi&egrave;re et al., 1986; Bodmer et al., 1987; Bodmer et al., 1989), any aberrations to these systems can be easily identified using antibodies to different neuronal proteins. The developing embryos are collected at certain times to ensure that the embryos are in the proper developmental stages for visualization. After collection, the outer layers of the embryo, the chorion membrane and the vitelline envelope that surrounds the embryo, are removed before fixation. Embryos are then incubated with neuronal antibodies and visualized using fluorescently labeled secondary antibodies. Embryos at stages 12-17 are visualized to access the embryonic nervous system. At stage 12 the CNS germ band starts shortening and by stage 15 the definitive pattern of the commissure has been achieved. By stage 17 the CNS contracts and the PNS is fully developed (Campos-Ortega et al. 1985). Thus changes in the pattern of the PNS and CNS can be easily observed during these developmental stages.

Visualization of the Embryonic Nervous System in Whole-mount Drosophila Embryos

We describe the procedure to prepare staged Drosophila embryos for the visualization of the embryonic nervous system during embryogenesis.

The Drosophila embryo is an attractive model system for investigating the cellular and molecular basis of neuronal development. Here we describe the ...

Isolation and Culture of Human Fungiform Taste Papillae Cells

Taste cells are highly specialized, with unique histological, molecular and physiological characteristics that permit detection of a wide range of simple stimuli and complex chemical molecules contained in foods. In human, individual fungiform papillae contain from zero to as many as 20 taste buds. There is no established protocol for culturing human taste cells, although the ability to maintain taste papillae cells in culture for multiple cell cycles would be of considerable utility for characterizing the molecular, regenerative, and functional properties of these unique sensory cells. Earlier studies of taste cells have been done using freshly isolated cells in primary culture, explant cultures from rodents, or semi-intact taste buds in tissue slices1,2,3,4. Although each of these preparations has advantages, the development of long-term cultures would have provided significant benefits, particularly for studies of taste cell proliferation and differentiation. Several groups, including ours, have been interested in the development and establishment of taste cell culture models. Most attempts to culture taste cells have reported limited viability, with cells typically not lasting beyond 3-5 d5,6,7,8. We recently reported on a successful method for the extended culture of rodent taste cells9. We here report for the first time the establishment of an in vitro culture system for isolated human fungiform taste papillae cells. Cells from human fungiform papillae obtained by biopsy were successfully maintained in culture for more than eight passages (12 months) without loss of viability. Cells displayed many molecular and physiological features characteristic of mature taste cells. Gustducin and phospholipase C &beta;2, (PLC-&beta;2) mRNA were detected in many cells by reverse transcriptase-polymerase chain reaction and confirmed by sequencing. Immunocytochemistry analysis demonstrated the presence of gustducin and PLC-&beta;2 expression in cultured taste cells. Cultured human fungiform cells also exhibited increases in intracellular calcium in response to appropriate concentrations of several taste stimuli indicating that taste receptors and at least some of the signalling pathways were present. These results sufficient indicate that taste cells from adult humans can be generated and maintained for at least eight passages. Many of the cells retain physiological and biochemical characteristics of acutely isolated cells from the adult taste epithelium to support their use as a model taste system. This system will enable further studies of the processes involved in proliferation, differentiation and function of mammalian taste receptor cells in an in vitro preparation.
Human fungiform taste papillae used for establishing human fungiform cell culture were donated for research following proper informed consent under research protocols that were reviewed and approved by the IRB committee. The protocol (#0934) was approved by Schulman Associates Institutional Review Board Inc., Cincinnati, OH. Written protocol below is based on published parameters reported by Ozdener et al. 201110.

We aimed to develop a reproducible protocol for isolating and maintaining long-term cultures of human fungiform taste papillae cells. Cells from human fungiform papillae obtained by biopsy were successfully maintained in culture for more than eight passages (12 months) without loss of viability.

Taste cells are highly specialized, with unique histological, molecular and physiological characteristics that permit detection of a wide range of simple ...

Measuring Oral Fatty Acid Thresholds, Fat Perception, Fatty Food Liking, and Papillae Density in Humans

Emerging evidence from a number of laboratories indicates that humans have the ability to identify fatty acids in the oral cavity, presumably via fatty acid receptors housed on taste cells. Previous research has shown that an individual&#39;s oral sensitivity to fatty acid, specifically oleic acid (C18:1) is associated with body mass index (BMI), dietary fat consumption, and the ability to identify fat in foods. We have developed a reliable and reproducible method to assess oral chemoreception of fatty acids, using a milk and C18:1 emulsion, together with an ascending forced choice triangle procedure. In parallel, a food matrix has been developed to assess an individual&#39;s ability to perceive fat, in addition to a simple method to assess fatty food liking. As an added measure tongue photography is used to assess papillae density, with higher density often being associated with increased taste sensitivity.

Oral chemoreception of fatty acids and the association with diet and fatty food preferences may enable the identification of mechanisms involved with the development of obesity and why dietary changes may be difficult for many individuals.

Emerging evidence from a number of laboratories indicates that humans have the ability to identify fatty acids in the oral cavity, presumably via fatty ...

Denver Papillae Protocol for Objective Analysis of Fungiform Papillae

The goal of the Denver Papillae Protocol is to use a dichotomous key to define and prioritize the characteristics of fungiform papillae (FP) to ensure consistent scoring between scorers. This protocol builds off of a need that has arisen from the last two decades of taste research using FP as a proxy for taste pore density. FP density has historically been analyzed using Miller &#38; Reedy&#8217;s 1990 characterizations of their morphology: round, stained lighter, large, and elevated. In this work, the authors forewarned that stricter definitions of FP morphology needed to be outlined. Despite this call to action, follow up literature has been scarce, with most studies continuing to cite Miller &#38; Reedy&#8217;s original work. Consequently, FP density reports have been highly variable and, combined with small sample sizes, may contribute to the discrepant conclusions on the role of FP in taste sensitivity. The Genetics of Taste Lab explored this apparent inconsistency in counting and found that scorers were individually prioritizing the importance of these characteristics differently and had no guidance for when a papilla had some, but not all, of the reported qualities of FP. The result of this subjectivity is highly variable FP counts of the same tongue image. The Denver Papillae Protocol has been developed to remedy this consequence through use of a dichotomous key that further defines and prioritizes the importance of the characteristics put forth by Miller &#38; Reedy. The proposed method could help create a standard way to quantify FP for researchers in the field of taste and nutritional studies.

Here we present a protocol to measure fungiform papilla density from digital photographs. This method builds prioritization and objective characteristic metrics into the original descriptive work on fungiform papillae by Miller &#38; Reedy (1990).

The goal of the Denver Papillae Protocol is to use a dichotomous key to define and prioritize the characteristics of fungiform papillae (FP) to ensure ...

Taste Exam: A Brief and Validated Test

The emerging importance of taste in medicine and biomedical research, and new knowledge about its genetic underpinnings, has motivated us to supplement classic taste-testing methods in two ways. First, we explain how to do a brief assessment of the mouth, including the tongue, to ensure that taste papillae are present and to note evidence of relevant disease. Second, we draw on genetics to validate taste test data by comparing reports of perceived bitterness intensity and inborn receptor genotypes. Discordance between objective measures of genotype and subjective reports of taste experience can identify data collection errors, distracted subjects or those who have not understood or followed instructions. Our expectation is that fast and valid taste tests may persuade researchers and clinicians to assess taste regularly, making taste testing as common as testing for hearing and vision. Finally, because many tissues of the body express taste receptors, taste responses may provide a proxy for tissue sensitivity elsewhere in the body and, thereby, serve as a rapid, point-of-care test to guide diagnosis and a research tool to evaluate taste receptor protein function.

This protocol measures human taste responses and includes a brief anatomical assessment, a short taste test, and a validation method using the subject&#39;s reported sensation and taste receptor genotype.

The emerging importance of taste in medicine and biomedical research, and new knowledge about its genetic underpinnings, has motivated us to supplement ...

In vivo Calcium Imaging of Mouse Geniculate Ganglion Neuron Responses to Taste Stimuli

Within the last ten years, advances in genetically encoded calcium indicators (GECIs) have promoted a revolution in in vivo functional imaging. Using calcium as a proxy for neuronal activity, these techniques provide a way to monitor the responses of individual cells within large neuronal ensembles to a variety of stimuli in real time. We, and others, have applied these techniques to image the responses of individual geniculate ganglion neurons to taste stimuli applied to the tongues of live anesthetized mice. The geniculate ganglion is comprised of the cell bodies of gustatory neurons innervating the anterior tongue and palate as well as some somatosensory neurons innervating the pinna of the ear. Imaging the taste-evoked responses of individual geniculate ganglion neurons with GCaMP has provided important information about the tuning profiles of these neurons in wild-type mice as well as a way to detect peripheral taste miswiring phenotypes in genetically manipulated mice. Here we demonstrate the surgical procedure to expose the geniculate ganglion, GCaMP fluorescence image acquisition, initial steps for data analysis, and troubleshooting. This technique can be used with transgenically encoded GCaMP, or with AAV-mediated GCaMP expression, and can be modified to image particular genetic subsets of interest (i.e., Cre-mediated GCaMP expression). Overall, in vivo calcium imaging of geniculate ganglion neurons is a powerful technique for monitoring the activity of peripheral gustatory neurons and provides complementary information to more traditional whole-nerve chorda tympani recordings or taste behavior assays.

Here we present how to expose the geniculate ganglion of a live, anesthetized laboratory mouse and how to use calcium imaging to measure the responses of ensembles of these neurons to taste stimuli, allowing for multiple trials with different stimulants. This allows for in depth comparisons of which neurons respond to which tastants.

Within the last ten years, advances in genetically encoded calcium indicators (GECIs) have promoted a revolution in in vivo functional imaging. Using ...

&#181;Tongue: A Microfluidics-Based Functional Imaging Platform for the Tongue In Vivo

Intravital fluorescence microscopy is a tool used widely to study multicellular dynamics in a live animal. However, it has not been successfully used in the taste sensory organ. By integrating microfluidics into the intravital tongue imaging window, the &#181;Tongue provides reliable functional images of taste cells in vivo under controlled exposure to multiple tastants. In this paper, a detailed step-by-step procedure to utilize the &#181;Tongue system is presented. There are five subsections: preparing of tastant solutions, setting up of a microfluidic module, sample mounting, acquiring functional image data, and data analysis. Some tips and techniques to solve the practical issues that may arise when using the &#181;Tongue are also presented.

 &#181;Tongue: A Microfluidics-Based Functional Imaging Platform for the Tongue In Vivo

The article introduces the &#181;Tongue (microfluidics-on-a-tongue) device for functional taste cell imaging in vivo by integrating microfluidics into an intravital imaging window on the tongue.

Intravital fluorescence microscopy is a tool used widely to study multicellular dynamics in a live animal. However, it has not been successfully used in ...

The Tongue and Taste Buds

The surface of the tongue is covered with various small bumps called papillae, which either distribute what has been ingested (filiform papillae) or contain the sensory taste (or gustatory) receptor cells (fungiform, circumvallate, and foliate papillae). Embedded within each taste-related papilla are the taste buds&mdash;clusters of 30 to 100 gustatory receptor cells.

Gustatory receptor cells extend finger-like projections called gustatory hairs (or microvilli) into a region known as the taste pore. Here, many of the cells contain receptors that detect different tastants&mdash;the molecules that can be tasted. The average number of taste buds varies significantly among individuals, with estimates ranging from 2,000-10,000 taste buds. Taste cells have a lifespan of about 10-14 days and are continually replaced. Thus, each taste bud contains taste cells at different stages of development.

<h4>Different Types of Taste Papillae</h4>

Aside from the filiform papillae, which do not contain taste buds, the mushroom-shaped fungiform papillae are the most numerous. Fungiform papillae are predominantly located on the anterior two-thirds of the tongue and contain between one and eight taste buds each.

In contrast, the other two types of papillae&mdash;circumvallate and foliate&mdash;contain more than 100 taste buds per papilla. Circumvallate papillae, the largest type, are located at the back of the tongue in &ldquo;V&rdquo;-like formation. Nearby, on the sides of the tongue, are the foliate papillae.

<h4>The Myth of the Tongue&rsquo;s Taste Map</h4>

The work of many scientists, including Collings, Yanagisawa, and colleagues, indicates that the five basic tastes can be perceived anywhere across the tongue. Thus, distinct tastes are not restricted to particular regions, as typically indicated on tongue maps.

The surface of the tongue is covered with various small bumps called papillae, which either distribute what has been ingested (filiform papillae) or ...

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KEY TERMS AND CONCEPTS

Taste Buds and Receptors

Gustation, or the sense of taste, is intrinsically linked to the anatomical structures located on the tongue. This organ&#39;s surface, along with the entirety of the oral cavity, is adorned with stratified squamous epithelium. Evident on the tongue are elevated structures known as papillae (singular = papilla), which house the mechanisms for the transduction of gustatory stimuli. Four distinct types of papillae exist, each identified by their unique morphological attributes: the circumvallate, foliate, filiform, and fungiform papillae. Nestled within the papillae architecture are taste buds, which harbor specific gustatory receptor cells dedicated to the transduction of taste stimuli. These cells exhibit sensitivity to the chemical composition of ingested food, releasing neurotransmitters commensurate with the chemical concentration of the food. The released neurotransmitters can stimulate sensory neurons in the cranial nerves: facial, glossopharyngeal, and vagus.
The human gustatory system, responsible for perceiving taste, is an intricate matrix of processes that combine to discern food flavors. On the microscopic level, gustatory cells are activated by chemical constituents in our food, triggering the release of neurotransmitters. These chemicals relay signals to the brain, where taste perception, such as &#39;sweet,&#39; is formed. Despite its rapid execution, this system&#39;s complexity is evident in its various stages: chemical detection by gustatory receptors, accurate and swift signal transmission via nerves, and efficient information processing by the brain. Furthermore, taste perception is not a solitary phenomenon but is influenced by other sensory inputs like olfactory cues and tactile sensations. For instance, sweet-smelling food might be perceived as bitter if the texture is undesirable. This exemplifies the gustatory system&#39;s remarkable intricacy, hinting at integrating multiple sensory modalities to generate a precise flavor profile. Besides contributing to the hedonic enjoyment of food, taste perception plays a crucial role in assessing food safety. A comprehensive understanding of the biology and sensory perception surrounding taste can provide insights into our body&#39;s food processing mechanisms and flavor experiences, aiding in making informed, health-conscious dietary selections and enhancing our appreciation of taste subtleties.
Commonly Known Gustatory Dysfunction
1) Ageusia refers to the complete loss of taste, while hypogeusia is a reduced ability to taste sweet, sour, bitter, salty, and umami flavors. Conversely, dysgeusia is a condition characterized by a distorted sense of taste.
Common symptoms of these disorders include difficulty identifying specific tastes or experiencing an unpleasant or strange taste in the mouth. They may also cause changes in appetite and dietary habits, potentially leading to weight gain or loss.
2) Phantogeusia is a less common but equally impactful gustatory disorder. It involves tasting something that is not present, often described as a persistent, phantom flavor. This can be particularly distressing and disruptive to daily life, making eating and drinking unpleasant experiences.
Causes of Gustatory Dysfunction
The causes of gustatory disorders are diverse. They range from aging, which naturally diminishes taste sensitivity, to more specific factors, such as medication side effects, infections, and head injuries. Other potential causes include radiation therapy, certain neurological conditions like Parkinson&#39;s or Alzheimer&#39;s disease, and nutritional deficiencies.
Treatment Options
Treatment for gustatory disorders largely depends on the underlying cause. A doctor may adjust the dosage or switch to a different drug if medication is the culprit. Infections may be treated with antibiotics, while nutritional deficiencies can be addressed through diet modifications or supplements.
Surgical interventions may be considered in some cases, particularly if a nerve injury or tumor is causing the taste disorder. However, these are usually last-resort options due to their invasive nature and potential risks.
Pharmacological interventions are another treatment avenue. These may involve drugs that aim to enhance taste sensation or manage symptoms. For instance, zinc supplements have shown promise in improving taste function in some individuals.
The Future of Gustatory Disorder Treatment
Research into gustatory disorders is ongoing, with studies exploring new treatment options and seeking to understand these conditions&#39; underlying mechanisms better. While progress has been made, much remains to be discovered. By continuing to advance our knowledge in this area, we hope to improve the lives of those living with these challenging disorders.
In conclusion, gustatory disorders are complex conditions that can significantly impact an individual&#39;s ability to enjoy food and maintain a healthy diet. Understanding their causes, symptoms, and treatments is essential for providing adequate care and improving patients&#39; quality of life.

Taste buds&#8212;the sensory organs of the taste&#8212;are oval-shaped structures consisting of two major types of epithelial cells.
Gustatory epithelial ...

Whole-Mount Staining, Visualization, and Analysis of Fungiform, Circumvallate, and Palate Taste Buds

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