This work was supported by the Institute of Basic Science (IBS-R015-D1), the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2019M3A9E2061789), and by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2019M3E5D2A01058329). We are grateful to Eunsoo Kim and Eugene Lee for their technical assistance.

All surgical procedures were approved by the Institutional Animal Care and Use Committee (IACUC) of Sungkyunkwan University and Seoul National University.
1. Preparation of solutions: artificial saliva and tastants
<ol>
	<li>Prepare artificial saliva by dissolving 2 mM NaCl, 5 mM KCl, 3 mM NaHCO3, 3 mM KHCO3, 0.25 mM CaCl2, 0.25 mM MgCl2, 0.12 mM K2HPO4, 0.12 mM KH2PO4, and 1.8 mM HCl in distilled water (...

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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Breadth+of+tuning+and+taste+coding+in+mammalian+taste+buds.">Breadth of tuning and taste coding in mammalian taste buds.</a> Journal of Neuroscience. 27 (40), 10840-10848 (2007).</li><li>Dando, R., Roper, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell-to-cell+communication+in+intact+taste+buds+through+ATP+signalling+from+pannexin+1+gap+junction+hemichannels.">Cell-to-cell communication in intact taste buds through ATP signalling from pannexin 1 gap junction hemichannels.</a> The Journal of Physiology. 587 (24), 5899-5906 (2009).</li><li>Chandrashekar, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+cells+and+peripheral+representation+of+sodium+taste+in+mice.">The cells and peripheral representation of sodium taste in mice.</a> Nature. 464 (7286), 297-301 (2010).</li><li>Oka, Y., Butnaru, M., von Buchholtz, L., Ryba, N. J. P., Zuker, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+salt+recruits+aversive+taste+pathways.">High salt recruits aversive taste pathways.</a> Nature. 494 (7438), 472-475 (2013).</li><li>Choi, M., Lee, W. M., Yun, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intravital+microscopic+interrogation+of+peripheral+taste+sensation.">Intravital microscopic interrogation of peripheral taste sensation.</a> Scientific Reports. 5 (8661), 1-6 (2015).</li><li>Han, J., Choi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comprehensive+functional+screening+of+taste+sensation+in+vivo.">Comprehensive functional screening of taste sensation in vivo.</a> bioRxiv. 16419 (371682), 1-22 (2018).</li><li>Thestrup, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimized+ratiometric+calcium+sensors+for+functional+in+vivo+imaging+of+neurons+and+T+lymphocytes.">Optimized ratiometric calcium sensors for functional in vivo imaging of neurons and T lymphocytes.</a> Nature Methods. 11 (2), 175-182 (2014).</li><li>Danilova, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glossopharyngeal+nerves+to+taste+stimuli+in+C57BL+/+6J+mice.">Glossopharyngeal nerves to taste stimuli in C57BL / 6J mice.</a> BME Neuroscience. 15, 1-15 (2003).</li><li>Wu, A., Dvoryanchikov, G., Pereira, E., Chaudhari, N., Roper, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Breadth+of+tuning+in+taste+afferent+neurons+varies+with+stimulus+strength.">Breadth of tuning in taste afferent neurons varies with stimulus strength.</a> Nature Communications. 6 (8171), 1-11 (2015).</li><li>Schindelin, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fiji:+An+open-source+platform+for+biological-image+analysis.">Fiji: An open-source platform for biological-image analysis.</a> Nature Methods. 9 (7), 676-682 (2012).</li><li>Tan, H. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+gut-brain+axis+mediates+sugar+preference.">The gut-brain axis mediates sugar preference.</a> Nature. 580 (7804), 511-516 (2020).</li><li>Roebber, J. 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Described here is a detailed protocol to apply &#181;Tongue to the investigation of functional activities of taste cells in vivo. In this protocol, the functional imaging on the taste cells using genetically encoded calcium indicators is performed. In addition to the use of transgenic mice, the electrophoretic loading of calcium dyes (or voltage sensing dyes) onto the taste cells can be an alternative option.
All the taste solutions less than 1.336 of refractive index were used in thi...

The intravital fluorescence microscope is used widely to study the spatiotemporal dynamics on living tissues. Researchers are rapidly developing genetically encoded sensors that provide specific and sensitive transformations of the biological processes into fluorescence signals - which can be recorded readily using fluorescence microscopes that are widely available1,2. Although most internal organs in rodents have been investigated using the microscope, its successful application to the tongue has not yet been successful3.
Previous studies on the calcium imaging of taste cells were conducted ex vivo by thin-sectioning a tongue tissue to obtain circumvallate taste buds4,5,6 or by peeling off the taste epithelium to obtain fungiform taste buds7,8. The preparation of these samples was inevitably invasive, thus the natural microenvironments such as nerves innervation, permeability barriers, and blood circulation, were largely perturbed. The first intravital tongue imaging window was reported in 2015 by Choi et al., but reliable functional recording was not achievable because of the movement and optical artifacts caused by fluidic tastant stimuli9.
Recently, microfluidics-on-a-tongue (&#181;Tongue) was introduced10. This device integrates a microfluidic system with an imaging window on the mouse tongue. By attaining a quasi-steady-state flow of tastant stimuli throughout the imaging period, artifacts from fluidic motion could be minimized (Figure 1). The input port is fed by a series of multichannel pressure controllers, whereas the output port is connected to a syringe pump, which maintains 0.3 mL/min. Additionally, optical artifacts caused by the difference in refractive indices of tastant solutions were minimized by ratiometric analysis introducing a calcium-insensitive indicator (tdTomato) as well as the calcium indicator (GCaMP6)11. This design provided microscopic stability of taste cells in vivo even with abrupt switching between fluidic channels. Consequently, the &#181;Tongue implement a reliable functional screening of multiple tastants to the mouse taste buds in vivo.
In this protocol, the experimental procedures are explained in detail for calcium imaging of the mouse fungiform taste buds in vivo using &#181;Tongue. First, the preparation of artificial saliva and tastant solutions is described. Second, the setting up of the microfluidic system to achieve the quasi-steady-state flow is introduced. Third, the procedures used to mount the mouse tongue on the &#181;Tongue to permit image acquisition are delineated. Lastly, each step for image analysis, including correction of lateral motion artifacts and ratiometry, is specified. This protocol can be adapted readily to any research laboratory with a mouse facility and a two-photon microscope or equivalent equipment.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>acesulfame K</td>
			<td>Sigma Aldrich</td>
			<td>04054-25G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>calcium chloride solution</td>
			<td>Sigma Aldrich</td>
			<td>21115-100ML</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>citric acid</td>
			<td>Sigma Aldrich</td>
			<td>C0759-100G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>cycloheximide</td>
			<td>Sigma Aldrich</td>
			<td>01810-5G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>denatonium</td>
			<td>Sigma Aldrich</td>
			<td>D5765-5G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>Dental glue</td>
			<td>Denkist</td>
			<td>P0000CJT-A2</td>
			<td>Animal preparation</td>
		</tr>
		<tr>
			<td>Image J</td>
			<td>NIH</td>
			<td>ImageJ</td>
			<td>Data analysis</td>
		</tr>
		<tr>
			<td>IMP</td>
			<td>Sigma Aldrich</td>
			<td>57510-5G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>Instant adhesive</td>
			<td>Loctite</td>
			<td>Loctite 4161, Henkel</td>
			<td>Animal preparation</td>
		</tr>
		<tr>
			<td>K2HPO4</td>
			<td>Sigma Aldrich</td>
			<td>P3786-100G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma Aldrich</td>
			<td>P9541-500G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>Ketamine</td>
			<td>Yuhan</td>
			<td>Ketamine 50</td>
			<td>Animal preparation</td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Sigma Aldrich</td>
			<td>P0662-25G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>KHCO3</td>
			<td>Sigma Aldrich</td>
			<td>237205-500G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>MATLAB</td>
			<td>Mathwork</td>
			<td>MATLAB</td>
			<td>Data analysis</td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Sigma Aldrich</td>
			<td>M8266-100G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>MPG</td>
			<td>Sigma Aldrich</td>
			<td>49601-100G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>Mutiphoton microscope</td>
			<td>Thorlab</td>
			<td>&#160;Bergamo II</td>
			<td>Microscope</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma Aldrich</td>
			<td>S3014-500G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Sigma Aldrich</td>
			<td>792519-500G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>Objective</td>
			<td>Nikon</td>
			<td>N16XLWD-PF</td>
			<td>Microscope</td>
		</tr>
		<tr>
			<td>Octaflow</td>
			<td>ALA Scientific Instruments</td>
			<td>OCTAFLOW II</td>
			<td>Fluidic control</td>
		</tr>
		<tr>
			<td>PC</td>
			<td>LG</td>
			<td>Lg15N54</td>
			<td>Fluidic control</td>
		</tr>
		<tr>
			<td>PH meter</td>
			<td>Thermoscientific</td>
			<td>ORION STAR AZ11</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>Phosphate-buffered saline</td>
			<td>Sigma Aldrich</td>
			<td>806562</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>quinine</td>
			<td>Sigma Aldrich</td>
			<td>Q1125-5G</td>
			<td>Artificial saliva / tastant</td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>Havard Apparatus</td>
			<td>PHD ULTRA 4400</td>
			<td>Fluidic control</td>
		</tr>
		<tr>
			<td>TRITC-dextran</td>
			<td>Sigma Aldrich</td>
			<td>52194-1G</td>
			<td>Animal preparation</td>
		</tr>
		<tr>
			<td>Ultrafast fiber laser</td>
			<td>Toptica</td>
			<td>FFultra920 01042</td>
			<td>Microscope</td>
		</tr>
		<tr>
			<td>Xylazine</td>
			<td>Bayer Korea</td>
			<td>Rompun</td>
			<td>Animal preparation</td>
		</tr>
	</tbody>
</table>

&#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.

The Pirt-GCaMP6f-tdTomato mouse was used to obtain a taste bud image. The surface of the mouse tongue was covered with autofluorescent filiform papillae. Taste buds are spread sparsely over the surface of the tongue (Figure 4A). The images of the taste bud and its structure were acquired using three different filter detectors. Using the 607/70 nm filter set, the tdTomato signal from the taste cells was obtained for ratiometric analysis (Figure 4B). Using the 525...

Watch this Scientific Journal Video about ÂµTongue: A Microfluidics-Based Functional Imaging Platform for the Tongue In Vivo at JoVE.com

 &amp;#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.

&#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 ...

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4.0K vistas.  Sungkyunkwan University. Este protocolo permite observar las funciones de las células gustales en un microambiente natural con conexiones neuronales y circulación sanguínea que permanecen intactas. Usando esta técnica, la comunicación de célula a célula se puede investigar in vivo. Para comenzar, llene los reservorios del sistema de perfusión de flujo presurizado con saliva artificial y saborizantes.Conecte la línea de aire comprimido a la entrada del regulador y ajuste la presión de aire en el siste...