This study was supported by the National Natural Science Foundation of China (grants 31972908, 81991500, 81991502, 81771093, and 81974151) and the Beijing Natural Science Foundation (grant 7202082).

All experimental procedures were approved by the Ethics Committee of Animal Research, Peking University Health Science Center, and complied with the Guide for the Care and Use of Laboratory Animals (NIH Publication No. 85-23, revised 1996). Male wild-type (WT) mice in the age group of 8-10 weeks were used for the present study. The experimental animals were carefully treated to minimize their pain and discomfort.
1. Animal procedures
<ol>
	<li>Prepare and administer the anesthetics and tracers.
	<ol>
		<li>Maintain sterile conditions throughout the study and sterilize the instruments by autoclaving. Divide the mice into two groups. 
		NOTE: The control group was left untreated, and the other group with unilateral SMG duct ligation for 1 day served as the experimental group. When grouping, mice with similar body weight and age need to be selected to reduce the influence of weight and age on vascular permeability.</li>
		<li>Choose appropriate tracers such as fluorescein isothiocyanate (FITC)-labeled dextran (molecular weight: 4 kDa; FD4) and rhodamine B-labeled dextran (molecular weight: 70 kDa; RD70) (see Table of Materials) with distinct excitation/emission spectra to minimize the interference between fluorescence signals (using the FITC or rhodamine B filter, respectively) for the permeability assay. 
		NOTE: The excitation wavelengths of FD4 and RD70 are 488 nm and 594 nm, respectively, and the selected emission wavelengths are 511-564 nm and 617-669 nm, respectively.</li>
		<li>Dilute the tracers in sterile phosphate-buffered saline (1x PBS) into 100 mg/mL stocks and store the aliquots protected from light at &#8722;20 &#176;C. 
		NOTE: Dextran with a molecular weight such as 4&#160;kDa will rapidly leak from the blood in mouse SMGs even without pathological conditions10.</li>
		<li>Intraperitoneally inject the tribromoethanol (the dose for a 25 g mouse was about 600 &#181;L) to anesthetize the mice. Provide analgesia as recommended by the local animal ethics committee. 
		NOTE: After the induction of anesthesia, use vet ointment on the eyes to prevent dryness. Take good care of the animals11. Wait until the mouse tolerates mechanical stimulation e.g. toe pinch without motor response.</li>
		<li>Inject a mixture of two paracellular permeability tracers with different molecular weights (FD4 and RD70) into the angular vein (0.5 mg/g body weight). Inject each mouse with a 100 &#181;L tracer solution mixture, with 50 &#181;L of each dye mixed in a 1:1 ratio.
		<ol>
			<li>After anesthesia, gently hold the head and neck of the mouse to make one side of the eyeball protrudes slightly. Insert an insulin syringe containing fluorescent tracers (be careful not to introduce any air into the syringe) along the corner of the eye at a right angle to the eye. 
			&#8203;NOTE: If the angular vein is inserted correctly, the dye solution will be easily injected into the vein, and there will be no resistance during the injection. Additionally, tail vein injection in mice might also be a candidate for intravenous tracer molecules.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Perform the SMG isolation following the steps below. 
	NOTE: Use sterile tools, including tissue scissors and separation nickels, for the surgery.
	<ol>
		<li>Separate a unilateral gland carefully so as not to damage the surrounding blood vessels and nerves under a stereoscopic microscope.
		<ol>
			<li>After the injection of paracellular permeability tracers, quickly put the mice on the cardboard and place them in a supine position with their limbs and heads taped. Apply hair removal cream to the neck skin to remove the mouse&#39;s hair. Use 75% ethanol to disinfect the skin before surgery.</li>
			<li>Then, under a stereomicroscope, cut the epidermis of the neck with general tissue scissors to expose both sides of the SMGs (the right gland was treated in this experiment). Next, use a blunt tissue separation nickel (see Table of Materials) to gently separate the capsule from the gland surface, taking care not to damage the gland tissue and blood vessels.</li>
			<li>Separate the capsule from the gland surface without damaging the glandular structure. In addition, ensure that the entire process of mouse restraint and gland separation is accomplished within 10 min.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Two-photon microscope set-up
<ol>
	<li>Connect the customized holder to the negative pressure device, and check whether the negative pressure effect is properly achieved in advance. 
	NOTE: The holder is shaped like a miniature magnifying glass with a flat piece of round glass in the center (diameter: 4.32 mm, Figure 1). The negative pressure device was designed in-house in such a way that the holder is connected to a rubber tube, which is linked with a drainage bottle, and the bottle is attached to the negative pressure controller through a short rubber tube. In this way, the negative pressure controller can adjust the pressure to ensure that the tissue is sucked up into the holder.
	<ol>
		<li>Link one side of the holder with the negative pressure device. To test whether the negative pressure device is intact and appropriate, turn the holder upside down, add a drop of water, and set the negative pressure value to 20 units. If the water is completely and quickly sucked away, the negative pressure device is successfully installed with the holder.</li>
	</ol>
	</li>
	<li>Gently place the exposed SMG of the mouse on the customized holder, and suck up the tissue by negative pressure suction as far away from the mouse body as possible to reduce motion artifacts caused by respiration and other conditions.</li>
	<li>Image the support material attached to the gland under a 25x/NA 1.0 water immersion objective (special for NIR). 
	&#8203;NOTE: Use an upright two-photon microscope (see Table of Materials) in this experiment. The blood vessels must be visible immediately with obvious fluorescence after the tracer injection.</li>
</ol>
3. Vessel imaging and permeability detection
<ol>
	<li>Commence imaging soon after the sight of the gland was chosen. 
	NOTE: Typically, time series of 45-50 images in 20 s or longer are generally captured depending on the experimental design.</li>
	<li>Acquire sequential images along the Z-axis, stepped 2 &#181;m apart, from the gland&#39;s surface up to 70-140 &#181;m into the tissue to generate a three-dimensional (3D) construction.</li>
	<li>Acquire time-lapse imaging of the vessels to measure vascular permeability in the SMG. 
	NOTE: Set the conditions of the program menu as follows after running the microscope software (see Table of Materials).
	<ol>
		<li>In the Explorer dialog box, click on Add New Folder and change the file name.</li>
		<li>Go back to the Acquisition column. In XY, the Format is 512 x 512, and the Speed is 400 Hz. Turn Bidirectional X on.</li>
		<li>Set the Zoom factor to 0.75 and 1.5 for Zoom.</li>
		<li>To acquire time-lapse imaging, select xyt under Acquisition Mode. Set Duration to 20 s, 30 min, or longer according to the experimental need.</li>
		<li>To make the 3D construction, set the Acquisition Mode to xyz. Z-Step size can be set according to the actual situation.</li>
		<li>After setting the conditions, click on Live to observe the vascular imaging of two channels and overlapping channels in the photo forming frame and choose the areas of interest.</li>
		<li>Click on Start to start imaging. 
		&#8203;NOTE: The mouse must not be left unattended during the imaging process while under anesthesia.&#160;</li>
	</ol>
	</li>
</ol>
4. Data analysis
<ol>
	<li>To evaluate the vessel permeability, use Image J software to calculate the fluorescence intensity ratio of FD4 and RD70 between the outside and inside vessels and denote them as extra- and intravascular intensity4. 
	NOTE: The alteration of vascular permeability through tracing the transport of dextrans reflects the change in endothelial barrier function. Moreover, observe the vascular morphology and density by calculating the diameter and number of vessel changes.
	<ol>
		<li>Run Image J software (see Table of Materials).</li>
		<li>Click on File and select Open to open the blood vessel images captured under the two-photon microscope.</li>
		<li>Select Image and set Type to 16-bit to convert the image format.</li>
		<li>Select Analyze and select Area, Mean, IntDen under Set Measurements. Click on OK to confirm.</li>
		<li>Under Analyze, select Tools, open ROI Manger, and select Show All and Labels.</li>
		<li>Measure the intravascular fluorescence intensity value: click on the lasso tool on the main interface to sketch the outline of the blood vessel. Click on Add in ROI Manager. Follow this step to continue to select multiple vessels. Select all of the ROI Manager&#39;s objects and click on Measure.</li>
		<li>Measure the total fluorescence intensity value: outline the whole image, click Measure, and the result is the total fluorescence intensity value of the image.</li>
		<li>Calculate the extravascular fluorescence intensity value. Copy the data to Excel for calculation. Extravascular fluorescence intensity ratio = (1 &#8722; intravascular fluorescence intensity value/total fluorescence intensity value) &#215; 100%.</li>
	</ol>
	</li>
</ol>
5. Downstream applications
<ol>
	<li>During the experiment, calculate the blood flow rate by measuring the distance that a red cell (shown as a black dot under the two-photon microscope)4 undergoes in a time duration.</li>
	<li>To visualize the movement of blood cells across the endothelial cells, label the blood cells by fluorescence. Then, inject the fluorescence-labeled cells with FD4 or RD70 via the mouse tail vein. After circulating for 5 min, trace the interested cells for a period. 
	&#8203;NOTE: A total of 2 x 106 CFSE (carboxyfluorescein succinimidyl ester, a membrane-permeable fluorescent dye)-labeled lymphocytes derived from the spleen of donor mice were transferred into recipients by tail vein injection, and the infiltration of lymphocytes into SMGs was investigated in experimental animal models4.</li>
</ol>
6. Animal care and recovery
<ol>
	<li>Take good care of the animals throughout the experiment. 
	NOTE: Ensure that the animal that has undergone surgery is not returned to the company of other animals until fully recovered during the experiment.</li>
	<li>Do not leave the animal unattended until it regains enough consciousness. 
	NOTE: Observe the breathing status of the mice continuously and keep them warm by putting them on the animal heating pad. Provide postsurgical pain recovery housing and analgesia, as recommended by&#160;the local animal ethics committee.</li>
</ol>

<ol>
	<li>Carpenter, G. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+secretion,+components,+and+properties+of+saliva.">The secretion, components, and properties of saliva.</a> Annual Review of Food Science and Technology. 4, 267-276 (2013).</li><li>Garrett, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+proper+role+of+nerves+in+salivary+secretion:+A+review.">The proper role of nerves in salivary secretion: A review.</a> Journal of Dental Research. 66 (2), 387-397 (1987).</li><li>Berndt, P., 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=Tight+junction+proteins+at+the+blood-brain+barrier:+Far+more+than+claudin-5.">Tight junction proteins at the blood-brain barrier: Far more than claudin-5.</a> Cellular and Molecular Life Sciences. 76 (10), 1987-2002 (2019).</li><li>Cong, X., 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=Disruption+of+endothelial+barrier+function+is+linked+with+hyposecretion+and+lymphocytic+infiltration+in+salivary+glands+of+Sj&#246;gren's+syndrome.">Disruption of endothelial barrier function is linked with hyposecretion and lymphocytic infiltration in salivary glands of Sj&#246;gren's syndrome.</a> Biochimica et Biophysica Acta - Molecular Basis of Disease. 1864 (10), 3154-3163 (2018).</li><li>Helmchen, F., Denk, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deep+tissue+two-photon+microscopy.">Deep tissue two-photon microscopy.</a> Nature Methods. 2 (12), 932-940 (2005).</li><li>Zipfel, W. R., Williams, R. M., Webb, W. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonlinear+magic:+Multiphoton+microscopy+in+the+biosciences.">Nonlinear magic: Multiphoton microscopy in the biosciences.</a> Nature Biotechnology. 21 (11), 1369-1377 (2003).</li><li>Masedunskas, A., Sramkova, M., Weigert, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Homeostasis+of+the+apical+plasma+membrane+during+regulated+exocytosis+in+the+salivary+glands+of+live+rodents.">Homeostasis of the apical plasma membrane during regulated exocytosis in the salivary glands of live rodents.</a> Bioarchitecture. 1 (5), 225-229 (2011).</li><li>Masedunskas, A., 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=Role+for+the+actomyosin+complex+in+regulated+exocytosis+revealed+by+intravital+microscopy.">Role for the actomyosin complex in regulated exocytosis revealed by intravital microscopy.</a> Proceedings of the National Academy of Sciences of the United States of America. 108 (33), 13552-13557 (2011).</li><li>Balda, M. S., 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=Functional+dissociation+of+paracellular+permeability+and+transepithelial+electrical+resistance+and+disruption+of+the+apical-basolateral+intramembrane+diffusion+barrier+by+expression+of+a+mutant+tight+junction+membrane+protein.">Functional dissociation of paracellular permeability and transepithelial electrical resistance and disruption of the apical-basolateral intramembrane diffusion barrier by expression of a mutant tight junction membrane protein.</a> The Journal of Cell Biology. 134 (4), 1031-1049 (1996).</li><li>Enis, D. R., 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=Induction,+differentiation,+and+remodeling+of+blood+vessels+after+transplantation+of+Bcl-2-transduced+endothelial+cells.">Induction, differentiation, and remodeling of blood vessels after transplantation of Bcl-2-transduced endothelial cells.</a> Proceedings of the National Academy of Sciences of the United States of America. 102 (2), 425-430 (2005).</li><li>Wang, X., 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=Application+of+digital+subtraction+angiography+in+canine+hindlimb+arteriography.">Application of digital subtraction angiography in canine hindlimb arteriography.</a> Vascular. 30 (3), 474-480 (2022).</li><li>Trani, M., Dejana, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+insights+in+the+control+of+vascular+permeability:+vascular+endothelial-cadherin+and+other+players.">New insights in the control of vascular permeability: vascular endothelial-cadherin and other players.</a> Current Opinion in Hematology. 22 (3), 267-272 (2015).</li><li>Viazzi, F., 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=Vascular+permeability,+blood+pressure,+and+organ+damage+in+primary+hypertension.">Vascular permeability, blood pressure, and organ damage in primary hypertension.</a> Hypertension Research. 31 (5), 873-879 (2008).</li><li>Scheppke, L., 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=Retinal+vascular+permeability+suppression+by+topical+application+of+a+novel+VEGFR2/Src+kinase+inhibitor+in+mice+and+rabbits.">Retinal vascular permeability suppression by topical application of a novel VEGFR2/Src kinase inhibitor in mice and rabbits.</a> The Journal of Clinical Investigation. 118 (6), 2337-2346 (2008).</li><li>Blanchet, M. R., 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=Loss+of+CD34+leads+to+exacerbated+autoimmune+arthritis+through+increased+vascular+permeability.">Loss of CD34 leads to exacerbated autoimmune arthritis through increased vascular permeability.</a> Journal of Immunology. 184 (3), 1292-1299 (2010).</li><li>Egawa, G., Ono, S., Kabashima, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intravital+Imaging+of+vascular+permeability+by+two-photon+microscopy.">Intravital Imaging of vascular permeability by two-photon microscopy.</a> Methods in Molecular Biology. 2223, 151-157 (2021).</li><li>Vestweber, D., Wessel, F., Nottebaum, A. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Similarities+and+differences+in+the+regulation+of+leukocyte+extravasation+and+vascular+permeability.">Similarities and differences in the regulation of leukocyte extravasation and vascular permeability.</a> Seminars in Immunopathology. 36 (2), 177-192 (2014).</li><li>Schulte, D., 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=Stabilizing+the+VE-cadherin-catenin+complex+blocks+leukocyte+extravasation+and+vascular+permeability.">Stabilizing the VE-cadherin-catenin complex blocks leukocyte extravasation and vascular permeability.</a> The EMBO Journal. 30 (20), 4157-4170 (2011).</li><li>Uhl, B., 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=A+novel+experimental+approach+for+in+vivo+analyses+of+the+salivary+gland+microvasculature.">A novel experimental approach for in vivo analyses of the salivary gland microvasculature.</a> Frontiers in Immunology. 11, 604470 (2020).</li></ol>

The authors have nothing to disclose.

The maintenance and regulation of endothelial barrier function are essential for vascular homeostasis. Endothelial cells and their intercellular junctions play a critical role in maintaining and controlling vascular integrity12. The shear force of blood flow, growth factors, and inflammatory factors can cause changes in vascular permeability and, thus, participate in the occurrence and development of systemic diseases such as hypertension, diabetes, and autoimmune diseases13</sup...

Various salivary glands produce saliva, which primarily acts as the first line of defense against infections and helps digestion, thereby playing an essential role in oral and overall health1. Blood supply is crucial for salivary gland secretion since it constantly provides water, electrolytes, and molecules that form the primary saliva. Endothelial barrier function, regulated by the tight junction (TJ) complex, strictly and delicately limits the permeation of capillaries, which are highly permeable to water, solutes, proteins, and even cells moving from the circulating blood vessels into the salivary gland tissues2,3. We have previously found that the opening of the endothelial TJs in response to a cholinergic stimulus facilitates saliva secretion, whereas the impairment of the endothelial barrier function is interlinked with hyposecretion and lymphocytic infiltration in the submandibular glands (SMGs) in Sj&#246;gren&#39;s syndrome4. These data suggest that the contribution of endothelial barrier function needs to be paid enough attention regarding a variety of salivary gland diseases.
A two-photon laser-scanning microscope is a powerful tool for observing the dynamics of cells in intact tissue in vivo. One of the advantages of this technique is that near-infrared light (NIR) has deeper tissue penetration than visible or ultraviolet light when specimens are excited by NIR and does not cause obvious light damage to tissues under appropriate conditions5,6. Indeed, the salivary glands are a very homogenous and superficial tissue, in which the surface acinar cells are only around 30 &#181;m away from the gland surface7,8. It has been shown that intravital confocal microscopy can study exocrine secretion and actin cytoskeleton in live mouse salivary glands at subcellular resolution8. Two-photon laser-scanning microscopy, nevertheless, not only has the advantage of conventional confocal microscopy but can also be used to detect deeper tissue and image more clearly. Here, fluorescence-labeled dextrans, which are frequently used as paracellular permeability tracers and have the advantage of different sizes, can be used to test the magnitude of TJ pore9. In the present study, an intravital real-time two-photon laser-scanning microscopy technique is established for in situ evaluation of endothelial barrier function in mouse SMGs. Each work step for in vivo vascular permeability detection in mouse SMGs is described in the current protocol. Here is an example of detecting endothelial barrier function in the mouse SMG duct ligation model.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2-photon microscope (TCS-SP8 DIVE)</td>
			<td>Leica, Germany</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>4 kDa FITC-labeled dextran</td>
			<td>Sigma Aldrich</td>
			<td>46944</td>
			<td></td>
		</tr>
		<tr>
			<td>70 kDa rhodamine B-labeled dextran</td>
			<td>Sigma Aldrich</td>
			<td>R9379</td>
			<td></td>
		</tr>
		<tr>
			<td>Blunt tissue separation nickel</td>
			<td>Bejinghuabo Company</td>
			<td>NZW28</td>
			<td></td>
		</tr>
		<tr>
			<td>Depilatory cream</td>
			<td>Veet</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable sterile syringe</td>
			<td>Zhiyu Company</td>
			<td></td>
			<td>1 mL</td>
		</tr>
		<tr>
			<td>Image J software</td>
			<td>National Institutes of Health</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Insulin syringe</td>
			<td>Becton, Dickinson and Company</td>
			<td>0253316</td>
			<td>1 mL</td>
		</tr>
		<tr>
			<td>Leica Application Suite X software</td>
			<td>Leica Microsystems</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Microtubes</td>
			<td>Axygen</td>
			<td>MCT-150-C</td>
			<td>1.5 mL</td>
		</tr>
		<tr>
			<td>Phosphate buffered saline 1x</td>
			<td>Servicebio</td>
			<td>G4207-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue scissors</td>
			<td>Bejinghuabo Company</td>
			<td>M286-05</td>
			<td></td>
		</tr>
		<tr>
			<td>Tribromoethanol</td>
			<td>JITIAN Bio</td>
			<td>JT0781</td>
			<td></td>
		</tr>
	</tbody>
</table>

in vivo vascular permeability detection in mouse submandibular gland

Saliva plays an important role in oral and overall health. The intact endothelial barrier function of blood vessels enables saliva secretion, whereas the endothelial barrier dysfunction is related to many salivary gland secretory disorders. The present protocol describes an in vivo paracellular permeability detection method to evaluate the function of endothelial tight junctions (TJs) in mouse submandibular glands (SMG). First, fluorescence-labeled dextrans with different molecular weights (4 kDa, 40 kDa, or 70 kDa) were injected into the angular veins of mice. Afterward, the unilateral SMG was dissected and fixed in the customized holder under a two-photon laser-scanning microscope, and then images were captured for blood vessels, acini, and ducts. Utilizing this method, the real-time dynamic leakage of the different-sized tracers from blood vessels into the basal sides of the acini and even across the acinar epithelia into the ducts was monitored to evaluate the alteration of the endothelial barrier function under physiological or pathophysiological conditions.

Following the protocol, the unilateral SMG was attached to a custom-made holder, and the gland was kept as far away from the mouse body as possible to prevent breathing from causing motion artifacts. The rapid flow of the red blood cells (black dots) in blood vessels was observed under the microscope. After finding the tissue field under an ocular lens, one must switch to manipulate the microscope software. In the control group, both the tracers existed in the blood vessels of the mouse SMG. In particular, due to its sma...

Watch this Scientific Journal Video about In Vivo Vascular Permeability Detection in Mouse Submandibular Gland at JoVE.com

In Vivo Vascular Permeability Detection in Mouse Submandibular Gland

In the present protocol, the endothelial barrier function of the submandibular gland (SMG) was evaluated by injecting different molecular weighted fluorescent tracers into the angular veins of test animal models in vivo under a two-photon laser-scanning microscope.

In Vivo Vascular Permeability Detection in Mouse Submandibular Gland

Saliva plays an important role in oral and overall health. The intact endothelial barrier function of blood vessels enables saliva secretion, whereas the ...

in-vivo-vascular-permeability-detection-in-mouse-submandibular-gland

Research

JoVE Journal

Biology

1.8K Views.  Ministry of Education, and Beijing Key Laboratory of Cardiovascular Receptors Research. In the present protocol, the endothelial barrier function of the submandibular gland (SMG) was evaluated by injecting different molecular weighted fluorescent tracers into the angular veins of test animal models in vivo under a two-photon laser-scanning microscope.

Video: In Vivo Vascular Permeability Detection in Mouse Submandibular Gland

Single-cell Suction Recordings from Mouse Cone Photoreceptors

Rod and cone photoreceptors in the retina are responsible for light detection. In darkness, cyclic nucleotide-gated (CNG) channels in the outer segment are open and allow cations to flow steadily inwards across the membrane, depolarizing the cell. Light exposure triggers the closure of the CNG channels, blocks the inward cation current flow, and thus results in cell hyperpolarization. Based on the polarity of photoreceptors, a suction recording method was developed in 1970s that, unlike the classic patch-clamp technique, does not require penetrating the plasma membrane 1. Drawing the outer segment into a tightly-fitting glass pipette filled with extracellular solution allows recording the current changes in individual cells upon test-flash exposure. However, this well-established "outer-segment-in (OS-in)" suction recording is not suitable for mouse cone recordings, because of the low percentage of cones in the mouse retina (3%) and the difficulties in identifying the cone outer segments. Recently, an inner-segment-in (IS-in) recording configuration was developed to draw the inner segment/nuclear region of the photoreceptor into the recording pipette 2,3. In this video, we will show how to record from individual mouse cone photoresponses using single-cell suction electrode.

We will show how to record flash responses from single mouse cones using a suction electrode.

Rod and cone photoreceptors in the retina are responsible for light detection. In darkness, cyclic nucleotide-gated (CNG) channels in the outer segment ...

In vivo Imaging and Therapeutic Treatments in an Orthotopic Mouse Model of Ovarian Cancer

Human cancer and response to therapy is better represented in orthotopic animal models. This paper describes the development of an orthotopic mouse model of ovarian cancer, treatment of cancer via oral delivery of drugs, and monitoring of tumor cell behavior in response to drug treatment in real time using in vivo imaging system. In this orthotopic model, ovarian tumor cells expressing luciferase are applied topically by injecting them directly into the mouse bursa where each ovary is enclosed. Upon injection of D-luciferin, a substrate of firefly luciferase, luciferase-expressing cells generate bioluminescence signals. This signal is detected by the in vivo imaging system and allows for a non-invasive means of monitoring tumor growth, distribution, and regression in individual animals. Drug administration via oral gavage allows for a maximum dosing volume of 10 mL/kg body weight to be delivered directly to the stomach and closely resembles delivery of drugs in clinical treatments. Therefore, techniques described here, development of an orthotopic mouse model of ovarian cancer, oral delivery of drugs, and in vivo imaging, are useful for better understanding of human ovarian cancer and treatment and will improve targeting this disease.

In vivo Imaging and Therapeutic Treatments in an Orthotopic Mouse Model of Ovarian Cancer

Orthotopic animal models of ovarian cancer replicate better human disease and therefore enhance our understanding of cancer progression and tumor response to therapy. A mouse model receives an intrabursal injection of luciferase-expressing ovarian tumor cells. Treatment is administered via oral gavage. Tumor growth is monitored by in vivo imaging system.

Human cancer and response to therapy is better represented in orthotopic animal models.  This paper describes the development of an orthotopic mouse model ...

Evaluation of Mammary Gland Development and Function in Mouse Models

The human mammary gland is composed of 15-20 lobes that secrete milk into a branching duct system opening at the nipple. Those lobes are themselves composed of a number of terminal duct lobular units made of secretory alveoli and converging ducts1. In mice, a similar architecture is observed at pregnancy in which ducts and alveoli are interspersed within the connective tissue stroma. The mouse mammary gland epithelium is a tree like system of ducts composed of two layers of cells, an inner layer of luminal cells surrounded by an outer layer of myoepithelial cells denoted by the confines of a basement membrane2. At birth, only a rudimental ductal tree is present, composed of a primary duct and 15-20 branches. Branch elongation and amplification start at the beginning of puberty, around 4 weeks old, under the influence of hormones3,4,5. At 10 weeks, most of the stroma is invaded by a complex system of ducts that will undergo cycles of branching and regression in each estrous cycle until pregnancy2. At the onset of pregnancy, a second phase of development begins, with the proliferation and differentiation of the epithelium to form grape-shaped milk secretory structures called alveoli6,7. Following parturition and throughout lactation, milk is produced by luminal secretory cells and stored within the lumen of alveoli. Oxytocin release, stimulated by a neural reflex induced by suckling of pups, induces synchronized contractions of the myoepithelial cells around the alveoli and along the ducts, allowing milk to be transported through the ducts to the nipple where it becomes available to the pups 8. Mammary gland development, differentiation and function are tightly orchestrated and require, not only interactions between the stroma and the epithelium, but also between myoepithelial and luminal cells within the epithelium9,10,11. Thereby, mutations in many genes implicated in these interactions may impair either ductal elongation during puberty or alveoli formation during early pregnancy, differentiation during late pregnancy and secretory activation leading to lactation12,13. In this article, we describe how to dissect mouse mammary glands and assess their development using whole mounts. We also demonstrate how to evaluate myoepithelial contractions and milk ejection using an ex-vivo oxytocin-based functional assay. The effect of a gene mutation on mammary gland development and function can thus be determined in situ by performing these two techniques in mutant and wild-type control mice.

This method describes how to dissect and assess mammary gland development and function from mice. Excised mammary glands are assessed for the degree of development using whole mount while milk ejection is evaluated using an oxytocin-based myoepithelial cell contraction assay.

The human mammary gland is composed of 15-20 lobes that secrete milk into a branching duct system opening at the nipple. Those lobes are themselves ...

Multi-parameter Measurement of the Permeability Transition Pore Opening in Isolated Mouse Heart Mitochondria

The mitochondrial permeability transition pore (mtPTP) is a non specific channel that forms in the inner mitochondrial membrane to transport solutes with a molecular mass smaller than 1.5 kDa. Although the definitive molecular identity of the pore is still under debate, proteins such as cyclophilin D, VDAC and ANT contribute to mtPTP formation. While the involvement of mtPTP opening in cell death is well established1, accumulating evidence indicates that the mtPTP serves a physiologic role during mitochondrial Ca2+ homeostasis2, bioenergetics and redox signaling 3.
mtPTP opening is triggered by matrix Ca2+ but its activity can be modulated by several other factors such as oxidative stress, adenine nucleotide depletion, high concentrations of Pi, mitochondrial membrane depolarization or uncoupling, and long chain fatty acids4. In vitro, mtPTP opening can be achieved by increasing Ca2+ concentration inside the mitochondrial matrix through exogenous additions of Ca2+ (calcium retention capacity). When Ca2+ levels inside mitochondria reach a certain threshold, the mtPTP opens and facilitates Ca2+ release, dissipation of the proton motive force, membrane potential collapse and an increase in mitochondrial matrix volume (swelling) that ultimately leads to the rupture of the outer mitochondrial membrane and irreversible loss of organelle function.
Here we describe a fluorometric assay that allows for a comprehensive characterization of mtPTP opening in isolated mouse heart mitochondria. The assay involves the simultaneous measurement of 3 mitochondrial parameters that are altered when mtPTP opening occurs: mitochondrial Ca2+ handling (uptake and release, as measured by Ca2+ concentration in the assay medium), mitochondrial membrane potential, and mitochondrial volume. The dyes employed for Ca2+ measurement in the assay medium and mitochondrial membrane potential are Fura FF, a membrane impermeant, ratiometric indicator which undergoes a shift in the excitation wavelength in the presence of Ca2+, and JC-1, a cationic, ratiometric indicator which forms green monomers or red aggregates at low and high membrane potential, respectively. Changes in mitochondrial volume are measured by recording light scattering by the mitochondrial suspension. Since high-quality, functional mitochondria are required for the mtPTP opening assay, we also describe the steps necessary to obtain intact, highly coupled and functional isolated heart mitochondria.

A spectrofluorometric protocol for the measurement of the mitochondrial permeability transition pore opening in isolated mouse heart mitochondria is presented here. The assay involves the simultaneous measurement of mitochondria Ca2+ handling, mitochondrial membrane potential and mitochondrial volume. The procedure for obtaining high-quality and functional heart mitochondria is also described.

The mitochondrial permeability transition pore (mtPTP) is a non specific channel that forms in the inner mitochondrial membrane to transport solutes with ...

Intraductal Injection for Localized Drug Delivery to the Mouse Mammary Gland

Herein we describe a protocol to deliver various reagents to the mouse mammary gland via intraductal injections. Localized drug delivery and knock-down of genes within the mammary epithelium has been difficult to achieve due to the lack of appropriate targeting molecules that are independent of developmental stages such as pregnancy and lactation. Herein, we describe a technique for localized delivery of reagents to the mammary gland at any stage in adulthood via intraductal injection into the nipples of mice. The injections can be performed on live mice, under anesthesia, and allow for a non-invasive and localized drug delivery to the mammary gland. Furthermore, the injections can be repeated over several months without damaging the nipple. Vital dyes such as Evans Blue are very helpful to learn the technique. Upon intraductal injection of the blue dye, the entire ductal tree becomes visible to the eye. Furthermore, fluorescently labeled reagents also allow for visualization and distribution within the mammary gland. This technique is adaptable for a variety of compounds including siRNA, chemotherapeutic agents, and small molecules.

A protocol for the non-invasive intraductal delivery of aqueous reagents to the mouse mammary gland is described. The method takes advantage of localized injection into the nipples of mammary glands targeting mammary ducts specifically. This technique is adaptable for a variety of compounds including siRNA, chemotherapeutic agents and small molecules.

Herein we describe a protocol to deliver various reagents to the mouse mammary gland via intraductal injections. Localized drug delivery and knock-down of ...

Measuring the Osmotic Water Permeability Coefficient (Pf) of Spherical Cells: Isolated Plant Protoplasts as an Example

Studying AQP regulation mechanisms is crucial for the understanding of water relations at both the cellular and the whole plant levels. Presented here is a simple and very efficient method for the determination of the osmotic water permeability coefficient (Pf) in plant protoplasts, applicable in principle also to other spherical cells such as frog oocytes. The first step of the assay is the isolation of protoplasts from the plant tissue of interest by enzymatic digestion into a chamber with an appropriate isotonic solution. The second step consists of an osmotic challenge assay: protoplasts immobilized on the bottom of the chamber are submitted to a constant perfusion starting with an isotonic solution and followed by a hypotonic solution. The cell swelling is video recorded. In the third step, the images are processed offline to yield volume changes, and the time course of the volume changes is correlated with the time course of the change in osmolarity of the chamber perfusion medium, using a curve fitting procedure written in Matlab (the &#8216;PfFit&#8217;), to yield Pf.

Measuring the Osmotic Water Permeability Coefficient Pf of Spherical Cells: Isolated Plant Protoplasts as an Example

Measuring the osmotic water permeability coefficient (Pf) of cells can help understand the regulatory mechanisms of aquaporins (AQPs). Pf determination in spherical plant cell protoplasts presented here involves protoplasts isolation and numerical analysis of their initial rate of volume change as a result of an osmotic challenge during constant bath perfusion.

Studying AQP regulation mechanisms is crucial for the understanding of water relations at both the cellular and the whole plant levels. Presented here is ...

Measuring the Stiffness of Ex Vivo Mouse Aortas Using Atomic Force Microscopy

Arterial stiffening is a significant risk factor and biomarker for cardiovascular disease and a hallmark of aging. Atomic force microscopy (AFM) is a versatile analytical tool for characterizing viscoelastic mechanical properties for a variety of materials ranging from hard (plastic, glass, metal, etc.) surfaces to cells on any substrate. It has been widely used to measure the stiffness of cells, but less frequently used to measure the stiffness of aortas. In this paper, we will describe the procedures for using AFM in contact mode to measure the ex vivo elastic modulus of unloaded mouse arteries. We describe our procedure for isolation of mouse aortas, and then provide detailed information for the AFM analysis. This includes step-by-step instructions for alignment of the laser beam, calibration of the spring constant and deflection sensitivity of the AFM probe, and acquisition of force curves. We also provide a detailed protocol for data analysis of the force curves.

Measuring the Stiffness of Ex Vivo Mouse Aortas Using Atomic Force Microscopy

We present detailed protocols for isolation of aortas from mouse and measurement of their elastic modulus using atomic force microscopy.

Arterial stiffening is a significant risk factor and biomarker for cardiovascular disease and a hallmark of aging. Atomic force microscopy (AFM) is a ...

In Vivo Detection and Analysis of Rb Protein SUMOylation in Human Cells

The post-translational modifications of proteins are critical for the proper regulation of intracellular signal transduction. Among these modifications, small ubiquitin-related modifier (SUMO) is a ubiquitin-like protein that is covalently attached to the lysine residues of a variety of target proteins to regulate cellular processes, such as gene transcription, DNA repair, protein interaction and degradation, subcellular transport, and signal transduction. The most common approach to detecting protein SUMOylation is based on the expression and purification of recombinant tagged proteins in bacteria, allowing for an in vitro biochemical reaction which is simple and suitable for addressing mechanistic questions. However, due to the complexity of the process of SUMOylation in vivo, it is more challenging to detect and analyze protein SUMOylation in cells, especially when under endogenous conditions. A recent study by the authors of this paper revealed that endogenous retinoblastoma (Rb) protein, a tumor suppressor that is vital to the negative regulation of the cell cycle progression, is specifically SUMOylated at the early G1 phase. This paper describes a protocol for the detection and analysis of Rb SUMOylation under both endogenous and exogenous conditions in human cells. This protocol is appropriate for the phenotypical and functional investigation of the SUMO-modification of Rb, as well as many other SUMO-targeted proteins, in human cells.

In Vivo Detection and Analysis of Rb Protein SUMOylation in Human Cells

Small ubiquitin-related modifier (SUMO) family proteins are conjugated to the lysine residues of target proteins to regulate various cellular processes. This paper describes a protocol for the detection of retinoblastoma (Rb) protein SUMOylation under endogenous and exogenous conditions in human cells.

The post-translational modifications of proteins are critical for the proper regulation of intracellular signal transduction. Among these modifications, ...

In Vitro and In Vivo Approaches to Determine Intestinal Epithelial Cell Permeability

The intestinal barrier defends against pathogenic microorganism and microbial toxin. Its function is regulated by tight junction permeability and epithelial cell integrity, and disruption of the intestinal barrier function contributes to progression of gastrointestinal and systemic disease. Two simple methods are described here to measure the permeability of intestinal epithelium. In vitro, Caco-2BBe cells are plated in tissue culture wells as a monolayer and transepithelial electrical resistance (TER) can be measured by an epithelial (volt/ohm) meter. This method is convincing because of its user-friendly operation and repeatability. In vivo, mice are gavaged with 4 kDa fluorescein isothiocyanate (FITC)-dextran, and the FITC-dextran concentrations are measured in collected serum samples from mice to determine the epithelial permeability. Oral gavage provides an accurate dose, and therefore is the preferred method to measure the intestinal permeability in vivo. Taken together, these two methods can measure the permeability of the intestinal epithelium in vitro and in vivo, and hence be used to study the connection between diseases and barrier function.

In Vitro and In Vivo Approaches to Determine Intestinal Epithelial Cell Permeability

Two methods are presented here to determine intestinal barrier function. An epithelial meter (volt/ohm) is used for measurements of transepithelial electrical resistance of cultured epithelia directly in tissue culture wells. In mice, the FITC-dextran gavage method is used to determine the intestinal permeability in vivo.

The intestinal barrier defends against pathogenic microorganism and microbial toxin. Its function is regulated by tight junction permeability and ...

Micron-scale Phenotyping Techniques of Maize Vascular Bundles Based on X-ray Microcomputed Tomography

It is necessary to accurately quantify the anatomical structures of maize materials based on high-throughput image analysis techniques. Here, we provide a 'sample preparation protocol' for maize materials (i.e., stem, leaf, and root) suitable for ordinary microcomputed tomography (micro-CT) scanning. Based on high-resolution CT images of maize stem, leaf, and root, we describe two protocols for the phenotypic analysis of vascular bundles: (1) based on the CT image of maize stem and leaf, we developed a specific image analysis pipeline to automatically extract 31 and 33 phenotypic traits of vascular bundles; (2) based on the CT image series of maize root, we set up an image processing scheme for the three-dimensional (3-D) segmentation of metaxylem vessels, and extracted two-dimensional (2-D) and 3-D phenotypic traits, such as volume, surface area of metaxylem vessels, etc. Compared with traditional manual measurement of vascular bundles of maize materials, the proposed protocols significantly improve the efficiency and accuracy of micron-scale phenotypic quantification.

We provide a novel method to improve the X-ray absorption contrast of maize tissue suitable for ordinary microcomputed tomography scanning. Based on CT images, we introduce a set of image-processing workflows for different maize materials to effectively extract microscopic phenotypes of vascular bundles of maize.

It is necessary to accurately quantify the anatomical structures of maize materials based on high-throughput image analysis techniques. Here, we provide a ...