Name: visualization and quantification of the cell-free layer in arterioles of the rat cremaster muscle
Uploaded: 2016-10-19T13:00:00.000+00:00
Duration: 6 min 10 s
Description: Watch this Scientific Journal Video about Visualization and Quantification of the Cell-free Layer in Arterioles of the Rat Cremaster Muscle at JoVE.com

This work was supported by National Medical Research Council (NMRC)/Cooperative Basic Research Grant (CBRG)/0078/2014.

This study is in accordance with the National University of Singapore Institutional Animal Care and Use Committee (approved protocol no. R15-0225).
1. Surgical Preparation of the Animal Model
<ol>
	<li>Vessel cannulations
	<ol>
		<li>Anesthetize a male Sprague-Dawley rats (6 - 7 weeks old) weighing (203 &#177; 20) g with ketamine (37.5 mg/ml) and xylazine (5 mg/ml ) cocktail through intraperitoneal (i.p.) injection (2 ml/kg). Do not recap the needle or remove it from the syringe after the injection.</li>
		<li>Once the animal has been anesthetized (confirmed by toe pinching), place it on a heating pad to maintain its body temperature at 37 &#176;C. Gently shave the hair on the scapulae, anterior cervix, lower abdomen, medial hind leg and scrotal sac. Gently restrain the legs using adhesive paper tapes.</li>
		<li>Perform all surgical procedures using microdissection scissors and angled forceps while viewing through a stereomicroscope. Place all sharp surgical tools on a puncture-resistant tray to prevent injury during the surgery.</li>
		<li>Scrub all surgical sites 3 times with alternating iodine and 70% alcohol before performing the incision. Flush all catheters with 30 IU/ml heparin-saline solution.</li>
		<li>Make a 1 - 1.5 cm midline skin incision on the scapulae using a pair of surgical scissors over the right jugular vein. Separate the fascia by blunt dissection to expose the jugular vein and cannulate it with a polyethylene tube (PE-50) filled with heparin-saline using 5-0 silk sutures. Infuse supplemental anesthesia when necessary (1/3 to 1/2 of initial dosage, intravenous (i.v.)) throughout the course of surgery and experiment.</li>
		<li>Perform tracheostomy to maintain airway patency. Make a 1 - 1.5 cm incision in the anterior cervical area. Cannulate the trachea using a polyethylene tube (PE-205) with 2-0 silk sutures to secure the catheter in place.</li>
		<li>Monitor blood pressure through cannulation at the femoral artery. Make a 1 - 1.5 cm incision at the left medial surface of the hind leg. Separate the femoral artery by blunt dissection. Cannulate the femoral artery with a polyethylene tube (PE-10) filled with heparin-saline using 5-0 silk sutures.</li>
	</ol>
	</li>
	<li>Cremaster Muscle Preparation and Flow Visualization
	<ol>
		<li>Insert a 5-0 silk suture through the apex of the scrotal sac to extend it. Make an incision along the ventral surface of the scrotal sac. Regularly apply warm isotonic solution (37 &#176;C; pH 7.4) to the exposed muscle.</li>
		<li>Remove surrounding connective tissues carefully and thoroughly using a cotton-tipped applicator.</li>
		<li>Insert a 5-0 silk suture through the apex of the cremaster muscle. Cut the suture into two pieces of equal length and tie a knot on each side. Cut the muscle between the two knots and stretch it onto a customized transparent Plexiglas platform by gently pulling the suture. Fix the end of the suture onto the platform with blue tack. 
		NOTE: Thorough removal of surrounding connective tissues is crucial in obtaining optimum image contrast.</li>
		<li>Repeat step 1.2.3 until 5 to 6 fixations are made. Carefully remove the cremaster muscle from the epididymis using high temperature cautery. Superfuse warm isotonic solution to the exposed muscle to prevent dehydration of the tissue.
		<ol>
			<li>Surround the cremaster muscle with folded pieces of gauze. Cover the exposed muscle with a polyvinyl film. The gauze pieces with the film form a shallow basin to hold warm isotonic solution for the water-immersion microscope objective (Figure 1A).</li>
		</ol>
		</li>
		<li>Transfer the animal onto the animal stage of an intravital microscope (Figure 1C). Connect the arterial cannulation to a physiological data-acquisition system for continuous pressure monitoring (Figure 1E).</li>
		<li>Maintain the muscle temperature at 35 &#176;C with a heating element attached beneath the animal platform (Figure 1B). Place a temperature probe beside the muscle to provide negative feedback to the power controller of the heating element (Figure 1D).</li>
		<li>Leave the animal on the stage for 15 min to equilibrate with the environment.</li>
		<li>Visualize blood flow under an intravital microscope with a 40X water-immersion objective and a long working condenser.</li>
		<li>Choose an unbranched arteriole (&#60; 60 &#181;m) based on a clear image focus and contrast between the RBC core, CFL and vessel walls, in order to focus the microscope on the diametric plane of the blood vessel. Rotate the camera mounted onto the microscope to align the vessel wall vertically.</li>
		<li>Record the blood flow using a high-speed video camera at a frame rate of 3,000/sec for 1 sec. Save the recorded video as uncompressed 8-bit grayscale AVI format to preserve the image quality. 
		NOTE: A minimum recording frame rate of 3,000 frames/sec is recommended to ensure that the CFL measurement can be performed at least once per RBC under physiological arteriolar flow conditions.</li>
		<li>Use a blue filter with peak transmission at a wavelength of 394 nm and spectral bandpass at 310 - 510 nm to enhance the contrast between the RBCs and plasma. 
		NOTE: Ensure that the light spectrum passing through the blue filter from the microscopic light source (100 W halogen lamp) is of low light intensity to prevent any potential tissue damage.</li>
		<li>At the end of the experiment, euthanize the animal with an overdose of pentobarbital sodium.</li>
	</ol>
	</li>
</ol>
2. Image Analysis
<ol>
	<li>Preprocessing for the CFL width measurement
	<ol>
		<li>Open MATLAB and run the &#39;CFL_pre.m&#39; file. (This and other MATLAB files can be found in the <a href="https://www.jove.com/files/ftp_upload/54550/CFL_MATLAB_script.zip">Supplemental MATLAB Archive</a>.)</li>
		<li>Click &#39;Open file&#39; to select the video file to analyze.</li>
		<li>Adjust the &#39;Rotation&#39; slider to align the vessel walls vertically. 
		NOTE: Users can display the assisting grid lines for the vessel alignment by selecting the &#39;Grid On&#39; radio button, and adjust the zoom level of the image by sliding the &#39;Zoom&#39; slider.</li>
		<li>Click the &#39;Confirm Editing&#39; button to confirm the vessel alignment.</li>
		<li>Click the &#39;Set ROI to crop&#39; button to define the region of interest (ROI). The aligned image will be displayed in a pop-up window. Adjust the rectangular objective on the image, and double click to confirm the ROI. Skip this step if the cropping of image is not required. 
		NOTE: Only include a single vessel in the ROI to analyze the CFL width from the vessel. Click the &#39;Reset Image&#39; button to restore the image to its original form, if necessary.</li>
		<li>Click the &#39;Extract Images&#39; button to extract all edited video frames into consecutive bit map images (8-bit grayscale &#39;bmp&#39; format). The extracted images can be found in the folder with the same name as the selected video file.</li>
	</ol>
	</li>
	<li>Measurement of CFL width
	<ol>
		<li>Open MATLAB and run the &#39;CFL_measure.m&#39; file.</li>
		<li>Click &#39;Select Folder&#39; to select the folder containing the extracted images.</li>
		<li>Click on the folder containing the images and click &#39;Select Folder&#39;. The first image frame in the folder will be loaded and shown in the &#39;Grayscale image&#39; panel, along with its gray intensity histogram in the &#39;Image Histogram&#39; panel.</li>
		<li>Select the desired image frame from the list box to perform the analysis, otherwise the first image frame will be selected.</li>
		<li>Click &#39;Find Vessel Walls&#39; to identify the inner vessel wall in the image, which is determined at the location where the light intensity profile peak transits from dark to light over two pixels.</li>
		<li>Check &#39;Median Filter&#39; to apply a median filter to the image to reduce the &#39;salt and pepper&#39; noise.</li>
		<li>Check &#39;Auto Contrast&#39; to adjust the image intensities digitally to enhance the image contrast.</li>
		<li>Select a thresholding algorithm in the list box which automatically determines a thresholding value (&#964;) that divides the gray levels into two classes &#8212; white pixels with gray levels above &#964; (CFL), and black pixels with gray levels below &#964; (RBC core). 
		NOTE: As an alternative method, use manual thresholding if none of automated-thresholding algorithm provides an appropriate image thresholding. Click on the &#39;Manual&#39; radio button and adjust the slider to define the manual thresholding value.</li>
		<li>To measure the spatial variation of the CFL widths, enter the pixel resolution in the &#39;Pixel Resolution&#39; box (the resolution with this experimental setup was 0.42 &#181;m/pixel).</li>
		<li>Click the &#39;Calculate&#39; button to obtain the spatial variation of the CFL widths. Click &#39;Export .csv&#39; to export the CFL width data in a tabulated format.</li>
		<li>To measure the temporal variation of the CFL widths at a specific analysis line along the vessel, click on the &#39;Temporal Variation&#39; radio button and enter the frame rate information (the frame rate used in this experimental setup was 3,000 frames/sec).</li>
		<li>Enter the first frame and last frame of the images for the analysis in the &#39;Start Frame&#39; and &#39;Last Frame&#39; boxes, respectively.</li>
		<li>Select the position of the analysis line along the vessel by sliding the &#39;Analysis Line&#39; slide bar. Confirm the position of the analysis line, which is illustrated on both the &#39;Grayscale image&#39; and &#39;Binary image&#39;.</li>
		<li>Click &#39;Calculate&#39; to obtain the temporal variation of the CFL widths. Click &#39;Export .csv&#39; to export the CFL width data in a tabulated format.</li>
	</ol>
	</li>
</ol>

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The authors declare no competing financial interests.

The measurement of CFL width is essential for a better understanding of the hemodynamics in the microcirculation. In particular, the measurement of CFL widths has been performed in mesenteric6, spinotrapezius24 and cerebral25 microcirculations. Conventional measurement of in vivo CFL widths was restricted to estimations by manual inspection of the recorded video frames. The manual measurements required the averaging of several successive video frames before visually identifying t...

In vivo animal studies are instrumental to basic science for understanding human physiology and pathology. In particular, in vivo microhemodynamic studies can elucidate the potential impairment of microcirculatory functions altered by abnormal rheological conditions of blood. A number of previous microhemodynamic studies1 have used the rat cremaster muscle model for visualizing microvascular blood flow. The cremaster muscle is a thin layer of striated muscle surrounding the testes. Thus, the blood flow in the muscle can be visualized with a trans-illumination microscope by means of surgical exposure. This enables us to acquire the in vivo blood flow images without the use of any fluorescence or contrast agents. In addition, the entire blood perfusion of the muscle network can be controlled by reducing the upstream blood flow with abdominal aorta occlusion2. Owing to these advantages, the cremaster muscle model has been widely used to investigate the formation of cell-free layer (CFL) in microvessels1,3. 
The CFL width is a prominent hemodynamic parameter in microcirculation, which has been of great interest for its important roles in regulating microcirculatory functions. The CFL is formed by the shear-induced transverse inward migration of red blood cells (RBCs) towards the flow center4. Consequently, this migration leads to the depletion of RBCs near the vessel walls, eventually resulting in a cell-free plasma layer. Accordingly, the parietal CFL naturally becomes a diffusion barrier to oxygen (O2) delivery from the RBC core to the tissues, and to the scavenging of nitric oxide (NO) by the RBCs5,6. In addition, the production of NO can also be modulated by the dynamic variations of the CFL width7,8. Therefore, the roles of the CFL in both gas transport and the regulation of homeostasis in microcirculation need to be fully ascertained to better understand blood flow in microcirculation. Recent studies have focused on bridging the hemodynamics and gas transport functions of the CFL in the microcirculation9-12. Furthermore, a separate set of studies has also investigated how the pathological elevation in RBC aggregation modulates CFL formation and its effect on O2 and NO bioavailability in tissues13,14. 
The roles of the CFL become more significant in microcirculation where the relative size of the CFL width to the vessel diameter is prominent. This necessitates an effective approach of quantifying the CFL in in vivo blood flow. Particularly, image acquisition and image analysis are the two key components determining the accuracy of CFL width measurement. Successful visualization of tissue blood flow should be preceded by an appropriate surgical preparation of the animal model. Additionally, a proper image analysis technique is needed to overcome the limitations of conventional manual measurements that are mostly induced by human errors15,16. With advancements in optical instrumentation and computing power for digital image processing, it is now possible to achieve a more accurate and consistent measurement of the CFL width17-19. Nonetheless, the accuracy of these measurements, being image-based, still ultimately depends on the quality of the images.
Therefore, this study explores the factors influencing the measurement of the in vivo CFL width. We focused particularly on demonstrating the surgical preparation and digital image analysis for measurements of the CFL width in arterioles of the rat cremaster muscle.

<table><tbody><tr><td>Intravital microscope</td><td>Olympus</td><td>BX51WI</td><td>Equipment</td></tr><tr><td>High speed camera</td><td>Photron</td><td>1024PCI</td><td>Equipment</td></tr><tr><td>Blue filter</td><td>HOYA</td><td>B390</td><td>Equipment</td></tr><tr><td>Pressure sensor &amp;amp; biopac system</td><td>Biopac system</td><td>TSD104A, MP100</td><td>Equipment</td></tr><tr><td>Temperature controller</td><td>Shimaden</td><td>SR 1</td><td>Equipment</td></tr><tr><td>Plasma Lyte A</td><td>Baxter</td><td>NDC:0338-0221</td><td>Warm in 37 &amp;deg;C water bath before use</td></tr><tr><td>Saline 0.9%</td><td>Braun</td><td></td><td></td></tr><tr><td>Heparin (5,000 IU/ml)</td><td>LEO</td><td></td><td></td></tr><tr><td>PE-10 polyethylene tube</td><td>Becton Dickinson</td><td>427400</td><td>.024&quot; OD x .011&quot; ID&amp;nbsp;</td></tr><tr><td>PE-50 polyethene tube</td><td>Becton Dickinson</td><td>427411</td><td>.038&quot; OD x .023&quot; ID</td></tr><tr><td>PE-205 polyethene tube</td><td>Becton Dickinson</td><td>427446</td><td>.082&quot; OD x .062&quot; ID</td></tr><tr><td>2-0 non-absorbable silk suture</td><td>Deknatel</td><td>113-S</td><td></td></tr><tr><td>5-0 non-absorbable silk suture</td><td>Deknatel</td><td>106-S</td><td></td></tr><tr><td>Water circulating heating pad</td><td>Gaymar</td><td></td><td></td></tr><tr><td>Water bath</td><td>Fisher Scientific</td><td>Isotemp 205</td><td>Equipment</td></tr><tr><td>Sterile Cotton Gauze&amp;nbsp;</td><td>Fisher Scientific</td><td>22-415-468</td><td></td></tr><tr><td>Cotton-tipped applicators</td><td>Fisher Scientific</td><td>23-400-124</td><td></td></tr><tr><td>Dumont Forceps</td><td>Kent Scientific</td><td>INS14188</td><td>Surgical instrument</td></tr><tr><td>Micro Dissecting forceps</td><td>Kent Scientific</td><td>INS15915</td><td>Surgical instrument</td></tr><tr><td>Iris forceps 1 x 2 teeth</td><td>Kent Scientific</td><td>INS15917</td><td>Surgical instrument</td></tr><tr><td>Vessel cannulation forceps</td><td>Kent Scientific</td><td>INS500377</td><td>Surgical instrument</td></tr><tr><td>Micro scissor</td><td>Kent Scientific</td><td>INS14177</td><td>Surgical instrument</td></tr><tr><td>Iris scissor</td><td>Kent Scientific</td><td>INS14225</td><td>Surgical instrument</td></tr><tr><td>Vessel clip</td><td>Kent Scientific</td><td>INS14120</td><td>Surgical instrument</td></tr><tr><td>Gemini cautery system</td><td>Braintree Scientific</td><td>GEM 5917</td><td>Surgical instrument</td></tr></tbody></table>

visualization and quantification of the cell-free layer in arterioles of the rat cremaster muscle

The cell-free layer is defined as the parietal plasma layer in the microvessel flow, which is devoid of red blood cells. The measurement of the in vivo cell-free layer width and its spatiotemporal variations can provide a comprehensive understanding of hemodynamics in microcirculation. In this study, we used an intravital microscopic system coupled with a high-speed video camera to quantify the cell-free layer widths in arterioles in vivo. The cremaster muscle of Sprague-Dawley rats was surgically exteriorized to visualize the blood flow. A custom-built imaging script was also developed to automate the image processing and analysis of the cell-free layer width. This approach enables the quantification of spatiotemporal variations more consistently than previous manual measurements. The accuracy of the measurement, however, partly depends on the use of a blue filter and the selection of an appropriate thresholding algorithm. Specifically, we evaluated the contrast and quality of images acquired with and without the use of a blue filter. In addition, we compared five different image histogram-based thresholding algorithms (Otsu, minimum, intermode, iterative selection, and fuzzy entropic thresholding) and illustrated the differences in their determination of the cell-free layer width.

The visualization of the CFL in vivo is largely dependent on the surgical preparations of the animal. Excessive blood loss or extended surgery duration may subject the animal to shock and blood flow aberrations. Maintenance of tissue temperature using a heating pad as well as a customized platform during the surgery and experiment is also crucial for maintaining the physiological conditions of the rat. By using a 100 W halogen lamp in the microscope system, no discernible tissue damage was observed even at the e...

Watch this Scientific Journal Video about Visualization and Quantification of the Cell-free Layer in Arterioles of the Rat Cremaster Muscle at JoVE.com

Visualization and Quantification of the Cell-free Layer in Arterioles of the Rat Cremaster Muscle

This study demonstrates the surgical preparation of the rat cremaster muscle for the visualization of the in vivo cell-free layer. Considerable factors affecting the accuracy of the cell-free layer width measurement are discussed in this study.

The cell-free layer is defined as the parietal plasma layer in the microvessel flow, which is devoid of red blood cells. The measurement of the in vivo ...

visualization-quantification-cell-free-layer-arterioles-rat-cremaster

Research

JoVE Journal

Biology

6.3K Views.  National University of Singapore. This study demonstrates the surgical preparation of the rat cremaster muscle for the visualization of the in vivo cell-free layer. Considerable factors affecting the accuracy of the cell-free layer width measurement are discussed in this study.

Video: Visualization and Quantification of the Cell-free Layer in Arterioles of the Rat Cremaster Muscle

Real-time Digital Imaging of Leukocyte-endothelial Interaction in Ischemia-reperfusion Injury (IRI) of the Rat Cremaster Muscle

Ischemia-reperfusion injury (IRI) has been implicated in a large array of pathological conditions such as cerebral stroke, myocardial infarction, intestinal ischemia as well as following transplant and cardiovascular surgery.1 Reperfusion of previously ischemic tissue, while essential for the prevention of irreversible tissue injury, elicits excessive inflammation of the affected tissue. Adjacent to the production of reactive oxygen species, activation of the complement system and increased microvascular permeability, the activation of leukocytes is one of the principle actors in the pathological cascade of inflammatory tissue damage during reperfusion.2, 3 Leukocyte activation is a multistep process consisting of rolling, firm adhesion and transmigration and is mediated by a complex interaction between adhesion molecules in response to chemoattractants such as complement factors, chemokines, or platelet-activating factor.4
While leukocyte rolling in postcapillary venules is predominantly mediated by the interaction of selectins5 with their counter ligands, firm adhesion of leukocytes to the endothelium is selectin-controlled via binding to intercellular adhesion molecules (ICAM) and vascular cellular adhesion molecules (VCAM).6, 7 
Gold standard for the in vivo observation of leukocyte-endothelial interaction is the technique of intravital microscopy, first described in 1968.8
Though various models of IRI (ischemia-reperfusion injury) have been described for various organs, 9-12 only few are suitable for direct visualization of leukocyte recruitment in the microvascular bed on a high level of image quality.8 
We here promote the digital intravital epifluorescence microscopy of the postcapillary venule in the cremasteric microcirculation of the rat 13 as a convenient method to qualitatively and quantitatively analyze leukocyte recruitment for IRI-research in striated muscle tissue and provide a detailed manual for accomplishing the technique. We further illustrate common pitfalls and provide useful tips which should enable the reader to truly appreciate, and safely perform the method.
In a step by step protocol we depict how to get started with respiration controlled anesthesia under sufficient monitoring to keep the animal firmly anesthetized for longer periods of time. We then describe the cremasteric preparation as a thin flat sheet for outstanding optical resolution and provide a protocol for leukocyte imaging in IRI that has been well established in our laboratories.

Real-time Digital Imaging of Leukocyte-endothelial Interaction in Ischemia-reperfusion Injury IRI of the Rat Cremaster Muscle

Digital intravital epifluorescence microscopy of postcapillary venules in the cremasteric microcirculation is a convenient method to gain insights into leukocyte-endothelial interaction in vivo in ischemia-reperfusion injury (IRI) of striated muscle tissue. We here provide a detailed protocol to safely perform the technique and discuss its applications and limitations.

Ischemia-reperfusion injury (IRI) has been implicated in a large array of pathological conditions such as cerebral stroke, myocardial infarction, ...

Medicine

Real-time Imaging of Heterotypic Platelet-neutrophil Interactions on the Activated Endothelium During Vascular Inflammation and Thrombus Formation in Live Mice

Interaction of activated platelets and leukocytes (mainly neutrophils) on the activated endothelium mediates thrombosis and vascular inflammation.1,2 During thrombus formation at the site of arteriolar injury, platelets adherent to the activated endothelium and subendothelial matrix proteins support neutrophil rolling and adhesion.3 Conversely, under venular inflammatory conditions, neutrophils adherent to the activated endothelium can support adhesion and accumulation of circulating platelets. Heterotypic platelet-neutrophil aggregation requires sequential processes by the specific receptor-counter receptor interactions between cells.4 It is known that activated endothelial cells release adhesion molecules such as von Willebrand factor, thereby initiating platelet adhesion and accumulation under high shear conditions.5 Also, activated endothelial cells support neutrophil rolling and adhesion by expressing selectins and intercellular adhesion molecule-1 (ICAM-1), respectively, under low shear conditions.4 Platelet P-selectin interacts with neutrophils through P-selectin glycoprotein ligand-1 (PSGL-1), thereby inducing activation of neutrophil &beta;2 integrins and firm adhesion between two cell types. Despite the advances in in vitro experiments in which heterotypic platelet-neutrophil interactions are determined in whole blood or isolated cells,6,7 those studies cannot manipulate oxidant stress conditions during vascular disease. In this report, using fluorescently-labeled, specific antibodies against a mouse platelet and neutrophil marker, we describe a detailed intravital microscopic protocol to monitor heterotypic interactions of platelets and neutrophils on the activated endothelium during TNF-&alpha;-induced inflammation or following laser-induced injury in cremaster muscle microvessels of live mice.

Here we report an experimental technique of fluorescence intravital microscopy to visualize heterotypic platelet-neutrophil interactions on the activated endothelium during vascular inflammation and thrombus formation in live mice. This microscopic technology will be valuable to study the molecular mechanism of vascular disease and to test pharmacologic agents under pathophysiological conditions.

Interaction of activated platelets and leukocytes (mainly neutrophils) on the activated endothelium mediates thrombosis and vascular inflammation.1,2 ...

Immunology and Infection

Videomorphometric Analysis of Hypoxic Pulmonary Vasoconstriction of Intra-pulmonary Arteries Using Murine Precision Cut Lung Slices

Acute alveolar hypoxia causes pulmonary vasoconstriction (HPV) - also known as von Euler-Liljestrand mechanism - which serves to match lung perfusion to ventilation. Up to now, the underlying mechanisms are not fully understood. The major vascular segment contributing to HPV is the intra-acinar artery. This vessel section is responsible for the blood supply of an individual acinus, which is defined as the portion of lung distal to a terminal bronchiole. Intra-acinar arteries are mostly located in that part of the lung that cannot be selectively reached by a number of commonly used techniques such as measurement of the pulmonary artery pressure in isolated perfused lungs or force recordings from dissected proximal pulmonary artery segments1,2. The analysis of subpleural vessels by real-time confocal laser scanning luminescence microscopy is limited to vessels with up to 50 &#181;m in diameter3.
We provide a technique to study HPV of murine intra-pulmonary arteries in the range of 20-100 &#181;m inner diameters. It is based on the videomorphometric analysis of cross-sectioned arteries in precision cut lung slices (PCLS). This method allows the quantitative measurement of vasoreactivity of small intra-acinar arteries with inner diameter between 20-40 &#181;m which are located at gussets of alveolar septa next to alveolar ducts and of larger pre-acinar arteries with inner diameters between 40-100 &#181;m which run adjacent to bronchi and bronchioles. In contrast to real-time imaging of subpleural vessels in anesthetized and ventilated mice, videomorphometric analysis of PCLS occurs under conditions free of shear stress. In our experimental model both arterial segments exhibit a monophasic HPV when exposed to medium gassed with 1% O2 and the response fades after 30-40 min at hypoxia.

Hypoxic pulmonary vasoconstriction (HPV) is an important physiological phenomenon by which at alveolar hypoxia lung perfusion is matched to ventilation. The major vascular segment contributing to HPV is the intra-acinar artery. Here, we describe our protocol for the analysis of HPV of murine pulmonary vessels with diameters of 20-100 &mu;m.

Acute alveolar hypoxia causes pulmonary vasoconstriction (HPV) - also known as von Euler-Liljestrand mechanism - which serves to match lung perfusion to ...

The Mouse Cremaster Muscle Preparation for Intravital Imaging of the Microcirculation

Throughout the body, the maintenance of homeostasis requires the constant supply of oxygen and nutrients concomitant with removal of metabolic by-products. This balance is achieved by the movement of blood through the microcirculation, which encompasses the smallest branches of the vascular supply throughout all tissues and organs. Arterioles branch from arteries to form networks that control the distribution and magnitude of oxygenated blood flowing into the multitude of capillaries intimately associated with parenchymal cells. Capillaries provide a large surface area for diffusional exchange between tissue cells and the blood supply. Venules collect capillary effluent and converge as they return deoxygenated blood towards the heart. To observe these processes in real time requires an experimental approach for visualizing and manipulating the living microcirculation.
The cremaster muscle of rats was first used as a model for studying inflammation using histology and electron microscopy post mortem1,2. 
The first in vivo report of the exposed intact rat cremaster muscle investigated microvascular responses to vasoactive drugs using reflected light3. However 
curvature of the muscle and lack of focused illumination limited the usefulness of this preparation. The major breakthrough entailed opening the muscle, 
detaching it from the testicle and spreading it radially as a flat sheet for transillumination under a compound microscope4. While shown to be a valuable 
preparation to study the physiology of the microcirculation in rats5 and hamsters6, the cremaster muscle in mice7 has proven particularly useful in dissecting 
cellular pathways involved in regulating microvascular function8-11 and real-time imaging of intercellular signaling12. 
The cremaster muscle is derived from the internal oblique and transverse abdominus muscles as the testes descend through the inguinal canal13. 
It serves to support (Greek: cremaster = suspender) and maintain temperature of the testes. As described here, the cremaster muscle is prepared as a thin flat sheet 
for outstanding optical resolution. With the mouse maintained at a stable body temperature and plane of anesthesia, surgical preparation involves freeing the muscle 
from surrounding tissue and the testes, spreading it onto transparent pedestal of silastic rubber and securing the edges with insect pins while irrigating it 
continuously with physiological salt solution. The present protocol utilizes transgenic mice expressing GCaMP2 in arteriolar endothelial cells. GCaMP2 is a 
genetically encoded fluorescent calcium indicator molecule12. Widefield imaging and an intensified charge-coupled device camera enable in vivo study of 
calcium signaling in the arteriolar endothelium.

A tissue preparation is described for visualization and experimental manipulation of the living microcirculation. In anesthetized male mice, the thin, highly vascularized cremaster muscle is prepared for intravital microscopy to study microvascular networks including arterioles, capillaries and venules. This preparation is readily adapted for rats and hamsters.

Throughout the body, the maintenance of homeostasis requires the constant supply of oxygen and nutrients concomitant with removal of metabolic ...

Imaging of Estrogen Receptor-&alpha; in Rat Pial Arterioles using a Digital Immunofluorescent Microscope

Many of estrogen's effects on vascular reactivity are mediated through interaction with estrogen receptors 1, 2, 3. Although two sub-types exist (estrogen receptor -&alpha; and &beta;),estrogen receptor-&alpha; has been identified in both the smooth muscle and in endothelial cells of pial arterial segments using fluorescent staining combined with confocal laser scanning microscopy 4. Furthermore, ER-&alpha; is located in the nuclei and in the cytoplasm of rat basilar arteries 5. The receptors are abundant and fluoresce brightly, but clear visualization of discrete groups of receptors is difficult likely due to the numbers located in many cell layers of pial vessel segments. Additionally, many reports using immunohistochemical techniques paired with confocal microscopy poorly detail the requirements critical for reproduction of experiments 6. Our purpose for this article is to describe a simple technique to optimize the staining and visualization of ER-&alpha; using cross-sectional slices of pial arterioles obtain from female rat brains. We first perfuse rats with Evans blue dye to easily identify surface pial arteries which we isolate under a dissecting microscope. Use of a cryostat to slice 8 &mu;m cross sections of the arteries allows us to obtain thin vessel sections so that different vessel planes are more clearly visualized. Cutting across the vessel rather than use of a small vessel segment has the advantage of easier viewing of the endothelial and smooth muscle layers. In addition, use of a digital immunofluorescent microscope with extended depth software produces clear images of ten to twelve different vessel planes and is less costly than use of a confocal laser scanning microscope.

Imaging of Estrogen Receptor-&#945; in Rat Pial Arterioles using a Digital Immunofluorescent Microscope

The goal of this article is to demonstrate a method to optimize immunofluorescent detection of estrogen receptor-&#945; (ER&#945;) in rat pial arterial slices using a digital immunofluorescent microscope.

Many of estrogen's effects on vascular reactivity are mediated through interaction with estrogen receptors 1, 2, 3. Although two sub-types exist (estrogen ...

Evaluation of Vascular Control Mechanisms Utilizing Video Microscopy of Isolated Resistance Arteries of Rats

This protocol describes the use of in vitro television microscopy to evaluate vascular function in isolated cerebral resistance arteries (and other vessels), and describes techniques for evaluating tissue perfusion using Laser Doppler Flowmetry (LDF) and microvessel density utilizing fluorescently labeled Griffonia simplicifolia (GS1) lectin. Current methods for studying isolated resistance arteries at transmural pressures encountered in vivo and in the absence of parenchymal cell influences provide a critical link between in vivo studies and information gained from molecular reductionist approaches that provide limited insight into integrative responses at the whole animal level. LDF and techniques to selectively identify arterioles and capillaries with fluorescently-labeled GS1 lectin provide practical solutions to enable investigators to extend the knowledge gained from studies of isolated resistance arteries. This paper describes the application of these techniques to gain fundamental knowledge of vascular physiology and pathology in the rat as a general experimental model, and in a variety of specialized genetically engineered &#34;designer&#34; rat strains that can provide important insight into the influence of specific genes on important vascular phenotypes. Utilizing these valuable experimental approaches in rat strains developed by selective breeding strategies and new technologies for producing gene knockout models in the rat, will expand the rigor of scientific premises developed in knockout mouse models and extend that knowledge to a more relevant animal model, with a well understood physiological background and suitability for physiological studies because of its larger size.

This manuscript describes in vitro video microscopy protocols for evaluating vascular function in rat cerebral resistance arteries. The manuscript also describes techniques for evaluating microvessel density with fluorescently labeled lectin and tissue perfusion using Laser Doppler Flowmetry.

This protocol describes the use of in vitro television microscopy to evaluate vascular function in isolated cerebral resistance arteries (and other ...

Leukocyte Infiltration of Cremaster Muscle in Mice Assessed by Intravital Microscopy

Intravital microscopy (IVM) is widely used to monitor physiological and pathophysiological processes within the leukocyte recruitment cascade in vivo. The current protocol represents a practical and reproducible method to visualize the leukocyte endothelium interaction leading to leukocyte recruitment in skeletal muscle derived tissue within the intact organism of the mouse. The model is applicable to all fields of research that focus on granulocyte activation and their role in disease.
We provide a step by step protocol to guide through the method and to highlight potential pitfalls and technical difficulties. The protocol covers the following aspects: experimental settings and required material, anesthesia of the mouse, dissection of the cremaster muscle as well as tracheal and carotid cannulation, IVM recordings and offline analysis. Data formats like adherent leukocytes, rolling flux (RF) and rolling flux fraction (RFF) are explained in detail and appropriate applications are discussed. Representative results from dystrophin deficient mdx mice are provided in the results section.
IVM is a powerful tool to assess leukocyte recruitment in an in vivo setting; however, delineating for example endothelial and leukocyte function may require a combination with ex vivo setups like flow chamber experiments. Furthermore, the genetic background of animals of interest may greatly influence baseline recruitment, requiring individual fine tuning of the protocol provided. Despite its limitations, IVM may serve as a platform to readily translate in vitro findings into a living vertebrate organism.

Here, we show how to perform intravital microscopy on post-capillary venules of the mouse cremaster muscle. Commonly applied to different models of inflammation and sepsis, particularly those induced by chemokines and cytokines, we highlight its relevance in the study of muscolopathies involving exaggerated muscular leukocyte infiltration.

Intravital microscopy (IVM) is widely used to monitor physiological and pathophysiological processes within the leukocyte recruitment cascade in vivo. The ...

Intravital Microscopy of the Microcirculation in the Mouse Cremaster Muscle for the Analysis of Peripheral Stem Cell Migration

In the era of intravascular cell application protocols in the context of regenerative cell therapy, the underlying mechanisms of stem cell migration to nonmarrow tissue have not been completely clarified. We describe here the technique of intravital microscopy applied to the mouse cremaster microcirculation for analysis of peripheral bone marrow stem cell migration in vivo. Intravital microscopy of the M. cremaster has been previously introduced in the field of inflammatory research for direct observation of leucocyte interaction with the vascular endothelium. Since sufficient peripheral stem and progenitor cell migration includes similar initial steps of rolling along and firm adhesion at the endothelial lining it is conceivable to apply the M. cremaster model for the observation and quantification of the interaction of intravasculary administered stem cells with the endothelium. As various chemical components can be selectively applied to the target tissue by simple superfusion techniques, it is possible to establish essential microenvironmental preconditions, for initial stem cell recruitment to take place in a living organism outside the bone marrow.

Intravital microscopy of the mouse M. cremaster microcirculation offers a unique and well-standardized in vivo model for the analysis of peripheral bone marrow stem cell migration.

In the era of intravascular cell application protocols in the context of regenerative cell therapy, the underlying mechanisms of stem cell migration to ...

Dynamic Measurement and Imaging of Capillaries, Arterioles, and Pericytes in Mouse Heart

Coronary arterial tone along with the opening or closing of the capillaries largely determine the blood flow to cardiomyocytes at constant perfusion pressure. However, it is difficult to monitor the dynamic changes of the coronary arterioles and the capillaries in the whole heart, primarily due to its motion and non-stop beating. Here we describe a method that enables monitoring of arterial perfusion rate, pressure and the diameter changes of the arterioles and capillaries in mouse right ventricular papillary muscles. The mouse septal artery is cannulated and perfused at a constant flow or pressure with the other dynamically measured. After perfusion with a fluorescently labeled lectin (e.g., Alexa Fluor-488 or -633 labeled Wheat-Germ Agglutinin, WGA), the arterioles and capillaries (and other vessels) in right ventricle papillary muscle and septum could be readily imaged. The vessel-diameter changes could then be measured in the presence or absence of heart contractions. When genetically encoded fluorescent proteins were expressed, specific features could be monitored. For examples, pericytes were visualized in mouse hearts that expressed NG2-DsRed. This method has provided a useful platform to study the physiological functions of capillary pericytes in heart. It is also suitable for studying the effect of reagents on the blood flow in heart by measuring the vascular/capillary diameter and the arterial luminal pressure simultaneously. This preparation, combined with a state-of-the-art optic imaging system, allows one to study the blood flow and its control at cellular and molecular level in the heart under near-physiological conditions.

Presented here is a protocol to study the coronary microcirculation in living murine heart tissue by ex vivo monitoring of the arterial perfusion pressure and flow that maintains the pressure, as well as vascular tree components including the capillary beds and pericytes, as the septal artery is cannulated and pressurized.

Coronary arterial tone along with the opening or closing of the capillaries largely determine the blood flow to cardiomyocytes at constant perfusion ...

Isolation of Retinal Arterioles for Ex Vivo Cell Physiology Studies

The retina is a highly metabolically active tissue that requires a substantial blood supply. The retinal circulation supports the inner retina, while the choroidal vessels supply the photoreceptors. Alterations in retinal perfusion contribute to numerous sight-threatening disorders, including diabetic retinopathy, glaucoma and retinal branch vein occlusions. Understanding the molecular mechanisms involved in the control of blood flow through the retina and how these are altered during ocular disease could lead to the identification of new targets for the treatment of these conditions. Retinal arterioles are the main resistance vessels of the retina, and consequently, play a key role in regulating retinal hemodynamics through changes in luminal diameter. In recent years, we have developed methods for isolating arterioles from the rat retina which are suitable for a wide range of applications including cell physiology studies. This preparation has already begun to yield new insights into how blood flow is controlled in the retina and has allowed us to identify some of the key changes that occur during ocular disease. In this article, we describe methods for the isolation of rat retinal arterioles and include protocols for their use in patch-clamp electrophysiology, calcium imaging and pressure myography studies. These vessels are also amenable for use in PCR-, western blotting- and immunohistochemistry-based studies.

Isolation of Retinal Arterioles for Ex Vivo Cell Physiology Studies

This manuscript describes a straightforward protocol for the isolation of arterioles from the rat retina that can be used in electrophysiological, calcium imaging and pressure myography studies.

The retina is a highly metabolically active tissue that requires a substantial blood supply. The retinal circulation supports the inner retina, while the ...

Visualization and Quantification of the Cell-free Layer in Arterioles of the Rat Cremaster Muscle

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Real-time Digital Imaging of Leukocyte-endothelial Interaction in Ischemia-reperfusion Injury (IRI) of the Rat Cremaster Muscle

Real-time Imaging of Heterotypic Platelet-neutrophil Interactions on the Activated Endothelium During Vascular Inflammation and Thrombus Formation in Live Mice

Videomorphometric Analysis of Hypoxic Pulmonary Vasoconstriction of Intra-pulmonary Arteries Using Murine Precision Cut Lung Slices

The Mouse Cremaster Muscle Preparation for Intravital Imaging of the Microcirculation

Imaging of Estrogen Receptor-α in Rat Pial Arterioles using a Digital Immunofluorescent Microscope

Evaluation of Vascular Control Mechanisms Utilizing Video Microscopy of Isolated Resistance Arteries of Rats

Leukocyte Infiltration of Cremaster Muscle in Mice Assessed by Intravital Microscopy

Intravital Microscopy of the Microcirculation in the Mouse Cremaster Muscle for the Analysis of Peripheral Stem Cell Migration

Dynamic Measurement and Imaging of Capillaries, Arterioles, and Pericytes in Mouse Heart

Isolation of Retinal Arterioles for Ex Vivo Cell Physiology Studies