This research was supported by the Brigham &#38; Women&#8217;s Hospital and the March of Dimes. The authors would like to thank all of the members of the Whited Lab for their support and advice.

All axolotl experimentation was performed in accordance with Brigham and Women&#39;s Hospital&#39;s (BWH) Institutional Animal Care and Use Committee.
1. Set up Perfusion Experiment
<ol>
	<li>Place an adult axolotl in a plastic container filled with 0.1% tricaine solution (MS222) for 15-20 min or until completely anesthetized. Ensure that the container is filled with enough tricaine solution such that the axolotl is completely submerged. 
	Note: All procedures must be performed in accordance with institutional animal care guidelines. At BWH, an axolotl is considered fully anesthetized when it fails a foot-pinch test, meaning there is no reflexive movement when the foot is gently squeezed. 
	Caution: Though tricaine is an anesthetic specifically used for aquatic organisms, direct skin contact with the tricaine solution should be avoided.</li>
	<li>Set up the axolotl perfusion station.
	<ol>
		<li>Place the absorbent pad on a flat, level surface with the absorbent side facing up.</li>
		<li>Cut a hole in the polystyrene foam frame that is the appropriate size and shape for the anesthetized axolotl to lay in the supine position. Place the frame on the absorbent pad. 
		Note: Some extra paper towels can be placed immediately under the frame for additional absorbency.</li>
		<li>Load the peristaltic pump with the perfusion tubing. Set the pump to a flow rate of 0.7 ml/min, flowing in the clockwise direction.</li>
		<li>Make the dilutent solution with 0.7x PBS and 5% glucose in a 1:4 mixture.</li>
		<li>Mix 10 mL of diluent solution with 200 &#181;L of the DiI stock solution in a 50 mL conical tube. Cap and mix by inversion. Cover this tube with aluminum foil paper to protect the working solution from exposure to light. 
		Note: Volumes should be changed according to the size of the axolotl proportionally. These values are for an approximately 15 cm axolotl (snout-to-tail length). Animals of this size may not have reached full sexual maturity so animal sex may not be determined at this time.</li>
		<li>Fill a 50 mL conical tube with 0.7x PBS. 
		Note: PBS will be used for priming the loop and axolotl exsanguination.</li>
		<li>Attach the 27-gauge butterfly needle to the exit end of the perfusion tubing. Fold the butterfly wings onto each other and place in the clamp stand.</li>
		<li>Place the free end of the perfusion tubing in the 50 mL conical tube filled with 0.7x PBS and run the perfusion pump until the entire tubing is filled with solution. Pause the pump once the entire tubing is filled with PBS. 
		Note: Be sure the tubing is free of air bubbles at all times, as these will cause air emboli in the axolotl and prevent full perfusion.</li>
		<li>Place a paper towel in the axolotl-shaped mold in the polystyrene foam frame. Using a transfer pipette, soak the towel with tricaine solution. 
		Note: Cut a small square in the middle of the paper towel to allow for the drainage of fluids during the perfusion procedure.</li>
		<li>Place the anesthetized axolotl supine on the paper towel inside the polystyrene foam frame.</li>
	</ol>
	</li>
</ol>
2. Opening the Axolotl Chest
<ol>
	<li>Use surgical forceps to pinch the skin along the central axis of the axolotl&#39;s chest, just below the line of the shoulders. Pull up.</li>
	<li>Use a scalpel to make a small incision where the skin has been pulled.</li>
	<li>Remove a square patch of skin over the chest in order to reveal two cartilage plates.
	<ol>
		<li>Remove the skin to open a window over the thoracic cavity large enough to clearly see the heart and approximately 5 mm of the aorta branching off of the heart.</li>
	</ol>
	</li>
	<li>Carefully tear the connective tissue using forceps or the closed scissors in order to avoid cutting any major blood vessels.</li>
	<li>Lift each cartilage plate individually using the forceps and excise them with the surgical scissors.</li>
	<li>Carefully pinch the pericardium with the forceps, pull up, and puncture it using the surgical scissors; this incision should be just deep enough to puncture the very thin pericardium and should be large enough to allow for removal of the pericardium. Take care not to cut the heart.</li>
	<li>Delicately remove the pericardium to expose the heart and the aorta. 
	Note: Using a transfer pipette, periodically flush the chest cavity and the gills with tricaine solution to keep the area clear and keep the axolotl anesthetized.</li>
</ol>
3. Perfusion of the Axolotl
<ol>
	<li>Place the clamp stand with the loaded butterfly needle next to the polystyrene foam frame, such that the arm of the clamp can easily be manipulated to insert the needle into the axolotl aorta. Point the needle&#39;s tip toward the rostral aspect of the animal during insertion and keep the needle parallel to the aorta to avoid puncturing it through the opposite side.</li>
	<li>Turn on the peristaltic pump. 0.7x PBS should continue to flow through tubing.</li>
	<li>Insert the needle into the aorta.
	<ol>
		<li>Slide the forceps under the aortic arch and pull up slightly to allow for easy access.</li>
		<li>Maneuver the needle-clamp combination such that the needle runs along the length of the aorta, pointing up towards the head. Insert the needle while using the forceps for support behind the aorta. 
		Note: The needle should be inserted deep enough into the aorta to ensure that it will not slip out during perfusion. This may be about 5 mm for a 15 cm axolotl. Ensure that the needle is perfectly in line with the aorta to avoid complete puncture of the vessel. Through-and-through punctures can cause massive hemorrhage and decrease success rates of perfusion. Successful insertion can be confirmed by visible enlargement of the atria of the heart.</li>
	</ol>
	</li>
	<li>Quickly lacerate one atrium with the scissors and allow blood to drain.
	<ol>
		<li>Flush with tricaine solution to prevent blood accumulation and clot formation in the chest cavity.</li>
	</ol>
	</li>
	<li>Perfuse the axolotl with about 20-30 mL of PBS. The animal should change from light pink in color to white in a successful perfusion.</li>
	<li>Pause the peristaltic pump and move the free end of the tubing into the 15 mL tube of DiI solution. Restart the pump, take care to avoid creating any air bubbles in the tubing.</li>
	<li>Perfuse the axolotl with the entire working stock of DiI. 
	Note: In a successful perfusion, the axolotl with change color to the bright pink of the DiI. This will be most noticeable in the gills.</li>
	<li>Pause the pump after the perfusion with DiI is complete and place the free end of the tubing into 4% Paraformaldehyde (PFA) solution to fix the tissue. Restart the pump and perfuse at least 10 mL of PFA. 
	Caution: PFA is toxic and should be handled and disposed of appropriately. Gloves and safety glasses should be worn, and solutions should be made inside a fume hood. Perfusion of the axolotl with PFA to fix the tissue results in the death of the animal.</li>
</ol>
4. Ending the Perfusion and Visualization Preparation
<ol>
	<li>Stop the peristaltic pump and remove the needle from the axolotl aorta.</li>
	<li>Place the axolotl on a plastic plate. 
	Note: Using one half of a large Petri dish works well and allows for pouring a small amount of Tricaine or PBS onto the axolotl to keep its skin wet and improve visualization quality.</li>
	<li>Dispose of all used materials in the appropriate waste bins. Clean surgical tools with 70% ethanol, disinfect using a glass-bead sterilizer between animals, and sterilize by autoclaving following the procedure. Flush tubing with the PBS solution and then drain, dry fully, and store for further use.</li>
</ol>
5. Visualization the Perfused Axolotl
<ol>
	<li>Place the axolotl under a fluorescent confocal microscope.</li>
	<li>Turn the lights off as visualization of the DiI-stained vessels is impeded by light.</li>
	<li>Use a green fluorescence emission filter cube (e.g. ET-CY3) with the confocal microscope to visualize the vasculature of the axolotl. Use excitation light of wavelength 545 nm. 
	Note: To obtain an image of high quality, the following parameters can be used: exposure for 1.1 s, gain of 1x, saturation of 1.0, magnification of 2X.</li>
</ol>

<ol>
	<li>Giuvarasteanu, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scanning+electron+microscopy+of+vascular+corrosion+casts+-+standard+method+for+studying+microvessels.">Scanning electron microscopy of vascular corrosion casts - standard method for studying microvessels.</a> Rom J Morphol Embryo. 48 (3), 257-261 (2007).</li><li>Hasan, M. R., Herz, J., Hermann, D. M., Doeppner, T. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intravascular+perfusion+of+carbon+black+ink+allows+reliable+visualization+of+cerebral+vessels.">Intravascular perfusion of carbon black ink allows reliable visualization of cerebral vessels.</a> J Vis Exp. (71), e4374 (2013).</li><li> Minnich, B., Lametschwandtner, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=+Scanning+electron+microscopy+and+vascular+corrosion+casting+for+the+characterization+of+microvascular+networks+in+human+and+animal+tissues."> Scanning electron microscopy and vascular corrosion casting for the characterization of microvascular networks in human and animal tissues.</a> Microscopy: Science, Technology, Applications, and Education. 1, 29-39 (2010).</li><li> Honig, M., Hume, R. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=+DiI+and+DiO:+versatile+fluorescent+dyes+for+neuronal+labelling+and+pathway+tracing."> DiI and DiO: versatile fluorescent dyes for neuronal labelling and pathway tracing.</a> Trends Neurosci. 13, 333-335 (1989).</li><li>Honig, M. G., Hume, R. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+carbocyanine+dyes+allow+living+neurons+of+identified+origin+to+be+studied+in+long-term+cultures.">Fluorescent carbocyanine dyes allow living neurons of identified origin to be studied in long-term cultures.</a> J Cell Biol. 103 (1), 171-187 (1986).</li><li>Schwartz, M., Agranoff, B. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Outgrowth+and+maintenance+of+neurites+from+cultured+goldfish+retinal+ganglion+cells.">Outgrowth and maintenance of neurites from cultured goldfish retinal ganglion cells.</a> Brain Res. 206 (2), 331-343 (1981).</li><li>Li, Y., Song, Y., Zhao, L., Gaidosh, G., Laties, A. M., Wen, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+labeling+and+visualization+of+blood+vessels+with+lipophilic+carbocyanine+dye+DiI.">Direct labeling and visualization of blood vessels with lipophilic carbocyanine dye DiI.</a> Nat Protoc. 3 (11), 1703-1708 (2008).</li><li>Kuo, T. H., Kowalko, J. E., DiTommaso, T., Nyambi, M., Montoro, D. T., Essner, J. J., Whited, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+of+TALEN-mediated+gene+editing+of+an+endogenous+locus+in+axolotl.">Evidence of TALEN-mediated gene editing of an endogenous locus in axolotl.</a> Regeneration. 2 (1), 37-43 (2015).</li><li>Brockes, J. P., Kumar, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Appendage+Regeneration+in+Adult+Vertebrates+and+Implications+for+Regenerative+Medicine.">Appendage Regeneration in Adult Vertebrates and Implications for Regenerative Medicine.</a> Science. 310 (5756), 1919-1923 (2005).</li><li>Smith, A. R., Wolpert, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nerves+and+angiogenesis+in+amphibian+limb+regeneration.">Nerves and angiogenesis in amphibian limb regeneration.</a> Nature. 257 (5523), 224-225 (1975).</li></ol>

The authors have nothing to disclose.

Visualization of the vasculature of the axolotl can be successfully accomplished via perfusion with the lipophilic carbocyanine dye, DiI. In this study, we describe a novel protocol for the perfusion of the axolotl with DiI using a peristaltic pump. We also show the subsequent visualization of the axolotl vasculature using a fluorescent confocal microscope. This protocol was an adaptation of the rodent DiI perfusion protocol seen in Li et al.7, however major differences between the rodent and the axolotl required a revision of the protocol to fit the axolotl model.
This study discusses a method of DiI perfusion of the axolotl in order to successfully visualize the vasculature. Differences in the anatomy and physiology between the salamander and rodent demand alterations in major aspects of the perfusion, including location of needle insertion, method of perfusion, and the reagents used. In order to achieve a successful perfusion, we limited the damage done to the vasculature of the axolotl. While opening the chest cavity, care was taken to fully expose the heart and aorta while avoiding any damage or lacerations to major blood vessels. Limiting the use of the surgical scissors prevented accidental clipping of major vessels while small incisions maintained control over the exposure of the heart and aorta. Success rates of perfusions also increased when the DiI needle was inserted through the aorta, rather than directly into the chambers of the heart. The axolotl, unlike the mouse, has a three chambered heart, containing only one ventricle with significantly less musculature than that of the mouse. Because of these differences, the location of needle insertion had to be moved to the more stable aorta. The aorta was determined to be the optimal location for insertion of the perfusion needle as it is large enough for puncture by a 27 G needle and has limited movement. Movement was minimized in order to avoid accidental removal or slipping of the perfusion needle or through-and-through puncture of the aorta. Cardiac perfusions using the ventricle as an insertion point proved to have a much lower rate of success than those with an aortic insertion point. Erroneous puncture of the vasculature often resulted in the formation of emboli or prevented perfusion, resulting in very low rates of successful vascular labeling. By using a clamp stand to hold the butterfly needle during perfusion, we have decreased its movement, therefore increasing the rate of successful perfusions. Additionally, due to the delicacy of the axolotl tissue, when compared to the mouse, a peristaltic perfusion pump was necessary, as opposed to the manual perfusion previously used. The use of this pump allowed for a hands-free approach to the axolotl perfusion to minimize mistaken puncture of the thin tissues. Perfusions were unsuccessful for many additional reasons, including through-and-through puncture, clotting, and embolism. In the case that the needle was inserted into the aorta and a second puncture was created through the posterior wall, the DiI solution would flow directly into the chest cavity rather than pass through the systemic circulation. Additionally, once blood exited the vasculature, it quickly formed a blood clot which could impede perfusion. Clots and air bubbles could also form in the vasculature, causing emboli which preclude successful perfusion. Lastly, this protocol incorporated reagents adjusted to fit the axolotl osmolality, which differs significantly from that of the mammal. Adaptation of this protocol and the significant changes made to fit the axolotl model will assist in the pursuit of understanding the process of revascularization of tissues during regeneration.
DiI, which is pink in color, will perfuse the animal and give it a bright pink hue. Successfully perfused axolotls became bright pink to the naked eye, with highly vascularized regions appearing more intensely stained. Perfused animals viewed with a fluorescent confocal microscope using a green filter can be visualized in the red-orange emission spectrum. Vasculature was best visualized in thinner tissues that minimized accidental DiI staining of non-vascular tissues. Perfusion of the tissue with 4% Paraformaldehyde (PFA) immediately after DiI perfusion should be done to fix the tissue.
DiI perfusions are end-point experiments for the axolotl. During the procedure, all of the animal&#8217;s blood is effectively drained and replaced with 0.7x PBS, followed immediately by DiI solution, and finally 4% PFA. This disrupts the axolotl&#8217;s ability to engage in the vital act of gas exchange and it loses the ability to oxygenate its body tissues. Due to this end-point nature, each perfusion captures only a single time-point of vascular growth, and the animal cannot be further perfused at a later time. Due to this time-limiting factor, multiple animals must be used in order to describe a time course of vascular development.
This DiI protocol, and the modifications applied to improve it, can be used to successfully label and visualize the vasculature of the axolotl. Since the axolotl is an essential model organism for the study of regeneration, successful perfusions open up opportunities to interrogate the process of angiogenesis during regeneration. The axolotl is a model organism for the study of regeneration because it is a neotenous animal and therefore retains a remarkable ability to regenerate throughout adulthood8. The revascularization process of regenerating tissues, however, is not well understood, therefore the adaptation of the DiI perfusion to the axolotl system presents opportunities to understand regeneration that were not available with the mammalian model. The perfusion of the axolotl using DiI is a novel technique for the study of revascularization of regenerating tissue in this animal model, therefore, this protocol can be further used to understand organogenesis during development and angiogenesis during disease as well as be utilized as an important tool during the study of regeneration.

Visualization of vasculature plays a vital role in understanding the structure and function of organisms across many species. Starting in the 16th century with Leonardo da Vinci, models and graphic representations of the circulation have been studied1. Using waxes and rubber molds, tissues were perfused to create three-dimensional models of the vasculature, which allowed for the study of organogenesis and pathogenesis1,2. Resins and waxes were colored with dyes such as India Ink or carmine red to allow for their easy visualization1,2. However, these techniques caused many issues because their high viscosities prevented full perfusion of the tissue of interest1. As the field became more sophisticated, the use of confocal and electron microscopes came into play, moving the perfusion techniques away from cast-molds and toward liquid perfusions of the vasculature, some of which allowed for the perfusion and imaging of blood vessels without destroying the initial tissue3. DiI, a fluorescent carbocyanine dye, is one such stain that allows for the perfusion of animals without damage to the vascular tissue.
Carbocyanine dyes are lipophilic dyes that incorporate into cell membranes upon contact. These dyes allow for easy and instantaneous staining of vascular endothelial cells, which can then be viewed under a fluorescent confocal microscope. DiI moves via lateral diffusion in the lipid membrane of cells, as shown in the labeling and tracing of neurons4. Chemically, the two alkyl chains of DiI give the dye its high affinity for cell membranes, while two conjugated rings from a fluorochrome which is responsible for emitting a red wavelength when excited by green fluorescent light filters4. DiI has been utilized in many capacities, including successful labeling of the plasma membrane and both anterograde and retrograde labeling in neurons5,6. DiI has previously been used in perfusion protocols while visualizing the vasculature of mice7.
Axolotls (Ambystoma mexicanum) are salamanders that live exclusively in brackish lakes near Mexico City, Mexico. These animals have become an important model for understanding regenerative processes as they can regenerate full limbs, tail (including nerve cord), portions of the heart and other internal organs, and portions of the eye as adults8,9. Additionally, with the recent application of genetic tools in axolotls, unprecedented insight into the molecules and cells driving these processes is now possible8. The successful regeneration of an entire limb requires an extensive revascularization process, which may play a significant role in regeneration beyond simply the traditional functions of blood vessels in providing oxygen and nutrients. Understanding revascularization in the context of tissue regeneration is imperative. Axolotl blood vessels have previously been visualized using India Ink, and while the results were intriguing, this process has not been revisited in subsequent decades10. We sought to adapt a DiI perfusion protocol developed for use in mammals to allow for a complete perfusion and visualization of the axolotl vasculature7. This protocol describes the steps taken to successfully perfuse and subsequently visualize the axolotl circulation with a DiI staining technique. This procedure will allow for precise visualization of patent blood vessels in homeostatic tissues, as well as in regenerating tissues, and provides a novel method for visualization and analysis of the revascularization process in the axolotl.

<table border="0" cellpadding="0" cellspacing="0" width="1583">
	<tbody>
		<tr height="24">
			<td height="24" style="height:24px;width:405px;">Peristaltic Pump&#160;</td>
			<td style="width:195px;">Marshall Scientific&#160;</td>
			<td style="width:152px;">RD-RP1</td>
			<td style="width:831px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:405px;">Perfusion tubing</td>
			<td style="width:195px;">Excelon Lab &#38; Vacuum Tubing</td>
			<td>436901705</td>
			<td>size S1A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">27g butterfly needle</td>
			<td style="width:195px;">EXELint Medical Products</td>
			<td>26709</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">NaCl</td>
			<td style="width:195px;">AmericanBio</td>
			<td>7647-14-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">KCl</td>
			<td style="width:195px;">AmericanBio</td>
			<td>7747-40-7</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Na2HPO4&#160;</td>
			<td style="width:195px;">AmericanBio</td>
			<td>7558-79-4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NaH2PO4</td>
			<td style="width:195px;">AmericanBio</td>
			<td>10049-21-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Distilled water</td>
			<td style="width:195px;"></td>
			<td style="width:152px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HCl</td>
			<td style="width:195px;">AmericanBio</td>
			<td>7647-01-0</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glucose</td>
			<td style="width:195px;">ThermoFischer</td>
			<td>A2494001</td>
			<td></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">1,1&#8242;-Dioctadecyl-3,3,3&#8242;,3&#8242;-tetramethylindocarbocyanine perchlorate</td>
			<td style="width:195px;">Sigma Aldrich</td>
			<td>468495</td>
			<td></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Ethanol (100% vol/vol)</td>
			<td style="width:195px;">Sigma Aldrich</td>
			<td>64-17-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Surgical foreceps&#160;</td>
			<td style="width:195px;">Medline</td>
			<td>MDG0748741</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Polystyrene foam frame</td>
			<td style="width:195px;"></td>
			<td style="width:152px;"></td>
			<td>any polystyrene foam square with an axolotl-shaped&#160; cut out</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Surgical scissors</td>
			<td style="width:195px;">Medline</td>
			<td>DYND04025</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Scalpel&#160;</td>
			<td style="width:195px;">Medline</td>
			<td>MDS15210</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Absorbent underpad</td>
			<td style="width:195px;">Avacare Medical</td>
			<td>PKUFSx</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Paper towels</td>
			<td style="width:195px;"></td>
			<td style="width:152px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Standard disposable transfer pipette</td>
			<td style="width:195px;">Fisherbrand</td>
			<td>50216954</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Clamp stand</td>
			<td style="width:195px;">Adafruit</td>
			<td style="width:152px;">291</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ethyl 3-aminobenzoate methanesulfonate</td>
			<td style="width:195px;">Sigma Aldrich</td>
			<td>E10521</td>
			<td>Tricaine powder</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Adult axolotl</td>
			<td style="width:195px;"></td>
			<td style="width:152px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">MgSO4</td>
			<td>AmericanBio</td>
			<td>10034-99-8</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">CaCl2</td>
			<td style="width:195px;">Sigma Aldrich</td>
			<td>C1016-100G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">NaHCO3</td>
			<td style="width:195px;">Sigma Aldrich</td>
			<td>S5761-500G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Plastic tanks</td>
			<td style="width:195px;"></td>
			<td style="width:152px;"></td>
			<td>Varying size appropriate for the axolotl</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Paraformaldehyde</td>
			<td style="width:195px;">Sigma Aldrich</td>
			<td>30525-89-4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Axolotl</td>
			<td style="width:195px;"></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Leica Microscope</td>
			<td style="width:195px;">Leica</td>
			<td style="width:152px;">M165 FC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">ET-CY3 Fluorescent Filter</td>
			<td style="width:195px;">Leica</td>
			<td>M205FA/M165FC</td>
			<td></td>
		</tr>
	</tbody>
</table>

dii perfusion as a method for vascular visualization in ambystoma mexicanum

Perfusion techniques have been used for centuries to visualize the circulation of tissues. Axolotl (Ambystoma mexicanum) is a species of salamander that has emerged as an essential model for regeneration studies. Little is known about how revascularization occurs in the context of regeneration in these animals. Here we report a simple method for visualization of the vasculature in axolotl via perfusion of 1,1&#8217;-Dioctadecy-3,3,3&#8217;,3&#8217;-tetramethylindocarbocyanine perchlorate (DiI). DiI is a lipophilic carbocyanine dye that inserts into the plasma membrane of endothelial cells instantaneously. Perfusion is done using a peristaltic pump such that DiI enters the circulation through the aorta. During perfusion, dye flows through the axolotl&#8217;s blood vessels and incorporates into the lipid bilayer of vascular endothelial cells upon contact. The perfusion procedure takes approximately one hour for an eight-inch axolotl. Immediately after perfusion with DiI, the axolotl can be visualized with a confocal fluorescent microscope. The DiI emits light in the red-orange range when excited with a green fluorescent filter. This DiI perfusion procedure can be used to visualize the vascular structure of axolotls or to demonstrate patterns of revascularization in regenerating tissues.

With DiI staining, the vasculature of the axolotl can be easily visualized. Blood vessels of animals perfused with the lipophilic dye are immediately visible under a fluorescent confocal microscope. Figure 1.1-1.5 is a schematic representation of the perfusion protocol. After perfusion with the bright pink dye, a successfully perfused axolotl will appear pink. Using a green fluorescent filter on a confocal microscope a red emission of the vascular network will appear. The DiI staining occurs in all body tissues when perfusion is successful, including the tail, limbs, gills, and eyes (Figure 2A, Figure 2B, Figure 2C, Figure 2D, repectively). Unsuccessful perfusions result in a lack of red-stained vasculature or in patchy staining of the vessels.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/55740/55740fig1.jpg" /> 
Figure 1: Schematic of the perfusion protocol. Axolotls successfully perfused with the lipophilic dye, DiI, demonstrate full staining of the vasculature upon imaging. 1: Full supine axolotl before perfusion experiment. 2: Opening the chest of the axolotl. 2: Axolotl with an open chest cavity. 3: Insertion of the 27 G butterfly needle into the aorta of the axolotl. 4: Tubing should first contain 0.7x PBS, then the DiI working solution, and lastly 4% PFA. 5: Fully perfused axolotls appear pink. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55740/55740fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/55740/55740fig2.jpg" /> 
Figure 2: Images of a Fully Perfused Axolotl. Images of the axolotl vasculature were taken using a fluorescent confocal microscope after successful perfusion with the DiI stain. 2A: Tail. 2B: Foot. 2C: Gills. 2D: Eye. Imaging is done using a confocal microscope with an green fluorescent emission filter cube. Magnification for images A, B, C, and D, are 1.74X, 2.16X, 1.18X, and 5.69X, respectively. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55740/55740fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about DiI Perfusion as a Method for Vascular Visualization in Ambystoma mexicanum at JoVE.com

DiI Perfusion as a Method for Vascular Visualization in Ambystoma mexicanum

Using a lipophilic 1,1&#39;-Dioctadecy-3,3,3&#39;,3&#39;-tetramethylindocarbocyanine perchlorate (DiI) staining technique, Ambystoma mexicanum can undergo vascular perfusion to allow for easy visualization of the vasculature.

DiI Perfusion as a Method for Vascular Visualization in Ambystoma mexicanum

Perfusion techniques have been used for centuries to visualize the circulation of tissues. Axolotl (Ambystoma mexicanum) is a species of salamander that ...

dii-perfusion-as-method-for-vascular-visualization-ambystoma

Nanyang Technological University

Research

JoVE Journal

Biology

9.8K Views.  Harvard Medical School and Brigham and Women's Hospital. Using a lipophilic 1,1'-Dioctadecy-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) staining technique, Ambystoma mexicanum can undergo vascular perfusion to allow for easy visualization of the vasculature.

Video: DiI Perfusion as a Method for Vascular Visualization in Ambystoma mexicanum

Pyrosequencing: A Simple Method for Accurate Genotyping

Pharmacogenetic research benefits first-hand from the abundance of information provided by the completion of the Human Genome Project. With such a tremendous amount of data available comes an explosion of genotyping methods. Pyrosequencing(R) is one of the most thorough yet simple methods to date used to analyze polymorphisms. It also has the ability to identify tri-allelic, indels, short-repeat polymorphisms, along with determining allele percentages for methylation or pooled sample assessment. In addition, there is a standardized control sequence that provides internal quality control. This method has led to rapid and efficient single-nucleotide polymorphism evaluation including many clinically relevant polymorphisms. The technique and methodology of Pyrosequencing is explained.


Pyrosequencing(R) is one of the most thorough yet simple methods to date used to analyze polymorphisms. This method has led to rapid and efficient single-nucleotide polymorphism evaluation including many clinically relevant polymorphisms. The technique and methodology of Pyrosequencing is explained.

Pharmacogenetic research benefits first-hand from the abundance of information provided by the completion of the Human Genome Project. With such a ...

Use of Rotorod as a Method for the Qualitative Analysis of Walking in Rat

High speed videoanalysis of the details of movement can provide a source of information about qualitative aspects of walking movements. When walking on a rotorod, animals remain in approximately the same place making repetitive movements of stepping. Thus the task provides a rich source of information on the details of foot stepping movements. Subjects were hemi-Parkinson analogue rats, produced by injection of 6-hydroxydopamine (6-OHDA) into the right nigrostriatal bundle to deplete nigrostriatal dopamine (DA). The present report provides a video analysis illustration of animals previously were filmed from frontal, lateral, and posterior views as they walked (15). Rating scales and frame-by-frame replay of the video records of stepping behavior indicated that the hemi-Parkinson rats were chronically impaired in posture and limb use contralateral to the DA-depletion. The contralateral limbs participated less in initiating and sustaining propulsion than the ipsilateral limbs. These deficits secondary to unilateral DA-depletion show that the rotorod provides a use task for the analysis of stepping movements.

The rotorod test is used to assess motor status in the walking movement of hemi-Parkinson analogue rats.

High speed videoanalysis of the details of movement can provide a source of information about qualitative aspects of walking movements. When walking on a ...

Patch Clamp and Perfusion Techniques for Studying Ion Channels Expressed in Xenopus oocytes

The protocol presented here is designed to study the activation of the large conductance, voltage- and Ca2+-activated K+ (BK) channels. The protocol may also be used to study the structure-function relationship for other ion channels and neurotransmitter receptors1. BK channels are widely expressed in different tissues and have been implicated in many physiological functions, including regulation of smooth muscle contraction, frequency tuning of inner hair cells and regulation of neurotransmitter release2-6. BK channels are activated by membrane depolarization and by intracellular Ca2+ and Mg2+ 6-9. Therefore, the protocol is designed to control both the membrane voltage and the intracellular solution. In this protocol, messenger RNA of BK channels is injected into Xenopus laevis oocytes (stage V-VI) followed by 2-5 days of incubation at 18&deg;C10-13. Membrane patches that contain single or multiple BK channels are excised with the inside-out configuration using patch clamp techniques10-13. The intracellular side of the patch is perfused with desired solutions during recording so that the channel activation under different conditions can be examined. To summarize, the mRNA of BK channels is injected into Xenopus laevis oocytes to express channel proteins on the oocyte membrane; patch clamp techniques are used to record currents flowing through the channels under controlled voltage and intracellular solutions.

Patch Clamp and Perfusion Techniques for Studying Ion Channels Expressed in Xenopus oocytes

Ionic current of BK channels is recorded using patch clamp techniques. BK channels are expressed in Xenopus oocytes by injecting messenger RNA. The intracellular solution during patch clamp recordings is controlled by a perfusion system.

The protocol presented here is designed to study the activation of the large conductance, voltage- and Ca2+-activated K+ (BK) channels. The protocol may ...

Visualization of Caenorhabditis elegans Cuticular Structures Using the Lipophilic Vital Dye DiI

The cuticle of C. elegans is a highly resistant structure that surrounds the exterior of the animal1-4. The cuticle not only protects the animal from the environment, but also determines body shape and plays a role in motility4-6. Several layers secreted by epidermal cells comprise the cuticle, including an outermost lipid layer7.
Circumferential ridges in the cuticle called annuli pattern the length of the animal and are present during all stages of development8. Alae are longitudinal ridges that are present during specific stages of development, including L1, dauer, and adult stages2,9. Mutations in genes that affect cuticular collagen organization can alter cuticular structure and animal body morphology5,6,10,11. While cuticular imaging using compound microscopy with DIC optics is possible, current methods that highlight cuticular structures include fluorescent transgene expression12, antibody staining13, and electron microscopy1. Labeled wheat germ agglutinin (WGA) has also been used to visualize cuticular glycoproteins, but is limited in resolving finer cuticular structures14. Staining of cuticular surface using fluorescent dye has been observed, but never characterized in detail15. We present a method to visualize cuticle in live C. elegans using the red fluorescent lipophilic dye DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), which is commonly used in C. elegans to visualize environmentally exposed neurons. This optimized protocol for DiI staining is a simple, robust method for high resolution fluorescent visualization of annuli, alae, vulva, male tail, and hermaphrodite tail spike in C. elegans.

Visualization of Caenorhabditis elegans Cuticular Structures Using the Lipophilic Vital Dye DiI

We present a method to visualize cuticle in live C. elegans using the red fluorescent lipophilic dye DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), which is commonly used in C. elegans to visualize environmentally exposed neurons. With this optimized protocol, alae and annular cuticular structures are stained by DiI and observed using compound microscopy.

The cuticle of C. elegans is a highly resistant structure that surrounds the exterior of the animal1-4. The cuticle not only protects the animal from the ...

A Simple Method for Imaging Arabidopsis Leaves Using Perfluorodecalin as an Infiltrative Imaging Medium

The problem of acquiring high-resolution images deep into biological samples is widely acknowledged1. In air-filled tissue such as the spongy mesophyll of plant leaves or vertebrate lungs further difficulties arise from multiple transitions in refractive index between cellular components, between cells and airspaces and between the biological tissue and the rest of the optical system. Moreover, refractive index mismatches lead to attenuation of fluorophore excitation and signal emission in fluorescence microscopy. We describe here the application of the perfluorocarbon, perfluorodecalin (PFD), as an infiltrative imaging medium which optically improves laser scanning confocal microscopy (LSCM) sample imaging at depth, without resorting to damaging increases in laser power and has minimal physiological impact2. We describe the protocol for use of PFD with Arabidopsis thaliana leaf tissue, which is optically complex as a result of its structure (Figure 1). PFD has a number of attributes that make it suitable for this use3. The refractive index of PFD (1.313) is comparable with that of water (1.333) and is closer to that of cytosol (approx. 1.4) than air (1.000). In addition, PFD is readily available, non-fluorescent and is non-toxic. The low surface tension of PFD (19 dynes cm-1) is lower than that of water (72 dynes cm-1) and also below the limit (25 - 30 dyne cm-1) for stomatal penetration4, which allows it to flood the spongy mesophyll airspaces without the application of a potentially destructive vacuum or surfactant. Finally and crucially, PFD has a great capacity for dissolving CO2 and O2, which allows gas exchange to be maintained in the flooded tissue, thus minimizing the physiological impact on the sample. These properties have been used in various applications which include partial liquid breathing and lung inflation5,6, surgery7, artificial blood8, oxygenation of growth media9, and studies of ice crystal formation in plants10. Currently, it is common to mount tissue in water or aqueous buffer for live confocal imaging. We consider that the use of PFD as a mounting medium represents an improvement on existing practice and allows the simple preparation of live whole leaf samples for imaging.

A Simple Method for Imaging Arabidopsis Leaves Using Perfluorodecalin as an Infiltrative Imaging Medium

We describe the use of perfluorodecalin as an infiltrative mounting medium. This is a simple method for improving depth of imaging in Arabidopsis thaliana leaf tissue with minimal physiological impact.

The problem of acquiring high-resolution images deep into biological samples is widely acknowledged1. In air-filled tissue such as the spongy mesophyll of ...

Visualization of Vascular Ca2+ Signaling Triggered by Paracrine Derived ROS

Oxidative stress has been implicated in a number of pathologic conditions including ischemia/reperfusion damage and sepsis. The concept of oxidative stress refers to the aberrant formation of ROS (reactive oxygen species), which include O2&bull;-, H2O2, and hydroxyl radicals. Reactive oxygen species influences a multitude of cellular processes including signal transduction, cell proliferation and cell death1-6. ROS have the potential to damage vascular and organ cells directly, and can initiate secondary chemical reactions and genetic alterations that ultimately result in an amplification of the initial ROS-mediated tissue damage. A key component of the amplification cascade that exacerbates irreversible tissue damage is the recruitment and activation of circulating inflammatory cells. During inflammation, inflammatory cells produce cytokines such as tumor necrosis factor-&alpha; (TNF&alpha;) and IL-1 that activate endothelial cells (EC) and epithelial cells and further augment the inflammatory response7. Vascular endothelial dysfunction is an established feature of acute inflammation. Macrophages contribute to endothelial dysfunction during inflammation by mechanisms that remain unclear. Activation of macrophages results in the extracellular release of O2&bull;- and various pro-inflammatory cytokines, which triggers pathologic signaling in adjacent cells8. NADPH oxidases are the major and primary source of ROS in most of the cell types. Recently, it is shown by us and others9,10 that ROS produced by NADPH oxidases induce the mitochondrial ROS production during many pathophysiological conditions. Hence measuring the mitochondrial ROS production is equally important in addition to measuring cytosolic ROS. Macrophages produce ROS by the flavoprotein enzyme NADPH oxidase which plays a primary role in inflammation. Once activated, phagocytic NADPH oxidase produces copious amounts of O2&bull;- that are important in the host defense mechanism11,12. Although paracrine-derived O2&bull;- plays an important role in the pathogenesis of vascular diseases, visualization of paracrine ROS-induced intracellular signaling including Ca2+ mobilization is still hypothesis. We have developed a model in which activated macrophages are used as a source of O2&bull;- to transduce a signal to adjacent endothelial cells. Using this model we demonstrate that macrophage-derived O2&bull;- lead to calcium signaling in adjacent endothelial cells.

Visualization of Vascular Ca2+ Signaling Triggered by Paracrine Derived ROS

An efficient method to gain insights into visualizing the paracrine-derived ROS induction of endothelial Ca2+ signaling is described. This method takes advantage of measuring paracrine derived ROS triggered Ca2+ mobilization in vascular endothelial cells in a co-culture model.

Oxidative stress has been implicated in a number of pathologic conditions including ischemia/reperfusion damage and sepsis. The concept of oxidative ...

Using SecM Arrest Sequence as a Tool to Isolate Ribosome Bound Polypeptides

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway that polypeptide chain follows during co-translational folding to achieve its functional form is still an enigma. In order to understand this process and to determine the exact conformation of the co-translational folding intermediates, it is essential to develop techniques that allow the isolation of RNCs carrying nascent chains of predetermined sizes to allow their further structural analysis.
SecM (secretion monitor) is a 170 amino acid E. coli protein that regulates expression of the downstream SecA (secretion driving) ATPase in the secM-secA operon6. Nakatogawa and Ito originally found that a 17 amino acid long sequence (150-FSTPVWISQAQGIRAGP-166) in the C-terminal region of the SecM protein is sufficient and necessary to cause stalling of SecM elongation at Gly165, thereby producing peptidyl-glycyl-tRNA stably bound to the ribosomal P-site7-9. More importantly, it was found that this 17 amino acid long sequence can be fused to the C-terminus of virtually any full-length and/or truncated protein thus allowing the production of RNCs carrying nascent chains of predetermined sizes7. Thus, when fused or inserted into the target protein, SecM stalling sequence produces arrest of the polypeptide chain elongation and generates stable RNCs both in vivo in E. coli cells and in vitro in a cell-free system. Sucrose gradient centrifugation is further utilized to isolate RNCs.
The isolated RNCs can be used to analyze structural and functional features of the co-translational folding intermediates. Recently, this technique has been successfully used to gain insights into the structure of several ribosome bound nascent chains10,11. Here we describe the isolation of bovine Gamma-B Crystallin RNCs fused to SecM and generated in an in vitro translation system.

We describe here a technique that is now routinely used to isolate stably bound ribosome nascent chain complexes (RNCs). This technique takes advantage of the discovery that a 17 amino acid long SecM "arrest sequence" can halt translation elongation in a prokaryotic (E. coli) system, when inserted into (or fused to the C-terminus) of virtually any protein.

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway ...

Using Caenorhabditis elegans as a Model System to Study Protein Homeostasis in a Multicellular Organism

The folding and assembly of proteins is essential for protein function, the long-term health of the cell, and longevity of the organism. Historically, the function and regulation of protein folding was studied in vitro, in isolated tissue culture cells and in unicellular organisms. Recent studies have uncovered links between protein homeostasis (proteostasis), metabolism, development, aging, and temperature-sensing. These findings have led to the development of new tools for monitoring protein folding in the model metazoan organism Caenorhabditis elegans. In our laboratory, we combine behavioral assays, imaging and biochemical approaches using temperature-sensitive or naturally occurring metastable proteins as sensors of the folding environment to monitor protein misfolding. Behavioral assays that are associated with the misfolding of a specific protein provide a simple and powerful readout for protein folding, allowing for the fast screening of genes and conditions that modulate folding. Likewise, such misfolding can be associated with protein mislocalization in the cell. Monitoring protein localization can, therefore, highlight changes in cellular folding capacity occurring in different tissues, at various stages of development and in the face of changing conditions. Finally, using biochemical tools ex vivo, we can directly monitor protein stability and conformation. Thus, by combining behavioral assays, imaging and biochemical techniques, we are able to monitor protein misfolding at the resolution of the organism, the cell, and the protein, respectively.

Using Caenorhabditis elegans as a Model System to Study Protein Homeostasis in a Multicellular Organism

To study the relationship between protein homeostasis, stress and aging, we monitored changes in protein folding by following protein dysfunction, protein localization in the cell and protein stability at the organismal, cellular and protein levels, using the genetically tractable metazoan Caenorhabditis elegans as a model system.

The folding and assembly of proteins is essential for protein function, the long-term health of the cell, and longevity of the organism. Historically, the ...

FRET Imaging in Three-dimensional Hydrogels

Imaging of F&#246;rster resonance energy transfer (FRET)&#160;is a powerful tool for examining cell biology in real-time. Studies utilizing FRET commonly employ two-dimensional (2D) culture, which does not mimic the three-dimensional (3D) cellular microenvironment. A method to perform quenched emission FRET imaging using conventional widefield epifluorescence microscopy of cells within a 3D hydrogel environment is presented. Here an analysis method for ratiometric FRET probes that yields linear ratios over the probe activation range is described. Measurement of intracellular cyclic adenosine monophosphate (cAMP) levels is demonstrated in chondrocytes under forskolin stimulation using a probe for EPAC1 activation (ICUE1) and the ability to detect differences in cAMP signaling dependent on hydrogel material type, herein a photocrosslinking hydrogel (PC-gel, polyethylene glycol dimethacrylate) and a thermoresponsive hydrogel (TR-gel). Compared with 2D FRET methods, this method requires little additional work. Laboratories already utilizing FRET imaging in 2D can easily adopt this method to perform cellular studies in a 3D microenvironment. It can further be applied to high throughput drug screening in engineered 3D microtissues. Additionally, it is compatible with other forms of FRET imaging, such as anisotropy measurement and fluorescence lifetime imaging (FLIM), and with advanced microscopy platforms using confocal, pulsed, or modulated illumination.

F&#246;rster resonance energy transfer (FRET) imaging is a powerful tool for real-time cell biology studies. Here a method for FRET imaging cells in physiologic three-dimensional (3D) hydrogel microenvironments using conventional epifluorescence microscopy is presented. An analysis for ratiometric FRET probes that yields linear ratios over the activation range is described.

Imaging of F&#246;rster resonance energy transfer (FRET)&#160;is a powerful tool for examining cell biology in real-time. Studies utilizing FRET commonly ...

Retinal Cryo-sections, Whole-Mounts, and Hypotonic Isolated Vasculature Preparations for Immunohistochemical Visualization of Microvascular Pericytes

Retinal pericytes play an important role in many diseases of the eye. Immunohistochemical staining techniques of retinal vessels and microvascular pericytes are central to ophthalmological research. It is vital to choose an appropriate method of visualizing the microvascular pericytes. We describe retinal microvascular pericyte immunohistochemical staining in cryo-sections, whole-mounts, and hypotonic isolated vasculature using antibodies for platelet-derived growth factor receptor &#946; (PDGFR&#946;) and nerve/glial antigen 2 (NG2). This allows us to highlight advantages and shortcomings of each of the three tissue preparations for the visualization of the retinal microvascular pericytes. Cryo-sections provide transsectional visualization of all retinal layers but contain only a few occasional transverse cuts of the microvasculature. Whole-mount provides an overview of the entire retinal vasculature, but visualization of the microvasculature can be troublesome. Hypotonic isolation provides a method to visualize the entire retinal vasculature by the removal of neuronal cells, but this makes the tissue very fragile.

We demonstrate three different tissue preparation techniques for immunohistochemical visualization of rat retinal microvascular pericytes, i.e., cryo-sections, whole-mounts, and hypotonic isolation of the vascular network.