NIH/NINDS R01NS112706 (R.L.)

Institutional Animal Care and Use Committee of Columbia University Medical Center&#39;s approvals were obtained for all methods described. Wild-type C57Bl/6 male postnatal day 10 mice were used for the study.
1. Preparation of Langendorff apparatus
<ol>
	<li>To minimize complexity, use non-recirculating oxygenated perfusate within the Langendorff apparatus (see Table of Materials) via constant flow or constant pressure.
	<ol>
		<li>Use Krebs-Henseleit buffer (KHB), containing 120 mmol/L of NaCl, 4.7 mmol/L of KCl, 1.2 mmol/L of MgSO4, 1.2 mmol/L of KH2PO4, 1.25 mmol/L of CaCl2, 25 mmol/L of NaHCO3,&#160;and 11 mmol/L of glucose at pH 7.4 (see Table of Materials), equilibrate with 95% of O2 and 5% of CO2 within the Langendorff apparatus and maintain at 37 &#176;C.</li>
	</ol>
	</li>
	<li>For the constant flow approach, maintain a continuous flow rate at ~2.5 mL&#8729;min-1. 
	NOTE: This flow rate will approximate coronary flow of ~75-80 mL/g&#8729;min, given that the average weight of a 10 day old (P10) mouse heart is ~30 mg17,18.</li>
</ol>
2. Fabrication of aortic cannula
<ol>
	<li>Fabricate the newborn mouse aortic cannula from a 26 G stainless steel needle (see Table of Materials). Using sharp scissors, cut off the tip of the needle to blunt the end. Take care not to crimp or restrict the diameter of the needle lumen. Smooth the cut edge and remove any burs by gently scraping the blunted end on the laboratory benchtop using a to-and-fro motion. 
	NOTE: Microscopic burs and sharp edges must be removed because they can tear the newborn mouse aorta and damage the aortic valve. Alternatively, use fine-grit sandpaper.</li>
	<li>Attach the fabricated cannula to the Langendorff apparatus and assess flow and resistance. Measure flow rates through the cannula by collecting and measuring buffer quantity over a known time period. Ensure actual flow is equal to the set flow rate of 2.5 mL min-1.</li>
	<li>Quantify the pressure differential across the cannula with KHB flowing by following the steps below.
	<ol>
		<li>Measure pressure in the system with and without the fabricated cannula attached.</li>
		<li>Divide pressure differential across cannula by the flow rate to obtain cannula resistance as per Ohm&#39;s law15.</li>
		<li>Ensure that the fabricated cannula resistance comprises ~16.0 &#177; 1.9 mmHg&#8729;min&#8729;mL-1 of the total resistance6. Excessive resistance suggests a potentially compromised cannula lumen. 
		NOTE: Sample calculation: Pwith cannula - P without cannula = &#916;P. If Pwith = 48 and Pwithout = 8 then &#916;P = 40. At a flow rate (Q) of 2.5 mL min-1 and &#916;P of 40 cannula resistance equals 16 mmHg&#8729;min&#8729;mL-1 using R =&#160;&#916;P/Q&#160;= 40 / 2.5 = 16.</li>
	</ol>
	</li>
	<li>Remove the 26 G cannula and attach the high-pressure tubing (see Table of Materials) to the cannulation site on the Langendorff apparatus. Attach the aortic cannula to the distal end of the tubing. De-air the tubing and the cannula with oxygenated buffer, ensuring that all bubbles are removed. 
	NOTE: The use of high-pressure tubing in this manner permits the cannula to be extended to a more remote position. This is necessary to allow aortic cannulation with a dissecting microscope adjacent to the setup (Figure 1).</li>
</ol>
3. Organ harvesting
<ol>
	<li>Anticoagulate mice via intraperitoneal (IP) injection of heparin (10 kU/kg) (see Table of Materials) to prevent the formation of coronary microthrombi using a 26 G needle on 1 mL syringe. Allow several minutes for heparin to circulate before proceeding with the injection of any anesthetic.</li>
	<li>Anesthetize the animal with an IP injection using a 26 G needle on 1 mL syringe. 
	NOTE: It is essential to carefully monitor the animal after anesthetic injection to avoid apnea and subsequent hypoxia. Pentobarbital (70 mg/kg) is a reliable choice of anesthetic, as it allows for rapid onset of sedation without inducing apnea19,20. Other anesthetic agents can be utilized, provided that the doses used do not cause apnea21. Investigators should consider the effects of alternative sedative-hypnotics on cardiac function22,23. Cervical dislocation as a primary mode of euthanasia may prolong pre-cannulation hypoxia and ischemia.</li>
	<li>Place the mouse in the supine position and secure limbs immediately upon loss of consciousness. Use small gauge hypodermic needles to secure each limb.&#160;Begin harvesting as soon as the animal is unresponsive to toe pinch; the animal should breathe spontaneously during the initial dissection.</li>
	<li>Make a transverse subxiphoid incision across the animal&#39;s width to expose the abdominal cavity using straight dissecting scissors (see Table of Materials). 
	NOTE: Sterile technique is not necessary given that the procedure represents nonsurvival surgery.
	<ol>
		<li>Identify the diaphragm superiorly and incise the anterior portion completely. Cut the ribcage bilaterally along the mid-axillary line in a cephalad direction. Ask an assistant to grasp the xiphoid process with forceps and reflect the sternum and ribs cranially to expose the thoracic organs.</li>
	</ol>
	</li>
	<li>Identify the infra-diaphragmatic inferior vena cava (IVC) above the liver. Transect the IVC with a curved iris scissor while maintaining slight anterior and cephalad tension on the proximal segment with iris forceps (see Table of Materials).
	<ol>
		<li>Cut posteriorly along the anterior surface of the spine using curved iris scissors while pulling the IVC up and out of the thoracic cavity. As the heart is mobilized, angle the scissors anteriorly and sever&#160;the great vessels superiorly to completely remove the heart and lungs. 
		&#8203;NOTE: This method permits rapid explantation of the heart and lungs en bloc.</li>
	</ol>
	</li>
	<li>Immediately submerge the specimen in ice-cold KHB or saline. The heart should stop beating within seconds.</li>
</ol>
4. Cannulation
<ol>
	<li>Cut a piece of paper towel and place it at the bottom of a shallow Petri dish to provide friction to stabilize the heart during cannulation. Moisten with ice-cold KHB to prevent the heart from adhering to it.
	<ol>
		<li>Place the prepared Petri dish under the dissecting microscope and adjust the focus. Place the aortic cannula attached to the high-pressure extension tubing under the dissecting microscope along with a 5-0 silk suture loosely tied around its hub (see Table of Materials). 
		NOTE: Care must be taken to limit the amount of fluid in the Petri dish because the air-filled lungs can float and cause the excised organs to move.</li>
	</ol>
	</li>
	<li>Place the excised thoracic organs in the Petri dish. Under the microscope, identify the thymus by its white sheen and two lobes and orient the specimen such that the thymus is anterior and superior24. This will ensure proper orientation of the heart.</li>
	<li>Using forceps, bluntly separate the lobes of the thymus to expose the great vessels. Identify the aorta by locating distinguishing branching features of the aortic arch. 
	NOTE: A dark purple hue often demarcates the right ventricle and the pulmonary artery. The ascending aorta is located between the main pulmonary artery and the right atrium.</li>
	<li>Transect the aorta with fine sharp scissors (see Table of Materials) just proximal to the subclavian artery takeoff. 
	NOTE: If the aorta is transected too close to the aortic valve, there will not be enough aortic tissue to enable the cannula to be secured. Alternatively, if the aorta is transected too high, perfusate can leak out of one or more aortic branches (such as the subclavian artery).</li>
	<li>Gently grasp the transected aorta using jeweler-style fine curved forceps (see Table of Materials). Carefully cannulate the aorta with a 26 G blunt needle, taking care not to damage the aortic valve. Hold in place by grasping the aorta with the fine curved forceps around the cannula. Once control of the aorta is established, initiate retrograde perfusion to limit the ischemic time. 
	NOTE: The heart should begin to beat and will become pale as blood is drained from the myocardium and KHB perfuses the coronary arteries. Failure to spontaneously beat, presence of ventricular engorgement, or lack of color change of the heart indicates a malpositioned cannula.</li>
	<li>Ask the assistant to grasp the ends of the loosely tied suture and carefully ensnare the aorta around the cannula. Cinch the suture above or below the curved fine forceps (holding the cannula in place), depending on the amount of aortic tissue and anatomical considerations. Tighten the suture and confirm the adequacy of coronary flow.</li>
	<li>Disconnect the high-pressure tubing from the Langendorff apparatus. Grasp the hub of the cannula and disconnect the blunt needle from the high-pressure extension tubing. Rapidly attach the hub of the cannula to the apparatus. 
	NOTE: Care must be taken not to dislodge the heart or entrain air into the cannula.</li>
	<li>Once the heart is hung on the Langendorff apparatus in the usual position, and adequate perfusion is confirmed, carefully trim off lung, thymus, and excess tissue. Incise the right atrium to permit coronary sinus effluent to drip freely.</li>
</ol>
5. Functional measurement
<ol>
	<li>Make a small knot at the end of a 5-0 silk suture (attached to a curved needle). Pierce a small piece of paraffin film (2-3 mm x 2-3 mm) with the needle and slide the paraffin to the knotted end. Carefully pass the needle through the apex of the ventricle and pull the suture through the heart until the paraffin film is snug against the lateral wall of the ventricle. 
	NOTE: The paraffin film helps to prevent the knot from tearing the heart and pulling through the ventricle.</li>
	<li>Pass the needle through the opening of the water-filled warming jacket of the Langendorff apparatus. The heart can now be encased and warmed.</li>
	<li>Attach the needle to the force transducer (see Table of Materials) in such a manner that avoids the coronary sinus drip. Adjust the suture to apply 1-2 g of basal tension, as indicated by the diastolic tension or nadir in tension tracing. 
	NOTE: Avoid pulling the heart off the cannula or twisting the aorta, thereby compromising coronary perfusion.</li>
	<li>Place surface electrodes on the superior and inferior poles of the heart to record the electrocardiogram. 
	NOTE: Use pediatric temporary epicardial pacing wire with the needle removed for flexible surface electrode connected to Bio Amp (see Table of Materials).</li>
	<li>Sample the coronary sinus effluent for analysis using a 24 G IV catheter (see Table of Materials).</li>
	<li>Subtract the cannula resistance from the total system resistance to obtain coronary resistance per Kirchhoff&#39;s law25.</li>
</ol>

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(60), e3756 (2012).</li><li>Bednarczyk, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Incorporating+dynamic+assessment+of+fluid+responsiveness+into+goal-directed+therapy:+A+systematic+review+and+meta-analysis.">Incorporating dynamic assessment of fluid responsiveness into goal-directed therapy: A systematic review and meta-analysis.</a> Critical Care Medicine. 45 (9), 1538 (2017).</li><li>Louch, W., Sheehan, K., Wolska, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+in+cardiomyocyte+isolation,+culture,+and+gene+transfer.">Methods in cardiomyocyte isolation, culture, and gene transfer.</a> Journal of Molecular and Cellular Cardiology. 51 (3), 288-298 (2011).</li><li>Ackers-Johnson, M., Foo, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Langendorff-free+isolation+and+propagation+of+adult+mouse+cardiomyocytes.">Langendorff-free isolation and propagation of adult mouse cardiomyocytes.</a> Methods in Molecular Biology. 1940, 193-204 (2019).</li><li>Peng, Y., Buller, C., Charpie, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+N-acetylcysteine+on+neonatal+cardiomyocyte+ischemia-reperfusion+injury.">Impact of N-acetylcysteine on neonatal cardiomyocyte ischemia-reperfusion injury.</a> Pediatric Research. 70 (1), 61-66 (2011).</li><li>Jarmakani, J., Nakazawa, M., Nagatomo, T., Langer, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+hypoxia+on+mechanical+function+in+the+neonatal+mammalian+heart.">Effect of hypoxia on mechanical function in the neonatal mammalian heart.</a> American Journal of Physiology-Heart and Circulatory Physiology. 235 (5), 469-474 (1978).</li><li>Podesser, B., Hausleithner, V., Wollenek, G., Seitelberger, R., Wolner, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Langendorff+and+ischemia+in+immature+and+neonatal+myocardia:+Two+essential+key-words+in+Today's+cardiothoracic+research.">Langendorff and ischemia in immature and neonatal myocardia: Two essential key-words in Today's cardiothoracic research.</a> Acta Chirurgica Austriaca. 25 (6), 434-437 (1993).</li><li>Popescu, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Getting+an+early+start+in+understanding+perinatal+asphyxia+impact+on+the+cardiovascular+system.">Getting an early start in understanding perinatal asphyxia impact on the cardiovascular system.</a> Frontiers in Pediatrics. 8, 68 (2020).</li></ol>

The authors have nothing to disclose.

The present work describes successful aortic cannulation and retrograde perfusion in the isolated newborn mouse heart. Importantly, it allows researchers to overcome the barriers that young murine age and small heart size previously presented8. While not complex in design, the approach does require a significant degree of technical skill. Key steps that will inevitably challenge even the most technically proficient investigators will be cannulation of the aorta and securing the cannula in place. D...

Ex-vivo heart preparations have been a staple of physiologic, pathophysiologic, and pharmacologic studies for over a century. Stemming from the work of Elias Cyon in the 1860s, Oskar Langendorff adapted the isolated frog model for retrograde perfusion, pressurizing the aortic root to provide coronary flow with an oxygenated perfusate1. Using his adaptation, Langendorff was able to demonstrate a correlation between coronary circulation and mechanical function2. The ex-vivo retrograde perfused heart, later eponymously dubbed the Langendorff technique, has remained a cornerstone of physiologic investigation, leveraging its simplicity to powerfully study the isolated heart in the absence of potential confounders. The Langendorff preparation has been modified further to permit the heart to eject (the so-called &#34;working heart&#34;) and allow the perfusate to recirculate3. However, the primary physiologic endpoints of interest have remained unchanged. Such endpoints include measures of contractile function, electrical conduction, cardiac metabolism, and coronary resistance4.
To evaluate cardiac function in his original frog heart preparation, Langendorff measured the tension generated by ventricular contraction in the longitudinal axis using a suture connected between the heart&#39;s apex and a force transducer.5 Isometric contraction was quantified in this manner with basal tension applied to the heart in the absence of ventricular filling. Refinement of the approach has led to fluid-filled balloons placed into the left ventricle via the left atrium to evaluate myocardial performance during isovolumic contraction6. To assess cardiac rhythm and the heart rate, surface leads can be placed on the poles of the heart to enable investigators to record the electrocardiogram. However, relative bradycardia can be expected, given the obligatory denervation. Extrinsic pacing may serve to overcome this and eliminate heart rate variability between experiments1. Another outcome measure, myocardial metabolism, can be assessed by measuring the oxygen and metabolic substrate content in the coronary perfusate and effluent and calculating the difference between them7. Lactate quantification in the coronary effluent can aid in characterizing periods of anaerobic metabolism as is seen with hypoxia, hypoperfusion, ischemia-reperfusion, or metabolic perturbations7.
Langendorff&#39;s original work enabled the study of the ex-vivo mammalian heart, using cats as the primary subject5. Evaluation of the isolated rat heart gained popularity in the mid-1900s with Howard Morgan, who detailed the &#39;working heart&#39; rat model in 19675. The use of mice began only 25 years ago due to the technical complexity, tissue fragility, and relatively small murine heart size. Despite the challenges associated with mice study, the lower costs and ease of genetic manipulation have increased the appeal and demand of such murine ex-vivo preparations. Unfortunately, the application of the technique has been limited to adult animals, with juvenile 4-week-old mice being the youngest subjects utilized for ex-vivo study until quite recently8,9. While juvenile mice are &#34;relatively immature&#34; compared with adults, their utility as subjects for developmental biology studies is limited because they have, by and large, weaned from their birth dam and will soon begin puberty10. Adolescence occurs well beyond the postnatal transition in myocardial substrate utilization from glucose and lactate to fatty acids11. Thus, most information about the metabolic changes in the neonatal heart has historically resulted from ex-vivo work in larger species such as rabbits and guinea pig11.
Indeed, alternative approaches to the Langendorff preparation exist. These include in vitro experimentation, which lacks the whole organ functional data and context, or in vivo studies. This can be technically challenging and complicated by confounding variables such as the cardiovascular and respiratory effects of a requisite anesthetic agent, the influence of neurohumoral input, the consequences of core temperature, the nutritional status of the animal, and substrate availability12,13. Because the Langendorff approach permits the study of the isolated-perfused heart in an ex-vivo manner in a more controlled manner in the absence of such confounders, it has been and continues to be considered a powerful investigational tool. Therefore, the technique presented here gives researchers an experimental approach for the ex-vivo study of the newborn murine heart and limits time to reperfusion.
Investigating the heart during periods of development is an important consideration given the wide-ranging biochemical, physiologic, and anatomical transitions that occur during myocardial maturation. Shifts from anaerobic metabolism to oxidative phosphorylation, changes in substrate utilization, and progression from cell proliferation to hypertrophy are dynamic processes that uniquely occur in the immature heart11,14. Another critical aspect of the developing heart is that stressors encountered during necessary periods may produce heightened responses in the newborn heart and alter future susceptibility to insults in adulthood15. Although prior work has utilized newborn rats, lambs, and rabbits to study the Langendorff-perfused neonatal heart, advances permitting mice use are necessary given the importance of this species to developmental biology research16. To address this need, the first murine Langendorff-perfused newborn heart model using 10-day old animals was recently established6. Presented here is a method to enable successful aortic cannulation and establish retrograde perfusion of the isolated newborn murine heart. This approach may be utilized for pharmacology, ischemia-reperfusion, or metabolism studies focusing on whole organ function or can be adapted for the isolation of cardiomyocytes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Rodent Langendorff Apparatus</td>
			<td>Radnoti</td>
			<td>130102EZ</td>
			<td></td>
		</tr>
		<tr>
			<td>24 G catheter</td>
			<td>BD</td>
			<td>381511</td>
			<td></td>
		</tr>
		<tr>
			<td>26 G needle on 1 mL syringe combo</td>
			<td>BD</td>
			<td>309597</td>
			<td></td>
		</tr>
		<tr>
			<td>26 G steel needle</td>
			<td>BD</td>
			<td>305111</td>
			<td></td>
		</tr>
		<tr>
			<td>5-0 Silk Suture</td>
			<td>Ethicon</td>
			<td>S1173</td>
			<td></td>
		</tr>
		<tr>
			<td>Bio Amp</td>
			<td>ADInstruments</td>
			<td>FE135</td>
			<td></td>
		</tr>
		<tr>
			<td>Bio Cable</td>
			<td>ADInstruments</td>
			<td>MLA1515</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Sigma-Aldrich</td>
			<td>C4901-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Circulating heating water Bath</td>
			<td>Haake</td>
			<td>DC10</td>
			<td></td>
		</tr>
		<tr>
			<td>curved iris scissor</td>
			<td>Medline</td>
			<td>MDS10033Z</td>
			<td></td>
		</tr>
		<tr>
			<td>dissecting microscope</td>
			<td>Nikon</td>
			<td>SMZ-2B</td>
			<td></td>
		</tr>
		<tr>
			<td>find spring scissors</td>
			<td>Kent</td>
			<td>INS600127</td>
			<td></td>
		</tr>
		<tr>
			<td>Force Transducer</td>
			<td>ADInstruments</td>
			<td>MLT1030/D</td>
			<td></td>
		</tr>
		<tr>
			<td>glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G8270-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Heparin</td>
			<td>Sagent</td>
			<td>400-01</td>
			<td></td>
		</tr>
		<tr>
			<td>High pressure tubing</td>
			<td>Edwards Lifesciences</td>
			<td>50P184</td>
			<td></td>
		</tr>
		<tr>
			<td>iris dressing forceps</td>
			<td>Kent</td>
			<td>INS650915-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Jeweler-style curved fine forceps</td>
			<td>Miltex</td>
			<td>17-307-MLTX</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma-Aldrich</td>
			<td>P3911-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Sigma-Aldrich</td>
			<td>P0662-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Sigma-Aldrich</td>
			<td>M7506-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma-Aldrich</td>
			<td>S9888-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Sigma-Aldrich</td>
			<td>S6014-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>Roller Pump</td>
			<td>Gilson</td>
			<td>Minipuls 3</td>
			<td></td>
		</tr>
		<tr>
			<td>straight dissecting scissors</td>
			<td>Kent</td>
			<td>INS600393-G</td>
			<td></td>
		</tr>
		<tr>
			<td>Temporary cardiac pacing wire</td>
			<td>Ethicon</td>
			<td>TPW30</td>
			<td></td>
		</tr>
		<tr>
			<td>Wide Range Force Transducer</td>
			<td>ADInstruments</td>
			<td>MLT1030/A</td>
			<td></td>
		</tr>
	</tbody>
</table>

modified technique for the use of neonatal murine hearts in the langendorff preparation

The use of the ex-vivo retrograde perfused heart has long been a cornerstone of ischemia-reperfusion investigation since its development by Oskar Langendorff over a century ago. Although this technique has been applied to mice over the last 25 years, its use in this species has been limited to adult animals. Development of a successful method to consistently cannulate the neonatal murine aorta would allow for the systematic study of the isolated retrograde perfused heart during a critical period of cardiac development in a genetically modifiable and low-cost species. Modification of the Langendorff preparation enables cannulation and establishment of reperfusion in the neonatal murine heart while minimizing ischemic time. Optimization requires a two-person technique to permit successful cannulation of the newborn mouse aorta using a dissecting microscope and a modified commercially available needle. The use of this approach will reliably establish retrograde perfusion within 3 min. Because the fragility of the neonatal mouse heart and ventricular cavity size prevents direct measurement of intraventricular pressure generated using a balloon, use of a force transducer connected by a suture to the apex of the left ventricle to quantify longitudinal contractile tension is necessary. This method allows investigators to successfully establish an isolated constant-flow retrograde-perfused newborn murine heart preparation, permitting the study of developmental cardiac biology in an ex-vivo manner. Importantly, this model will be a powerful tool to investigate the physiological and pharmacological responses to ischemia-reperfusion in the neonatal heart.

P10 mice were used to model&#160;a timepoint in human infancy26,27. Fifteen isolated C57Bl/6 newborn mouse hearts were harvested and cannulated successfully. Hearts were perfused with a continuous flow of 2.5 mL min-1 of warmed oxygenated KHB. Metabolic parameters, including glucose extraction, oxygen consumption, lactate production, and physiological parameters such as heart rate, perfusion pressure, and coronary resistance, were measured. Surface ele...

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Modified Technique for the Use of Neonatal Murine Hearts in the Langendorff Preparation

The present protocol describes aortic cannulation and retrograde perfusion of the ex-vivo neonatal murine heart. A two-person strategy, using a dissecting microscope and a blunted small gauge needle, permits reliable cannulation. Quantification of longitudinal contractile tension is achieved using a force transducer connected to the apex of the left ventricle.

The use of the ex-vivo retrograde perfused heart has long been a cornerstone of ischemia-reperfusion investigation since its development by Oskar ...

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2.4K Views.  Vanderbilt University Medical Center. The present protocol describes aortic cannulation and retrograde perfusion of the ex-vivo neonatal murine heart. A two-person strategy, using a dissecting microscope and a blunted small gauge needle, permits reliable cannulation. Quantification of longitudinal contractile tension is achieved using a force transducer connected to the apex of the left ventricle.

Video: Modified Technique for the Use of Neonatal Murine Hearts in the Langendorff Preparation

Modified Technique for Coronary Artery Ligation in Mice

Myocardial infarction (MI) is one of the most important causes of mortality in humans1-3. In order to improve morbidity and mortality in patients with MI we need better knowledge about pathophysiology of myocardial ischemia. This knowledge may be valuable to define new therapeutic targets for innovative cardiovascular therapies4. Experimental MI model in mice is an increasingly popular small-animal model in preclinical research in which MI is induced by means of permanent or temporary ligation of left coronary artery (LCA)5. In this video, we describe the step-by-step method of how to induce experimental MI in mice.
The animal is first anesthetized with 2% isoflurane. The unconscious mouse is then intubated and connected to a ventilator for artificial ventilation. The left chest is shaved and 1.5 cm incision along mid-axillary line is made in the skin. The left pectoralis major muscle is bluntly dissociated until the ribs are exposed. The muscle layers are pulled aside and fixed with an eyelid-retractor. After these preparations, left thoracotomy is performed between the third and fourth ribs in order to visualize the anterior surface of the heart and left lung. The proximal segment of LCA artery is then ligated with a 7-0 ethilon suture which typically induces an infarct size ~40% of left ventricle. At the end, the chest is closed and the animals receive postoperative analgesia (Temgesic, 0.3 mg/50 ml, ip). The animals are kept in a warm cage until spontaneous recovery.

The surgical procedure used to induce experimental myocardial infarction in mice begins with left thoracotomy between the third and the fourth ribs in order to visualize the anterior surface of the heart and left lung. The left coronary artery is ligated, the chest is closed and the mouse is allowed to recover spontaneously.

Myocardial infarction (MI) is one of the most important causes of mortality in humans1-3. In order to improve morbidity and mortality in patients with MI ...

NADH Fluorescence Imaging of Isolated Biventricular Working Rabbit Hearts

Since its inception by Langendorff1, the isolated perfused heart remains a prominent tool for studying cardiac physiology2. However, it is not well-suited for studies of cardiac metabolism, which require the heart to perform work within the context of physiologic preload and afterload pressures. Neely introduced modifications to the Langendorff technique to establish appropriate left ventricular (LV) preload and afterload pressures3. The model is known as the isolated LV working heart model and has been used extensively to study LV performance and metabolism4-6. This model, however, does not provide a properly loaded right ventricle (RV). Demmy et al. first reported a biventricular model as a modification of the LV working heart model7, 8. They found that stroke volume, cardiac output, and pressure development improved in hearts converted from working LV mode to biventricular working mode8. A properly loaded RV also diminishes abnormal pressure gradients across the septum to improve septal function. Biventricular working hearts have been shown to maintain aortic output, pulmonary flow, mean aortic pressure, heart rate, and myocardial ATP levels for up to 3 hours8.
When studying the metabolic effects of myocardial injury, such as ischemia, it is often necessary to identify the location of the affected tissue. This can be done by imaging the fluorescence of NADH (the reduced form of nicotinamide adenine dinucleotide)9-11, a coenzyme found in large quantities in the mitochondria. NADH fluorescence (fNADH) displays a near linearly inverse relationship with local oxygen concentration12 and provides a measure of mitochondrial redox state13. fNADH imaging during hypoxic and ischemic conditions has been used as a dye-free method to identify hypoxic regions14, 15 and to monitor the progression of hypoxic conditions over time10.
The objective of the method is to monitor the mitochondrial redox state of biventricular working hearts during protocols that alter the rate of myocyte metabolism or induce hypoxia or create a combination of the two. Hearts from New Zealand white rabbits were connected to a biventricular working heart system (Hugo Sachs Elektronik) and perfused with modified Krebs-Henseleit solution16 at 37 &deg;C. Aortic, LV, pulmonary artery, and left &amp; right atrial pressures were recorded. Electrical activity was measured using a monophasic action potential electrode. To image fNADH, light from a mercury lamp was filtered (350&plusmn;25 nm) and used to illuminate the epicardium. Emitted light was filtered (460&plusmn;20 nm) and imaged using a CCD camera. Changes in the epicardial fNADH of biventricular working hearts during different pacing rates are presented. The combination of the heart model and fNADH imaging provides a new and valuable experimental tool for studying acute cardiac pathologies within the context of realistic physiological conditions.

The objective is to monitor the mitochondrial redox state of isolated hearts within the context of physiologic preload and afterload pressures. A biventricular working rabbit heart model is presented. High spatiotemporal resolution fluorescence imaging of NADH is used to monitor the mitochondrial redox state of epicardial tissue.

Since its inception by Langendorff1, the isolated perfused heart remains a prominent tool for studying cardiac physiology2. However, it is not well-suited ...

Intramyocardial Cell Delivery: Observations in Murine Hearts

Previous studies showed that cell delivery promotes cardiac function amelioration by release of cytokines and factors that increase cardiac tissue revascularization and cell survival. In addition, further observations revealed that specific stem cells, such as cardiac stem cells, mesenchymal stem cells and cardiospheres have the ability to integrate within the surrounding myocardium by differentiating into cardiomyocytes, smooth muscle cells and endothelial cells.
Here, we present the materials and methods to reliably deliver noncontractile cells into the left ventricular wall of immunodepleted mice. The salient steps of this microsurgical procedure involve anesthesia and analgesia injection, intratracheal intubation, incision to open the chest and expose the heart and delivery of cells by a sterile 30-gauge needle and a precision microliter syringe.
Tissue processing consisting of heart harvesting, embedding, sectioning and histological staining showed that intramyocardial cell injection produced a small damage in the epicardial area, as well as in the ventricular wall. Noncontractile cells were retained into the myocardial wall of immunocompromised mice and were surrounded by a layer of fibrotic tissue, likely to protect from cardiac pressure and mechanical load.

Intramyocardial cell delivery in murine models of cardiovascular diseases, such as hypertension or myocardial infarction, is widely used to test the therapeutic potential of different cell types in regenerative studies. Therefore, a detailed description and a clear visualization of this surgical procedure will help to define the limits and advantages of cardiovascular cell therapeutic analyses in small rodents.

Previous studies showed that cell delivery promotes cardiac function amelioration by release of cytokines and factors that increase cardiac tissue ...

Induction and Assessment of Ischemia-reperfusion Injury in Langendorff-perfused Rat Hearts

The biochemical events surrounding ischemia reperfusion injury in the acute setting are of great importance to furthering novel treatment options for myocardial infarction and cardiac complications of thoracic surgery. The ability of certain drugs to precondition the myocardium against ischemia reperfusion injury has led to multiple clinical trials, with little success. The isolated heart model allows acute observation of the functional effects of ischemia reperfusion injury in real time, including the effects of various pharmacological interventions administered at any time-point before or within the ischemia-reperfusion injury window. Since brief periods of ischemia can precondition the heart against ischemic injury, in situ aortic cannulation is performed to allow for functional assessment of non-preconditioned myocardium. A saline filled balloon is placed into the left ventricle to allow for real-time measurement of pressure generation. Ischemic injury is simulated by the cessation of perfusion buffer flow, followed by reperfusion. The duration of both ischemia and reperfusion can be modulated to examine biochemical events at any given time-point. Although the Langendorff isolated heart model does not allow for the consideration of systemic events affecting ischemia and reperfusion, it is an excellent model for the examination of acute functional and biochemical events within the window of ischemia reperfusion injury as well as the effect of pharmacological intervention on cardiac pre- and postconditioning. The goal of this protocol is to demonstrate how to perform in situ aortic cannulation and heart excision followed by ischemia/reperfusion injury in the Langendorff model.

The isolated rat heart is an enduring model for ischemia reperfusion injury. Here, we describe the process of harvesting the beating heart from a rat via in situ aortic cannulation, Langendorff perfusion of the heart, simulated ischemia-reperfusion injury, and infarct staining to confirm the extent of ischemic insult.

The biochemical events surrounding ischemia reperfusion injury in the acute setting are of great importance to furthering novel treatment options for ...

Neonatal Murine Cochlear Explant Technique as an In Vitro Screening Tool in Hearing Research

While there have been remarkable advances in hearing research over the past few decades, there is still no cure for Sensorineural Hearing Loss (SNHL), a condition that typically involves damage to or loss of the delicate mechanosensory structures of the inner ear. Sophisticated in vitro and ex vivo assays have emerged in recent years, enabling the screening of an increasing number of potentially therapeutic compounds while minimizing resources and accelerating efforts to develop cures for SNHL. Though homogenous cultures of certain cell types continue to play an important role in current research, many scientists now rely on more complex organotypic cultures of murine inner ears, also known as cochlear explants. The preservation of organized cellular structures within the inner ear facilitates the in situ evaluation of various components of the cochlear infrastructure, including inner and outer hair cells, spiral ganglion neurons, neurites, and supporting cells. Here we present the preparation, culture, treatment, and immunostaining of neonatal murine cochlear explants. The careful preparation of these explants facilitates the identification of mechanisms that contribute to SNHL and constitutes a valuable tool for the hearing research community.

Neonatal Murine Cochlear Explant Technique as an In Vitro Screening Tool in Hearing Research

The goal of this protocol is to demonstrate the preparation, culture, treatment, and immunostaining of neonatal murine cochlear explants. The technique can be utilized as an in vitro screening tool in hearing research.

While there have been remarkable advances in hearing research over the past few decades, there is still no cure for Sensorineural Hearing Loss (SNHL), a ...

Optocardiography and Electrophysiology Studies of Ex Vivo Langendorff-perfused Hearts

Small animal models are most commonly used in cardiovascular research due to the availability of genetically modified species and lower cost compared to larger animals. Yet, larger mammals are better suited for translational research questions related to normal cardiac physiology, pathophysiology, and preclinical testing of therapeutic agents. To overcome the technical barriers associated with employing a larger animal model in cardiac research, we describe an approach to measure physiological parameters in an isolated, Langendorff-perfused piglet heart. This approach combines two powerful experimental tools to evaluate the state of the heart: electrophysiology (EP) study and simultaneous optical mapping of transmembrane voltage and intracellular calcium using parameter sensitive dyes (RH237, Rhod2-AM). The described methodologies are well suited for translational studies investigating the cardiac conduction system, alterations in action potential morphology, calcium handling, excitation-contraction coupling and the incidence of cardiac alternans or arrhythmias.

The objective of this study was to establish a method for investigating cardiac dynamics using a translational animal model. The described experimental approach incorporates dual-emission optocardiography in conjunction with an electrophysiological study to assess electrical activity in an isolated, intact porcine heart model.

Small animal models are most commonly used in cardiovascular research due to the availability of genetically modified species and lower cost compared to ...

Advanced Cardiac Rhythm Management by Applying Optogenetic Multi-Site Photostimulation in Murine Hearts

Ventricular tachyarrhythmias are a major cause of mortality and morbidity worldwide. Electrical defibrillation using high-energy electric shocks is currently the only treatment for life-threatening ventricular fibrillation. However, defibrillation may have side-effects, including intolerable pain, tissue damage, and worsening of prognosis, indicating a significant medical need for the development of more gentle cardiac rhythm management strategies. Besides energy-reducing electrical approaches, cardiac optogenetics was introduced as a powerful tool to influence cardiac activity using light-sensitive membrane ion channels and light pulses. In the present study, a robust and valid method for successful photostimulation of Langendorff perfused intact murine hearts will be described based on multi-site pacing applying a 3 x 3 array of micro light-emitting diodes (micro-LED). Simultaneous optical mapping of epicardial membrane voltage waves allows the investigation of the effects of region-specific stimulation and evaluates the newly induced cardiac activity directly on-site. The obtained results show that the efficacy of defibrillation is strongly dependent on the parameters chosen for photostimulation during a cardiac arrhythmia. It will be demonstrated that the illuminated area of the heart plays a crucial role for termination success as well as how the targeted control of cardiac activity during illumination for modifying arrhythmia patterns can be achieved. In summary, this technique provides a possibility to optimize the on-site mechanism manipulation on the way to real-time feedback control of cardiac rhythm and, regarding the region specificity, new approaches in reducing the potential harm to the cardiac system compared to the usage of non-specific electrical shock applications.

This work reports a method for controlling the cardiac rhythm of intact murine hearts of transgenic channelrhodopsin-2 (ChR2) mice using local photostimulation with a micro-LED array and simultaneous optical mapping of epicardial membrane potential.

Ventricular tachyarrhythmias are a major cause of mortality and morbidity worldwide. Electrical defibrillation using high-energy electric shocks is ...

Creating Radio-cephalic Arteriovenous Fistula in the Forearm with a Modified No-Touch Technique

Autologous arteriovenous fistula (AVF) is the primary and best option to obtain vascular access for hemodialysis treatment; other options are arteriovenous graft (AVG) and central venous catheterization (CVC). The implementation of radio-cephalic autologous arteriovenous fistula (RC-AVF) in the forearm was preferred among patients with superior vascular conditions. However, there is a high rate of early fistula failure. The chosen surgical method is understood to have an effect on the maturation of the fistula. New surgical procedures such as radial artery deviation and reimplantation (RADAR) have been significantly improved for juxta-anastomotic stenosis. Nevertheless, new problems such as stenosis of arteries and narrowing of surgical indication were also found. In this report, we presented a modified no-touch technique (MNTT) to create an RC-AVF, in which the venous and arterial wall avoid devascularization and the radial artery does not sever.

We present a modified no-touch technique (MNTT) to create a radio-cephalic arteriovenous fistula (RC-AVF) in which the venous and arterial wall avoid devascularization and the radial artery does not sever.

Autologous arteriovenous fistula (AVF) is the primary and best option to obtain vascular access for hemodialysis treatment; other options are ...

A Modified Simple Method for Induction of Myocardial Infarction in Mice

Myocardial infarction (MI) represents one of the leading causes of death. MI models are widely used for investigating the pathomechanisms of post-MI remodeling and evaluation of novel therapeutics. Different methods (e.g., isoproterenol treatment, cryoinjury, coronary artery ligation, etc.) have been used to induce MI. Compared with isoproterenol treatment and cryoinjury, coronary artery ligation may better reflect the ischemic response and chronic remodeling after MI. However, traditional methods for coronary ligation in mice are technically challenging. The current study describes a simple and efficient process for induction of MI in mice with readily available materials. The mouse chest skin was cut open under stable anesthesia. The heart was immediately externalized through the intercostal space after blunt separation of the pectoralis major and pectoralis minor. The left anterior descending branch (LAD) was ligated with a 6-0 suture 3 mm from its origin. Following LAD ligation, staining with 2,3,5-Triphenyltetrazolium chloride (TTC) indicated successful induction of MI and temporal changes of post-MI scar size. Meanwhile, survival analysis results showed overt mortality within 7 days after MI, mainly due to cardiac rupture. Moreover, post-MI echocardiographic assessment demonstrated successful induction of contractile dysfunction and ventricular remodeling. Once mastered, an MI model can be established in mice within 2-3 min with readily available materials.

Under adequate anesthesia, the mouse heart was externalized through the intercostal space, and myocardial infarction was successfully induced by ligating the left anterior descending artery (LAD) using materials readily available in most laboratories.

Myocardial infarction (MI) represents one of the leading causes of death. MI models are widely used for investigating the pathomechanisms of post-MI ...

Biological Preparation and Mechanical Technique for Determining Viscoelastic Properties of Zonular Fibers

Elasticity is essential to the function of tissues such as blood vessels, muscles, and lungs. This property is derived mostly from the extracellular matrix (ECM), the protein meshwork that binds cells and tissues together. How the elastic properties of an ECM network relate to its composition, and whether the relaxation properties of the ECM play a physiological role, are questions that have yet to be fully addressed. Part of the challenge lies in the complex architecture of most ECM systems and the difficulty in isolating ECM components without compromising their structure. One exception is the zonule, an ECM system found in the eye of vertebrates. The zonule comprises fibers hundreds to thousands of micrometers in length that span the cell-free space between the lens and the eyewall. In this report, we describe a mechanical technique that takes advantage of the highly organized structure of the zonule to quantify its viscoelastic properties and to determine the contribution of individual protein components. The method involves dissection of a fixed eye to expose the lens and the zonule and employs a pull-up technique that stretches the zonular fibers equally while their tension is monitored. The technique is relatively inexpensive yet sensitive enough to detect alterations in viscoelastic properties of zonular fibers in mice lacking specific zonular proteins or with aging. Although the method presented here is designed primarily for studying ocular development and disease, it could also serve as an experimental model for exploring broader questions regarding the viscoelastic properties of elastic ECM&#39;s and the role of external factors such as ionic concentration, temperature, and interactions with signaling molecules.

The protocol describes a method for the study of extracellular matrix viscoelasticity and its dependence on protein composition or environmental factors. The matrix system targeted is the mouse zonule. The performance of the method is demonstrated by comparing the viscoelastic behavior of wild-type zonular fibers with those lacking microfibril-associated glycoprotein-1.

Elasticity is essential to the function of tissues such as blood vessels, muscles, and lungs. This property is derived mostly from the extracellular ...