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Lab Animal Research
 

Sterile Tissue Harvest

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Many experiments demand collection of cells from the excised tissue. In such cases, it is imperative that the tissue harvest procedure be performed in a sterile manner. The use of cell lines and tissue cultures that originate from research animals allows for many experiments to be conducted in vitro, whichin turn reduces the animal usage in research.

In this video, we will discuss the aseptic method for harvest of commonly extracted organs from lab animals. And this will be followed by a short review of a few example experiments employing this sterile technique to achieve different research goals.

Let's begin with the prepping steps required to ensure sterility of the space, instruments, and personnel during animal tissue harvest.

This procedure is performed in a laminar flow hood. Prior to the process, the hood fan should run for at least 15 minutes and the area should be disinfected with 70% alcohol. Next, place some paper towels into the hood and wet them with 70% ethanol. After that, load the sterile equipment and organize by the order in which each instrument will be used, usually from left to right. This allows for the workflow to occur in a unidirectional manner, preventing accidental contamination from the animal carcass.

It is recommended that a non-sterile technician be present to assist the sterile technician. Both operators must wear a mask and a bouffant. The sterile technician must don a sterile gown and two pairs of sterile surgical gloves. Note that the gown and gloves must cover the wrists to prevent the shedding of skin cells into the opened body cavity, petri dishes, or sterile media.

The non-sterile person opens the sterile instrument package without touching the inner surface, so that the sterile person can remove the tool aseptically. Lastly, the non-sterile technician euthanizes the animal, places the carcass on the paper towels and completely soaks it with 70% alcohol, so that the sterile person can begin the harvest.

First, we will review the extraction of abdominal organs, including the spleen, liver, kidneys, ovaries, and testes.

Using a set of sterile scissors and forceps make a horizontal cut in the skin just anterior to the prepuce in males and the pelvic bone in females. Avoid cutting through the abdominal musculature. Next, place your thumb under the cut and grasp the cranial edge of the cut. Using the other hand, securely hold the hind limbs and tail, while pulling the skin toward the head. The skin will tear away from the body just above the hind limbs, and can be turned inside out over the head and forelegs. This effectively removes hair contaminants that might interfere with the sterile organ harvest. Then, soak the body again with 70% alcohol and remove the superficial pair of gloves, which are no longer sterile. Also discard all the instruments that were used on the skin.

To harvest the spleen, position the body in right lateral recumbency. The spleen should be visible through the abdominal muscle. Use scissors to make a cut directly over the spleen, and gently retract the organ from the body cavity. Cut all the attachments between the spleen and the stomach and pancreatic tissue, but avoid puncturing or tearing the organ.

To harvest all other abdominal organs, place the body in dorsal recumbency. Then, lift and cut away the abdominal muscle leaving an oval opening directly over the abdominal cavity. To harvest the liver, reflect the organ caudally away from the diaphragm. Now use scissors to carefully sever any membranes between the two structures. Next, make a cut perpendicular to the spine through the blood vessels. Then lift the liver and reflect it toward the diaphragm to visualize the attachments beneath it. There will be thin membranes attaching the smaller liver lobes to the stomach and small intestine. Grasp the fibrous node in the center of the liver on the underside and lift the organ to find all the attachments. Now separate the organ from the underlying tissues. Note that the liver is fragile and can be easily punctured resulting in excessive release of blood. Therefore, it must be handled carefully.

To harvest the kidneys, push the intestines to the left to expose the right kidney or to the right to expose the left kidney. Now use the forceps blades to grasp beneath the kidney and using scissors cut under the forceps, removing the organ from the body.

To harvest the ovaries, move the intestines cranially to visualize the uterus. Follow the left and the right uterine horns to the ovaries. These are small organs and in older animals they may be imbedded in fat. Slide the forceps under the ovary to isolate it from the body and cut it free from the fat and the fallopian tube.

In males, to remove testes, gently grasp the inguinal fat pad and pull anteriorly. This will pull the testis from the scrotum. Once they become visible, cut the attachments to the scrotum and the vas deferens to free these structures from the body.

Next, let's learn how to harvest thoracic organs, such as the heart and lungs. The heart and lungs are most easily removed together. To open the thoracic cavity, begin by placing the animal in dorsal recumbency. First, grasp and lift the xiphoid process. Then make a cut through the abdominal muscle just caudal to the ribs. Extend the cut along the lower curve of the rib cage on both sides, exposing the diaphragm.

Next, puncture the diaphragm by making a small cut in the rib cage at the most lateral point possible on each side. Then, cut the diaphragm away from the ribs. Now lift the ribs at the xiphoid to visualize the thoracic organs. Extend the lateral cut to the top of the sternum on both sides to open the chest. Then place the forceps perpendicular to the trachea and grasp the windpipe firmly. Now, using scissors, make a perpendicular cut just anterior to the forceps. This should sever the trachea and the esophagus. Without loosening the grip on the trachea, lift it up caudally and snip any attachments of the lungs to the spinal surface in the rib cage. Continue until you are able to lift the heart and lungs free of the chest cavity.

To remove just the heart, lift the organ and carefully cut through the pericardial sac. Next, hold the aorta with the forceps and make a cut distal to the forceps. Then sever the anterior vena cava, pulmonary arteries, and veins. After that, you should be able to lift the heart free of the thoracic cavity.

Now, let's review the procedure of harvesting the brain using aseptic technique. In instances where the brain is the only organ to be collected, the prepping steps are the same.

To start the harvest, saturate the body with alcohol, and strip the skin from the body as before -- up and over the skull. This allows for everything to be sterile from this point forward. Then, saturate the animal again with alcohol, remove the outer gloves and discard the instruments used on the skin. Now make a cut at the nape of the neck and extend it along the midline from the dorsal cervical area to the tip of the nose.

Now, using a dedicated pair of sterile brain harvest scissors, make a cut through the spine at the base of the skull. To open the cranium, place the point of the scissors in the foramen magnum and cut along the midline. Note that during this brain harvesting procedure, one hand is considered non-sterile as it grasps the skin from the skull reflected beneath the chin to stabilize the head, while the sterile hand is being used to cut the skull. After that, use the flat edge of the scissor blade to lever the parietal bones away from the brain. And using the spatula, carefully disrupt the nerve attachments at the brain stem and the optic chiasm beneath the brain. Lastly, slide the closed forceps anteriorly and break the attachments at the olfactory bulbs. And the brain can then be dropped from the skull directly into the sterile media.

Now that we've reviewed the essentials of sterile tissue harvest, let's discuss some of the many uses of this procedure in biomedical research.

Neural stem researchers use sterile harvesting technique to extract tissue from mouse neonatal brain, to grow these cells in vitro. This allows them to study the role of neural stem cells in development, and cancer progression.

Another active area of research that involves tissue harvest is metabolic profiling, which involves studying tissue physiology by analyzing the different metabolites in a sample. In this example, scientists, using aseptic technique, collected liver biopsies from wild type and germ-free mice and used nuclear magnetic resonance spectroscopy, or NMR, to elucidate the difference in the liver metabolic profile of the two animal populations.

Lastly, immunologists often perform sterile tissue harvest to study the spread of infection. In this particular experiment, researchers performed intratracheal injection of bacteria Pseudomonas aeruginosa to induce chronic lung infection. Following that, animals were euthanized and lungs were extracted using aseptic technique to determine the bacterial load at 3, 7, 14, and 28 days post-infection.

You've just watched JoVE's video on harvesting tissues from lab animals using aseptic technique. You should now have a better sense of the steps you need to take to ensure that sterility is maintained throughout the harvest. And you should be able to extract the abdominal and thoracic organs, and brains from these animals without causing any damage to the tissue. As always, thanks for watching!

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