Virtual Mouse Necropsy
Instruments, Fixatives, and Other Handy Devices
Don't start a necropsy without them.
Fume Hood
Safety is the most important concern in any necropsy. By using a fume hood, you are protecting yourself from any inhalants from the animal or the preservatives. Keep the work area clean by washing it down with ethanol or disinfectant.
Dissecting Board
A good surface is needed to perform a necropsy. A dissecting board with a corked surface works best, but carboard boxes, multiple layers of paper towels, and discarded calendars have been used in the past. It is always a good idea to wrap your board in paper towel and then lay a few free pieces on the surface. When you are finished with your necropsy, wrap up the carcass in the paper towels. This way, liquids will not stain or ruin the surface of the board.
Scissors and Forceps
Scissors are a necessity. It is a good idea to have a few pairs on hand of various sizes and sharpness. For the more delicate dissections, a fine-tipped pair allows for precise and controlled cuts. For the big incisions, a rounded-tipped pair protects the surrounding tissue from any unwanted nicks. For cutting bone, use an old pair of scissors or special bone tools. When maintaining the sharpness of the blades is no longer a concern, a pair of retired tissue-cutting scissors usually works best. Forceps are also a staple item when performing a necropsy. There are many uses for them: gripping, holding, pinching, prodding, snipping, and retrieving.
Saline
Saline is very important. Removing anything from the animal coats surfaces with a great deal of debris, blood, and fluid, which are best cleaned with saline. You also need saline to rinse the tissue itself in order to study the structure. Never rinse tissue in your fixative or water. The difference in osmolarity between the tissue and the water causes cellular swelling and rupture, which is very bad. Rinsing in fixative starts the fixation process, causing discoloration and fusion of the debris to the surface of the tissue. Physiologic saline solution or phosphate-buffered saline maintains the tissue's appearance and doesn't harm the cellular structure.
Preservatives
To prepare slides from the tissues being taken, you will have to preserve them. 10% neutral buffered formalin meets the requirements for general preservation and histology techniques. For more specific and sophisicated techniques, numerous fixatives are available on the market. When deciding how much fixative is needed, a good rule of thumb is to use 10 parts of fixative to every 1 part of tissue. Also, if the tissue is not processed by histology immediately, periodic changing of the preservative should ensure that the tissue will not dry out. Preservative will fully penetrate tissues 1 cm thick or less. Mouse tissues are small enough to be fully penetrated by the preservative, with the exception of the liver, which can be sectioned or separated. For larger species, scoring the surface of the tissue or sectioning before fixation leads to good results.
Metric Scale
With any necropsy, you must make quantitative as well as qualitative observations. It is important to measure the body weight of the animal before necropsy, as well as weighing certain selected organs specified by your protocol. The object is to weigh only the item of choice. This means you must judiciously trim the attached tissue and debris to get the clearest picture. Some structures in a mouse will only weigh a few thousandth's of a gram, so an electronic scale is needed.
Pins
Whether or not to pin is strictly up to the necropsy technician, depending on his or her personal preference. There are pros and cons to both techniques. In pinning the animal, the necropsy technician creates a stable work foundation. The animal cannot slide or slip if all four paws are pinned to the board. According to the majority of necropsy techniques, special commerical necropsy pins are required; however, tacks work just as well and are significantly cheaper. On the other hand, if the animal is not pinned to the board, the necropsy technician has freedom of movement. Using this method, it is possible to perform many more manipulations than if the animal is pinned down. The choice is up to you.
Ethanol
Performing a necropsy is messy, so it is a good idea to have a squirt or squeeze bottle of 70% ethanol for cleaning. Ethanol spray is very versatile. Not only does it aid in the necropsy by sterilizing the incision site and keeping fur out of tissues, it can be used during clean-up. You can use it to clean your instruments, your work area, your hands, and just about anything else.
Selected pictures illustrated by Erin Parsoneault, inspired by D.E.Devor-Henneman
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