Guidelines for Techniques with Rodents (Duke University)
HANDLING & RESTRAINT
MOUSE: Mice are small rodents that are hard to grasp. Care should be taken to avoid getting bit or causing harm to the animal. One method of moving mice from one cage to another is by grasping the skin behind the neck with a pair of forceps. When using this method be careful not to grasp too hard. Restraining the mouse can be done by grasping the base of the tail with one hand and with the other grasp the loose skin behind its neck. Take extra precaution to avoid getting bitten. When you have a firm grasp you may secure the tail in the same hand you have the scruff in to accomplish a one handed restraint. Care should be taken not to excite any of these animals. Slow deliberate movements will make the job of restraining much easier. Noise should also be kept to a minimum.
RAT: Rats can inflict a painful bite. DO NOT grasp the rat by the scruff, as it will react violently to this type of restraint. First grab the rat by the base of the tail and lift out of the cage and place on a soft surface. Hard smooth surfaces can make the rat tense. Secondly, gently pet the rats – this will calm it. Place your index and middle fingers along side the rat’s head and your thumb and ring fingers under its forelegs. Use your index and middle fingers to secure its head and the remaining fingers to support the chest. Hold the tail and support the lower body with your other hand. Be careful not to squeeze hard as this may interfere with the rat’s ability to breathe. Care should be taken not to excite any of these animals. Slow deliberate movements will make the job of restraining much easier. Noise should also be kept to a minimum.
GUINEA PIG: Guinea pigs are curious, easy to handle animals. They are not aggressive by nature. Do not grasp the guinea pig by the loose skin. Body hair is easily pulled out and the guinea pig will often object when handled in this manner. Calmly grasp it with one hand under the chest and use your other hand to support its hindquarters. Care should be taken not to excite any of these animals. Slow deliberate movements will make the job of restraining much easier. Noise should also be kept to a minimum.
SEX DETERMINATION
MOUSE: Restrain the mouse and lift the base of the tail. Sex is most easily determined by ano-genital distance. Males normally have a greater distance between the anus and urogenital openings. Male mice also have a larger genital papilla.
RAT: Procedure same as in the mouse.
GUINEA PIG: Both male and female guinea pigs display similar ano-genital distances. The female has a separate urethal orifice, a vaginal membrane, a perineal sac, and an anus; the male has a penis, a larger perineal sac, and an anus. The penis lies just under the skin and can be inverted with gentle pressure. The testes and penis are palpable in adults.
ORAL GAVAGE
MOUSE: Restrain the mouse and measure the gavage tube from the tip of the nose to the last rib. This is the length you must insert the tube. With the use of the tube push the mouse’s head slightly upward and back to straighten the esophagus. Position tube to the right or left of the mouth and slowly pass the tube watching for the swallowing reflex. The tube should pass freely into the esophagus. DO NOT FORCE. When desired length of insertion is achieved, inject solution. Observe mouse after the procedure for signs of distress, such as gasping or frothing of the mouth.
RAT: Procedure same as in the mouse.
GUINEA PIG: The guinea pig has a small palatal ostium that is easily damaged. For this reason this procedure is not recommended in the guinea pig.
SPECIAL NOTE: When using a plastic tube, care should be taken to ensure animal does not bite down and sever the tube. An artificial device to hold the mouth open can be used.
INJECTION TECHNIQUES - GENERAL OVERVIEW
MOUSE: Injection sites should be cleaned with a suitable disinfectant, typically isopropyl alcohol. Sterile syringes and needles must be used for all injections. The one time use of disposable supplies insures aseptic techniques and sharp needles. Always select the smallest gauge needle possible to limit tissue trauma and injection discomfort. A 25-30 gauge needle is recommended for use in a mouse. Before injecting, check for correct placement by pulling back on the plunger of the syringe to create a vacuum. This is known as aspiration.
RAT: Same overview as the mouse except it is recommended that 21-30 gauge needles be used.
GUINEA PIG: Same overview as the mouse except it is recommended that 22-30 gauge needles be used.