Basic Biomethodology
For Laboratory Mice

When attempting to restrain mice, sudden, jerky moves should be avoided to decrease the likelihood of being bitten.

Approaching mice with gentle confidence is best.

It is important to select the appropriate method of restraint for the procedure you wish to perform and one that will offer the best access to the area requiring manipulation.

If you have questions concerning restraint selection, please consult your veterinarian.

Restraint by the tail or with forceps is only intended for short-term manipulations, such as transferring animals from one cage to another.

Tail Restraint

Mice may be picked up by grasping the base of the tail.

Do not grasp the tip of the tail, as this may cause the skin to be stripped off.

This method is only used for brief restraint; for example transferring animals from cage to cage.

Never suspend the mouse for prolonged periods of time by its tail.

Forceps Restraint

Mice may also be picked up with rubber-tipped forceps by gently grasping the animal by the scruff of the neck or the base of the tail.

The forceps should be dipped in disinfectant between cages.

This method of restraint should only be used for short-term procedures such as transferring animals to a new cage.

Never suspend the animal for a prolonged period of time with the forceps.

Scruff Restraint

Using the scruff or mechanical devices is suggested for procedures requiring more than momentary restraint, such as injections or blood withdrawal.

Restraining the mouse by the scruff will allow you to perform many technical procedures such as examination, injection and blood collection.

There is a one-hand and a two-hand variation of this technique.

The one-hand method places you at greater risk for being bitten, so beginners should perfect the two-hand restraint method before attempting the one-hand method.

For the two-hand technique, restrain the mouse by grasping it near the base of the tail and placing it on a toe-gripping surface, such as a wire bar lid.

Pulling back gently on the tail of the mouse causes it to pull forward on the toe-gripping surface.

Caution must be used to avoid injuring the tail or toes of the mouse.

While grasping the tail with one hand, grasp the nape or scruff of the neck with the other.

Position the animal's body firmly across your hand by extending your forefinger and thumb back as far as possible, while maintaining a firm grip on the scruff. Place the tail between the fingers of this same hand to secure the animal.

This type of restraint will allow the handler complete access to the ventral side of the mouse.

Again, caution must be used.

If you do not grasp enough of the scruff, the animal will be able to turn and bite.
If you grasp too much skin, the airway will become restricted and the mouse will become cyanotic.

Monitor the condition of the animal the entire time it is restrained, being careful to observe the breathing rate and color of the ears, nose and oral cavity.

The animal should be released immediately if there are any signs of gasping or change in coloring from pink to blue.
Revised 4/6/04 4

For the one-hand technique, restrain the mouse by grasping it near the base of the tail and placing it on a toe-gripping surface.

A good example of an appropriate surface is the wire bar lid.

Place the base of the tail between or underneath your last one or two fingers.

With the thumb and first finger of the same hand, grasp the nape or scruff of the neck.

The same precautions as described for the two-hand technique must be followed.

Mechanical Restrainers

Plexiglass restrainers are available from several different manufacturers in a variety of styles.

They allow the user to have both hands free for manipulation.

Depending on the type of restraint device, the mouse is placed in the restrainer either tail or head first.

If it is a head-first restrainer, you can use a variety of methods to encourage the mouse to enter the restrainer.

Restrain the mouse by the scruff, as described earlier, and direct its head into the opening of the restrainer.

Once you release the scruff, most mice will readily enter the restrainer.

If the restrainer has a securing device, affix it firmly to prevent the mouse from exiting the apparatus.

Alternatively, grasp the mouse by the base of the tail with one hand and cover the top of the restrainer with the other to form a darkened tunnel.

Most mice, once they are shown the entrance to the tunnel, will readily enter the restrainer.

Affix the securing device.

Tail-first restrainers are appropriate for procedures such as tail vein injections and blood collections.

If you are using a tail-first restrainer, grasp the mouse by the base of the tail and slide it hindquarters first into the restrainer, using the slot as a tail guide.

Once the mouse is in the restrainer, insert the securing device to prevent the animal from exiting the apparatus. Use caution when placing the securing device to prevent injury or restriction of the animal's breathing. Monitor the breathing rate and color of the ears and nose for the duration of the restraint.

Release the animal immediately should there be any signs of gasping or change in color from pink to blue.

Plastic bag restrainers are another option for short-term restraint of mice.

Only use bag restrainers that are specifically designed for use with animals.

AIMS is one example of a commercial vendor that distributes bag restrainers.

The bags are available in two sizes for mice, depending on whether the mouse weighs more or less than 20 grams.

Grasp the mouse by the scruff and direct it head first into the large end of the bag.

Release the scruff and the animal will move forward into the bag.

Ensure that the animal's nose is situated in the opening located in the small end of the bag.

Use a twist tie to loosely close the large end of the bag around the tail.

Remember

• Select the appropriate restraint method for the procedure you wish to perform.
• Release the animal immediately should you observe any change in breathing rate or change in coloration.
• Consult your veterinarian should you have any questions concerning animal restraint options.