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Specific guidance for mice when conducting minor procedures without anaesthesia

Handling

Many mice will attempt to bite when restrained, so a careful approach is necessary. For many years, the technique taught in most facilities has been to grasp the animal by the base of its tail, and lift it clear of its cage. It can then be placed on a rough surface such as a piece of towelling, or allowed to rest on the sleeve of the handler’s laboratory coat.


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However, it has been clearly shown that that picking up mice in this way induces aversion and high levels of anxiety (Hurst & West 20101), adversely affects their welfare (Clarkson et al, 20182) and can influence the outcome of behavioural and other studies (Ghosal et al, 20153, Gouveia and Hurst, 20174). Using tunnels or cupping the mice in open hands leads to more rapid acceptance of physical restraint. Habituation to this type of initial restraint persists even when mice are subsequently restrained more securely, for example by the scruff to allow injections to be carried out.

After restraint using a handling tube or by cupping in the operator’s hands, the mouse can easily be examined so that’s its clinical appearance can be assessed. If needed, it can then be restrained by the base of the tail and placed on the cage lid or a rough surface, and additional restraint provided by gripping the scruff. This enables administration of substances or blood sampling to be undertaken.

Oral dosing

Material can be administered orally using a number of different techniques, although gavage using a stomach tube is the most widely used. To minimise the risk of adverse effects associated with this procedure, it is important that the operator is skilled both in the technique and the restraint method needed.

Although gavage can be undertaken using rigid dosing cannulae, flexible catheters or tubes are preferred, and these are less likely to cause oesophageal trauma. Inadvertent dosing into the lung may occur, and this usually results in the animal showing immediate signs of respiratory distress. If this is observed, then the animal should be humanely killed.

As an alternative to gavage, some materials may be consumed voluntarily in palatable mixtures (e.g. flavoured syrups, Leach et al, 20105, Corbett et al, 20126, Zhang, 20117, Küster, et al, 20128, Gonzales et al, 20149). Material can also be dosed using a small flexible catheter introduced only into the animal’s mouth.

When possible, these approaches are to be preferred to dosing using a stomach tube, since they are not associated with complications, such as tracheal dosing or oesophageal rupture.

If stomach tubing is necessary, A 2-3 f.g. polyethylene catheter, about 2-3 cm in length, provides a suitable tube (an 18 gauge “Medicut” is a suitable size, and purpose-made catheters can be purchased). Alternatively, metal tubes can be made by blunting a 19-20 gauge needle, as described for the rat or purchased from a commercial supplier. The mouse should be grasped by the skin of the neck and back; this ensures that the head and neck are extended and in line with the back. The tube can then be passed into the mouth via the interdental space. After passing the tube gently down into the oesophagus, the fluid can be administered. Considerable struggling may ensue during this procedure, and it is often preferable to lightly anaesthetise the mouse, for example by inhalation of Isoflurane (Jones et al, 201410), before attempting to pass the tube. If undertaken in conscious mice, the plastic tubing will require frequent replacement due to biting by the animal, and it will usually be preferable to use metal dosing needles.

Intraperitoneal injection

Intraperitoneal injection can be carried out as described for other species of rodent, although the small size of the mouse also enables single-handed injection into a posterior quadrant of the abdomen.

Subcutaneous injection

Subcutaneous injection can be made into the scruff, with the mouse restrained and intramuscular injection into the quadriceps. Both of these techniques require an assistant to administer the injection.

Intravenous injection

Intravenous injection into the lateral tail vein is most easily undertaken with the mouse restrained in a purpose-made restraining device.

Next Article : Specific guidance for rats when conducting minor procedures without anaesthesia

Updated on 12th May 2020

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