Mice in Need of Special Care

Care and use of vascular catheters

For blood withdrawal, carotid catheterization is recommended.
For infusion of compounds, jugular catheterization is recommended.

• Mice with catheters should be individually housed.
• Catheter should be flushed with sterile saline and refilled with sterile lock solution within 24 hours of arrival and then every 3-4 days.
• Always clamp the catheter before removing the plug or syringes.
• 1 ml syringe
• Blunted 23-gauge needles
• Catheter clamp; we recommend a non-serrated micro-serrefine clamp.
• Lumen lock solution: 1 ml sodium heparin (1000 IU/ml) added to 1ml glycerol for a final concentration of 500 IU heparin/ml lock solution
• Saline

Materials required

Procedure for sampling and infusion

1. Immobilize the mouse. We recommend gas anesthesia. Wound clips are used to secure the catheter in place; they may need to be removed for catheter access and replaced after the procedure is performed.
    
2. Clamp the catheter, below the plug and gently remove the plug.
    
3. Attach to the catheter an empty syringe with a blunted 23-gauge needle. Remove the clamp and slowly aspirate the lock solution until blood fills the catheter.* For catheter maintenance proceed to step 5.
    
4. Withdraw blood sample or infuse compound with a new syringe.
    
5. Flush the catheter with 0.05 ml of sterile saline.
    
6. Refill the catheter with 0.01 ml of lumen lock solution. Use caution when refilling the catheter with lock solution to avoid heparin being introduced into the bloodstream.
    
7. Re-clamp the catheter and re-insert the plug.  Remove the clamp.

*If the solution cannot be removed, reposition the mouse and retry. If the solution still cannot be withdrawn, clamp catheter, replace empty syringe with saline filled syringe, unclamp catheter, and inject a small amount of saline to clear the line.

For additional help with catheter maintenance, please contact Surgical Services: Andree Lapierre, 207-288-1468 or andree.lapierre@jax.org

Care and use of brain and intracerebroventricular (ICV) cannulated mice

The cannula implanted in mice consists of a guide cannula and a dummy cannula.  The guide cannula is placed into the brain at predetermined coordinates through a hole drilled in the skull. The dummy cannula consists of a cap that screws onto the guide cannula and has a stylet that inserts into the guide cannula to prevent materials from entering it when it's not being used.

An internal/injector cannula, which is used to deliver material (e.g., drugs, test compounds) through the guide cannula into the ventricle, is shipped separately.

To administer a compound into the ventricle

• Use aseptic technique.
• Attach a length of PE50 tubing to the injector cannula. To the opposite end of the tubing, insert a 23g blunted needle attached to an appropriately sized micro-syringe loaded with the test compound.
• Fill the tubing and injector with the test compound.
• Immobilize the mouse. We recommend gas anesthesia.
• Unscrew the dummy cannula and set aside.
• Insert the injector cannula into the guide cannula. When correctly seated, the injector cannula locks onto the guide cannula.
• The test material can now be injected through the cannula.
• The total volume injected should not exceed 5µl, and the infusion rate should not exceed 1µl/min.
• Remove the injector cannula and reinsert the dummy cannula into the guide cannula.
• To prevent cannulated mice from chewing on each other’s cannulas, we recommend housing them individually.
• We recommend housing them in cages without wire bar lids. Otherwise, the lids might interfere with the cannulas.

Housing of cannulated mice

For additional information please contact Andree Lapierre at Surgical Services: 207-288-1468 or surgicalservices@jax.org.

Highly immunodeficient strains require special considerations

NSG™ mice are severely immunodeficient and sensitive to infection by a wide range of normal pathogens, opportunistic pathogens and commensal organisms (Foreman, et al. 2011). Barrier practices that are sufficient to maintain nude and scid colonies may not be adequate for NSG™ mice. Here are some suggestions for ensuring the health status of NSG™ and related immunodeficient strains.

• NSG™ mice and other immunodeficient mice are maintained in maximum barriers and at our highest health status. A facility-barrier-levels is available on our website, as is a list-of-agents-monitored.
• Microisolator or pressurized individually ventilated (PIV) caging is recommended.
• Acidification of water to pH 2.5 - 3.0 helps to prevent infection by Pseudomonas species.
• Weekly cage changes can prevent the accumulation of commensal organisms that might infect NSG™.
• Following the specific suggestions for NSG™ mice on the Frequently asked questions page can reduce the overall incidence of bacterial disease to less than 1% of mice in a breeding colony.

Breeding considerations for NOD scid gamma (NSG™) immunodeficient mice

NSG™ mice are good breeders if they are maintained under optimal housing conditions that ensure their health status. Breeding characteristics of our NSG™ colony include:

• Litter sizes are large (averaging 8 pups per litter) and frequent (most females deliver 7-8 litters over the course of 6 month breeding period).
• Breeding performance of NSG™ mice improves when breeding pairs or trios are established at the age of 5-6 weeks.
• The breeding lifespan of NSG™ mice is not limited by the development of thymic lymphoma as in other scid strains. Mice can remain productive breeders for as long as one year, and some older breeders can occasionally develop osteosarcomas and mammary carcinomas (Kavirayani and Foreman, 2010). Approximately 90-95% of breeders reach the end of the breeding period at the age of 7-8 months.

Tips for maintaining obese mice

Many strains of obese mice are sensitive to stress. To keep stresses at a minimum, try the following:

• Locate cages with obese mice that have thermoregulatory defects away from cold walls and drafts.
• House polyuric mice at a low density.
• Position cage racks a couple of inches away from a wall that may transmit disturbing vibrations (from equipment such as air exchangers).
• Ensure that food for hyperphagic obese models (especially if the food has been autoclaved) is not too hard (hard-to-chew food may lead to excessive tooth wear and weight loss).
• Place mouse cages away from a door or sink where there may be heavy traffic or loud noises.
• Handle the mice gently, slowly and quietly.
• Change cage bedding at appropriate frequency (from once a week or, if the strain is diabetic and polyuric, as often as necessary).
• Resist the temptation to check on the mice too frequently.
• Handle the mice with gloves (a fresh pair for each cage) or forceps.
• Try using Nestlets or Kimwipes^® for nesting material.
• Check water and food supplies frequently.

Factors to consider when choosing diabetes and obesity mouse models

To choose the most appropriate model(s) for type 2 diabetes and obesity research, many factors need to be considered, including the following:

• Genetic nature of the phenotypes. The diabetic and obesity phenotypes of different models are very dependent on the genetic background of the mice. The diabetic and obesity phenotypes can be either monogenic or polygenic. For example, in some models the diabetes is polygenic and the obesity is monogenic.
• The environmental stimulus for the phenotypes. The diabetic and obesity phenotypes develop spontaneously or are environmentally induced (e.g., by diet, chemicals, surgery or housing conditions).
• Sex in which the phenotype develops. In some models, a phenotype develops in only one sex or much more dramatically in one sex. Additionally, though a phenotype may develop in both sexes, past research may have focused on only one sex. Generally, male mice are more severely affected by type 2 diabetes than female mice, and they are used exclusively in diet-induced diabetes studies.
• Degree of model characterization. Diabetes and obesity are more thoroughly characterized in some models (e.g. C57BL/6J DIO, ob/ob and db/db mutants) than in others.
• Onset. Phenotype onset varies depending on the model and the genetic background.
• Severity. The severity of the phenotype is different for each model, and in the case of monogenic obesity mutants this is highly dependent on the genetic background.
• Associated phenotypes. Associated phenotypes, such as the integrity of the leptin/leptin receptor axis, lifespan, fertility and the development and/or severity of hyperinsulinemia, insulin resistance, glucose intolerance, hyperglycemia, islet atrophy, hypertriglyceridemia, hypercorticism, hyperphagia, thermoregulatory defects and organ-specific diabetic complications, vary among models and inbred strain backgrounds.
• Compound dosing method accepted. In some strains, such as NONcNZO10/LtJ (004456), strong stress responses to oral administration of compounds by gavage produce very high placebo effects.

C57BL/6J diet-induced obesity (DIO) mice: appearance and care

Appearance

Because they're eating extra high-fat chow and often rubbing against their food and/or hydration source during shipping, DIO mice fed a 60% at diet often appear “greasy.” In contrast, control mice have normal looking fur.

Shipment and acclimation

DIO mice are expected to lose weight during shipment. When they arrive, acclimate them to your vivarium and provide an appropriate high-fat diet.

Housing and stress reduction

Reducing stress can help DIO mice perform and gain/maintain the proper weight.

• Reduce the possibility of fighting by keeping mice from different shipping containers separate. 
• Minimize excess noise, vibrations and other disturbances by placing cages away from areas of heavy traffic and maintaining some space between them and walls.
• Prevent food spoilage by completely replacing the food with each cage change (To encourage weight gain, place a small amount of the old food in the bottom of the cage). 
• Avoid using corn cob bedding as mice will eat that bedding and therefore will eat less of the high-fat diet, thereby gaining less weight.
• Handle mice gently, slowly, quietly and as little as possible. 
• Use enrichment materials such as Nylabones and/or soft fibrous nesting.

Most wild–derived inbred mice are hyperactive and require special handling. Problems associated with receiving them and establishing a breeding colony can be reduced by following the guidelines outlined below.

Ordering note:

It is recommended that investigators order more than one pair of breeders because wild-derived mice will sometimes fail to breed with the first mate provided.

Upon arrival

Unlike most common inbred mice, which try to run from light, some wild-derived inbred mice run toward light, presumably associating it with an escape route. So, be careful when removing them from their shipping containers:

• Have a new cage and forceps ready to facilitate picking them up as the shipping box is opened.
   
• Place the entire shipping container in the bottom of a sterilized garbage can, box or other deep container. Escapees are much easier to catch if contained. Alternatively, place an extra cage lid over the opening of the shipping container. As you open the container, slide the lid into place over the opening and maneuver it as needed to create smaller openings from which to remove the mice.
   
• Some wild–derived inbred mice tend to burrow in bedding, making the shipping container appear empty. Verify the number of mice shipped (indicated on the container) with the number received and check the bedding thoroughly for any burrowing mice. 

Colony care

Once wild–derived inbred mice are in your animal facility, inform ALL animal caretakers involved in their care of the following:

Wild-derived inbred mice are more sensitive than common inbred strains to stresses associated with shipping, new surroundings and new handlers. Pairs should be housed in a quiet room, away from areas of heavy traffic and noise. They should be handled as little as possible (this includes moving the entire cage). Animal caretakers should allocate enough time to work slowly and patiently when changing their cages, weaning them, etc. We recommend handling all wild-derived strains with forceps: they do not traumatize the mice as much as do human hands, and, more importantly, do not deposit human scent on newborn pups (human scent may induce a mother to cannibalize her litter). If you must handle the mice directly, use a clean pair of disposable gloves, and change gloves between cages.

Allow 8-12 weeks for a pair of wild-derived mice to settle down and produce a litter. If the pair does not produce after this time, place a different female in the male’s cage. Also note that when males are six to eight weeks old, they may fight. If this becomes a problem, either place the males alone in cages or pair them with females. Fighting is particularly prevalent among mice of the CZECHII/Ei strain and progeny from any crosses involving Mus musculus castaneus.

To decrease the incidence of cannibalism, avoid changing a cage if it contains a litter less than three days old. If cages containing newborns must be changed, the nest and pups should be moved as a unit using a gloved hand.

Placing either Nestlets or Kimwipes® in a cage often encourages nesting, improves overall productivity and provides environmental enrichment.

If, despite all measures taken to improve the environment, a female develops a history of either abandoning or cannibalizing her litters, fostering litters to another female is usually the best alternative. For more information on fostering, go to our general husbandry tips webpage.

Tips on care and handling

Because of hybrid vigor, F1 and F2 hybrid mice resist disease, tolerate the stress of shipping and experimental manipulations, live longer, and, if used as breeders, produce larger litters than do their parents. However, they are not self–perpetuating and must be produced by mating the original parental strains.