Laboratory Animal Medicine: Rats & Mice

Flashcards for VET 215 - Laboratory Animal Medicine: Rats & Mice

Rattus norvegicus

Laboratory rat

Common name for Rattus norvegicus

Brown or Norway Rat

Order of Rattus norvegicus

Rodentia

Family of Rattus norvegicus

Muridae

Common name of Mus musculus

Swiss albino mouse or house mouse

Mus musculus

Laboratory mouse

Peromyscus maniculatus

• Deer mouse

• Most common native North American mammal

Stock

A rat/mouse that has been randomly bred, also referred to as outbred.

Strain

a rat/mouse that has been inbred (when at least 20 generations of brother-sister or parent-offspring mating has occurred).

Wistar (WI)

Albino rat stock with tail usually shorter than body

Sprague Dawley (SD)

Albino rat stock that grows faster than Wistar with longer tail

Long-Evans (LE)

Hooded rat stock that is smaller in size

Common outbred stocks

Swiss, Swiss-Webster, CD-1,CF1 SKH1(hairless)

BALB/c

albino mouse strain

C3H

dark brown mouse strain with rings of yellow at tip of fur

C57BL/6

black mouse strain

DBA/2

gray (oldest inbred strain) mouse strain

Axenic (germ free)

no microflora

Gnotobiotic

known microflora

SPF

free of specific pathogens

Conventional

undefined microflora

F1 Hybrid

first offspring of mating's between two different inbred strains.

Transgenic

an animal that results from the introduction of genetic material (DNA) from one animal into the fertilized egg of a different animal

Athymic (nude)

naturally occurring genetic defect in which the animal is hairless and has a deficiency in its immune system

Knockout

an animal that results from the removal of one or more genes from the fertilized egg. Used to study disease associated w/defective genes

mischief

A group of rats

Barbering

chewing of hair by cage mates

Environmental enrichment

reduces boredom and contributes to the animal’s well being

Direct Bedding

Rodents are burrowers (create nests) by nature, and it is important that they have material that is nontoxic, absorbent and comfortable

Indirect Bedding

• Toxicology studies: Eliminates the ingestion of bedding

• Diabetes studies: Prevents animals from lying in urine-soaked bedding  

• Special diet studies: Allows for the collection of “wasted food”

• Survival surgery: Bedding won’t contaminate surgical sites    

• Metabolic studies: Allows for collection of feces & urine 

Husbandry

• Food & Water: checked daily

• Humidity: 40-60%

• Ventilation changes: 10-15/hr.

• Room temperature:  65-75° F

• Light: 12-14 hrs. (12 stock/14 breeders)

Nutrition

• Nutritionally complete (balanced) diets are produced by lab animal vendors (at least14% protein, 4-5% fat)

• Shelf life of commercial rat chow is 6 months from milling date

• Omnivores- can eat fresh fruit and vegetables

Rats Food and Water Consumption

• Food consumption – 5g/100g weight/day

  • Around 15-25g/day   

• Water consumption– 13-20mL/100g weight/day

  • Around 30-80 mL/day

Mice Food and Water Consumption

• Food consumption 5g/100g weight/day

  • Around 3-5g/day

• Water consumption 15 mL/100g weight/day

  • Around 4-7mL/day

Rats Physiological Data

• Body temp:     99-100.0 F

• Heart rate:       300-500 bpm

• Respiratory rate:   70-150 bpm

• Weight:

  • Male 267 – 500g

  • Female 225 –325g

• Life span:       2.5 – 3.5 years

Mice Physiological Data

• Body temp:             98-99.0 F

• Heart rate:      400 – 700 BPM

• Respiratory rate:   90 – 220 BPM

• Weight: 

  • Male 20 – 40 g

  • Female 22 – 63 g

• Life span:      1 – 3 years

Well developed sense of smell

used to detect pheromones used in social interactions

Poor vision

unable to detect color. Red light is used to observe during dark cycle.

Acute hearing

makes them sensitive to ultrasounds and high- pitched noises causing stress and can cause cannibalism of pups by their dam.

Harderian gland

type of lacrimal gland, produces a red secretion containing Porphyrin “red tears”.

During times of stress or illness it may increase in red tear production causing a  condition called

chromodacryorrhea.

Dental formula

2 ( I 1/1, C 0/0, P 0/0, M 3/3) 16 teeth

hypsodontic

• Incisors are open rooted and grow continuously

• the molars do not

Mice have an

orbital sinus- a space adjacent to the eyes that communicates with the nasal cavity.

Rats have an

orbital plexus- a network of blood vessels around the eye that also communicates with the nasal cavity.

Digestion

• Glandular stomach and non-glandular forestomach are separated by a fold/ridge called a limiting ridge.  This ridge covers the entrance to the esophagus making it impossible for Rats/Mice to vomit.

• Mice have a gall bladder (rats do not)

• Have a large store of brown fat, also called hibernation tissue (located around neck and between shoulders)

• 10x the energy storage of other fat

Coprophagic

eat own feces to recycle vitamins

Breeding and Reproductive Data

Female comes into “heat” 24 hrs. after parturition

postpartum estrus in which they can be bred again

Monogamous

one male, one female

Polygamous (harem)

one male to 2-6 females

Bruce effect (only in mice)

Pregnant female exposed to strange male within 4 days of breeding will often result in abortion, failure of implantation, or pseudopregnancy.

Lee-Boot effect

• Estrous cycle of females caged together is suppressed (anestrus)

• Especially true if females are overcrowded

Whitten effect

• Synchronization of estrus

• Induced by introduction of male or smell of male (urine)

• Within 72 hr. 40%-50% will be in estrus after introduction of male

• (Lee-Boot and Whitten effects are utilized to “time-mate” rats & mice)

Vaginal (copulatory) plug

• Straw colored mucoid plug formed from secretions in the semen of the male rodent.

• Plug lasts 12-24hrs.

altricial

Newborns are pink, hairless, deaf, and blind

Milk spot

white spot visible on the left side of the abdomen through the pink skin

Retroorbital plexus

A network of blood vessels located behind the eye, commonly used in laboratory animals for blood collection. RATS

Retroorbital sinus

An anatomical cavity that contains the retroorbital plexus and is used to access blood vessels behind the eye in laboratory animals. MICE

Retro-orbital Collection

A microhematocrit tube is placed at the medial canthus.  Slight pressure is applied while “rotating” the microhematocrit tube.  Blood will fill the tube by capillary action.

Blood Collection
How much blood can I take?

• 10% of the circulating blood volume can be taken on a single collection from a normal, healthy animal with no adverse affect.

• The mouse has 80 ml/kg circulating blood

• The rat’s total blood volume is 20-40 mL (Single sample collection can be no greater than 2-3 ml in a rat)

• Exsanguination of a rat will occur with 8-12 mLs collected

• For repeat bleeds at shorter intervals a maximum of 1% of the animals circulating blood can be taken every 24 hrs.

• Example:

          (80 X .04 kg X 1%) = 0.03 ml

• Example:

          How much blood can safely be taken from a 40 gm mouse?      Hint:  1000g = 1 kg

         (80 X .04 kg X 10%) = 0.32 ml

Injectable Drug Administration

• Subcutaneous- Easy to perform, can be done by one person

• Intramuscular- Difficult due to small muscle mass, can only administer less that 0.05mL can be irritating and cause self- mutilation

• Intravenous- Not commonly performed, requires anesthesia (22 gauge or smaller needle)

• Intraperitoneal- Well tolerated, can be done by one person, allows for large volumes of medication to be injected. The right caudal quadrant is used (23 gauge or smaller needle)

Subcutaneous Injection

• In loose skin over the back 23-gauge needle or smaller

• 5-8 ml max vol. in a rat, less than 1 mL in mice.

Intramuscular Injection

• small muscle mass

• 0.3 ml max vol. in rat

• 0.05 ml max vol. in mice

• 25 g needle

• Irritating drugs may cause self mutilation

Intraperitoneal Injection

• Tilt head downward at a 30-degree angle, enter lower abdomen, just off the midline.

• Well tolerated, preferred over IM

• 23 g needle or smaller

• 5-10 ml max vol. in a rat

• 1 mL max vol. in mice

Intravenous Injection

• not practical, small veins

• Researchers may prefer to place catheter in jugular

• Lateral tail vein

• 0.5 ml max and 23g needle (in a rat)

Chromodacryorrhea

secretion of porphyrin

Ringtail

housing suckling or preweaned rats at <30% relative humidity (optimum 50%)

Pododermatitis (bumblefoot)

Caused by improper housing (bedding)

Cholesteatoma

A mass of keratinizing squamous epithelium in the middle ear

Murine respiratory mycoplasmosis (MRM)

• Caused by Mycoplasma pulmonis – most common & important respiratory pathogen of rats

• less likely to affect mice unless concurrent infection present or immunocompromised

• Mice can develop a fatal pneumonia if they develop MRM while affected by the Sendai virus or Cilia-associated respiratory(CAR) bacilli

Tyzzer’s Disease

• Caused by Clostridium piliforme (forms resistant spores hard to eradicate)

• Reported in nearly all lab animal species

• Poor sanitation and over crowding increase susceptibility

• Weanlings and immunosuppressed animals primarily affected

• Transmitted by fecal-oral route

Hanta virus

• Wild rodent serve as reservoir hosts

• No clinical signs

• Virus is shed in feces, urine, and saliva

• Known as hemorrhagic fever w/renal syndrome (HFRS) in humans

Sialodacryoadenitis Virus (SDA)

• Most significant viral disease of rats

• Infections are self-limiting

• Highly contagious short 2-day incubation period

• Transmitted through aerosol or direct contact from respiratory secretions

• Causes inflammation of the salivary & harderian glands, rhinitis, cervical swelling, photophobia, chromadacryorrhea

• Keratoconjunctivitis  is the only clinical sign in some outbreaks

• Signs regress in 10-14 days

• Long lasting immunity once recovered

Sendai virus

• Most significant viral disease of rats

• Highly contagious

• Causes viral respiratory disease

• Clinical signs:  weight loss, dyspnea, teeth chattering

• High mortality rates in young mice

Ectromelia (Mousepox)

Euthanasia

1. 70% CO2 in a prefilled chamber

2. Overdose of a barbiturate solution IP

3. Cervical dislocation

Pinworms

• Syphacia muris  (most common)

• S. obvelata

• Aspicularis tetraptera

• Detection:  cellophane tape prep, fecal exam

• Tx:  Ivermectin, fenbendazole, piperazine