Rats/Mice Flashcards
What is the order, suborder, family and genus that rats belong to?
Order: rodentia
Suborder: myomorphia
Family: muridae
Genus: rattus
What is the species of rat seen in private practice? What is the other species of rat?
Rattus norvegicus (norway rat)
Rattus rattus is the other species (black or roof rat)
What is the order, suborder, family and genus that mice belong to?
Order: rodentia
Suborder: myomorphia
Family: muridae
Genus: mus
Species: musculus
Describe some of the obvious external characteristics of rats and mice
Short hair, long naked tails, erect round ears, protruding eyes, pointed snouts, five toes on hind feet (4 on front), variety of coat colors
T/F: rodent incisors grow continuously throughout life
True
- very important that lower and upper incisors match up to prevent overgrowth, and that they have enough solid food/chew teeth to wear teeth down
What are some causes of incisor overgrowth in rodents?
-lack of solid food/chew toys
- broken teeth
-calcium deficiency- leads to wobbly teeth
Leads to malocclusion and overgrowth
What is the treatment for malocclusion of rodent teeth?
Clipping of teeth (nail trimmer, human nail clippers)
- nerves are deep within root
What are brown fat deposits?
-also known as hibernating gland
- used to generate heat during exposure to cold environments
- allows for non-shivering thermogenesis (rodents dont shiver)
T/F: the brain of rodents lacks gyri and sulci
True
What is the issue with prolonged light exposure in rodents (24 hrs a day for several days)?
Can lead to retinal degeneration
- can be avoided by cage rotation in a lab animal setting
What is the function of the harderian gland?
It secretes porphyrin, an iron containing reddish pigment
- stress leads to hypersecretion (red tears) aka chromodacryorrhea
- can see redness in other areas due to grooming
T/F: There is 3 left lung lobes and 1 right lung lobe in rats
F- other way around (1 left, 3 right)
Which animal contains a gall bladder: rats or mice?
Mice have a gall bladder, rats do not
Why can rats not vomit?
The limiting ridge between the glandular and non-glandular stomach blocks the esophagus during contraction of the stomach
-rodenticides contain emetic agents as protective mechanism for animals that vomits
Describe the cecum of rodents
Large- where microbes aid in digestion of cellulose and other plant materials
-in germ free animals, the cecum became enlarged and distended with ingesta leading to the death of these animals early in life
Where does the urethra open in males and females?
Males- in the penis (within genital papilla)
Females: in the genital papilla near the base of the clitoris (not in vagina)
What glands are present in male rodents?
Paired seminal vesicles, coagulating glands, prostate, bulbourethral glands
- secretions from these glands together yields a “sperm plug” or vaginal plug
What is the function of the sperm plug?
Prevents other males from mating female
-also allows researchers to determine day 1 of gestation (day the plug forms)
T/F: rats can pull testicles into abdomen
True- when stressed/cold they can pull testicles up through inguinal rings
What is unique about the reproductive tract of female rodents?
They have a cervix for each uterine horn
Describe the vaginal closure membrane in rodents
A membrane present at birth that disappears prior to sexual maturity
-once open it stays open
-in guinea pigs, it closes back after bred and after parturition
How do you determine the gender of rodents?
Anogenital distance
-shorter in females
-longer in males
-keep your mouth shut until you compare multiple animals
Describe the mammary glands of rats
6 pairs of nipples
-mammary tissue is widely distributed and may extend up onto the lateral and dorsal areas of the abdomen and thorax
-extends up over the shoulders and around the anus
T/F: mammary tumors are easy to remove in rodents
True
-does not require much hemostasis
-however, it is likely that if one forms, multiple will form
How long do rats/mice live?
Rats: 2-3 years
Mice: 1.5-3 years
Describe the behavioral characteristics of rats/mice
-nocturnal animals (for research studying behavior, utilize darkness during working hours)
-males are more aggressive than females
-group housed females rarely fight (prefer cagemates)
Mice
- pheromones plat a major role in marking territory and reproduction
-social dominance may be manifested by “barbering” (excessive grooming/nibbling)? more likely a form of OCD (trichotillomania) that can be treated with N acetylcysteine
How should you feed a rat/mouse?
-feed and water should be available ad libitum
-adult rats eat 5g/100g BW per day, adult mice ear 1.2/10 g BW per day
-measuring feed consumption is useful for assessing animal health and determining dose received for toxicology studies
Why is mash feed not recommended for rodents?
-can lead to incisor overgrowth
-animals may dig food out of feeder making measuring consumption difficult
Can be used in research if adding antibiotics/drugs as pelleting destroys some compounds due to heat and pressure
What can obesity in rodents lead to?
Cardiovascular problems, diabetes, joint problems, shortened lifespan
-caloric restricted diet can increase the lifespan
What are the main causes of PUPD in rodents?
Diabetes and kidney disease
Describe the estrous cycle of rats/mice
5 day estrus cycle with heat occurring at day 3
-can determine stage of cycle with vaginal lavage/cytology or a vaginal impedance meter
What are the 2 types of natural mating/breeding in rodents?
Monogamous pairing/breeding: one male and one female, more animals (males) needed, more costly for caging and husbandry
Harem mating/breeding: one male and 2-4 females, fewer males needed, more efficient use of males, more economical
What is the main sign of estrus in rodents?
Lordosis when pressure is placed on the hindquarters
In which species is the sperm plug more adherent and less likely to fall out?
Mice
- can also look for presence of sperm using an otoscope into the vagina or perform vaginal lavage
What is unique about the appearance of rodent sperm?
Hooked heads
How long is gestation in rats and mice?
Rats: 21-23 days
Mice: 18-21 days
Describe parturition in rats/mice
-periodic stretching and extension of the hindlegs signals impending parturition
-for delivery, females stand in a semi-crouched position
-fetuses are delivered either head first or breech
-female usually eats placenta then turns attention to pups
-delivery of all pups may take 1-4 h (do not disturb them or they will take longer)
What is the normal litter size in rodents?
Smallest in the 1st litter and increases in subsequent litters
-declines towards the end of the reproductive lifespan
-smaller in inbred strains
When does weaning occur in rodents?
21 days
Describe the maturation of rodent neonates
-born hairless, blind and toothless
-they double their body weight in 5 days
-they develop a fine lanugo hair around 7 days
-their hair coat is developed by 9-10 days
-they start gnawing by 9 days
-their eyes open around 12-13 days
-pups are weaned at 21-28 days
What are some considerations when handling rats/mice?
Rats
-Tail restraint is ok for brief periods, such as when moving from one cage to another but must grasp base of tail to avoid degloving injury
- thoracic encirclement is ideal: grasp over shoulders, place thumb and forefinger behind rats elbows and make forelimbs cross and restrain tail
Mice
- Tail restraint is ok for brief periods when grasped near base of tail (mouse can climb tail and bite handler)
- scruff hold is also ok- skin between ears and as far down back as you can
can also use rigid plastic containers, decapitone
What is the lee-boot effect? the whitten effect? the bruce effect?
Lee-boot: grouping of females in absence of male will lead to estrus suppression and decreased incidence of pseudopregnancy
Whitten: exposure of females to a strange male will result in induction of estrus- can be used for synchronization
Bruce: before ova implants in uterus, if female is exposed to strange male the pregnancy will be spontaneously terminated
Where should intramuscular injections be given in rodents? subcutaneous? IP or IV?
IM- hindleg
SC- scruff over neck
IP- into abdomen (inject along midline of top of the lower 2 quadrants to avoid the bladder, dont use overly long needles, dont insert needle to its hub, insert needle at shallow angle and never reuse needles)
IV-tail vein
What are some general rules of thumb regarding injections in rodents?
-warm any replacement fluids given SQ or IP
-dilute potentially irritating drugs before giving IP
-avoid giving ketamine IM
What are the options for blood collection in rats and mice?
Facial vein- wont be sterile
Lateral saphenous
Submandibular
Lateral tail vein
What is the limit for safe volume of blood to be collected in a mouse?
<0.2 mL (0.1 mL serum), 3 mL ok for rats
-only 2 mL total blood volume
Wait 7-10 days in between blood collections
What is gavage?
- a passage of a special needle or tube into the stomach via the mouth (measure from corner of the mouth up until the last rib)
-ensures delivery of a known amount of material
-can be used for treatment with compounds that animals will not drink due to taste
What are the main options used for anesthesia in rodents?
Isoflurane
- 3-4% for induction, 2% for maintenance
- 3 L/min oxygen flow rate
- can induce in induction chamber or convert a Tupperware
- use non rebreathing system
Injectable
- IM ketamine may cause muscle necrosis and apresis
- injectable anesthetics should be given IP
- injectable anesthetics should be diluted with sterile saline to reduce peritoneal irritation
How can you assess anesthetic depth?
-check reflexes (be aware that animal may still be anesthetized with intact spinal reflexes, palpebral reflex is a good thing to use)
-assess muscle tone
-depth and rate of breathing
-HR and BP
What is a unique option used for post op pain relief in rodents?
Buprenorphine jello
What are the different approaches for ovariectomy in rats?
-ventral midline
-dorsal lateral approach
What is the problem with cedar chip bedding?
Gives off some aromatic compounds that can affect cytochrome P450 altering the mechanism of drug breakdown
- masks the smell of ammonia which can be causing problems in lungs of animals (damage can be done at 5 ppm, humans detect smell at 25 ppm)
Describe the ideal characteristics of a bedding?
-should keep animals dry between changeouts
-should not cause injury to the animal
-should not lead the animal to ingest it
-should not have properties that would interfere with the research
Corncob bedding- may be contaminated with chemicals
Sawdust may be inhaled
Tech board- used mainly for rabbits
Course, fine and hardwood chips are good options
What are some of the main clinical problems that occur in rats?
Respiratory disease, anorexia, lethargy, overgrown teeth, tumors
-mites, heart disease, kidney disease, obesity, pododermatitis
What is ectoromelia or mouse pox?
A viral infection in rodents that is so painful and irritating that animals will gnaw their own limbs off
What is the type of tumor that most commonly results in mammary masses in rodents?
Fibroadenoma
-inbred strains are at higher risk
What are the diseases that are most commonly responsible for stunting/runting or death of pups due to effects on immune system and GI tract?
- Mouse parvovirus type 1
- mouse rotavirus
-reovirus type 3
Diagnose with serological testing and treat with fluids and supportive care
What respiratory diseases can cause stunting/runting or death of pups, pneumonia, or death in immunocompromised mice?
Pneumonia virus of mice
-sendai virus
Diagnose with serological testing
What are some bacterial diseases of the digestive system in rodents?
Helicobacter, citrobacter rodenticum (causes diarrhea and prolapse of rectum–> quick death), clostridium piliforme (Tyzzers- will see white spots in liver), salmonellosis (can see white spots in liver), pseudomonas aeruginosa (infects inner ear)
Tyzzers and pseudomonas both zoonotic
