Biology of laboratory animals

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Biology of laboratory animals

• Dag Eide
• Norwegian Institute of Public Health

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Aim of the presentation

• Introduce animal models and discuss how suitable
  they may or may not be.
• common criticism of animal experiments
• Introduce how species differences in behavior and
  biology may
• affect your experiment
• give different conclusions about animal welfare

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Experimental biology is about choosing the right
model

• Relevant models gt good science
• limited aim of study
• based upon knowledge about species and strains

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Animal experiments are performed to provide
knowledge about

• The species we study itself
• (veterinary research)
• General biological mechanisms
• Mechanisms in humans

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General biological mechanisms / basic science

• Descriptive studies
• Physiology, pathology, ethology, ecology
• Lack of hypotheses gt quality assessment is hard,
  no experimental design
• Response to an intervention
• Physiology, pathology, behavior
• Experimental design is of paramount importance

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Mechanisms in humans

• Studied in animals
• Where most of the animals are used
• Therapy - preclinical studies
• Toxicology / Safety assessment
• All chemicals have a MSDS
• Anatomy surgery
• Infection immunity
• Tumor development
• Research and diagnosis
• Behavior /psychology

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and the conclusion is..

• Do we extrapolate?
• MSDS LD50 values - a comparison between toxic
  levels in common species may or may not be
  relevant for humans
• Simple models with clear answers should always be
  selected

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4 categories animal models

• 1/ Spontaneous models
• 2/ Induced models
• 3/ Negative models
• 4/ orphan models

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1/ Spontaneous models

• Similar mechanisms in test species and humans

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2/ Induced models

• manipulated animals may be a model
• Behavior - stress - learning
• Is stress analogous human - animal?
• Surgical intervention
• Nerve cuts, ligatures on vessels
• Genetic manipulation
• transgenics, knockouts, knock-ins

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3/ Negative models

• why DOESNT - models
• Why doesnt..
• Dogs get atherosclerosis
• HIV infected chimpanzees get AIDS

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4/ orphan

• Species with characteristics that may reveal
  important biological knowledge
• Pigs have many CD4CD8 T-cells
• Ruminants have lots of gd-T-cells
• leucosis in animals are infectious
• Induced mutations in animals
• Important research field
• MRC (UK) and Jax (US) have large archives
• Pharmaceutical companies

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Source of info
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Knowledge of animal biology is important for
choosing the best model

• Does the model serve its purpose?
• Some characteristics to consider
• Albinism
• behavior
• Gut physiology
• Pathophysiology
• Reproduction
• Pheromones
• Pregnancy

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Rat is the standard test species
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Albinism

• A defect lacks tyrosinase
• Nerve system affected
• Sensitive for light, retinal damage
• Reduced hearing
• histology different
• low P450 activity
• serum protein levels low, affects xenobiotics
• streptomycin, clindamycin, chloroquin,
  klorpromazin, nikotin, pilocarpin, serotonin,
  adrenalin, noradrenalin, dopamin.

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Behavior

• Nocturnal or active during daylight
• Reverse lightning cycle?
• Social ranking
• male fighting?
• Whisker chewers - strain differences
• Social needs - different between species
• Natural behavior or experimental model
• Do rats swim?
• Thigmotropism - sticks to each other
• Animal crowding
• In breeding
• In experiments

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Digestive system

• Teeth
• Stomach - empty or not?
• Fiber content in feed
• Cecum - proc vermiformis
• cecotrophi - coprophagi

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Patophysiology

• Signs of disease
• Fever or hypothermia
• mice, shrews?
• Water bottle control
• Feces control
• rabbits
• Fur and hårballer
• rabbits
• Harderian glands - disease
• rats

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Reproduction

• Estrus cycle
• Pheromones
• Pregnancy

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Estrus cycle

• Spontaneous ovulation (Kt,Ka)
• Seasonal changes
• postpartum estrus - delayed implantation (Ro,Ra)
• Lactation anestrus (Mu, Rat)
• Seminal plugs
• Timing of estrus ?

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Pheromones

• urine (MUP, RUP)
• Females w/o males anestrus (Lee-Boot)
• Introduce males ovulation appears 72hrs
  (Whitten)
• Introduce new male within 24hrs p.c. stops
  implantation (Bruce)

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A genetically altered male mouse that seemingly
cannot distinguish the sex of other mice, a task
normally accomplished in rodents through the
detection of sex-specific pheromones. Without
TRP2, an ion channel necessary for activation of
the vomeronasal organ by pheromones, such mice
display unusual lack of aggression toward other
male mice and initiate mating behavior with both
males and females.
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Pregnancy

• 19-21d (M,R),32d (Ra), 63d (GP,Dog,Cat)
• Pseudo pregnancy
• Placenta different
• Pregnancy check
• hormones? ultrasound? palpation?
• Litter size
• Strain differences large
• 15 days old mice may be separated from mother
• Do not mate too young animals - dead puppies
• mice gt8 weeks old

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The biological clock is evolutionary persistent

• Strain differnces (The Jackson Labs)
• Hvordan vet de at det er vår?

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Strain differences in fecundity
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The fate of drugs in different Species

• affects pharmacology, toxicology, anesthesia

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Plasma proteins in 5 species

• Reigner et al. Hum. Exp. Tox. 12215-2251993

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free Acridin-4- carboxamide in plasma

• Evans et al. J. Pharm. Pharmacol. 4663-671994

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Plasma half life for salicylates

• aspirin etc

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Elimination half life for trimetoprim
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Metabolism

• Temperature dependent
• Species differneces often related to body surface

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Allometric extrapolation

• Watanabe Bois. Risk Analysis 16 741-754 1996
• K. Schmidt-Nielsen Scaling, Cambridge 1984
• Y dosage level
• A species independent scaling coefficient
• bw body weight
• B 1.00 if Y depends upon body weight
• B 0,75 if Y depends upon metabolic rate
• B 0,67 if Y depends upon body surface

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Dose scaling factor

• Related to body weight
• Peters-Volleberg et al. Reg. Tox. Pharmacol.
  20248-2581994

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Last word

• The single most important issue in an experiement
  is
• RELEVANT CONTROLS