The document discusses the biology and senses of laboratory rodents, specifically rats and mice. It provides details on their use in research, anatomy, physiology, senses such as vision, hearing and smell, vocalizations, and whiskers. Rats and mice are commonly used as they are small, easy to handle, low cost to maintain, and have a similar genetics to humans. Their vision is poor but they have acute hearing up to 90kHz and strong sense of smell used for communication. The document is a presentation on rodent biology for researchers.

1. Dr. Vasanthi Balan, M. V. Sc.
CLAS (FELASA)
Assistant Professor
TANUVAS
Chennai
BIOLOGY OF
RODENTS (RATS &
MICE)

2. FLOW OF TALK
❖ Introduction & use of animals for different
areas of research
❖ History of animal experimentation
❖ Biology of laboratory animals
(comparative anatomy, physiology)
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3. ANIMAL EXPERIMENTATION
90%
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4. WHY ?
❖Small & easy to handle
❖Short life span
❖Require relatively inexpensive care - small housing
space and economic to maintain
❖Reproduce quickly (short gestation period ) and
❖Have a high genetic similarity to humans
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5. RODENTS
• Latin rodere - “to gnaw”
• Mammals – order Rodentia – single pair of continuous
growing incisor teeth – both jaws
• About 40% mammal sp. – rodents (2277 sp)
• Well known examples are mice, rat, guinea pig,
hamster, gerbils etc.
• Herbivores/ omnivores
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6. History of animal experimentation
Which is the first rodent species to be used for scientific purposes?
Lady Abbie Lathrop with a mouse
Dr. Halsey J. Bagg developer of BALB/c
Wistar rat (1828)
Sourchttps://www.smithsonianmag.com/science-nature/history-breeding-mice-science-
leads-back-woman-barn-180968441/e
Sourcehttps://en.wikipedia.org/wiki/Rat-baiting
Sourcehttps://hiddencityphila.org/
https://www.findagrave.com/memorial/37246551/halsey-joseph-bagg
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7. Task
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8. Source http://www.ratbehavior.org/QuizRatOrMouse.htm

10. http://www.ratbehavior.org/RatsMice.htm#TellApart
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13. SUPPLIERS AND REPOSITORIES
Most widely used mouse strains :- C57BL/6 mice, BALB/c mice
Rat strain:- Sprague-Dawley & Wistar (Labome survey, 2018)
Suppliers of animals
• The Jackson Laboratory,
• Charles River Laboratories,
• Taconic Farms and
• Harlan Laboratories.
WEB RESOURCES
• Where to look for a specific mouse strain?
• International Mouse Strain Resource (IMSR): collaboration
of many international mouse repositories, containing
information for 51,503 strains and 217,063 cell lines as of
Nov 2018.
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14. SALIENT BIOLOGICAL FEATURES
MOUSE
•Most commonly used among rodents
• Use tail & brown fat - thermoregulation
(young ones)
•No sweat glands ….only in foot pad??
•Incisor teeth - open rooted (hypsodontic)
grow continuously throughout life
•5 pairs of mammary gland
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15. RAT
• Dental formula: 2 (incisors 1/1 canines % premolars % molars 3/3) =
16.
• Incisors grow continuously throughout life (hypsodontic)
• No tonsil or gallbladder or receptors for water and taste
• Diffuse pancreas - diabetic model??
• Coprophagic - not ideal - nutritional studies.
• 6 pairs of mammary gland
Malocclusion
Sourcehttp://www.lasaindia.in/journal/artvolume.php?v
olno=01&&full=14&&page=6
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16. SALIENT BIOLOGICAL FEATURES - RAT
• Body temperature regulation -Tail vein & hibernating gland
(brown fat) - No sweat glands.
• Do not vomit - strong cardio-esophageal sphincter & lack
vomiting centre
• Alternatives to vomiting
• Adaptive response
• Nausea
• Avoidance
• Harderian gland - Porphyrin secretion
• Hypersecretion-red staining around eyes &
nose.
Red tears/ Chromodacryorrhea - sickness/
stress Sohttps://www.omicsonline.org/articles-images/2157-
7099-S5-006-g001.htmlurce
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17. NATURE OF RATS AND MICE
•Intelligent – docile, easily trained
(exceptions: strains /mishandling –
nervous/aggressive)
•Curious & investigative – burrower
•Groom & clean
•Social animals – colonies - Male rats, do not
fight – group housing preferred else stress
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18. SENSES OF RATS AND MICE
• Nocturnal - poor vision- acute sense of hearing & smell - recognition
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19. VISION
• Nocturnal - retina dominated by
rods (dim light vision)
• Cones comprise two spectral
types
• Diurnals- dichromatic vision
with more cones blue UV cones
and green type
• Dim red light – out of the
visible spectrum – insensitive
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20. • Would artificial light could impair communication
and/or distort vision ?
• Easy to train rats to behaviorally differentiate
brightness, but difficult to train them to
behaviorally differentiate colors (Jacobs et al.
2011)
• Vision of Albino rats ?
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VISION contd….

21. WHAT DO RATS SEE ?
normal human vision
Normally-pigmented rats have blurry
dichromatic vision with low color
saturation
Albino rats may see a very blurry, light-
flooded world
On a bright day, albino rats may be
completely dazzled
Source: http://www.ratbehavior.org/perception.htm
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22. OLFACTION
• 1% of rat’s genes code for olfaction
• 500-1000 olfactory receptors + vomeronasal organ
• Rodents use a variety of specialized scent glands, together
with urine, faeces and vaginal secretions for olfactory
communication
https://link.springer.com/referenceworkentry/10.1007%2F978-
1-4614-1997-6_29
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23. • Identification of pups
• Home cage: familiar vs. unfamiliar animals (differentiate strangers
from members of one's own colony)
• Social status (dominant from subordinate individuals)
• Reproductive status: if the urine is from a female, rats can determine
whether she is receptive to mating, pregnant, or lactating.
• Sexual maturity (juvenile vs. sexually mature adult)
• Individual recognition
• Stress level
• Cleaning of cages?
OLFACTION contd…..
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24. HEARING
Rat world - high frequency sound which we cannot hear
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25. WHAT DO RATS HEAR?
•Rats can hear ULTRASOUND : Range of the rat's
hearing is around 200 Hz to 80 or 90 kHz - low
frequency vibrations transmitted via air and
seismically through the ground
•Human finger movements makes a scratchy sound in
the ultrasonic range.
•Wire cages make a lot of ultrasonic noise in addition
to audible noise when rats move around in them.
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26. SOUNDS OF RAT’S WORLD
❖Rat world low frequency sound which we cannot
hear - perceptual difference we should not forget
❖AVOIDI low frequency sounds in animal houses -
sources of air or seismic waves in the laboratory
(e.g. construction work, lifts, cages or racks being
moved or knocked, items being dropped)
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27. RAT’S VOCALIZATION
❖ Rats make ultrasounds
❖ Emit long 20 kHz vocalizations – when ?
• unhappy or stressed
• adult or juvenile is defeated socially
• sees a predator
• experiences pain or anticipation of pain or
• when an untamed rat is handled
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28. RAT’S VOCALIZATION
❖Emit 30-50 kHz range when ?
➢ infants produce very high pitched distress calls -
maternal care such as retrieving the infants to the
nest
❖Emit short, high-pitched calls under positive contexts
when ?
➢Adults and juveniles during rough and tumble play
and in anticipation of feeding
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29. RAT’S VOCALIZATION
❖ Male and female rats also call in a sexual context.
Before copulation, males and females emit such calls
as they approach and sniff each other. Female calling
also solicits male sexual behavior.
❖ Provide opportunity to build tunnel systems for them
to communicate effectively
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30. ROLE OF WHISKERS ?
❖Whiskers resonate (like the strings of a harp) - certain frequencies.
• Longer whiskers vibrate at lower frequencies
• Shorter whiskers vibrate at higher frequencies.
❖Rat has short whiskers near the nose and long ones further back,
❖Array of whiskers creates an orderly map of frequencies on its face
❖Whisker vibration – explains extreme sensitivity of rat's sense of
whisker-touch. (et al. 2013).
❖ Rats can make fine distinctions between different textures,
https://www.cell.com/trends/neurosciences/comments/S0166-2236(08)00264-6
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32. References
➢ S. Andrew Hires,1 Alexander L. Efros,2 and Karel Svobodo (2013)
Whisker Dynamics Underlying Tactile Exploration, The Journal
of neuroscience, 33(23):9576 –9591
➢ Barnett, A. (2002). The Story of Rats: Their Impact on Us,
and Our Impact on Them. Allen & Unwin, Crows Nest,
NSW. ISBN 186508-519-7
➢ http://www.ratbehavior.org/
➢ https://en.wikipedia.org/