Module 3: Basic biology

Question 1

Describe the oestrous cycle/ovarian cycle of rodents and describe how pheromones can affect the ovarian cycle and pregnancy.

Answer 1

o initial phase: rising levels of estrogen lead to growth & development of follicles + endometrium thickens to prepare for implantation
o Estrus („heat”) is the period of fertility (estrogen levels peak). Females display behaviors, like vocalizations, scent marking & lordosis (arching of the back).
o After estrus, the corpus luteum forms from the remaining follicular tissue. The corpus luteum produces progesterone, which helps maintain the endometrial lining in preparation for pregnancy. If fertilization does not occur, corpus luteum regresses, leading to a decrease in progesterone levels

Four physiological effects in mice (both Vandenberg and Bruce effects are also seen in rats):
- Lee-boot effect: female mouse housed without the scent from a male –> cycle stops and the female mice remain anoestrus
- Whitten effect: anostral female mice are exposed to pheromones from male mice –> their oestrus cycle restarts
- Bruce effect: a pregnant female exposed to scent stimulation from an unfamilliar male –> insufficient impantation of the fertilised egg/abortion
- Vandenberg effect: an intact male mouse is nearby –> young female mice becomes sexually mature more quickly

Question 2

Describe the rodents’ sense of hearing, and discuss the importance of being aware of how this sense differ between rodents and humans.

Answer 2

• highly developed: can range into ultresonic frequencies (starting at 20 kHz)
• humans are not able to hear ultrasounds, and are thereby not able to hear a lot of the communication nor the sounds that may stress them out
• some rodent communication are however audible to humans, e.g., agonistic encounters, distress/fear
• echolocation: rats use echolocation for navigating in the dark - they seem to emit very fast clicks (like bats) and use the reflection to navigate (not sure mice does the same)

Question 3

Discuss what temperature is optimal for mice, how the preference for a specific temperature can be established and how mice can thermoregulate

Answer 3

• In labs, mice are housed at 20-24 degrees C
• The thermo-neutral zone: 26-34 degrees C
• Lower critical temp for single housed mouse: 30 degrees C
• It is seen as a mild chronic stressor for the mice to be housed below 30 degree C
• an experiment showed that both sexes preferred warmer temps only for maintenance and inactive behavior
• it may not be possible to find a single preferred temp for all mice (it is therefore important to provide the opportunity to thermoregulate by nesting)

Question 4

Give examples of stressors (i.e. any adverse stimulus; physical, mental, or emotional, internal or external, that tends to disturb the homeostasis of an organism) and discuss the physiological consequences and manifestations of stress in rodents.

Answer 4

Examples:
- lack of food
- tilted cage
- lack of nest building material
- social deprivation

Physiological concequences:
- SAM –> fight or flight responses, quick
- HPA –> slower
- activation of parasympathetic system: freeze

Behavioral manifestations:
- stereotypies: a repetitive, invariant behavior pattern with no obvious goal/function

Question 5

Discuss how different handling methods of mice can affect animal welfare and animal behaviour.

Answer 5

• Gentle Handling:
  o cupping mice in hand or using tunnels for transfer, are less stressful
  o leads to less fear-related behaviors & reduces stress responses.
  o increases exploratory behavior & sociability
  Tunnel handling:
• best way
• less stressful
• lifting them by the tail has proven both painful and more stressful
• Invasive or Rough Handling:
  o tail handling or forceful grasping, can cause physical discomfort & distress.
  o This may lead to injuries, pain & fear responses
  o can result in chronic stress, affecting behavior and physiological health.
  o can bias experimental results & affects emotional state of staff

Question 6

Describe the rodents’ sense of vision, and discuss the importance of being aware of how this sense differ between rodents and humans.

Answer 6

• Most likely have a low acuity of vision (surroundings may very well be quite blurry)
• Di-chromatic (only have two photoreceptors - UV and green-ish)
• rodents have fluorenscent urine –> UV vision may be used to communicate by urine markings
• It may be important to provide rodents with UV-light to avoid stress
• red light: rodents lack the photoreceptors necessary for red light perception, but studies indicate that the red light are still important for the animals, as they may influence the circadian rhythms and thereby their physiology

Question 7

Describe the rodents’ sense olfaction, and discuss the importance of being aware of how this sense differ between rodents and humans.

Answer 7

• very important for rodents, as they are nocturnal and burrowing by nature
• important for communication (reproduction, hierachy) –> pheromones: can be found in e.g., urine, feces and saliva
• male mice: in nature, male mice are extremely territorial, whereas in labs, male mice housed in groups will form a hierarchy (they will sometimes however still fight, even to death)
• cage cleaning: intermale aggression may increase significantly unless the cage is completely cleaned and only nesting material is transferred to the clean cage (all bedding must be changed, and no urine or feces should be in the transferred nesting materiel)
• in inbred mice, their urine smell almost identical, which may lead to unstable hiearchies, or that subordinate males may try an avoid urinating
• ‘Lee-Boot effect’: females housed without male scent –> oestrus cycle stops
• ‘Whitten effect’: female mice that are anoestrus due to the Lee-Boot effect are exposed to male scent –> 75 % of females will be pregnant when housed with the male mice after 3 days of exposure to the scent
• ‘Bruce effetc’: insufficient implantation of the fertilized egg/abortion if a pregnant female is exposed to the scent of another male
• ‘Wandenberg effect’: young female mice will be sexually mature earlier when exposed to male pheromones