Ming, I often observe various unusual behaviors in mice during breeding. What could be causing these?

 

Laboratory mice sometimes exhibit abnormal behaviors, which may indicate underlying health issues, environmental stress, or effects of experimental interventions. Let's take a detailed look at these "strange" behaviors in research mice today.

 

Common Abnormal Behaviors in Mice
 

1. Circling / Hyperactivity

● Presentation: Mice continuously circle or flip inside the cage, showing hyperactivity during movement.

● Potential Causes: May be due to genetic factors, infection, transport stress, etc.

● Recommended Measures:

○ Genetic Factors: If a genetic issue is suspected, check the mouse's genetic background and avoid using strains with known genetic defects.

○ Infection: Conduct a comprehensive health check, including blood tests and pathogen screening. Treat infections promptly.

○ Transport Stress: Provide mice with adequate recovery time after transport, ensuring a comfortable environment with sufficient food and water.

 

2. Paralysis

● Presentation: Inability to move (hemiplegia / paralysis below the thoracic spine). Note: Differentiate from weakness or loss of consciousness.

● Potential Causes: Paralysis is typically caused by spinal nerve damage, which can result from surgical procedures, disease, or injury.

● Recommended Measures: Strictly adhere to surgical protocols to avoid spinal nerve injury. Provide a safe environment to prevent physical trauma.

 

3. Macrocephaly (Large Head)

● Presentation: Mice display a large, round head with a thin, weak body, appearing lethargic. Symptoms become more pronounced with age, accompanied by increased lethargy.

 (Image source: Laboratory Animal Science Department, Tianjin Medical University)

● Potential Causes: A large head is usually caused by congenital hydrocephalus, which is associated with certain mutations and transgenes.

● Recommended Measures: There is currently no effective treatment. It is recommended to cull affected mice promptly to prevent breeding.
 

4. Head Tilt / Torticollis

● Presentation: Head tilted to one side; mice circle rapidly when lifted by the tail vertically; weight loss occurs, potentially leading to death in severe cases.

● Potential Causes:

○ Middle/Inner Ear Infection: Common pathogens include Pseudomonas aeruginosa, Mycoplasma, Streptobacillus moniliformis, and Burkholderia gladioli.

○ Neurological Issues: Spontaneous unilateral cerebral infarction, brain tumors, etc.

○ Genetic Problems.

● Recommended Measures: Administer antibiotic treatment; improve housing conditions to reduce infection risk. Conduct a comprehensive neurological examination; imaging may be necessary. Avoid using strains with genetic defects.

 

5. Overgrown Teeth (Malocclusion)

● Presentation: Malocclusion makes eating and drinking difficult, leading to progressive weight loss, poor growth, and worsening tooth misalignment.
 

(Image source: Laboratory Animal Science Department, Tianjin Medical University)

● Potential Causes: Mice have continuously growing teeth. Malocclusion occurs when upper and lower incisors are misaligned, preventing proper wear. Dental malformations can be due to congenital jaw structure defects, impaired tooth development, or oral trauma.

● Recommended Measures: Regular trimming of incisors provides short-term relief. Mice exhibiting malocclusion upon caging can be culled to prevent breeding.

 

6. Ulcerative Dermatitis

● Presentation: Often occurs on the neck; intense itching leads to self-trauma from scratching, progressing from epidermal abrasions to deep ulcers.

● Potential Causes: According to official statistics, mice with a C57BL/6J genetic background have an overall incidence of ulcerative dermatitis around 4.1%. The pathogenesis is not fully understood and is influenced by multiple factors including environment, diet, sex, genetics, and compulsive disorders.

● Recommended Measures: Dietary supplements like Vitamin E can alleviate symptoms. Maintain a clean, dry environment to reduce skin infection risk.

 

7. Hunched Posture

● Presentation: Abdomen arched upward, back hair erect, head lowered onto forepaws, often remaining still and quiet.

● Potential Causes: Pain (abdominal or elsewhere), infectious or other diseases, respiratory distress, etc.

● Recommended Measures: Perform a thorough health check to identify and treat the source of pain. Provide targeted treatment for infectious or other diseases.

 

8. Stereotypic Behavior

● Presentation: Repetitive, rhythmic movements with no apparent purpose. Examples include persistent circling along the cage perimeter or repetitive grooming/scratching of a specific body part.

● Potential Causes: Often due to a barren environment, lack of space, and insufficient stimulation or activity opportunities.

● Recommended Measures:  Enrich the environment: Add toys, tunnels, etc., to the cage and provide more space. Increase stimulation: Periodically change the cage layout to encourage exploration.

 

9. Aggressive Behavior

● Presentation: Frequent and intense fighting.

● Potential Causes: May be due to strong territorial instincts or forced co-housing of mice from different origins or with incompatible temperaments.

● Recommended Measures:  Proper Grouping: Group mice based on origin and temperament to avoid unnecessary conflict. Environmental Adjustment: Provide sufficient space and hiding places to reduce territorial disputes.

 

10. Polydipsia (Excessive Drinking) or Food Refusal

● Presentation: Sudden excessive water consumption or refusal to eat.

● Potential Causes:

○ Polydipsia: Could be disease-related (e.g., polyuria/polydipsia in diabetic models) or due to high ambient temperature, where mice increase water intake for thermoregulation.

○ Food Refusal: May be due to spoiled feed, illness (gastrointestinal disease, infection, or other systemic diseases), or negative effects from experimental procedures on appetite.

● Recommended Measures:  Health Check: Perform a comprehensive examination to identify and treat illness. Environmental Adjustment: Regulate ambient temperature and ensure feed is fresh.

11. Abnormal Sleep Patterns

● Presentation: Excessively long or short sleep duration, frequent awakenings.

● Potential Causes: Disruption of circadian rhythm by noise, light, etc., in the experimental environment; or underlying illnesses (e.g., infections causing discomfort).

● Recommended Measures: Minimize noise and light disturbances; provide a quiet, comfortable sleep environment. Conduct a thorough health check to identify and treat disease.

 

12. Self-Mutilation

● Presentation: Mice may bite their own tail, paws, etc.

● Potential Causes: Often a sign of extreme stress or anxiety, e.g., from overly frequent experimental procedures or major environmental changes.

● Recommended Measures:  Reduce Stressors: Minimize unnecessary experimental handling; provide a comfortable environment. Behavioral Intervention: In some cases, stress-relieving interventions or medications (under veterinary guidance) may be considered.

 

13. Abnormal Social Behavior

● Presentation: Mice normally interact via olfaction, touch, etc. Abnormal behavior includes social avoidance, such as actively躲避ing other mice or consistently hiding in a corner when approached.

● Potential Causes: May result from traumatic experiences or be a side effect of certain experimental drugs, impairing social function.

● Recommended Measures:  Environmental Enrichment: Provide a stimulating social environment with opportunities for interaction. Drug Adjustment: If drug effects are suspected, consider adjusting dosage or changing the drug under professional guidance.

 

References:

[1] Lin Na, Li Jianhong, Bao Jun. Abnormal behaviors in mice and their transgenerational inheritance. Acta Ecologica Sinica, 2007, 27(8): 3520-3526.

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