How does a mouse tolerate cold? - briefly
Mice maintain body temperature in low ambient temperatures by rapidly increasing metabolic heat production through brown adipose tissue activation and shivering, while peripheral vasoconstriction reduces heat loss. They also seek insulated microhabitats and huddle to conserve warmth.
How does a mouse tolerate cold? - in detail
Mice maintain core temperature through a combination of physiological and behavioral strategies that become active when ambient temperature falls below the thermoneutral zone.
Thermogenic processes include:
- Activation of brown adipose tissue, where uncoupling protein 1 (UCP1) dissipates the proton gradient to generate heat without ATP synthesis.
- Shivering of skeletal muscle fibers, producing rapid contractions that raise metabolic heat output.
- Up‑regulation of mitochondrial uncoupling proteins (UCP2, UCP3) in white adipose tissue, providing a secondary source of non‑shivering thermogenesis.
Hormonal control relies on elevated thyroid hormone levels, which increase basal metabolic rate, and heightened catecholamine release, which stimulates both brown fat activity and glycogenolysis for immediate energy supply.
Behavioral responses reduce heat loss and conserve energy:
- Construction of insulated nests from shredded material, creating a microenvironment with temperatures up to 10 °C above the surrounding air.
- Group huddling, allowing individuals to share surface warmth and lower individual heat‑loss rates.
- Selection of burrow depths where soil temperature remains relatively stable, often several centimeters below the surface.
- Reduction of locomotor activity during cold periods, decreasing metabolic demand.
Genetic adaptation manifests in populations inhabiting colder climates through increased expression of thermogenic genes, especially those encoding UCP1 and its regulatory factors. Polymorphisms that enhance promoter activity of these genes correlate with improved cold tolerance.
The lower critical temperature for laboratory mice ranges from 20 °C to 22 °C; below this threshold, metabolic rate rises sharply, and prolonged exposure can lead to hypothermia and mortality if thermogenic capacity is exhausted. Energy costs associated with sustained heat production may compromise growth and reproductive output, illustrating the trade‑off between thermoregulation and other physiological functions.