The mouse: An “average” homeotherm

Mice, rats, and nearly all mammals and birds are classified as homeothermic, meaning that their core temperature is regulated at a constant level over a relatively wide range of ambient temperatures. In one sense, this homeothermic designation has been confirmed by the advent of radiotelemetry and other techniques that allow for the remote monitoring of awake, unrestrained animals in laboratory or natural settings. This technology confirmed that, when averaged over many hours, core temperature of mammals is regulated at a nearly constant level. On the other hand, telemetric sampling in relatively small mammals such as mice and rats also revealed that their core temperature often varies markedly from hour to hour. In other words, the mouse could be defined as a homeotherm only when core temperature is averaged over a relatively long period. Many researchers ascribe equal homeothermic capabilities to mice and other small rodents as they do to humans. Such an assumption could lead to errors in extrapolating physiological, pharmacological, and toxicological findings from experimental test species to humans.

► Mice are a predominant test species in biomedical research. ► Their average core temperature is similar to other mammals. ► Monitoring core temperature with telemetry shows marked variability of core temperature compared to large homeotherms, including humans. ► This variability probably reflects unique thermoregulatory mechanisms compared to larger mammals. ► Extrapolating from rodent to human requires an understanding of the stability of core temperature.