Body temperature is the regulated variable of the thermoregulatory system. That is, the thermoreceptors, integrative neural systems, and thermoregulatory motor outputs function to maintain thermal homeostasis throughout the body. Measuring the body temperatures of normal and compromised individuals can provide insight into the nature of a species’ thermoregulatory mechanisms. This chapter attempts to explore the properties of rodents’ body temperatures, including variations in normal core temperature, ambient limits of normothermia, modulations in temperature from day to night and during sleep, and the responses to psychological stress.

Partitioning of body temperature

Thermal physiologists conventionally divide body temperature into three components: (1) the core, including the body trunk (e.g., spinal cord, abdominal and thoracic cavities); (2) the shell, which includes the skin and subcutaneous tissues that are directly affected by changes in ambient temperature; (3) the brain. The internal or core body temperature is perhaps the most frequently measured parameter in thermal physiology. The thermal core is composed of “inner tissues of the body whose temperatures are not changed in their relationship to each other by circulatory adjustments and changes in heat dissipation to the environment” (IUPS, 1987). Thus, the temperature of any organ or tissue in the thermal core is considered to be extremely stable over a wide range of ambient temperatures.

Body sites such as the brain, spinal cord, rectum, colon, esophagus, and visceral and thoracic organs usually are considered to be parts of the thermal core.