Behavioral thermoregulation by the white rat at high ambient temperatures

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Abstract
At ambient temperatures greater than 40°C, rats must spread salvia on themselves to prevent lethal hyperthermia. This study examined the effect of other behavioral parameters on a rat's ability to thermoregulate. The animals were exposed to 42°C in a cylindrical wire cage; records of time spent saliva spreading and moving about the cage were made; and body temperatures were measured with thermocouples implanted in the animals' abdominal cavities. Very little time spent saliva spreading was necessary for an animal to become thoroughly wetted on its ventral surface. Once wetted, an animal's thermoregulatory ability depended on its amount of locomotion. Animals which spent a considerable amount of time climbing about the cage were unable to stabilize their body temperatures and suffered increasing hyperthermia. Those which had low levels of locomotion were able to hold a constant body temperature for an hour or more. Several of the animals were given seven successive exposures to 40°C, followed by a second exposure to 42°C. Most of these animals showed greatly improved thermoregulatory abilities in the second exposure at 42°C as compared with the first, and this improvement was associated with markedly decreased locomotion. Several animals showed increased saliva spreading, but this change was not well correlated with improved thermoregulatory ability. It was concluded that low levels of locomotion are essential for evaporative cooling by saliva spreading to be adequate, and that repeated exposures to heat can modify an animal's behavior to the type associated with prolonged thermoregulation.

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