Relation of general activity in rats to environmental temperature

The relation between ambient temperature and amount and pattern of wheel running was examined in four experiments, with a total of 88 adult male albino rats of the Sprague-Dawley strain, under conditions of 12-hr. light/12-hr. dark. While lowering of temperature from baseline of 21--25 degrees C to 4--7 degrees C most typically led to increased running, consistently reduced running characterized a substantial number of individuals, especially those with relatively high baseline scores. When comparison trials were run at 27 degrees C, reduced activity was recorded for virtually all subjects. As temperature was elevated above 27 degrees C, however, there was in most cases an upturn. At 34 degrees C, 24-hr. running scores tended to exceed baseline level for about half the animals, and running during the light 12 hr. of the day was above baseline for virtually all. Analysis of the temporal distribution suggests that the thermoregulatory reduction of activity, readily demonstrated at the moderately warm temperature, is complicated by efforts to escape as the environment becomes aversively hot. Failure of previous investigators to observe this is attributable in part to apparatus and recording differences. It is speculated that the pattern of response to extreme temperatures is closely related to the circadian fluctuation of internal temperature.