Spontaneous activity and heat avoidance of mice.

Experiments were conducted with eight female mice on the avoidance of heat stress over the ambient temperature range from 25 to 34 degrees C. Significant avoidance behavior of the animals was observed at Ta = 30 degrees C, becoming more noticeable as the ambient temperature was raised. When exposed to heat, the animals showed peaks of avoidance during the second half of the dark period. This result seemed closely related to the spontaneous activity pattern of mice which reached a maximum between 1800 and 2000 at each experimental temperature. In this experiment, mice were more apt to choose a comfortable place during their inactive period than during their active period. This hypothesis on the relation between mice's heat avoidance and spontaneous activity was supported by the results of an additional experiment conducted in a cold environment of Ta = 18 degrees C.