Decreased body temperature dependent appearance of behavioral despair in the forced swimming test in mice

Effects of body temperature on the immobile response and brain glucose metabolism were examined in the forced swimming test in mice. The first experiment was performed to study behavior, after initial periods of vigorous activity, a characteristic immobile posture occurred when the water was 25 and 35 degrees C. However, several minutes after forced swimming at 25 degrees C, significantly decreased spontaneous motility occurred in a time-dependent manner, but no changes was observed at 35 degrees C. Our interpretation was that mechanisms of acquisition and retention of the forced swim-induced immobile response differed. Body temperature was also significantly decreased at 25 degrees C but not at 35 degrees C in the forced swimming test. This lowering of body temperature almost paralleled the immobile response. The second experiment was a biochemical study in which the uptake of [(14)C] 2-deoxy-d-glucose into the brain significantly decreased after forced swimming at 25 degrees C but did not change in the forced swim loaded mice when the water was 35 degrees C. These results suggested two types of immobile mechanisms in the forced swimming test: (1) an early phase acquisition of the immobile response which might be related to adaptive response and (2) a late phase to retain the immobile response which might be related to the decrease in brain glucose metabolism.