BODY CORE TEMPERATURE OF RATS SUBJECTED TO DAILY EXERCISE LIMITED TO A FIXED TIME

Several timed daily environmental cues alter the pattern of nycthemera l variations in body core temperature in rodents. The present study in vestigated the effect of timed exercise on variations of daily body co re temperature. Male rats were housed in cages with a running wheel at an ambient temperature of 24 degrees C with a 12:12 h light/dark cycl e. Timed daily exercise rats (TEX) were allowed access to the wheel fo r 6 h in the last half of the dark phase, freely exercising rats (FEX) could run at any time, and sedentary rats (NEX) were not allowed to r un. After a 3-week exercise period, all animals were denied access to the wheel. The intraabdominal temperatures (T-ab) and spontaneous acti vities of rats were measured for 6 days after the exercise period. The T-ab values of the TEX rats were significantly higher than those of t he other two groups only in the last half of the dark phase, while T-a b in the FEX and NEX rats showed no significant difference. The specif ic T-ab changes in the TEX rats lasted for 2 days after the exercise p eriod. Spontaneous activity levels were higher in the TEX rats than th e FEX and NEX rats in the last half of the dark phase for 1 day after the exercise period. The results suggest that daily exercise limited t o a fixed time per day modifies nycthemeral variations of body core te mperature in rats so that the temperature increases during the period when the animals had previously exercised. Such a rise in body core te mperature is partly attributed to an increase in the spontaneous activ ity level.