CHANGES IN HYPOTHALAMIC TEMPERATURE OF RATS AFTER DAILY EXPOSURE TO HEAT AT A FIXED TIME

Rats were subjected to an ambient temperature (T-a) of 33 degrees C fo r ca. 5 h during the last half of the dark phase for 5, 14 or 28 conse cutive days (heat-exposed rats, HE), while control rats were kept at a constant T-a of 24 degrees C. After the heat exposure schedule, the l evels of hypothalamic temperature (T-hy) as an index of body core temp erature in the HE were significantly lower than those of the controls for 2 - 4 h in the last half of the dark phase. The low levels of T-hy persisted during the specific period for 1, 3 and 6 days after the en d of the 5-, 14- and 28-day heat exposure schedules, respectively. The se results confirm that, in rats subjected to daily heat exposure for ca. 5 h at a fixed time per day, their T-hy falls during the period wh en the rats were previously exposed to heat, and suggest that the dura tion of the specific T-hy change observed after completing the heat ex posure schedule depends on the length of the heat exposure schedule.