Proliferation of neuronal progenitor cells and neuronal differentiation in the hypothalamus are enhanced in heat-acclimated rats

Male Wistar rats, initially maintained at an ambient temperature (T (a)) of 24A degrees C, were subjected to a constant high T (a) of 32A degrees C (HE) or were constantly kept at 24A degrees C (controls, CN). Bromodeoxyuridine (BrdU) was intraperitoneally injected daily for five consecutive days after commencing heat exposure. On the 6th, 13th, 23rd, 33rd, 43rd, and 53rd day of heat exposure, rats' brains were removed. Immunohistochemical analysis showed that the numbers of BrdU-positive cells in the hypothalamus of HE were significantly and consistently greater than those of CN. In HE, the number of BrdU-positive cells double-stained by a mature neuron marker increased abruptly after 33 days of heat exposure by about seven times. This was not the case in CN. The results suggest that heat exposure facilitates proliferation of neuronal progenitor cells in the hypothalamus and promotes differentiation to neurons, which might have certain relation to establishing long-term heat acclimation in rats.