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 24 degrees C, were subjected to a constant high T (a) of 32 degrees C (HE) or were constantly kept at 24 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.