cFos expression in the preoptic area (PO), which is thermoregulatory center increased by both heat and cold exposures; however, the regional difference is unknown yet. We aimed to determine if cFos expression in the PO was regionally different between heat and cold exposures. Mice were exposed to 27, 10, or 38 °C for 90 min, and body temperature (Tb) was measured. cFos-immunoreactive (cFos-IR) cells in the PO were counted by separating the PO into the ventral and dorsal parts in the rostral (bregma 0.38 mm), central (−0.10 mm), and caudal (−0.46 mm) planes. Tb at 10 °C remained unchanged; however, it increased at 38 °C. Counts of cFos-IR cells in all areas were greater at 38 °C than at 27 °C. In the dorsal and ventral parts of the central and the dorsal part of caudal PO, counts of cFos-IR cells were greater at 10 °C than at 27 °C. In conclusion, the areas of increased cFos expression in the PO in the heat were different that in the cold in mice.
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