Differences in Fos expression in the rat brains between cold and warm ambient exposures

Fos expression in the rat diencephalon, brain stem, cerebellum, and spinal cord was examined after warm (33°C) and cold (10°C) ambient exposures. Fos expression was examined with use of immunohistochemical method and the number of Fos-positive neurons In each nucleus was quantitatively analyzed. When rats were exposed to cold ambient, significant number of Fos-positive neurons was found in the lateral septal nucleus (LS), preoptic hypothalamic area (POA), parvocallular paraventricular hypothalamic nucleus (PPVN), lateral preoptic area (1-130), zone incerta (ZI), pareventricular thalamic nucleus (PV), ventromedial hypothalamic nucleus (VMH), subparafesclcutm thalamic nucleus (SPF), postrior hypothalamic area (PH), supramammillary nucleus (SuM), microcellular tegmental nucleus (MiTg), lateral iemomscus nucleus (LL), lateral dorsal central grey (CGLD), lateral ventral central grey (CGLV), dorsal parabrachial nucleus (DPS), locus coeruleus (LC), dorsal tegmental nucleus (DTg), vestibular nucleus (Ves), nucleus of solitary tract (Sol), spinal cord, and cerebellum. When animals were exposed to warm ambient, the numbers of Fos-positive neurons in the LS, POA, PV, LPO, and SuM were significantly increased to be equal to those of cold ambient However, after warm ambient exposure the numbers of Fos-positive neurons in the DPB and spinal cord were increased but less than those of cold ambient, and those in the pPVN, VMH, ZI, SPF, PH, CGLD, CGLV, Mg, LL, LC, DTg, Ves, Sol, and cerebellum were not significantly increased as compared with those of control or cold ambient Abdominal temperature was not changed doing cold ambient exposure, but the temperature was sWNcantly increased during warn ambient exposure. These results demonstrate that Fos-positive regions in the rat brains are sagraficantly different between cold and worm ambient exposures although several hypothalamic brain regions reveal the same degree of Fos expression, irxiCating the differences of neural patiwways concerning thennoregulation between cold and warm ambients.