DIFFERENCES IN FOS EXPRESSION IN THE RAT BRAINS BETWEEN COLD AND WARMAMBIENT EXPOSURES

Fos expression in the rat diencephalon, brain stem, cerebellum, and sp inal cord was examined after warm (33 degrees C) and cold (10 degrees C) ambient exposures. Fos expression was examined with use of immunohi stochemical method and the number of Fos-positive neurons in each nucl eus was quantitatively analyzed. When rats were exposed to cold ambien t, significant number of Fos-positive neurons was found in the lateral septal nucleus (LS), preoptic hypothalamic area (POA), parvocellular paraventricular hypothalamic nucleus (pPVN), lateral preoptic area (LP O), zona incerta (ZI), paraventricular thalamic nucleus (PV), ventrome dial hypothalamic nucleus (VMH), subparafascicular thalamic nucleus (S PF), posterior hypothalamic area (PH), supramammillary nucleus (SUM), microcellular tegmental nucleus (MiTg), lateral lemniscus nucleus (LL) , lateral dorsal central grey (COLD), lateral ventral central grey (CG LV), dorsal parabrachial nucleus (DPB), locus coeruleus (LC), dorsal t egmental 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 col d ambient. However, after warm ambient exposure the numbers of Fos-pos itive 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, MiTg, LL, LC, DTg, Ves, Sol, and cerebellum were not significant ly increased as compared with those of control or cold ambient. Abdomi nal temperature was not changed during cold ambient exposure, but the temperature was significantly increased during warm ambient exposure. These results demonstrate that Fos-positive regions in the rat brains are significantly different between cold and warm ambient exposures al though several hypothalamic brain regions reveal the same degree of Fo s expression, indicating the differences of neural pathways concerning thermoregulation between cold and warm ambients.