Expression of Fos in the hypothalamus of rats exposed to warm and cold temperatures

Fos-like immunoreactivity was investigated in hypothalamic areas involved i n central thermoregulatory processes. Different groups of urethane anaesthe tized rats (n = 36) were exposed to: (1) 23.5 degreesC for 1 h (control); ( 2) 5 degreesC for 20 min (short cold); (3) 5 degreesC for 1 h (long cold); (4) 47 degreesC for 10 min (short warm) and (5) 47 degreesC for 1 h (long w arm). Fos was present in the supramammillary nucleus, supraoptic nucleus an d paraventricular hypothalamus of all (control and long and short, warm- an d cold-exposed) rats. Fos was seen in the dorsomedial, medial and ventromed ial hypothalamus of rats with long or short exposure to both warm and cold temperatures, and in the medial preoptic area and lateral anterior hypothal amus of long and short warm-exposed, and long cold-exposed, rats. Fos was p resent in the hypothalamus of long and short cold-exposed animals only in t he posterior hypothalamus, and in the anterior hypothalamus (central and an terior divisions), suprachiasmatic nucleus and ventrolateral preoptic area of short and long warm-exposed rats. These results provide information on t he location of neurons in rat hypothalamus activated by exposure to warm an d cold temperatures and may aid in the functional identification of central thermoregulatory pathways. (C) 2000 Elsevier Science Inc.