Activation of brain areas in rat following warm and cold ambient exposure.

Environmental thermal stimuli result in specific and coordinated thermoregulatory response in homeothermic animals. Warm exposure activates numerous brain areas within the cortex, hypothalamus, pons and medulla oblongata. We identified these thermosensitive cell groups in the medulla and pons that were suggested but not outlined by previous physiological studies. Using Fos immunohistochemistry, we localized all the nuclei and cell groups in the rat brain that were activated by warm and cold ambient exposure. These neurons located in the hypothalamus and the brainstem, are part of a network responsible for the thermospecific response elicited by thermal stress. Comparison of the distribution of Fos-immunoreactive cells throughout the rat brain revealed topographical differences between the patterns of activated cells following warm and cold environmental exposure. Among several brain regions, warm exposure elicited c-fos expression specifically in the ventrolateral part of the medial preoptic area, the central subdivision of the lateral parabrachial nucleus and the caudal part of the peritrigeminal nucleus, whereas cold stress resulted in c-fos expression in the ventromedial part of the medial preoptic area, the external subdivision of the lateral parabrachial nucleus and the rostral part of the peritrigeminal nucleus. These neurons are part of a network coordinating specific response to warm or cold exposure. The topographical differences suggest that well-defined cell groups and subdivisions of nuclei are responsible for the specific physiological (endocrine, autonomic and behavioral) changes observed in different thermal environment.