Involvement of the parabrachial nucleus in thermogenesis induced by environmental cooling in the rat.

The parabrachial nucleus (PBN), an integration site for autonomic regulation in the mesopontine brainstem, receives sensory information about cold temperatures from the skin. Here we investigated the role of the PBN in thermoregulation. Unilateral stimulation of the PBN (10-40 microA, 5 min) immediately increased the rate of O(2) consumption ( VO(2)) and heart rate, and the magnitude of these responses increased with the intensity of the stimulus in urethane-anesthetized rats. High-intensity (40 microA) stimulation of the PBN increased the temperature of the interscapular brown adipose tissue and that of the colon but had no effect on that of the tail skin, although weaker stimulation was without effect on these temperatures. Next, we examined the effects of bilateral lesioning of the PBN on environmental cooling-induced thermogenesis in conscious rats. Exposure of PBN-lesioned rats to a cool (16.6 degrees C) environment induced a significantly smaller increase in VO(2) than did that of rats with a sham operation or with lesions made outside of the PBN, and resulted in a marked decrease in body temperature in PBN-lesioned rats but not in other rats. Both frequency and duration of gross motor activity in the cool environment were similar between PBN-lesioned and sham-operated rats. These results suggest that the PBN is involved in the central mechanisms of cooling-induced thermogenesis.