Suppression of non-shivering thermogenesis in the rat by heat-seeking behaviour during cold exposure.

Changes in rectal temperature (Tre) during cold exposure (0 +/- 1 degrees C) were observed in three groups of rats: heat-seeking, no-behaviour and semi-restrained groups. Significant increases in Tre were observed in the no-behaviour and the semi-restrained groups during cold exposure. In the heat-seeking behaviour group Tre remained constant during cold exposure. The increased Tre in the semi-restrained group during cold exposure was markedly attenuated by the systemic injection of beta-blocker (propranolol: 10 mg/kg, I.P.), indicating that this increase of Tre was caused by activation of non-shivering thermogenesis (n.s.t.). Furthermore, the rise in Tre in the semi-restrained group was preceded by a greater increase in the temperature of the interscapular brown adipose tissue. Using the autoradiographic [14C]deoxyglucose technique, it was revealed that the enhanced n.s.t. in the no-behaviour and the semi-restrained groups was accompanied by a significant increase of metabolic activity in the anterior part of the ventromedial hypothalamus. We conclude that during cold exposure motionlessness of slightly restrained animals increase n.s.t. when thermoregulatory behaviour to gain heat is not available. This increased n.s.t. is mediated by activation of hypothalamic function.