Abstract
In bears and squirrels, core temperature is decreased in winter. On the other hand, it has been considered that core temperature is not decreased in humans and mice. However, when energy intake is insufficient in mice, they enter torpor, in which core temperature is daily decreased. Furthermore, Swoap et al. and Zhang et al. report that intraperitoneal injection of adenosine monophosphate (AMP) reduces core temperature in mice. Therefore, we hypothesized that thermoregulatory system of mammals has a shutdown switch to stop thermoregulatory responses. The purpose of this study is to verify this hypothesis. Mice were injected with AMP (3.0-7.5 μmol/g, i.p.), and their core temperatures and autonomic and behavioral heat-gain responses were investigated. Saline was used as control. After AMP injection, core temperature was decreased. This temperature drop was dose-dependent. Core temperature of AMP-injected mice was changed with ambient temperature, indicating that mice acted like heterotherms. When ambient temperature was low, skin temperature around the brown adipose tissue (BAT) was higher than that of other skin areas. In AMP-injected mice, however, skin temperature around BAT was as low as that of other skin areas, showing that BAT activity was decreased by AMP. These results demonstrate that thermoregulatory system of mammals has a shutdown switch to stop thermoregulatory responses. [J Physiol Sci. 2008;58 Suppl:S60]
