書誌： Chronobiology International ,2012
Chronobiology International, 29(6): 736–746, (2012)
Ken Tokizawa, Yuki Onoue, Yuki Uchida, and Kei Nagashima
Fasted mice show torpor-like hypothermia in the cold in their inactive phase. The aim of the present study was toelucidate whether leptin and/or ghrelin are involved in this reaction and to identify its neurophysiologicalmechanisms. In ob/ob mice, which lack leptin, metabolic heat production (oxygen consumption, VO2) wassuppressed in 20°C cold in both the light and dark phases, resulting in hypothermia. When wild-type mice receiveda systemic injection of 8 µg ghrelin in the early light phase, followed by a 2-h cold exposure to 10°C, their corebody temperature (Tb) decreased by 1.7°C, and they displayed a less marked increase in VO2 compared with vehicleinjected mice. However, ghrelin injection in the early dark phase resulted in the maintenance of Tb and increasedVO2 in the mice, which was similar to the result observed in the vehicle-injected mice. The number of doublylabeled neurons with cFos and neuropeptide Y (NPY) in the suprachiasmatic nucleus was greater in the light phasein the ghrelin-injected mice, which may suggest that ghrelin activates NPY neurons. On the contrary, in theparaventricular nucleus, the counts became greater only when they were exposed to the cold in the dark phase.These results indicate that ghrelin plays an important role in inducing time-dependent changes in thermoregulationin the cold via hypothalamic pathways. (Author correspondence: tokizawa@aoni.waseda.jp)
Keywords: Body temperature, Circadian rhythm, Food deprivation, Ghrelin, Hypothalamus, Metabolism