Energetics of fasting heterothermia in TRPV1-KO and wild type mice.

To learn the possible role of TRPV1 in the changes of temperature regulation induced by short-term energy lack, TRPV1-KO and wild type mice were exposed to complete fasting for 2 or 3 days while their core temperature and locomotor activity were recorded using a biotelemetry method. In both types of mice, fasting led to progressive daytime hypothermia with night-time core temperature being maintained at normothermia (collectively called heterothermia). During fasting rises of locomotor activity were observed parallel to night-time normothermia with occasional increases of both parameters recorded every 2 to 3 hours (ultradian rhythms). The daytime fall of core temperature was significantly greater in wild type than in TRPV1-KO mice, in the former an advance of the temperature/activity rhythm having been observed in spite of the presence of a 12/12 hour light/darkness schedule. Re-feeding applied at the beginning of the light-period led to rapid reappearance of normothermia in both types of mice without a large increase in locomotor activity. It is concluded that the TRPV1-gene may have a role in the development of adaptive daytime hypothermia (and hence saving some energy) in mice during complete fasting but still allowing normothermia maintained at night, a strategy probably serving survival under natural conditions in small size rodents such as the mouse. The possible role of muscle thermogenesis either with or without gross bodily movement during fasting or on re-feeding, respectively, may be based on different mechanisms yet to be clarified.