The Effect of Ambient Temperature on Body Mass, Torpor, Food Intake, and Leptin Levels: Implications on the Regulation of Food Intake in Mammalian Hibernators

Abstract

The effect of ambient temperature (T a) on the body mass, food intake, and leptin concentrations in the Golden-Mantled Ground Squirrels (Callospermophilus lateralis) (GMGS) was investigated. We hypothesized GMGS would begin feeding in winter due to declining plasma leptin levels, if forced to undergo torpor bouts at high T a (22°C). Our rationale was that GMGS would have an elevated metabolism at a high T a, and therefore would utilize their fat stores faster causing a decrease in serum leptin. The torpor bout results demonstrated that animals kept at high T a spent significantly (P < 0.01) less time at low body temperature compared to cold room animals (52 vs. 142 h). Furthermore, the body mass of warm room GMGS was lower compared to cold room (5°C) animals during the winter months, suggesting a higher metabolism. Warm room animals that had stopped eating, started eating again when body mass declined to near their trapped body mass. Leptin levels were significantly (P < 0.05) lower in warm room animals compared to cold room animals (4.5 vs. 7.3 ng/ml), when they commenced eating again. We conclude that as fat mass decreased due to the higher metabolism in the warm room, this decreased leptin levels, which in turn stimulated food intake in warm room animals. The cold room animals had food at the same time as the warm room animals but did not feed and their leptin concentrations remained higher. We conclude that leptin is an important part of the feedback signal involved in the cessation of food intake during hibernation.