Effects of photoperiod on body mass, thermogenesis and serum leptin in Apodemus draco during cold exposure

Abstract

Many small mammals respond to seasonal changes in photoperiod by altering body mass and adiposity. These animals may provide valuable models for understanding the regulation of energy balance. In the present study, we examined the effect on body mass, resting metabolic rate, food intake and body composition in cold-acclimated Apodemus draco by transferring them from a short to long day photoperiod. During the first 4 weeks of exposure to short days, A. draco’s body mass decreased. After the next 4 weeks of exposure to long days, body mass increased in the long day group compared to the short day group. This increase in body mass reflected significant increases in absolute amounts of body components, including wet carcass mass, dry carcass mass and body fat mass. Liver, kidney, and small intestine were enlarged due to longer photoperiod during cold exposure. A. draco increased its resting metabolic rate and energy intake after exposure to long days. Serum leptin levels were positively correlated with body mass, body fat mass, resting metabolic rate as well as energy intake. All of the results indicate that A. draco may provide an attractive novel animal model for investigation of the regulation of body mass and energy balance at the organismal levels. Leptin is potentially involved in the photoperiod-induced body mass regulation and thermogenesis of A. draco during cold exposure.