Influence of photoperiod on cold-adapted thermogenesis and endocrine aspects in the tree shrew (Tupaia belangeri)

Abstract

Environmental factors play an important role in the regulation of a mammal’s physiology and behavior. Consequently, particular species may provide valuable models for understanding the regulation of energy balance. In the present study, tree shrews (Tupaia belangeri) were transferred from a short to a long day photoperiod in cold conditions, in order to test our prediction that short photoperiod may stimulate an increase in thermogenic capacity and energy intake in tree shrews. During the first four weeks of acclimation to short days, T. belangeri increased body mass, whereas during the second four weeks of acclimation to long days, the body mass of tree shrews decreased compared with the short day group. The increase in body mass reflected a significant increase in absolute amounts of body components, such as carcass mass. During long photoperiod associated with cold exposure, livers, kidney, and small intestine mass decreased. T. belangeri decreased resting metabolic rate and energy intake after exposure to long days while during the exposure to short days the shrews started to maintain a stable level after 28 days. Serum leptin levels were positively correlated with body mass, as well as resting metabolic rate and energy intake. The results show that T. belangeri may provide an attractive novel model system for investigation of the regulation of body mass and energy balance at individual levels. Leptin is potentially stimulated by the photoperiod and cold exposure and is responsible for body mass regulation and thermogenesis in T. belangeri.