The energy budget, thermogenic capacity and behavior in Swiss mice exposed to a consecutive decrease in temperatures

Abstract

SUMMARYThe limitation on sustainable energy intake (SusEI) is important because it establishes the upper energetic limit on the ability of animals to disperse, survive and reproduce. However, there are still arguments about what factors impose that limitation. Thermoregulation in cold environments imposes great energy demands on small mammals. A cold-exposed animal has been suggested to be a model suitable for testing these factors. Here, we examined the changes in food intake and digestible energy intake (DEI) as measures of SusEI, thermogenic capacity and behavioral patterns in Swiss mice exposed to consecutively lower ambient temperatures from 23 to -15°C. Cold-exposed mice showed significant decreases in body mass, fat content of the carcass and body temperature, and increases in DEI compared with controls. The time spent on feeding significantly increased with decreasing temperatures, and time spent on general activity decreased following cold exposure. Resting metabolic rate, nonshivering thermogenesis and serum tri-iodothyronine levels significantly increased in mice exposed to lower temperatures in comparison with controls, whereas these thermogenic variables were not significantly different between 0 and -15°C. It might suggest that SusEI in cold exposed Swiss mice was constrained peripherally by the capacity to produce heat and also by the ability to dissipate body heat, but to a different extent. Moderate cold exposure might result in a relaxation of the heat dissipation limit (HDL), allowing the animals to increase food intake to meet cold stress. When animals are exposed to severe cold, the thermogenenic capacity might reach a ceiling, failing to compensate for the heat loss and which would finally result in lower body temperature and considerable weight loss. This might indicate that the HDL was set at a higher level than peripheral limits for Swiss mice exposed to a consecutive decrease in ambient temperatures.

Heat dissipation does not suppress an immune response in laboratory mice divergently selected for basal metabolic rate (BMR)

“…We thus created conditions in which the effect of overheating should be particularly discernible. We paid special attention to monitoring changes in core body temperature, which, surprisingly, has been rarely reported in studies on HD limitation, except some of the most recent papers (Zhao et al, 2010;Gamo et al, 2013a,b;Valencak et al, 2013). We did so because elevation of T b should be expected when animals are unable to dissipate excess heat generated as a by-product of compulsory metabolic processes.…”

“…Our study adds to the still small number of studies on the HDL hypothesis testing the effect of applied metabolic challenges on T b (e.g. Zhao et al, 2010;Valencak et al, 2013;Gamo et al, 2013a,b versus Zhao et al, 2013aYang et al, 2013;Duah et al, 2013;van der Vinne et al, 2014 and many others published before 2012), as well as numerous studies that have demonstrated only the effect of high ambient temperatures on an immune response without discussing constraints imposed by the ability of animals to lose heat (e.g. Bartlett and Smith, 2003;Mashaly et al, 2004;Niu et al, 2009;Jin et al, 2011).…”

Hypothalamic Inflammation: Marker or Mechanism of Obesity Pathogenesis?

“…To survive, a marked increase of energy expenditure is required to support thermogenesis and maintain core body temperature. Increased heat production occurs initially at the expense of modest body fat depletion, but as fat loss proceeds, food intake increases in a commensurate manner to offset further loss of body fat stores (10). Consequently, graded decreases of environmental temperature trigger proportionate increases of energy expenditure that are compensated by increased energy intake so as to maintain body fat stores.…”

Group housing and nest building only slightly ameliorate the cold stress of typical housing in female C57BL/6J mice

“…The cold stress on mice from a T a that is comfortable for humans can have significant effects on the murine cardiovascular system, food balance, the immune system, skeletal muscle, and autonomic outflow (19,41,47). The comprehensive and drastic physiological and biochemical changes that occur in mice as a result of the housing conditions may influence translational success for human clinical trials and may place limitations on modeling of human disease (25).…”