title: Integration of body temperature into the analysis of energy expenditure in the mouse.
abstract: OBJECTIVE
  We quantified the effect of environmental temperature on mouse energy homeostasis and body temperature.
  
  
  METHODS
  The effect of environmental temperature (4-33 °C) on body temperature, energy expenditure, physical activity, and food intake in various mice (chow diet, high-fat diet, Brs3 (-/y) , lipodystrophic) was measured using continuous monitoring.
  
  
  RESULTS
  Body temperature depended most on circadian phase and physical activity, but also on environmental temperature. The amounts of energy expenditure due to basal metabolic rate (calculated via a novel method), thermic effect of food, physical activity, and cold-induced thermogenesis were determined as a function of environmental temperature. The measured resting defended body temperature matched that calculated from the energy expenditure using Fourier's law of heat conduction. Mice defended a higher body temperature during physical activity. The cost of the warmer body temperature during the active phase is 4-16% of total daily energy expenditure. Parameters measured in diet-induced obese and Brs3 (-/y) mice were similar to controls. The high post-mortem heat conductance demonstrates that most insulation in mice is via physiological mechanisms.
  
  
  CONCLUSIONS
  At 22 °C, cold-induced thermogenesis is ∼120% of basal metabolic rate. The higher body temperature during physical activity is due to a higher set point, not simply increased heat generation during exercise. Most insulation in mice is via physiological mechanisms, with little from fur or fat. Our analysis suggests that the definition of the upper limit of the thermoneutral zone should be re-considered. Measuring body temperature informs interpretation of energy expenditure data and improves the predictiveness and utility of the mouse to model human energy homeostasis.
authors.affiliation: Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA ; Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, 106 91 Stockholm, Sweden.
authors.forename: Gustavo
authors.initials: G
authors.lastname: Abreu-Vieira
authors.affiliation: Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA.
authors.forename: Cuiying
authors.initials: C
authors.lastname: Xiao
authors.affiliation: Mouse Metabolism Core, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA.
authors.forename: Oksana
authors.initials: O
authors.lastname: Gavrilova
authors.affiliation: Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA.
authors.forename: Marc L
authors.initials: ML
authors.lastname: Reitman
keywords: BMR, basal metabolic rate; Basal metabolic rate; Body temperature; CIT, cold-induced thermogenesis; Cold-induced thermogenesis; EE, energy expenditure; Energy expenditure; HFD, high-fat diet; Heat conductance; LCT, lower critical temperature; PAEE, physical activity energy expenditure; RQ, respiratory quotient; TEE, total energy expenditure; TEF, thermic effect of food; Ta, environmental temperature; Tb, core body temperature; Thermoneutrality; dTb, defended body temperature