Metabolic Physiology and Energy Balance Core

In vivo studies in mice

• Continuous glucose monitoring
• Body composition: DEXA analysis of body fat, lean mass, and bone density
• Body composition: MRI analysis of body fat or lean mass, and water mass
• Energy expenditure measurement by indirect calorimetry
• Food and water intake
• Wireless monitoring of body temperature or heart rate
• Energy content in diet or feces by bomb calorimetry
• Thermal imaging studies

Equipment

Body composition analysis: EchoMRI. With quantitative MRI, it is possible to measure metabolic parameters serially to noninvasively acquire longitudinal measurements. These measurements allow for assessment of body composition in the same animals before and after a dietary or pharmacological treatment intervention. An investigator can determine, for example, whether alterations in insulin resistance precede or follow the development of increased adiposity.

The EchoMRI (EchoMRI 3-in-1 MRI for mice, Echo Medical Systems) can measure total body fat mass, lean mass, and water mass in mice up to 100g in mass. The advantages of the EchoMRI are a fast measurement time (under 2 minutes) and the animals do not require sedation for the procedure. The disadvantage of this machine is that these scans cannot be performed on animals implanted with electronic devices, including glucose or body temperature probes. Our core has two EchoMRI devices, one maintained in the specific pathogen free barrier facility, and one which is kept in the laboratory for terminal measurements. With this setup, investigators can bring their mice to BIDMC to a designated location outside our barrier animal facility and use the EchoMRI. This makes body composition analysis available to investigators who house their mice at other institutions.

Indirect Calorimetry System. We operate a state-of-the art Sable Systems Promethion Indirect Calorimeter allowing for high-resolution data collection. Our system is equipped with 32 cages with temperature- and light-controlled environments (4 independently operated cabinets each containing 8 cages). This allows for measurement at 4 distinct environmental conditions. This facility utilizes a Sable Systems Promethion, with 32 individual indirect calorimetry cages. This systems allows for a powerful research and discovery platform for investigating factors affecting metabolism in mice. We collect data in unrestrained, conscious mice, yielding quantitative measurements of oxygen consumption (VO₂), carbon dioxide production (VCO₂), respiratory exchange ratio – an indicator of substrate utilization – and total energy expenditure. It also provides measures of locomotor activity and caloric intake. Our indirect calorimeter is specialized, allowing for precise control of ambient temperature ranging from thermoneutrality (35°C) to cold (4°C) and for non-standard photoperiods.

Optional experimental features.

• Wireless body temperature measurements
• Wireless continuous blood glucose monitoring and body temperature
• In-cage running wheels
• Optogenetics for inducible brain circuit activation and inhibition
• Sleep monitoring with Electroencephalogram (EEG)
• HEPA-filtered isolation cages for studies in germ-free mice or those with defined microbiota.
• [¹³C/¹²C] Stable isotope detection in vivo.

The Bomb Calorimeter (Parr Instrument Company) allows for the quantitation of energy content of either food or of feces. Direct calorimetry can measure the caloric value of novel or experimental diets. When coupled with measurements of food intake and indirect calorimetry, a complete picture of energy intake, energy absorption, and energy expenditure can be quickly determined.

Infrared thermography using a thermal camera (FLIR) will help to quantitate heat lost due to differences in vasodilation and vasoconstriction. Thermography has helped to visualize differences in brown fat thermogenesis.

Data analysis. Data will be analyzed according to the internationally recognized standards as defined by the International Indirect Calorimetry Consensus Committee using ANCOVA, the General Linear Model and ANOVA (Banks et al., Nature Metabolism 2025).

From our understanding of mammalian metabolism, the limitations and advantages of indirect calorimetry methods, and common analysis pitfalls, we developed a free online statistical software package for the analysis of indirect calorimetry experiments–CalR (Mina et al Cell Metabolism 2018). We provide a comprehensive data analysis with CalR including time plots, box plots, regression plots, statistical analysis, and a written summary. We also provide data and metadata in a format readable by CalR (CalRapp.org) allowing the investigator to perform their own exploratory data analysis.

Publications

Activin type II receptor signaling in cardiac aging and heart failure

Apolipoprotein J is a hepatokine regulating muscle glucose metabolism and insulin sensitivity

Costs