Energetics

The incorporation of quantitative measures of energetics is important for understanding aspects of the basic biology in relation to the physiology of aging and disease in organisms. Assessing changes in energy balance, body composition and activity over the life course are important evaluating interventions for functional improvements reflecting improvements foundational, biological changes that occur during the aging process. Multiple methods for the assessment of energetics have been validated and are available through the COEC.

Indirect Calorimetry (Mice)

Energy balance studies are conducted using the TSE Systems PhenoMaster/Labmaster animal monitoring system (Bad Homburg, Germany). This system allows us to collect data on oxygen consumption, carbon dioxide production, food consumption and locomotor activity in 8 animals in parallel during the same measurement period. The entire unit is housed in an environmental chamber (Powers Scientific), allowing precise control of ambient temperature and photoperiod. Data are obtained using the TSE software. Mice are acclimated to the metabolic cage for two days prior to all measurements. Measurements are then taken for 22 hours or longer depending on the experimental design. Energy expenditure is calculated using 1-minute samples every nine minutes. Total energy expenditure is determined by calculating the average hourly energy expenditure over 22 hrs and then multiplying by 24. Resting energy expenditure is calculated by averaging the three lowest 18 consecutive-minute periods of energy expenditure, with at least one hour between each period. Locomotor activity is determined with infrared sensor pairs arranged in a grid pattern for horizontal (x, y level) activity. Movement is monitored continuously and reported as total counts every 9 minutes and expressed as counts/24 hrs. Food intake is monitored using hanging baskets attached to force transducers. Data on food intake is acquired every 9 minutes, and hence meal size, duration, and timing can be acquired. An automated food access system can be programmed to restrict access to food by time of day, duration of feeding, or by the amount consumed. Cages can contain a running wheel (n=8), which allows for exercise energy expenditure to be measured. The wheel can be always available, always locked, or controlled to allow only a certain time for running, or a specific distance run. A suspended tube in the cage is connected to a force transducer, which allows for measurement of body weight whenever the mouse enters the tube in its cage (n=8).

Indirect Calorimetry (Fish)

The Loligo® respirometry system (Viborg, Denmark) measures resting oxygen consumption rates in aquatic organisms using intermittent flow respirometry. The system uses a fiber optic oxygen sensor, and data is collected and analyzed using AutorespTM data acquisition software. Oxygen consumption rates in up to four individuals can be measured simultaneously. The system is currently being optimized to measure individual oxygen consumption rates in fish ranging from early juvenile to adult under controlled temperature conditions. However, it can be adapted to measure oxygen consumption rates in a variety of aquatic organisms in either fresh or salt water. The system is currently being adapted to measure oxygen consumption rates in terrestrial organisms, specifically Drosophila melanogaster, and services should be available in the near future through the COEC.

Temperature/Activity

The E-Mitter transponder/receiver system is used to measure core body temperature and consists of battery-free transponders that are implanted into the animal’s abdominal cavity and linked to a receiver base on which that the cage rests. The transponders transmit information on core body temperature via the base to a computer. Locomotor activity is assessed as the mouse moves over the top of the receiver. Thus activity and body temperatures can be measured continuously while the animal is in its home cage.

Wheel Running Cages

Spontaneous exercise can be measured during or independently of indirect calorimetry using running wheels. Individual cage wheel use is recorded continuously for assessments of activity including total distance, speed and time of day.

Forced Exercise Wheels

For investigators interested in the effect of forced exercise, the COEC has a system of running wheels on a rolling bed, for which the speed and time of the exercise can be determined and changed by the investigator.

Bomb Calorimetry

Digestive efficiency can be assessed by measuring food intake and weight of feces produced and then measuring the energy content of samples of food and feces using a bomb calorimeter. By measuring the weight of food consumed and the energy content of that food, energy intake can be calculated. The weight and energy content of the feces can be measured to give an estimate of fecal energy lost, and together these give an indication of how much energy the animals are absorbing from the food.

Body Composition Analysis

Body composition can be determined at the whole animal and/or tissue level using a variety of techniques. Which particular method would be best for your study design and organism can be determined in consultation with the COEC leadership.

Chemical Carcass Analysis

Chemical carcass analysis sets the benchmark for determination of body composition and the COEC still uses this method to validate new instruments and techniques. It is also useful for animals (and derived tissues) that have been euthanized and frozen. The carcasses/samples are dried (for water content), fat is extracted, and combusted to quantify ash content. Common models include mice, rats and fish. For other species, please contact the COEC.

Dual energy x-ray absorptiometry (DXA)

DXA uses two different X-ray intensities to measure fat, soft-lean tissue, and bone in living animals. Animals are anesthetized (Isoflurane) and imaged with the front and back legs extended away from the body. The COEC DXA machines can measure small (12~50g) and larger (250g-120kg) animals. A typical scan takes approximately five minutes.

Quantitative magnetic resonance (QMR)

QMR is used to measure water content, fat, and fat-free mass in vivo with no need for anesthesia. The core routinely utilizes QMR to measure body composition across species (organisms/tissues) ranging in size from groups of 10 fruit flies, tissue samples (1g-10g), mice (15~80g), and rats (up to 900g). Scans take approximately two minutes for mice and rats, up to nine minutes for fruit flies. QMR measures with other species (e.g. aquatic, reptilian) may also be possible – please contact the COEC for more information.

COEC Energetics-Related Equipment List

Indirect Calorimetry/Metabolism Measurements

  • 8-cage TSE indirect calorimetry system with oxygen and carbon dioxide analyzers, infra-red beam break activity system
  • 8-cage TSE indirect calorimetry system with oxygen and carbon dioxide analyzers, infra-red beam break activity system running wheels, and automated feeders
  • 16-cage acclimation system for the indirect calorimetry system
  • Environmental Variables and Energetics Assessment - 3 environmental chambers (Powers Scientific) to measure indirect calorimetry of mice at different temperatures and light cycles

Activity and Energetics Measures

  • 32 wheel running cages: 16 for rats, 16 for mice
  • 20 walking wheel forced exercise system (Lafayette Instruments®)
  • 12 E-mitter receiver bases; 12 PDT-4000 (rats) and 20 G2 (mice) implantable transponders to measure temperature and activity in home cages
  • 1 rectal probe for measurement of rectal body temperature in mice

Body Composition Measurements

  • 2 drying ovens
  • 12 Soxhlet fat extractors
  • 1 muffle furnace
  • 3 industrial blenders
  • 3 DXA systems to measure in vivo body composition in animals from 12~50g and 250g to 120kg
  • 2 QMR systems to measure in vivo body composition in mice and rats (or similar sized animals)
  • 1 bomb calorimeter for the measurement of the energy content of food and feces