This core provides state-of-the-art instrumentation and methodology for the determination of energy balance and body composition in small animals. This includes the measurement of energy expenditure, via indirect calorimetry; food intake, activity and core body temperature. Body composition techniques involve both ex vivo, via chemical carcass analysis and in vivo methods using dual energy x-ray absorptiometry (DXA), quantitative magnetic resonance (QMR) and micro computed tomography.
Chemical carcass analysis has long been the “gold standard” for the determination of body composition and the SAPC still uses this as the standard for validating new instruments and techniques. Although useless for longitudinal studies, it is useful when an investigator’s animals have been killed and frozen. The carcasses/samples are dried (for water content), fat extracted, and then burnt at 600 degrees Celsius to get ash content.
Dual energy x-ray absorptiometry (DXA) uses two different X-rays to measure fat, soft-lean tissue and bone in vivo. Animals are anesthetized (Isoflurane) and placed prostrate in the imaging area with the front and back legs extended away from the body. The DXA machines in the core can measure animals from 12g to 80g and also from 250g to 120kg. A typical scan takes approximately 5 minutes.
Quantitative magnetic resonance (QMR) is used to measure fat and lean mass as well as water content in vivo with no need for anesthesia. The core is able to use QMR to measure body composition in groups of 10 fruit flies, tissue samples (1g-10g), mice (15-100g), and rats (up t0 900g). Scans take approximately 2 minutes for mice and rats, up to 9 minutes for the fruit flies.
Micro computed tomography can be used to identify and quantify regional distribution of body fat and lean tissue. Mice are anesthetized during the scan which takes 15-25 minutes. Unlike, DXA which gives a two dimensional image, microCT provides a three dimensional reconstruction of the mouse. Different tissues can be identified and outlined based on differences in density. Fat content of the liver can also be determined based on the lower density of the tissue with higher amounts of fat. Although labor intensive, subcutaneous and visceral fat can be identified, as well as individual fat pads.
The TSE indirect calorimetry system collects data on oxygen consumption, carbon dioxide production, food consumption and locomotor activity in up to 8 animals at a time. Mice are acclimated in 16 cages for 2 days, before the measurement period of at least one day. Total and resting energy expenditure are calculated for the measurement period. Locomotor activity is measured in the x-y planes using a system of infra-red beams surrounding the cage and is collected continuously during the measurement. Data on meal size and the timing of meals is obtained from the food hoppers attached to transducers. Body composition is always assessed between the acclimation and measurement periods, using QMR, to allow for the energy expenditure measurements to be normalized appropriately for body composition.
The E-Mitter transponder/receiver system comprises of battery-free transponders that are implanted into the abdominal cavity and a receiver base that the cage sits on. 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.
The core currently has two wheel running systems for mice and rats in which the wheel in the cage sends information to a computer as to the number of revolutions and the timing of the revolutions. This allows for investigators to assess voluntary physical activity.
For investigators interested in the effect of forced exercise, the core 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.
Digestive efficiency can be assessed by measuring food intake, weight of feces produced and then measuring the energy content of both 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 energy lost, and together these give an indication of how much energy the animals are absorbing from the food.
Tim R. Nagy, Ph.D.
Department of Nutrition Sciences
Phone: (205) 934-4088
Maria S. Johnson, Ph.D.
Department of Nutrition Sciences,
Phone: (205) 934-4008
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