Calorimetry was performed using the Oxymax system from Columbus Instruments (Columbus, OH) as previously described (Powers et al. 2013 (link)). Calorimetry was evaluated for 9h during the initial light phase, 10 h for the dark phase and 4 h during the morning light phase. Resting oxygen consumption and carbon dioxide production rates (VO2 and VCO2 respectively) were measured every 10 minutes and normalized to body weight. Animals were given free access to water and food during testing. Food was weighed following testing. A total of 8 Crt+/y and 10 Crt−/y mice were used.
The following day, mice were exercised on a motorized treadmill placed inside of a sealed chamber. The initial speed of the treadmill was 5 m/min and was increased stepwise by 5 m/min every 5 min until a final speed of 25 m/min was reached. VO2 and VCO2 were sampled every 30 sec and normalized to the body weight of the animal. Respiratory exchange ratio (RER), a measure that determines if carbohydrates, fatty acids, or protein are being utilized for energy (Simonson and DeFronzo 1990 (link)), and energy expenditure were calculated using CLAX software from Columbus Instruments.
The following day, mice were exercised on a motorized treadmill placed inside of a sealed chamber. The initial speed of the treadmill was 5 m/min and was increased stepwise by 5 m/min every 5 min until a final speed of 25 m/min was reached. VO2 and VCO2 were sampled every 30 sec and normalized to the body weight of the animal. Respiratory exchange ratio (RER), a measure that determines if carbohydrates, fatty acids, or protein are being utilized for energy (Simonson and DeFronzo 1990 (link)), and energy expenditure were calculated using CLAX software from Columbus Instruments.
