Heat production measured by CLAMS at different ages. Heat production is plotted over a 44~48 hour cycle at 2~3 months of age (A) and at 12~14 months of age (B), with mean ± SE indicated in (C) and (D), respectively. MAI (D) refers to interval during the light cycle when all three groups of mice showed matched low levels of locomotor activity. Data were analyzed using one-way ANOVA followed by Newman-Keuls multiple-comparison test. At 2~3 months of age, for the dark cycle, F(2,87)=8.55, p=0.0004; for light cycle, F(2,105)=6.10, p = 0.0031. At 12~14 months of age, for the dark cycle, F(2,105)=395.1, p<0.0001; for the light cycle, F(2,123)=162.7, p<0.0001; for MAI, F(2,24)=75.74, p<0.0001. *p < 0.05 (C) or #p < 0.001 (D). n = 5~13 in each group.