Figure 8.

Thermogenic activity is increased in mice that show high rates of evaporative cooling. A. Live imaging of thermogenic activity. Representative images show a hairless SKH1 female mouse housed at warm temperature (31 °C, for >1 week) and after a minor cool exposure (room temperature 24 °C, for 10 min). Side views show percolation of warmed blood throughout the internal organs, possibly also revealing autonomous heat sources (indicated with arrows). Maximum temperatures were visualized over BAT depot (interscapular area) and quantified for different ambient housing temperatures (equilibrated for >4 h; n = 8), and for mice after cool exposure (31/24; 31 °C–24 °C for 10 min; n = 8; right hand side). Thermographic images were analyzed by FLIR software; a box drop was used to measure the maximum temperature of a region of interest, expressed as the mean ± SEM and analyzed using an unpaired 2-tailed t test (****P < 0.0001; **P < 0.01; *P < 0.05; ns = not significant). B–D. Correlating BAT activation with high rates of evaporative cooling. TEWL and BAT activation were measured for 8 SKH1 female mice (14–18 weeks of age), housed at 31 °C, using a molecular marker (UCP1 protein signal from Western blotting of BAT; B), a histological marker (relative area of lipid droplets in BAT; C) and live imaging of surface temperature of BAT (FLIR; D). Increasing TEWL was significantly correlated with increasing UCP1 protein (B; p = 0.013) and decreasing BAT lipid content (C; p = 0.017), trending towards significance with respect to live BAT temperature (D; p = 0.06). Individual mice (n = 8) are represented by the data points on B–D (shown as mean ± SD), and correlation analysis was performed to generate r values, the Pearson correlation coefficient.