LEPR and obesity due to melanocortin 4 receptor deficiency: LepR-Cre Slc7a5fl/fl mice displayed a significant decrease in norepinephrine turnover in both BAT and soleus muscle tissue compared with control mice at 7 weeks of age (Figure 5, I and J), thereby indicating that Slc7a5 deficiency in LepR-expressing neurons led to loss of sympathetic innervation of BAT and muscle before the onset of obesity.