To evaluate the consequences of UCP-1 deficiency on emotionality, we applied a series of paradigms for the examination of anxiety-related and depression-related behavior in UCP-1 KO mice and WT littermate controls, after confirming the absence of the UCP-1 transcript in KO mice (Extended Data Fig. 1-1A) Consistent with previous reports (Liu et al., 2003), we also found no alterations in the body weight of UCP-1 KO mice at 3 months of age (Extended Data Fig. 1-1B). This evidence concerns the gene UCP1 and major depressive disorder.