As various mental disorders, including anxiety (Davis, 1992), depression (Siegle et al., 2007; Shen et al., 2019), and PTSD (Shin et al., 2006), are highly correlated with hyperactivation and dysfunction of the amygdala and the fear memory circuitry, our finding supports CCK and its receptors as potential new targets for future therapeutic applications for these disorders. This evidence concerns the gene CCK and major depressive disorder.