CRY2 and major depressive disorder: Considering that anhedonia is one of the core symptoms of depression in humans and that it is commonly used as indicator of depression-like behavior in animal models (Willner et al. 1992), the observed augmented anhedonic behavior in Cry2−/− mice supports previous observations that link altered expression of Cry2 to depression, both in humans (Lavebratt et al. 2010) and in experimental animals (Griesauer et al. 2014; Savalli et al. 2014).