Additionally, β2-AR KO mice showed high motivational effects of cocaine in coincident with the higher anxiety-like behavior observed in elevated plus maze and light-dark box model, consistent with the previous studies, which demonstrated that anxiety-like behavior predicted cocaine-CPP (i.e., the more anxious mice showed more preference for the cocaine-paired compartment) and anxiety increased vulnerability for cocaine (Ladrón de Guevara-Miranda et al., 2016). This evidence concerns the gene ADRB2 and Anxiety.