ADORA2A and Anxiety: It has been demonstrated that not only A1R-knockout mice, but also adenosine A2A receptor/A2AR-knockout mice showed enhanced level of anxiety, suggesting that both adenosine receptor types influence anxiety behavior (Ledent et al., 1997; Johansson et al., 2001; Giménez-Llort et al., 2002; Cunha et al., 2008).