It has also been demonstrated that: (i) KD may increase extracellular adenosine level (Masino et al., 2012; Lutas and Yellen, 2013); (ii) inhibition of adenosine receptors (A1R and A2AR) by means of caffeine promotes anxious behavior (Klein et al., 1991); (iii) A1R- or A2AR-knockout mice showed anxiogenic-like behaviors (Ledent et al., 1997; Johansson et al., 2001); and (iv) modulation of adenosine receptor activity might be an effective treatment strategy for patients with anxiety disorders (Kovács and Dobolyi, 2013). This evidence concerns the gene ADORA2A and anxiety disorder.