Bilbao and colleagues [122] demonstrated that, while A2AR KO mice were characterized by significant increase of diarrhea, sniffing, and the global withdrawal score, the manifestations of naloxone-precipitated morphine withdrawal syndrome were not modified in CB1/A2AR double KO mice, which may suggest opposite roles of these receptors in the morphine dependence [123]. This evidence concerns the gene ADORA2A and morphine dependence.