DRD2 and opiate dependence: This study shows that the DEGs that are implicated in the development of opioid dependence and addiction in the winners are Oprk1 in the VTA (upregulation) and STR (downregulation); Oprd1 (upregulation) in MRNs and Oprd1 and Penk (upregulation) in the PFC; Pdyn gene (upregulation) in the NAcc as well as Th, Ddc, Slc6a2, Slc6a3, and Snca in the VTA (upregulation) and Drd2 and Pdyn (upregulation) in the NAcc.