To investigate whether caffeine and A2A antagonists can modulate the dopaminergic system in the striatum that underlies drug addiction and treatment of PD, we chose low dosage of caffeine (10 mg/kg/day) and A2A antagonist SCH58261 (2 mg/kg/day), which can induce the sensitization of locomotor activity and reward behavior, to evaluate the roles of dopaminergic neurons in the striatum. This evidence concerns the gene IGKV2D-29 and Parkinson disease.