Although D2/3R agonists are considered a strong risk factor for ICD, other dopamine replacement therapies, such as levodopa, induce ICD (albeit at lower rates), suggesting the involvement of both D1R and D2R signalling.69 As with the D2R agonist, we chose a low dose of a D1R agonist to produce therapeutic locomotor effects in parkinsonian mice, as higher doses of D1R agonists induced aversive behaviour in 6-OHDA-lesioned rats.68 We found that the D1R agonist A77636 produced impulsivity only in parkinsonian mice, consistent with our findings with PPX. This evidence concerns the gene DRD1 and impulse control disorder.