GPR6 and Parkinson disease: Supporting this hypothesis, a recent study has shown that depletion of the orphan G-protein coupled receptor 6 (GPR6) in D2-MSNs reduced intracellular cyclic adenosine monophosphate (cAMP) concentrations, leading to increased striatal dopamine and decreased involuntary movements following apomorphine treatment in 6-OHDA-lesioned PD mice (Sun et al., 2021).