Furthermore, the expression of D2R, A2AR and mGluR5 heteromers, and therefore the interaction between these receptors, within the dendritic spines of dorsal and ventral striato-pallidal GABAergic neurons involved in PD, may suggest an involvement of these receptors in the pathogenesis of PD (Fuxe et al., 2003). This evidence concerns the gene GRM5 and Parkinson disease.