DRD3 and Parkinson disease: In addition to neurotrophic factors, dopamine receptor D3 (DRD3) and dopamine receptor D5 (DRD5) are known to be involved in adult neurogenesis as well as the pathophysiology of PD (Borta and Höglinger, 2007; Chen et al., 2013; Chetrit et al., 2013; Lao et al., 2013; Elgueta et al., 2017).