DRD1 and Parkinson disease: Given the evidence that striatal levels of D1R (Shinotoh et al., 1993; Turjanski et al., 1997: Hurley et al., 2001) and other major mediators of D1R signaling (Girault et al., 1989; Nishino et al., 1993) are unchanged in PD patients, the dramatic increase in striatal Gαolf protein level may be a key event in the D1R hypersensitivity that develops in PD (Alcacer et al., 2012).