Of particular relevance here, chronic L-DOPA treatment, at doses that induce dyskinesia, restores spine density on D2R expressing MSNs (Fieblinger et al., 2014; Nishijima et al., 2014; Suarez et al., 2014, 2016; Gomez et al., 2019) and, while not restoring spine density, leads to increases spine size in D1R expressing MSNs (Fieblinger et al., 2014; Nishijima et al., 2014). This evidence concerns the gene DRD1 and drug-induced dyskinesia.