GRM1 and schizophrenia: Moreover, an unbalance of mGluR1-dependent LTD, due to altered NRG1/ErbB signaling in SNpc DA neurons, could contribute to the dysfunctions in the nigrostriatal DA transmission occurring in PD and schizophrenia (Perez-Costas et al., 2010; Yoon et al., 2013; Ledonne and Mercuri, 2017; Weinstein et al., 2017).