Finally, given the proposed importance of striatal cholinergic action through the M4 receptor for modulation of cortico-striatal plasticity and dopamine action in the context of schizophrenia (Watt et al., 2013), Parkinson’s disease (Shen et al., 2016), Huntington’s disease (Pancani et al., 2015), and substance abuse (de la Cour et al., 2015), the example of Chrm4 illustrates the potential of scRNA-Seq for the discovery of cell type-specific drug targets in the CNS. Here, CHRM4 is linked to Parkinson disease.