Diverse Mechanisms Lead to Common Dysfunction of Striatal Cholinergic Interneurons in Distinct Genetic Mouse Models of Dystonia.

Clinical and experimental data indicate striatal cholinergic dysfunction in dystonia, a movement disorder typically resulting in twisted postures via abnormal muscle contraction. Three forms of isolated human dystonia result from mutations in the (DYT1), (DYT6), and (DYT25) genes. Experimental models carrying these mutations facilitate identification of possible shared cellular mechanisms. Recently, we reported elevated extracellular striatal acetylcholine by microdialysis and paradoxical excitation of cholinergic interneurons (ChIs) by dopamine D2 receptor (D2R) agonism using slice electrophysiology in mice. The paradoxical excitation was caused by overactive muscarinic receptors (mAChRs), leading to a switch in D2R coupling from canonical G to noncanonical β-arrestin signaling. We sought to determine whether these mechanisms in mice are shared with knock-in and knock-out dystonia models and to determine the impact of sex. We found mice of both sexes have elevated extracellular striatal acetylcholine and D2R-induced paradoxical ChI excitation, which was reversed by mAChR inhibition. Elevated extracellular acetylcholine was absent in male and female mice, but the paradoxical D2R-mediated ChI excitation was retained and only reversed by inhibition of adenosine A2ARs. The G-preferring D2R agonist failed to increase ChI excitability, suggesting a possible switch in coupling of D2Rs to β-arrestin, as seen previously in a DYT1 model. These data show that, whereas elevated extracellular acetylcholine levels are not always detected across these genetic models of human dystonia, the D2R-mediated paradoxical excitation of ChIs is shared and is caused by altered function of distinct G-protein-coupled receptors. Dystonia is a common and often disabling movement disorder. The usual medical treatment of dystonia is pharmacotherapy with nonselective antagonists of muscarinic acetylcholine receptors, which have many undesirable side effects. Development of new therapeutics is a top priority for dystonia research. The current findings, considered in context with our previous investigations, establish a role for cholinergic dysfunction across three mouse models of human genetic dystonia: DYT1, DYT6, and DYT25. The commonality of cholinergic dysfunction in these models arising from diverse molecular etiologies points the way to new approaches for cholinergic modulation that may be broadly applicable in dystonia.