PROJECT SUMMARY There is a fundamental gap in understanding the pathophysiology of isolated adult-onset dystonia due to genotypic and phenotypic heterogeneity. Determining common pathophysiologic mechanisms across dystonia subtypes is a critical step toward developing more generalizable and effective therapies. Emerging evidence points to striatal cholinergic interneurons (ChIs) playing a key role in the pathophysiology of dystonia, including biochemical and network-level dysfunction. In addition to offering a common therapeutic target, our findings are likely to benefit gene discovery and research on other disabling, less common forms of dystonia. Over the long term, results could guide researchers to perform greater in depth histopathological and biochemical studies in the brain that can lead to identification of new targets for therapeutic intervention. Our goal is to apply a recently developed PET radioligand, [18F]VAT, which possesses high selectivity for vesicular acetylcholine transporters, to investigate striatal ChIs. Structural and resting state functional MRI will examine the relationship of striatal ChIs to related brain networks across different focal dystonia subtypes. Identification of network-level changes across dystonia subtypes will provide better understanding of common pathophysiology and could potentially provide means to assess target engagement for future therapeutic interventions. The central hypothesis is that striatal ChIs contribute to a common pathophysiological mechanism in humans with isolated adult-onset focal dystonia, and that cholinergic integrity relates to striatal functional connectivity and clinical features of dystonia. The rationale for the proposed research is the likely involvement of striatal ChIs in a) normal motor control and b) animal models of dystonia. ChIs are autonomously active and mediate a baseline presynaptic inhibitory tone on striatal medium spiny neurons against the excitatory cortical drive, likely via modulation of dopamine release via presynaptic cholinergic receptors on nigrostriatal dopaminergic terminals. They also receive input from intralaminar thalamic neurons innervated by cerebellar afferents, that when dysfunctional may contribute to dystonic phenotypes. Thus, ChIs may contribute to a common pathogenic mechanism involving cortico-striata-thalamic or cerebello-thalamo-striatal networks. This hypothesis will be tested by pursuing three specific aims: Determine if 1) dysfunction of striatal ChIs is a common mechanism across isolated dystonia subtypes; 2) common aberrations in functional striatal brain networks underlie the isolated dystonia subtypes; 3) clinical characteristics relate to markers of ChIs and brain network dysfunction across different isolated adult-onset focal dystonias. This approach is innovative as it uses comprehensive multimodal imaging to investigate novel PET- measured cholinergic integrity and related functional networks. The proposed research is significan...