This research plan is focused on neurochemical positron emission tomography (PET) studies of Parkinson disease (PD). PD is the most common neurodegenerative movement disorder, and considerable progress has been made in understanding and treating the "typical" movement abnormalities of resting tremor, bradykinesia and rigidity. These cardinal PD features are all initially responsive to dopamine replacement therapy, and have been investigated intensively with respect to their relationships to degeneration of the nigrostriatal dopamine projection. More recently, increased attention has focused on the "non-motor" clinical aspects of PD, including cognitive, mood, chronobiological and peripheral autonomic defects. These clinical features are less reliably affected by dopaminergic therapy, and are likely to be associated with other, non-dopaminergic neural degenerations. Indeed, detailed postmortem assessments of PD brain reveal substantial neuronal losses in a variety of chemically-defined neurons, including brainstem serotonin and norepinephrine neurons and basal forebrain cholinergic neurons. Projects in the proposal will focus on dementia, depression, sleep-apnea and dysautonomia in PD patients, employing PET measures of presynaptic dopaminergic, serotoninergic and cholinergic CNS neurons and of peripheral sympathetic neurons. Results of the investigations may identify associations of non-motor PD signs and symptoms with the non-dopaminergic neuronal losses. These findings will establish additional therapeutic targets for symptomatic, but also for potential neuroprotective PD therapies. In addition, a majority of patients will be characterized with all 3 CNS PET measures. The availability of multiple markers of distinct neuronal populations involved in PD neurodegeneration will permit exploratory analyses to assess whether the degenerations are correlated (possibly manifestations of a common pathophysiology) or apparently independent (possibly a manifestation of multiple PD subtypes or pathophysiologies). Ultimately, better understanding of these non-motor features will be essential to developing future treatments that address the entire PD patient.