SUMMARYDiagnosis of Parkinsons Disease (PD) is made late delaying treatment and limiting the ability to halt diseaseprogression. Treatments that target the prodromal phase of PD prior to the appearance of the cardinal motorsigns (tremor rigidity etc) and the degeneration of dopamine-producing neurons do not exist because we lackreliable biomarkers of early disease. Based on accumulating evidence vocal dysfunction is present during theprodromal phase of PD and offers a convenient entry point to identify early neuropathological changes aspotential treatment targets. Data from our laboratory and others has shown that the overexpression of a knownhuman-PD causing gene alpha-synuclein (-syn SNCA) in the rodent and finch brain leads to early vocalabnormalities consistent with human disease. As a synaptic protein -syn is critically involved in cell functionsincluding facilitating neurotransmitter release. Its cellular toxicity in PD has been targeted in human clinical trialsbut late in the disease when the neuropathology is already widespread. In fact little is known about how thephysiological role of -syn shifts to a pathophysiological one early on in PD. This R21 proposal addresses theseshortcomings by investigating early stage abnormalities in vocal motor output that can occur years beforetraditional motor symptoms. We propose to develop an integrated early stage platform for the evaluation of the-syn-mediated changes in neuronal and synaptic activity that drive abnormal vocal output. To do so we usethe zebra finch model system because it has specialized song-dedicated brain nuclei that can be experimentallytargeted; cell-specific changes in activity are then directly related to the vocal output. Area X is a song-dedicatednucleus within the finch basal ganglia. Within Area X striatal Medium Spiny Neurons (MSNs) and GlobusPallidus-like (PAL) projection neurons show singing-related firing activity that is directly related to variations insong structure. When -syn is virally overexpressed in Area X we detect PD-like changes in song includingreduced pitch amplitude and abnormal timing. In Aim 1 we test the hypothesis that these song changes resultfrom reduced MSN activity and increased PAL activity in freely behaving birds implanted with extracellularelectrode arrays. Aim 2 tests the hypothesis that -syn overexpression in Area X results in a time-dependentsuppression of glutamatergic currents in MSNs and enhanced GABAergic currents in PAL neurons in living brainslices. Our powerful integrative approach uses in vivo and ex vivo measurements of neural activity to evaluatehow -syn driven changes in specific neuronal sub-types correlates to the behavioral output. Thecharacterization of neuropathophysiological mechanisms underlying early stage PD-like vocal deficits will offernew disease-modifying treatment targets.