Role of Glutamatergic Neurons in External Globus Pallidus in the Behavioral Deficits in Animal Models of Progressive Dopamine Depletion

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SUMMARY The basal ganglia are a group of subcortical nuclei that regulates motor and cognitive functions. Recent identification of neuronal heterogeneity in the basal ganglia suggests that functionally distinct neural circuits defined by their molecular identity and efferent projections exist even within the same nuclei. This distinction may account for a multitude of symptoms associated with basal ganglia disorders such as Parkinson's disease (PD). However, our incomplete understanding of the basal ganglia functional organization has hindered further investigation of individual circuits that may underlie distinct behavioral symptoms in different disease states. The external globus pallidus (GPe) is a central basal ganglia nucleus that can influence numerous downstream regions. While the prevailing circuit model assumes that the GPe is a homogeneous population of neurons transferring the signal in the indirect pathway of the basal ganglia, accumulating evidence suggests that neurons in the GPe are more heterogeneous than previously appreciated. Although GPe is known to be a nucleus with GABAergic neurons, we have identified novel cell types expressing VGLUT2, glutamatergic neuronal marker, at the outer layer of GPe. In our careful anatomical and molecular examination showed that VGLUT2GPe neurons project mainly to inner part of GPe, making synaptic contacts onto other neuronal populations. Recent evidence showed that the distinct cell types in GPe may have different roles in modulating basal ganglia circuitry and associated behaviors. Thus, elucidating the anatomical and functional organization of VGLUT2GPe neurons will provide novel cellular and circuit information to understand basal ganglia function. The progressive nature of behavioral deficits associated with PD is very well documented in human patients. However, what neural adaptations associated with behavioral deficits at different stages of PD are not fully understood. In this application, we try to address this with two different animal models. First, as in our preliminary results and recent reports, we will administer different doses of neurotoxin administration to induce different degrees of DA neuronal loss, which elicit the different behavioral deficits. Second, we will confirm the neurotoxin- induced PD-related behaviors in MitoPark mice which show the progressive loss of DA neurons. Examining the circuit adaptation in two animal models will provide an important information on the neural mechanisms underlying the progressive nature of PD. Therefore, using cutting-edge techniques including optogenetic, genetic and viral-mediated manipulation, in vivo multi-unit recording, and so on, we will decipher roles of VGLUT2GPe neurons in behavioral deficits in these two animal models for PD.