Dissecting the inhibitory architecture governing basal ganglia output

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Abstract. The subthalamic nucleus (STN) is part of the basal ganglia. It plays a role in motor behavior through its connections with the globus pallidus, substantia nigra, and possibly through direct connections with the pedunculopontine nucleus (PPN). Retrograde labeling shows that the STN synapses onto PPN neurons, but it is unclear whether this connection has a functional role in motor output. Because both the STN and PPN are targeted in deep brain stimulation to alleviate motor symptoms in degenerative disorders, understanding their connectivity will yield deeper insights into the circuit mechanisms of motor control. Using in vivo optogenetic stimulation, we will directly test the behavioral effects of activating this connection. Specifically, we will infect STN neurons with channelrhodopsin and activate STN axons via a fiber implanted above the PPN. We will activate this circuit in freely-moving mice, during motor skill learning, and during a challenging balance task. While stimulating the STN input onto the substantia nigra inhibits motion, we hypothesize that stimulating the STN-PPN connection will modulate locomotion, balance, and motor learning. This hypothesis is based on previous findings that the STN sends excitatory inputs to the PPN and that direct stimulation of STN cell bodies affects motion and motor skill learning. This project will yield a better understanding of the functional relationship between the STN and the PPN and is the first step toward developing more specific deep brain stimulation treatments.