Convection-Enhanced Delivery to Study the Pathophysiology Underlying the Clinical Features of Parkinson s Disease

Background: * Parkinson s disease (PD) is a progressive neurodegenerative disorder that affects the brain cells that make the chemical dopamine. The primary medical treatment for PD has been to use medications to replace the dopamine that is missing from the brain. These medications can be effective at first, but after many years side effects and tolerance develop. * Surgery can treat basic PD symptoms and complications. Deep brain stimulation (DBS) offers a safer alternative as the therapy can be adjusted and reversed to minimize side effects and optimize beneficial effects. DBS treats the symptoms of PD but does not alter its course. * Infusions of neurochemicals or medications are another PD treatment method. NIH researchers have developed the technique of convection-enhanced delivery, which very precisely and consistently delivers infusions of many types into the brain. This project will allow researchers to infuse a medication, Muscimol, into the subthalamic region of the brain to see if it is as safe and effective as DBS. Objectives: * To determine whether an infusion of Muscimol into the brain is safe and relieves the symptoms of Parkinson s disease. * To demonstrate that the infusion can be monitored with magnetic resonance imaging (MRI) using gadolinium. Eligibility: * Patients 18 years of age and older who have Parkinson s disease and are preparing for bilateral subthalamic nucleus (STN) DBS surgery. * Patients will be divided into two groups. One group of patients will have a partial infusion of Muscimol into the STN, and the second group of patients will have complete infusion of Muscimol into the STN. Design: * This study will begin 5 days before the patient undergoes bilateral subthalamic DBS surgery. * On Day 1 of the study, small thin tubes (microcatheters) will be inserted into the STN through the same incision and burr holes that are used for DBS. Two infusion studies of Muscimol will be performed on successive days: the first without PD med