How the Loss of Dopamine and Dopamine-Restoring Medicines Affect Movement Performance

This study has two purposes: 1) to understand the effect of a decline of dopamine in the brain during normal aging and in patients with Parkinson's disease, and 2) to investigate how medicines used to treat Parkinson's disease improve movement performance in patients.

Patients with Parkinson's disease have difficulty performing precise finger movements, mainly because of a dramatic decrease of a substance called dopamine in parts of the brain. Medicines such as levodopa, which help restore dopamine levels, can greatly improve function; however, little is known about how these drugs work. In normal aging, dopamine decreases slightly in certain parts of the brain, but the importance of this decline is poorly understood. This study may provide new information about Parkinson's disease and normal aging that might lead to better treatment strategies.

Patients with mild to moderate Parkinson's disease and healthy volunteers 21 years of age and older may be eligible for this study. All participants must be right-handed. All candidates will be screened with a medical history and physical and neurological examinations, including memory tests and mood examination.

Brain function will be studied using functional magnetic resonance imaging (fMRI) study and positron emission tomography (PET). Participants may be asked to stop using medications that can affect the central nervous system, such as sleeping pills or drugs for depression or anxiety, for 1 week before each study visit. Patients with Parkinson's disease may also be asked to stop using antiparkinsonian medications at least 12 hours before each visit. In addition, all participants will be asked to abstain from alcoholic beverages at least 24 hours before the fMRI and PET scans, and from nicotine and caffeine for at least 12 hours before the scans.

Participants will have fMRI, which uses a strong magnetic field and radio waves to create images of the brain. The subject lies on a table in a tunnel-like cylinder (the scanner) for 1 to 2 hours, lying still for 5 to 15 minutes at a time. He or she can communicate with the technician or researcher at all times during the test through an intercom system. Scans will be done while the subject is at rest and while he or she is performing finger movements. The movements involve pushing five buttons on a box-each button every 3 seconds on average in a specific order. Patients with Parkinson's disease will be studied off- and then on- medications that restore the levels of levodopa in the brain.

Some participants may be asked to undergo a PET scan on a separate visit. A PET scanner is a doughnut-shaped machine similar in appearance to a CT (computed tomography) scanner. PET scans detect radioactivity used to provide information on brain activity. Before the test begins, subjects are given a dose of carbidopa-a medicine that increases the amount of levodopa in the brain. A catheter (thin, plastic tube) is then inserted into an arm or wrist vein, and a radioactive form of levodopa called 18Fluorodopa is injected through the catheter. A moldable plastic mask with large openings for eyes, nose, and mouth is placed on the face to help keep the head still during scanning. The total scan time is 2 hours or less.