The Pharmacological Effects of Levodopa in Patients with TouretteSyndrome and Parkinson's Disease.

Claire Devine, Mentor: Dr. Kevin Black, Neuroimaging Laboratory, Mallinckrodt Institute of Radiology, Washington University School of Medicine

Tourette Syndrome (TS) is a neuropsychiatric disorder characterized by motor and vocal tics. It is often treated with dopamine antagonists. These drugs, also called neuroleptics, block the action of dopamine, a neurotransmitter integral to regulating movement, and lessen the severity of tics in patients. However, dopamine antagonists often produce unacceptable side effects, making a different form of treatment desirable.

The research in Dr. Kevin Black's lab explores the effect of pro-dopamine medicines in patients with TS. Specifically, research is being done with levodopa, a clinical drug that the brain turns into dopamine. Levodopa is a major treatment for Parkinson's Disease (PD), a disorder in which the dopamine-producing cells in the substantia nigra die. Levodopa is administered to patients with PD to correct the imbalance in the dopaminergic system. This treatment alleviates the tremors, rigidity, and immobility that PD patients experience.

Levodopa is an attractive form of treatment because it does not produce the severe side effects that neuroleptics do. Its pharmacology has been extensively researched, and the way that it reacts in the brain is being analyzed as well. While using the drug as a form of treatment for TS may at first seem counterintuitive, since tics are usually alleviated by blocking dopamine, there are indications that both blocking or increasing dopamine can treat TS.

The research that I participated in on the effect of levodopa on TS is a randomized, double-blind, placebo controlled study still in progress. Thirty patients with TS were given either levodopa and carbidopa or a matching placebo during the first eight weeks of a ten-week study period. Tic severity and the severity of any comorbid disorders (depression, attention-deficit/hyperactivity disorder, and obsessive compulsive disorder are common in patients with TS) were measured to evaluate the effectiveness and side effects of the drug. The results of the study, however, are unknown, as the lab is still blind to treatment assignment.