Chronic tic disorders including Tourette syndrome (TS) affect at least 2% of all school children and often persist into adulthood. Symptoms commonly interfere with education, employment, or social relationships, and in some individuals symptoms produce marked disability. Neuroleptics and other drugs reduce tic severity, but all TS treatment is empiric since the pathophysiology of tics is incompletely understood. However, a recent functional imaging study showed a medication- sensitive abnormality of brain function. A cognitive task involving working memory (WM) produced excessive activation of several brain regions, but the excessive activation normalized after administration of the dopamine precursor levodopa. This drug is well suited for neuroimaging studies as it is well tolerated in TS and (when given with carbidopa) essentially delivers dopamine to the brain only. The research proposed herein aims to clarify the cognitive task components and the clinical variables that combine to produce the abnormal responses to the WM task and levodopa. Adults with TS or chronic tic disorders, and matched controls, will be studied using functional MRI and WM tasks after levodopa or saline infusion on different days. Cognitive tasks will include parametric scaling of working memory load and matched spatial and verbal working memory tasks. Careful characterization of subjects will allow tests of how the imaging findings are affected by clinical variables such as comorbidity (e.g., ADHD, OCD), severity, or past medication exposure. Additionally, a mixed (pergolide) and D2-like-selective (pramipexole) dopamine receptor agonist, or placebo, will be given on separate scanning days with the same cognitive tasks to help determine the pharmacological mechanism of the levodopa effect. The significance of this research includes its potential to define an endophenotype for future developmental or genetic studies of TS.
| Siddiqi, Shan H; Creech, Mary L; Black, Kevin J (2015) Orthostatic stability with intravenous levodopa. PeerJ 3:e1198 |
