Modified high-performance liquid chromatography with electrochemical detection method for plasma measurement of levodopa, 3-O-methyldopa, dopamine, carbidopa and 3,4-dihydroxyphenyl acetic acid.

Plasma measurements of levodopa and its major metabolites including dopamine and 3-O-methyldopa have been limited by cumbersome methods and poor sensitivity within relatively narrow ranges of plasma levels. We now report a modification of an HPLC method that permits concomitant measurements of a wide range of concentrations of levodopa, dopamine (DA), carbidopa, 3-O-methyldopa (3-OMD) and 3,4-dihydroxyphenyl acetic acid (DOPAC) from one HPLC injection. The recoveries ranged from 77 to 107% with an intra-day precision around 5% (CV) and inter-day CV's about 10-20%.

Levodopa challenge neuroimaging of levodopa-related mood fluctuations in Parkinson's disease.

Some patients with advanced Parkinson's disease (PD) develop dose-related fluctuations in mood. This may reflect alterations in dopamine-influenced brain circuits that mediate emotion. However, there is no available information to localize which dopamine-influenced neurons may be most affected.

Dopaminergic modulation of response inhibition: an fMRI study.

Dopamine has been hypothesized to modulate response inhibition. To test this hypothesis, we used functional magnetic resonance imaging (fMRI) to measure the effects of the dopamine prodrug levodopa on the brain responses to a well-validated response inhibition task (go/no-go, or GNG). Since abnormalities of response inhibition and dopamine have been thought to underlie tics and other symptoms of Tourette syndrome, we studied 8 neuroleptic-naive adults with tic disorders as well as 10 well-matched healthy controls.

Cognitive-pharmacologic functional magnetic resonance imaging in tourette syndrome: a pilot study.

Background: Dopamine agonists and antagonists can reduce abnormal movements and vocalizations (tics) in Tourette syndrome (TS); however, dopamine-responsive abnormal function in specific brain regions has not been directly demonstrated in TS. We sought to identify dopamine-modulated brain regions that function abnormally in TS by combining functional magnetic resonance imaging (fMRI), a working memory (WM) task, and infusion of the dopamine prodrug levodopa (while blocking dopamine production outside the brain).

Methods: We obtained complete fMRI data in 8 neuroleptic-naive adults with a chronic tic disorder and in 10 well-matched tic-free control subjects.

Rapid intravenous loading of levodopa for human research: clinical results.

Levodopa has several advantages as a pharmacological challenge agent for human neuroscience research. Exogenous levodopa changes striatal neuronal activity and increases extracellular dopamine concentrations, and with adequate inhibition of peripheral metabolism levodopa does not change mean cerebral blood flow. For neuroimaging studies of Parkinson disease (PD) and Tourette syndrome, we sought to rapidly produce a biologically relevant steady-state levodopa concentration and then maintain that concentration for at least an hour.