Effect of disease and drug treatment on blood serotonin and monoamine oxidase B activity in Parkinson's disease.

Serotonin (5-hydroxytryptamine, 5HT) content and monoamine oxidase (MAO) activity were determined in whole blood of patients with Parkinson's disease (PD) with and without drug treatment and compared with controls. From that comparison a significant reduction in platelet 5HT became apparent in PD. Selegiline, which was always used in combination with L-dopa, not only inhibited MAO activity, as expected, but it also appeared to induce an increase in 5HT content.