Alterations in the concentration of serotonergic and dopaminergic substances in the cerebrospinal fluid of patients with Parkinson's disease, and their changes after L-dopa administration.

In untreated patients with Parkinson's disease (PD), the total (free and conjugated) serotonin (5-HT) and dopamine (DA) concentrations in the cerebrospinal fluid decreased significantly. While the 5-HT concentration displayed a non-significant trend of negative correlation with the DA concentration in controls, it had a significant positive correlation with the DA concentration in untreated PD patients. In L-dopa-treated patients, the DA concentration increased remarkably, whereas the 5-HT concentration decreased further compared with untreated patients. The tryptophan, 5-hydroxyindolacetic acid (5-HIAA), and 3-OH kynurenine concentrations had significant positive correlations with L-dopa doses. The 5-HT concentration had a significant positive correlation with scores of psychomatric testing in L-dopa-treated patients.