[18F]FDOPA uptake in the raphe nuclei complex reflects serotonin transporter availability. A combined [18F]FDOPA and [11C]DASB PET study in Parkinson's disease

Brain uptake of [F-18]FDOPA, measured with PET, reflects the activity of aromatic amino acid decarboxylase, an enzyme largely expressed in monoaminergic nerve terminals. This enzyme catalyzes a number of decarboxylation reactions including conversion of L-dopa into dopamine and 5-hydroxytryptophan into serotonin. For more than 20 years [F-18]FDOPA PET has been used to assess dopaminergic nigrostriatal dysfunction in patients with Parkinson's disease (PD). More recently, however, [F-18]FDOPA PET has also been employed as a marker of serotoninergic and noradrenergic function in PD patients. In this study, we provide further evidence in support of the view that [F-18]FDOPA PET can be used to evaluate the distribution and the function of serotoninergic systems in the brain. Eighteen patients with PD were investigated with both [F-18]FDOPA and [C-11]DASB PET, the latter being a marker of serotonin transport (SERT) availability. We then assessed the relationship between measurements of the two tracers within brain serotoninergic structures. [F-18]FDOPA uptake in the median raphe nuclei complex of PD patients was significantly correlated with SERT availability in the same structure. Trends towards significant correlations between [F-18]FDOPA Ki values and [C-11]DASB binding values were also observed in the hypothalamus and the anterior cingulate cortex, suggesting a serotoninergic contribution to [F-18]FDOPA uptake in these regions. Conversely, no correlations were found in brain structures with mixed dopaminergic, serotoninergic and noradrenergic innervations, or with predominant dopaminergic innervation. These findings provide evidence that [F-18]FDOPA PET represents a valid marker of raphe serotoninergic function in PD and supports previous studies where [F-18]FDOPA PET has been used to assess serotoninergic function in PD. (C) 2011 Elsevier Inc. All rights reserved.