Effects of citalopram infusion on the serotonin transporter binding of [11C] DASB in healthy controls

The positron emission tomography ( PET) ligand [C-11] DASB is currently the most widely used imaging agent for quantitative studies of the serotonin transporter ( SERT) in human brain. The aim of this work was to assess the effects of an intravenous infusion of 10mg citalopram, a selective serotonin reuptake inhibitor ( SSRI), before the PET scan on the kinetics of [C-11] DASB in arterial plasma and in selected brain regions. Four healthy male volunteers underwent two PET scans with a mean of 523MBq injected activity after either placebo or citalopram infusion in a randomised design. The citalopram infusion led to a substantial increase of the area under the curve of the metabolitecorrected arterial plasma input function. Total volumes of distribution VT were estimated applying the Logan plot to regional time - activity curves or by generating parametric maps with spectral analysis. A mean reduction of the cerebellar VT of 19% with Logan analysis and of 24% with spectral analysis was observed after citalopram infusion, which confirms previous findings of displaceable SERT ligand binding in cerebellar grey matter. The SERT occupancy for six target regions with moderate to high binding was 60% derived from BPND and 69% derived from BPP.