Differential kinetics of [123I]β-CIT binding to dopamine and serotonin transporters

Iodine-123-labelled 3β-(4-iodophenyl)tropane-2β-carboxylic acid ([123I]β-CIT) labels both the dopamine transporter (DAT) and the serotonin transporter (5-HTT) and this ligand is able to clarify pathological changes in both dopaminergic and serotonergic systems. However, the differential kinetics of β-CIT binding to DAT and 5-HTT has not been clarified fully. In this study we examined time-activity curves of [123I]β-CIT in individual regions in the rat brain. Using cerebellum as the reference region, k3 and k 4 values were estimated by a two-compartment kinetic analysis. In the striatum, the kinetics was slowest among all brain areas. In this area specific binding reached its peak 4 h after the injection. In the hypothalamus, specific binding reached its peak 1 h after the injection and its amount did not change until 4 h after the injection. In the occipital cortex, the binding and washout of the ligand were fastest among all brain regions. Estimated k 3 values were 0.040 ±0.003 in the striatum, 0.019 ±0.002 in the hypothalamus and 0.082 ±0.011 in the occipital cortex (min -1, mean ±SD). Estimated k 4 values were 0.0034 ±0.0005 in the striatum, 0.0071 ±0.0009 in the hypothalamus and 0.083 ±0.013 in the occipital cortex (min -1, mean ±SD). Therefore binding kinetics of [ 123I] β-CIT in the region rich in DAT is apparently different from that in the region rich in 5-HTT. These results will provide fundamental data to image both DAT and 5-HTT in one series of examinations with [ 123I] β-CIT. (orig.). With 3 figs., 1 tab