SPECT imaging of dopamine and serotonin transporters with [123I]?-CIT. Binding kinetics in the human brain

Abstract

Single photon emission computerized tomography (SPECT) studies in non-human primates have previously shown that the cocaine derivative [¹²³I]-2-β-carbomethoxy-3-β-(4-iodophenyl)-tropane ([¹²³I]β-CIT) labels dopamine transporters in the striatum and serotonin transporters in the hypothalamusmidbrain area. Here, we report on the regional kinetic uptake of [¹²³I]β-CIT in the brain of 4 normal volunteers and 2 patients with Parkinson's disease. In healthy subjects striatal activity increased slowly to reach peak values at about 20 hours post injection. In the hypothalamus-midbrain area peak activities were observed at about 4 hours with a slow decrease thereafter. Low activity was observed in cortical and cerebellar areas. The striatal to cerebellar ratio was about 4 after 5 hours and 9 after 20 hours. In 2 patients with idiopathic Parkinson's disease striatal activity was markedly decreased while the activity in hypothalamus-midbrain areas was only mildly diminished. Uptake into cortical and cerebellar areas appeared to be unchanged in Parkinson's disease. Consequently, in Parkinson's disease the striatal to cerebellar ratio was decreased to values around 2.5 after 20 hours. These preliminary methodological studies suggest that [¹²³I]β-CIT is a useful SPECT ligand for studying dopamine and possibly also serotonin transporters in the living human brain.