DOPAMINE D2-RECEPTOR DENSITY IN HUMANS AS ASSESSED WITH SPET AND THE NEW HIGH-AFFINITY LIGAND I-123 NCQ298 - A PILOT-STUDY

Astra (S)-3-[I-123] -5,6-dimethoxyl-N-[(1-ethyl-2-pyrrolidinyl)methyl] -salicylamide (I-123-NCQ298) is a new high-affinity D2-receptor ligan d for use in single photon emission tomography (SPET) studies. We have studied the biodistribution and absorbed radiation dose of I-123-NCQ2 98 in humans. The mean effective dose for adults was 0.055 mSv MBq-1. Brain uptake and clearance was measured with a head dedicated SPET cam era. 123 I-NCQ298 showed specific uptake in the basal ganglia with a l ow clearance rate (time constant of 9-34 h). The extrastriatal binding was variable (average 30%, maximum 60% of that in the basal ganglia a t 1 h), but with a clearance rate twice that of the basal ganglia. The fairly high level of extrastriatal binding precluded the use of a quo tient between the basal ganglia and cerebellum-to-frontal cortex I-123 -NCQ298 concentration as a measure for basal ganglia D2-receptor densi ty. Chronic schizophrenic patients treated with conventional neurolept ics had a decreased affinity for I-123-NCQ298 in the basal ganglia in the range 10-60% of the median value for the control, untreated subjec ts. ((C) 1998 Chapman & Hall Ltd.).