In the present protocol, dopaminergic function will be directly examined in schizophrenic patients and healthy controls by estimating synaptic dopamine concentrations through amphetamine-induced displacement 11-C-raclopride (RAC) with PET. Raclopride, a highly specific D-2 ligand, competes with synaptic dopamine for D-2 receptor binding. By increasing synaptic dopamine concentrations with amphetamine, thereby decreasing the amount of bound radiotracer, an estimate of synaptic dopamine concentration is derived. We have completed nonhuman primate studies which validated the amphetamine/raclopride methodology. We found that a constant infusion of RAC in a single study had a number of advantages over a two-scan bolus approach (Carson et al 1995); amphetamine (.4mg/kg) produced 18% (mean, N=5) RAC displacement (Carson et al 1995); and there was a good relationship between RAC displacement and simultaneaously-derived extracellular dopamine levels (Breier et al 1995: Breier et al 1995). Our normal volunteer studies demonstrate between 10% and 20% RAC displacement (Breier et al 1995) and have addressed methodologic issues such as the effects of movement and nonspecific effects of 'nondopaminergic' psychotogenic agents (e.g., ketamine). We are well into the schizophrenia study (neuroleptic-niave patients N=2; neuroleptic withdrawn patients N=5) with preliminary anlysis suggesting greater dopamine release compared to controls).
