PET imaging of neuroreceptors in schizophrenia

Among the brain imaging techniques developed during the past two decades positron emission tomography has the highest sensitivity, allowing the analysis of specific neurotransmitter mechanisms in the living human brain. By using a combination of selective ligands labelled with positron emitting isotopes, D1 and D2 dopamine, serotonin 5HT2 and benzodiazepine receptors were examined in schizophrenic patients (DSM-IIIR) and healthy control subjects. With this technique receptor populations could be excellently visualized and quantified with regard to number and binding characteristics in several brain regions. The characteristics of total D1 and D2 dopamine receptor populations in the caudate and putamen did not differ significantly in young drug naive schizophrenic patients and age matched control subjects. On the other hand, there was a highly significant reduction of the D1 signal in high intensity regions of the basal ganglia when [11C]SCH 23390, a selective D1 dopamine receptor antagonist, was used. These results suggest the possibility of a reduced D1 dopamine receptor density in the patch compartment of the basal ganglia in schizophrenia. For 5HT2 and benzodiazepine receptors no major alteration of receptor characteristics was observed in several neocortical and limbic brain regions.