Bimodal Distribution of Brain Dopamine D2 Receptors in Schizophrenic Patients Explained by In Vivo Binding Studies
The so-called dopamine bypothesis in schizophrenia can be divided into two subhypotheses: one involving pathogenetic aspects of the dopamine systems in the brain and the other the mode of action of antipsychotic drugs (Carlsson 1988). In particular, the D2 type dopamine receptor has been studied both in vitro (e.g., Seeman et al. 1984, 1987; Kornhuber et al. 1989) and very recently in vivo (e.g., Wong et al. 1986; Farde et al. 1987, 1988; Sedvall et al. 1986). Reports showing a pathogenetically increased dopamine D2 type receptor density in vivo (e.g., Seeman et al. 1984, 1987; Kornhuber et al. 1989, and references therein) have been challenged as being the result of long-term antipsychotic medication (e.g., Kornhuber et al. 1989). In the most extensive report on in vitro D2 receptor investigations, published by Seeman and collaborators (1984, 1987), more than 100 schizophrenic brain specimens were analyzed. There appeared to be a bimodal distribution in the density in three brain areas: caudate nucleus and putamen, structures belonging to the extrapyramidal system, and the nucleus accumbens, a limbic structure. Interestingly, the mean densities of the two modes differed by twofold and the lowest density was rather similar to that of controls or of nonschizophrenic patients treated with antipsychotic medication.
KeywordsPositron Emission Tomography Dopamine Receptor Schizophrenic Patient Neuroleptic Treatment Acetylcholine Level
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