Are Striatal Dopamine D₄ Receptors Increased in Schizophrenia?

Abstract: The density of dopamine D₂-like receptors was determined using [³H]emonapride binding in putamen tissue taken postmortem from schizophrenic subjects and matched controls. A 72% increase in number of these receptors was identified in the schizophrenics, although three patients not receiving antipsychotic drug treatment before death exhibited receptor densities in the control range. Displacement of 1 nM [³H]emonapride binding by raclopride was used to define the contribution of the D₄ subtype of dopamine receptors to total [³H]emonapride binding. No evidence was obtained for the presence of D₄ receptors in putamen tissue from either control or schizophrenic subjects, indicating that the increase in D₂-like receptor density in schizophrenia is due not to an increase in number of D₄ sites in the disease, but to an up-regulation of D₂ or D₃ receptors probably induced by chronic treatment with antipsychotic drugs.