ARE STRIATAL DOPAMINE D-4 RECEPTORS INCREASED IN SCHIZOPHRENIA

The density of dopamine D-2-like receptors was determined using [H-3]e monapride binding in putamen tissue taken postmortem from schizophreni c subjects and matched controls. A 72% increase in number of these rec eptors was identified in the schizophrenics, although three patients n ot receiving antipsychotic drug treatment before death exhibited recep tor densities in the control range. Displacement of 1 nM [H-3]emonapri de binding by raclopride was used to define the contribution of the D- 4 subtype of dopamine receptors to total [H-3]emonapride binding. No e vidence was obtained for the presence of D-4 receptors in putamen tiss ue from either control or schizophrenic subjects, indicating that the increase in D-2-like receptor density in schizophrenia is due not to a n increase in number of D-4 sites in the disease, but to an up-regulat ion of D-2 or D-3 receptors probably induced by chronic treatment with antipsychotic drugs.