IBZM-SPECT imaging of dopamine D(2) receptors with typical and atypical antipsychotics

Considerable progress has been achieved over the past 15 years in uncovering the biological basis of major psychiatric disorders. Since psychopharmacological treatment is thought to act on the underlying biological basis of the disease, brain imaging techniques enable us to understand the mechanism of action of such compounds. One important tool used to determine patterns of brain dysfunction and how psychopharmacological agents such as antipsychotic compounds work is single-photon emission computerised tomography (SPECT). This technique allows determination of striatal D(2) receptor occupancy rates, which are associated with the extrapyramidal side effects (EPS) of antipsychotic drugs. Studies have confirmed that atypical antipsychotic agents have lower occupancy rates than typical agents. No association has been found between D(2) receptor occupancy rates in the striatum and antipsychotic efficacy, and it therefore appears that striatal D(2) receptor occupancy rates are not necessary for the antipsychotic effect of such agents in schizophrenia. The availability of more refined radioligands will help us not only to understand the action of antipsychotics but also the pathophysiology of schizophrenia.