IMAGING OF RECEPTORS IN CLINICAL NEUROSCIENCES

This article deals with the question why should one determine receptor s in the brain with positron and single photon emission tomography (PE T and SPECT, respectively). Radiopharmaceuticals for a wide variety of receptors are available now. Receptors studies with PET and SPECT hav e thus far focused on the following issues : occupancy during drug tre atment, quantification in neuropsychiatric diseases and visualizing sp ecific pathology. Far most studies on receptor occupancy are concerned with antipsychotic treatment in schizophrenic patients. During treatm ent with classical antipsychotic drugs more than 65% of the receptors are occupied in both responding and drug therapy resistant patients. H igh occupancy appeared to be linked to frequent occurrence of extrapyr amidal symptoms (parkinsonism). Atypical antipsychotic drugs, producin g no parkinsonism, are effective even when less than 50% dopamine D-2 receptors are blocked. Quantification of receptor density in vivo depe nds very much on the mathematical models used, and is often very diffi cult and thus far of little clinical use. Finally, receptors can be us ed as markers for specific neurons or other cells. In the caudate nucl eus dopamine receptors are localized in neurons that degenerate in Hun tington's disease, so early in the disease decreases in receptor bindi ng can be shown. In Alzheimer disease decreases in neural receptor and increases in omega-3 receptors are observed indicating degeneration a nd inflammation, respectively.