Tracer and maximal specific binding of tritiated spiperone or N-n-propylnorapomorphine to quantify dopamine receptors in rat brain regions in vivo

Abstract

Specific tracer and maximal specific binding (B max) were determined in rat brain regions from radioactivity accumulation after intravenous administration of 3H N-n-propylnorapomorphine (NPA) or 3H spiperone at various specific activities. With NPA the highest B max-values (expressed in pmol.g −1 tissue) were found in the striatum (26 pmol.g −1) nucleus accumbens (about 27 pmol.g −1) and the olfactory tubercle (11 pmol.g −1). Saturable NPA binding was also found in the amygdaloid complex, medulla oblongata and inferior colliculi, but not in the frontal cortex. B max values for spiperone were high in the striatum (73 pmol.g −1), the nucleus accumbens (48 pmol.g −1), the olfactory tubercle (34 pmol.g −1) and the frontal cortex (18 pmol.g −1). A similar order was found for the tracer contents in these regions. There was no linear relationship between these contents and B max values. The possible implcations of these findings and usefulness of NPA for brain imaging are discussed.