Variability in D 2 ‐dopamine receptor density and affinity: A PET study with [ 11 C]raclopride in man

The variability of D 2 ‐dopamine receptor binding parameters in man was determined using Positron Emission Tomography (PET) and [ 11 C]raclopride. A saturation analysis based on five PET‐experiments was performed in each of ten men and ten women. The mean density of D 2 ‐dopamine receptors (B max ) was 28 ± 6.9 pmol/ml (mean ± S.D.) and the apparent affinity (K d app )9.1 ± 1.9 pmol/ml. The Hill coefficient was in all subjects close to unity (n H : 0.999 ± 0.020), thereby indicating binding to a homogeneous class of receptors. No significant differences between males and females were found in B max or K d app . The interindividual difference in B max was statistically significant (α = 0.01). The difference in K d app was not significant. Upregulation of the receptor density (B max ) has been widely discussed as a mechanism for increased dopaminergic neurotransmission in schizophrenia. This study indicates that receptor density varies considerably in a group of healthy subjects. © 1995 Wiley‐Liss, Inc.