Decrease in Human Striatal Dopamine D2 Receptor Density with Age: A PET Study with [11C]Raclopride

Abstract
The effect of age on human striatal dopamine D2 receptors was investigated with positron emission tomography (PET) using [11C]raclopride as a radioligand. Twenty-one healthy volunteers aged from 20 to 81 years were studied. An equilibrium method was applied and two separate PET scans with different specific activities of [11C]raclopride were performed. The maximal number of receptors ( Bmax) and their dissociation constant ( Kd) were calculated using Scatchard analysis. There was an age-dependent decline in the Bmax ( r = 0.49; p = 0.02) of striatal D2 receptors while the Kd remained unchanged. The results show that there is an age-related loss of striatal D2 receptors, which, together with other changes in the brain nigrostriatal dopaminergic system, may contribute to extrapyramidal symptoms associated with aging.