Effect of Age on D2 Dopamine Receptors in Normal Human Brain Measured by Positron Emission Tomography and 11C-Raclopride

Human postmortem and animal experimental results suggest a decline of the cerebral dopaminergic neuronal system with age. In this study, the radiotracer carbon 11-labeled-raclopride and positron emission tomography were applied to determine the effect of age on striatal D2 dopamine receptors in 32 healthy volunteer subjects (age range, 21 to 68 years; median, 31 years). An index of specific 11C-raclopride binding was calculated for putamen, caudate nucleus, and other brain regions in each subject. A significant decrease with age of the index for specific tracer uptake was found in putamen and caudate nucleus. The decrease was steep until 30 years, but slower afterward. After approximately 30 years of age, the decline of specific 11C-raclopride binding in putamen was found to be 0.6% per year. Our results suggest that D2 dopamine receptor binding sites (mainly postsynaptically located) decrease as a consequence of normal aging in parallel with the decline of the presynaptic nigrostriatal dopaminergic neuronal system.