Dopamine D2 receptors in normal human brain: Effect of age measured by positron emission tomography (PET) and [11C]-raclopride

Human post-mortem and animal experimental results suggest a decline of the cerebral dopaminergic neuronal system with age. In this study, the radiotracer [¹¹C]raclopride (dopamine D2 antagonist) and positron emission tomography were applied to determine the effect of age on striatal dopamine D2 receptors in 32 healthy volunteer subjects (age range 21-68 years). Subjects were divided in two age groups on the basis of median age (31 years). An index for specific tracer uptake was calculated for caudate nucleus and putamen. Uptake indices in the older group of subjects were reduced on average 26% in putamen and 20% in caudate nucleus. The decline appeared to be steep until 30 years, but slower afterwards. After 30 years of age the decline of specific raclopride binding was found to be 0.6% per year. These results suggest that dopamine D2 receptor binding sites (mainly post-synaptically located) decrease as a consequence of normal aging in parallel with the decline of the pre-synaptic nigrostriatal dopa-minergic system.