Measuring age-related changes in dopamine D₂ receptors with ¹¹C-raclopride and ¹⁸F-N-methylspiroperidol

Abstract

This study investigates the rate of age-related dopamine D₂ receptor loss as determined by positron emission tomography (PET) and ¹¹C-raclopride and compares it with D₂ loss previously estimated with ¹⁸F-N-methylspiroperidol (NMS). Dopamine D₂ receptors were measured with ¹¹C-raclopride in 24 healthy volunteers (24–73 years of age) using the ratio of the distribution volume in striatum to that in cerebellum ($\text{B}{}_{\mathrm{<mtext>max</mtext>}}\text{K}{}_{\mathrm{<mtext>d</mtext>}}\text{+1}$). The results were compared with those obtained in 20 healthy male volunteers (20–49 years of age) in whom D₂ receptors were measured with NMS using the ratio index (slope of the striatum-to-cerebellum ratio as a function of time). Findings of correlational analysis between age and dopamine D₂ receptor availability were significant for both ligands. Estimates of dopamine D₂ receptors loss per decade corresponded to 7.9% for the ¹¹C-raclopride study and 7.8% for the NMS study. Both ligands documented significant age-related decreases in dopamine D₂ receptors that occurred relatively early in life (40 years of age).