Loss of D-2 receptor binding with age in rhesus monkeys: Importance of correction for differences in striatal size

The relation between striatal dopamine D-2 receptor binding and aging was i nvestigated in rhesus monkeys with PET. Monkeys (n = 18, 39 to 360 months o f age) were scanned with C-11-raclopride; binding potential in the striatum was estimated graphically. Because our magnetic resonance imaging analysis revealed a concomitant relation between size of striatum and age, the dyna mic positron emission tomography (PET) data were corrected for possible par tial volume (PV) artifacts before parameter estimation. The age-related dec line in binding potential was 1% per year and was smaller than the apparent effect if the age-related change in size was ignored. This is the first in vivo demonstration of a decline in dopamine receptor binding in nonhuman p rimates. The rate of decline in binding potential is consistent with in vit ro findings in monkeys but smaller than what has been measured previously i n humans using PET. Previous PET studies in humans, however, have not corre cted for PV error, although a decline in striatal size with age has been de monstrated. The results of this study suggest that PV correction must be ap plied to PET data to accurately detect small changes in receptor binding th at may occur in parallel with structural changes in the brain.