Effects of age on dopamine transporters in healthy humans

99mTc-TRODAT-1 is a new radiopharmaceutical that selectively binds the dopamine transporters. This study characterized the effects of aging on its regional cerebral distribution in healthy human volunteers.

The sample consisted of 27 men and 28 women with a mean age of 41.1 +/- 17.1 y (age range 18.7-73.8 y). Dynamic SPECT scans of the brain were obtained with a standardized acquisition and processing protocol on a triple-head camera. Mean counts per pixel were measured in multiple regions of interest within each basal ganglia. Regression analyses were used to relate the specific uptake values at 3-4 h after administration to age. Both linear and nonlinear models of aging were tested.

The relative concentration of radioactivity in most subregions of the basal ganglia decreased significantly with age (all P values < 0.0001). Nonlinear models of aging fit the data significantly better than a straight line. The rate of decline was significantly faster in young adults than in older volunteers (P < 0.001). The break-point age at which the rate of change slowed down and became more stable was 36 y old for the whole striatum and ranged from 32 to 44 y old depending on subregion.

The effects of aging on central nervous system dopamine transporters do not appear to be linear. Most effects seem to occur during young adulthood before people reach their 40s. The distribution then appears to remain relatively stable until late in life. The findings suggest that the adult life cycle is better characterized as a series of phases than as a continuum.