Measurement of age effects on dopamine transporter expression using [¹¹C]altropane PET

Objectives Decreases in striatal dopamine transporter (DAT) levels have been implicated as a marker of neurodegeneration. SPECT has been used to measure DAT levels in the aging process, however, little has been done with PET. Compared to SPECT, PET yields better image quantitation and provides higher spatial resolution which minimizes partial volume effects that are exacerbated by age- and disease-related atrophy. The goal of this work was to determine the effects of age on DAT expression measured with [¹¹C]altropane PET in a group of normal controls.

Methods Dynamic PET scans were acquired in 18 healthy subjects (19-45 yrs) with an ECAT EXACT HR+ for 1 hour and were initiated with bolus injection of [¹¹C]Altropane. Regional binding potential (BP_ND) (Innis, 2007) estimates were generated using MRTM2 (Ichise-2003) in the basal ganglia including the caudate (CAU), putamen (PUT), pallidum (PAL), and nucleus accumbens (NAcc). Linear regressions were performed to determine the effects of age on DAT binding.

Results DAT BP_ND was found to decrease with age in the CAU (R²=0.36, p<0.01, BP_ND = -0.045*Age + 4.3), PUT (R²=0.41, p<0.01, BP_ND = -0.044*Age + 4.4), and NAcc (R²=0.34, p=0.01, BP_ND = -0.042*Age + 3.4). No age effects were found in the PAL (R²=0.04, p=0.4, BPND = -0.001*Age + 0.01).

Conclusions We found a negative correlation between age and DAT BP_ND in the CAU, PUT, and NAcc. Our results are similar to a previous PET study, which demonstrated a decline in DAT with age (Kazumata, 1998). These results help substantiate that decreases in DAT expression are part of a healthy aging process.