Lack of age-dependent decrease in dopamine D3 receptor availability: a [11C]-(+)-PHNO and [11C]-raclopride positron emission tomography study

Positron emission tomography with antagonist radiotracers has showed that striatal dopamine D-2/3 receptor (D2/3R) availability decreases with age. However, no study has specifically assessed whether D2/3R availability decreases with age in healthy persons as measured with agonist radiotracers. Moreover, it is unknown whether D3R availability changes with age in healthy humans. Thus, we explored the relationship between age and D2/3R availability in healthy humans using the D-3 receptor (D3R)-preferential agonist radiotracer [C-11]-(+)-PHNO (n=72, mean s.d. age = 40 +/- 15, range =18 to 73) and the antagonist [C-11]-Raclopride (n=70, mean s.d. age = 40 +/- 14, range = 18 to 73) (both, n=33). The contribution of D3R to the [C-11]-(+)-PHNO signal varies across regions of interest; the substantia nigra and hypothalamus represent D3R-specific regions, the ventral pallidum, globus pallidus, and ventral striatum represent D2/3R-mixed regions, and the caudate and putamen represent D-2 receptor (D2R)-specific regions. With [C-11]-(+)-PHNO, a negative correlation was observed between age and nondisplaceable. binding potential (BPND) in the caudate (r(70)=-0.32, P=0.005). No correlations were observed in the other regions. With [C-11]-Raclopride, negative correlations were observed between age and BPND in the caudate (r(68)=-0.50, P < 0.001), putamen (r(68)=-0.41, P <0.001), and ventral striatum (r(68)=-0.43, P < 0.001). In conclusion, in contrast with the age-dependent decrease in D2R availability, these findings suggest that D3R availability does not change with age.