Lack of Age-Dependent Decrease in Dopamine D <sub>3</sub> Receptor Availability: A [ <sup>11</sup> C]-(+)-PHNO and [ <sup>11</sup> C]-Raclopride Positron Emission Tomography Study
Bibliographic record
Abstract
Positron emission tomography with antagonist radiotracers has showed that striatal dopamine D2/3 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 D3 receptor (D3R)-preferential agonist radiotracer [(11)C]-(+)-PHNO (n=72, mean±s.d. age=40±15, range=18 to 73) and the antagonist [(11)C]-Raclopride (n=70, mean±s.d. age =40±14, range=18 to 73) (both, n=33). The contribution of D3R to the [(11)C]-(+)-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 D2 receptor (D2R)-specific regions. With [(11)C]-(+)-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 [(11)C]-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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".