Exercise Increases Tryptophan Availability to the Brain in Older Men Age 57–70 Years
Bibliographic record
Abstract
PURPOSE: Many aspects of serotonergic activity, both central and peripheral in origin, undergo significant changes with human aging. These alterations might predispose elderly people to develop mood disorders. Because previous work showed that increasing the peripheral availability of tryptophan (TRP) to the brain holds antidepressant properties, this study evaluated whether TRP availability to the brain is increased during prolonged exercise in older men. METHODS: Nineteen males age 64 ± 3 yr completed a treadmill exercise bout at an HR eliciting ∼68% V˙O(2peak) for 60 min. Fasting blood was collected at rest, after 30 and 60 min of exercise, and at 90 min (after exercise). Branched-chain amino acids (BCAA), total and free TRP, prolactin, ammonia, nonesterified fatty acids, glucose, and lactate were measured. RESULTS: Changes in free TRP/BCAA ratio and prolactin were used as peripheral proxies of central serotonin synthesis rate and activity. The free TRP/BCAA ratio observed at baseline was increased by 102% after 1 h of exercise (P < 0.0001) and remained elevated after exercise (78% above baseline, P < 0.001). The free TRP portion in serum increased from 2.8 ± 0.7 to 5.7 ± 1.8 μmol·L⁻¹ after 1 h of exercise (P < 0.001) and was strongly correlated with plasma nonesterified fatty acid contents (r₁₇ = 0.887, P < 0.0001, all time points). Serum prolactin was significantly elevated after 1 h of exercise (8.6 ± 2.4 μg·L⁻¹, P < 0.001) and was positively correlated with free TRP/BCAA ratio (r₁₆ = 0.48, P < 0.05, all time points). CONCLUSIONS: These results concur with previous observations in younger men and unveil that significant elevations in TRP availability to the brain are encountered during sustained exercise in older men. These results provide support to the hypothesis that increases in serotonin synthesis and activity might be involved in the antidepressant effect of exercise in the elderly.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".