Interactions between glutamate and capsaicin in inducing muscle pain and sensitization in humans
Bibliographic record
Abstract
The aim of the study was to investigate the interaction between glutamate and capsaicin in inducing muscle pain and sensitization in humans. Fifteen male volunteers participated. Glutamate or capsaicin or isotonic saline, in a paired-sequence order, was injected randomly into the right or left masseter muscle. Two injections were given in a double-blinded design 25 min apart in 1 session/week over 4 weeks: saline (A1) followed by glutamate (A2), capsaicin (B1) followed by glutamate (B2), saline (C1) followed by capsaicin (C2), and glutamate (D1) followed by capsaicin (D2). The subjects drew the area of perceived pain and scored pain intensity on a 0-10 visual analogue scale (VAS). Pressure pain threshold (PPT) at the injection site, at a site 2-cm away, and on the contralateral side, as well as pressure pain tolerance (PPTol) at the injection site and contralateral site, were also measured before and after injection and subsequently at 5-min intervals. Paired t-test analyses showed that the pain drawing area was significantly smaller in the B2 compared to the A2 condition (P=0.028), and significantly larger in the D2 compared to the C2 condition (P=0.027). It also revealed significantly lower VAS peak pain intensity (P=0.008) and smaller VAS area under the curve (P=0.003) for the B2 compared to the A2 condition, and significantly higher VAS peak pain (P=0.015) and larger VAS area under the curve (P=0.037) for the D2 compared to the C2 condition. There was a significant PPT and PPTol decrease at the injection site after glutamate or capsaicin injection (ANOVA: P<0.028). The percentage decrease in PPT or PPTol (at the injection site) was not significantly different for the B2 compared to the A2 condition (Paired t-test: P>0.682) or for the D2 compared to the C2 condition (P>0.133). Significant PPT changes were also observed at the site 2 cm away, but not on the contralateral side. In conclusion, these findings indicate that intramuscular administrations of glutamate and capsaicin interact and influence pain and sensitization of muscle nociceptors: glutamate causes a sensitization to subsequent administration of capsaicin, whereas capsaicin is associated with a desensitization to subsequent injection of glutamate. These findings support previous animal data.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.003 | 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) | 0.000 | 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 teacher head, 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".