Serotonin (5-HT) excites rat masticatory muscle afferent fibers through activation of peripheral 5-HT3 receptors
Bibliographic record
Abstract
In the present study, we combined immunohistochemical experiments with in vivo single unit recordings to examine whether 5-HT(3) receptors are expressed by masticatory (masseter and temporalis) sensory ganglion neurons and to investigate the effects of intramuscular injection of 5-HT on the excitability and mechanical threshold of rat masticatory muscle afferent fibers. The expression of 5-HT(3) receptors by masticatory ganglion neurons was examined using immunohistochemical techniques. In vivo extracellular single unit recording techniques were used to assess changes in the excitability of individual masticatory muscle afferent fibers. Immunohistochemical experiments detected a relatively high frequency (52%) of 5-HT(3) receptor expression by masticatory ganglion neurons. Injection of 5-HT (10(-4), 10(-3), 10(-2)M) evoked concentration-related increases in the magnitude of afferent discharge, but did not significantly sensitize muscle afferent fibers to mechanical stimuli. No significant sex-related differences in 5-HT-evoked afferent discharge were identified. Afferent discharge evoked by 5-HT was significantly attenuated by co-injection with the selective 5-HT(3) receptor antagonist tropisetron (10(-3)M). Afferent discharge was also evoked by the selective 5-HT(3) receptor agonist 2-methyl-5-HT. Unexpectedly, a significant concentration-related decrease in median blood pressure in response to 5-HT injection was found. This 5-HT-induced decrease in blood pressure was not antagonized by tropisetron or mimicked by 2-methyl-5-HT, indicating that the drop in blood pressure was not 5-HT(3) receptor-mediated. The present results indicate that 5-HT excites slowly conducting masticatory muscle afferent fibers through activation of peripheral 5-HT(3) receptors, and suggest that similar mechanisms may contribute to 5-HT-evoked muscle pain in human subjects.
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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".