Proteinase-Activated Receptor-4 (PAR<sub>4</sub>) Activation Leads to Sensitization of Rat Joint Primary Afferents Via a Bradykinin B<sub>2</sub>Receptor-Dependent Mechanism
Bibliographic record
Abstract
The G-protein-linked receptor, proteinase-activated receptor-4 (PAR(4)) is activated by proteinases released into the joint during inflammation. It is unclear whether PAR(4) has a pro- or anti-nociceptive effect and whether it directly affects nerve activity. In this study, we examined the expression of PAR(4) in joints and dorsal root ganglion (DRG) neurons and whether activation of PAR(4) has an effect on nociception in normal rat knee joints. Electrophysiological recordings were made from joint primary afferents in male Wistar rats during both nonnoxious and noxious rotations of the knee. Afferent firing rate was recorded for 15 min post close intra-arterial injection of 10(-9)-10(-5) mol of the PAR(4) activating peptide, AYPGKF-NH(2), or the inactive peptide, YAPGKF-NH(2) (100 mul bolus). Rats were either naive or pretreated with the selective PAR(4) antagonist, pepducin P4pal-10, the transient receptor potential vanilloid-1 (TRPV1) antagonist, SB366791, or the bradykinin B(2) receptor antagonist, HOE140. Immunofluorescence experiments showed extensive PAR(4) expression in the knee joint and in sensory neurons projecting from the joint. AYPGKF-NH(2) significantly increased joint afferent firing during nonnoxious and noxious rotation of the knee. The inactive control peptide, YAPGKF-NH(2) was without effect. Systemic pretreatment with the PAR(4) antagonist, pepducin P4pal-10, inhibited the AYPGKF-NH(2)-induced increase in firing rate. Pretreatment with HOE140, but not SB366791, also blocked this increase in firing rate. These data reveal that in normal rat knee joints, PAR(4) activation increases joint primary afferent activity in response to mechanical stimuli. This PAR(4)-induced sensitization is TRPV1-independent but involves B(2) receptor activation, suggesting a role for kinins in this process.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".