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The proteinase-activated receptor 2 (PAR₂) is a putative therapeutic target for arthritis. We hypothesized that the early pro-inflammatory effects secondary to its activation in the temporomandibular joint (TMJ) are mediated by neurogenic mechanisms. Immunofluorescence analysis revealed a high degree of neurons expressing PAR₂ in retrogradely labeled trigeminal ganglion neurons. Furthermore, PAR₂ immunoreactivity was observed in the lining layer of the TMJ, co-localizing with the neuronal marker PGP9.5 and substance-P-containing peripheral sensory nerve fibers. The intra-articular injection of PAR₂ agonists into the TMJ triggered a dose-dependent increase in plasma extravasation, neutrophil influx, and induction of mechanical allodynia. The pharmacological blockade of natural killer 1 (NK₁) receptors abolished PAR₂-induced plasma extravasation and inhibited neutrophil influx and mechanical …