P ₂Y ₂ Receptors Mediate Masseter Muscle Mechanical Hypersensitivity in Rats

Abstract

Purpose

P ₂Y ₂ receptors (P ₂Y ₂Rs) are among the various receptors that play an important role in nociception. The goal of this research was to investigate possible P ₂Y ₂R expression changes in the trigeminal ganglion (TRG) in bilateral masseter muscle (MM) hypersensitivity following unilateral MM inflammation. The impact of unilateral intramasseteric administration of P ₂Y ₂R antagonist on bilateral MM hypersensitivity was also explored.

Materials and Methods

Bilateral MM hypersensitivity was provoked by unilateral intramasseteric injection of complete Freund’s adjuvant (CFA). The head withdrawal threshold (HWT) was assessed bilaterally 4 days later. Bilateral TRG and MM isolation were followed, and quantitative real-time polymerase chain reaction (qRT-PCR) and histopathological analysis were carried out on these tissues, respectively. The involvement of P ₂Y ₂Rs in nocifensive behavior was evaluated by administering two doses of P ₂Y ₂R antagonist AR-C118925 (0.2 or 1 mg/100 μL) in inflamed MM 4 days post-CFA administration. Bilateral HWT was assessed at different time points following antagonist injection.

Results

qRT-PCR analysis demonstrated P ₂Y ₂R up-regulation in TRG ipsilateral to the site of CFA administration. Compared to the controls, both doses of AR-C118925 injected ipsilateral to the TRG increased the bilateral HWT at 30, 60, 90, and 120 minutes after antagonist administration.

Conclusion

The findings suggest that P ₂Y ₂Rs may affect MM inflammatory hypersensitivity owing to its up-regulation in the TRG in MM inflammatory pain states.