Involvement of P2X7 Receptor on the Inflammatory Hyperalgesia in TMJ

Evidence is accumulating that supports a role for P2X7 receptors in inflammatory pain. Objective: Investigate whether P2X7 receptors play a role in temporomandibular (TMJ) pain. Methods: To investigate the presence of functional P2X7 receptors in rat TMJ the nociceptive behavioral response to the application of the selective P2X7 receptor agonist BzATP was investigated in the rat's TMJ. The involvement of these receptors in the development of TMJ inflammatory hyperalgesia was also investigated by evaluating the effect of the selective P2X7 receptor antagonist Oxidized ATP (oATP) on carrageenan-induced TMJ inflammatory hyperalgesia. The presence of P2X7 mRNA on trigeminal ganglia was evaluated by RT-PCR. Results: Application of BzATP (225 µg) in the TMJ induced a significant nociceptive response that was significantly reduced by the co-application of lidocaine N-ethyl bromide quaternary salt, QX-314, (2%) or by oATP (n=6 for all groups, p<0,05, Tukey test). However, co-application of oATP (2.0 µg, 18 µg or 162 µg) with carrageenan (100 µg) in the TMJ did not affect hyperalgesia (p>0.05, ANOVA, n=6). Although data from RT-PCR analysis also indicate that P2X7 receptor is expressed in the trigeminal ganglia of rats (mean±SD: 0.034±0.007, n=8), however the inflammatory response induced by the TMJ injection of carrageenan did not significantly increase its expression (0.046±0.014, n=8). Conclusion: The results suggest that although functional P2X7 receptors are expressed on trigeminal ganglia, in contrast to the observed in others body regions it does not contribute to inflammatory pain in TMJ. This work was supported by Fapesp, Brazil.