Increased COX2 in the trigeminal nucleus caudalis is involved in orofacial pain induced by experimental tooth movement.

Pain is among the major problems during orthodontic treatment. Recent studies have shown that central Cyclooxygenase2 (COX2) pathway was involved in several pain models. The present study investigated whether inducible COX2 within the trigeminal nucleus caudalis (Vc) contributed to experimental tooth movement pain in freely moving rats. Elastic rubber bands were inserted between the first and second maxillary molars bilaterally to establish tooth movement model. The directed mouth wiping behavior was used to evaluate the pain during tooth movement. COX2 distribution in Vc was studied by immunohistochemistry and the changes of COX2 expression were detected by Western blot at different time point after rubber band insertion. Our results showed that tooth movement significantly increased COX2 expression in Vc and the time spent on mouth wiping, reaching a maximum at 1 day and then decreasing gradually. Furthermore, the rhythm change of COX2 expression in Vc and the mouth wiping behavior were much correlative with each other. All of the COX2-immunoreactive structures in Vc exhibited NeuN-immunopositive staining and most of these COX2-immunoreactive neurons were Fos-immunopositive. Importantly, the mouth wiping behavior could be attenuated by intracisternal injection of NS-398 (a selective COX2 inhibitor) but not by periodontal administration of NS-398. All these results suggested that increased COX2 in Vc was involved in tooth movement pain and thus may be a central target for orthodontic pain treatment.