Tooth movement upregulates preproenkephalin mRNA in rat trigeminal subnucleus

Objectives: Orthodontic tooth movement causes pain and the nociceptive pathway has been extensively studied in experimental tooth movement. However, it remains unclear how orthodontic pain is modulated in the central nervous system. To investigate the possible involvement of the enkephalinergic system during experimental tooth movement, we investigated the Preproenkephalin (PPE) mRNA expression pattern in brainstem. Methods: Twenty-four hrs after application of the tooth movement, the Preproenkephalin (PPE) mRNA expression pattern was analyzed using in situ hybridization in the trigeminal subnucleus complex of the rats.Results: In spinal tract nucleus, PPE expression was constitutively expressed in several nuclei. Twenty-four hours after the start of experimental tooth movement, PPE mRNA expression was significantly upregulated about two-fold (P<0.01) in the dorsomedial trigeminal subnucleus caudalis on the ipsilateral side. Furthermore, upregulation was also observed in the trigeminal subnucleus oralis. Conclusion: These findings, together with previous findings, suggested that the endogenous enkephalinergic system was activated during experimental tooth movement, presumably to depress the ascending nociceptive sensation within both trigeminal subnucleus oralis and caudalis. This study was supported by a Grant-In-Aid for Scientific Research from Japan Society for the Promotion of Science (14571948, 14207092, 15659491).