The Effect of Minocycline on Induced Glial Activation by Experimental Tooth Movement

Objectives: Orthodontic tooth movement causes pain to a patient. Glial cells are non-neuronal cells in the central nervous system (CNS), and implicated in various types of pain. The present study assessed glial activation responses following experimental tooth movement using immunocytochemical detection of OX-42 and glial fibrillary acidic protein (GFAP) immunoreactivity (ir) to illustrate the microglial and astrocytes response, respectively. In addition, the effect of minocycline in reducing pain during tooth movement was also investigated.

Methods: Fifty-five Sprague Dawley rats with and without administration of minocycline after 1,3,5,7,14 days (n=5, for each) of tooth movement were used. Immunohistochemistry for microglia (OX-42) and astrocyte (GFAP) were performed at the medullary dorsal horn (MDH; trigeminal subnucleus caudalis). Three-dimensional quantitative analysis was performed with confocal fluorescence microscope and WinRoof software program.
Results: There was a significant increase in the OX-42 and GFAP-ir in response to tooth movement in the MDH. Furthermore, systematic administration of minocycline, a selective inhibitor of microglial activation, significantly attenuated the nociceptive c-Fos expression in MDH that was induced by experimental tooth movement.
Conclusions:
These data indicate the possible importance of microglial activation in the development of orthodontic pain. This is also the first report on the systematic application of minocycline.