Increase of Galanin-immunreactive trigeminal ganglion cells during tooth movement

Objectives: It is known that neuropeptide such as galanin (GAL) and calcitonin gene-relate peptide (CGRP) increase in the periodontal ligament during tooth movement. The presence of these neuropetides has also been reported in the trigeminal ganglion (TG). However, there has been no study that reported the changes in the number of TG neurons that contain these neuropeptides during tooth movement. Furthermore, the origin of GAL in the periodontal ligament remains unclear. Thus, we investigated the expression of GAL in the TG during tooth movement. Methods: A total of 42 adult male Sprague-Dawley rats were used in this study. A piece of elastic band was inserted between the mandibular molars in 36 rats, and after 1,3,5,7,14,28 days, rats were anesthetized followed by dissection of the right TG. Six rats served as control. Then, 10µm-thick serial sections were cut, and double immunohistochemistry for GAL and CGRP was performed. Histomorphometric analysis of the number of GAL-immunoreactive (-ir) and/or CGRP-ir TG cells was counted at the mandibular region of the TG. Results:In control, GAL-ir TG cells were rare, and predominantly observed in small TG cells. After 3 days (p<0.001) of tooth movement, GAL-ir TG cells significantly increased and the most marked increase was observed at 5 days (p<0.0001) after. There was no significant difference in the number of CGRP-ir neurons throughout the experimental periods. Furthermore, cell size spectrum of GAL-ir neurons also significantly shifted to medium and large –sized neurons after 3 and 5 days and continued until 14 days after tooth movement. Conclusion: These findings suggest that the increase of GAL at periodontal ligament during tooth movement at least partially originate from TG and may play a role in pain transmission and/or periodontal remodeling. This study was supported by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science.