Neuropeptides have been suggested to play a role in pain transmission during orthodontic tooth movement. We examined this hypothesis by examining the effect of orthodontic tooth movement on the expression of galanin (GAL)-immunoreactive (ir) nerve fibers in the periodontal ligament (PDL) of one mesial root (MR) and two distal roots (DRs) of the rat maxillary first molar. In control rats, GAL-ir fibers were very rare in the PDL. One day after the insertion of the elastic band, the number of GAL-ir fibers increased, becoming most numerous at 3 days. From 5 to 28 days, GAL-ir fibers tended to decrease. Electron microscopic observation showed that all of the GAL-ir fibers were unmyelinated. These findings suggest that GAL-containing nerve fibers in the PDL may play an important role in the response of the tissue to experimental tooth movement.
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