CALRETININ-LIKE IMMUNOREACTIVITY IN THE REGENERATING PERIODONTAL RUFFINI ENDINGS OF THE RAT INCISOR FOLLOWING INJURY TO THE INFERIOR ALVEOLAR NERVE

Regeneration of calretinin (CR)-like immunoreactive (IR) nerve fibers was investigated in the periodontal ligament of the rat lower incisor following resection of the inferior alveolar nerve (IAN). Ln addition, the degeneration and regeneration processes of periodontal nerve fibe rs were examined by immunohistochemistry for protein gene product 9.5 (PGP 9.5), a general neuronal marker. in normal animals, the periodont al nerve fibers showing PGP 9.5-like immunoreactivity (LI) formed eith er periodontal Ruffini endings with expanded arborization and thin fre e nerve endings in the alveolar half of the ligament. Thick CR-IR nerv e fibers also appeared in a dendritic fashion in the same region, but thin CR-IR nerve fibers were rarely observed. Five days following rese ction of the IAN, a major population of PGP 9.5-IR and all CR-IR nerve fibers disappeared except for some thin PGP 9.5-IR nerves in the peri odontal Ligament. Regenerated PGP 9.5-IR nerve fibers appear:ed around 7 days following resection, in contrast to a very small number of reg enerated CR-IR nerve fibers. Around 14-21 days following resection, th e number and terminal morphology of regenerated PGP 9.5-IR nerve fiber s were comparable to those observed in normal animals, but the number of regenerated CR-IR nerve fibers was still smaller than that of norma l animals. The number of regenerated CR-IR nerve fibers increased to r eturn to normal by 56 days following injury. The delay of expression o f CR-LI in the regenerated periodontal Ruffmi endings suggests that fu nctional recovery of periodontal Ruffini endings occurred after the co mpletion of the regeneration of periodontal nerve fibers. (C) 1998 Els evier Science B.V. All rights reserved.