Delayed Expression of Calbindin D28k during Regeneration of the Periodontal Ruffini Endings of the Rat Incisor following Injury to the Inferior Alveolar Nerve

Abstract

Expression of calbindin D28k (CB)-like immunoreactivity (-LI) was compared with that of protein gene product 9.5 (PGP 9.5), a general neuronal marker, in the periodontal ligament of the rat lower incisor following resection of the inferior alveolar nerve (IAN). In normal animals, the periodontal nerve fibers showing PGP 9.5-LI formed either Ruffini endings with expanded arborization or thin free nerve endings in the alveolar half of the ligament. Thick CB-like immunoreactive (-IR) nerve fibers terminated in a dendritic fashion in the same region, but thin CB-IR nerve fibers were rarely detected. During the 3 days following resection of the IAN, most of the PGP 9.5-IR and all CB-IR nerve fibers disappeared. Regenerated PGP 9.5-IR nerve fibers appeared around 7 days after resection, in contrast to the very small number of regenerated CB-IR nerve fibers. Around 21–28 days following resection, the number and terminal morphology of regenerated PGP 9.5-IR nerve fibers were comparable to those observed in normal animals, but the number of regenerated CB-IR nerve fibers was still smaller. The terminal morphologies of these regenerated CB-IR nerve fibers showed less expansion compared with normal animals at these post-injured periods. The number of regenerated CB-IR nerve fibers increased gradually to return to normal by 56 days following injury. The delayed expression of CB in the regenerated periodontal Ruffini endings suggests that the functional recovery of periodontal Ruffini endings occurred after the regeneration of periodontal Ruffini endings had been completed.