Coexpression of calretinin and parvalbumin in Ruffini-like endings in the rat incisor periodontal ligament.

The coexpression of calretinin- (CR) and parvalbumin-immunoreactivities (irs) was examined in oro-facial tissues of the rat. Nerve fibers coexpressing these calcium-binding proteins (CaBPs) were observed in the lingual periodontal ligament of incisors but not other tissues. In the part of periodontal ligament adjacent to the alveolar bone, such nerve fibers left nerve bundles and formed bush-like endings, i.e., they ramified repeatedly and terminated with one to four twigs. An immunoelectron microscopic method indicated that these endings were identical to Ruffini-like endings, 4% of trigeminal neurons retrogradely labeled from the inferior alveolar nerve coexpressed CR- and parvalbumin-irs. The present observations suggest that the coexpression of these CaBPs may be a specific marker for low-threshold mechanoreceptors in the trigeminal ganglion.