A possible mechanism of mechanoreception in Ruffini endings in the periodontal ligament of hamster incisors

Abstract

The topographical relationship between Ruffini endings and the surrounding collagen fibers in the periodontal ligament of hamster incisors was investigated by means of both immunohistochemistry for neurofilament protein (NFP) and electron microscopy. Periodontal Ruffini endings, a type of stretch receptor, were present exclusively in the alveolar half of the periodontal ligament. Their axon terminals were densely and regularly associated with transverse collagen fibers, possibly forming a mechanoreceptive complex. Since blood sinuses with frequent anastomoses extended throughout the alveolus-related part, the densely innervated collagen bundles were separated from each other by the vascular spaces. Electron microscopic observation of specimens stained with tannic acid revealed a linkage between the axon terminals of the Ruffini endings and the surrounding collagen filaments. The axon terminals were enveloped by multiple layers of the basal lamina, which were penetrated by collagen filaments. The irregularly arranged collagen filaments were sandwiched between electron-dense laminae of the multilayered basal lamina. The possible mechanism of mechanoreception by the periodontal Ruffini endings is discussed on the basis of the immunohistochemical and ultrastructural findings.

Innervation of the Periodontal Ligament in the Dog with Special Reference to the Morphology of Ruffini Endings.

“…The predominant type of nerve ending in the dog periodontal ligament was shown in the present study to be the thick type of tree-like ending without any specialized terminal structures such as capsules or lamellae. Their distribution and intimate relationship with collagen fibers remind us of the Ruffini endings in rodent periodontal ligament (SATO et al, 1988(SATO et al, , 1989KANNARI, 1990;KANNARI et al, 1991). Their shape, In comparison with the rodent type, the dog-type of Ruffini ending is represented by a tree-like profile, less repeatedly branching and not remarkably swollen at the end of each branch.…”

“…The electron microscope study by BYERS (1985) first reported the existence of Ruffini endings, a type of stretch receptor which is predominant in the collagenous tissues, in the periodontal ligament of rat molars. Recently, our research group demonstrated an extremely rich distribution of Ruffini endings in the periodontal ligament of rodents (SATO et al, 1988(SATO et al, , 1989KANNARI, 1990;KANNARI et al, 1991). In these studies, immunohistochemical techniques enabled us to visualize the entire configuration of Ruffini endings in molars of rats (MAEDA et al, 1987) and in the incisors of all rodents examined (SATO et al, 1988(SATO et al, , 1989KANNARI, 1990;KANNARI et al, 1991): the endings repeatedly branched in a dendritic fashion, each terminal twig being expanded.…”

“…Recently, our research group demonstrated an extremely rich distribution of Ruffini endings in the periodontal ligament of rodents (SATO et al, 1988(SATO et al, , 1989KANNARI, 1990;KANNARI et al, 1991). In these studies, immunohistochemical techniques enabled us to visualize the entire configuration of Ruffini endings in molars of rats (MAEDA et al, 1987) and in the incisors of all rodents examined (SATO et al, 1988(SATO et al, , 1989KANNARI, 1990;KANNARI et al, 1991): the endings repeatedly branched in a dendritic fashion, each terminal twig being expanded. The Ruffini endings in the periodontal ligament of rodents have been regarded to have a typical shape This study was partly supported by a Grant-in-Aid for Scientific Research (No.…”

“…In some thicker axon terminals (more than 4urn in diameter), the exposed portions of the axons were equipped with finger-like projections reminiscent of the reported feature of the periodontal Ruffini endings in rodent incisors (Fig. 10) (MAEDA et al, 1989;KANNARI, 1990;KANNARI et al, 1991).…”

“…The axon terminals here were approximately twice as thick as the preterminal fibers and ended in a tapering fashion, not forming any specialized terminal portions. The Ruffini endings of the rodent type, which consisted of repeatedly branched nerve fibers terminating in remarkable expansions (SATO et al, 1988(SATO et al, , 1989KANNARI, 1990;KANNARI et al, 1991), were also detected, though not frequently, in the apical periodontal ligament of dogs (Fig. 3).…”