Immunohistochemical detection of heme oxygenase-2 in the periodontal Ruffini ending of the rat incisor

The present study was carried out to examine the occurrence of heme oxygena se-2 (HO-2) in the periodontal ligament of the rat incisor. HO-2-like immun oreactive (-IR) structures showed dendritic profiles, resembling the Ruffin i endings, in the alveolar half of the ligament of rat incisor. Neither thi n nerve fibers nor perivascular nerve fibers displayed HO-2-like immunoreac tivity (-LI). No non-neural elements exhibited HO-2-LI. Electron microscopy revealed that immunoreactions were diffusely observed in the axon terminal s of the Ruffini endings, but neither terminal Schwann cells nor Schwann sh eaths contained immunoreactions for HO-2. Both most neurons in the trigemin al ganglion and trigeminal mesencephalic nucleus showed HO-2-LI. The presen ce of HO-2 in the periodontal Ruffini endings and its absence in the period ontal thin nerve fibers suggest the involvement of carbon monoxide produced by HO-2 in mechanoreception in the periodontal ligament. (C) 2000 Elsevier Science B.V. All rights reserved.