Epithelial rests of Malassez express immunoreactivity of TrkA and its distribution is regulated by sensory nerve innervation

The periodontal ligament is the connective tissue that fills the space betw een the tooth and its bony socket. It is abundantly innervated by the senso ry and sympathetic nerves. We first investigated the immunoreactivity of Tr kA, which is a high-affinity receptor of nerve growth factor (NGF), in the periodontal ligament of rats. Immunoreactivity was observed at the epitheli al cells in the cervical and furcation regions of the molars. These epithel ial cells, which gather together to form clusters or networks, are known as the epithelial rests of Malassez. Immunoreactivity was not observed in oth er non-neuronal cells, such as osteoblasts, fibroblasts, odontoblasts, ceme ntoblasts, endothelial cells, and/or osteoclasts. On the basis of these fin dings, we investigated the possible involvement of sensory nerve innervatio n in the immunoreactivity of the epithelial cells. Denervation of the infer ior alveolar nerve resulted in a marked decrease in the distribution area a nd size of the clusters of immunoreactive cells compared with those of sham -operated rats. These findings suggest that sensory nerve innervation may h ave a regulatory role in maintenance of the epithelial rests of Malassez ex pressing TrkA in the periodontal ligament.