Neuroendocrine cells in Malassez epithelium and gingiva of the cat

Malassez epithelium has been designated as epithelial cell rests, the biological significance of which is still under debate. This study was designed to analyze Malassez epithelium for the presence of neuroendocrine cells. Gingival tissue was included as a positive control. Using immunohistochemistry, confocal and light microscopy, Malassez epithelium and gingival epithelium from mature cats (n=5) were examined for cells containing the neuropeptides calcitonin gene-related peptide (CGRP), substance P (SP), and vasoactive intestinal peptide (VIP). Both Malassez epithelium and the basal epithelial cell layers in gingival rete pegs regularly displayed cells immunoreactive to CGRP, SP, and VIP. The immunopositive cells were most frequently present in the epithelial cell clusters and strands of Malassez located in the cervical half of the periodontal ligament. Double immunolabeling revealed cellular co-expression of CGRP or SP with VIP, and the neuropeptides were co-localized in the cellular compartments. Labeled cells in both epithelia were occasionally supported by immunoreactive nerve fibers. This study shows that cells immunoreactive to CGRP, SP, and VIP are located within the cat Malassez epithelium. The localization of neuroendocrine cells verifies the diversity of this epithelium and confirms that Malassez epithelium is composed of different cell types, in common with epithelia from other locations. The presence of neuroendocrine cells in Malassez epithelium strongly suggests biological functions of this tissue, and the neuropeptide content may thus indicate endocrine functions of the cells.