Immunohistochemical and electron microscopic demonstration of nerve fibres in relation to gingiva, tooth germs and functional teeth in the lower jaw of the cichlid Tilapia mariae

Abstract

Immunohistochemistry revealed the presence of numerous neurofilament (NF)-like immunoreactive axons in relation to gingiva and dental follicles surrounding mineralizing tooth germs. The gingival nerve fibres frequently approached the prospective papilla of early tooth primordia. Electron microscopic (EM) analysis revealed the presence of bundles of unmyelinated axons immediately below the epithelial-proprial junction of the gingiva. Bundles of nerve fibres were also present in the border zone between the prospective papilla of bud-stage tooth germs and surrounding mesenchyme and in close proximity to blood vessels of the follicles surrounding older tooth germs, but no axons were observed within the emerging dental papilla. In the individual functional tooth, a bundle of NF-like immunoreactive nerve fibres entered the apical part of the pulp forming a subodontoblastic plexus at mid-pulpal levels. EM analysis showed that the apical bundle consisted of many unmyelinated and a few myelinated axons invested by Schwann cell processes. The subodontoblastic plexus contained unmyelinated axons only. Thin, axon-like profiles were also seen in predentinal tubules. Nerve fibres were not observed at pulpal horn levels and in the ligamentous attachment. It is concluded that both immature and mature parts of the lower-jaw dentition of the cichlid T. mariae are innervated and that the microscopic anatomy of this innervation is partly similar to the pattern seen in developing and adult mammals.