NERVE-FIBERS AND CELLS IMMUNOREACTIVE TO NEUROCHEMICAL MARKERS IN DEVELOPING RAT MOLARS AND SUPPORTING TISSUES

The distribution of nerve fibres immunoreactive to calcitonin gene-rel ated peptide (CGRP), substance P (SP) and neuropeptide Y (NPY) was com pared to the general neurochemical markers for nerves and neuroendocri ne cells protein gene product 9.5 (PGP 9.5) and neurone-specific enola se (NSE), by use of the avidin-biotin peroxidase complex method in dev eloping dental structures in rats aged 13 to 27 days. A substantially greater part of the nerve fibres was immunoreactive to CGRP and SP tha n to NPY. In the bell stage, nerve fibres immunoreactive to PGP 9.5, C GRP and SP were found in the dental follicle but not in the dental pap illa and stellate reticulum. In the advanced bell stage, after initiat ion of dentine and enamel formation, PGP 9.5, CGRP- and SP-immunoreact ive fibres were found in the dental papilla, while the first NPY-immun oreactive fibres were observed in the papilla when root formation star ted. Concomitant with the beginning of root development, a subodontobl astic nerve plexus was gradually formed and PGP 9.5-, CGRP- and SP imm unoreactive fibres were found within the dentinal tubules. From the st art of root formation, CGRP-, SP- and NPY-immunoreactive nerves were s hown in the developing periodontal ligament, although a mature distrib ution pattern was not observed until root formation was nearly complet ed. Ameloblasts, odontoblasts and cell-like structures in the outer en amel epithelium and within the dental lamina were PGP 9.5-immunoreacti ve at the bell stage. As the tooth matured, the immunolabelling gradua lly decreased, but was still present in some odontoblasts after tooth eruption. NSE-immunoreactive, cell-like structures were found in the p eriphery of the dental follicle, and persisted close to alveolar bone in the periodontal ligament when the tooth reached occlusion. Hence, i t may be concluded that sensory nerves containing SP and CGRP are pres ent in the pulp in advance of sympathetic nerves immunoreactive to NPY .