Immunohistochemical evidence for the presence of nerve fibres with substance P- or calcitonin gene-related peptide-like immunoreactivity in the proliferating epithelium in the developing teeth of rats

By immunohistochemistry using the avidindashbiotin peroxidase complex method, nerve fibres with substance P- or calcitonin gene-related peptide (CGRP)-like immunoreactivity (IR) were examined in the dental lamina, cells external to the reduced ameloblasts and oral epithelium in the developing upper first molars of postnatal rats. At birth, very few varicosities with substance P- or CGRP-IR were found in the dental lamina over the mesial cusp of the dental germ. In 5-day-old rats, nerve fibres with substance P- or CGRP-IR in the dental lamina over the mesial cusp gradually increased in number. In 7-day-old rats, over the mesial portion of the dental germ, the oral half of the dental lamina began to thicken on the buccopalatal side, in which many nerve fibres with substance P- or CGRP-IR were observed. A few nerve fibres began to penetrate the cells external to the reduced ameloblasts over the middle buccal cusp. In 10-day-old rats, the oral epithelium over the mesial cusp gradually thickened, and nerve fibres with substance P- or CGRP-IR were found especially in its basal layer. In 13-15-day-old rats, a great many nerve fibres with substance P- or CGRP-IR were distributed all over the fused, thickened dental lamina and cells external to the reduced ameloblasts proliferated over the middle and distal cusps. Nerve fibres with substance P- or CGRP-IR formed a plexus in the thickened oral epithelium, which spread to the mesiopalatal end of the mesial cusp. In 19-day-old rats, after the partial eruption of the molars, numerous nerve fibres were still observed in the fused oral epithelium and cells external to the reduced ameloblasts that remained at the tip of the gingiva around the grooves.