IMMUNOHISTOCHEMICAL EVIDENCE FOR THE PRESENCE OF NERVE-FIBERS WITH SUBSTANCE POR CALCITONIN-GENE-RELATED PEPTIDE-LIKE IMMUNOREACTIVITY IN THE PROLIFERATING EPITHELIUM IN THE DEVELOPING TEETH OF RATS

By immunohistochemistry using the avidin-biotin peroxidase complex met hod, 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 va ricosities with substance P- or CGRP-IR were found in the dental lamin a over the mesial cusp of the dental germ. In 5-day-old rats, nerve fi bres 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 mesia l 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 pen etrate the cells external to the reduced ameloblasts over the middle b uccal cusp. In 10-day-old rats, the oral epithelium over the mesial cu sp 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 gre at many nerve fibres with substance P- or CGRP-IR were distributed all over the fused, thickened dental lamina and cells external to the red uced ameloblasts proliferated over the middle and distal cusps. Nerve fibres with substance P- or CGRP-IR formed a plexus in the thickened o ral epithelium, which spread to the mesiopalatal end of the mesial cus p. In 19-day-old rats, after the partial eruption of the molars, numer ous 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.