Immunohistochemical study of nerve fibres with substance P- or calcitonin gene-related peptide-like immunoreactivity in the junctional epithelium of developing rats.

The beginning of innervation in the junctional epithelium of maxillary first molars was examined in gingival tissues from 19 to 32-day-old rats. Substance P- or calcitonin gene-related peptide (CGRP)-like immunoreactivity was demonstrated by the avidin-biotin peroxidase complex method. In 19-day-old rats, nerve fibres with substance P- or CGRP-like immunoreactivity were seen in the connective tissue and oral epithelium, but not in the reduced enamel epithelium, which would be transformed into the junctional epithelium. In 21-day-old rats, the fibres with substance P- or CGRP-like immunoreactivity formed a plexus in the oral sulcular epithelium and thin varicose fibres were seen for the first time entering the adjacent reduced enamel epithelium. These fibres also penetrated the middle portion of the reduced enamel epithelium, but did not reach the cuboidal reduced ameloblasts. More nerve fibres had CGRP-like immunoreactivity than substance P-like immunoreactivity. In 23-day-old rats, many fibres with both immunoreactivities were seen in the basal layers of the junctional epithelium, but only a few were seen in its superficial layers. In 28-32-day-old rats, numerous fibres with both immunoreactivities were distributed in the whole junctional epithelium and showed a similar pattern of innervation. For all immunoreactive fibres, the density in the middle portion in the junctional epithelium was the highest. The nerve plexus was formed in the basal layers and some fibres with a varicose appearance were found in the superficial layers.