Innervation of the hard palate in the rat studied by anterograde transport of horseradish peroxidase conjugates

The innervation of the rat hard palate and the bordering part of the soft palate was studied after anterograde transport of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) and to choleragenoid (B-HRP) in separate experiments. WGA-HRP labeling showed leakage from several types of nerve endings, whereas B-HRP did not. Both conjugates gave rise to heavy labeling of a variety of nerve endings. Intragemmal and, especially, perigemmal fibers were labeled in chemosensory corpuscles, which were most common in the medial wall of the incisive canal and in the most anterior part of the soft palate. Ruffini endings of different sizes were labeled in the incisive papilla. Other subepithelial endings forming elongated expanded profiles with medium- to large-caliber source fibers were most common in protruding parts of the palate. Labeled intraepithelial endings included Merkel endings, which were most frequent in the incisive papilla and the rugae. Other labeled profiles were medium-caliber afferents giving rise to irregular, beaded, and sometimes branched endings often located far superficially in the epithelium. Such endings were present both within and between protruding parts of the palate. Fine-caliber intraepithelial endings were labeled almost exclusively in WGA-HRP experiments.