Parvalbumin- and calbindin D-28k-immunoreactive innervation of orofacial tissues in the rat

Parvalbumin- and calbindin D-28k-immunoreactive (-ir) innervation was examined in orofacial tissues of the rat. Labial and facial skins were devoid of the calcium-binding protein (CaBP)-ir nerve endings, while the infraorbital and mental nerves contained numerous parvalbumin-ir axons. Labial and gingival mucosae were also devoid of the CaBP-ir nerve endings. The buccal mucosa and incisive papilla contained both encapsulated and unencapsulated endings, while the hard palate mucosa excluding the incisive papilla contained only unencapsulated endings. Encapsulated endings were found just beneath the epithelium or attached to the cartilaginous core of the incisive papilla. Unencapsulated endings in the lamina propria were subdivided into two types: simple (unramified) and complex (ramified). Neurites of simple endings were straight, curved, or coiled, while those of complex endings exhibited a bush-like appearance due to the ramification. In addition, palatal rugae contained intraepithelial endings. The unencapsulated complex endings in palatal rugae coexpressed parvalbumin- and calbindin D-28k-irs, whereas other endings were immunoreactive for parvalbumin alone. The pterygopalatine ganglion contained calbindin D-28k-ir pericellular fibers but not the ir cell bodies. A subpopulation of trigeminal ganglion neurons coexpressed both CaBPs. CaBP-ir encapsulated and unencapsulated endings in the oral mucosa probably include low-threshold mechanoreceptors, while parvalbumin-ir intraepithelial endings in the palatal mucosa may be involved in nociception.