Filiform papillae as a sensory apparatus in the tongue: an immunohistochemical study of nervous elements by use of neurofilament protein (NFP) and S-100 protein antibodies.

Nervous elements supplying the filiform papillae of the tongue of cattle and rats were investigated using immunohistochemistry against neurofilament protein (NFP) and glia-specific S-100 protein. The rod-shaped bovine filiform papillae were heavily keratinized along their entire length and lacked the connective tissue core that occurs in other mammals. Instead, the core was located posterior to the filiform papilla. The base of the bovine filiform papillae was invaded vertically by laminar connective tissue papillae. The core contained a large number of NFP-positive nerve fibers, most of them terminating as free endings in its anterior margin. NFP-positive nerves gathered around the anterior ridge of the epithelium at the base of the core and occasionally penetrated into the epithelium. The laminar connective tissue papillae at the base of the filiform papilla also contained NFP-positive nerve fibers. The core contained S-100-immunoreactive lamellated corpuscles, which were identified as "simple corpuscles" in electron micrographs. The structure and innervation of the bovine filiform papilla suggest that they represent a specialized sensory apparatus. The pyramidal filiform papillae of the rat were smaller, each containing a simple connective tissue core. Few NFP-positive nerve fibers from the nerve plexus entered the core. Filiform papillae are thus less specialized in rats than in cattle.