Ultrastructure of intra-epithelial nerve endings in the hard palate of the rat, Rattus norvegicus.

The ultrastructure is described of lanceolate and free nerve endings within the epithelium of the papillae of the intermolar palatal rugae, located either between the basement membranes and the bases of the epithelial cells, or suprabasally in the intercellular spaces of the epithelium. Cytoplasmic processes of epithelial cells invaginated the Schwann cells of the nerve endings; junctions between, or fusion of, the cell membranes of the epithelial cells and the Schwann cells were not found. The neurites of the nervous structures were characterized by numerous mitochondria, clear-cored vesicles and an axoplasmic reticulum. In lanceolate endings, asymmetric membrane densities existed between the neurite and its Schwann cell, the Schwann cell showing signs of pinocytotic activity at all sides of its plasma membrane. The basal lamina of the Schwann cell covering of the nerve endings appeared to be continuous with the basal lamina of the epithelium.