Unusual nerve endings found in the rat palatine mucosa.

The fine structure of an unusual type of nerve ending found in the subepithelial spaces of rat palatine mucosa is described. The endings, with their tortuous courses and terminal bulbous portions, form a complicated plexus. An unusually thick basal lamina of filamentous reticular structure envelops the Schwann cell ensheathing the endings. Several irregular microvillous projections extend from the axon terminals through gaps in the Schwann cell envelope. The nerve terminals present numerous mitochondria, microtubules, neurofilaments, myelin figures and clear vesicles approximately 50 nm in diameter. The laminar cytoplasm of Schwann cells enveloping the nerve terminals shows a large number of caveolae. Desmosome-type junctions are noted between axons and Schwann cells.