Ultrastructure of the submucous nerves of the rat ureter

The fine structure and distribution of the nerves in the submucosa of the middle part of the ureter were studied in the adult rat. As in the rabbit, the nerves were concentrated on the inner surface of the muscle and beneath the epithelium. The nerves beneath the epithelium were smaller than those on the surface of the muscle, but they were much more numerous. They gave off small branches which ran for only short distances in the subepithelial connective tissue before terminating. Axonal varicosities were common and almost all appeared to represent the terminals of a single type of axon. The varicosities contained clusters of clear vesicles and variable numbers of larger dense-cored vesicles. The dense-cored vesicles were unaffected by short-term treatment with 6-OHDA and in this and other respects compared well with those of the terminals classified by Burnstock (1972) as purinergic. The possibility that the axons are sensory, and are the source of impulses which are recognized as being painful in nature, is discussed.