Comparative ultrastructure of ureteric innervation.

The distribution and structure of the ureteric nerves in a small series of mammals was compared with that previously demonstrated in the rat. There was marked interspecies variation in the extent to which the nerves penetrated the wall of the ureter and in the degree of development of the deep submucous plexus. In animals with a highly developed deep submucous plexus, terminal arterioles frequently passed through the muscle coat before breaking up into capillaries. These vessels were surrounded by a fine periarteriolar plexus and were accompanied in their course through the muscle coat by one or more branches of the adventitial nerves. Intramuscular nerves not related to arterioles contained few axons with terminals classifiable as either adrenergic or cholinergic, and in animals in which the muscle cells were arranged in fascicles rather than in sheets, the nerves were typically interfascicular in position. As in the rat, only the periarteriolar plexuses contained large numbers of adrenergic axons. Cholinergic axons were generally few, but were not uncommon in the deep submucous plexus when this was well-developed. The majority of the terminals encountered in the intramural nerves contained variable and usually small numbers of both clear and large dense-cored vesicles. The relationship between these terminals and those defined in the submucous nerves of the rat ureter was discussed and it was suggested that the marked variations in the diameter of the axons in the terminal areas and in the number of vesicles in the terminals were related to the effects of the mechanical and other derangements which occur during processing.