Abstract
Ureteral contractions are initiated by pacemaker cells in the calyceal wall, but the mechanism of conduction of peristalsis is still debatable. Nitric oxide (NO) and acetylcholine (Ach) are well-known messengers of inhibitory nerves in the peripheral autonomic nervous system and may be of importance even in the upper urinary system (UUT). Previous studies used mainly conventional histologic sections and failed to show clearly the organization of nerve fibers in the UUT wall. Therefore, whole-mount preparation techniques providing 3-dimensional (3D) morphology were used in the evaluation of UUTs of 10 rabbits, 5 pigs, and 4 adult humans. A dense, uniform, meshlike neuronal network of nitrergic and cholinergic nerve fibers could be seen in all 3 species in the submucosal as well as in the muscular layer. The nerve fibers were mainly running longitudinally making interconnections within the plexus and with the other layer. This allows the assumption that nitrergic and cholinergic nerves mediate ureteral relaxation and have an important modulatory role in regulating the transport of urine in the UUT. Further studies have to look for new insights into not only the pathophysiology of anomalies of the UUT, but even into the exact differentiated function of the neuronal networks of the submucous and muscular layer.—Peter Schmittenbecher
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