The distribution of intramural nerves in urinary bladder after partial denervation in the female rat.

We evaluated the degree of neuronal plasticity following a partial denervation of the rat urinary bladder. Using acetylcholinesterase staining we found that the postganglionic nerves from the pelvic ganglion reach the intact bladder as 1-4 nerve trunks on each side, slightly ventral and caudal to the ureteral orifices. Normally a few thinner nerves also reach the bladder posterolateral to the ureterovesical junction. The nerves ventral to the ureters run in the ventral longitudinal muscle layer as well-defined trunks with a pattern that does not differ much from one animal to another. The nerves reaching the bladder dorsolaterally innervate the dorsolateral aspects in a more irregular fashion. Some anastomoses are found across the midline between nerves from either side. This nerve pattern is already in place in newborn rats. After removal of the pelvic ganglion on one side in the adult rat the ipsilateral ventral nerves rapidly degenerate, whereas some dorsolateral nerves usually survive. Axons from the intact ventral nerves can be seen crossing over to the denervated side in the anastomoses. After 13 weeks the surviving ventral nerves, which normally run at some distance from the ventral midline, now run in the midline with equal amounts of ventral longitudinal muscle on either side, and with their branches evenly distributed to both sides. The same pattern is seen after 27 weeks. Unilateral ganglionectomy in 3-week-old rats leads to the same changes in nerve distribution as in the adult rat. We conclude that there is a high degree of plasticity in the bladder innervation following a partial denervation, and that this plasticity includes the distribution of its main intramural nerve trunks.