Quantitative analysis for innervation of smooth muscle cells in the wall of the urinary bladder.

The distribution of nerve terminals to different parts of the urinary bladder was studied by electron microscopy with the aid of 6-hydroxydopamine treatment. A quantitative analysis was made for each region. In the sphincter and trigone areas nerve terminals were found to be much more numerous (3 times more) than in sections from the body and the apex of the bladder. In much of the bladder there were 6--7 smooth muscle cells for each nerve fiber, however in the trigone area 1--2 muscle cells were supplied by terminal nerve fiber. The narrowest gap between nerve terminals and smooth muscle cells was found to be 150--250 nm. It was commonly seen that Desmosome-like attachments, called nexuses, connected adjacent smooth muscle cells. After 6-hydroxydopamine treatment degenerated terminals could be found mostly in the fine periarterial plexuses but some were also observed that were not related to blood vessels, especially in the trigone area. Summation of our figures and results for terminal density suggests to us that contractions of the urinary bladder are initiated or controlled in the trigone region and that other parts of the wall are activated by local nerve processes and the numerous nexal contacts.