Distribution of sacral afferent axons in cat urinary bladder

Terminal axon density was examined in five selected regions of the urinary bladder in five cats. The trigone region had more terminal axons than other bladder regions. Extra‐terminal axons in the trigone were outside muscle fascicles and thought to be afferent axons related to the hypogastric nerve. In four of the cats, afferent axons of the pelvic nerve were identified by degeneration following sacral spinal ganglionectomy. The afferent axons were distributed equally to all regions of the bladder, implying that micturition sensitivity is not preferentially organized in the bladder. One‐third of the sacral afferent axons crossed to the contralateral side of the bladder. This bilateral redundancy constitutes a safety feature. Afferent terminal axons were more numerous outside than inside muscle fascicles. Morphologically, afferent terminations outside muscle fascicles appeared to be tension receptors, while terminations inside the fascicles are candidates for volume receptors. The greatest number of degenerating terminal axons was found 14 days after ganglionectomy. Thirteen percent of degenerating axons contained agranular vesicles, and these were presumed to be autonomic postganglionic neurons with cell bodies in spinal ganglia.