AB301. SPR-28 Determining integrity of the nerve-smooth muscle functional unit of the bladder after long-term decentralization

Objective: Somatic nerve transection causes rapid loss of skeletal muscle mass and contractility. While skeletal muscle degeneration following nerve injury has been well investigated, less is known about the effects of autonomic nerve transection on smooth muscle. We explored changes in the nerve-smooth muscle functional unit following sacral root decentralization to determine integrity after decreased innervation.

Methods: Female mixed-breed hound dogs were surgically decentralized by bilateral transection of all spinal roots caudal to L7, including the dorsal root of L7 in a subgroup. Three weeks prior to the terminal surgery, bladders were injected cystoscopically with fluorogold around the ureterovesical junction for retrograde neuronal labeling. Tissue function was tested during the terminal procedure after 6-month (n=2) and 12-month (n=6) decentralization and compared to sham/unoperated control animals (n=13). Immediately prior to euthanasia, in vivo detrusor pressure after stimulation of nerves originating from the pelvic plexus (e.g., the anterior vesicle branch) was recorded. Collected bladder and pelvic plexus tissues from controls and 6-month decentralized dogs were harvested (n=3–6/group), cryosectioned, and examined for fluorogold labeling. Bladder tissues were stained for caspase-3 and immunostaining was quantified. Gastric tissue and red blood cells within bladder walls were used as positive controls. Data was analyzed using unpaired ANOVA.

Results: Nerve stimulation caused a robust increase in detrusor pressure in both control and decentralized groups. Likewise, abundant fluorogold-labeled neuronal cell bodies were observed in ganglia in the pelvic plexus of both sham and decentralized animals. Immunohistochemical stain for caspase-3 showed no difference across groups. Also, we did not observe co-localization of fluorogold-positive neuronal tissue and caspase-3, or presence of caspase-3 in smooth muscle fibers of the bladder wall.

Conclusions: The presence of fluorogold-labeled pelvic plexus ganglia in decentralized animals demonstrates that the ganglia remained intact up to 6 months after decentralization. Caspase-3 staining results showed no increase in apoptosis in the neuronal tissues or bladder smooth muscle in decentralized dogs, suggesting no increased apoptotic cell death. No significant difference between detrusor pressure responses across groups after nerve-evoked stimulation indicates that the nerve-smooth muscle functional unit of the bladder is intact up to 12 months after injury and therefore, nerve reinnervation strategies could be successful.

Funding Source(s): NIH-NINDS NS070267

Keywords: Neuromodulation; innervation; neural plasticity; bladder; pelvic ganglia; dog