Bladder reinnervation by somatic nerve transfer to pelvic nerve vesical branches does not reinnervate the urethra

Abstract

Aims: We sought to determine whether somatic lumbar nerve transfer to the pelvic nerve's anterior vesical branch after sacral decentralization for detrusor muscle reinnervation also leads to aberrant innervation of the bladder outlet.

Methods: Twenty-six female mongrel hound dogs underwent transection of sacral dorsal and ventral spinal roots (ie, sacral decentralization). Immediately afterward, 12 received genitofemoral nerve transfer and 9 received femoral nerve branch transfer. Five were left sacrally decentralized. Controls included 3 sham-operated and 6 unoperated. Eight months postsurgery, the bladder and urethra were injected with retrograde tracing dyes cystoscopically. After 3 weeks, detrusor and urethral pressures were assayed electrophysiologically immediately before euthanasia and characterization of neural reinnervation.

Results: Electrical stimulation of spinal cords or roots did not lead to increased urethral sphincter pressure in nerve transfer animals, compared with decentralized animals, confirming a lack of functional reinnervation of the bladder outlet. In contrast, mean detrusor pressure increased after lumbar cord/root stimulation. In sham/unoperated animals, urethral and bladder dye injections resulted in labeled neurons in sacral level neural structures (dorsal root ganglia [DRG], sympathetic trunk ganglia [STG], and spinal cord ventral horns); labeling absent in decentralized animals. Urethral dye injections did not result in labeling in lumbar or sacral level neural structures in either nerve transfer group while bladder dye injections lead to increased labeled neurons in lumbar level DRG, STG, and ventral horns, compared to sacrally decentralized animals.

Conclusion: Pelvic nerve transfer for bladder reinnervation does not impact urethral sphincter innervation.

Keywords: bladder reinnervation; nerve transfer; retrograde dye; somatic nerve; urethral sphincter.

Figure 1

Experimental design and urethral sphincter injection sites (indicated by arrows). A, Experimental design showing time of recovery after nerve transfer surgery (8 months), then time of recovery after dye injection (3 weeks). B, Injection sites representative of 46% of animals showing that the depth of the injection did not reach the external urethral sphincter. C, Enlargement of box shown in A showing presence of True‐Blue labeling. C, Injection sites representative of 54% of animals showing that the depth of the injection reached the inner boundaries of the external urethral sphincter in the area indicated by box. D, Enlargement of box shown in C showing presence of True‐Blue labeling

Figure 2

Maximum urethral sphincter pressure (A) and detrusor pressure (B) after spinal cord and root electrical stimulation. Results for electrical stimulation of sacral cord and/or root stimulation are shown for sham/unoperated (Sham/Unop) and sacral roots transected animals and for lumbar levels of GFNT and FNT animals. *P < .05, and **P < .01, compared with Sham/unoperated controls. FNT, femoral nerve branch transfer; GFNT, genitofemoral nerve transfer

Figure 3

Numbers of retrogradely‐labeled neurons in dorsal root ganglia (DRG) (n = animals assayed per group). A, Labeled neurons in DRG after dye injections into the urethral sphincter. B, Labeled neurons in DRG after dye injections into the bladder wall. Insets show a representative labeled neuron for each dye (True Blue in A (indicated with an arrow) and Fluorogold in B, 200× magnification. *P < .05, and **P < .01 compared with Sacral Roots Transected group

Figure 4

Numbers of retrogradely‐labeled neurons in segmental sympathetic trunk ganglia (STG) (n =  animals assayed per group). A, Labeled neurons in STG after dye injections into the urethral sphincter. B, Labeled neurons in STG after dye injections into the bladder wall. *P < .05, and **P < .01, compared with Sacral Roots Transected group

Figure 5

Numbers of retrogradely‐labeled neurons in segmental spinal cord ventral horn regions (n =  animals assayed per group). A, Labeled neurons in spinal cord ventral horn after dye injections into the urethral sphincter. B, Labeled neurons in spinal cord ventral horn after dye injections into the bladder wall. Insets show representative labeled neuron(s) for each dye (true blue in panel A and Fluorogold in panel B, 200× magnification. *P < .05, and **P < .01 compared with Sacral Roots Transected results