Bypassing spinal cord injury: surgical reconstruction of afferent and efferent pathways to the urinary bladder after conus medullaris injury in a rat model.

Afferent and efferent nerve function in the atonic bladder caused by conus medullaris injury in a rat model was established by intradural microanastomosis of the left L5 ventral root (VR) to right S2 VR to restore pure motor-to-motor reinnervation coupled with extradural postganglionic spinal nerve transfer of L5 dorsal root (DR) to S2 DR for pure sensory-to-sensory reinnervation. Early function of the reflex arc was evaluated by electrophysiological study, as well as by intravesicular pressure measurement and histological examination. The results demonstrated that single focal stimulation of the left S2 DR elicited evoked potentials at the left vesicular plexus before and after horizontal spinal cord damage between the L6 and S4 level. Bladder contraction was successfully initiated by trains of stimuli targeting the left L5-S2 DR anastomosis. Achievable bladder pressures and amplitude of bladder smooth muscle complex action potentials were unchanged before and after induced paraplegia and comparable to those of the control. Prominent axonal sprouting was seen in the distal part of nerve graft. Both afferent and efferent nerve pathways in the atonic bladder can be reconstructed by suprasacral motor-to-motor and sensory-to-sensory nerve transfer after spinal cord injury in rats. This reconstructive strategy has significant potential in clinical application.