The Study Of The Artificial Somato-autonomic Neuroanastomosis For Restoring Anorectal Function

Objective:To study the physiological functions of the regenerated "spinal cord-major pelvic ganglion (MPG)-rectum" and "spinal cord-external anal sphincter (EAS) neural reflex pathways and to investigate the possible mechanisms underlying the artificial somato-autonomic neuroanastomosis for initiating defecation in the spinal cord injury rats.Methods:In normal male Sprague-Dawley rats, under anesthesia the new regenerated neural pathway was established by intradural microanastomosis of left L4 ventral root(L4VR) to the L6 ventral root (L6VR) while leaving the L4 dorsal root intact to trigger the new the regenerated neural pathway. Then L4VR-L6VR formed the foreign nerve root. Twelve weeks later the model rats were randomly divided into two groups of 8 and 4 respectively (n1=8, n2=4). The rats in the group 1 were used for electrophysiological experiment. Then the L4VR-L6VR foreign nerve root was stimulated by silver electrode and the evoked potentials were recorded on the preganglionic fibers and postganglionic fibers of the major pelvic ganglia (MPG). The rectal pressure and electromyologram of EAS were recorded. The stimulation of the right L4VR and L6VR in contralateral side were used as controls. The rats in the group 2 were used for neural retrograde tracing study. Fluorogold (FG) was injected into the left major pelvic ganglia (MPG). Retrograde tracing technique was used to investigate the material transmitting function of regenerated efferent nerve. Normal rats were used as controls.Results:(1)In the group 1, stimulation of the L4VR proximal end to the anastomosis evoked potentials on the left preganglionic fibers and the postganglionic fibers of the MPG, and change of rectal pressure (16.89±9.86mmHg) and electromyologram of EAS (127.91±28.73μV). Stimulation of the contralateral L4VR failed to evoke potentials on the right preganglionic fibers and the postganglionic fibers of MPG, and can't induce rectum and EAS to contract. (2) The conduction velocity of the regenerated motor axons was 35.43m/s±12.25m/s, significantly higher than that of the control group(12.33m/s±1.77 m/s). (3)After FG was microinjected into the left major pelvic ganglia (MPG) in the model rats FG labeled neurons were observed in the segment of L4. FG labeled neurons were observed in L6 segment after FG was injected into the left major pelvic ganglia (MPG) in the normal rats.Conclusion:Somatic nerve axons (L4VR) can regenerate to replace the peripheral autonomic and somatic motor nerve fibers through axonal regeneration. And the regenerated nerves can innervate the rectum and EAS to initiate defecating. Objective:A new artifical somatic-autonomic neuroanastomosis has been estabilished in male rat with spinal cord injury (SCI). Anorectal manometry and neural retrograde tracing were conducted in such animal model after estabilishing the regenerated reflex pathway to analyze the mechanisms, and the effects on restoring anorectal function and rectum external sphincter synergetic status.Methods:In normal male Sprague-Dawley rats with weight of 280-300 g, under anesthesia the rats were subjected to limited laminectomy of L4-L6 vertebrae to expose the spinal cord, and the new reflex pathways were estabished by intradural microanastomosis of left L4 ventral root to the L6 ventral root while leaving the L4 dorsal root intact to trigger the new defecation reflex pathway. Then L4VR-L6VR formed the foreign nerve root. Three months later the spinal cord was completely transected at the T9-10 level. Eight weeks later the model rats were randomly divided into two groups of 8 and 4 respectively (n1=8, n2=4). The rats in the group 1 were applied in anorectal manometry. When the left L4VR proximal to the anastomosis and left sciatic nerve were stimulated by silver electrode, the rectal pressure and EMG of external anal sphincter (EAS) were simultaneously recorded. The stimulated L6VR and the right sciatic nerve in contralateral side served as controls. The rats in the group 2 were used for neural retrograde tracing study. Fluorogold (FG) was injected into the left major pelvic ganglia (MPG) and dextran tetramethylrhodamine (TMR) was injected into the left external anal sphincter. Retrograde tracing technique was used to investigate important neuromechanism for defecation of regenerated efferent nerve. The normal rats were used as controls.Result:Stimulation of the L4VR proximal end to the anastomosis and the left sciatic nerve induced rectum to contract and simultaneously electric activity of EAS to become weak or disappearing(indicating synergetic relaxation of EAS). But stimulation of the contralateral L6VR evoked simultaneous contraction of rectum and EAS. After FG was injected into the left major pelvic ganglia (MPG) and TMR was injected into the external anal sphincter (EAS), FG-TMR dual labelled neurons and FG or TMR single labeled neurons were mainly observed in the angulus anterior ofL4 segment in the model rats. FG-TMR positive neurons were not observed in the spinal cord of the normal rats.Conclusion:After established the artifical somato-autonomic neuroanastomosis the regenerated neural pathways are effective to improve the rectum external sphincter synergetic status and restore the anorectal function. Simultaneous reinnervation of MPG and EAS by one group of the dual labelled neurons in L4 may be the key neural anatomy infrastructure for controllable defecation via the somatic-autonomic reflex pathway.