Effect of the artificial somato-autonomic neuroanastomosis on defecation after spinal cord injury and its underlying mechanisms

Abstract

Objective A new artificial somatic-autonomic neuroanastomosis has been established in male rats with spinal cord injury (SCI). Anorectal manometry and neural retrograde tracing were conducted in such animal model after establishing 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 weighing 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 established 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 (n1=8,n2=4). The rats in the group 1 were applied in anorectal manometry, and those in the group 2 for neural retrograde tracing study. Results Stimulation of the L4VR proximal end to the anastomosis and the left sciatic nerve induced rectum to contract, and simultaneously greatly weakened electric activity of external anal sphincter (EAS) ( 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 into the EAS, FG-TMR dual labeled neurons and FG or TMR single labeled neurons were mainly observed in the angulus anterior of L4segment in the model rats. FG-TMR positive neurons were not observed in the spinal cord of the normal rats. Conclusion After establishment of the artificial somato-autonomic neuroanastomosis the regenerated neural pathways can effectively improve the rectum EAS synergetic status and restore the anorectal function.Simultaneous reinnervation of MPG and EAS by one group of the dual labeled neurons in L4 may be the key neural anatomy infrastructure for controllable defecation via the somatic-autonomic reflex pathway. Key words: Somato-autonomic neuroanastomosis; Spinal cord injury; Synergetic defecation