Experimental Study On The Changes Of Rectal Structure After Defecation Reconstruction Following Spinal Cord Injury In Rats

Objectives: To establish rat models of spinal cord injury and nerve transfer to reconstruct defecation function,and to explore the changes of bowel function in rats.To investigate the changes of the rectal neuromuscular structure by various histological methods.To explore the influence of nerve transferring surgery in the innervation area of L5 nerve roots in rats.Methods: Female adult SD rats were selected to build models of spinal cord injury and nerve transferring to reconstruct defecation function through mechanical polishing method.The spinal cord injury model was established by transecting the spinal cord between L5 and L6 sections.Nerve transferring model was established by neuroanastomosis of bilateral L5 and S1 nerve roots after transecting the spinal cord between L5 and L6(except S1),to reconstruct the defecation nerve arc with the restoration of sensory and motor nerve simultaneously.The changes of bowel function were examined by measuring the bowel transit time and the weight of fecal pellets within 24 h.The changes of rectal neuromuscular structure were evaluated by HE staining,Masson staining and immunohistochemistry of α-SMA and S100.Subsequently,the wet weight and the proportion of fibrosis detected by histological staining of muscle tissue were measured,which was used to verify whether nerve transferring caused damage to the function of the biceps femoris that is mainly innervated by L5.Results: Compared with the control group,the intestinal transit time of spinal cord injury group was significantly prolonged,and the mass of fecal pellets within 24 h was significantly reduced.Compared with the spinal cord injury group,the intestinal transit time was significantly shortened,and the mass of fecal pellets within 24 h was significantly increased in the nerve transfer group.In conclusion,spinal cord injury can cause severe defecation dysfunction in rats,and defecation reconstruction with bilateral L5-S1 nerve transferring of the anterior and posterior roots can restore defecation function to a certain extent.HE staining of the rectal tissue showed that smooth muscles atrophied,the arrangement of smooth muscle cells was disordered,and a large amount of cytoplasmic vacuolation occurred in the spinal cord injury group.While in the nerve transferring group,the smooth muscle cells were arranged in normal order,and only a small amount of cytoplasmic vacuolation was seen.Masson staining showed that only a small amount of collagen fibers infiltrated between the rectal smooth muscles in the control group,while a large number of collagen fibers infiltrated both in the smooth muscle layers and between smooth muscle layers in spinal cord injury group.A small number of collagen fibers infiltrated inside and between the smooth muscle layers in the nerve transferring group.The percentage of collagen fiber area in smooth muscle layer detected by IPP(Image-Pro Plus)quantitative analysis was 8.04%,33.86% and20.28% in the control group,spinal cord injury group and nerve transferring group,respectively.Immunohistochemical staining showed that compared with the control group,the expression of α-smooth muscle actin(α-SMA)and S100 in rectal smooth muscles decreased in spinal cord injury group,while the nerve transferring group had a higher expression compared with the spinal cord injury group.Compared with the spinal cord injury group,there was no significant change in the wet weight of bilateral biceps femoris in the nerve transferring group;Masson staining did not show fibrosis in these two groups.Conclusions: After spinal cord injury,rats have defecation dysfunction,which is characterized by prolonged intestinal transit time,reduced stool weight within 24 hours;There are also significant changes in rectal smooth muscle structure,mainly manifested by smooth muscle atrophy,fibrosis,and decreased α-SMA,S100 expression.The nerve transferring surgery can improve the defecation function of rats,shortening the intestinal transit time and increasing the weight of feces in24 hours;the changes of the rectal neuromuscular structure have reached partly reversal,and the expression levels of α-SMA and S100 increased.In addition,this surgery did not cause significant damage to the biceps femoris muscle,which is mainly innervated by L5.It can be safely used for rebuilding defecation function and provides a theoretical basis for possible future clinical applications.