Quantitative Analysis Of Parasympathetic Neurons Innervating The Rectum In Rats With Anorectal Malformation

Anorectal malformation ( ARM) is a common surgical problem affecting 1 in 5,000 to 1 in 1,500 live births. Patients with anorectal malformation often developed postoperative fecal incontinence and constipation. With the improvement of the surgical techniques especially with the introduction of posterior sagittal anorectoplasty (PSARP) , postoperative incontinence had been decreased but constipation had been increasing. The latter had been taken into place. Nowadays the pathogenesis of postoperative constipation, however, remained uncertain. Parasympathetic nucleus in the lumbosacral spinal cord(SPN) , innervating the rectum, control the anorectal functions. When the parasympathetic nerves are excited, the motility of the colon and rectum will be increased. We hypothesized poor postoperative anorectal functions might be due to fewer SPN neurons. To confirm our hypothesis, we sought to quantify the SPN neurons innervating the rectum, observe their distribution and morphology by retrograde tract - tracing in a rat model of anorectal malformation. We try to find the pathegenesis and some useful ways of the therapy of postoperative constipation.Materials and methodsAnorectal malformation was induced in fetuses by gavage feeding of 1% ethylenethiourea (ETU; 125mg/kg body weight) to pregnant Wistar rats at day 10 of gestation. The ETU - administration group had 15 pregnant rats while the saline -administration group had 5. At the 20th day of gestation, fetal surgery was performed to expose the rectum or the rectal pouch and then injected 5% fluorogold (FG). Fetuses were collected 24 hours later, fixed by paraformaldehyde infusion cardially. The lumbosacral spinal cords were removed for cryosection. Serial transverse sections (45um) were studied with fluorescent microscopy. The number of FG - labelled SPN neurons were scored, the morphology and distribution of the neurons were observed. The results were compared among fetuses with or without malformations in the ETU - administration group and normal controls.ResultsIn the ETU -administration group, 62.3% (76/122) of the fetuses displayed anorectal malformation. The total number of FG -labelled SPN neurons in the fetuses without defects of anorectum ,with low type of deformity, high type of deformity and normal controls were determined to be (x ±s) 899 ±36, 588 ± 102, 242 ±92,901 ±46 respectively. At the same time, the size of the FG - labelled SPN neurons in the fetuses with deformity decreased. The SPN neurons innervating rectum were located mainly in the lateral zone of the 6th segment of lumber and the 1th sacral cord.Conclusion1. FG - labelled SPN neurons in the fetuses with imperforate anus is significantly fewer than that in the fetuses without defects of anorec-tum (P < 0. 05) and in normal controls. The higher type of the deformity, the more decrease of the SPN neurons.2. From the results of the experiment, we hypothesized the decrease of the SPN neurons quantity and the developmental defect of SPN might be one of the causes of the postoperative constipation in ARM.