[Quantitative analysis of sensory neurons innervating the muscle levator ani in rats with anorectal malformation]

To quantitatively observe the sensory neurons innervating the levator ani muscle and explore the cause of poor post-operative anorectal function in patients with anorectal malformation (ARM).

Combining the microsurgery and microinjection techniques, we investigated the deficiency of sensory neurons of the spinal cord in fetal rats with anorectal malformation by injecting the retrograde tracer fluorogold (FG) into the muscle levator ani. Sixty 11 days pregnant female rats were fed with ethylenethiourea (ETU) so as to cause ARM in the fetuses. When the female rats were 20 days pregnant they underwent hysterectomy and the male fetal rats were taken out. Fluorogold (FG), a tracer, was injected into their levator ani muscles. Then the fetal rats were put back into the uteri. Twenty-four hours later hysterectomy was performed for the second time to take out and kill the live fetuses that had undergone FG injection. Their lumbo-sacral spinal cords were taken out, fixed and made into serial longitudinal sections. Digital camera system and fluorescent microscopy were used to observe the FG-labeled sensory neurons. Fifteen normal female rats were used as controls.

The FG-labeled sensory neurons innervating levator ani muscle were located mainly in the posterior root ganglia of the 5 th segment of lumber and the 1 st sacral cord. The number of FG-labeled sensory neurons in the normal control fetuses, fetuses without defect of the ETU-fed female rats, fetuses with low type imperforate anus, and fetuses with high type imperforate anus were 11 804 +/- 2362, 10 429 +/- 708, 2886 +/- 705, and 1026 +/- 425 respectively, the latter 2 number being significantly fewer than that in the fetuses without defects (P < 0.05) and that in the normal controls (P < 0.05).

Defective sensory neurons innervating the levator ani muscle co-exists with the alimentary tract anomaly in rat fetuses with ARM. The defective development of sensory neurons is an important factor likely to contribute to poor post-operative anorectal function despite surgical correction of the ARM.