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NEUROREGULATION AND MOTILITY

A new possibility for repairing the anal dysfunction by promoting regeneration of the reflex pathways in the enteric nervous system

Departments of ¹Physiology II, ²Surgery, and ³Molecular Pathology, Nara Medical University School of Medicine, Kashihara, Japan

Submitted 28 July 2007 ; accepted in final form 27 February 2008

Moderate rectal distension elicits recto-rectal reflex contractions and simultaneous recto-internal anal sphincter reflex relaxations that together comprise the defecation reflex. Both reflexes are controlled by 1) pelvic nerves, 2) lumbar colonic nerves, and 3) enteric nervous system. The aim of the present study was to explore a novel approach to repairing the defecation reflex dysfunction by using the plasticity of enteric nervous pathways. Experiments were performed in anesthetized guinea pigs with ethyl carbamate. The rectum 30 mm oral from the anal verge was transected without damage to extrinsic nerves, and subsequent end-to-end one-layer anastomosis was performed. Recovery of the defecation reflex and associated reflex pathways were evaluated. Eight weeks after sectioning of intrinsic reflex nerve pathways in the rectum, the defecation reflex recovered to the control level, accompanied with regeneration of reflex pathways. The 5-HT₄-receptor agonist mosapride (0.5 and 1.0 mg/kg) significantly (P < 0.01) enhanced the recovered defecation reflex 8 wk after surgery. Two weeks after local treatment with brain-derived neurotrophic factor (BDNF: 10^–6 g/ml) at the rectal anastomotic site, the recto-internal anal sphincter reflex relaxations recovered and some bundles of fine nerve fibers were shown to interconnect the oral and anal ends of the myenteric plexus. These results suggested a possibility for repairing the anal dysfunction by promoting regeneration of the reflex pathways in the enteric nervous system with local application of BDNF.

brain-derived neurotrophic factor; internal anal sphincter