Usefulness of An Anal Sphincter Injury Mouse Model by Means of a Balloon Catheter and a New Method of Evaluating Anal Sphincter Function

BACKGROUND: The incidence of fecal incontinence is ~2%, and the associated symptoms significantly impact daily life. New treatment methods including electrical stimulation and regenerative therapy using stem cells for fecal incontinence have been reported. We explored the usefulness of an anal sphincter injury mouse model by means of a balloon catheter and focused on the defecation status of mice as a novel method for evaluating anal function. We examined the utility of the mouse model of anal sphincter injury and the efficacy of electrical stimulation as a treatment modality using this model. METHODS: A 10‐mm balloon catheter was used to create an anal sphincter injury model in mice. Sphincter function was evaluated in the noninjured (n = 4), injured (n = 4), noninjured electrical stimulation (n = 4), and injured electrical stimulation (n = 4) groups. Defecation status (defecation frequency in 24 h and fecal weight per stool) and pathological evaluation were used for comparison. RESULTS: The defecation frequency increased and the fecal weight per stool decreased significantly in the anal sphincter injury model. Pathological evaluation revealed that anal sphincter tears occurred the day after the injury. Meanwhile, the defecation frequency improved on d 7, and the fecal weight per stool gradually normalized to that of the control group and exhibited significant sphincter muscle hypertrophy in the electrical stimulation group. CONCLUSION: Anal sphincter injury using a balloon catheter in mice allowed us to create a uniform model. The evaluation of defecation status in mice is a useful method for comparatively evaluating anal function.