Swallowing Dysfunction and Histopathological Changes in a Rat Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is associated with progressive dysphagia. Although histopathological changes in the masseter and tongue muscles have been reported in DMD rats, little is known regarding swallowing-related muscles, especially those involved in the pharyngeal phase. Therefore, this study evaluated the swallowing function and pathology of swallowing-related muscles in a DMD rat model. Seven male DMD rats and five wild-type (WT) rats were used. Their body weight and food intake amount were monitored weekly. Electromyography (EMG) was performed on the geniohyoid muscle to assess the compound muscle action potential (CMAP) amplitude, swallow frequency, and swallowing duration. It was conducted at 90 weeks in WT rats and at the time point of 10% body weight loss in DMD rats. Histopathological examination of the geniohyoid, mylohyoid, digastric, and tongue muscles was performed using hematoxylin and eosin and Masson's trichrome staining. DMD rats exhibited significant reductions in body weight and food intake amount. In four out of five muscles examined, the muscle fiber area significantly decreased. However, all five muscles showed increased fibrosis and central nuclei. EMG revealed that DMD rats had significantly reduced CMAP amplitude, reduced swallow frequency, and prolonged hyoid elevation duration. DMD rats exhibited impaired swallowing function and pathological changes in swallowing-related muscles, similar to those observed in patients with DMD. DMD rats are useful for basic research on swallowing function in DMD and for developing therapeutic strategies targeting dysphagia.