The effect of isometric tongue exercise in a novel rodent model of dysphagia

Abstract

The tongue plays a crucial role in the swallowing process and impairment can lead to dysphagia, particularly in neurological conditions such as amyotrophic lateral sclerosis (ALS), Parkinson's Disease, and stroke. This project utilizes our previously established rodent model that develops dysphagia as a consequence of only tongue dysfunction. This model was created by injecting a toxin into the genioglossus muscle of the tongue for selective death of motor neurons in the hypoglossal nucleus, a brainstem region that directly innervates the tongue via the hypoglossal nerve. Our goal is to investigate the effect of tongue exercise on tongue function in three groups of male rats: 1) toxin injection plus exercise (n=7); 2) toxin injection plus sham exercise (n=7); and 3) control injection plus exercise (n=7). For each group, a custom spout with adjustable lick force requirement was placed in the home cage overnight for 12 hours on days 4 and 6 post-tongue injection. For the two exercise groups, the lick force requirement was set to 50% greater than the maximum voluntary tongue force, measured using a force lickometer. Assessment of the following outcome measures included: 1) baseline and end-line swallow function measured using videofluoroscopic swallow studies (VFSS); and 2) baseline and end-line lick force measured using a force lickometer. Swallow metrics were analyzed using our custom semi-automated VFSS analysis software. Our lingual exercise program resulted in statistically significant differences in tongue force and lick rate but had no effect on swallow rate. Results provide insight regarding tongue exercise as a potential treatment to ameliorate alterations in tongue function in neurologically impaired patients.