Reduced tongue force and functional swallowing changes in a rat model of post stroke dysphagia

Abstract

Purpose: Dysphagia is a common problem after stroke that is often associated with tongue weakness. However, the physiological mechanisms of post-stroke tongue muscle weakness and optimal treatments have not been established. To advance understanding of physiological mechanisms of post stroke dysphagia, we sought to validate the unilateral transient middle cerebral artery occlusion (MCAO) rat model of ischemic stroke as a translational model of post stroke dysphagia. Our goal was to establish clinically relevant measures and chronicity of functional deficits; criteria that increase the likelihood that findings will translate to the clinic. We hypothesized that MCAO would cause tongue weakness and functional swallowing changes.

Methods: Maximum voluntary tongue forces and videofluoroscopic swallowing studies were collected in 8-week old male Sprague-Dawley rats prior to receiving either a left MCAO (N = 10) or sham (N = 10) surgery. Tongue forces and VFSS were reassessed at 1 and 8 weeks post-surgery.

Results: Maximum voluntary tongue force, bolus area, and bolus speed were significantly reduced in the MCAO group at the 1 and 8-week timepoints.

Conclusion: Clinically relevant changes to swallowing and tongue force support the use of the MCAO rat model as a translational model of post stroke dysphagia. This model will allow for future studies to improve our understanding of the physiology contributing to these functional changes as well as the impact of therapeutic interventions on physiological targets and function.

Keywords: Dysphagia; Model; Rat; Stroke; Swallowing; Tongue.

Fig. 1

Body weight and infarct volume. Both stroke (black boxes) and sham (gray boxes) groups gained weight over time (p < 0.001), however no significant weight differences were found between MCAO and Sham (Top). Bodyweight at the 8-week time point, normalized to baseline, was negatively correlated with infarct volume (Pearson’s r = - 0.726, p = 0.017); the animals with the largest infarcts had gained the least weight. Inset: Representative image of a Cresyl violet stained brain section used to calculate infarct volume (infarct area outlined).

Fig. 2

Tongue force and inter-press interval. Asterisks indicate significant differences between the MCAO (black) and sham (gray) groups. The MCAO groups tongue force was significantly lower at 1 and 8 weeks (p = 0.034, 0.003), and was significantly reduced from baseline at both time points (p < 0.001, p = 0.011). The sham group was not significantly different than baseline at 1-week but was significantly larger than baseline at 8 weeks (p = 0.355, p = 0.007). At 3 days post-surgery the inter-press interval of both groups was slower than baseline (MCAO p = 0.003, Sham p = 0.015). At 8 weeks, neither group was significantly different from baseline (MCAO p = 0.33, Sham p = 0.15), but the MCAO group was significantly slower than sham at the 8-week time point (p = 0.02).

Fig. 3

Videofluoroscopic swallowing study detected reduced bolus area and peak speed after MCAO. Example videofluoroscopic images of swallowing in the same rat before and 8 weeks after MCAO (A1 and A2), with the bolus outlined in white. B: The MCAO group (black) swallowed smaller boluses at both 1 and 8 weeks after MCAO (p = 0.002, p < 0.001). At both time points peak bolus speed was lower in the MCAO group (C; p = 0.006, p = 0.048). No significant differences were found between groups for inter-swallow interval (D).

Fig. 4

Mastication rate and jaw excursion. Mastication rate did not significantly differ between the MCAO (black) and Sham (gray) groups at any time point (Left). The jaw excursion distance was significantly less in the MCAO group (Right panel, data from week 8 shown).