Swallowing Disrupts Tongue-Jaw Coordination During Chewing in a Rat Model of Parkinson\u27s Disease

The primary motor symptoms of Parkinson’s disease, including bradykinesia, rigidity, and tremor, are associated with difficulties regulating transitions between motor behaviors due to basal ganglia dysfunction. Chewing and swallowing, which are disordered in most patients with Parkinson’s disease, are two complex motor behaviors which overlap in time and share some neuromuscular components. The objective of this study is to identify how Parkinson’s disease affects the coordination of chewing and swallowing. We hypothesize that as a result of impaired regulation of shift between motor patterns, chewing cycles that occur with a swallow will be more affected that chewing cycles occurring in isolation in a rat model of Parkinson’s disease. Four adult Lewis rats were treated with daily IP injections of rotenone for 7 days to induce Parkinsonian symptoms. Prior to injections radio opaque markers were implanted into the tongue and jaw. Animals were filmed using high speed (2oofps) videofluoroscopy before the first injection and on injection day 7. Markers in the tongue and jaw were tracked to measure chew cycle duration and tongue-jaw coordination. Swallows times were identified from videofluoroscopic recordings. We tested whether chews occurring before, during, or after a swallow were longer, and whether tongue jaw coordination changed in rats before and after treatment using linear mixed models and post hoc pairwise contrasts. Chews that co-occur with swallows are significantly longer after treatment than before (p=0.006), whereas the lengths of pre and post swallow chews do not changes. Tongue jaw coordination after treatment is different in post chew swallows (p=0.016). The effects of Parkinsonian neurodegeneration on chewing are most pronounced when chewing and swallowing co-occur, which is in line with expectation given the role of the basal ganglia in coordinating motor functions. Lingering impacts on tongue–jaw coordination after the swallow suggest that return to baseline function is also impaired. The coordination of overlapping motor functions in feeding is affected in Parkinson’s disease, with potential implications for feeding difficulties and dysphagia