Impact of Rotenone Treatment on Respiration and Swallowing Rate in Drinking Rats

Parkinson’s disease is a neurodegenerative disorder known to cause dysphagia, the major contributor to mortality via aspiration pneumonia. The neurological basis of swallowing dysfunction in Parkinson patients is poorly understood. To explore the mechanisms of swallowing dysfunction, we studied the impact of rotenone treatment on respiration rate and swallowing rate in liquid-drinking rats. We hypothesized that rotenone treatment will cause a decrease in respiratory and swallowing rate compared to untreated liquid-drinking rats. Six rats were injected with 2.75 mg/kg/day intraperitoneal rotenone for 16 days to create the parkinsonian phenotype and subsequently recorded with 200fps video fluoroscopy during barium-infused liquid drinking. Before the first injection and on day 4, 7, 10 and 16, the number of swallows and number of breaths in a ten second period of continuous drinking were scored. The data was then analyzed using a type 3 Analysis of Variance with Satterthwaite's method to determine whether the rotenone injections impacted the respiration or swallowing rate. Rotenone injections led to a decrease in respiration rate, but no change in swallowing rate over a 16-day period. The p-value for respiration rate was less than 0.05 (0.02731) indicating a significant result, however the p-value for swallow rate was greater than 0.05. Immunohistochemistry of the dorsolateral striatum of rats that received rotenone treatment for 8 days and 16 days showed significant reduction in tyrosine hydroxylase (TH) immunofluorescence with increased impact due to prolonged treatment. TH is the rate limiting step of catecholamine synthesis from tyrosine, confirming that rotenone is affecting dopamine production in order to influence swallowing dynamics. These results indicated that rotenone induced parkinsonian treatment has differential impacts on different brainstem mediated processes, swallowing and respiration. Thus, swallow-respiration coordination is likely impacted in these animals, potentially increasing risk of airway protection failure.