The broad, long-term objective of this research proposal is to gain a better understanding of the neuropathology of swallowing impairment (dysphagia) in neurological diseases. Several mouse models currently exist that are suitable and readily available for translational research in neurological diseases. However, relatively little is known about the swallowing function of these mouse models because experimental methods to evaluate the function of the individual neural components of the swallow reflex circuit have not yet been developed. The purpose of the proposed research is to develop an experimental protocol for using brainstem evoked potentials recorded in response to stimulation of the superior laryngeal nerve in mice to quantify the function of the individual sensory, central integration, and motor components of the swallowing reflex circuit.
Three specific aims will serve this purpose.
Specific Aim 1 will test the hypothesis that it is possible to record swallow evoked potentials (SwEPs) in mice. The optimal stimulus and recording parameters will be identified using 3-4 month old wild-type (C57BL/6J) mice. Waveform morphology (i.e., number of positive and negative peaks, peak-to-peak amplitudes, and peak latencies) will be compared relative the following variables: electrode placement, filter settings, signal amplification, signal averaging, stimulus rate, and stimulus amplitude.
Specific Aim 2 will evaluate the utility of the SwEP testing protocol established in Specific Aim 1 to phenotype the swallowing function of a transgenic mouse model of amyotrophic lateral sclerosis (ALS;SOD1-G93A) and nontransgenic littermates at four time points: 1, 2, 3, and 4 months of age.
Specific Aim 3 will begin to investigate the generator sources for the SwEP peaks. Histological and immunohistochemical methods will be performed on a subset of animals from Specific Aim 2 to identify the brainstem nuclei (and subnuclei) that are activated during swallowing;these regions also will be investigated for evidence of histopathology (vacuoles). The findings will guide future lesioning experiments and near-field recording studies directed toward positive identification of generator sources of SwEP response peaks. These three specific aims will permit: 1) objective quantification of dysphagia in SOD1-G93A transgenic mice, 2) description of the time-course of neurogenic dysphagia in this strain, and 3) identification of the central neural correlates for dysphagia in this animal model of ALS. The knowledge gained from this work will directly extend the scientific knowledge of normal swallowing and the pathogenesis of dysphagia in ALS. In addition, the SwEP testing protocol established by this work has the potential to be used to identify additional mouse models of dysphagia for various neurological diseases, as well as to quantify the effect of various treatments (e.g., pharmacological agents, stem cell therapy, etc.) on the function of the individual neural components of the swallow relay circuit in these animal models. Thus, development of this experimental protocol in mice may ultimately lead to novel and effective treatment options for dysphagia in humans with neurological diseases.
Neurogenic dysphagia (i.e., swallowing impairment caused by neurological disorders such as Lou Gehrig's disease) affects approximately 500,000 individuals, including pediatric and adult populations, annually in the United States. Common symptoms include malnutrition, dehydration, and respiratory complications, all of which may result in a poor quality of life and contribute to death in affected individuals. Few effective treatments for neurogenic dysphagia have been identified;therefore, neurogenic dysphagia is certainly an important area for research that has the potential to benefit hundreds of thousands of individuals living within the United States, as well as many more living beyond these borders, who are afflicted by various neurological diseases.