Fatigue and weakness are common complaints of elderly people related to sarcopenia, or the loss of skeletal muscle mass, organization, and strength. Little is known concerning the pathophysiology and age-related sequelae of sarcopenia in muscles of the head and neck. This knowledge is important inasmuch as alterations in muscle character may underlie deficits in speech and swallowing, which are significant clinical problems in elderly people. The tongue has a vital role in speech and swallowing, and poor lingual control is associated with both speech and swallowing impairment. However, muscles of the tongue have been understudied. Our hypothesis is that age-related alterations in tongue function are based upon naturally occurring denervation-reinnervation processes, and that these processes can be reversed or prevented via exercise. This hypothesis will be tested in a rat model by comparing physiological, molecular, and histological parameters of old rat tongue muscles with young muscles, and with old tongue muscles that have undergone chronic nerve stimulation to model exercise. The proposed research has 2 specific aims: (1) To quantify changes in neuromuscular morphology predictive of age-related tongue weakness; and (2) To determine underlying morphological and physiological changes induced by tongue exercise in old rats. Physiological experiments will be performed in vivo in the tongue in young rats and in 2 groups of older rats. In the same animals, molecular analyses of myosin heavy chain expression, and histological analyses of neuromuscular junctions will be performed. Exercise will be modeled via bilateral chronic stimulation of the hypoglossal nerves. Analyses of covariance (a combination of analysis of variance and regression) will be used to determine the degree to which muscle contractile properties can be predicted from molecular and histological characteristics. Further analyses of variance will be performed to compare the physiological, molecular, and histological variables of interest as a function of age group (Specific Aim 1) or age by exercise (Specific Aim 2). This work is innovative and important in establishing potential morphological bases for the alterations in physiological function observed with tongue muscle senescence. Further, this work will be highly significant in discovering a neuromuscular basis for the putative benefits of exercise in the prevention and treatment of age-related swallowing impairment.
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