BILABYRINTHECTOMY EFFECTS ON MUSCLE FIBER TYPES

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The vestibular system comprises both motor and sensory components. While central nervous system connections involved in the vestibular system have been lelineated, the system's effect of motor control is less clear, basing most conclusions on motor behavior. It is clear that limb extensor and extraocular musculature performances are facilitated by vestibular input; however, no studies have been completed which demonstrate whether or not the steady input of the vestibular system influences the development of muscle fiber types, fiber diameter or compartmentalization in either group of muscles. Additionally, the cause of abnormal motor behavior seen in lesion studies of vestibular components is not well-understood. By examining muscle fiber changes in the presence of peripheral vestibular loss, this study will contribute to the understanding of normal and pathological movement. We hypothesize that bilateral labyrinthectomy will alter muscle fiber type distribution and biomechanical consistency in anti-gravity muscles secondary to lost input from both labyrinths. The fibers involved will be the least fatigable, compartmentalized, and lie closest to the bone. The vestibular contribution to motor development will be studied in a ferret model. Neonatal ferrets will undergo bilateral labyrinthectomy to destroy the vestibular sensory receptors. The histology and biochemical myosin content of muscle from these ferrets will be compared with unaltered control animals. The results will demonstrate the effect of peripheral vestibular components on muscle fiber and compartment development. During the final year of this proposal, we will go on the investigate the possibility of a critical period of vestibular effects, and, in the future, examine the contractile characteristics of the limb and extraocular muscles. The ultimate goal is to better understand the role of the peripheral vestibular input on motor development and contribute to the understanding of motor behavior in the presence of bilateral peripheral vestibular lesions.