Gravity Dependence of Otolith System Function

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The primary objective of the present proposal is to determine how gravity affects the functional development of the vestibular otolith system. It is known that even moderate exposure to altered gravity conditions in adult animals can produce modifications in the anatomy, physiology, and neuromotor responses related to the vestibular system. In addition, more limited evidence shows that exposure to either microgravity or hypergravity conditions during embryogenesis and neonatal development can produce profound alterations in vestibular system structure and function. This project will compare otolith system morphology, physiology, and behavioral responses in quails that have developed from fertilization through post-hatch maturity in either Earth normal, rotational 1g, or different levels of hypergravity. The first aim is to examine and compare the distribution and type of otolith receptors and macula afferent innervation in quails raised in different gravity conditions. We predict that the number of cells and the terminal innervation patterns of afferents will increase proportionally dependent upon the force of gravity experienced during development. The second aim will examine the sensitivity, spatial tuning, and dynamic responses of otolith afferents in mature quails that have developed in different gravity conditions. The third aim will examine the effects of development in altered gravity environments upon the vestibuloocular refelex and head gaze stability in mature quails during linear motion. We hypothesize that the gaze reflex components are tuned to direct gaze behavior relative to the gravito-inertial acceleration constant experienced during development. These studies will for the first time provide basic information regarding how the presence of gravity affects the acquisition of linear motion responsiveness by receptors and primary afferents, as well as the formation of head postural stability during linear motion. This information will provide new insight into mechanisms for recovery from vestibular injury and could lead to new treatment regimens for vestibular related disease or trauma.