This application represents an exploratory and development proposal to design, test, and fabricate an experimental model in which acute perfusions of the inner ear labyrinth can be achieved for investigations of vestibular pharmacology. The principal advantage of this new model is that the pharmacologic manipulations can be introduced directly into the labyrinth while recording the discharge of primary afferent neurons, representing the output of vestibular sensory epithelia. Therefore, the effect of the manipulations on spontaneous and stimulus-evoked discharge can be directly determined, enabling future investigations addressing a wide variety of questions for which contemporary pharmacologic tools (e.g. receptor agonists and antagonists, conductance-specific agonists and antagonists, etc.) are applicable. Two hypotheses will be tested through a set of specific aims that will fully test the efficacy of the model. A perfusate delivery system will be constructed that addresses key technical issues, specific to the basic function of the peripheral vestibular system, in its design. Pilot studies have identified potential artifacts in afferent discharge that likely resulted from abrupt changes in perfusate pressure. The perfusate delivery system will be specifically designed and fabricated to eliminate or minimize these artifacts. The design and fabrication of this system will reflect a collaboration between neurobiology and microfluidics engineering, using tools of micro-electro- mechanical systems (MEMS) engineering to construct a microfluidics device (chip) to manage the flow of perfusate directly to the inner ear perilymphatic space of specially prepared chinchillas. A test battery of perfusate solutions will be utilized that address the accessibility of specific solution constituents to hair cells and afferent neurons projecting throughout the crista and utricular neuroepithelia. These experiments have electrophysiologic as well as morphologic components, whereby test solutions will be delivered and the effects monitored through afferent discharge recordings as well as from direct imaging of the incorporation of these solutions by vestibular hair cells. Experiments will be conducted that will test a second hypothesis regarding the presence of transmembrane AMPA-receptor regulatory proteins (TARPs) within the afferent neurons. While providing a detailed direct test of the efficacy of the preparation for pharmacologic manipulations, these experiments will also address the functionality of TARPs in vestibular afferents. These results have the potential to motivate a new line of investigation for sensory processing in the peripheral vestibular system.
The research to be conducted under this exploratory and development proposal will produce a mammalian model system through which direct testing of pharmaceutical agents can be conducted with respect to their influence on the inner ear vestibular system and the signals that are transmitted to the central nervous system. The results from this investigation will lead to future studies ameliorating our understanding of neurochemical and pharmacologic interactions within the inner ear. This system may also provide a test bed for new treatments of inner ear disorders, as well as contribute to the development of new therapies that will assist in neural rehabilitation of damaged inner ear tissues.