This project will focus on the neurogenic regulation of cochlear blood flow and on the interactions between neurogenic and endothelium-mediated mechanisms. Receptors controlling vascular diameter of the spiral modiolar artery and the identity of locally released vasoactive substances will be determined. Locally-released vasoactive substances will include those from neuronal elements innervating the spiral modiolar artery and those from endothelial cells lining the lumen of this vessel. The spiral modiolar artery is the main blood supply of the cochlea. Aberrations in the regulation of cochlear blood flow have been suspected to play a major part in the etiology of a variety of inner ear disorders including sudden and fluctuating hearing loss, Meniere's disease, tinnitus and autoimmune-related hearing loss. Fundamental to these etiologies are the receptors present on the cochlear blood vessels and their function in the regulation of cochlear blood flow. Hypotheses pertaining to the presence of receptors and to the identity of released vasoactive substances will be tested with a functional assay based on newly-developed in vitro preparations of the isolated spiral modiolar artery. The vascular diameter and the release of vasoactive substance from neuronal elements and from the endothelium will be measured. The measurement of the vascular diameter is the most physiologically- relevant parameter since change in the vascular diameter is the single most effective means of regulating blood flow. Receptors will be determined pharmacologically utilizing selective agonists and antagonists. Release of neurotransmitter from neuronal elements which remain with the isolated spiral modiolar artery will be triggered by electric field stimultation. The identity of the released neurotransmitters will be determined by their functional effect on their respective target receptors and by a highly specific bioluminescence assay. All techniques are well established in this laboratory. This project evolved out of the previous one on isolated medial efferent nerve terminals. Common to both projects is the focus on the function of isolated nerve terminals. Whereas the experimental access was previously limited to prejunctional processes, the proposed studies include both pre- and post junctional mechanisms and their complex interactions leading to the regulation of cochlear blood flow. The completion of the proposed studies are expected to provide a foundation for the pharmacologic management of inner ear disorders.
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