An Electron-Microscopic Study of Adrenergic Innervation in the Cochlea

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Abstract
By using electron-microscopic techniques including the administration of a “false transmitter” it has been possible to identify adrenergic terminals filled with characteristic dense-cored vesicles in the cochlea. A continuous sympathetic perivascular plexus is found up to the limit of the habenula region. Adrenergic terminals are also found independent of blood vessels and this innervation is especially rich in the habenula region. Terminals are frequently found just before the demyelinization zone and they surround the afferent nerve bundles when they have lost their myelin sheaths. In the habenula, terminals are seen to make direct contact with non-myelinated afferent nerve fibres. Clusters of terminals are found in the tissue near the inner sulcus and toward the scala tympani. No adrenergic nerve terminals were found in the organ of Corti or vascular stria. The morphological localization of the sympathetic terminals support an influence on sound perception either via a direct action on sensory neurons or by vasomotor control.