The objective of this proposal is to study the molecular mechanisms by which neurotransmitters released by olivocochlear efferents influence outer hair cells (OHCs) of the cochlea. One theory about the contributions that cochlear efferents make to hearing is that they protect the cochlea from high frequency acoustic over-stimulation, whereas another theory is that they enhance sound recognition in the presence of background noise. The primary neurotransmitters of the efferents projecting on high frequency OHCs are acetylcholine (ACh) and calcitonin gene-related peptide (CGRP). The proposed experiments will test the hypothesis that CGRP exerts its effects by initiating a cascade of events resulting in desensitization of the cholinergic receptors present on OHCs. The first specific aim is to clone full-length cDNAs for ACh and CGRP receptor subtypes from the guinea pig cochlea using as probes partial cDNAs encoding the guinea pig a9 ACh and CGRP receptors. In situ hybridization techniques will be used to establish which cells in the guinea pig organ of Corti express these receptors. The second specific aim will use immunohistochemical and Western blotting techniques to verify the presence and distribution of proteins for the cochlear ACh a9 and CGRP efferent receptors. The third specific aim employs electrophysiological techniques to investigate whether the cloned CGRP and Ach receptors are able to interact functionally, such that CGRP preincubation causes second messenger effects, which leads to Ach receptor desensitization. Information gained from these studies may contribute to future drug therapies that target the cochlear efferents system, and thus, help decrease the occurrence of, and improve the treatment for patients with high-frequency hearing loss.
