The long-range goal of this project is to understand the descending neural systems that control information output from the cochlea and cochlear nucleus to higher brain centers. Among the general hypotheses for the function of descending systems are that 1) they extend the dynamic range of the auditory system, 2) they enable selective attention to signals in noisy environments, and 3) they help to protect the inner ear from overstimulation. Existence of descending innervation to hair-cell systems in virtually every vertebrate species examined thus far is strong presumptive evidence for the importance of these feedback systems. This project will concentrate on one particular descending system, the medial olivocochlear (MOC) system in mammals. MOC neurons send projections from a part of the lower brain, the superior olivary complex, to the outer hair cells of the cochlea. In addition to innervating outer hair cells, MOC neurons give off side branches to both the cochlear nucleus and the vestibular nuclei. The proposed research will investigate which cells in the cochlear nucleus are the target neurons of the MOC branches, how the target neurons are affected physiologically, and which neurotransmitters are likely to be involved in mediating those effects. One approach that will be used in the proposed research is to use transneuronal labeling by the neuronal tracer, horseradish peroxidase (HRP). Preliminary studies indicate that both afferent fibers of the auditory nerve and MOC branches can label their associated cochlear-nucleus neurons when heavily loaded with HRP. Very dense labeling of the primary elements is achievable with very small rodents such as the mouse, our chosen animal model. Transneuronal labeling should yield important new information for the auditory system and for neurobiology in general. Our proposed research will also address the differences found in projections of olivocochlear (0C) fibers to the basal and apical regions of the cochlea. Questions such as the fields innervated by single 0C fibers in both the cochlea and cochlear nucleus will influence theoretical formulations of how the MOC system controls afferent signals sent to more central regions of the brain.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC001089-04
Application #
2126248
Study Section
Hearing Research Study Section (HAR)
Project Start
1991-06-01
Project End
1995-05-31
Budget Start
1994-06-01
Budget End
1995-05-31
Support Year
4
Fiscal Year
1994
Total Cost
Indirect Cost
Name
Massachusetts Eye and Ear Infirmary
Department
Type
DUNS #
073825945
City
Boston
State
MA
Country
United States
Zip Code
02114
Guinan Jr, John J (2018) Olivocochlear efferents: Their action, effects, measurement and uses, and the impact of the new conception of cochlear mechanical responses. Hear Res 362:38-47
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Hight, Ariel Edward; Kozin, Elliott D; Darrow, Keith et al. (2015) Superior temporal resolution of Chronos versus channelrhodopsin-2 in an optogenetic model of the auditory brainstem implant. Hear Res 322:235-41
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Verma, Rohit U; Guex, Amélie A; Hancock, Kenneth E et al. (2014) Auditory responses to electric and infrared neural stimulation of the rat cochlear nucleus. Hear Res 310:69-75
Brown, M Christian (2014) Single-unit labeling of medial olivocochlear neurons: the cochlear frequency map for efferent axons. J Neurophysiol 111:2177-86

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