Efferent Components of the Auditory System

1980 ◽  
Vol 89 (5_suppl) ◽  
pp. 114-120 ◽  
Author(s):  
W. Bruce Warr
Keyword(s):  
Axonal Transport ◽  
Hair Cells ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Superior Olivary Complex ◽  
Cell Group ◽  
Efferent Innervation ◽  
Tissue Sections ◽  
Cells Of Origin ◽  
Medial Olivocochlear

The origins and terminations of the olivocochlear bundle, which provides an efferent innervation to the organ of Corti, are described on the basis of experiments using axonal transport of tracer substances and light microscopy in the cat. The cells of origin were labeled by the retrograde tracer horseradish peroxidase which was injected unilaterally into the cochlea. Labeled cells in the superior olivary complex could be dichotomized according to their location (lateral or medial), their size (small or large), and their preferred side of projection (uncrossed or crossed). All labeled olivocochlear neurons exhibited a positive reaction for acetylcholinesterase. To determine the cochlear projections of the neurons, injections of a radioactive amino acid were made into either the lateral or medial olivocochlear cell group. After allowing time for synthesis and axonal transport of radio-labeled protein to reach synaptic endings in the cochleas, the tissue sections of these specimens were processed for autoradiography. The results indicate that lateral olivocochlear neurons project to the region beneath the inner hair cells of both sides, whereas medial olivocochlear neurons project to the region beneath the outer hair cells of both sides. These findings are in substantial accord with previous experimental work but suggest that the organ of Corti receives a dual efferent innervation which is organized according to the location and morphology of its cells of origin. Accordingly, it is proposed that the two efferent components of the cochlear innervation described here be referred to as the lateral and medial olivocochlear systems, replacing the current designations of crossed and uncrossed olivocochlear bundles, the latter which are demonstrably heterogeneous in their origins and terminations and, probably, also in their functions.

scholarly journals Single-unit labeling of medial olivocochlear neurons: the cochlear frequency map for efferent axons

2014 ◽  
Vol 111 (11) ◽  
pp. 2177-2186 ◽  
Author(s):  
M. Christian Brown
Keyword(s):  
Hair Cells ◽  
Single Unit ◽  
Dynamic Range ◽  
Organ Of Corti ◽  
Nerve Fibers ◽  
Outer Hair Cells ◽  
Cochlear Amplifier ◽  
Noise Masking ◽  
Efferent Neurons ◽  
Medial Olivocochlear

Medial olivocochlear (MOC) neurons are efferent neurons that project axons from the brain to the cochlea. Their action on outer hair cells reduces the gain of the “cochlear amplifier,” which shifts the dynamic range of hearing and reduces the effects of noise masking. The MOC effects in one ear can be elicited by sound in that ipsilateral ear or by sound in the contralateral ear. To study how MOC neurons project onto the cochlea to mediate these effects, single-unit labeling in guinea pigs was used to study the mapping of MOC neurons for neurons responsive to ipsilateral sound vs. those responsive to contralateral sound. MOC neurons were sharply tuned to sound frequency with a well-defined characteristic frequency (CF). However, their labeled termination spans in the organ of Corti ranged from narrow to broad, innervating between 14 and 69 outer hair cells per axon in a “patchy” pattern. For units responsive to ipsilateral sound, the midpoint of innervation was mapped according to CF in a relationship generally similar to, but with more variability than, that of auditory-nerve fibers. Thus, based on CF mappings, most of the MOC terminations miss outer hair cells involved in the cochlear amplifier for their CF, which are located more basally. Compared with ipsilaterally responsive neurons, contralaterally responsive neurons had an apical offset in termination and a larger span of innervation (an average of 10.41% cochlear distance), suggesting that when contralateral sound activates the MOC reflex, the actions are different than those for ipsilateral sound.

scholarly journals Immunohistochemistry localises myosin-7a to cochlear efferent boutons

2022 ◽  
Vol 7 ◽  
pp. 1
Author(s):  
Piotr Sirko ◽  
Andrei S. Kozlov
Keyword(s):  
Hearing Loss ◽  
Vestibular System ◽  
Hair Cells ◽  
Usher Syndrome ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Actin Binding ◽  
Adult Rat ◽  
Cochlear Gain ◽  
Medial Olivocochlear

Background: Myosin 7a is an actin-binding motor protein involved in the formation of hair-cell stereocilia both in the cochlea and in the vestibular system. Mutations in myosin 7a are linked to congenital hearing loss and are present in 50% of Type-1 Usher syndrome patients who suffer from progressive hearing loss and vestibular system dysfunction. Methods: Myosin 7a is often used to visualise sensory hair cells due to its well characterised and localised expression profile. We thus conducted myosin-7a immunostaining across all three turns of the adult rat organ of Corti to visualise hair cells. Results: As expected, we observed myosin 7a staining in both inner and outer hair cells. Unexpectedly, we also observed strong myosin 7a staining in the medial olivocochlear efferent synaptic boutons contacting the outer hair cells. Efferent bouton myosin-7a staining was present across all three turns of the cochlea. We verified this localisation by co-staining with a known efferent bouton marker, the vesicular acetylcholine transporter. Conclusions: In addition to its role in stereocilia formation and maintenance, myosin 7a or certain myosin-7a expression variants might play a role in efferent synaptic transmission in the cochlea and thus ultimately influence cochlear gain regulation. Our immunohistochemistry results should be validated with other methods to confirm these serendipitous findings.

Melatonin and other antioxidants prolong the postmortem activity of the outer hair cells of the organ of Corti: Its relation to the type of death

1999 ◽  
Vol 27 (2) ◽  
pp. 73-77 ◽  
Author(s):  
Miguel A. Lopez-Gonzalez ◽  
Juan M. Guerrero ◽  
Francisco Rojas ◽  
Carmen Osuna ◽  
Francisco Delgado
Keyword(s):  
Hair Cells ◽  
Organ Of Corti ◽  
Outer Hair Cells

Innervation Densities of Inner and Outer Hair Cells of the Human Organ of Corti

ORL ◽  
1988 ◽  
Vol 50 (6) ◽  
pp. 363-370 ◽  
Author(s):  
Joseph B. Nadol, Jr.
Keyword(s):  
Hair Cells ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Human Organ

Some Unresolved Problems concerning the Cochlear Nerve

1976 ◽  
Vol 85 (6_suppl2) ◽  
pp. 1-28 ◽  
Author(s):  
R. Lorente de Nó
Keyword(s):  
Light Microscopy ◽  
Hair Cells ◽  
Organ Of Corti ◽  
Bushy Cell ◽  
Afferent Fibers ◽  
Cells Of Origin ◽  
Structural Details ◽  
Synaptic Junctions ◽  
Ventral Nucleus ◽  
Spiral Fibers

Three types of afferent fibers innervate the hair cells of the organ of Corti: 1) specific radial fibers which establish contacts with a very few neighboring internal hair cells; 2) spiral fibers, each one of which establishes contact with a number of external hair cells distributed throughout long segments of the cochlea; and 3) unspecific radial fibers which are collaterals arising radially at irregular intervals from fibers of the ganglionic spiral bundles and which establish contact with internal hair cells. The existence of spiral ganglionic bundles of fibers oriented apicalward has long been described, and the fact that a number of ganglionic spiral fibers give off radial collaterals to innervate internal hair cells was illustrated by Cajal and by Lorente de Nó. However, those structural details are not mentioned in the modern literature. In the ventral nucleus there are neurons with efferent axons which join the trapezoid body and cells with short axons ramified within the ventral nucleus itself. Two types of cells with efferent axons are illustrated and described, the spherical or bushy cell and the basket cell; and it is shown that branches of division of the two types of efferent axons form association tracts which end in the tuberculum acusticum. Also, the fact is illustrated that fibers having their cells of origin in that tuberculum form association paths which end in the ventral nucleus by means of extensive ramifications which form numerous synaptic endings. The dendritic and fibrillar plexuses in the ventral nucleus are described, an analysis is made of the relationships between the two plexuses and of the synaptic junctions that mediate transmission of nerve impulses. The synaptic junctions belong to a considerable number of types and in all illustrations the important fact repeatedly appears that one and the same fiber may form synaptic endings of widely different sizes and shapes located either on the same neuron or, more frequently, on different neurons. The intimate structure of each type of synaptic ending cannot be revealed by light microscopy, but only light microscopy can reveal to which kind of fiber the synaptic endings do belong. The presentation is concluded with a brief and preliminary discussion of physiological corollaries of certain general features of the anatomy of the acoustic system.

scholarly journals A detection method for lactic dehydrogenase activity in the inner ear.

1978 ◽  
Vol 26 (4) ◽  
pp. 313-317 ◽  
Author(s):  
T Omata ◽  
I Ohtani ◽  
K Ohtsuki ◽  
J Ouchi
Keyword(s):  
Hair Cells ◽  
Osmium Tetroxide ◽  
Light And Electron Microscopy ◽  
Organ Of Corti ◽  
Lactic Dehydrogenase ◽  
Outer Hair Cells ◽  
Water Soluble ◽  
Reaction Products ◽  
Frozen Sections ◽  
Membranous Labyrinth

A method for the detection of lactic dehydrogenase enzymatic activity in outer hair cells of the rabbit is described. The membranous labyrinth with temporal bone was prefixed in glutaraldehyde. After being placed into the incubation medium, it was postfixed in osmium tetroxide. Specimens of the organ of Corti were removed. Then the specimens were embedded in water-soluble glycol and cut with a cryostat for light microscopy, and also they were embedded in Epon and cut for light and electron microscopy. Sectioning of the membranous labyrinth was very easily made when the specimens were embedded in both the water-soluble glycol and the Epon. The structures of the frozen sections as well as the Epon-embedded ones were well preserved. In the frozen sections the preservation and localization of reaction products were thoroughly kept, but monoformazan of the Epon-embedded sections was soluble.

scholarly journals Active radial and transverse motile responses of outer hair cells in the organ of corti

1990 ◽  
Vol 43 (2-3) ◽  
pp. 219-230 ◽  
Author(s):  
Günter Reuter ◽  
Hans-Peter Zenner
Keyword(s):  
Hair Cells ◽  
Organ Of Corti ◽  
Outer Hair Cells

scholarly journals Oncomodulin Is Expressed Exclusively by Outer Hair Cells in the Organ of Corti

1998 ◽  
Vol 46 (1) ◽  
pp. 29-39 ◽  
Author(s):  
Nobuki Sakaguchi ◽  
Michael T. Henzl ◽  
Isolde Thalmann ◽  
Ruediger Thalmann ◽  
Bradley A. Schulte
Keyword(s):  
Hair Cells ◽  
Calcium Binding ◽  
Organ Of Corti ◽  
Ultrastructural Level ◽  
Outer Hair Cells ◽  
Regulatory Function ◽  
Electron Microscopic ◽  
Wide Range ◽  
Intracellular Organelles ◽  
Functional Relevance

Oncomodulin (OM) is a small, acidic calcium-binding protein first discovered in a rat hepatoma and later found in placental cytotrophoblasts, the pre-implantation embryo, and in a wide variety of neoplastic tissues. OM was considered to be exclusively an oncofetal protein until its recent detection in extracts of the adult guinea pig's organ of Corti. Here we report that light and electron microscopic immunostaining of gerbil, rat, and mouse inner ears with a monoclonal antibody against recombinant rat OM localizes the protein exclusively in cochlear outer hair cells (OHCs). At the ultrastructural level, high gold labeling density was seen overlying the nucleus, cytoplasm, and the cuticular plate of gerbil OHCs. Few, if any, gold particles were present over intracellular organelles and the stereocilia. Staining of a wide range of similarly processed gerbil organs failed to detect immunoreactive OM in any other adult tissues. The mammalian genome encodes one α- and one β-isoform of parvalbumin (PV). The widely distributed α PV exhibits a very high affinity for Ca2+ and is believed to serve as a Ca2+ buffer. By contrast, OM, the mammalian β PV, displays a highly attenuated affinity for Ca2+, consistent with a Ca2+-dependent regulatory function. The exclusive association of OM with cochlear OHCs in mature tissues is likely to have functional relevance. Teleological considerations favor its involvement in regulating some aspect of OHC electromotility. Although the fast electromotile response of OHCs does not require Ca2+, its gain and magnitude are modulated by efferent innervation. Therefore, OM may be involved in mediation of intracellular responses to cholinergic stimulation, which are known to be Ca2+ regulated.

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