scholarly journals How do the medial olivocochlear efferents influence the biomechanics of the outer hair cells and thereby the cochlear amplifier? Simulation results

2015 ◽  
Author(s):  
Amin Saremi ◽  
Stefan Stenfelt ◽  
Sarah Verhulst
Keyword(s):  
Hair Cells ◽  
Outer Hair Cells ◽  
Cochlear Amplifier ◽  
Medial Olivocochlear Efferents ◽  
Simulation Results ◽  
Medial Olivocochlear

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 Limiting Frequency of the Cochlear Amplifier Based on Electromotility of Outer Hair Cells

2003 ◽  
Vol 84 (2) ◽  
pp. 739-749 ◽  
Author(s):  
Mark Ospeck ◽  
Xiao-xia Dong ◽  
Kuni H. Iwasa
Keyword(s):  
Hair Cells ◽  
Outer Hair Cells ◽  
Cochlear Amplifier

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.

scholarly journals Gentamicin Blocks Both Fast and Slow Effects of Olivocochlear Activation in Anesthetized Guinea Pigs

1999 ◽  
Vol 82 (6) ◽  
pp. 3168-3174 ◽  
Author(s):  
Naohiro Yoshida ◽  
M. Charles Liberman ◽  
M. Christian Brown ◽  
William F. Sewell
Keyword(s):  
Hair Cells ◽  
Guinea Pigs ◽  
Aminoglycoside Antibiotic ◽  
Outer Hair Cells ◽  
Response Curves ◽  
Similar Time ◽  
Efferent System ◽  
Time Courses ◽  
Medial Olivocochlear ◽  
Unanesthetized Animals

The medial olivocochlear (MOC) efferent system, which innervates cochlear outer hair cells, suppresses cochlear responses. MOC-mediated suppression includes both slow and fast components, with time courses differing by three orders of magnitude. Pharmacological studies in anesthetized guinea pigs suggest that both slow and fast effects on cochlear responses require an initial acetylcholine activation of α-9 nicotinic receptors on outer hair cells and that slow effects require additional intracellular events downstream from those mediating fast effects. Gentamicin, an aminoglycoside antibiotic, has been reported to block fast effects of sound-evoked OC activation following intramuscular injection in unanesthetized guinea pigs, without changing slow effects. In the present study, we show that electrically evoked fast and slow effects in the anesthetized guinea pig are both blocked by either intramuscular or intracochlear gentamicin, with similar time courses and/or dose-response curves. We suggest that sound-evoked slow effects in unanesthetized animals are fundamentally different from electrically evoked slow effects in anesthetized animals, and that the former may arise from effects of the lateral OC system.

scholarly journals Preventing presbycusis in mice with enhanced medial olivocochlear feedback

2020 ◽  
Vol 117 (21) ◽  
pp. 11811-11819 ◽  
Author(s):  
Luis E. Boero ◽  
Valeria C. Castagna ◽  
Gonzalo Terreros ◽  
Marcelo J. Moglie ◽  
Sebastián Silva ◽  
...  
Keyword(s):  
Hearing Loss ◽  
Hair Cells ◽  
Outer Hair Cells ◽  
Auditory Brainstem Responses ◽  
Cochlear Function ◽  
Gain Of Function ◽  
Distortion Product ◽  
Age Related ◽  
Medial Olivocochlear ◽  
Age Related Hearing Loss

“Growing old” is the most common cause of hearing loss. Age-related hearing loss (ARHL) (presbycusis) first affects the ability to understand speech in background noise, even when auditory thresholds in quiet are normal. It has been suggested that cochlear denervation (“synaptopathy”) is an early contributor to age-related auditory decline. In the present work, we characterized age-related cochlear synaptic degeneration and hair cell loss in mice with enhanced α9α10 cholinergic nicotinic receptors gating kinetics (“gain of function” nAChRs). These mediate inhibitory olivocochlear feedback through the activation of associated calcium-gated potassium channels. Cochlear function was assessed via distortion product otoacoustic emissions and auditory brainstem responses. Cochlear structure was characterized in immunolabeled organ of Corti whole mounts using confocal microscopy to quantify hair cells, auditory neurons, presynaptic ribbons, and postsynaptic glutamate receptors. Aged wild-type mice had elevated acoustic thresholds and synaptic loss. Afferent synapses were lost from inner hair cells throughout the aged cochlea, together with some loss of outer hair cells. In contrast, cochlear structure and function were preserved in aged mice with gain-of-function nAChRs that provide enhanced olivocochlear inhibition, suggesting that efferent feedback is important for long-term maintenance of inner ear function. Our work provides evidence that olivocochlear-mediated resistance to presbycusis-ARHL occurs via the α9α10 nAChR complexes on outer hair cells. Thus, enhancement of the medial olivocochlear system could be a viable strategy to prevent age-related hearing loss.

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