mGluR1 enhances efferent inhibition of inner hair cells in the developing rat cochlea.

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mGluR1 enhances efferent inhibition of inner hair cells in the developing rat cochlea.

J Physiol. 2017 Feb 17;:

Authors: Ye Z, Goutman JD, Pyott SJ, Glowatzki E

Abstract
Just before the onset of hearing, the inner hair cells (IHCs) receive inhibitory efferent input from cholinergic medial olivocochlear (MOC) neurons originating in the brainstem. This input may serve a role in the maturation of the ascending (afferent) auditory system by inhibiting spontaneous activity of the IHCs. To investigate the molecular mechanisms regulating these IHC efferent synapses, we combined electrical stimulation of the efferent fibres with patch clamp recordings from the IHCs to measure efferent synaptic strength. By examining evoked responses, we show that activation of mGluRs by general and group I specific mGluR agonists enhances IHC efferent inhibition. This enhancement is blocked by application of a group I mGluR1-specific antagonist, indicating that enhancement of IHC efferent inhibition is mediated by group I mGluRs and specifically by mGluR1s. By comparing spontaneous and evoked responses, we show that group I mGluR agonists act presynaptically to increase neurotransmitter release without affecting postsynaptic responsiveness. Moreover, endogenous glutamate released from the IHCs also enhances IHC efferent inhibition via the activation of group I mGluRs. Finally, immunofluorescent analysis indicates that the efferent terminals are sufficiently close to IHC glutamate release sites to allow activation of mGluRs on the efferent terminals by glutamate spillover. Together, these results suggest that glutamate released from the IHCs activates group I mGluRs (mGluR1s), likely present on the efferent terminals, which, in turn, enhances release of acetylcholine and inhibition of the IHCs. Thus, mGluRs establish a local negative feedback loop positioned to regulate IHC activity and maturation of the ascending auditory system in the developing cochlea. This article is protected by copyright. All rights reserved.

PMID: 28211069 [PubMed - as supplied by publisher]

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mGluR1 enhances efferent inhibition of inner hair cells in the developing rat cochlea.

Related Articles

mGluR1 enhances efferent inhibition of inner hair cells in the developing rat cochlea.

J Physiol. 2017 Feb 17;:

Authors: Ye Z, Goutman JD, Pyott SJ, Glowatzki E

Abstract
Just before the onset of hearing, the inner hair cells (IHCs) receive inhibitory efferent input from cholinergic medial olivocochlear (MOC) neurons originating in the brainstem. This input may serve a role in the maturation of the ascending (afferent) auditory system by inhibiting spontaneous activity of the IHCs. To investigate the molecular mechanisms regulating these IHC efferent synapses, we combined electrical stimulation of the efferent fibres with patch clamp recordings from the IHCs to measure efferent synaptic strength. By examining evoked responses, we show that activation of mGluRs by general and group I specific mGluR agonists enhances IHC efferent inhibition. This enhancement is blocked by application of a group I mGluR1-specific antagonist, indicating that enhancement of IHC efferent inhibition is mediated by group I mGluRs and specifically by mGluR1s. By comparing spontaneous and evoked responses, we show that group I mGluR agonists act presynaptically to increase neurotransmitter release without affecting postsynaptic responsiveness. Moreover, endogenous glutamate released from the IHCs also enhances IHC efferent inhibition via the activation of group I mGluRs. Finally, immunofluorescent analysis indicates that the efferent terminals are sufficiently close to IHC glutamate release sites to allow activation of mGluRs on the efferent terminals by glutamate spillover. Together, these results suggest that glutamate released from the IHCs activates group I mGluRs (mGluR1s), likely present on the efferent terminals, which, in turn, enhances release of acetylcholine and inhibition of the IHCs. Thus, mGluRs establish a local negative feedback loop positioned to regulate IHC activity and maturation of the ascending auditory system in the developing cochlea. This article is protected by copyright. All rights reserved.

PMID: 28211069 [PubMed - as supplied by publisher]

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Is Newborn Hearing Screening Worthwhile in India?: Authors Reply.

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Is Newborn Hearing Screening Worthwhile in India?: Authors Reply.

Indian Pediatr. 2016 May 08;53(5):442

Authors: Paul AK

PMID: 27254070 [PubMed - indexed for MEDLINE]

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[Diagnosis of Cochleovestibular Neurovascular Compression Syndrome:A Scoring System Based on Five Clinical Characteristics].

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[Diagnosis of Cochleovestibular Neurovascular Compression Syndrome:A Scoring System Based on Five Clinical Characteristics].

No Shinkei Geka. 2017 Feb;45(2):117-125

Authors: Okamura T, Nishizaki T, Ikeda N, Nakano S, Sakakura T, Fujii N, Okuda T

Abstract
The optimal method for diagnosing cochleovestibular neurovascular compression syndrome(CNVC)remains controversial, and the aim of this study is to develop a standard diagnostic instrument for the condition. The clinical features of 53 sides of 50 patients with a combination of vertigo, tinnitus, and/or hearing loss were retrospectively evaluated. The following five clinical features were evaluated and given a score of 1 or 0:1)a long history of recurrent vertigo, tinnitus, or hearing loss;2)neurological findings related to positional vertigo, nystagmus, tinnitus, or hearing loss;3)neuro-otological findings involving tinnitus, audiometry, or vestibular testing;4)auditory brainstem response(ABR)evaluation with the detection of a low 25-75% II wave amplitude on the contralateral side and delayed interpeak latency in the I-III or I-V waves(usually low II wave amplitude combined with double peaks and a wide-based form)during ABR evaluation using 80 and 90dB clicks;and 5)the detection of vascular contact with the eighth cranial nerve on magnetic resonance imaging-constructive interference in steady state or air computed tomography imaging. Finally, the sum of these scores was evaluated. For cases in which more than one of the features of the items 1), 2), or 3) were present, the score was evaluated based on the most representative of the items.
RESULTS: The patients were divided into those with scores of 4-5 and those with scores of 2-3. All the patients with scores of 4-5 exhibited CNVC, while those with scores of 2-3 had other diseases. Therefore, CNVC should be suspected in patients with scores of 4-5, but can be ruled out in those with scores of 2-3.

PMID: 28202828 [PubMed - in process]

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Population responses in primary auditory cortex simultaneously represent the temporal envelope and periodicity features in natural speech

Publication date: Available online 17 February 2017
Source:Hearing Research
Author(s): Daniel A. Abrams, Trent Nicol, Travis White-Schwoch, Mitra Hartmann, Steven Zecker, Nina Kraus
Speech perception relies on a listener’s ability to simultaneously resolve multiple temporal features in the speech signal. Little is known regarding neural mechanisms that enable the simultaneous coding of concurrent temporal features in the speech signal. Here we show that two categories of temporal features in speech, the low-frequency speech envelope and periodicity cues, are processed by distinct neural mechanisms within the same population of cortical neurons. We measured population activity in primary auditory cortex of anesthetized guinea pig in response to three variants of a naturally produced speech sentence. Results show that the envelope of population responses closely tracks the speech envelope, and this cortical activity more closely reflects wider bandwidths of the speech envelope compared to narrow bands. Additionally, neuronal populations represent the fundamental frequency of speech robustly with phase-locked responses. Importantly, these two temporal features of speech are simultaneously observed within neuronal ensembles in auditory cortex in response to clear, conversation, and compressed speech exemplars. Results show that auditory cortex is adept at simultaneously resolving multiple temporal features in extended speech sentences using discrete coding mechanisms.



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Pitch Ranking with Different Virtual Channel Configurations in Electrical Hearing

Publication date: Available online 17 February 2017
Source:Hearing Research
Author(s): Monica Padilla, Natalia Stupak, David M. Landsberger
Monopolar Virtual Channels (MPVCs) use current steering to increase the number of spectral channels provided to cochlear implant users beyond the physical number of electrodes. The current spread created with a current steered channel is similar to the spread found for monopolar stimulation, and this spread may be one of the bottlenecks for improved performance with an increased number of channels. Quadrupolar Virtual Channels (QPVCs) use current focusing in combination with steering in an attempt to increase the number of channels while reducing channel interaction. However, due to the potentially asymmetric current field generated by QPVCs, there may be distortions in the place pitch representation using this mode. A Virtual Tripole (VTP) is introduced as a current focused virtual channel with a relatively symmetrical electric field distribution. In this study, we looked at pitch ranking in cochlear implant users with QPVC, VTP, and MPVC configurations to determine if place pitch shifts similarly across the cochlea or if any of the stimulation modes shift non-monotonically. Results suggest that MPVC and VTP stimulation provide a consistent monotonic shift across cochlear positions while the place shift provided by QPVCs was more variable. The use of VTP stimulation would be recommended instead of QPVC for a speech processing strategy.



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The pattern and degree of capsular fibrous sheaths surrounding cochlear electrode arrays

Publication date: Available online 17 February 2017
Source:Hearing Research
Author(s): Reuven Ishai, Barbara S. Herrmann, Joseph B. Nadol, Alicia M. Quesnel
An inflammatory tissue reaction around the electrode array of a cochlear implant (CI) is common, in particular at the electrode insertion region (cochleostomy) where mechanical trauma often occurs. However, the factors determining the amount and causes of fibrous reaction surrounding the stimulating electrode, especially medially near the perimodiolar location, are unclear. Temporal bone (TB) specimens from patients who had undergone cochlear implantation during life with either Advanced Bionics (AB) Clarion ^TM or HiRes90K^TM (Sylmar, CA, USA) devices that have a half-band and a pre-curved electrode, or Cochlear ^TM Nucleus (Sydney, Australia) device that have a full-band and a straight electrode were evaluated. The thickness of the fibrous tissue surrounding the electrode array of both types of CI devices at both the lower (LB) and upper (UB) basal turns of the cochlea was quantified at three locations: the medial, inferior, and superior aspects of the sheath. Fracture of the osseous spiral lamina and/or marked displacement of the basilar membrane were interpreted as evidence of intracochlear trauma. In addition, post-operative word recognition scores, duration of implantation, and post-operative programming data were evaluated.Seven TBs from six patients implanted with AB devices and five TBs from five patients implanted with Nucleus devices were included. A fibrous capsule around the stimulating electrode array was present in all twelve specimens. TBs implanted with AB device had a significantly thicker fibrous capsule at the medial aspect than at the inferior or superior aspects at both locations (LB and UB) of the cochlea (Wilcoxon signed-ranks test, p<0.01). TBs implanted with a Nucleus device had no difference in the thickness of the fibrous capsule surrounding the track of the electrode array (Wilcoxon signed-ranks test, p>0.05). Nine of fourteen (64%) basal turns of the cochlea (LB and UB of seven TBs) implanted with AB devices demonstrated intracochlear trauma compared to two of ten (20%) basal turns of the cochlea (LB and UB of five TBs) with Nucleus devices, (Fisher exact test, p<0.05). There was no significant correlation between the thickness of the fibrous tissue and the duration of implantation or the word recognition scores (Spearman rho, p=0.06, p=0.4 respectively). Our outcomes demonstrated the development of a robust fibrous tissue sheath medially closest to the site of electric stimulation in cases implanted with the AB device electrode, but not in cases implanted with the Nucleus device. The cause of the asymmetric fibrous sheath may be multifactorial including insertional trauma, a foreign body response, and/or asymmetric current flow.



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