ABR/DPOAE publications

Objectives: We report the in vivo biodistribution and ototoxicity of cationic liposomal-ceftriaxone (CFX) delivered via ear drop formulation in adult chinchilla. Methods: CFX was encapsulated in liposomes with size of ∼100 nm and surface charge of +20 mV. 100 μl liposomes or free drug was applied twice daily in both external ear canals of adult chinchillas for either 3 or 10 days. Study groups included free ceftriaxone (CFX, Day 3: n = 4, Day 10: n = 8), liposomal ceftriaxone (CFX-Lipo, Day 3: n = 4, Day 10: n = 8), and a systemic control group (Day 3: n = 4, Day 10: n = 4). Ceftriaxone delivery to the middle ear and systemic circulation was quantified by HPLC assays. Liposome transport was visualized via confocal microscopy. Auditory brainstem response (ABR) tests and cochlear histology were used to assess ototoxicity. Results: Liposomal ceftriaxone (CFX-Lipo) displayed a ∼658-fold increase in drug delivery efficiency in the middle ear relative to the free CFX (8.548 ± 0.4638% vs. 0.013 ± 0.0009%, %Injected dose, Mean ± SEM). CFX measured in blood serum (48.2 ± 7.78 ng/ml) following CFX-Lipo treatment in ear was 41-fold lower compared to systemic free-CFX treatment (1990.7 ± 617.34 ng/ml). ABR tests and histological analysis indicated no ototoxicity due to the treatment. Conclusion: Cationic liposomal encapsulation results in potent drug delivery across the tympanic membrane to the middle ear with minimal systemic exposure and no ototoxicity.

Adeno-associated viral (AAV) vectors are increasingly used as vehicles for gene delivery to treat hearing loss. However, lack of specificity of the transgene expression may lead to overexpression of the transgene in nontarget tissues. In this study, we evaluated the expression efficiency and specificity of transgene delivered by AAV-PHP.eB under the inner ear sensory cell-specific Myo15 promoter. Compared with the ubiquitous CAG promoter, the Myo15 promoter initiates efficient expression of the GFP fluorescence reporter in hair cells, while minimizing non-specific expression in other cell types of the inner ear and CNS. Furthermore, using the Myo15 promoter, we constructed an AAV-mediated therapeutic system with the coding sequence of OTOF gene. After inner ear injection, we observed apparent hearing recovery in Otof-/- mice, highly efficient expression of exogenous otoferlin, and significant improvement in the exocytosis function of inner hair cells. Overall, our results indicate that gene therapy mediated by the hair cell-specific Myo15 promoter has potential clinical application for the treatment of autosomal recessive deafness and yet for other hereditary hearing loss related to dysfunction of hair cells.

This study assessed whether the effects of contralateral acoustic stimulation (CAS) are consistent with eliciting the medial olivocochlear (MOC) reflex for measurements sensitive to outer hair cell (otoacoustic emissions, OAEs), auditory-nerve (AN; compound action potential, CAP), and brainstem/cortical (envelope-following response, EFR) function. The effects of CAS were evaluated for simultaneous measurement of OAEs, CAPs, and EFRs in participants with normal hearing. Clicks were presented at 40 or 98 Hz in three ipsilateral noise conditions (no noise, 45 dB SPL, and 55 dB SPL). For the no noise condition, CAS suppressed or enhanced EFR amplitudes for 40- and 98-Hz clicks, respectively, while CAS had no significant effect on CAP amplitudes. A follow-up experiment using slower rates (4.4–22.2 Hz) assessed whether this insignificant CAS effect on CAPs was from ipsilateral MOC stimulation or AN adaptation; however, CAS effects remained insignificant despite favorable signal-to-noise ratios. CAS-related enhancements of EFR and CAP amplitudes in ipsilateral noise were not observed, contrary to the anti-masking effect of the MOC reflex. EFR and OAE suppression from CAS were not significantly correlated. Thus, the effects of CAS on EFRs may not be solely mediated by the MOC reflex and may be partially mediated by higher auditory centers.

Pure-tone audiograms often poorly predict elderly humans’ ability to communicate in everyday complex acoustic scenes. Binaural processing is crucial for discriminating sound sources in such complex acoustic scenes. The compromised perception of communication signals presented above hearing threshold has been linked to both peripheral and central age-related changes in the auditory system. Investigating young and old Mongolian gerbils of both sexes, an established model for human hearing, we demonstrate age-related supra-threshold deficits in binaural hearing using behavioral, electrophysiological, anatomical and imaging methods. Binaural processing ability was measured as the binaural masking level difference (BMLD), an established measure in human psychophysics. We tested gerbils behaviorally with “virtual headphones”, recorded single-unit responses in the auditory midbrain and evaluated gross midbrain and cortical responses using positron-emission tomography (PET) imaging. Furthermore, we obtained additional measures of auditory function based on auditory brainstem responses, auditory-nerve synapse counts, and evidence for central inhibitory processing revealed by PET. BMLD deteriorates already in middle-aged animals having normal audiometric thresholds and is even worse in old animals with hearing loss. The magnitude of auditory brainstem response measures related to auditory-nerve function and binaural processing in the auditory brainstem also deteriorate. Furthermore, central GABAergic inhibition is affected by age. Because the number of synapses in the apical turn of the inner ear was not reduced in middle-aged animals, we conclude that peripheral synaptopathy contributes little to binaural processing deficits. Exploratory analyses suggest increased hearing thresholds, altered binaural processing in the brainstem and changed central GABAergic inhibition as potential contributors. Significance statement Older people often have difficulty communicating in everyday situations involving multiple speakers and other sound sources. Binaural processing facilitates hearing in such complex listening situations. Peripheral damage, such as synapse loss in the inner ear, is thought to be an important factor contributing to these difficulties. However, the role of central processing deficits has received less attention. Here, we investigate age-related binaural processing in Mongolian gerbils using brainstem responses, midbrain single-unit responses, positron emission tomography, and reward-based animal psychophysics. Behavioral deficits in binaural processing precede increases in audiometric threshold, as do changes in central inhibition and physiological binaural processing. Synapse loss in cochlear regions tuned to the stimulus frequency, however, does not change and therefore unlikely contributes to age-related binaural deficits.

There is considerable interest in whether sensory deficiency is associated with the development of Alzheimer's disease (AD). Notably, the relationship between hearing impairment and AD is of high relevance but still poorly understood. In this study, we found early-onset hearing loss in two AD mouse models, 3xTgAD and 3xTgAD/Polβ+/-. The 3xTgAD/Polβ+/- mouse is DNA repair deficient and has more humanized AD features than the 3xTgAD. Both AD mouse models showed increased auditory brainstem response (ABR) thresholds between 16 and 32 kHz at 4 weeks of age, much earlier than any AD cognitive and behavioral changes. The ABR thresholds were significantly higher in 3xTgAD/Polβ+/- mice than in 3xTgAD mice at 16 kHz, and distortion product otoacoustic emission signals were reduced, indicating that DNA damage may be a factor underlying early hearing impairment in AD. Poly ADP-ribosylation and protein expression levels of DNA damage markers increased significantly in the cochlea of the AD mice but not in the adjacent auditory cortex. Phosphoglycerate mutase 2 levels and the number of synaptic ribbons in the presynaptic zones of inner hair cells were decreased in the cochlea of the AD mice. Furthermore, the activity of sirtuin 3 was downregulated in the cochlea of these mice, indicative of impaired mitochondrial function. Taken together, these findings provide new insights into potential mechanisms for hearing dysfunction in AD and suggest that DNA damage in the cochlea might contribute to the development of early hearing loss in AD.

Polystyrene nanoplastics are a novel class of pollutants. They are easily absorbed by living organisms, and their potential toxicity has raised concerns. However, the impact of polystyrene nanoplastics on auditory organs remains unknown. Here, our results showed that polystyrene nanoplastics entered the cochlea of mice, HEI-OC1 cells, and lateral line hair cells of zebrafish, causing cellular injury and increasing apoptosis. Additionally, we found that exposure to polystyrene nanoplastics resulted in a significant elevation in the auditory brainstem response thresholds, a loss of auditory sensory hair cells, stereocilia degeneration and a decrease in expression of Claudin-5 and Occludin proteins at the blood-lymphatic barrier in mice. We also observed a significant decrease in the acoustic alarm response of zebrafish after exposure to polystyrene nanoplastics. Mechanistic analysis revealed that polystyrene nanoplastics induced up-regulation of the Nrf2/HO-1 pathway, increased levels of malondialdehyde, and decreased superoxide dismutase and catalase levels in cochlea and HEI-OC1 cells. Furthermore, we observed that the expression of ferroptosis-related indicators GPX4 and SLC7A11 decreased as well as increased expression of ACLS4 in cochlea and HEI-OC1 cells. This study also revealed that polystyrene nanoplastics exposure led to increased expression of the inflammatory factors TNF-α, IL-1β and COX2 in cochlea and HEI-OC1 cells. Further research found that the cell apoptosis, ferroptosis and inflammatory reactions induced by polystyrene nanoplastics in HEI-OC1 cells was reversed through the pretreatment with N-acetylcysteine, a reactive oxygen species inhibitor. Overall, our study first discovered and systematically revealed the ototoxicity of polystyrene nanoplastics and its underlying mechanism.

The stria vascularis (SV) is a stratified epithelium in the lateral wall of the mammalian cochlea, responsible for both endolymphatic ion homeostasis and generation of the endocochlear potential (EP) critical for normal hearing. The SV has three layers consisting predominantly of basal, intermediate, and marginal cells. Intermediate and marginal cells form an intricate interdigitated network of cell projections making discrimination of the cells challenging. To enable intermediate cell visualization, we engineered by BAC transgenesis, reporter mouse lines expressing ZsGreen fluorescent protein under the control of Kcnj10 promoter and regulatory sequences. Kcnj10 encodes KCNJ10 protein (also known as Kir4.1 or Kir1.2), an ATP-sensitive inwardly-rectifying potassium channel critical to EP generation, highly expressed in SV intermediate cells. In these transgenic mice, ZsGreen fluorescence mimics Kcnj10 endogenous expression in the cochlea and was detected in the intermediate cells of the SV, in the inner phalangeal cells, Hensen’s, Deiters’ and pillar cells, in a subset of spiral ganglion neurons, and in glial cells. We show that expression of the transgene in hemizygous mice does not alter auditory function, nor EP. These transgenic Tg( Kcnj10 -ZsGreen) mice allow live and fixed tissue visualization of ZsGreen-expressing intermediate cells and will facilitate future studies of stria vascularis cell function.

Cochlear implants are among the most successful neural prosthetic devices to date but exhibit poor frequency selectivity and the inability to consistently activate apical (low frequency) spiral ganglion neurons. These issues can limit hearing performance in many cochlear implant patients, especially for understanding speech in noisy environments and in perceiving or appreciating more complex inputs such as music and multiple talkers. For cochlear implants, electrical current must pass through the bony wall of the cochlea, leading to widespread activation of auditory nerve fibers. Cochlear implants also cannot be implanted in some individuals with an obstruction or severe malformations of the cochlea. Alternatively, intraneural stimulation delivered via an auditory nerve implant could provide direct contact with neural fibers and thus reduce unwanted current spread. More confined current during stimulation can increase selectivity of frequency fiber activation. Furthermore, devices such as the Utah Slanted Electrode Array can provide access to the full cross section of the auditory nerve, including low frequency fibers that are difficult to reach using a cochlear implant. However, further scientific and preclinical research of these Utah Slanted Electrode Array devices is limited by the lack of a chronic large animal model for the auditory nerve implant, especially one that leverages an appropriate surgical approach relevant for human translation. This paper presents a newly developed transbullar translabyrinthine surgical approach for implanting the auditory nerve implant into the cat auditory nerve. In our first of a series of studies, we demonstrate a surgical approach in non-recovery experiments that enables implantation of the auditory nerve implant into the auditory nerve, without damaging the device and enabling effective activation of the auditory nerve fibers, as measured by electrode impedances and electrically evoked auditory brainstem responses. These positive results motivate performing future chronic cat studies to assess the long-term stability and function of these auditory nerve implant devices, as well as development of novel stimulation strategies that can be translated to human patients.

In the ear, inner hair cells (IHCs) employ sophisticated glutamatergic ribbon synapses with afferent neurons to transmit auditory information to the brain. The presynaptic machinery responsible for neurotransmitter release in IHC synapses includes proteins such as the multi-C2-domain protein otoferlin and the vesicular glutamate transporter 3 (VGluT3). Yet, much of this likely unique molecular machinery remains to be deciphered. The scarcity of material has so far hampered biochemical studies which require large amounts of purified samples. We developed a subcellular fractionation workflow combined with immunoisolation of VGluT3-containing membrane vesicles, allowing for the enrichment of glutamatergic organelles that are likely dominated by synaptic vesicles (SVs) of IHCs. We have characterized their protein composition in mice before and after hearing onset using mass spectrometry and confocal imaging and provide a fully annotated proteome with hitherto unidentified proteins. Despite the prevalence of IHC marker proteins across IHC maturation, the profiles of trafficking proteins differed markedly before and after hearing onset. Among the proteins enriched after hearing onset were VAMP-7, syntaxin-7, syntaxin-8, syntaxin-12/13, SCAMP1, V-ATPase, SV2, and PKCα. Our study provides an inventory of the machinery associated with synaptic vesicle-mediated trafficking and presynaptic activity at IHC ribbon synapses and serves as a foundation for future functional studies.

Altered expression of peripheral myelin protein 22 (PMP22) results in demyelinating peripheral neuropathy. PMP22 exhibits a highly restricted tissue distribution with marked expression in the myelinating Schwann cells of peripheral nerves. Auditory and vestibular Schwann cells and the afferent neurons also express PMP22, suggesting a unique role in hearing and balancing. Indeed, neuropathic patients diagnosed with PMP22-linked hereditary neuropathies often present with auditory and balance deficits, an understudied clinical complication. To investigate the mechanism by which abnormal expression of PMP22 may cause auditory and vestibular deficits, we studied gene-targeted PMP22 -null mice. PMP22 -null mice exhibit an unsteady gait, have difficulty maintaining balance, and live for only ∼3–5 weeks relative to unaffected littermates. Histological analysis of the inner ear revealed reduced auditory and vestibular afferent nerve myelination and profound Na + channel redistribution without PMP22. Yet, Na + current density was unaltered, in stark contrast to increased K + current density. Atypical postsynaptic densities and a range of neuronal abnormalities in the organ of Corti were also identified. Analyses of auditory brainstem responses (ABRs) and vestibular sensory-evoked potential (VsEP) revealed that PMP22 -null mice had auditory and vestibular hypofunction. These results demonstrate that PMP22 is required for hearing and balance, and the protein is indispensable for the formation and maintenance of myelin in the peripheral arm of the eighth nerve. Our findings indicate that myelin abnormalities and altered signal propagation in the peripheral arm of the auditory nerve are likely causes of auditory deficits in patients with PMP22-linked neuropathies.

In the mammalian cochlea, moderate acoustic overexposure leads to loss of ribbon-type synapse between the inner hair cell (IHC) and its postsynaptic spiral ganglion neuron (SGN), causing a reduced dynamic range of hearing but not a permanent threshold elevation. A prevailing view is that such ribbon loss (known as synaptopathy) selectively impacts the low-spontaneous-rate and high-threshold SGN fibers contacting predominantly the modiolar IHC face. However, the spatial pattern of synaptopathy remains scarcely characterized in the most sensitive mid-cochlear region, where two morphological subtypes of IHC with distinct ribbon size gradients coexist. Here, we used volume electron microscopy to investigate noise exposure-related changes in the mouse IHCs with and without ribbon loss. Our quantifications reveal that IHC subtypes differ in the worst-hit area of synaptopathy. Moreover, we show relative enrichment of mitochondria in the surviving SGN terminals, providing key experimental evidence for the long-proposed role of SGN-terminal mitochondria in synaptic vulnerability.

Background The cochlear sympathetic system plays a key role in auditory function and susceptibility to noise-induced hearing loss (NIHL). The formation of reactive oxygen species (ROS) is a well-documented process in NIHL. In this study, we aimed at investigating the effects of a superior cervical ganglionectomy (SCGx) on NIHL in Sprague-Dawley rats. Methods We explored the effects of unilateral and bilateral Superior Cervical Ganglion (SCG) ablation in the eight-ten weeks old Sprague-Dawley rats of both sexes on NIHL. Auditory function was evaluated by auditory brainstem response (ABR) testing and Distortion product otoacoustic emissions (DPOAEs). Outer hair cells (OHCs) counts and the expression of α 2A -adrenergic receptor (AR) in the rat cochlea using immunofluorescence analysis. Cells culture and treatment, CCK-8 assay, Flow cytometry staining and analysis, and western blotting were to explore the mechanisms of SCG fibers may have a protective role in NIHL. Results We found that neither bilateral nor unilateral SCGx protected the cochlea against noise exposure. In HEI-OC1 cells, H 2 O 2 -induced oxidative damage and cell death were inhibited by the application of norepinephrine (NE). NE may prevent ROS-induced oxidative stress in OHCs and NIHL through the α 2A -AR. Conclusion These results demonstrated that sympathetic innervation mildly affected cochlear susceptibility to acoustic trauma by reducing oxidative damage in OHCs through the α 2A -AR. NE may be a potential therapeutic strategy for NIHL prevention.

Purpose: Frequency selectivity is a fundamental property of the peripheral auditory system; however, the invasiveness of auditory nerve (AN) experiments limits its study in the human ear. Compound action potentials (CAPs) associated with forward masking have been suggested as an alternative to assess cochlear frequency selectivity. Previous methods relied on an empirical comparison of AN and CAP tuning curves in animal models, arguably not taking full advantage of the information contained in forward-masked CAP waveforms. Methods: To improve the estimation of cochlear frequency selectivity based on the CAP, we introduce a convolution model to fit forward-masked CAP waveforms. The model generates masking patterns that, when convolved with a unitary response, can predict the masking of the CAP waveform induced by Gaussian noise maskers. Model parameters, including those characterizing frequency selectivity, are fine-tuned by minimizing waveform prediction errors across numerous masking conditions, yielding robust estimates. Results: The method was applied to click-evoked CAPs at the round window of anesthetized chinchillas using notched-noise maskers with various notch widths and attenuations. The estimated quality factor Q10 as a function of center frequency is shown to closely match the average quality factor obtained from AN fiber tuning curves, without the need for an empirical correction factor. Conclusion: This study establishes a moderately invasive method for estimating cochlear frequency selectivity with potential applicability to other animal species or humans. Beyond the estimation of frequency selectivity, the proposed model proved to be remarkably accurate in fitting forward-masked CAP responses and could be extended to study more complex aspects of cochlear signal processing (e.g., compressive nonlinearities).

The pathogenesis of age‐related hearing loss (ARHL) remains unclear. OPA1 is the sole fusion protein currently known to be situated in the inner mitochondrial membrane, which is pivotal for maintaining normal mitochondrial function. While it has already been demonstrated that mutations in OPA1 may lead to hereditary deafness, its involvement in the occurrence and development of ARHL has not been previously explored. In our study, we constructed D‐gal‐induced senescent HEI‐OC1 cells and the cochlea of C57BL/6J mice with a mutated SUMOylation site of SIRT3 using CRISPR/Cas9 technology. We found enhanced L‐OPA1 processing mediated by activated OMA1, and increased OPA1 acetylation resulting from reductions in SIRT3 levels in senescent HEI‐OC1 cells. Consequently, the fusion function of OPA1 was inhibited, leading to mitochondrial fission and pyroptosis in hair cells, ultimately exacerbating the aging process of hair cells. Our results suggest that the dysregulation of mitochondrial dynamics in cochlear hair cells in aged mice can be ameliorated by activating the SIRT3/OPA1 signaling. This has the potential to alleviate the senescence of cochlear hair cells and reduce hearing loss in mice. Our study highlights the significant roles played by the quantities of long and short chains and the acetylation activity of OPA1 in the occurrence and development of ARHL. This finding offers new perspectives and potential targets for the prevention and treatment of ARHL.

A fundamental property of sensory systems is their ability to detect novel stimuli in the ambient environment. The auditory brain contains neurons that decrease their response to repetitive sounds but increase their firing rate to novel or deviant stimuli; the difference between both responses is known as stimulus-specific adaptation or neuronal mismatch (nMM). Here, we tested the effect of microiontophoretic applications of ACh on the neuronal responses in the auditory cortex (AC) of anesthetized rats during an auditory oddball paradigm, including cascade controls. Results indicate that ACh modulates the nMM, affecting prediction error responses but not repetition suppression, and this effect is manifested predominantly in infragranular cortical layers. The differential effect of ACh on responses to standards, relative to deviants (in terms of averages and variances), was consistent with the representational sharpening that accompanies an increase in the precision of prediction errors. These findings suggest that ACh plays an important role in modulating prediction error signaling in the AC and gating the access of these signals to higher cognitive levels.

The inner ear is the hub where hair cells (HCs) transduce sound, gravity, and head acceleration stimuli to the brain. Hearing and balance rely on mechanosensation, the fastest sensory signals transmitted to the brain. The mechanoelectrical transducer (MET) channel is the entryway for the sound-balance-brain interface, but the channel-complex composition is not entirely known. Here, we report that the mouse utilizes Piezo1 (Pz1) and Piezo2 (Pz2) isoforms as MET-complex components. The Pz channels, expressed in HC stereocilia, and cell lines are co-localized and co-assembled with MET complex partners. Mice expressing non-functional Pz1 and Pz2 at the ROSA26 locus have impaired auditory and vestibular traits that can only be explained if the Pzs are integral to the MET complex. We suggest that Pz subunits constitute part of the MET complex and that interactions with other MET complex components yield functional MET units to generate HC MET currents.

There are no Food and Drug Administration‐approved drugs for treating noise‐induced hearing loss (NIHL), reflecting the absence of clear specific therapeutic targets and effective delivery strategies. Noise trauma is demonstrated results in nicotinamide adenine dinucleotide (NAD+) downregulation and mitochondrial dysfunction in cochlear hair cells (HCs) and spiral ganglion neurons (SGNs) in mice, and NAD+ boosted by nicotinamide (NAM) supplementation maintains cochlear mitochondrial homeostasis and prevents neuroexcitatory toxic injury in vitro and ex vivo, also significantly ameliorated NIHL in vivo. To tackle the limited drug delivery efficiency due to sophisticated anatomical barriers and unique clearance pathway in ear, personalized NAM‐encapsulated porous gelatin methacryloyl (PGMA@NAM) are developed based on anatomy topography of murine temporal bone by micro‐computed tomography and reconstruction of round window (RW) niche, realizing hydrogel in situ implantation completely, NAM sustained‐release and long‐term auditory preservation in mice. This study strongly supports personalized PGMA@NAM as NIHL protection drug with effective inner ear delivery, providing new inspiration for drug‐based treatment of NIHL.

Background Sensorineural hearing loss (SNHL) poses a major threat to both physical and mental health; however, there is still a lack of effective drugs to treat the disease. Recently, novel biological therapies, such as mesenchymal stem cells (MSCs) and their products, namely, exosomes, are showing promising therapeutic potential due to their low immunogenicity, few ethical concerns, and easy accessibility. Nevertheless, the precise mechanisms underlying the therapeutic effects of MSC-derived exosomes remain unclear. Results Exosomes derived from MSCs reduced hearing and hair cell loss caused by neomycin-induced damage in models in vivo and in vitro. In addition, MSC-derived exosomes modulated autophagy in hair cells to exert a protective effect. Mechanistically, exogenously administered exosomes were internalized by hair cells and subsequently upregulated endocytic gene expression and endosome formation, ultimately leading to autophagy activation. This increased autophagic activity promoted cell survival, decreased the mitochondrial oxidative stress level and the apoptosis rate in hair cells, and ameliorated neomycin-induced ototoxicity. Conclusions In summary, our findings reveal the otoprotective capacity of exogenous exosome-mediated autophagy activation in hair cells in an endocytosis-dependent manner, suggesting possibilities for deafness treatment.

Cartwheel interneurons of the dorsal cochlear nucleus (DCN) potently suppress multisensory signals that converge with primary auditory afferent input, and thus regulate auditory processing. Noradrenergic fibers from locus coeruleus project to the DCN, and α2-adrenergic receptors inhibit spontaneous spike activity but simultaneously enhance synaptic strength in cartwheel cells, a dual effect leading to enhanced signal-to-noise for inhibition. However, the ionic mechanism of this striking modulation is unknown. We generated a glycinergic neuron-specific knockout of the Na + leak channel NALCN in mice and found that its presence was required for spontaneous firing in cartwheel cells. Activation of α2-adrenergic receptors inhibited both NALCN and spike generation, and this modulation was absent in the NALCN knockout. Moreover, α2-dependent enhancement of synaptic strength was also absent in the knockout. GABA B receptors mediated inhibition through NALCN as well, acting on the same population of channels as α2 receptors, suggesting close apposition of both receptor subtypes with NALCN. Thus, multiple neuromodulatory systems determine the impact of synaptic inhibition by suppressing the excitatory leak channel, NALCN.

Background Redox imbalance and inflammation have been proposed as the principal mechanisms of damage in the auditory system, resulting in functional alterations and hearing loss. Microglia and astrocytes play a crucial role in mediating oxidative/inflammatory injury in the central nervous system; however, the role of glial cells in the auditory damage is still elusive. Objectives Here we investigated glial-mediated responses to toxic injury in peripheral and central structures of the auditory pathway, i.e., the cochlea and the auditory cortex (ACx), in rats exposed to styrene, a volatile compound with well-known oto/neurotoxic properties. Methods Male adult Wistar rats were treated with styrene (400 mg/kg daily for 3 weeks, 5/days a week). Electrophysiological, morphological, immunofluorescence and molecular analyses were performed in both the cochlea and the ACx to evaluate the mechanisms underlying styrene-induced oto/neurotoxicity in the auditory system. Results We showed that the oto/neurotoxic insult induced by styrene increases oxidative stress in both cochlea and ACx. This was associated with macrophages and glial cell activation, increased expression of inflammatory markers (i.e., pro-inflammatory cytokines and chemokine receptors) and alterations in connexin (Cxs) and pannexin (Panx) expression, likely responsible for dysregulation of the microglia/astrocyte network. Specifically, we found downregulation of Cx26 and Cx30 in the cochlea, and high level of Cx43 and Panx1 in the ACx. Conclusions Collectively, our results provide novel evidence on the role of immune and glial cell activation in the oxidative/inflammatory damage induced by styrene in the auditory system at both peripheral and central levels, also involving alterations of gap junction networks. Our data suggest that targeting glial cells and connexin/pannexin expression might be useful to attenuate oxidative/inflammatory damage in the auditory system.