Animal Model Of Hearing Loss Research Articles

Clinical relevance of the cat as a model of hearing loss

Reliable, clinically relevant, animal models of hearing loss are vital to both increase our understanding of changes that occur during hearing loss and to test the safety and efficacy of interventions designed to treat hearing loss. This presentation will outline the variety of deafening techniques than can be used in the cat to induce either profound or partial hearing loss over a range of ages (from neonatal to adult). We will also discuss the range of behavioral measures, long-term and acute electrophysiological measures (including DPOAEs, CAPs, ABRs), and histological techniques (including whole cochlea imaging) that are available when using the cat as a model that make it an invaluable resource for the hearing field.

A multi-channel EEG mini-cap can improve reliability for recording auditory brainstem responses in chinchillas

Background:Disabling hearing loss affects nearly 466 million people worldwide (World Health Organization). The auditory brainstem response (ABR) is the most common non-invasive clinical measure of evoked potentials, e.g., as an objective measure for universal newborn hearing screening. In research, the ABR is widely used for estimating hearing thresholds and cochlear synaptopathy in animal models of hearing loss. The ABR contains multiple waves representing neural activity across different peripheral auditory pathway stages, which arise within the first 10 ms after stimulus onset. Multi-channel (e.g., 32 or higher) caps provide robust measures for a wide variety of EEG applications for the study of human hearing. However, translational studies using preclinical animal models typically rely on only a few subdermal electrodes. New Method:We evaluated the feasibility of a 32-channel rodent EEG mini-cap for improving the reliability of ABR measures in chinchillas, a common model of human hearing. Results:After confirming initial feasibility, a systematic experimental design tested five potential sources of variability inherent to the mini-cap methodology. We found each source of variance minimally affected mini-cap ABR waveform morphology, thresholds, and wave-1 amplitudes. Comparison with Existing Method:The mini-cap methodology was statistically more robust and less variable than the conventional subdermal-needle methodology, most notably when analyzing ABR thresholds. Additionally, fewer repetitions were required to produce a robust ABR response when using the mini-cap. Conclusions:These results suggest the EEG mini-cap can improve translational studies of peripheral auditory evoked responses. Future work will evaluate the potential of the mini-cap to improve the reliability of more centrally evoked (e.g., cortical) EEG responses.

The impact of targeted ablation of one row of outer hair cells and Deiters' cells on cochlear amplification.

The mammalian cochlea contains three rows of outer hair cells (OHCs) that amplify the basilar membrane traveling wave with high gain and exquisite tuning. The pattern of OHC loss caused by typical methods of producing hearing loss in animal models (noise, ototoxic exposure, or aging) is variable and not consistent along the length of the cochlea. Thus, it is difficult to use these approaches to understand how forces from multiple OHCs summate to create normal cochlear amplification. Here, we selectively removed the third row of OHCs and Deiters' cells in adult mice and measured cochlear amplification. In the mature cochlear epithelia, expression of the Wnt target gene Lgr5 is restricted to the third row of Deiters' cells, the supporting cells directly underneath the OHCs. Diphtheria toxin administration to Lgr5DTR-EGFP/+ mice selectively ablated the third row of Deiters' cells and the third row of OHCs. Basilar membrane vibration in vivo demonstrated disproportionately lower reduction in cochlear amplification by about 13.5 dB. On a linear scale, this means that the 33% reduction in OHC number led to a 79% reduction in gain. Thus, these experimental data describe the impact of reducing the force of cochlear amplification by a specific amount. Furthermore, these data argue that because OHC forces progressively and sequentially amplify the traveling wave as it travels to its peak, the loss of even a relatively small number of OHCs, when evenly distributed longitudinally, will cause a substantial reduction in cochlear amplification.NEW & NOTEWORTHY Normal cochlear physiology involves force production from three rows of outer hair cells to amplify and tune the traveling wave. Here, we used a genetic approach to target and ablate the third row of outer hair cells in the mouse cochlea and found it reduced cochlear amplification by 79%. This means that the loss of even a relatively small number of OHCs, when evenly distributed, causes a substantial reduction in cochlear amplification.

Current Advances in Adeno-Associated Virus-Mediated Gene Therapy to Prevent Acquired Hearing Loss.

Adeno-associated viruses (AAVs) are viral vectors that offer an excellent platform for gene therapy due to their safety profile, persistent gene expression in non-dividing cells, target cell specificity, lack of pathogenicity, and low immunogenicity. Recently, gene therapy for genetic hearing loss with AAV transduction has shown promise in animal models. However, AAV transduction for gene silencing or expression to prevent or manage acquired hearing loss is limited. This review provides an overview of AAV as a leading gene delivery vector for treating genetic hearing loss in animal models. We highlight the advantages and shortcomings of AAV for investigating the mechanisms and preventing acquired hearing loss. We predict that AAV-mediated gene manipulation will be able to prevent acquired hearing loss.

The Genomics of Auditory Function and Disease.

Current estimates suggest that nearly half a billion people worldwide are affected by hearing loss. Because of the major psychological, social, economic, and health ramifications, considerable efforts have been invested in identifying the genes and molecular pathways involved in hearing loss, whether genetic or environmental, to promote prevention, improve rehabilitation, and develop therapeutics. Genomic sequencing technologies have led to the discovery of genes associated with hearing loss. Studies of the transcriptome and epigenome of the inner ear have characterized key regulators and pathways involved in the development of the inner ear and have paved the way for their use in regenerative medicine. In parallel, the immense preclinical success of using viral vectors for gene delivery in animal models of hearing loss has motivated the industry to work on translating such approaches into the clinic. Here, we review the recent advances in the genomics of auditory function and dysfunction, from patient diagnostics to epigenetics and gene therapy.

Effect of N-acetyl-cysteine treatment on sensorineural hearing loss: a meta-analysis.

N‐acetyl‐cysteine (NAC) is an efficacious treatment for sensorineural hearing loss in animal models, such as noise‐induced hearing loss (NIHL), however previous research into the effect of NAC on patients with hearing loss produced contradictory results. In this study, we investigated the effect of NAC treatment on sensorineural hearing loss. PubMed, Web of Science and Embase databases were searched in their entirety using the key words: hearing loss, NAC, N‐acetylcysteine, and sensorineural hearing loss. Studies which included assessment of hearing loss with pure‐tone threshold (PTA) data were selected. Eligible studies regarding the effects of NAC treatment on patients with hearing loss were collected by two independent reviewers. A total of 1197 individuals were included from seven published studies. Two studies reported data for a sudden idiopathic sensorineural hearing loss (SISNHL) group. Three studies reported data for a NIHL group. Other studies reported data for drug‐induced hearing loss. The meta‐analysis demonstrated that the overall effect of NAC treatment on sensorineural hearing loss was invalid. However, NAC treatment was linked with improved patient outcomes of hearing tests in cases of sudden hearing loss, but did not prevent hearing loss induced by noise or ototoxicity. However, there is a need for better‐designed studies with larger samples to further prove the correlation between the effect of NAC and hearing loss.

Biallelic ATOH1 Gene Variant in Siblings With Pontocerebellar Hypoplasia, Developmental Delay, and Hearing Loss.

Background and ObjectivesTo report on the novel association of biallelic variant in atonal basic helix-loop-helix transcription factor 1 (ATOH1) gene and pontocerebellar hypoplasia (PCH), severe global developmental delay, intellectual disability, and hearing loss in a family with 2 affected siblings.MethodsA detailed clinical assessment and exome sequencing of peripheral blood sample were performed. Segregation analysis with Sanger sequencing and structural modeling of the variant was performed to support the pathogenicity of the variant.ResultsA homozygous missense variant (NM_005172.1:c.481C>G) in the ATOH1 gene was identified in the proband and his affected sister. The segregation analysis subsequently confirmed its segregation with an apparently recessive PCH in this family. ATOH1 encodes for the atonal basic helix-loop-helix (bHLH) transcription factor 1, a core transcription factor in the developing cerebellum, brainstem, and dorsal spinal cord, and in the ear. The identified variant results in the p.(Arg161Gly) amino acid substitution in the evolutionarily conserved DNA-binding bHLH domain of the ATOH1 protein. Biallelic missense variants in this domain were previously reported to result in disordered cerebellar development and hearing loss in animal models. In silico homology modeling revealed that p.Arg161Gly in ATOH1 protein probably disrupts a salt bridge with DNA backbone phosphate and increases the flexibility of the bHLH helix–both of which together affect the binding capability of the bHLH domain to the DNA.DiscussionBased on the sequencing results and evidence from structural modeling of the identified variant, as well as with previous reports of ATOH1 gene disruption, we conclude that ATOH1 may represent a novel candidate gene associated with the phenotype of PCH, global developmental delay, and hearing loss in humans.

Genetic insights, disease mechanisms, and biological therapeutics for Waardenburg syndrome.

Waardenburg syndrome (WS), also known as auditory-pigmentary syndrome, is the most common cause of syndromic hearing loss (HL), which accounts for approximately 2-5% of all patients with congenital hearing loss. WS is classified into four subtypes depending on the clinical phenotypes. Currently, pathogenic mutations of PAX3, MITF, SOX10, EDN3, EDNRB or SNAI2 are associated with different subtypes of WS. Although supportive techniques like hearing aids, cochlear implants, or other assistive listening devices can alleviate the HL symptom, there is no cure for WS to date. Recently major progress has been achieved in preclinical studies of genetic HL in animal models, including gene delivery and stem cell replacement therapies. This review focuses on the current understandings of pathogenic mechanisms and potential biological therapeutic approaches for HL in WS, providing strategies and directions for implementing WS biological therapies, as well as possible problems to be faced, in the future.

Advances in Inner Ear Therapeutics for Hearing Loss in Children.

Hearing loss is a common congenital sensory disorder with various underlying causes. Here, we review and focus on genetic, infectious, and ototoxic causes and recent advances in inner ear therapeutics. While hearing aids and cochlear implantation are the mainstay of treatment for pediatric hearing loss, novel biological therapeutics are being explored. Recent preclinical studies report positive results in viral-mediated gene transfer techniques and surgical approaches to the inner ear for genetic hearing loss. Novel pharmacologic agents, on the other hand, show promising results in reducing aminoglycoside and cisplatin ototoxicity. Clinical trials are underway to evaluate the efficacy of antivirals for cytomegalovirus-related hearing loss, and its pathogenesis and other potential therapeutics are currently under investigation. Individualized therapies for genetic and infectious causes of sensorineural hearing loss in animal models as well as pediatric patients show promising results, with their potential efficacy being active areas of research.

ATP depletion induced cochlear hair cells death through histone deacetylation in vitro

Previous studies have shown histone modifications being present in cochlear hair cells in animal models of hearing loss. Our past studies have shown that ATP depletion, histone deacetylase (HDAC) upregulation, and histone deacetylation occur in cochlea after noise exposure, and these are linked to hair cell death. Whether ATP depletion correlates with the expression level of HDACs and acetylation of histones is still unknown. In this study, we investigated the changes in the expression of HDACs and the level of histone acetylation in cochlear hair cells using an ATP-depleted explant culture of mouse organ of Corti. We found that the expression of HDAC3 and HDAC6 increased and hair cells were lost after oligomycin A (OA) treatment. Meanwhile, the acetylation level of histone H2B reduced. However, when oligomycin was combined with an HDAC inhibitor, trichostatin A (TSA), the acetylation level of histone H3 was restored. Moreover, combined treatment of oligomycin and TSA or sodium butyrate (NaB) attenuated oligomycin-induced cochlear hair cell loss. In conclusion, our results indicated that ATP depletion led to histone deacetylation and eventually resulted in hair cell death.

Auditory and non-auditory effects of asymmetrical hearing loss in animal models

Animal models offer an opportunity to investigate the consequences of asymmetrical hearing loss with a level of control over extraneous variables that is not possible with human listeners. Experimental manipulations to induce unilateral conductive or sensorineural hearing loss in animal models have demonstrated substantial and diverse changes in physiological function, anatomical reorganization of neural projections, and adverse effects on auditory behaviors. Our experiments in rodents exposed to acoustic trauma with one ear plugged result in asymmetrical hearing loss and abnormal auditory brainstem response waveforms that occur when either the unprotected or protected ear is stimulated. Susceptibility to auditory brainstem response deficits appears to differ between the right and left sides. Asymmetrical hearing loss is associated with increased startle reactivity to loud sounds, suggesting abnormal loudness perception or an increased emotional response to sound. These animals also show abnormal social interaction, and some subjects show reduced exploratory behavior in a novel environment indicative of heightened anxiety. These studies provide a framework for investigating the interplay between the auditory and non-auditory behavioral consequences of hearing loss, as well as the underlying neuropathology.Animal models offer an opportunity to investigate the consequences of asymmetrical hearing loss with a level of control over extraneous variables that is not possible with human listeners. Experimental manipulations to induce unilateral conductive or sensorineural hearing loss in animal models have demonstrated substantial and diverse changes in physiological function, anatomical reorganization of neural projections, and adverse effects on auditory behaviors. Our experiments in rodents exposed to acoustic trauma with one ear plugged result in asymmetrical hearing loss and abnormal auditory brainstem response waveforms that occur when either the unprotected or protected ear is stimulated. Susceptibility to auditory brainstem response deficits appears to differ between the right and left sides. Asymmetrical hearing loss is associated with increased startle reactivity to loud sounds, suggesting abnormal loudness perception or an increased emotional response to sound. These animals also show abnormal social i...

High-Resolution fMRI of Auditory Cortical Map Changes in Unilateral Hearing Loss and Tinnitus.

Animal models of hearing loss and tinnitus observe pathological neural activity in the tonotopic frequency maps of the primary auditory cortex. Here, we applied ultra high-field fMRI at 7T to test whether human patients with unilateral hearing loss and tinnitus also show altered functional activity in the primary auditory cortex. The high spatial resolution afforded by 7T imaging allowed tonotopic mapping of primary auditory cortex on an individual subject basis. Eleven patients with unilateral hearing loss and tinnitus were compared to normal-hearing controls. Patients showed an over-representation and hyperactivity in a region of the cortical map corresponding to low frequencies sounds, irrespective of the hearing loss and tinnitus range, which in most cases affected higher frequencies. This finding of hyperactivity in low frequency map regions, irrespective of hearing loss range, is consistent with some previous studies in animal models and corroborates a previous study of human tinnitus. Thus these findings contribute to accumulating evidence that gross cortical tonotopic map reorganization is not a causal factor of tinnitus.

Prepulse inhibition of the acoustic startle reflex vs. auditory brainstem response for hearing assessment

The high prevalence of noise-induced and age-related hearing loss in the general population has warranted the use of animal models to study the etiology of these pathologies. Quick and accurate auditory threshold determination is a prerequisite for experimental manipulations targeting hearing loss in animal models. The standard auditory brainstem response (ABR) measurement is fairly quick and translational across species, but is limited by the need for anesthesia and a lack of perceptual assessment. The goal of this study was to develop a new method of hearing assessment utilizing prepulse inhibition (PPI) of the acoustic startle reflex, a commonly used tool that measures detection thresholds in awake animals, and can be performed on multiple animals simultaneously. We found that in control mice PPI audiometric functions are similar to both ABR and traditional operant conditioning audiograms. The hearing thresholds assessed with PPI audiometry in sound exposed mice were also similar to those detected by ABR thresholds one day after exposure. However, three months after exposure PPI threshold shifts were still evident at and near the frequency of exposure whereas ABR thresholds recovered to the pre-exposed level. In contrast, PPI audiometry and ABR wave one amplitudes detected similar losses. PPI audiometry provides a high throughput automated behavioral screening tool of hearing in awake animals. Overall, PPI audiometry and ABR assessments of the auditory system are robust techniques with distinct advantages and limitations, which when combined, can provide ample information about the functionality of the auditory system.

NOX3-TARGETED THERAPIES FOR INNER EAR PATHOLOGIES.

Inner ear pathologies are associated with major morbidity and loss of life quality in affected patients. In many of these conditions, production of reactive oxygen-species (ROS) is thought to be a key pathological mechanism. While the sources of ROS are complex (including for example mitochondria), there is increasing evidence that activation of NOX enzymes, in particular NOX3, plays a key role. NOX3 is a multi-subunit NADPH oxidase, functionally and structurally closely related to NOX1 and NOX2. In both the vestibular and the cochlear compartments of the inner ear, high levels of NOX3 mRNA are expressed. In NOX3 mutant mice, the vestibular function is perturbed due to a lack of otoconia, while only minor alterations of hearing have been documented. However, there is increasing evidence that activation of NOX3 through drugs, noise and probably also aging, leads to hearing loss. Thus, NOX3 is an interesting target to treat and prevent inner ear pathologies and a few first animal models based on drug - or molecular therapy have been reported. So far however, there are no specific NOX3 inhibitors with a documented penetration into the inner ear. Nevertheless, certain antioxidants and non-specific NOX inhibitors diminish hearing loss in animal models. Development of small molecules inhibitors or molecular strategies against NOX3 could improve specificity and efficiency of redox-targeted treatments. In this review, we will discuss arguments for the involvement of NOX3 in inner ear pathologies and therapeutic approaches to target NOX3 activity.

Gene therapy for sensorineural hearing loss.

Gene therapy is a promising treatment modality that is being explored for several inherited disorders. Multiple human gene therapy clinical trials are currently ongoing, but few are directed at hearing loss. Hearing loss is one of the most prevalent sensory disabilities in the world, and genetics play an important role in the pathophysiology of hearing loss. Gene therapy offers the possibility of restoring hearing by overcoming the functional deficits created by the underlying genetic mutations. In addition, gene therapy could potentially be used to induce hair cell regeneration by delivering genes that are critical to hair cell differentiation into the cochlea. In this review, we examine the promises and challenges of applying gene therapy to the cochlea. We also summarize recent studies that have applied gene therapy to animal models of hearing loss.

Effects of chronic furosemide on central neural hyperactivity and cochlear thresholds after cochlear trauma in Guinea pig.

Increased neuronal spontaneous firing rates have been observed throughout the central auditory system after trauma to the cochlea and this hyperactivity is believed to be associated with the phantom perception of tinnitus. Previously, we have shown in an animal model of hearing loss, that an acute injection with furosemide can significantly decrease hyperactivity after cochlear trauma and eliminate behavioral evidence of tinnitus of early onset. However, furosemide also has the potential to affect cochlear thresholds. In this paper, we measured the effects of a chronic (daily injections for 7 days) furosemide treatment on the spontaneous firing rate of inferior colliculus neurons and on cochlear thresholds in order to establish whether a beneficial effect on hyperactivity can be obtained without causing additional hearing loss. Guinea pigs were exposed to a 10–kHz, 124 dB, 2 h acoustic trauma, and after 5 days of recovery, were given daily i.p. injections of 80 mg/kg furosemide or an equivalent amount of saline. The activity of single IC neurons was recorded 24 h following the last injection. The furosemide treatment had no effect on cochlear thresholds compared to saline injections but did result in significant reductions in spontaneous firing rates recorded in inferior colliculus. These results that suggest a long-term beneficial effect of furosemide on hyperactivity after cochlear trauma may be achievable without detrimental effects on hearing, which is important when considering therapeutic potential.

Effect of low-level laser treatment on cochlea hair-cell recovery after ototoxic hearing loss

The primary cause of hearing loss includes damage to cochlear hair cells. Low-level laser therapy (LLLT) has become a popular treatment for damaged nervous systems. Based on the idea that cochlea hair cells and neural cells are from same developmental origin, the effect of LLLT on hearing loss in animal models is evaluated. Hearing loss animal models were established, and the animals were irradiated by 830-nm diode laser once a day for 10 days. Power density of the laser treatment was 900 mW/cm(2), and the fluence was 162 to 194 J. The tympanic membrane was evaluated after LLLT. Thresholds of auditory brainstem responses were evaluated before treatment, after gentamicin, and after 10 days of LLLT. Quantitative scanning electron microscopic (SEM) observations were done by counting remaining hair cells. Tympanic membranes were intact at the end of the experiment. No adverse tissue reaction was found. On SEM images, LLLT significantly increased the number of hair cells in middle and basal turns. Hearing was significantly improved by laser irradiation. After LLLT treatment, both the hearing threshold and hair-cell count significantly improved.

Effects of inner hair cell damage on temporal coding

It is widely believed that the neural patterns of temporal coding within the auditory periphery and CNS change following cochlear hearing loss, and a number of recent studies have aimed to more fully understand and characterize these changes. In these studies, noise exposure has been a common method for inducing hearing loss in animal models. Unfortunately, its effects are nonspecific, affecting both inner and outer hair cells as well as the surrounding tissues. Because of this mixed hair-cell damage, it has been difficult to tease apart the specific effects that each of these pathologies has on temporal coding. In the present study, we used the chemotherapy drug carboplatin to induce inner hair cell (IHC) specific lesions in the cochleae of chinchillas. Using acoustically evoked potentials and acute single fiber recordings from the auditory nerve, in parallel with computational modeling, we have investigated the effects of IHC damage on temporal coding. Preliminary findings in carboplatin exposed chinchillas, which show near-normal ABR thresholds, showed a decrease in ABR amplitudes at high sound levels, as well as a decrease in the strength of both envelope and fine-structure coding in frequency following responses. [Research supported by NIH (NIDCD) R01-DC009838 and T32-DC00030.]

Environmental Cadmium and Lead Exposures and Hearing Loss in U.S. Adults: The National Health and Nutrition Examination Survey, 1999 to 2004

Background: Although cadmium and lead are known risk factors for hearing loss in animal models, few epidemiologic studies have been conducted on their associations with hearing ability in the general population.Objectives: We investigated the associations between blood cadmium and lead exposure and hearing loss in the U.S. general population while controlling for noise and other major risk factors contributing to hearing loss.Methods: We analyzed data from 3,698 U.S. adults 20–69 years of age who had been randomly assigned to the National Health and Nutrition Examination Survey (NHANES) 1999–2004 Audiometry Examination Component. Pure-tone averages (PTA) of hearing thresholds at frequencies of 0.5, 1, 2, and 4 kHz were computed, and hearing loss was defined as a PTA > 25 dB in either ear.Results: The weighted geometric means of blood cadmium and lead were 0.40 [95% confidence interval (CI): 0.39. 0.42] µg/L and 1.54 (95% CI: 1.49, 1.60) µg/dL, respectively. After adjusting for sociodemographic and clinical risk factors and exposure to occupational and nonoccupational noise, the highest (vs. lowest) quintiles of cadmium and lead were associated with 13.8% (95% CI: 4.6%, 23.8%) and 18.6% (95% CI: 7.4%, 31.1%) increases in PTA, respectively (p-trends < 0.05).Conclusions: Our results suggest that low-level exposure to cadmium and lead found in the general U.S. population may be important risk factors for hearing loss. The findings support efforts to reduce environmental cadmium and lead exposures.

A Novel Animal Model of Hearing Loss Caused by Acute Endoplasmic Reticulum Stress in the Cochlea

Many stimuli such as ischemia, hypoxia, heat shock, amino acid starvation, and gene mutation, exhibit a cellular response called endoplasmic reticulum (ER) stress. ER stress induces expression of a series of genes, leading to cell survival or apoptosis. Previously, we found that in an animal model of hearing loss caused by acute mitochondrial dysfunction, several ER stress markers including C/EBP homologous protein were induced in the cochlear lateral wall. To elucidate the mechanism of hearing loss caused by ER stress, we established a novel animal model of hearing loss by perilymphatic perfusion of tunicamycin, an ER stress activator that inhibits N-acetylglucosamine transferases. Subacute and progressive hearing loss was observed at all sound frequencies studied, and stimulation of ER stress marker genes was noted in the cochlea. The outer hair cells were the most sensitive to ER stress in the cochlea. Electron microscopic analysis demonstrated degeneration of the subcellular organelles of the inner hair cells and nerve endings of the spiral ganglion cells. This newly established animal model of hearing loss from ER stress will provide additional insight into the mechanism of sensorineural hearing loss.