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Noise-induced hearing loss interacts with age, sex, and listening conditions to affect individuals' perception of ecologically relevant stimuli like speech. The present experiments assessed the impact of age and sex on vocalization detection by noise-exposed mice trained to detect a downsweep or complex ultrasonic vocalization in quiet or in the presence of a noise background. Daily thresholds before and following intense noise exposure were collected longitudinally and compared across several factors. All mice, regardless of age, sex, listening condition, or stimulus type showed their poorest behavioral sensitivity immediately after the noise exposure. There were varying degrees of recovery over time and across factors. Old-aged mice had greater threshold shifts and less recovery compared to middle-aged mice. Mice had larger threshold shifts and less recovery for downsweeps than for complex vocalizations. Female mice were more sensitive, had smaller post-noise shifts, and had better recovery than males. Thresholds in noise were higher and less variable than thresholds in quiet, but there were comparable shifts and recovery. In mice, as in humans, the perception of ecologically relevant stimuli suffers after an intense noise exposure, and results differ from simple tone detection findings.
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Pérdida Auditiva Provocada por Ruido , Percepción del Habla , Humanos , Persona de Mediana Edad , Masculino , Femenino , Animales , Ratones , Vocalización Animal , Ruido/efectos adversos , Pérdida Auditiva Provocada por Ruido/etiología , Prueba del Umbral de Recepción del Habla , Umbral AuditivoRESUMEN
Echolocating bats rely on precise auditory temporal processing to detect echoes generated by calls that may be emitted at rates reaching 150-200 Hz. High call rates can introduce forward masking perceptual effects that interfere with echo detection; however, bats may have evolved specializations to prevent repetition suppression of auditory responses and facilitate detection of sounds separated by brief intervals. Recovery of the auditory brainstem response (ABR) was assessed in two species that differ in the temporal characteristics of their echolocation behaviors: Eptesicus fuscus, which uses high call rates to capture prey, and Carollia perspicillata, which uses lower call rates to avoid obstacles and forage for fruit. We observed significant species differences in the effects of forward masking on ABR wave 1, in which E. fuscus maintained comparable ABR wave 1 amplitudes when stimulated at intervals of <3 ms, whereas post-stimulus recovery in C. perspicillata required 12 ms. When the intensity of the second stimulus was reduced by 20-30 dB relative to the first, however, C. perspicillata showed greater recovery of wave 1 amplitudes. The results demonstrate that species differences in temporal resolution are established at early levels of the auditory pathway and that these differences reflect auditory processing requirements of species-specific echolocation behaviors.
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Estimulación Acústica , Quirópteros , Ecolocación , Potenciales Evocados Auditivos del Tronco Encefálico , Enmascaramiento Perceptual , Especificidad de la Especie , Animales , Quirópteros/fisiología , Estimulación Acústica/métodos , Potenciales Evocados Auditivos del Tronco Encefálico/fisiología , Factores de Tiempo , Masculino , Femenino , Umbral Auditivo , Percepción Auditiva/fisiologíaRESUMEN
Medial olivocochlear (MOC) efferents modulate outer hair cell motility through specialized nicotinic acetylcholine receptors to support encoding of signals in noise. Transgenic mice lacking the alpha9 subunits of these receptors (α9KOs) have normal hearing in quiet and noise, but lack classic cochlear suppression effects and show abnormal temporal, spectral, and spatial processing. Mice deficient for both the alpha9 and alpha10 receptor subunits (α9α10KOs) may exhibit more severe MOC-related phenotypes. Like α9KOs, α9α10KOs have normal auditory brainstem response (ABR) thresholds and weak MOC reflexes. Here, we further characterized auditory function in α9α10KO mice. Wild-type (WT) and α9α10KO mice had similar ABR thresholds and acoustic startle response amplitudes in quiet and noise, and similar frequency and intensity difference sensitivity. α9α10KO mice had larger ABR Wave I amplitudes than WTs in quiet and noise. Other ABR metrics of hearing-in-noise function yielded conflicting findings regarding α9α10KO susceptibility to masking effects. α9α10KO mice also had larger startle amplitudes in tone backgrounds than WTs. Overall, α9α10KO mice had grossly normal auditory function in quiet and noise, although their larger ABR amplitudes and hyperreactive startles suggest some auditory processing abnormalities. These findings contribute to the growing literature showing mixed effects of MOC dysfunction on hearing.
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Estimulación Acústica , Conducta Animal , Ruido , Animales , Femenino , Masculino , Ratones , Vías Auditivas/fisiología , Vías Auditivas/fisiopatología , Percepción Auditiva/fisiología , Umbral Auditivo , Cóclea/fisiología , Cóclea/fisiopatología , Potenciales Evocados Auditivos del Tronco Encefálico , Audición , Ratones Endogámicos C57BL , Ratones Noqueados , Ruido/efectos adversos , Núcleo Olivar/fisiología , Enmascaramiento Perceptual , Fenotipo , Receptores Nicotínicos/genética , Receptores Nicotínicos/deficiencia , Reflejo de SobresaltoRESUMEN
OBJECTIVES: The author's objective was to evaluate sex and race representation in temporal bone histopathology studies. DESIGN: PubMed, Embase, Cochrane, Web of Science, and Scopus were searched for studies written in English examining temporal bone histopathology specimens from U.S.-based institutions from January 1, 1947, to September 1, 2021. Two authors then performed "snowballing" by reviewing references from the initial search and included the studies that fulfilled the inclusion criteria. For each study, the following information was collected: publication details, study design, funding, institution from where temporal bone specimens were procured, number of study specimens, and donor demographical information. RESULTS: The authors found that out of 300 studies, 166 (55%) report sex while only 15 (5%) reported race information. Over the past 70 years, the ratio of studies reporting sex to those that do not has increased from 1.00 to 2.19 and the number of female temporal bone histopathology subjects relative to male has increased from 0.67 to 0.75. Over 90% of studies that do report this information feature participant racial compositions that do not reflect the diversity of the U.S. population. CONCLUSIONS: Studies of temporal bone histopathology often do not report participant sex or race. The reporting of participant sex and the inclusion of specimens from female donors have both increased over time. However, temporal bone histopathology study cohorts are not representative of the racial diversity of the U.S. population. The otolaryngology community must strive to build temporal bone histopathology libraries that are representative of the diverse U.S. population.
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Hueso Temporal , Femenino , Humanos , Masculino , Proyectos de Investigación , Estados Unidos , Hueso Temporal/patología , Grupos Raciales , SexoRESUMEN
Numerous and non-acoustic experimental factors can potentially influence experimental outcomes in animal models when measuring the effects of noise exposures. Subject-related factors, including species, strain, age, sex, body weight, and post-exposure measurement timepoints, influence the observed hearing deficits. Experimenter effects, such as experience with experimental techniques and animal handling, may also factor into reported thresholds. In this study, the influence of subject sex, body mass, age at noise exposure, and timepoint of post-exposure recording are reported from a large sample of CBA/CaJ mice. Auditory brainstem response (ABR) thresholds differed between noise-exposed and unexposed mice, although the differences varied across tone frequencies. Thresholds across age at noise exposures and measurement delays after exposure also differed for some timepoints. Higher body mass correlated with higher ABR thresholds for unexposed male and female mice, but not for noise-exposed mice. Together, these factors may contribute to differences in phenotypic outcomes observed across studies or even within a single laboratory.
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Pérdida Auditiva Provocada por Ruido , Masculino , Femenino , Ratones , Animales , Pérdida Auditiva Provocada por Ruido/etiología , Potenciales Evocados Auditivos del Tronco Encefálico/fisiología , Estimulación Acústica , Umbral Auditivo/fisiología , Ratones Endogámicos CBA , Modelos Animales de EnfermedadRESUMEN
Information processing in the brain requires reliable synaptic transmission. High reliability at specialized auditory nerve synapses in the cochlear nucleus results from many release sites (N), high probability of neurotransmitter release (Pr), and large quantal size (Q). However, high Pr also causes auditory nerve synapses to depress strongly when activated at normal rates for a prolonged period, which reduces fidelity. We studied how synapses are influenced by prolonged activity by exposing mice to constant, nondamaging noise and found that auditory nerve synapses changed to facilitating, reflecting low Pr. For mice returned to quiet, synapses recovered to normal depression, suggesting that these changes are a homeostatic response to activity. Two additional properties, Q and average excitatory postsynaptic current (EPSC) amplitude, were unaffected by noise rearing, suggesting that the number of release sites (N) must increase to compensate for decreased Pr. These changes in N and Pr were confirmed physiologically using the integration method. Furthermore, consistent with increased N, endbulbs in noise-reared animals had larger VGlut1-positive puncta, larger profiles in electron micrographs, and more release sites per profile. In current-clamp recordings, noise-reared BCs had greater spike fidelity even during high rates of synaptic activity. Thus, auditory nerve synapses regulate excitability through an activity-dependent, homeostatic mechanism, which could have major effects on all downstream processing. Our results also suggest that noise-exposed bushy cells would remain hyperexcitable for a period after returning to normal quiet conditions, which could have perceptual consequences.
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Percepción Auditiva/fisiología , Tronco Encefálico/fisiología , Nervio Coclear/fisiología , Homeostasis/fisiología , Neurotransmisores/metabolismo , Sinapsis/fisiología , Estimulación Acústica , Animales , Nervio Coclear/metabolismo , Potenciales Postsinápticos Excitadores/fisiología , Inmunohistoquímica , Ratones , Microscopía Electrónica , Ruido/efectos adversos , Técnicas de Placa-Clamp , Sinapsis/metabolismo , Sinapsis/ultraestructuraRESUMEN
Alzheimer's disease (AD) is a progressive neurodegenerative disorder in which changes in hearing sensitivity precede cognitive decline. Despite a well-known link between dementia and hearing loss, few AD model mouse lines have hearing characterized. We screened for hearing loss using auditory brainstem responses (ABR) in young (3-4 months) and aging (9-10 months) mice with a P301S tauopathy (PS19 mice). Compared to wild types, aging PS19 mice did not show accelerated hearing loss but did show latency differences in centrally generated ABR waveform components. These results suggest that tauopathy causes mild central auditory dysfunction in the absence of overt hearing loss.
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Enfermedad de Alzheimer , Modelos Animales de Enfermedad , Potenciales Evocados Auditivos del Tronco Encefálico , Tauopatías , Animales , Enfermedad de Alzheimer/fisiopatología , Ratones , Tauopatías/fisiopatología , Tauopatías/patología , Ratones Transgénicos , Pérdida Auditiva/fisiopatología , Pérdida Auditiva/etiología , Humanos , Audiometría/métodosRESUMEN
Older listeners often report difficulties understanding speech in noisy environments. It is important to identify where in the auditory pathway hearing-in-noise deficits arise to develop appropriate therapies. We tested how encoding of sounds is affected by masking noise at early stages of the auditory pathway by recording responses of principal cells in the anteroventral cochlear nucleus (AVCN) of aging CBA/CaJ and C57BL/6J mice in vivo. Previous work indicated that masking noise shifts the dynamic range of single auditory nerve fibers (ANFs), leading to elevated tone thresholds. We hypothesized that such threshold shifts could contribute to increased hearing-in-noise deficits with age if susceptibility to masking increased in AVCN units. We tested this by recording the responses of AVCN principal neurons to tones in the presence and absence of masking noise. Surprisingly, we found that masker-induced threshold shifts decreased with age in primary-like units and did not change in choppers. In addition, spontaneous activity decreased in primary-like and chopper units of old mice, with no change in dynamic range or tuning precision. In C57 mice, which undergo early-onset hearing loss, units showed similar changes in threshold and spontaneous rate at younger ages, suggesting they were related to hearing loss and not simply aging. These findings suggest that sound information carried by AVCN principal cells remains largely unchanged with age. Therefore, hearing-in-noise deficits may result from other changes during aging, such as distorted across-channel input from the cochlea and changes in sound coding at later stages of the auditory pathway.
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Envejecimiento , Núcleo Coclear , Ratones Endogámicos C57BL , Ratones Endogámicos CBA , Ruido , Animales , Núcleo Coclear/fisiología , Envejecimiento/fisiología , Masculino , Estimulación Acústica , Neuronas/fisiología , Femenino , Umbral Auditivo/fisiología , Enmascaramiento Perceptual/fisiología , Ratones , Potenciales de Acción/fisiologíaRESUMEN
INTRODUCTION: The stria vascularis (SV) may have a significant role in various otologic pathologies. Currently, researchers manually segment and analyze the stria vascularis to measure structural atrophy. Our group developed a tool, SVPath, that uses deep learning to extract and analyze the stria vascularis and its associated capillary bed from whole temporal bone histopathology slides (TBS). METHODS: This study used an internal dataset of 203 digitized hematoxylin and eosin-stained sections from a normal macaque ear and a separate external validation set of 10 sections from another normal macaque ear. SVPath employed deep learning methods YOLOv8 and nnUnet to detect and segment the SV features from TBS, respectively. The results from this process were analyzed with the SV Analysis Tool (SVAT) to measure SV capillaries and features related to SV morphology, including width, area, and cell count. Once the model was developed, both YOLOv8 and nnUnet were validated on external and internal datasets. RESULTS: YOLOv8 implementation achieved over 90% accuracy for cochlea and SV detection. nnUnet SV segmentation achieved a DICE score of 0.84-0.95; the capillary bed DICE score was 0.75-0.88. SVAT was applied to compare both the ears used in the study. There was no statistical difference in SV width, SV area, and average area of capillary between the two ears. There was a statistical difference between the two ears for the cell count per SV. CONCLUSION: The proposed method accurately and efficiently analyzes the SV from temporal histopathology bone slides, creating a platform for researchers to understand the function of the SV further.
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Hearing mediates many behaviors critical for survival in echolocating bats, including foraging and navigation. Most mammals are susceptible to progressive age-related hearing loss; however, the evolution of biosonar, which requires the ability to hear low-intensity echoes from outgoing sonar signals, may have selected against the development of hearing deficits in echolocating bats. Although many echolocating bats exhibit exceptional longevity and rely on acoustic behaviors for survival to old age, relatively little is known about the aging bat auditory system. In this study, we used DNA methylation to estimate the ages of wild-caught big brown bats ( Eptesicus fuscus ) and measured hearing sensitivity in young and aging bats using auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs). We found no evidence for hearing deficits in aging bats, demonstrated by comparable thresholds and similar ABR wave and DPOAE amplitudes across age groups. We additionally found no significant histological evidence for cochlear aging, with similar hair cell counts, afferent, and efferent innervation patterns in young and aging bats. Here we demonstrate that big brown bats show minimal evidence for age-related loss of peripheral hearing sensitivity and therefore represent informative models for investigating mechanisms that may preserve hearing function over a long lifetime.
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Auditory brainstem responses (ABR) are a high-throughput assessment of auditory function. Many studies determine changes to the threshold at frequencies that span the normal hearing range of their test subjects, but fewer studies evaluate changes in waveform morphology. The goal of developing this program was to make a user-friendly semiautomatic peak-detection algorithm to encourage widespread analysis of the amplitudes and latencies of the ABR, which may yield informative details about the integrity of the auditory system with development, aging, genetic manipulations, or damaging conditions. This method incorporates automated peak detection with manual override and inter-rater validation to calculate the amplitude and latency for waves 1-5, as well as interpeak latencies and amplitude ratios between waves. The output includes raw data and calculations in a format compatible with graphical and statistical software.â¢The method yields a high-throughput peak-detection algorithm with manual override and inter-rater capabilities to streamline ABR waveform analysis.â¢Data output includes amplitudes, latencies, amplitude ratios, and interpeak latencies for generation of input-output curves.â¢While complete automation of peak detection with this tool is dependent on good signal-to-noise ratios, relevant amplitude and latency calculations are fully automated, and manual spot-checking is simplified to significantly reduce the time to analyze waveforms.
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Medial olivocochlear (MOC) efferents modulate outer hair cell motility through specialized nicotinic acetylcholine receptors to support encoding of signals in noise. Transgenic mice lacking the alpha9 subunits of these receptors (α9KOs) have normal hearing in quiet and noise, but lack classic cochlear suppression effects and show abnormal temporal, spectral, and spatial processing. Mice deficient for both the alpha9 and alpha10 receptor subunits (α9α10KOs) may exhibit more severe MOC-related phenotypes. Like α9KOs, α9α10KOs have normal auditory brainstem response (ABR) thresholds and weak MOC reflexes. Here, we further characterized auditory function in α9α10KO mice. Wildtype and α9α10KO mice had similar ABR thresholds and acoustic startle response (ASR) amplitudes in quiet and noise, and similar frequency and intensity difference sensitivity. α9α10KO mice had larger ABR Wave I amplitudes than wildtypes in quiet and noise, but the noise:quiet amplitude ratio suggested α9α10KOs were more susceptible to masking effects for some stimuli. α9α10KO mice also had larger startle amplitudes in tone backgrounds than wildtypes. Overall, α9α10KO mice had grossly normal auditory function in quiet and noise, though their larger ABR amplitudes and hyperreactive startles suggest some auditory processing abnormalities. These findings contribute to the growing literature showing mixed effects of MOC dysfunction on hearing.
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7-Tesla (T) magnetic resonance imaging may allow for higher resolution images but may produce greater acoustic noise than 1.5- and 3-T scanners. We sought to characterize the intensity of acoustic noise from 7- versus 3-T scanners. A-weighted sound pressure levels from 5 types of pulse sequences used for brain and inner ear imaging in 3- and 7-T scanners were measured. Time-averaged sound level and maximum sound levels generated for each sequence were compared. Time-averaged sound levels exceeded 95 dB and reached maximums above 105 dB on the majority of 3- and 7-T scans. The mean time-averaged sound level and maximum sound level across pulse sequences were greater in 7- than 3-T (105.6 vs 91.4, P = .01; 114.0 vs. 96.5 dB, P < .01). 7- and 3-T magnetic resonance imaging scanners produce high levels of acoustic noise that exceed acceptable safety limits, emphasizing the need for active and passive noise protection.
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Ménière's disease (MD) is a debilitating disorder with unclear pathophysiology whose diagnosis often relies on clinical judgment rather than objective testing. To complicate matters further, a dissociation has emerged between two vestibular function tests commonly used in patients with MD to examine the same end-organ (the semicircular canals): the caloric test and video head impulse testing (vHIT). Caloric responses are often abnormal, while vHIT results remain normal. Explaining this dissociation could reveal novel insights into MD pathophysiology. Here, we conduct a histopathological study using temporal bone specimens (N = 58, 21 MD-affected ears and 37 age-matched controls) and their clinical testing data to examine current hypotheses aimed at this dissociation. We find otolith membrane herniation into the horizontal semicircular canal in 69% of MD ears, with 90% of these ears demonstrating a diminished caloric response. No ears with a normal response had this herniation. Moreover, we evaluated the semicircular canals for endolymphatic hydrops, which had been hypothesized to contribute to the dissociation, and found no evidence of duct dilation/hydrops. We did, however, note a potentially novel morphologic finding-smaller bony labyrinth cross-sectional diameters/areas in some MD ear canals compared to controls, suggesting relative size of the membranous duct to the bony canal rather than absolute size may be of importance. Taken together, this study refines hypotheses on the vestibular test dissociation in MD, holding diagnostic implications and expanding our understanding of the mechanisms underlying this enigmatic disease.
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Enfermedad de Meniere , Vestíbulo del Laberinto , Humanos , Membrana Otolítica , Dilatación , Canales SemicircularesRESUMEN
Individuals with Kabuki syndrome type 1 (KS1) often have hearing loss recognized in middle childhood. Current clinical dogma suggests that this phenotype is caused by frequent infections due to the immune deficiency in KS1 and/or secondary to structural abnormalities of the ear. To clarify some aspects of hearing loss, we collected information on hearing status from 21 individuals with KS1 and found that individuals have both sensorineural and conductive hearing loss, with the average age of presentation being 7 years. Our data suggest that while ear infections and structural abnormalities contribute to the observed hearing loss, these factors do not explain all loss. Using a KS1 mouse model, we found hearing abnormalities from hearing onset, as indicated by auditory brainstem response measurements. In contrast to mouse and human data for CHARGE syndrome, a disorder possessing overlapping clinical features with KS and a well-known cause of hearing loss and structural inner ear abnormalities, there are no apparent structural abnormalities of the cochlea in KS1 mice. The KS1 mice also display diminished distortion product otoacoustic emission levels, which suggests outer hair cell dysfunction. Combining these findings, our data suggests that KMT2D dysfunction causes sensorineural hearing loss compounded with external factors, such as infection.
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Anomalías Múltiples , Síndrome CHARGE , Sordera , Cara , Pérdida Auditiva Sensorineural , Enfermedades Hematológicas , Enfermedades Vestibulares , Animales , Niño , Humanos , Ratones , Causalidad , Cara/anomalías , Audición , Pérdida Auditiva Sensorineural/genéticaRESUMEN
PURPOSE: To assess possible damage to the hearing of experimental and companion animal subjects of magnetic resonance imaging (MRI) scans. MATERIALS AND METHODS: Using animal hearing threshold data and sound level measurements from typical MRI pulse sequences, we estimated "equivalent loudness" experienced by several experimental and companion animals commonly subjects of MRI scans. We compared the equivalent loudness and exam duration to safe noise standards set by the National Institute for Occupational Safety and Health (NIOSH). RESULTS: Monkeys, dogs, cats, pigs, and rabbits are frequently exposed to equivalent loudness levels during MRI scans beyond what is considered safe for human exposure. The sensitive frequency ranges for rats and mice are shifted substantially upward and their equivalent loudness levels fall within the NIOSH safe zone. CONCLUSION: MRI exposes many animals to levels of noise and duration that would exceed NIOSH human exposure limits. Researchers and veterinarians should use hearing protection for animals during MRI scans. Experimental research animals used in MRI studies are frequently kept and reimaged, and hearing loss could result in changed behavior. Damage to companion animals' hearing could make them less sensitive to commands and generally worsen interactions with family members. Much quieter MRI scanners would help decrease stress and potential harm to scanned animals, normalize physiology during MRI, and enable MRI of awake animals.
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Exposición a Riesgos Ambientales/efectos adversos , Exposición a Riesgos Ambientales/análisis , Pérdida Auditiva Provocada por Ruido/prevención & control , Imagen por Resonancia Magnética/efectos adversos , Ruido/efectos adversos , Ruido/prevención & control , Espectrografía del Sonido/métodos , Animales , Gatos , Perros , Humanos , Ratones , Mascotas , Conejos , RatasRESUMEN
The role of the mammalian auditory olivocochlear efferent system in hearing has long been the subject of debate. Its ability to protect against damaging noise exposure is clear, but whether or not this is the primary function of a system that evolved in the absence of industrial noise remains controversial. Here we review the behavioral consequences of olivocochlear activation and diminished olivocochlear function. Attempts to demonstrate a role for hearing in noise have yielded conflicting results in both animal and human studies. A role in selective attention to sounds in the presence of distractors, or attention to visual stimuli in the presence of competing auditory stimuli, has been established in animal models, but again behavioral studies in humans remain equivocal. Auditory processing deficits occur in models of congenital olivocochlear dysfunction, but these deficits likely reflect abnormal central auditory development rather than direct effects of olivocochlear feedback. Additional proposed roles in age-related hearing loss, tinnitus, hyperacusis, and binaural or spatial hearing, are intriguing, but require additional study. These behavioral studies almost exclusively focus on medial olivocochlear effects, and many relied on lesioning techniques that can have unspecific effects. The consequences of lateral olivocochlear and of corticofugal pathway activation for perception remain unknown. As new tools for targeted manipulation of olivocochlear neurons emerge, there is potential for a transformation of our understanding of the role of the olivocochlear system in behavior across species.
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Percepción Auditiva , Audición , Estimulación Acústica , Animales , Percepción Auditiva/fisiología , Cóclea/fisiología , Vías Eferentes/fisiología , Audición/fisiología , Hiperacusia , Mamíferos , Ruido/efectos adversos , Núcleo Olivar/fisiologíaRESUMEN
Deer mice (genus Peromyscus) are an emerging model for aging studies due to their longevity relative to rodents of similar size. Although Peromyscus species are well-represented in genetic, developmental, and behavioral studies, relatively few studies have investigated auditory sensitivity in this genus. Given the potential utility of Peromyscus for investigations of age-related changes to auditory function, we recorded auditory brainstem responses (ABRs) in two Peromyscus species, P. californicus, and P. leucopus, across the lifespan. We compared hearing sensitivity and ABR wave metrics measured in these species with measurements from Mus musculus (CBA/CaJ strain) to assess age-related effects on hearing across species. Recordings in young animals showed that all species had similar hearing ranges and thresholds with peak sensitivity ranging from 8 to 16 kHz; however, P. californicus and P. leucopus were more sensitive to frequencies below 8 kHz. Although M. musculus showed significant threshold shifts across a broad range of frequencies beginning at middle age and worsening among old individuals, older Peromyscus mice retained good sensitivity to sound across their lifespan. Middle-aged P. leucopus had comparable thresholds to young for frequencies below 24 kHz. P. leucopus also had notably large ABRs that were robust to age-related amplitude reductions, although response latencies increased with age. Old P. californicus were less sensitive to mid-range tones (8-16 kHz) than young individuals; however, there were no significant age-effects on ABR amplitudes or latencies in this species. These results indicate that longevity in Peromyscus mice may be correlated with delayed aging of the auditory system and highlight these species as promising candidates for longitudinal hearing research.
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Peromyscus , Presbiacusia , Animales , Ratones , Roedores , Ratones Endogámicos CBA , Potenciales Evocados Auditivos del Tronco Encefálico/fisiología , Umbral Auditivo/fisiologíaRESUMEN
The Johns Hopkins Otologic Research Laboratory was founded in 1924 as the first human temporal bone laboratory within the United States. To better understand the contributions of the Johns Hopkins Otologic Research Laboratory to our understanding of presbycusis, we consulted with a medical librarian and archivist to search the Alan Mason Chesney Medical Archives, PubMed, JSTOR, and Johns Hopkins Bulletin for published and unpublished works from the lab. Between 1924 and 1938, Samuel J. Crowe, the Chairman of Otolaryngology, and anatomist Stacy R. Guild amassed a collection of â¼1,800 temporal bones. This collection allowed for an unprecedented period of discovery related to otologic disease. They combined hearing thresholds measured by the recently invented audiometer with new techniques for temporal bone decalcification, sectioning, and staining, and a method for the graphic reconstruction of the cochlea. Crowe and Guild used this unique opportunity to correlate otopathology with hearing and to make the first detailed descriptions of the otopathology of presbycusis. In 1931 and 1934, they observed spiral ganglion neuron and outer hair cell loss in the basal turn of the cochlea in individuals with high-frequency hearing loss. These were the first studies to reveal that stria vascularis degeneration and middle ear pathology were not the most common causes for high-frequency hearing loss. Aside from revealing the primary driving factors of presbycusis, this work provided insight into the tonotopic organization of the cochlea. After initially being recruited to help raise money for the laboratory, medical illustrator Max Brödel used the vertical histologic cross-sections of the cochlea to produce illustrations of the ear. The decision to produce histologic sections in the plane of the superior semicircular canal likely influenced Brödel's illustrations that share a similar orientation and would later become widely circulated. Significant contributions from the Otologic Research Laboratory were also made by Mary Hardy, D.Sc., a woman who has previously received little recognition for her work. The sectioning of temporal bones was stopped in 1938 due to World War II, but much of Crowe's and Guild's work continued into the 1940s until a rift between the two resulted in the temporary closure of the laboratory in 1949. Nearly 100âyears after its founding, discoveries from the Johns Hopkins Otologic Research Laboratory remain relevant and emphasize the importance of continued human temporal bone research to improve our understanding and treatment of otologic disease.
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Presbiacusia , Cóclea/patología , Femenino , Pérdida Auditiva de Alta Frecuencia , Humanos , Presbiacusia/patología , Estría Vascular/patología , Hueso Temporal/patología , Estados UnidosRESUMEN
Aging leads to degeneration of the peripheral and central auditory systems, hearing loss, and difficulty understanding sounds in noise. Aging is also associated with changes in susceptibility to or recovery from damaging noise exposures, although the effects of the interaction between acute noise exposure and age on the perception of sounds are not well studied. We tested these effects in the CBA/CaJ mouse model of age-related hearing loss using operant conditioning procedures before and after noise exposure and longitudinally measured changes in their sensitivity for detecting tones in quiet or noise backgrounds. Cochleae from a subset of the behaviorally tested mice were immunolabeled to examine organ of Corti damage relative to what is expected based on aging alone. Mice tested in both quiet and noise background conditions experienced worse behavioral sensitivity immediately after noise exposure, but mice exposed at older ages generally showed greater threshold shifts and reduced recovery over time. Surprisingly, day-to-day stability in thresholds was markedly higher for mice detecting signals in the presence of a noise masker compared with detection in quiet conditions. Cochlear analysis revealed decreases in the total number of outer hair cells (OHCs) and the number of ribbons per inner cell in high-frequency regions in aged, noise-exposed mice relative to aging alone. Our findings build on previous work showing interactions between age and noise exposure and add that background noise can increase the stability of behavioral hearing sensitivity after noise damage.