Early Sensorineural Hearing Loss in Ob/Ob Mouse, an Animal Model of Type 2 Diabetes

Objectives

There have been many studies on the relationship between diabetes mellitus and presbycusis. Microangiopathy and neuropathy that''s caused by chronic hyperglycemia may lead to damage to the inner ear. Several clinical studies on humans and animal studies have been performed to investigate the association between diabetes and hearing loss, however, this relationship is still a matter of debate. We investigated the association of diabetes and sensorineural hearing loss in an animal model of type-2 diabetes and obesity (the ob/ob mouse [OM]).

Methods

The auditory brainstem response (ABR) thresholds were obtained in the OM and the wild type mice (C57BL/6J mice) up to 25 weeks after birth. After the animals were sacrificed, their cochleae were retrieved and then subjected to histopathologic observations.

Results

The OM exhibited significantly elevated ABR thresholds at 21 weeks of age, yet the C57BL/6J mice exhibited no significant change until 25 weeks of age. On the histological findings, outer hair cell degeneration and loss of spiral ganglion cells were observed in the middle and basal turns of the OM. On the contrary, no degenerative change was observed until 25 weeks of age in the C57BL/6J mice.

Conclusion

This study suggests that chronic hyperglycemia and obesity may lead to early sensorineural hearing loss.     

Reduction in Sharpness of Frequency Tuning but not Endocochlear Potential in Aging and Noise-Exposed BALB/cJ Mice

Schuknecht proposed categories for human age-related hearing loss (ARHL) based upon whether the primary degeneration involves the organ of Corti (sensory ARHL), spiral ganglion cells (neural), stria vascularis (strial), or a combination of these (mixed). Genetically standardized mouse ARHL models can help validate Schuknecht's framework and clarify the underlying cellular processes. Much recent work has focused on the mouse Ahl locus, which promotes both ARHL and noise-induced hearing loss. On the C57BL/6 inbred background, Ahl has been associated with degeneration of organ of Corti, afferent neurons, and stria vascularis/spiral ligament, suggesting that it promotes mixed (sensory/neural/strial) ARHL. Some cochlear degeneration in C57BL/6 mice could be caused by genes other than Ahl, however. The question of what constitutes Ahl-related pathology can be addressed by comparing C57BL/6 mice with other strains that carry the same allele, including BALB/c substrains. We examined the effects of aging and broadband noise exposure in inbred BALB/cJ mice (1.5–13.0 mos) using measures of frequency tuning (compound action potential tuning curves) (CAPTCs), strial function (endocochlear potential recording, EP), and light microscopy. Aging and noise led to generally similar physiological and anatomical changes. Reductions in sensitivity and sharpness of frequency tuning were not consistently linked to hair cell loss, reduction in the EP, or changes in the lateral wall. Instead they appeared best explained by alterations in supporting cells in the basal half of the cochlear and in the spiral limbus in the apex. These results emphasize the importance of cell types other than hair cells in cochlear pathology. They also indicate that Ahl does not necessarily promote a strial form of ARHL.     

Cochlear changes in presbycusis with tinnitus

Objectives

The pathophysiology of tinnitus is obscure and its treatment is therefore elusive. Significant progress in this field can only be achieved by determining the mechanisms of tinnitus generation, and thus, histopathologic findings of the cochlea in presbycusis with tinnitus become crucial. We revealed the histopathologic findings of the cochlea in subjects with presbycusis and tinnitus.

Material and methods

The subjects were divided into 2 groups, presbycusis with tinnitus (tinnitus) group and presbycusis without tinnitus (control) group, with each group comprising 8 temporal bones from 8 subjects. We quantitatively analyzed the number of spiral ganglion cells, loss of cochlear inner and outer hair cells, and areas of the stria vascularis and spiral ligament.

Results

There was a significantly greater loss of outer hair cells in the tinnitus group compared with the control group in the basal and upper middle turns. The stria vascularis was more atrophic in the tinnitus group compared with the control group in the basal turn.

Conclusions

Tinnitus is more common in patients with presbycusis who have more severe degeneration of outer hair cells and stria vascularis.     

Neural-Induced Human Mesenchymal Stem Cells Promote Cochlear Cell Regeneration in Deaf Guinea Pigs

Objectives

In mammals, cochlear hair cell loss is irreversible and may result in a permanent sensorineural hearing loss. Secondary to this hair cell loss, a progressive loss of spiral ganglion neurons (SGNs) is presented. In this study, we have investigated the effects of neural-induced human mesenchymal stem cells (NI-hMSCs) from human bone marrow on sensory neuronal regeneration from neomycin treated deafened guinea pig cochleae.

Methods

HMSCs were isolated from the bone marrow which was obtained from the mastoid process during mastoidectomy for ear surgery. Following neural induction with basic fibroblast growth factor and forskolin, we studied the several neural marker and performed electrophysiological analysis. NI-hMSCs were transplanted into the neomycin treated deafened guinea pig cochlea. Engraftment of NI-hMSCs was evaluated immunohistologically at 8 weeks after transplantation.

Results

Following neural differentiation, hMSCs expressed high levels of neural markers, ionic channel markers, which are important in neural function, and tetrodotoxin-sensitive voltage-dependent sodium currents. After transplantation into the scala tympani of damaged cochlea, NI-hMSCs-injected animals exhibited a significant increase in the number of SGNs compared to Hanks balanced salt solution-injected animals. Transplanted NI-hMSCs were found within the perilymphatic space, the organ of Corti, along the cochlear nerve fibers, and in the spiral ganglion. Furthermore, the grafted NI-hMSCs migrated into the spiral ganglion where they expressed the neuron-specific marker, NeuN.

Conclusion

The results show the potential of NI-hMSCs to give rise to replace the lost cochlear cells in hearing loss mammals.     

Comparison of functional and morphologic characteristics of mice models of noise-induced hearing loss

Objectives

This study was conducted to compare morphologic and audiologic changes after noise exposure in two different strains of mice (CBA and C57) and to create morphologically proven models of noise-induced hearing loss.

Methods

Mice were exposed to white noise at 110-dB sound-pressure level for 60 minutes at the age of 1 month. Hearing thresholds and outer hair cell functions were evaluated by auditory brainstem response recordings and distortion product otoacoustic emission immediately and 22 days after noise exposure. Cochlear pathology was observed and compared by light and electron microscopic studies.

Results

Both mice strains showed hearing threshold shifts with decreased outer hair cell function immediately and 22 days after noise exposure. More severe auditory brainstem response threshold shifts were observed in C57 mice compared with CBA mice at click, 8-, 16-, and 32-kHz tone-burst stimuli. A cochlear morphologic study demonstrated predominant outer hair cell degeneration at all turns of the cochlea; degeneration was most severe at the basal turn in both mice strains. A scanning electron microscopic study revealed more severe ultrastructural damage of outer hair cells at each turn of the cochlea in C57 mice. The lateral wall of the cochlea was more severely degenerated in CBA mice.

Conclusion

Both mice strains showed consistent, permanent noise-induced hearing loss with different susceptibilities and site vulnerabilities. Further studies to investigate the mechanism of the different degree and cochlear site vulnerability to noise exposure between two mice strains are necessary.     

Apoptosis Progression in the Hair Cells in the Organ of Corti of GJB2 Conditional Knockout Mice

Objectives

Apoptosis may play an important role in the mechanism underlying the GJB2 gene conditional knockout (cCx26) mice cochlear cell death. The objective of this study was to explore the the damage mode of the outer hair cells (OHCs) and its real time point of apoptosis and provide information to further explore the role of apoptosis in the happening of hearing loss in cCx26 mice.

Methods

Cochleae from mice at various developmental stages (P8, P12, and P21) were dissected out and first used to be observed under the scanning electron microscope (SEM). Basilar membranes from mice at P8, P14, P18, and P21 were stained by fluorescein isothiocyanate-conjugated phalloidin and propidium iodide (PI) and examined under confocal microscope.

Results

The loss of OHCs of cCx26 knockout mice was first set between P12 and P21 under SEM. Whole mount phalloidin and PI staining revealed that obvious apoptotic appearance of the OHCs surface morphology was observed at P18.

Conclusion

Typical apoptotic morphology was found in the OHCs in the organ of Corti of the cCx26 mice at P18. This may provide information to further study the role of apoptosis in the occurrence of hearing loss of cCx26 mice.     

The effect of noise exposure on the aging ear.

The effect of noise exposure on auditory sensitivity and inner ear morphology was compared in aged and young mature mice. Hearing thresholds were obtained by auditory evoked brain stem responses (ABR) before and after noise exposure, and hair cell loss was quantified. The study was done in two parts: first to assess the effect of noise exposure on subjects with presbycusis, and second to assess its effect on aged subjects without measurable presbycusis. In the first experiment C57BL/6 mice, with an age-related hearing loss, were used as a model for presbycusis. C57BL/6 mice exhibiting presbycusis were more susceptible to noise injury than age-matched CBA/Ca mice. In the second experiment CBA/Ca mice were used. These mice retain normal hearing even with advancing age. The aged CBA/Ca mice had the same susceptibility to noise injury as young CBA/Ca mice.     

Age-related changes in the murine cochlear lateral wall

Cochleas from C57BL/6 mice were investigated electrophysiologically and histochemically to evaluate the pathology of presbycusis. The average auditory brainstem response thresholds from 6-week-old mice were significantly lower than those of 6-month-old mice and those of 1-year-old mice. Histologic observation revealed changes in the cochlea after age 6 months. Conventional hematoxylin and eosin (H&E) staining showed disorganization of the organ of Corti, a decrease in the number of spiral ganglion cells, and atrophy of the stria vascularis. Although H&E staining and type II collagen immunolabeling did not show obvious changes in the spiral ligament (SL), the density of connexin 26 staining was reduced in this region. Sodium-potassium-adenosinetriphosphatase immunolabeling was increased in the SL, whereas its average density was not significantly altered in the stria vascularis. These results suggest that the SL could be among the regions responsible for cochlear malfunction with aging.     

Age-related auditory pathology in the CBA/J mouse

Commercially obtained aged male CBA/J mice presented a complex pattern of hearing loss and morphological changes. A significant threshold shift in auditory brainstem responses (ABR) occurred at 3 months of age at 4kHz without apparent loss of hair cells, rising slowly at later ages accompanied by loss of apical hair cells. A delayed high-frequency deficit started at 24kHz around the age of 12 months. At 20-26 months, threshold shifts at 12 and 24kHz and the accompanying hair cell loss at the base of the cochlea were highly variable with some animals appearing almost normal and others showing large deficits. Spiral ganglion cells degenerated by 18 months in all regions of the cochlea, with cell density reduced by approximately 25%. There was no degeneration of the stria vascularis and the endocochlear potential remained stable from 3 to 25 months of age regardless of whether the animals had normal or highly elevated ABR thresholds. The slow high-frequency hearing loss combined with a modest reduction of ganglion cell density and an unchanged endocochlear potential suggest sensorineural presbycusis. The superimposed early hearing loss at low frequencies, which is not seen in animals bred in-house, may complicate the use of these animals as a presbycusis model.     

Inner ear pathology of alpha-galactosidase A deficient mice,a model of Fabry disease

Objective

Fabry disease is characterized by genetic alpha-galactosidase A deficiency, resulting in accumulation of glycolipids (GL-3) and tissue damage. Hearing loss is also common and attributed to GL-3 accumulation in the inner ear. The only reported histological studies dealt with murine and human specimens. Accordingly, histopathological studies of the cochlea were performed on an alpha-galactosidase A deficient murine model of Fabry disease, using C57BL6/J mice as the controls.

Methods

The hearing ability was evaluated using the ABR threshold, while cochlear specimens were observed light microscopically and ultrathin temporal bone sections by TEM.

Results

HE staining showed no accumulation of GL-3 or abnormal cochlear morphology in the alpha-galactosidase A deficient mice, but toluidine blue staining and TEM revealed GL-3 accumulation in the stria vascularis and kidney. No GL-3 accumulation was detected in the C57BL6/J controls by either HE staining or TEM. The alpha-galactosidase A deficient mice and the controls showed no clear differences in the ABR threshold (hearing acuity), but for older animals the threshold was higher in the C57BL6/J controls.

Conclusion

In summary, although the alpha-galactosidase A deficient mice showed no clear hearing loss, GL-3 accumulation was demonstrated in the cochlea.     

The functional age of hearing loss in a mouse model of presbycusis. I. Behavioral assessments

Presbycusis is a common form of hearing loss that progresses from high to low frequencies with advancing age. C57BL/6J mice experience a rapid progression of presbycusis-like hearing deficits and thus provide a convenient animal model for evaluating behavioral, physiological and anatomical correlates of the disorder. Previous studies of C57BL/6J mice have relied on short-term observations of age-matched subject groups to reconstruct a time course for auditory pathologies. Such statistical approaches are weakened by the variability of hearing thresholds in young mice and the inconsistent timing of degenerative effects in older mice. The present study was designed to resolve these ambiguities by tracking the hearing abilities of individual C57BL/6J mice from age 16 weeks until the onset of hearing loss in specific listening conditions. Testing at frequencies of 8 and 16 kHz in quiet confirmed the high-to-low frequency progression that is characteristic of presbycusis. Often the hearing loss developed in two phases, one gradual and the other abrupt. Testing in noise revealed deficits that were first manifested as threshold instability and then an increased susceptibility to masking. These changes occurred before hearing loss in quiet. CBA/CaJ mice did not show significant loss during a similar period of observation. Our findings provide a well-ordered chronology for isolating the functional consequences of multiple cochlear pathologies that arise during the time course of presbycusis. This neurobehavioral assessment is termed the functional age of hearing loss. Neuroanatomical assessments of behaviorally characterized C57BL/6J mice are presented in the companion paper [Hear. Res. 183 (2003) 29-36].     

Presbycusis: a human temporal bone study of individuals with flat audiometric patterns of hearing loss using a new method to quantify stria vascularis volume

OBJECTIVE: The purpose of this study was to determine the prevalence of stria vascularis atrophy in individuals with presbycusis and flat audiometric patterns of hearing loss. Individuals with presbycusis have historically been categorized by the shape of their audiograms, and flat audiometric thresholds have been reported to be associated with atrophy of the stria vascularis. Stria vascularis volume was not measured in these studies. STUDY DESIGN: Retrospective case review. METHODS: Archival human temporal bones from individuals with presbycusis were selected on the basis of strict audiometric criteria for flat audiometric thresholds. Six temporal bones that met these criteria were identified and compared with 10 temporal bones in individuals with normal hearing. A unique quantitative method was developed to measure the stria vascularis volume in these temporal bones. The hair cell and spiral ganglion cell populations also were quantitatively evaluated. RESULTS: Only one of the six individuals with presbycusis and flat audiometric thresholds had significant atrophy of the stria vascularis. This individual with stria vascularis atrophy also had reduced inner hair cell, outer hair cell, and ganglion cell populations. Three of the individuals with presbycusis had spiral ganglion cell loss, three individuals had inner hair cell loss, and all six individuals had outer hair cell loss. CONCLUSIONS: The results of this investigation suggest that individuals with presbycusis and flat audiometric patterns of hearing loss infrequently have stria vascularis atrophy. Outer hair cell loss alone or in combination with inner hair cell or ganglion cell loss may be the cause of flat audiometric thresholds in individuals with presbycusis.     

国产C57和BALB／c小鼠年龄相关性听力损失的畸变产物耳声发射检测

目的通过对国产C57和BALB/c近交系小鼠不同日龄时DPOAE的检测,探讨其听力随年龄变化的趋势.方法对不同日龄国产C57和BALB/c近交系小鼠进行DPOAE测试,设定初始音f1、f2(f1/f2=1.22),其强度L1=70dBSPL,L2=65dBSPL,在频率[(f1·     

Age-Related Changes in Cochlear Endolymphatic Potassium and Potential in CD-1 and CBA/CaJ Mice

The CD-1 mouse strain is known to have early onset of hearing loss that is progressive with aging. We sought to determine whether a disturbance of K⁺ homeostasis and pathological changes in the cochlear lateral wall were involved in the age-related hearing loss (AHL) of CD-1 as compared to the CBA/CaJ strain which has minimal AHL. In the present study, the endocochlear potential (EP) and endolymphatic K⁺ concentration ([K⁺]_e) were measured in both strains of mice with double-barrel microelectrodes at young (1–2 mo) and old (5–9 mo) ages. CBA/CaJ mice displayed no changes with aging in EP and [K⁺]_e of the basal turn. In the apical turn, there was a small positive shift of the EP (10 mV) with aging under both normoxic and acute anoxic conditions (–EP), without any change of [K⁺]_e. Further, there were no obvious pathological changes in the lateral wall of CBA/CaJ mice. By contrast, old CD-1 mice displayed a significantly reduced [K⁺]_e by 30% in both basal and apical turns with no significant changes in normoxic EP. The –EP in the apical turn was significantly reduced in magnitude by 6 mV. A severe loss of cells with aging was observed in the region of type IV fibrocytes of the apical and basal turns and of type II fibrocytes in the basal turn. A complete degeneration of organ of Corti was also observed at the basal turn of old CD-1 mice, as well as a basalward decline of spiral ganglion neuron density. The pathological changes in spiral ligament of CD-1 mice were similar to those of an inbred mouse strain C57BL/6J that expresses an AHL gene (ahl) and might be a primary etiology of AHL of CD-1 mice. These findings have ramifications for our understanding of AHL and for interpretation of genetic mutations in a CD-1 background.     

Idiopathic Sudden Sensorineural Hearing Loss With Minimal Hearing Impairment

Objectives

The aim of the study was to determine the characteristics of patients who did not match the audiometric criteria of idiopathic sudden sensorineural hearing loss (SSNHL) but complained of acute hearing loss.

Methods

By thorough medical chart reviews, historical cohort study was performed with consecutive data of 589 patients complaining of acute unilateral sensorineural hearing loss without identifiable causes between 2005 and 2013. Those patients demonstrating a hearing loss of at least 30 dB at three consecutive frequencies based on pure tone audiometry were classified as group I; the others were classified as group II. Patients'' characteristics, final hearing, and hearing improvement rate (HIR) between the two groups were compared.

Results

Group II exhibited distinctive characteristics, including an early age of onset of the hearing loss (P<0.01), an absence of accompanying diabetes (P<0.01) and hypertension (P<0.01), and better unaffected hearing and final hearing compared with group I (P<0.001). However, the HIR of the patients in the two groups was not significantly different (P>0.05).

Conclusion

Patients who did not meet the audiological criteria of SSNHL exhibited distinctive characteristics compared to SSNHL patients.     

Aging and the auditory brainstem response in mice with severe or minimal presbycusis

Threshold, latency, and amplitude of the auditory brainstem response (ABR) were obtained with filtered noise pips in young and aging C57BL/6J mice (to 16-months), which undergo severe progressive age-related sensorineural hearing loss (presbycusis) and CBA/J mice (to 19-months), which show only mild loss late in life. Aging per se (CBA mice) is not associated with significant changes in ABR parameters. Presbycusis, in aging C57 mice, is associated with increased thresholds; there is a trend toward increased latencies, but only when threshold elevations are substantial. Amplitudes of early waves, but not late waves, decrease greatly in aging C57 mice. In young C57 mice, amplitudes of early ABR waves vary monotonically with intensity, while amplitudes of later waves (IV and V) have a relatively flat, or even nonmonotonic, relationship to intensity; in older C57 mice, all waves have monotonie intensity functions. ABR parameters are not affected by gender in either strain. The mouse models can help to clarify some inconsistencies in the human literature on aging and the ABR.     

Age-related hearing loss and the ahl locus in mice

C57BL/6 (B6) mice experience hearing loss and cochlear degeneration beginning about mid-life, whereas CAST/Ei (CAST) mice retain normal hearing until old age. A locus contributing to the hearing loss of B6 mice, named age-related hearing loss (ahl), was mapped to Chromosome 10. A homozygous, congenic strain of mice (B6.CAST-+ahl ), generated by crossing B6 (ahl/ahl) and CAST (+ahl/+ahl) mice has the same genomic material as the B6 mice except in the region of the ahl locus, which is derived from CAST. In this study, we have determined the extent of the CAST-derived region of Chromosome 10 in the congenic strain and have examined mice of all three strains for hearing loss and cochlear morphology between 9 and 25 months of age. Results for B6 mice were similar to those described previously. CAST mice showed no detectable hearing loss even at 24 months of age; however, they had a small amount of ganglion cell degeneration. B6.CAST-+ahl mice were protected from early onset hearing loss and basal turn degeneration, but older animals did show some hearing loss and ganglion cell degeneration. We conclude that loci in addition to ahl contribute to the differences in hearing loss between B6 and CAST mice. These results illustrate the complex inheritance of age-related hearing loss in mice and may have implications for the study of human presbycusis.     

Inner ear morphology in CBA/Ca and C57BL/6J mice in relationship to noise,age and phenotype

Summary CBA/Ca mice showing moderate hearing losses with onset late in life and C57BL/6J mice with progressive hearing losses starting when animals were young adults were exposed to a 2–7 kHz, 120 dB SPL noise band for 5 min in order to investigate morphological consequences to noise as a function of age and genotype. Permanent threshold shifts were determined by auditory brainstem responses 1 month after noise exposure at 1, 3 and 6 months of age. CBA mice had a decreasing susceptibility to noise with increasing age, while C57 mice remained equally susceptible throughout all ages tested. The threshold shifts were then analyzed in relation to morphological changes of the organ of Corti as visualized by light microscopy (LM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). CBA mice exposed at 1 month and sacrificed at 2 months had seemingly normal cochlear morphologies under LM. In these animals SEM findings demonstrated mild stereocilia damage to noise trauma, but not when mice were exposed at 3 and 6 months. There was no visible morphological aging of hair cells found during the period tested. In contrast; the C57 mice had early hair cell changes including bent and fused stereocilia, bulging of the cuticular plates, hair cell loss and swelling of afferent dendrites. These changes became more pronounced throughout the test periods with the variability of damage in this strain more evident over time. This pattern was also aggravated in all C57 age groups tested after noise exposure. Quantification with cytocochleograms demonstrated a statistically different reaction pattern to noise trauma between the two different genotypes of mice.     

Hereditary deafness occurring in cd/1 mice.

Different strains of mice provide a valuable research tool for studying both hereditary and acquired forms of deafness. The cd/1 strain has been found to demonstrate hereditary cochlear pathology. The characteristics of hearing loss in cd/1 mice have not previously been reported. In this investigation auditory thresholds were obtained by measuring evoked brain stem responses in subjects of three different ages: 3 weeks, 10 weeks and 6 months. The results were compared with thresholds obtained from CBA/Ca mice (which have normal hearing) and C57BL/6 mice (which are known to have a genetically determined pre-senile progressive cochlear hearing loss). A significant hearing loss was observed which progressed from high to low frequencies, and with age. Extensive degeneration was observed throughout the organ of Corti. cd/1 mice may provide a useful model for studying genetically determined deafness.