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PubMedDate not supplied

Brainstem auditory evoked potentials following meningitis in children.

The report concerns findings for brainstem auditory evoked potentials (BAEPs) recorded in 116 children, aged between a few days and 7 years, having suffered from bacterial meningitis. 26% of cases occurred between birth and 6 months, 55% between 6 months and 2 years, and 19% after 2 years of age. Hemophilus was the most common bacteria (49%), followed by Pneumococcus (22%) and Meningococcus (15%). Neurological complications were found in 30% of the meningitis cases and accounted for 85% of all complications found. 29% of BAEPs were abnormal, of which 47% revealed transmission, 32% endocochlear and 21% retrocochlear impairment. Transmission impairment mainly occurred before the age of 2 years (88%), most frequently in meningococcus meningitis cases (44%), and independently of neurological complications. Retrocochlear impairment was found in association with neurological complications in 71% of cases. Endocochlear BAEP damage was found in 9.5% of cases, half of which were bilateral and total, representing cophosis: it was found at all ages, and without any particular associated neurological complication. Hemophilus was the commonest bacterial agent in endocochlear cases overall, with Pneumococcus underlying 50% of cophosis cases. The study shows BAEP recording in association with a clinical ear examination is useful following childhood bacterial meningitis, screening for definitive endocochlear and deafness, distinguishing total from partial hearing-loss and indicating suitable treatment.

Age Factors↗
PubMedDate not supplied

Otoacoustic emissions and brainstem auditory evoked potentials in children with neurological afflictions.

Findings are reported for evoked otoacoustic emissions (EOAEs) recorded from 22 children with neurological afflictions, whose brainstem auditory evoked potentials (BAEPs) were pathological on at least one side (41 ears explored). Our results confirmed that EOAEs are always present in children and infants having normal BAEPs. Absence of EOAE (n = 22) was almost always related to middle ear or cochlear damage with BAEPs indicating diagnoses, respectively, of transmission damage (n = 7) or endocochlear damage (n = 16). Conversely, for BAEP diagnoses of retrocochlear damage (n = 12), EOAEs were always present. EOAEs associated with BAEPs, therefore, appear to offer a well-adapted technique for precise etiological diagnosis of childhood hearing loss. When no wave is identifiable by BAEP recording, EOAE presence indicates retrocochlear damage.

Child↗
PubMed2005

Inhibition of caspases alleviates gentamicin-induced cochlear damage in guinea pigs.

The efficacy of caspase inhibitors for protecting the cochlea was evaluated in an in vivo study using guinea pigs, as the animal model system. Gentamicin (12 mg/ml) was delivered via an osmotic pump into the cochlear perilymphatic space of guinea pigs at 0.5 microl/h for 14 days. Additional animals were given either z-Val-Ala-Asp (Ome)-fluoromethyl ketone (z-VAD-FMK) or z-Leu-Glu-His-Asp-FMK (z-LEHD-FMK), a general caspase inhibitor and a caspase 9 inhibitor, respectively, in addition to gentamicin. The elevation in auditory brain stem response thresholds, at 4, 7, and 14 days following gentamicin administration, were decreased in animals that received both z-VAD-FMK and z-LEHD-FMK. Cochlear sensory hair cells survived in greater numbers in animals that received caspase inhibitors in addition to gentamicin, whereas sensory hair cells in animals that received gentamicin only were severely damaged. These results suggest that auditory cell death induced by gentamicin is closely related to the activation of caspases in vivo.

Administration, Topical↗
PubMed2004

Middle ear and cochlear disorders result in different DPOAE growth behaviour: implications for the differentiation of sound conductive and cochlear hearing loss.

Input/output functions of distortion product otoacoustic emissions (DPOAE I/O-functions) give an insight into the compressive, non-linear sound processing of the cochlea. With an inner ear dysfunction a steeper I/O-function is observed. Due to the linear sound processing of the middle ear, one can assume that the DPOAE growth behaviour remains unaltered with a sound conduction dysfunction. If that is true, a differentiation between middle and inner ear dysfunction will be possible by using the slope of DPOAE I/O-functions as a means for assessing cochlear compression. In order to test that hypothesis, DPOAE I/O-functions were recorded in a wide primary tone level range at up to 8 f2 frequencies between 2.0 and 8.0 kHz (15 dB SPL < L2< 60 dB SPL; L1=0.46 L2 + 41 dB SPL; f2/f1=1.2) in guinea pigs in which middle (saline solution in the bulla) and inner ear (exposure to loud broadband noise) disorders were induced. Middle ear dysfunction resulted in a reduction of the DPOAE amplitude independent of the primary tone level. Consequently, DPOAE growth behaviour was not affected. In contrast to that, during cochlear impairment, steepened DPOAE I/O-functions were observed reflecting loss of compression of the cochlear amplifier. Accordingly, DPOAE I/O-functions allow a differentiation between middle and inner ear dysfunction. Further studies will have to show the usability of this method for clinical diagnostics, e.g. for detecting sound conduction disturbances in newborn hearing screening due to amniotic fluid or Eustachian tube dysfunctions during the early postnatal period.

Animals↗
PubMed2005

Breed-dependent susceptibility to acute sound exposure in young chickens.

Commercially available chickens fall into two categories: egg layers and broilers. Durham et al. (Hear. Res. 166 (2002) 82-95) showed that despite similar noisy living environments, cochleae of most adult broilers show extensive damage, while cochleae of adult egg layers are largely normal. This finding suggests that egg layers and broilers differ in their susceptibility to noise damage. Here, we evaluate breed differences in susceptibility to acoustic trauma. Young egg layers and broilers (10-17 weeks) were exposed to a 1500Hz pure tone (120dB SPL; 24h) and killed 24 or 72h later. Cochleae were prepared for scanning electron microscopy and photomicrographs of the cochlear surface were used to determine location and severity of damage. Cochleae were grouped based upon damage severity (moderate or severe). While location and area of damage were similar between both breeds at each recovery time, cochlear damage at 72h was more extensive than at 24h. We found no quantitative breed differences within either damage category or recovery time. However, more egg layers (25/27) than broilers (16/32) displayed severely damaged cochleae. Our findings conflict with those reported by Durham et al. (2002). Our results identify a breed-dependent difference in susceptibility to acute sound exposure, with young egg layers displaying increased sensitivity.

Animals↗
PubMed2006

p27(Kip1) deficiency causes organ of Corti pathology and hearing loss.

p27(Kip1) (p27) has been shown to inhibit several cyclin-dependent kinase molecules and to play a central role in regulating entry into the cell cycle. Once hair cells in the cochlea are formed, p27 is expressed in non-sensory cells of the organ of Corti and prevents their re-entry into the cell cycle. In one line of p27 deficient mice (p27(-/-)), cell division in the organ of Corti continues past its normal embryonic time, leading to continual production of cells in the organ of Corti. Here we report on the structure and function of the inner ear in another line of p27 deficient mice originating from the Memorial Sloan-Kettering Cancer Center. The deficiency in p27 expression of these mice is incomplete, as they retain expression of amino acids 52-197. We determined that mice homozygote for this mutation had severe hearing loss and their organ of Corti exhibited an increase in the number of inner and outer hair cells. There also was a marked increase in the number of supporting cells, with severe pathologies in pillar cells. These data show similarities between this p27(Kip1) mutation and another, previously reported null allele of this gene, and suggest that reducing the inhibition on the cell cycle in the organ of Corti leads to pathology and dysfunction. Manipulations to regulate the time and place of p27 inhibition will be necessary for inducing functionally useful hair cell regeneration.

Animals↗
PubMed2004

Hearing loss following Gata3 haploinsufficiency is caused by cochlear disorder.

Patients with HDR syndrome suffer from hypoparathyroidism, deafness, and renal dysplasia due to a heterozygous deletion of the transcription factor GATA3. Since GATA3 is prominently expressed in both the inner ear and different parts of the auditory nervous system, it is not clear whether the deafness in HDR patients is caused by peripheral and/or central deficits. Therefore, we have created and examined heterozygous Gata3 knockout mice. Auditory brainstem response (ABR) thresholds of alert heterozygous Gata3 mice, analyzed from 1 to 19 months of age, showed a hearing loss of 30 dB compared to wild-type littermates. Neither physiological nor morphological abnormalities were found in the brainstem, cerebral cortex, the outer or the middle ear. In contrast, cochleae of heterozygous Gata3 mice showed significant progressive morphological degeneration starting with the outer hair cells (OHCs) at the apex and ultimately affecting all hair cells and supporting cells in the entire cochlea. Together, these findings indicate that hearing loss following Gata3 haploinsufficiency is peripheral in origin and that this defect is detectable from early postnatal development and maintains through adulthood.

Acoustic Stimulation↗
PubMed2006

The effects of the glucocorticoid receptor antagonist RU486 and phospholipase A2 inhibitor quinacrine on acoustic injury of the mouse cochlea.

Glucocorticoids are used clinically for the treatment of acoustic injury. However, the protective mechanism of glucocorticoid in acoustic injury has not been completely clarified. Also, the effects of phospholipase A2 (PLA2) on acoustic injury have not been examined to the best of our knowledge. The purpose of the present study was to examine the effects of methylprednisolone, a glucocorticoid receptor inhibitor (RU486) and a phospholipase A2 inhibitor (quinacrine) on cochlear injury induced by acoustic overexposure. Seventy-eight mice were exposed to a 4kHz pure tone at 128dB SPL for 4h. The auditory brainstem response (ABR) was used to examine the hearing thresholds. Cochlear morphology was examined to estimate the outer hair cell loss induced by acoustic overexposure. Methylprednisolone and quinacrine significantly alleviated the hearing threshold shift and hair cell loss induced by acoustic overexposure. RU486 antagonized the protective effect of methylprednisolone. The present findings suggest firstly that glucocorticoids exert protective effects against acoustic injury; secondly, that the protective effect of methylprednisolone was exerted by binding glucocorticoid receptors, and finally that activation of PLA2 may be involved in acoustic injury.

Acoustic Stimulation↗
PubMed2005

Cochlear changes in patients with type 1 diabetes mellitus.

OBJECTIVE: To evaluate the effects of diabetes on cochlear elements in human beings. STUDY DESIGN AND SETTING: Twenty-six temporal bones (mean age, 37.5 years) with type 1 diabetes and 30 age-matched controls were examined by light microscopy. We compared the findings of cochlear vessels, hair cells, spiral ganglion cells, and cochlear lateral walls. RESULTS: In diabetics, the walls of vessels of the basilar membrane (P < 0.001) and vessels of the stria vascularis were (P < 0.01) significantly thicker in all turns and loss of outer hair cells (OHCs) was significantly greater in the lower basal turn (P < 0.01). Atrophy of the stria vascularis in all turns (P < 0.0001) and loss of spiral ligament cells in upper turns (P < 0.01) were significantly higher than controls. No significant difference was obtained in the number of spiral ganglion cells between groups. CONCLUSION: This study suggests that type 1 diabetes mellitus can cause cochlear microangiopathy and subsequently degeneration of cochlear lateral walls and OHCs.

Adolescent↗
PubMed2002

[Cochlear hemorrhage. Unusual cause of sudden sensorineural deafness].

Sudden sensorineural hearing loss (SNHL) caused by intralabyrinthine hemorrhage is a rare entity usually associated to patients with previous pathological factors, such as blood dyscrasias, anticoagulant therapy and local hemorrhagic pathologies. We report the first-published case of sudden-onset deafness due to cochlear hemorrhage in a patient with no previous pathologies. We describe the history, diagnosis and follow-up of this patient in comparison to others previously published.

Adult↗
PubMedDate not supplied

[Immediate acoustic effect of the cochlear fistula in a guinen pig].

INTRODUCTION AND OBJECTIVES: To Evaluate objectively the effect that cochleostomy has in the cochlea as well as the exposition of the estria vascularis, through acoustic otoemissions immediatly after surgery. MATERIAL AND METHODS: Submandibular approach to the guinea pig's middle ear and cochlea. Triming of the timpanic and vestibular first turns and wide exposition of the estria vascularis in the first and second turns. Study of cochlear function through acoustic otoemissions of distortion products. CONCLUSIONS: Guinea Pig is a perfect experimentation animal for surgical work when monitoring functional state of the cochlea. Its acoustic response is similar to the one found in other mammals thoug its response is lower than that reported in other papers. The lack of intracochlear manipulation ensures the lower decrease hearing loss deterioration regarding the findings in the different methods of studying the acousting distortion. RESULTS: There is a decrease of amplitud in the audiograms of distortion for specific frequencies (4 and 6 KHz), located tonotopically near the cochleostomies carried out in the first turn (at the level of scala vestigularis and timpanic). Approadring the cochlea without intracochlear manipulation does not modify greathy the results of audiograms of distortion neither the growth slopes of the response. A lateral approach of the estric vascularis minimising the aggression to labrynth did not cause a significant acoustic deterioration.

Animals↗
PubMed1997

Protein kinase C may be involved in synaptic repair of auditory neuron dendrites after AMPA injury in the cochlea.

A suitable model of sudden deafness occurring after acoustic trauma or ischemia, is obtained in guinea pigs by an acute intracochlear perfusion of 200 microM alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), a glutamate analog. By overloading the AMPA/kainate receptors, located post-synaptically to inner hair cells (IHCs), it induces a massive swelling of primary auditory neuron dendrites, which disconnects the IHCs. This synaptic uncoupling and the resulting hearing loss are followed by a progressive regrowth of dendrites, which make new synapses with IHCs, leading to a functional recovery of auditory responses that is completed after 5 days. Knowing the role of protein kinase C in neuroplastic events, we studied the expression of its isoforms alpha,beta(I,II) and gamma, respectively pre- and post-synaptic, in auditory neurons at various times after AMPA administration. In untreated cochleas, we observed an expression of PKC alpha,beta(I,II) and gamma in cell bodies of primary auditory neurons. After the intracochlear administration of AMPA, both isozymes were transiently overexpressed, with a peak at 3-6 h, followed by a decrease after about 24 h. At this point in time immuno-electron microscopy revealed some regrowing dendrites immunoreactive for PKCgamma. Five days after AMPA, when the auditory responses were restored, PKCgamma levels were still elevated in ganglion cell bodies.

Animals↗
PubMed2000

Management options for acute versus chronic vertigo.

Optimal management of the dizzy patient depends on an accurate diagnosis and knowledge of medical, surgical, and rehabilitative options. Acute vertigo may represent labyrinthine dysfunction treated with medication or a more serious central nervous system process requiring prompt intervention to avoid long-term disability. Chronic vertigo, however, may require surgical or rehabilitative measures for lasting relief. This article outlines the rationale for treating both groups with a variety of therapeutic options.

Acute Disease↗
PubMed1993

Exploration of cochlear function by otoacoustic emissions: relationship to pure-tone audiometry.

The amplitudes, growth functions and detection thresholds of evoked otoacoustic emissions (EOE) were measured in 44 normally hearing subjects and 138 patients with two categories of cochlear dysfunctions: (a) acoustic trauma; and (b) presbycusis. Separate sets of experiments were also performed: (a) detection of stimulus frequency emissions; and (b) click EOE. EOE properties were studied around 2 kHz, 1 kHz and 0.75 kHz (+/- 0.1 kHz). A partial correlation and multivariate analysis was carried out to investigate the relationships between EOE properties and puretone auditory thresholds (from 0.25 to 8 kHz, half-octave steps). For each experiment and each frequency, only one highly significant correlation was found, linearly relating the n kHz EOE threshold with the hearing threshold at 2n kHz: there was a shift of about one octave between EOE amplitudes and audiometric data. This means that EOE thresholds give no direct information about the local cochlear state. A simplified model has been implemented, which assumes that EOE thresholds and amplitudes are proportional to the total number of residual active sites along the organ of Corti, i.e., to the total length of active basilar membrane towards the base of the cochlea. It is shown that this model accounts for the results revealed by the statistical analysis and closely fits the experimental data.

Acoustic Stimulation↗
PubMed1993

Distortion-product otoacoustic emissions in normal and impaired ears: insight into generation processes.

Otoacoustic emissions can be used to study cochlear function in an objective, non-invasive and rapid manner. These and other desirable features of emissions have inspired a significant amount of investigation into the practicalities of utilizing evoked emissions as clinical tests of hearing. Variables which affect the measurement of emissions can be sorted into two major categories consisting of factors affecting either emission generation or expression. The present report consolidates and summarizes recent findings of a series of experiments in our laboratory which address both the generation and expression of transiently evoked and distortion-product otoacoustic emissions. Because these two emission types have the greatest promise of becoming clinically useful, a complete understanding of the factors responsible for their measured properties is particularly important.

Animals↗
PubMed2002

Effect of MRI noise on cochlear function.

A disadvantage of magnetic resonance imaging (MRI) is the high level of noise produced (peaking between 122 dB and 131 dB). We used otoacoustic emissions (OAEs) as a method to quantify the effect of MRI-generated noise on the cochlea. OAEs were measured in 16 patients before and after MRI and in 16 controls. OAEs decreased in patients after MRI, but the controls, who were not exposed to MRI noise, showed no decrease over the same period. The change in OAEs shows a clear effect of MRI noise on cochlear function, despite use of earplugs. The importance of correctly fitted earplugs cannot be underestimated.

Cochlea↗
PubMed2000

Significance of spiral ligament fibrocytes with cochlear inflammation.

It has been recently suggested that the spiral ligament fibrocytes, which interconnect with the basal cells of the stria vascularis via gap junctions, may be critical in maintaining cochlear homeostasis. In animal models of pathological conditions such as labyrinthitis and otitis media, reduced immunostaining for gap junction protein connexin 26 is observed in the spiral ligament. This suggests that disruption of the spiral ligament fibrocytes could be among the causes of cochlear dysfunction due to cochlear inflammation. Cultured spiral ligament fibrocytes have been shown to secrete chemokines and other mediators after stimulation of proinflammatory cytokine TNF-alpha or IL-1beta. Each of these mediators might induce inflammatory cell movement, which would prolong the inflammatory response. It is reasonable that such enhanced biological defense ability could be the cause of spiral ligament fibrocyte damage.

Animals↗