Inner Ear Hearing Loss Research Articles

Claudin7b is required for the formation and function of inner ear in zebrafish.

Zebrafish has become an excellent model for studying the development and function of inner ear. We report here a zebrafish line in which claudin 7b (cldn7b) locus is interrupted by a Tol2 transposon at its first intron. The homozygous mutants have enlarged otocysts, smaller or no otoliths, slowly formed semicircular canals, and insensitiveness to sound stimulation. These abnormal phenotypes and hearing loss of inner ear could be mostly rescued by injection of cldn7b-mRNA into one-cell stage homozygous mutant embryos. Mechanistically, cldn7b-deficiency interrupted the formation of apical junction complexes (AJCs) in otic epithelial cells of inner ear and the ion-homeostasis of endolymph, which then led to the loss of proper contact between otoliths and normally developed hair cells in utricle and saccule or aberrant mechanosensory transduction. Thus, Cldn7b is essential for the formation and proper function of inner ear through its unique role in keeping an initial integrity of otic epithelia during zebrafish embryogenesis.

Stapedius Reflex in Functional Hearing Loss

Functional and inner-ear hearing loss must be differentiated to diagnose functional hearing loss based only on the stapedius reflex (SR). We statistically compared values obtained by subtracting the pure-tone audiometry threshold from the SR threshold in those with functional or inner-ear hearing loss. At hearing of less than 60 dB HL, no significant difference was seen between those with functional and inner-ear hearing loss. At 70 dB HL or 80 dB HL, values were statistically lower in those with functional hearing loss than with inner-ear hearing loss (p<0.01). At 90 dB HL or more, the value was 0 or less in many with functional hearing loss. Evaluating hearing loss using the SR alone is therefore not possible in functional hearing loss at less than 60 dB HL. It is possible, however, to diagnose some cases of functional hearing loss at 70 dB HL or 80 dB HL and in many cases of functional hearing loss of 90 dB HL or more.

遅発性内リンパ水腫について―ことにメニエール病との比較において―

Delayed endolymphatic hydrops (DEH) is a Meniere’s syndrome that typically occurs in patients suffering from longstanding unilateral profound inner-ear hearing loss. Approximately 55 to 65% of the hearing loss preceding DEH is due to juvenile unilateral profound deafness (early childhood unilateral profound sensorineural hearing loss of unknown etiology). The incidence of ipsilateral DEH (approximately 60%), in which the ear with profound hearing loss suffers progressive endolymphatic hydrops, is higher than that of the contralateral type of DEH (about 40%), in which the formation of progressive endolymphatic hydrops takes place in the ear opposite to the previously deafened ear. The prevalence of DEH in the general population (23 or less per 100,000) is similar to that of definitive Meniere’s disease, and the distribution of age at onset of DEH closely resembles that of Meniere’s disease except for some patients with childhood onset of DEH. Further, the rate of patients with the contralateral type of DEH (about 40%, although the rate is about 15% if the contralateral type is restricted to patients showing typical Meniere’s symptoms) is similar to that of patients with bilateral Meniere’s disease (about 40%, with a rate of about 14% if Meniere’s disease in the second ear is restricted to definitive Meniere’s disease). Since DEH is closely similar to Meniere’s disease not only in symptoms, but also in many clinical-statistical characteristics, the diseases may be identical in pathogenesis and the pathophysiology of progressive endolymphatic hydrops, although the two conditions have different etiologies.

A recovery from enhancement of activation in auditory cortex of patients with idiopathic sudden sensorineural hearing loss

Objective We previously reported enhanced activation of auditory cortex in patients with bilateral chronic inner-ear hearing loss. To determine whether this enhancement can exhibit a short-term alteration, we measured auditory evoked magnetic fields (AEFs) in patients with idiopathic sudden sensorineural hearing loss (ISSHL) in the acute phase (AP) and recovery phases (RPs). Methods We recorded AEFs in two unilateral ISSHL patients at three time points (AP, RP1, and RP2) using a whole-head neuromagnetometer. Tone bursts of 1 kHz were presented monaurally to the affected and healthy ear at four different intensities (40–70 dB HL). Results Both patients showed the enhancement of N100 m moment at AP and not at RPs in response to the affected ear stimulation, and stronger N100 m moment in ipsilateral than contralateral hemisphere in response to the healthy ear stimulation at AP. Conclusions Enhancement of N100 m amplitude occurs in ISSHL patients and disappears on the scale of days. Enhancement of activity in the auditory cortex derived from inner-ear hearing loss can thus exhibit short-term change. Significance The results of this study provide first evidence for a recovery from enhancement of activation in the auditory cortex following injury of peripheral hearing organ.

Sound-induced activation of auditory cortices in patients with inner-ear hearing loss

Studies on sound-induced activation of auditory cortices in patients with inner-ear hearing loss were reviewed. First, we recorded auditory evoked magnetic fields (AEFs) by presenting 1-kHz pure tone at four different intensities in normal subjects and in patients with inner-ear hearing loss. Increment of dipole moment of N100m was more rapid according to the stimulus intensity in patients compared with that in healthy subjects. Next, we measured AEFs by presenting white noise and speech-related sounds. AEF responses in patients were less dependent on the acoustic structure of the stimuli than in normal subjects. Although the N100m moments were larger in the right hemisphere in normal subjects, such interhemispheric differences were not identified in the patient group. In the third study, we made two word lists, well-perceived and poorly perceived words, and measured rCBF during their monaural presentation. Well-perceived words activated bilateral temporal lobes and left angular gyrus (AG), while poorly perceived words activated only the temporal lobe contralateral to the stimulated ear and little or no activation was observed in AG.

Selective aspects of human pathology in high-tone hearing loss of the aging inner ear

Accompanied with aging, the thresholds for high frequency sounds may elevate and result in a progressive hearing loss described as presbycusis. Based on correlations between audiometric measures of aged patients and histologic findings garnered from postmortem examinations, four types of presbycusis have been characterized: sensory–neural, neural, strial, and conductive [Schuknecht, H.F., Gacek, M.R., 1993. Ann. Otol. Rhinol. Laryngol. 102, 1–16]. Otopathologic changes to the inner ear as a direct function of age, however, remain controversial. The focus of this investigation involves the pathological impact on remaining sensory structures in patients having sensory–neural degeneration. The current study presents seven human temporal bones extracted from patients aged 53–67 years with high-tone hearing loss and with no known history of extraordinary environmental events involving head or noise trauma, acoustic overstimulation, or ototoxicity. In previously published findings of these specimens, all but one temporal bone failed to demonstrate a meaningful correlation between audiometric measurements and loss of functional hair cell populations with secondary retrograde degeneration of nerve fibers. Using the block surface method, electron microscopic micrographs demonstrate ultrastructural changes in the cuticular plate, stereocilia, pillar cells, stria vascularis, and the spiral ligament. In all pathological specimens, the greatest incidence of degeneration was seen at the cuticular plate. Conclusively, our findings present three implications in the aging human cochlea: firstly, audiometric measures that represent a high-tone hearing loss may take various forms with respect to ultrastructural patterns of degeneration and surviving structures; secondly, the incidence of lipofuscin and lysosome granules does not correlate with the degree of hearing loss and; thirdly, as shown only in guinea pigs [Anniko, M., 1988. Scanning Microsc. 2, 1035–1041], high-tone hearing loss can be associated with deformation of the cuticular plate.

Vector analysis of auditory brain-stem response (ABR) in patients with developmental disorders

Studies on sound-induced activation of auditory cortices in patients with inner-ear hearing loss were reviewed. First, we recorded auditory evoked magnetic fields (AEFs) by presenting 1-kHz pure tone at four different intensities in normal subjects and in patients with inner-ear hearing loss. Increment of dipole moment of N100m was more rapid according to the stimulus intensity in patients compared with that in healthy subjects. Next, we measured AEFs by presenting white noise and speech-related sounds. AEF responses in patients were less dependent on the acoustic structure of the stimuli than in normal subjects. Although the N100m moments were larger in the right hemisphere in normal subjects, such interhemispheric differences were not identified in the patient group. In the third study, we made two word lists, well-perceived and poorly perceived words, and measured rCBF during their monaural presentation. Well-perceived words activated bilateral temporal lobes and left angular gyrus (AG), while poorly perceived words activated only the temporal lobe contralateral to the stimulated ear and little or no activation was observed in AG.