Changes in cochlear microphonic response after Y-ray irradiation of the inner ear of the guinea-pig

Summary The effects of ionizing irradiation on the cochlear microphonic response of guinea-pigs were studied. The cochlear microphonics (CM) of both ears were recorded in a total of 36 animals. Recording was carried out by the differential electrode technique on the basal turn of the cochlea. One week prior to recording, the left ear of each animal had been exposed to 35–70 Gy radiation in increments of 5 Gy. Doses of 40 Gy and above led to a reduction in CM response. After doses of 60 Gy or more, no CM response could be detected. Damage most probably occurred in the outer and inner hair cells.     

The origin of the low-frequency microphonic in the first cochlear turn of guinea-pig

Low-frequency microphonic potentials (100 Hz to 2000 Hz) have been measured in the first turn of the guinea pig cochlea before and after a variety of manipulations of the cochlea. These included ablation of the apical turns, iontophoresis of streptomycin, dc current injection into the first turn, acoustic trauma and two-tone interference with pure tones. These manipulations indicate that the low-frequency microphonic measured in the first turn and at the round window is generated predominantly by the hair cells of this region. It is a convenient and relatively uncomplicated indicator of the integrity of the mechano-electrical transduction process of these cells.     

Increase in cochlear microphonic potential after toluene administration

Human and animal studies have shown that toluene can cause hearing loss. In the rat, the outer hair cells are first disrupted by the ototoxicant. Because of their particular sensitivity to toluene, the cochlear microphonic potential (CMP) was used for monitoring the cochlea activity of anesthetized rats exposed to both noise (band noise centered at 4 kHz) and toluene. In the present experiment, the conditions were specifically designed to study the toluene effects on CMP and not those of its metabolites. To this end, 100-μL injections of a vehicle containing different concentrations of solvent were made into the carotid artery connected to the tested cochlea. Interestingly, an injection of 116.2-mM toluene dramatically increased in the CMP amplitude (4 dB) in response to an 85-dB SPL noise. Moreover, the rise in CMP magnitude was intensity dependent at this concentration suggesting that toluene could inhibit the auditory efferent system involved in the inner-ear or/and middle-ear acoustic reflexes. Because acetylcholine is the neurotransmitter mediated by the auditory efferent bundles, injections of antagonists of cholinergic receptors (AchRs) such as atropine, 4-diphenylacetoxy-N-methylpiperidine-methiodide (mAchR antagonist) and dihydro-β-erythroidine (nAchR antagonist) were also tested in this investigation. They all provoked rises in CMP having amplitudes as large as those obtained with toluene. The results showed for the first time in an in vivo study that toluene mimics the effects of AchR antagonists. It is likely that toluene might modify the response of protective acoustic reflexes.     

Expression of glycoconjugates in the mouse inner ear after prenatal irradiation

Summary Irradiation of the murine fetal inner ear is known to produce damage both to the vestibular and cochlear parts in the adult mouse. Fluorescein-labelled lectins were used to reveal possible differences in the glycoconjugate content between normal and irradiated inner ears. In the vestibular part, the otoconia showed the highest uptake of labelled sugars. This uptake was weaker after irradiation when compared to non-irradiated specimens. The type I hair cells in the ampulla and in the utricle showed a weaker uptake, but no labelling was demonstrated in the type II hair cells compared to the non-irradiated controls. In the cochlear part of the inner ear almost no uptake of fluorescent-binding lectins could be demonstrated in the irradiated groups except for in the tectorial membrane. In the endolymphatic sac no uptake was shown after prenatal irradiation. These findings are discussed and correlated to the already known damage of the inner ear following prenatal irradiation.     

Audiological performance after cochlear implantation in children with inner ear malformations

OBJECTIVES: To prove that cochlear implantation is a beneficial method of rehabilitation in deaf children with malformations of the inner ear. DESIGN: The evaluation of auditory responses to speech (EARS) test battery was performed on the children in this study after an average implant use of 3 years. RESULTS: Individual results of six children with inner ear anomalies receiving cochlear implants are presented in this study. Three of the patients showed an incomplete partition (Mondini dysplasia), one had a cochlear hypoplasia and two suffered from an intraoperative cerebrospinal fluid leak. The majority of the children in this study are successful implant users. Wherever possible, test scores are included and subjective case reports given. CONCLUSIONS: Results are similar to those in children with normal cochleas, therefore inner ear malformations found in as many as 20% of patients with congenital sensorineural hearing loss are no contraindication for cochlear implantation. Nevertheless, factors influencing the success of implantation are multiple, including a thorough preoperative radiological examination, a well-performed surgery and an individually tailored postoperative rehabilitation programme.     

Variability in the depression of cochlear microphonic responses after noise exposure

20 guinea pigs were exposed to a broad band noise (120-140 dB SPL) for short durations. The conditions of stimulation were strictly identical for all animals. Cochlear microphonic responses (CM) were recorded with conventional differential electrodes after each exposure, from the first turn of the cochlea. Variations were observed in the degree of CM depression and also in the alteration of the CM transfer function. The origin of this variability is discussed.     

Development of auditory skills after cochlear implantation in children with inner ear malformations

Conclusions: CI improves hearing thresholds and auditory skills in children with most types of inner ear malformations. However, the development of sound detection skills is not as good as it is in children without inner ear malformations. Objectives: To investigate the influence of inner ear malformations on development of auditory skills after cochlear implantation (CI). Methods: Records of 20 children with inner ear malformations who underwent cochlear implantation before 4 years of age and followed up for more than 2 years were retrospectively reviewed. Hearing thresholds, the Meaningful Auditory Integration Scale (MAIS), and Meaningful Use of Speech Scale (MUSS) scores before and after CI were analyzed and compared with 20 age-matched deaf children who underwent CI. Results: The children with inner ear malformations showed significant improvements in hearing thresholds and the MAIS and MUSS scores 1 year after CI (p?p?p?相似文献   

Two-tone interactions in the cochlear microphonic

Two-tone interactions are explored for the cochlear microphonic (CM) in the guinea pig. Recordings are made from turns one and three using differential electrodes in the perilymphatic space or pipettes placed in scala media through a fenestra over the stria vascularis. We focus on magnitude changes associated with the introduction of appropriate interference tones and on various types of phase shift concomitant with these magnitude variations that have not received documentation in the literature. Based on extensive parametric data, it is suggested that some features of the gross interference phenomenon may be a consequence of the vectorial summation of outputs from contributing hair cell generators. These spatial effects appear to determine phase behavior and the influence of probe frequency on the frequency of maximal interference. In addition, the apparent interval between our defined best frequency (CF) and the frequency of maximal interference is most likely due to an underestimation of CF resulting from phase cancellation between CM-producing hair cell populations. However, after compensating for these spatial effects, several aspects of the CM interference phenomenon seem to be analogous to two-tone suppression in auditory nerve fibers. A direct one-to-one relationship is not implied since the latter reflect the outputs of inner hair cells while CM interference most likely reflects outer hair cell behavior. As a result, the association between suppression and interference must be sought in the process by which outer hair cells influence inner hair cell transduction.     

Role of suppressive interactions in the cochlear microphonic response to wide-band clicks

Cochlear microphonic responses (CM) were recorded from the guinea pig cochlea with conventional differential electrodes implanted in the first and second turns. The CM frequency functions were determined by calculating the Fast Fourier Transform of responses to wide-band clicks. These frequency functions appeared to be dependent upon the spectrum of the click. This effect was interpreted as resulting from suppressive interactions between the various components of the click. It is suggested that such CM interactions are related to corresponding effects reported previously concerning cochlear nerve responses.     

Observations on mastoid versus ear canal recorded cochlear microphonic in newborns and adults

The cochlear microphonic (CM) may play an important role in the diagnosis of auditory neuropathy (AN) in newborns. However, since the CM tends to mirror the waveform of the acoustic stimulus, conscientious recording methodology must be applied to separate true response from artifact. The difficulty in achieving this separation has limited the clinical usefulness of the CM. In an effort to call attention to the importance of recording protocol when measuring the CM, the present study was designed to optimize CM recordings in humans by investigating the following parameters: (1) secondary minus electrode recording site (mastoid versus ear canal [EC]), (2) stimulus parameters, and (3) grounding and shielding conditions. Normative data were collected in full-term newborns (n = 7) and adults (n = 4) with no known risk factors for cochlear or retrocochlear pathology. Results suggest that the CM is easier to separate from stimulus artifact using an EC electrode and toneburst stimuli. In addition, electromagnetic shielding and grounding of the electrode cables and the acoustic transducer were effective in reducing and/or eliminating stimulus artifact. Results from this normative study may be helpful in improving the diagnostic utility of the CM in AN and other hearing-related disorders.     

Preservation of basal inner ear structures in cochlear implantation

The aim of this report was to examine basal trauma in implanted human temporal bones and discuss modified approaches to the basal cochlear turn to avoid destruction of basal cochlear structures. Thirty-three human temporal bones were implanted with four different cochlear implant electrode arrays manufactured by MED-EL using either a caudal approach cochleostomy or round window membrane insertions. All specimens were processed with a special histological technique that allows sectioning of undecalcified bone with the electrode in situ. All bones were evaluated histologically in terms of basal cochlear trauma. Two pathomechanisms of basal trauma could be distinguished and were evaluated separately, buckling of the basal end of the array and trauma by drilling. Using the caudal approach cochleostomy, the total percentage of destructive basal trauma was 48% compared to less than 15% when performing round window membrane insertions. Although it is still unclear whether basal cochlear trauma influences apical cochlear function or not, adapted surgical procedures and no forceful insertion maneuvers should be used when performing cochlear implantations with hearing preservation.     

The influence of inner hair cell loss on the instantaneous frequency of the cochlear microphonic

The purpose of this study was to examine whether outer hair cells (OHCs), inner hair cells and the brainstem auditory pathway are impaired due to a mutation in a gap junction protein, connexin 26 (Cx26), 35delG. Fifty-six individuals, from a village with widespread consanguinity and profound, non-syndromic congenital deafness, due to 35delG mutation, were selected among relatives of deaf people. The individuals were either non-carriers (n=20), heterozygous (n=20) or homozygous (n=16) for the mutation. Distortion product oto-acoustic emissions (DPOAEs) and auditory brainstem evoked potentials (ABEPs) in mutation non-carriers, in heterozygotes (carriers) and in subjects homozygous for the mutation were compared in addition to audiometric evaluation. Most deaf homozygotes had no DPOAEs, except some sporadic responses at 1000, 8000 and 10000 Hz. This was also observed in audiometry which showed profound hearing loss in most cases. Two cases were unique: one had moderate to severe hearing loss and the other had severe to profound hearing loss. A significant difference was found between non-carriers and carriers of 35delG: non-carriers had larger DPOAE responses than heterozygotes at all frequencies. The prevalence of responses got lower with higher frequencies in both groups, but between 6000 and 10000 Hz 50-70% of the carriers had no DPOAE responses, compared to 30-60% of non-carriers. In both groups responses diminished with age, but no significant interaction was found between age and the genetic group. ABEPs among homozygotes were variable: in most homozygotes ABEPs were absent or partial (waves III, V) with prolonged latencies, but two subjects had ABEPs within normal limits, in one ear. ABEPs were normal with no differences between carriers and non-carriers. We suggest that OHC function is affected by the 35delG mutation in Cx26. In addition, the hearing of carriers of this mutation may be impaired at very high frequencies (8000-10000 Hz), which are not assessed in routine audiometry or ABEP testing.     

Changes in cochlear microphonic and neural sensitivity produced by acoustic trauma

The low-frequency (200 Hz) microphonic potentials at the round window and in the organ of Corti of the first turn of the guinea pig cochlea have been measured before and after acoustic overstimulation. Reductions in the amplitude of this microphonic after loud sound are highly correlated with neural threshold elevation in this region. The fall in the microphonic amplitude appears due to an inactivation of mechano-electrical transduction channels at the apex of the outer hair cells into a closed state. These results are consistent with the idea that the current through the outer hair cells controls the mechanical sensitivity of the organ of Corti, and that the temporary loss of mechanical and neural sensitivity following loud sound is due to a simple inactivation of the mechano-electrical transduction channels.     

电诱发听性脑干反应和电诱发镫骨肌反射阈值在内耳畸形儿童人工耳蜗植入术后调机中的运用

目的　探讨内耳畸形小儿人工耳蜗植入手术后,植入体电诱发听性脑干反应（electrically evoked auditory brainstem responses,EABR）、电诱发镫骨肌反射阈值（electrically evoked stapedius reflex threshold,ESRT）的变化特点及规律,以指导术后设备调试。方法　将88例澳大利亚Cochlear Nucleus24型人工耳蜗植入手术患儿分为耳蜗形态正常组与内耳畸形组,测试手术后1年内不同时期EABR和ESRT值,术后1年运用行为测试法检测主观阈值（T值）和最大舒适阈（C值）,分析特点及变化规律。结果  内耳畸形组患儿术后不同时期EABR和ESRT阈值较正常组高（P＜0.05）,两组EABR和ESRT阈值变化趋势相同,总的趋势是低频值较低,高频值较高,术后1年EABR和ESRT阈值逐渐增高;两组EABR与T值显著相关,ESRT与C值显著相关。结论　内耳畸形组人工耳蜗植入手术后EABR和ESRT阈值变化规律及特点与正常组患儿相同,阈值可用于指导内耳畸形人工耳蜗植入者手术后设备的调试。     

Antigen-specific immune response in the inner ear

The specificity of inner ear immune responses was investigated by challenging each inner ear of presensitized animals with different antigens. Animals presensitized systemically with keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) were challenged with KLH in the right and BSA in the left inner ears. Two weeks later perilymph anti-KLH levels were increased significantly in the right inner ears compared to the levels in the left inner ears. In contrast, perilymph anti-BSA levels were increased significantly in the left inner ears compared to the levels in the right inner ears. These results suggested that the rise in perilymph antibody following inner ear antigen challenge was predominantly the result of an antigen-specific immune response in the inner ear and not simply the result of an increase in vascular permeability of serum contamination from the experimental procedure itself.