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PubMedDate not supplied

Electrocochleography (ECochG) and brain stem evoked response recordings (BSER) in the diagnosis of acoustic neuromas.

Evaluation of the auditory evoked responses has hitherto been the most important otoneurological method for early diagnosis of acoustic neuromas. ECochG enables to recognize serious damage to the first neurone. Criteria are: increased latency of the action potential (N1) and a low amplitude of the action potential relative to a high amplitude of the microphonic potential. BSER is a more sensitive indicator for functional deficiency in the first neurone, especially by evaluating interaural differences of the interpeak intervals (IPI) I-V and I-III. Problems arising when wave I cannot be clearly detected can be overcome by combining ECochG and BSER and evaluating the latency N1-V or perhaps in a better way by applying derivation of BSER between promontory and vertex. In 24 of 25 patients with indistinctly defined wave I in the standard recording, evaluation was possible in promontory BSER.

Audiometry, Evoked Response↗
PubMed1980

The origin of tuning in turtle cochlear hair cells.

Intracellular recordings were made from single hair cells in an in vitro preparation of the cochlea of the turtle. The response of each hair cell to sound stimuli was sharply tuned with a characteristic frequency which was related to the position of the cell along the basilar membrane. When small current steps were injected through the recording electrode, the hair cell potential exhibited damped oscillations at the cell's characteristic frequency. We suggest that the property of the hair cells which is responsible for this oscillatory behaviour could make a major contribution to their acoustic tuning.

Acoustic Stimulation↗
PubMed1981

[Medium-latency acoustically evoked brain potentials used for examination of the auditory pathway (author's transl)].

Potentials of the 10-15 ms latency range evoked by acoustic clicks and Gauss-shaped tone bursts habe been investigated in normal hearing adults, 20 patients with cochlear damages, and 6 cases of temporal lobe processes. Methods and results are compared to those of brain stem audiometry. Mean and standard latency ranges are calculated for the different peaks (Fig. 1). Amplitudes should be used only for side difference evaluation in the same patient, because of their big interindividual variation. In cases of profound high frequency hearing loss (Fig. 2) medium-latency potentials yield true threshold values in the low frequency range, where brainstem potentials are failing. The medium latency potentials show a substantial decrease of amplitude for stimuli contralateral to the damaged side (Fig. 3). So this method can be a functional hearing test to detect or at least suspect temporal damages.

Audiometry↗
PubMed2000

Neither endocochlear potential nor tegmentum vasculosum are affected in hearing impaired belgian waterslager canaries.

We previously showed that the Belgian Waterslager canary strain is affected by a hereditary hearing loss that is associated with a reduced number of hair cells and hair cell pathologies in the basilar papilla. Since hair cell pathologies were also present in the sacculus, Weisleder et al. (1994) suggested that these birds are afflicted by Scheibe's like dysplasia, a cochleo-saccular defect. In mammals, cochleo-saccular defects are characterized primarily by the lack of an endocochlear potential and abnormalities in the Stria vascularis which only secondarily lead to hair cell loss (Steel and Bock, 1983; Steel, 1994; 1995). Here we report the endocochlear potential of six ears from three non-Belgian Waterslager canaries and three ears of two Belgian Waterslager canaries to decide if Waterslager canaries are affected by a cochleo-saccular or by a neuroepithelial defect. The mean endocochlear potential was 17.6+/-2. 5 mV in the non-Waterslager canaries and 20.3+/-0.6 mV in Waterslager canaries. In addition, and consistent with the presence of a normal endocochlear potential, light microscopy of the tegmentum vasculosum provided no evidence for pathology. These data show that Belgian Waterslager canaries are affected by a neuroepithelial rather than a cochleo-saccular inner ear defect.

Animals↗
PubMed1991

A review of otoacoustic emissions.

Otoacoustic emissions measured in the external ear canal describe responses that the cochlea generates in the form of acoustic energy. For the convenience of discussing their principal features, emitted responses can be classified into several categories according to the type of stimulation used to evoke them. On this basis, four distinct but interrelated classes can be distinguished including spontaneous, transiently evoked, stimulus-frequency, and distortion-product otoacoustic emissions. The present review details the findings that have been described for each emission type according to this classification schema. Additionally, the known features of emitted responses are discussed for both normally hearing and hearing-impaired humans and experimental animals, and with respect to their potential clinical applications. The findings reviewed here clearly indicate that future studies of otoacoustic emissions will significantly increase our understanding of the basic mechanisms of cochlear function while, at the same time, provide a new and important clinical tool.

Animals↗
PubMedDate not supplied

Effect of increased perilymphatic pressure on endocochlear potential.

A study was done to determine how increased fluid pressure in the inner ear influences cochlear blood flow. Hydrostatic pressure was applied to the scala vestibuli or scala tympani in guinea pigs. Endocochlear potential, which is sensitive to the lack of oxygen, was measured through the round window membrane or through the stria vascularis. Cochlear blood flow was confirmed by intravenous injection of India ink. When the perilymphatic pressure was raised to a relatively high level, endocochlear potential decreased, ina similar way as in response to anoxia, because of the cessation of the cochlear blood flow. This change was completely reversible upon applications of pressure for brief periods of time. We consider that the cochlear blood flow ceases when the fluid pressure reaches the level of intracochlear arterial pressure.

Animals↗
PubMed1997

[Protective effect of ciliary neurotrophic factor against the ototoxicity of gentamicin in guinea pigs].

The effect of ciliary neurotrophic factor (CNTF) on gentamycin induced deafness was observed by Preyer's reflex, auditory brainstem evoked potential, bioelectric response of the cochlea and histomorphological examination of surface preparation of cochlea. It was found that CNTF was capable of reducing ototoxicity of gentamicin in guinea pigs, thus protecting hair cells of cochlea and auditory nerves.

Animals↗
PubMed1985

Slow depolarizing response from supporting cells in the goldfish saccule.

Potentials were recorded intra- and extracellularly from the saccular macula of anaesthetized goldfish. Sound-evoked responses recorded intracellularly consisted of positive microphonic potentials, nerve responses and a slow depolarizing potential. Of these three potentials, only the slow depolarization was peculiar to intracellular records. It rose and fell exponentially with time constants of about 30 and 200 ms, respectively. The amplitude of slow depolarization never exceeded 5-6 mV, even when a loud sound was applied. It is argued that the impaled cell was a supporting cell and the slow depolarization presumably reflected a rise of extracellular K+ concentration, during sound stimulation. It was also shown that this nerve response, which was resistant to the action of tetrodotoxin, probably represented the excitatory post-synaptic current that flows into the dendrites of afferent fibres. Efferent stimulation suppressed the nerve response.

Acoustic Maculae↗
PubMed1980

Permeability to potassium of the endolymph-perilymph barrier and its possible relation to hair cell function.

The endocochlear potential and potassium concentrations in endolymph and perilymph were simultaneously measured in the basal turn of the guinea pig cochlea with double-barreled K+ selective electrodes. The K+ conductance and K+ permeability coefficient of the endolymph-perilymph barrier were calculated from the rate of change of endolymph K+ concentration relative to the K+ electrochemical potential difference recorded during permanent anoxia. When anoxia was induced in guinea pigs treated with kanamycin, the rate of decline of the electrochemical potential difference for K+ between the endolymph and perilymph was reduced when compared to normal guinea pigs. In guinea pigs exposed to broad band noise at 115 dBA for periods from 11-15 days, the rate of decline of the electrochemical potential difference for K+ across the endolymph-perilymph barrier was reduced but not to the extent found in guinea pigs treated with kanamycin. The K+ conductance and K+ permeability coefficient of the endolymph-perilymph barrier showed substantial decreases in noise exposed and kanamycin treated guinea pigs, as compared to normal guinea pigs. The magnitude of decrease of K+ permeability of the endolymph-perilymph barrier by noise or kanamycin was correlated with suppression of the maximum output of the cochlear microphonic.

Animals↗
PubMed1984

Relationship of gross cochlear potentials to hair cell pathology in the waltzing guinea pig.

Electrophysiological recordings were made from the hearing organs of young waltzing guinea pigs of different ages. Age-related morphological changes in the cochleas of the same animals were studied with scanning and transmission electron microscopy. Results were compared with the results of studying the cochleas of normal guinea pigs of the same age. Waltzing guinea pigs are born with a hearing loss, as can be concluded from the magnitude of the whole-nerve action potential and their lower than normal summating potentials. However, their cochlear microphonics are nearly normal until the time in the degeneration process when hair cells start to disappear. This degeneration process begins at the tops of the hair cells and is evident upon electron microscopical examination of these structures.

Action Potentials↗
PubMed1998

Spatial resolution of cochlear implants: the electrical field and excitation of auditory afferents.

This paper investigates the spatial resolution of electrical intracochlear stimulation in order to enable further refinement of cochlear implants. For this purpose electrical potential distributions around a conventional human intracochlear electrode (NUCLEUS-22) were measured in a tank, in cat cadaver cochleae and in living cat cochleae. Potential gradients were calculated where of importance. The values were compared to spatial tuning curves from cat primary auditory afferents in electrical mono-, bi-, and various tripolar stimulation modes. Finally, a lumped element model was developed to elucidate the single fiber data. Tank potential measurements show the principal features of the different stimulation modes but are not sufficient to explain all the features of experimental data from single fibers. Intracochlear potential measurements indicate an increase in spatial resolution in an apical direction. The single fiber data also confirm that a tripolar stimulus configuration provides significantly better spatial resolution than any other stimulation mode presently in use.

Animals↗
PubMed2003

Purinergic modulation of cochlear partition resistance and its effect on the endocochlear potential in the Guinea pig.

Introduction of adenosine 5'-triphosphate (ATP) into the endolymphatic compartment of the guinea-pig cochlea decreases the endocochlear potential (EP). To determine if this is due to an ATP-induced change in compartment resistance, the cochlear partition resistance (CoPR) was measured using constant current injections into scala media before, during, and after microinjection of ATP into the same compartment. The CoPR (mean = 3.13 +/- 0.13 kOmega) decreased with ATP in a dose-dependent manner (25.1 +/- 3.0% decrease in relation to baseline values) and this was linearly correlated ( R(2) = 0.91) to the magnitude of the ATP-induced decline in EP (41.6 +/- 7.0% decline in relation to the baseline). Pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, a P2X receptor antagonist) injected prior to ATP application blocked this ATP-induced reduction in EP and CoPR. This indicates that ATP-gated ion channels (P2X receptors) provide a latent shunt capable of regulating the majority of the electrical potential across the luminal surface of the sensory hair cells, which is necessary for sound transduction. The results suggest a novel sound transduction regulatory mechanism, which, via extracellular ATP, has the capability of adjusting hearing sensitivity.

Adenosine Triphosphate↗
PubMed1989

Effects of nitrogen mustard-N-oxide on ionic activities of inner ear fluid and ionic permeabilities of the cochlear partition in the guinea pig.

The effect of nitrogen mustard-N-oxide (NMO) on the endocochlear potential (EP) was investigated from the aspect of the ion concentrations and permeabilities in the cochlea. Compared with the untreated animals, in NMO-treated animals 20 to 30 hours after administration, the EP was decreased (30.8 +/- 3.5 mV in NMO versus 82.4 +/- 1.6 mV in control), the K+ concentration in perilymph of the scala tympani was increased (8.2 +/- 1.0 mM versus 5.3 +/- 0.7 mM), the K+ concentration in endolymph was decreased (128.5 +/- 10.6 mM versus 157.9 +/- 7.9 mM), and the Na+ concentration in endolymph was increased (9.6 +/- 3.6 mM versus 2.5 +/- 0.4 mM). The permeability coefficient for Na+ of the cochlear partition in the NMO-treated animals significantly decreased, while that for Cl- significantly increased. The negative EP, which presumably exists in the normal state, diminished further (-2.7 mV versus -27.8 mV), and the calculated electrogenic potential of the EP was depressed remarkably (33.5 mV versus 110.2 mV). The results suggest that the effects of NMO involved changes in ion permeabilities of the partition and the inhibition of electrogenic transport processes in the cochlea.

Animals↗
PubMed1980

Ototoxicity of kanamycin in developing rats: relationship with the onset of the auditory function.

In order to test the relationship between the ototoxicity of kanamycin and the onset of the auditory function, two groups of developing rats were intoxicated with kanamycin before and after the period of onset of cochlear potentials (8th postnatal day). Kanamycin was shown to have a weak ototoxic effect before the 8th postnatal day and a strong ototoxic effect after this period. These results indicate a critical period of sensitivity to ototoxic antibiotics during auditory development.

Acoustic Stimulation↗
PubMed1983

Mechanism of the production of the negative endocochlear DC potential in the guinea pig.

Changes in endocochlear DC potential (EP) and potassium ion concentrations in endolymph were measured simultaneously during anoxia or during perfusion of the perilymphatic space with furosemide, 10(-2)M, in normal and kanamycin-deafened guinea pigs. The potassium ion conductance (Gk) through the cochlear partitions was calculated. Thirty minutes after the onset of anoxia, the Gk is 22.1 microM/min/mV in normal guinea pigs and 4.8 microM/min/mV in kanamycin-deafened guinea pigs. At that time the EP is -29.5 mV in normal guinea pigs and 1.4 mV in kanamycin-deafened guinea pigs. In the early stage of anoxia the rate of potassium ion concentration decrease in the endolymph per unit time is greater in normal guinea pigs than in kanamycin-deafened guinea pigs. These results suggest a rapid increase in the permeability of potassium ions in the organ of Corti in the early stage of anoxia might produce a large negative potassium ion diffusion potential or negative EP in normal guinea pigs and the failure to develop the negative EP in kanamycin-deafened guinea pigs might be due to the lack of such a rapid increase in the permeability because of the loss of the hair cells.

Animals↗
PubMedDate not supplied

Neurophysiologic assessment of endolymphatic hydrops.

An electrophysiological method for assessing endolymphatic hydrops of the cochlea in an animal model of Meniere's disease is described. Eighth nerve gross action potentials (AP) were evoked by tone bursts presented at discrete phases of a simultaneously delivered 50-Hz pure tone. Hydropic cochleas showed significantly less modulation of AP amplitude and latency than normal cochleas. This method may be useful in objectively evaluating Meniere's disease with electrocochleography.

Animals↗
PubMed1994

Osmotically induced pressure difference in the cochlea and its effect on cochlear potentials.

The electrophysiological effects observed during scala tympani displacements in low-frequency biasing experiments, an increase of the summating potential (SP) together with a decrease of the compound action potential (CAP), correlate well with the effects found in guinea pigs with evoked endolymphatic hydrops. This contributes to the hypothesis that displacement of the basilar membrane underlies the changes found in endolymphatic hydrops. A major difference between both experimental situations is that in low-frequency biasing the basilar membrane is continuously moving, whereas in hydrops the hypothesized displacement would be static. To evaluate the importance of this difference, experiments were performed which attempted to evoke a static displacement of the basilar membrane by perfusing the perilymphatic spaces with perfusates of various osmolalities. Perfusion with hypotonic perfusate (183 mOsm/kg) increased the SP and decreased the CAP (4 kHz stimulation) whereas perfusion with a hypertonic perfusate (397 mOsm/kg) decreased both these potentials. The cochlear microphonics were hardly affected. These data demonstrate that both experimental situations (biasing, i.e. dynamic displacement and osmotic pressure, i.e. static displacement) cause similar changes in the SP and the CAP and the data support the hypothesis that basilar membrane displacement towards scala tympani is an important contributing factor to the electrophysiologic changes in endolymphatic hydrops.

Acoustic Stimulation↗
PubMed1981

The effect of transient anoxia upon the cochlear potentials.

To contribute to the analysis of the electrocochleographical findings in humans, the reversibility of the cochlear potentials (the AP, CM, and SP) after transient anoxia was examined using 24 albino guinea pigs. The durations of anoxia ranged from 5 to 120 min, and the AP, CM and SP were examined one hour after restoration of the blood supply. The mildest form of cochlear damage after transient anoxia was the disappearance of the L-part of the AP and the severest was the complete abolition of these potentials. The severity of the damage closely correlated with the duration of anoxia. The AP was poorer in reversibility than the CM and the SP. These results were analysed and discussed in the light of literature on clinical and basic studies.

Animals↗