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Results for “Cochlear Microphonic Potentials”

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PubMed1992

Coherence of frequency modulation is encoded by cochlear-generated distortion.

Nonlinearities of the peripheral auditory system generate distortion products which present to the central auditory system as apparent acoustic stimuli. The frequency and amplitude of distortion products reflect the frequency, phase and amplitude relationship of the components of a complex stimulus. When the stimulus consists of harmonically-related primaries, the amplitudes of the major distortion products are a function of the relative phase of the presented (primary) tones. We have previously shown (McAnally and Calford, 1990) that the variation of amplitude of the distortion as a function of the relative phase of a pair of harmonically-related primaries is well modelled as a function of the interaction of the multiple modes of distortion which fall at the same frequency (e.g. difference frequency and cubic difference frequency). A possibility raised by this result is that coherence of frequency modulation (that which maintains harmonicity) could be encoded in the amplitude of distortion. This was examined in measurements of both the cochlear microphonic potential (CM) and the responses of auditory nerve fibres in anaesthetized cats. Very small deviations from coherence of frequency modulation produced changes in the amplitude of the CM potential at the frequency of distortion. Also the discharges of auditory nerve fibres tuned to the frequency of distortion were found to be modulated at the same frequency as the amplitude changes observed in the CM. There was no variation in distortion amplitude in the CM and no modulation of auditory nerve discharges when primaries were frequency modulated coherently. It is suggested that amplitude modulation of distortion gives the auditory system its demonstrated sensitivity to minor departures from coherence of frequency-modulated, harmonically-related tones.

Acoustic Stimulation↗

PubMed1980

Analysis of auditory nerve-brainstem responses (ABR) in neonates and very young infants.

Auditory nerve-brainstem responses (ABR) to click stimuli were recorded in 26 normal infants when they were neonates and again in the same infants when they were 3 months old. The cochlear microphonic potential was also recorded in several of the neonates. The following response parameters were studied: latency and amplitude of the auditory nerve response, amplitude of the brainstem response elicited from the region of the interior colliculus, the ratio of the amplitudes of these two waves and brainstem transmission time (BTT): the time interval between these two responses. It was found that the auditory nerve response is only slightly prolonged in neonates with respect to adults and shortens by a small amount from birth to the age of 3 months. The latency of the auditory nerve response in neonates is only about 0.3 ms longer than in adults. BTT is longest in neonates and shortens significantly in 3-month-old infants.

Acoustic Stimulation↗

PubMed1995

The effect of contralateral stimulation on cochlear resonance and damping in the mustached bat: the role of the medial efferent system.

In the unanesthetized mustached bat, stimulation of the ear with an acoustic transient produces damped oscillations which are evident in the cochlear microphonic potential. In this report we demonstrate how the decay time of these oscillations is affected by broadband noise presented to the contralateral ear (CLN). In the absence of CLN, the mean decay time was 1.94 +/- 0.23 ms, but during the presentation of CLN the decay time consistently decreased. The changes were finely graded, the higher the CLN, the greater the change. The effect could be maintained at a constant level for extended periods of time and this was evident when the CLN exceeded 40 dB SPL. The latency of the reflex for 64 dB noise was about 11 ms and near maximum changes occurred within 15 ms of CLN onset. Sectioning medial efferent nerve fibers in the floor of the fourth ventricle or the administration of a single dose of gentamicin eliminated changes produced by CLN. The prominence of CM responses to damped oscillations and the robust changes in response to CLN make the mustached bat an excellent model for studying the influence of the medial efferent system on cochlear mechanics.

Acoustic Stimulation↗

PubMed1996

Inhibitory effect of erythromycin on ion transport by stria vascularis and vestibular dark cells.

A previous study showed that systemic administration of erythromycin caused a reversible decline in the endocochlear and cochlear microphonic potentials. Those data were thought to suggest that erythromycin caused hearing loss by interference with ion transport processes in the stria vascularis. The present study was undertaken to test this hypothesis by measuring the effects of erythromycin perfused on either the apical or basolateral side on the transepithelial short circuit current (Isc), a measure of the K+ secretion rate. Isc was measured from preparations of strial marginal cells and the homologous vestibular dark cells in vitro with a micro-Ussing chamber. Erythromycin was found to have no effect when perfused on the apical side but to cause a reversible decrease in Isc when perfused on the basolateral side for both epithelia. These data are consistent with the notion that at least one ototoxic effect of erythromycin is the inhibition of K+ secretion in the inner ear.

Animals↗

PubMed1998

Tonic efferent-induced cochlear damping in roosting and echolocating mustached bats.

The activity of the medial olivocochlear (MOC) efferent system in mustached bats, Pteronotus p. parnellii, was studied by monitoring changes in the mechanical properties of the cochlea. The changing properties were expressed by the decay time (DT) of cochlear microphonic potentials produced by transient-induced ringing (Henson et al., 1995). Tape-recorded roost noise (biosonar and communication sounds) produced sudden, marked decreases in DT when presented to the contralateral ear of animals adapted to the quiet. When the animals were first removed from their roosts the DT was relatively short (1.2-1.5 ms) but this gradually lengthened by about 0.5-1.0 ms as they rested in a quiet chamber. The time required to reach a stable, quiet-adapted state after noise exposure varied with SPL and exposure time; in many experiments recovery was in the range of 90-120 min. When quiet-adapted bats were isolated and allowed to fly and echolocate for 20 min, the DTs measured within a few minutes after the end of the flight were also short and only slowly returned to longer preflight values. The administration of a single dose of gentamicin, which blocks MOC effects, greatly reduced the amount of suppression (damping) observed after periods of noise and echolocation sound exposure. We conclude that tonic MOC activity is induced by the natural vocalizations and roost noise and this activity probably regulates and protects the highly resonant cochlear partition.

Adaptation, Physiological↗

PubMed1988

Contributions of the middle ear to the development of function in the cochlea.

The contribution of middle ear immaturities to the development of cochlear microphonic potential (CM) responses was studied throughout the ontogeny of auditory function in the Mongolian gerbil. CM produced by direct mechanical stimulation of the stapes was compared with CM generated by acoustic stimulation of the intact ear at various postnatal ages. The results indicated that during development acoustically generated CM reflects middle ear as well as inner ear maturational factors. With direct stapes driving, CM was first elicited at 10 days after birth (DAB), two days earlier than with acoustic stimulation. Controlling for the contributions of middle ear immaturity, maturation of the inner ear accounted for approximately a 75 dB improvement in CM thresholds between 10 and 18 DAB. Comparisons between the results obtained with the acoustic and stapes driving stimulation protocols suggested that the major maturational changes in the middle ear conduction apparatus occurred between 14 and 16 DAB. This period was associated with the final stages of resorption of middle ear mesenchyme and ossicular ossification. Before 16 DAB, acoustically evoked CM thresholds reflect approximately a 25 dB loss in sensitivity due to middle ear immaturity.

Acoustic Stimulation↗

PubMed1982

Calcium antagonism and reversibility of gentamicin-induced loss of cochlear microphonics in the guinea pig.

The perilymphatic space of the guinea pig cochlea was perfused with various concentrations of Ca2+, Mg2+ and gentamicin. Cochlear microphonic potentials (CM) were essentially stable when solutions contained 1 mM Ca2+ plus 2 mM Mg2+, 1 mM Ca2+ and no Mg2+ or when both Ca2+ and Mg2+ were omitted. In the absence of Ca2+, the presence of 2 mM Mg2+ or 1 mM EGTA markedly decreased CM. Addition of 3 mM gentamicin lowered CM, the magnitude of the effect depending on the concentration of Ca2+ present. Ten mM Ca2+ eliminated the action of the drug. In the absence of Ca2+, the effects of Mg2+ and gentamicin were additive. When the application of gentamicin was followed by perfusion with drug-free medium, suppression of CM by 3 mM drug could be reversed with 10 mM Ca2+ but not with 1 mM Ca2+. Loss of CM was irreversible when administration of 10 mM Ca2+ was delayed or when the drug concentration was increased to 10 mM. The results are consistent with our previous hypothesis of a biphasic mechanism of aminoglycoside toxicity: an initial action competitive with calcium ions and reversible and a second step, non-competitive and irreversible.

Aminoglycosides↗

PubMed2003

Degeneration of sensory outer hair cells following pharmacological blockade of cochlear KCNQ channels in the adult guinea pig.

In the inner ear, hair cell function is inextricably linked with intracellular potassium homeostasis. KCNQ potassium channels may play an important role by preventing accumulation of potassium in the hair cells. Linopirdine, a tool useful in targeting native or heterologous KCNQ channels, was used to study the role of KCNQ channels in the guinea pig cochlea. When perfused into intact cochlea, linopirdine transiently increases the summating potential and endocochlear potential, suggesting that it alters K+ homeostasis. The concomitant decrease in cochlear microphonic potential and distortion product otoacoustic emission amplitude indicates that linopirdine has an effect on the outer hair cells (OHCs). To determine the pathological consequences of the inhibition of cochlear KCNQ channels, we developed a hearing loss model based on a chronic intracochlear perfusion of linopirdine via an osmotic minipump. Ultrastructural analysis reveals that KCNQ channel blockade leads to OHC degeneration. Together, these results demonstrate that KCNQ channels, most probably of the KCNQ4 subtype, are crucial for the function and survival of sensory OHCs. Clinically, KCNQ4 channel dysfunction is known to be associated with the DFNA2 form of nonsyndromic dominant deafness. Our study shows that OHC KCNQ4 dysfunction could contribute to the early (40dB) hearing loss, but not for the profound deafness observed at the final stage of this disease.

Acoustic Stimulation↗

PubMed1997

Auditory neuropathy: a report on three cases with early onsets and major neonatal illnesses.

We report 3 children without any brainstem auditory evoked potential (BAEP) neural component who all retained isolated cochlear microphonic potentials as well as click-evoked otoacoustic emissions. Two of them demonstrated only moderately impaired audiometric thresholds. These features correspond to a peculiar pattern of auditory dysfunction recently coined "auditory neuropathy'. In contrast with the published previous cases of auditory neuropathy presenting with an acquired hearing deficit as children or young adults, all 3 children had a history of major neonatal illness and the auditory neuropathy was already demonstrated in the first months of their lives.

Age of Onset↗

PubMed2002

Dual action of olivocochlear collaterals in the guinea pig cochlear nucleus.

Axons of olivocochlear neurones in the superior olivary complex terminate on hair cells of the cochlea, reducing the sensitivity to sound. These axons also have collateral branches to neurones in the cochlear nucleus, the first processing centre in the brainstem. Anatomical data show that these collaterals terminate mainly in the granule cell area but their precise neuronal targets and the effects they might have are unknown. We have studied the effects of these collaterals in guinea pigs, by electrically stimulating the olivocochlear axons at the floor of the IVth ventricle while recording single neurone responses in the cochlear nucleus. We eliminated the peripheral effects of olivocochlear stimulation either by destruction of the target receptor cells using chronic administration of kanamycin, or by acute perfusion of the cochlea with strychnine, a specific blocker of the postsynaptic receptors. Electrical stimulation of the olivocochlear axons in normal animals caused a variety of effects on cochlear nucleus neurones. In some neurones, there was suppression of spontaneous firing and a reduction in sensitivity to sound, while in others there was an excitatory effect of olivocochlear axon stimulation. When the peripheral olivocochlear action was eliminated, we still found both inhibition and excitation in the cochlear nucleus. These results show that the effects of olivocochlear stimulation on cochlear nucleus responses are not a simple passive reflection of peripheral changes but are a result of complex interactions between peripheral suppression of afferent input and collateral-mediated excitation and possibly also inhibition.

Action Potentials↗

PubMed1982

Influence of argon laser stapedotomy on cochlear potentials. I: Alteration of cochlear microphonics (CM).

In guinea pigs the cochlea microphonics (CM) were recorded during and after argon laser stapedotomy. Short termed drastic depression of CM was observed. This effect involved the entire frequency range of the cochlea. The recovery was mostly complete and often started already during laser irradiation or at the end of the laser exposure. A marked sensitivity loss of the cochlea only occurred with large stapedotomy holes followed by massive perilymph leakage. A momentary heat related instability of the entire stapes is suggested to cause the CM depression. In addition we observed a thermoacoustic effect on the CM. This laser evoked response seems to cause no harm to the cochlea.

Animals↗

PubMed1987

Genetic and functional analysis of the otosclerosis-like condition of the LP/J mouse.

The LP/J mouse is the only available genetic model for otosclerosis. The otosclerosis-like condition of the LP/J mouse resembles the human condition in several ways, although there are differences in the two species in the most common locus of the dysplastic otic lesions. The mouse model would be more useful if its auditory dysfunction and genetic inheritance could also be compared with the human disease. Matings of the otosclerosis-like LP/J and the normal CBA/J inbred mice were used to generate F1 and backcross generations. The F1 showed neither functional (electrocochleographic) nor anatomical abnormalities, indicating a recessive nature of the mouse genetic disease. This is in contrast to some reports of dominance (with incomplete penetrance) of otosclerosis in humans. No evidence of X-chromosome-linked genetic influence was found in the mouse, in agreement with the human condition. These interpretations were confirmed in tests of the backcross of the F1 to the CBA/J parental genotype (BC). The anatomical and functional abnormalities were present in some of the backcrosses of the F1 to the LP/J parental genotype (BL). A comparison of bone-conducted and air-conducted electrocochleographic responses provided evidence for both conductive and sensorineural losses in the LP/J and BL mice.

Action Potentials↗

PubMed1984

An experimental study of the effects of lead acetate on hearing. Cochlear microphonics and action potential of the guinea pig.

Guinea pigs were poisoned with repeated i.p. injections of 1% lead acetate. After 5 weeks, the animals were examined electrophysiologically by using cochlear microphonics (CM) and action potential (AP). The thresholds of maximum voltage of N1 in the AP of the animals injected with a total of 100 mg lead acetate were elevated about 15 dB and increased N1 latency was also observed. However, no significant changes in those of CM were found. The results suggest that lead acetate not only induces damage to the peripheral nerves, but also to the cranial nerves.

Action Potentials↗

PubMed1981

Kainic acid: an evaluation of its action on cochlear potentials.

Artificial perilymph containing kainic acid (KA) at various concentrations was perfused through the scala tympani in guinea pigs, and its effects on the whole nerve action potential (AP), cochlear microphonics (CM), summating potential (SP), endocochlear potential (EP), crossed olivocochlear potential (COCP), and cochlear ganglion-cell spontaneous activity studied. The administration of a 10 nmol dose of KA abolished AP but had little, if any, effect on CM, SP, EP or the COCP. The elimination of AP at this dose of KA appeared to be irreversible. Results obtained at lower doses (0.1, 0.25, 0.5, 1.0, and 2.5 nmol) suggested a very steep dose-response relationship in the action of KA. As expected, auditory nerve ganglion-cell recordings revealed the elimination of AP is most probably consequent to the suppression of afferent neural activity following an excitatory process. All these findings provide evidence that KA may exert a selective action on afferent nerve fibers and are consistent with the hypothesis that KA interacts with excitatory receptors located on postsynaptic membranes.

Action Potentials↗

PubMed1989

Detuning of cochlear action potential tuning curves at high sound pressure levels: influence of temporal, spectral and intensity variables.

Action potential (AP) tuning curves (TCs), generated by probe stimuli of 60-65 dB SPL with short rise and decay (r&d) times, are less sensitive (have elevated tip thresholds) and are detuned (the frequency is shifted away from that of the probe stimulus, towards a middle frequency of the audiogram). These effects are more pronounced with forward than with simultaneous masking. TCs generated by masking tonal and narrow band noise stimuli are nearly identical, even though the spectrum is much wider for the noise stimulus. Decreasing r&d time has the same effect on TCs generated from both noise and tonal stimuli, even when it only measurably increases the acoustic splatter of the latter. Detuning appears to be related to a temporal-intensity interaction.

Action Potentials↗

PubMed1986

Comparative actions of quisqualate and N-methyl-D-aspartate, excitatory amino acid agonists, on guinea-pig cochlear potentials.

We examined dose-dependent changes in the amplitude of guinea-pig cochlear microphonic potentials (CM), summating potentials (SP) and compound auditory nerve action potentials (CAP) produced after perfusing perilymphatic scalae with artificial perilymph containing either the transmitter candidate, L-glutamate; one of the excitatory amino acid agonists, quisqualate, kainate, N-methyl-D-aspartate (NMDA) or D-glutamate; or the control, alpha-ketoglutarate. None of these compounds significantly altered CM or SP. Kainate abolished CAP, but only partial suppression occurred using maximal effective doses of quisqualate (67%) or L-glutamate (82%). The remaining compounds had only marginal effects on CAP. The potency of quisqualate (EC50 = 14.8 microM) exceeded that of both kainate (EC50 = 66.9 microM) and L-glutamate (EC50 = 1.41 mM). These data suggest the presence of neuronal, possibly postsynaptic, excitatory amino acid receptor subpopulations which are preferentially sensitive to quisqualate and to kainate, but not to NMDA. These findings are discussed in the framework of our hypothesis that the proposed quisqualate and kainate receptors are normally activated by an endogenous excitatory amino acid such as L-glutamate which the hair cells release as a neurotransmitter.

Action Potentials↗

PubMedDate not supplied

Electrocochleography potentials evoked by condensation and rarefaction clicks independently derived by a new numerical filtering approach.

The cochlear microphonic potential (CM) and the compound action potential (CAP) cannot be measured separately but only in combination. In the literature their individual estimates are conventionally recovered by the so-called CM cancellation technique. This method averages the potential obtained in response to rarefaction and condensation clicks under the assumption that changing the polarity of the clicks only affects the CM sign and does not alter the CAP in any way. However, both theory and evidence suggest that these hypotheses can be critical. In addition, recent contributions in the electrocochleography (ECochG) literature suggested that assessing the influence of stimulus polarity on the evoked CAP may constitute an indicator of clinical usefulness which the CM cancellation method cannot supply. In this work we propose a new algorithm to estimate the cochlear potentials evoked from positive clicks, CAP+ and CM+, and those evoked from negative clicks, CAP- and CM-, by processing the same kind and amount of data employed in the CM cancellation method. The application to real data taken from 3 subjects exhibiting quantitatively and qualitatively different ECochG responses at various levels of stimulation intensity is presented. In addition, simulated problems where the true CAP and CM are known are studied to permit a fair assessment of the proposed technique. Results suggest that the new algorithm is potentially able to point out small differences between CAP+ and CAP-. This encourages its further employment on a larger scale.

Audiometry, Evoked Response↗

PubMedDate not supplied

Transtympanic electrocochleography in patients with syphilis and hearing loss.

Transtympanic electrocochleography was carried out on 18 syphilitic patients (30 ears were tested) most of whom were suffering from the late onset congenital form of the disease. A diphasic action potential with a large negative summating potential on the descending limb was found in 77.7% of ears; the cochlear microphonic potential was always of small amplitude. While these findings are not pathognomonic of syphilis, they are characteristic and may be explained on pathological grounds.

Action Potentials↗