PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Cochlear Microphonic Potentials”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1977

[Microphonic cochlear potentials in the cat during exposure to 2-tons harmonic signals with different phase spectra].

Cochlear microphonic potentials (CM), i. e. the round window responses, evoked by the two-tone sound complexes consisting of the 1st and 2nd harmonics with different phase relation between the components were studied in cats. The spectral analysis of the CM responses showed high sensitivity of the CM potentials to phase changes in the complex sound stimuli. The 1st harmonic in the range of 350--750 Hz could be reduced at a certain phase shift of the 2nd harmonic in the complex signal. The phase and frequency limits of this phenomenon are described.

Animals↗
PubMed1976

Recording of the cochlear microphonic potential with surface electrodes.

The cochlear microphonic potential was recorded in human subjects with surface electrodes (earlobe clip and scalp vertex disc) and an averaging procedure. Special precautions were taken to identify and separate artefactual, neural and microphonic components. These included shielding of the earphone, a rubber tube to introduce a time delay between artefact and biological response and white noise to mask the neural component. The cochlear microphonic potential was larger in amplitude in response to low frequency sounds and had a high threshold. Two clinical cases of cochlear hearing loss are presented, both lacking neural responses. The cochlear microphonic potential was present in one of them (i.e., neural hearing loss) and absent in the other (i.e., sensory hearing loss).

Adult↗
PubMedDate not supplied

Surface-recorded cochlear microphonic potentials during temporary threshold shifts in man.

Cochlear microphonic potentials (CM) were recorded, by means of surface electrodes, before, during and after white-noise-induced temporary threshold shifts (TTS) in human volunteers. The behavioural threshold shift was not accompanied by a change in amplitude of CM. These findings indicate that in humans, the site affected by the noise exposure and which probably gives rise to the TTS is central to the site of generation of CM. In a previous study, the compound action potential generated in the auditory nerve was found to be of lower amplitude and longer latency during TTS, and it is thus proposed that the site affected is peripheral to the generation of conducted action potentials. The synapse between hair cells and the auditory nerve fibres is the most likely candidate to be the affected site.

Acoustic Stimulation↗
PubMed1975

Frequency dependent changes in the amplitude of the cochlear microphonic potential of the pigeon ear during transient anoxia.

The effect of transient anoxia on the cochlear microphonic potential at different sound frequencies was investigated. The microphonic potential was recorded with glass microelectrodes in the ductus cochlearis of the pigeon ear. Transient anoxia had different effects, related to frequency, on the amplitude and the relative phase angle of the microphonic potential recorded from one place in the ductus cochlearis. At frequencies equal to and higher than the best frequency the amplitude of the microphonic potential was more sensitive to anoxia than it was at lower frequencies. Microphonic potential at 1 kHz lower than the best frequency was often enlarged in amplitude during transient anoxia. The results suggest that this frequency-dependent effect is a positional one. Changes in the phase were largest around the best frequency. It is inferred that anoxia causes complex changes in the pattern of vibration in the cochlear partition. The observed changes in amplitude and also changes in phase are caused by the combined effects of reduction of the endolymphatic potential and changes in vibration pattern.

Acoustic Stimulation↗
PubMedDate not supplied

Effects of perilymphatic perfusion with neomycin on the cochlear microphonic potential in the guinea pig.

The effects of three concentrations of neomycin, administered by a method of acute perilymphatic perfusion of the guinea pig cochlea, on the cochlear microphonic potential (CM) at 4 kHz and 500 Hz are described. A concentration-dependent reduction in CM occured during the 60 minute perfusion period. Neomycin at 10-4 M did not change the CM magnitude, while at 10-3 and 102 M it caused 4 kHz (and 500 Hz) CM reductions which began within 24 (for both frequencies) minutes and 10 (and 12) minutes of drug application respectively. CM reduction proceeded at a higher rate for greater neomycin concentration. The perfusion technique, the implication of the frequency indifference, and the potential of the perfusion technique for inner ear biochemical analysis are discussed.

Action Potentials↗
PubMed1977

[Effect of single impulses on cochlear microphone potentials of the guinea-pig cochlea].

The influence of highly intensive single impulses on the cochlea of guinea pig was studied in an acute experiment. Very short impulses of less than or equal to 0.1 ms duration were produced by a sparknoise generator. The cochlear microphonics (CM) to a test stimulus (sinus tone, 3150 Hz) were recorded from the round window and measured prior to, during, and following impulse treatment. During the impulse treatment, the greatest amplitude reduction of CM occurred after the first impulse, while the further impulses caused a decreasing reduction. At first the number of impulses was varied: 1, 3, and 5 impulses were applied at intervals of 15 s each, at an impulse sound level of 164 dB sound pressure level re. 0.002 mubar (SPL). After these impulse treatments, in all cases a continual decrease of CM amplitudes up to a constant end value without recovery was found within a 2-hrs period of observation. The height of the end value depends on the number of impulses applied. Subsequently, at an exposure to 5 impluses the impulse sound level was stepwise reduced (164, 153, 144, 139 and 133 dB SPL). Again, a characteristic decrease of CM amplitudes was observed during the 2-hrs period of observation. The height of the end value is now dependent on the impluse sound level. Impulses of 164, 153 and 144 dB SPL cause a strong decrease of CM while the effect of impulses of 139 and 133 dB SPL is distinctly lower.

Acoustic Stimulation↗
PubMed1991

[Effects of heavy metal ions in endocochlear DC potential and cochlear microphonics in the guinea pig--the influence of calcium on the cochlea].

Endocochlear DC potential (EP) and cochlear microphonics (CM) in the guinea pig under the influence of the divalent heavy metal cations of manganese, nickel, cobalt and cadmium, and the trivalent cation of lanthanum were investigated. The area from the scala tympani to the scala vestibuli was perfused with control and test solutions. CM decreased gradually to 50-80%, but EP showed no change after perfusion with a solution containing 1 mM of metal ions. At a concentration of 10 mM, EP decreased from 80 mV to 10-20 mV and CM decreased to 15-55%. At 100 mM, EP increased by about 10 mV at the beginning of perfusion, remained steady for 1 min, and then rapidly decreased to 0-10 mV. Meanwhile, CM continued to decrease, finally sustaining a 10-56% reduction. The decrease in EP and CM were irreversible, and perfusion of the area with the standard solution for 20 min had no effect. The osmolarity of the artificial perilymph containing 100 mM of metal ions was twice as high as that of the normal physiological solution. The effects of osmolarity, however, were excluded because perfusion with an artificial perilymphatic solution made hypertonic by either NaCl or sucrose changed neither EP nor CM. The application of 100 mM of metal ions topically to the round window membrane caused no change in EP. The alkali metal ions are known to inhibit inward Ca2+ current. Therefore, the present results suggest that Ca2+ ions play a role in maintaining EP generation in the stria vascularis and CM generation in the organ of Corti.

Animals↗
PubMed1988

Effects of various vanadium compounds on cochlear potentials.

The effects of vanadium compounds, sodium vanadate, ammonium vanadate, potassium vanadate, vanadium oxysulfate, vanadium acetylacetonate, and vanadium trichloride, on endocochlear potential (EP) and cochlear microphonic potential (CM) were examined in the guinea pig cochlea. The perilymphatic space was perfused for 30 min with 1 mM solution of each compound and changes of EP, CM, and negative EP were observed. Upon perfusion with pentavalent vanadium solutions, such as sodium vanadate, ammonium vanadate, and potassium vanadate, the EP showed an overshoot at the beginning of perfusion and then a gradual decrease, while the CM showed only a gradual decrease. The other compounds had no effects on EP and CM. Since the negative EP showed no differences due to perfusion of any compound, it is concluded that the vanadate compounds have inhibitory effects on EP primarily, and on CM only secondarily. The chemical mechanism of the effects of vanadates was discussed concerning the function of the stria vascularis and also its participation in acute hearing loss.

Animals↗
PubMed1988

Effects of vanadate on EP and its distribution in guinea pig cochlea.

Effects of sigma-sodium vanadate on endocochlear d.c. potential (EP) and cochlear microphonic potential (CM) were examined and its distribution was observed by an X-ray microanalyzer in the guinea pig cochlea. The perilymphatic space was perfused with 1, 5, and 10 mM solutions of sodium vanadate, using a Harvard Microperfusion pump. By perfusing the scala vestibuli, EP and CM showed a rapid decrease. On the other hand, by perfusing the scala tympani, EP showed an overshoot at first, then a gradual decrease, while CM showed only a gradual decrease. The rates of decrease of EP and CM were dependent upon perfusion time and vanadate concentration. After the electrophysiological examinations, the specimen of the cochlea was observed by X-ray microanalyzer. An accumulation of vanadium was confirmed, especially in the stria vascularis and the hair cells. From the results obtained, the possibility of the responsibility of vanadate for a hypothetical sudden deafness originating in the stria vascularis was discussed.

Animals↗
PubMed1986

The depression of the auditory nerve-brain-stem evoked response in hypoxaemia--mechanism and site of effect.

During severe hypoxaemia in the cat the ABR was depressed in 2 different patterns: if mean arterial blood pressure (MAP) was maintained then all other evoked potentials (EPs--somatosensory and visual) remained. If MAP was not maintained, all of these EPs were depressed. This study sought to document these different patterns of ABR depression and to ascertain their mechanisms. When MAP fell, the ABR loss began with the later waves and progressed to the earlier waves. These are signs of a central brain lesion. The hypoxaemia, detrimental to normal function of the cardiovascular system, leads to depression of MAP, to a fall in cerebral perfusion pressure and blood flow, to cerebral ischaemia and ABR loss. On the other hand, when MAP was maintained, severe hypoxaemia was accompanied by a depression of all of the ABR waves at the same time. The cochlear microphonic potential was also simultaneously depressed. These are signs of a peripheral, cochlear effect similar to the demonstrated depression of the positive endocochlear resting potential of the scala media and of the cochlear microphonic potential during hypoxaemia. This leads to interference with the cochlear transduction mechanism so that all of the auditory evoked potentials, including the ABR, are simultaneously depressed. These results lead to the suggestion that the ABR abnormalities seen in patients who suffered a hypoxic (anoxic) insult or an ischaemic episode (prolonged interpeak latencies, loss of later waves and finally all waves absent or only the first wave remaining) is always due to ischaemia even when the initial insult was hypoxic.

Animals↗
PubMedDate not supplied

Central auditory fatigue.

The results of this study, based on evoked responses and single-neuronal responses, reveal that there is a central involvement in auditory fatigue. In these experiments, cochlear potentials (microphonic and whole-nerve action potential) and inferior colliculus electrical responses were simultaneously obtained before and after excessive sound exposure. In general, sound exposure produced a greater reduction of the collicular evoked responses than of the cochlear microphonics and action potentials. Recordings from single neurons support the evoked-response findings.

Animals↗
PubMed1990

[Effects of perilymphatic perfusion with cisplatin on the cochlear potential in guinea pigs].

The effects of three concentrations of cisplatin, administered by acute perilymphatic perfusion on the endocochlear potential (EP) and the cochlear microphonic potential (CM) of the guinea pig cochleae, at 1 kHz are reported. No change in EP magnitude was discovered and a concentration-dependent reduction in CM amplitude occurred during 60 minutes' perfusion period. The results suggest that cisplatin-induced hearing loss is not necessarily progressive degradation of EP.

Animals↗
PubMed1975

Ionic mechanism of the efferent olivo-cochlear inhibition studied by cochlear perfusion in the cat.

1. A method for perfusing the scala tympani of the cat's cochlea from basal turn to apex is described. The perfusion with modified Krebs solution did not interfere with the recording of cochlear microphonic (CM) and neural responses to sound, nor with the efferent inhibition elicited by stereotaxic stimulation of the crossed olivo-cochlear bundle (COCB) in the medulla. 2. Cochlear perfusion with solutions in which most of the chloride was replaced by large anions (sulphate or gluconate) decreased or eliminated auditory nerve or the ventral cochlear nucleus. These effects were reversible. They were only observed if the rate of perfusion (2-20 mul/min) was adequate to reduce the chloride concentration in perilymph below about 80 mM, this being estimated, in different perfusion of the same cochlea, by a chloride-selective electrode. 3. The COCB-induced negative shift of the endocochlear potential recorded with a glass micro-electrode inserted into the scala media was abolished by I.V. strychnine o.2 mg/kg. It was decreased when the perilymph chloride was reduced to 50-70 mM and could be abolished when the perilymph chloride dropped to about 5 mM. 4. The COCB-induced potentiation of the cochlear microphonic potential was also reduced by chloride substitution but the pattern of this effect differed from that of neural inhibition. 5. Similar cochlear perfusions with a solution in which the small diameter bromide anion was substituted for chloride did not affect the COCB-efferent effects. 6. The data indicate that the inhibitory transmitter released by COCB terminals elicits an increased conductance to small anions (normally to chloride) in the membrane of the auditory dendrite and of the outer hair cell. The significance of the COCB-induced negative shift of endocochlear potential and of the potentiation of CM is discussed, as well as the pre- and post-synaptic mechanisms involved in the efferent gating exerted on the auditory input. The latter would seem to involve primarily a post-synaptic mechanism at efferent axo-dendritic synapses.

Acoustic Stimulation↗
PubMed1992

[The use of 6-flavor Rehmannia decoction with additives in the prevention of ototoxic deafness induced by gentamicin in guinea pigs].

The purpose of this study is to discuss the effects of the Chinese medicine six-flavor Rehmannia Decoction with additives on preventing deafness induced by gentamicin (GM) in guinea pig by means of testing the thresholds of Preyer's reflex (PR) cochlear microphonic potential (CM), action potential of the auditory nerve (N1) and scanning electron microscope of inner ear (SEM). The results showed that the medicine is effective in reducing the ototoxic effect of GM on inner ear.

Action Potentials↗
PubMed1990

[Narrow-band action potentials of the guinea-pig cochlea as compared with the ordinary electrocochleograms under normal and pathological conditions].

The narrow-band action potentials (NAP) and the ordinary electrocochleograms were recorded from the guinea-pig cochlea under normal and pathological conditions in order to study whether the NAP could be a useful measure to detect cochlear dysfunctions. The cochlea damaged either by the administration of kanamycin or by a mechanical lesion of the round window served as pathological materials. Recordings showed that the threshold and amplitude measured for the N1 potential of NAPs ran in parallel with those of the cochlear microphonic potentials (CM), under both normal and pathological conditions of the cochlea. This implies that the CM could be replaced by the NAP when difficulties were present in recording CMs. It may be inferred that the NAP reflects responses of the inner hair-cells and cochlear nerves, while the CM would mainly be derived from responses of the outer hair-cells to the frequency-specific movements of the basilar membrane. If so, the NAP should offer a good means for the objective audiometry. Recording NAPs is also superior to the ordinary electrocochleography in that the method makes it possible to obtain responses generated near the apex of the cochlea, i.e., responses to low-pitch sound stimuli.

Action Potentials↗