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Results for “Cochlear Microphonic Potentials”

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At least 559 records · Page 31Linked to original sources
PubMed1983

Prenatal maturation of endocochlear potential and electrolyte composition of inner ear fluids in guinea pigs.

The maturation of the endocochlear potential (EP) and the inner ear fluid ionic composition were studied in fetal and neonate guinea pigs. The concentration of sodium and potassium in endolymph and perilymph approximated adult values more than 2 weeks before birth. Endolymph had acquired its specific ionic composition before the onset of cochlear microphonics (52-55 gestation days, results of other authors). Positive EP was recorded starting on day 62 of gestation. The EP rose fast to reach near adult level at birth. It is speculated that the negative EP recorded after the onset of cochlear microphonics was an artifact, probably a result of fetal hypoxia. The significance of the negative EP recorded before the onset of the cochlear microphonics is discussed in relation to the source of the anoxic negative EP in the adult animal.

Animals↗
PubMed1995

Effects of a dopaminergic agonist in the guinea pig cochlea.

This study investigates the role of dopamine, a putative lateral efferent neurotransmitter/modulator, in cochlear physiology and physiopathology. Cochlear potentials were recorded in guinea pigs after intracochlear perfusion of increasing doses (0.1-1 mM) of piribedil, an agonist of the D2/D3 receptors. A dose-dependent reduction in the amplitude of auditory nerve compound action potential (CAP) was observed, predominantly at high-intensity tone-burst stimulations, and without significant effect on CAP threshold. There was no variation of cochlear microphonic and summating potential. When 1 mM piribedil was perfused into the cochlea during continuous 130 dB SPL pure tone exposure (6 kHz, 15 min), CAP threshold shifts were significantly less than in control animals with artificial perilymph-perfused cochleas. No dendritic damage was observed, although there was evident hair cell damage. Similarly, radial dendrites were clearly protected against ischemia-induced damage when 1 mM piribedil was applied prior to a 10-min ischemia. These results suggest that dopamine modulates the activity of radial afferent fibers via D2/D3 receptors. The protective effect of piribedil during acoustic trauma or ischemia suggests that this modulation corresponds to a prevention of excitotoxicity due to dysfunction of inner hair cell neurotransmission.

Acoustic Stimulation↗
PubMed1983

Influence of argon laser stapedotomy on inner ear function and temperature.

The influence of argon laser stapedotomy on inner ear function was investigated in guinea pigs. The cochlear microphonics (CM) and the compound action potential (CAP) served as parameters for the functional status of the cochlear. Transitory depression of both potentials was found during and after laser stapedotomy. The time course of CM and CAP depression and recovery is compared to endocochlear temperature changes. Possible implications for clinical use are discussed.

Action Potentials↗
PubMed1982

Effect of furosemide upon endolymph potassium concentration.

Chinchillas were anesthetized with ketamine (40 mg/kg i.m.) and endocochlear potential (EP) and potassium concentration in endolymph (Ke+) were determined in control animals and in animals injected with various doses of furosemide (25, 50 or 100 mg/kg i.v.) by means of microelectrodes inserted into scala media. Control EP and Ke+ in the chinchilla were 81.3 +/- 3.8 mV and 158.5 +/- 3.2 mequiv./l, respectively. Following injection of furosemide, a dose-related fall in EP and Ke+ was observed. However, the EP declined much more rapidly than the Ke+, and recovered more quickly than the latter. The recovery of Ke+ tended to lag behind the EP recovery. The debate over whether potassium transport into endolymph and endocochlear potential generation are related or independent events is discussed in the light of recent literature and the present study.

Animals↗
PubMed1984

The potentiation of ototoxicity when aminooxyacetic acid and kanamycin are co-administered.

Aminooxyacetic acid (AOAA) has been shown to confer protection against noise-induced cochlear trauma [3]. We, therefore, decided to study the possible protective effect of AOAA against kanamycin (KM) ototoxicity and found, instead, that AOAA potentiated the toxicity. To produce ototoxicity in guinea pigs, KM is usually given in 10-14 daily doses of 400 mg/kg s.c. However, when combined with a single dose of AOAA (8, 11, 15, or 25 mg/kg) a single 400 mg/kg dose of KM is sufficient to cause cochlear damage. Such animals show a negative Preyer's reflex between 1 to 3 days post injection. 21 days later hearing thresholds as detected electrocochleographically at 2, 4, 8, 12 and 16 kHz have changed drastically sometimes to the point of being undetectable. The damage seen histologically at this time is destruction of both inner and outer hair cells. A pharmacokinetic analysis of this potentiation revealed a slight prolongation of KM's sojourn in the inner ear. The possible mechanisms of this unexpected, marked potentiation are discussed but remain unknown.

Acetates↗
PubMedDate not supplied

Effects of high-frequency sound on electrochemical potential using the single-barrel method in guinea pigs.

There are only a few studies investigating the effects of ultrasound on hearing. This paper reports on an experimental investigation on the effect of the long-time exposure to a moderate sound pressure level, high-frequency sound of 16 kHz on the guinea pig inner ear using electrophysiological methods. A decrease of the absolute value of negative potential was observed in the endocochlear potential (EP). The effects of high-frequency sound on EP and electrochemical potential could be explained by a change in the K+ permeability of hair cells.

Acoustic Stimulation↗
PubMed1998

The generation of DC potentials in a computational model of the organ of Corti: effects of voltage-dependent K+ channels in the basolateral membrane of the inner hair cell.

A computational model of the organ of Corti is described to assist in the interpretation of electrophysiological data concerning the role of the K+ channels residing in the basolateral membrane of cochlear hair cells. Recent in vivo data from Van Emst et al. (Hear. Res. 88, 27-35 (1995); Hear. Res. 102, 70-80 (1996)) about the effects of selective blocking of K+ channels indicate that these channels affect the magnitude of the summating potential. In order to understand the nature of this effect, the model of Dallos (Hear. Res. 14, 281-291 (1984)) was extended to account for the voltage- and time-dependent properties of the K+ channels in the basolateral membrane of the inner hair cell (IHC) (Kros and Crawford, J. Physiol. 421, 262-291 (1990)). The model shows that the K+ channels induce a shift in the mean IHC basolateral conductance when high-frequency stimuli are present. As a result, cochlear transduction shifts to a different electrical operating state and this is the source of a marked decrease in the stimulus-evoked DC response of the IHC. Extracellularly, in contrast, the magnitude of the DC response increases slightly. At low frequencies, the K+ channels respond to the stimulus waveform on a cycle-by-cycle basis. The waveform distortion associated with this dynamic basolateral impedance induces a further decrease in the intracellular stimulus-evoked DC response of the IHC. Thus, K+ channels in the IHC appear to be directly involved in the generation of the DC receptor potential at low frequencies, but at high frequencies they simply modify the size of the DC response.

Acoustic Stimulation↗
PubMed1989

Effects of round window membrane rupture on cochlear blood flow and inner ear pressures.

Effects of round window membrane rupture on cochlear blood flow and inner ear pressures were investigated using non-radioactive microspheres and a servo-micropipet system in guinea pigs. When perilymphatic pressure was raised through a glass capillary tube inserted into the perilymphatic space, both endolymph pressure and perilymph pressure rose. When these inner ear pressures were raised to relatively high levels, cochlear blood vessels could be compressed and endocochlear potential decreased to a negative value due to the interruption of cochlear blood flow. However, in the case when the round window membrane was ruptured by further increase in perilymph pressure, the inner ear pressures decreased and restoration of cochlear blood flow and endocochlear potential was observed. When the round window membrane was ruptured with a fine needle under ordinary inner ear pressures, cochlear blood flow did not change significantly.

Animals↗
PubMed1985

Abolition of the negative endocochlear potential as a consequence of the gentamicin-furosemide interaction.

The DC endocochlear potential and the AC cochlear potential in response to a 4 kHz tone were recorded in pigmented guinea pigs before and during ototoxic damage induced by sequential administration of the aminoglycoside antibiotic, gentamicin, and the loop diuretic, furosemide. Within 4 h significant diminution of the amplitude of the AC cochlear potential was accompanied by an almost complete abolition of the negative diffusion potential revealed by either furosemide administration or terminal anoxia. Thus, one of the effects of this interaction appears to involve a reduction in the potassium permeability of the cochlear partitions.

Animals↗
PubMed1980

Model for cochlear echoes and tinnitus based on an observed electrical correlate.

Experiments in cat have revealed evidence of temporal correspondence between round-window recorded electrical potentials and delayed acoustical responses in the sealed ear canal at low sound levels. This would be difficult to explain if the acoustic response contained an appreciable component of delay due to a reverse travelling wave. An alternative interpretation is offered in which outer hair cells are assumed to undergo periodic volumetric changes correlated with their electrochemical activity. These volume changes would act on, and be divided between, the oval window, giving acoustic reemission and the basilar membrane, giving a secondary travelling wave. Owing to the active nature of the hair cell, the output is potentially greater than the input, so that when the secondary travelling wave exceeds the initial one, the amplitude will build up and continuous oscillation occurs, giving 'tinnitus'.

Animals↗
PubMed1997

Expression and function of adenosine receptors in the chinchilla cochlea.

Previous studies indicate the presence of adenosine receptors in the cochlear tissues obtained from different animals. This study was initiated to determine the subtypes of adenosine receptor (AR) present in the chinchilla cochlea and to assess their function. Radioligand binding studies demonstrate the presence of both the A1AR and A3AR in membranes prepared from the cochlea, using the radioligands [3H]DPCPX and [125I]APNEA. Estimates of the number (Bmax) of A1AR and A1AR plus A3AR by saturation curves were 118 +/- 13 and 417 +/- 120 fmol/mg, respectively, with the respective equilibrium dissociation constants (Kd) averaging 2.7 +/- 0.2 and 26.3 +/- 13.8 nM. No significant number of A2aAR were detected using [3H]CGS21680. The nonhydrolyzable adenosine analog R-phenylisopropyladenosine (R-PIA, 1 microM) elicited a small but significant degree of inhibition of forskolin-stimulated adenylyl cyclase activity (10.4 +/- 2.5%) in cochlear membrane preparations, which was insensitive to blockade by theophylline (100 microM). Furthermore, R-PIA elicited an increase in inositol 1,4,5-trisphosphate production in dissociated cell preparations obtained from the cochlea. No significant effect of R-PIA was observed on auditory measures such as auditory brainstem evoked response, cochlear action potential and endocochlear potential following round window application. However, round window application of R-PIA elicited significant increases in the activities of antioxidant enzymes such as superoxide dismutase and glutathione peroxidase and significantly reduced the levels of malondialdehyde, a marker of lipid peroxidation. These results suggest a potential cytoprotective role of adenosine in the cochlea against oxidative damage.

Adenosine↗
PubMed1996

4-Aminopyridine effects on summating potentials in the guinea pig.

DC receptor potentials measured in hair cells, and the associated extracellular DC potential known as the summating potential (SP), originate with nonlinear elements in the mechanoelectric transduction chain. Nonlinear electric conductance has been demonstrated in the basolateral membrane of the hair cell, and is commonly attributed to the presence of voltage- and time-dependent K+ conductances in this part of the hair cell membrane. To study a possible contribution of these K+ channels to the SP we perfused the perilymphatic spaces of the guinea pig cochlea with the K+ channel blocker 4-aminopyridine (4-AP). Since 4-AP might also affect the afferent fibers and, thus, interfere with SP measurement, we added tetrodotoxin (TTX) to the perfusion solutions to block the neuronal discharges. Sound-evoked (2-12 kHz) intracochlear potentials were recorded from the basal turn of both scala vestibuli and scala tympani. The results showed a frequency- and level-dependent effect of 4-AP on the magnitude of the SP. At low and moderate levels of 8 and 12 kHz stimuli 4-AP mostly reduced the SP amplitude, while at high levels of these stimuli and at all levels of 2 and 4 kHz stimuli 4-AP enlarged the SP amplitude. These effects were reversible and occurred in both scala vestibuli and scala tympani. We attribute these bi-directional effects on the SP amplitude to a differential effect of 4-AP on inner hair cell (IHC) and outer hair cell (OHC) physiology. The decrease in SP was found for stimulus conditions where the SP presumably depends mainly on contributions from basal turn IHCs. Blocking the 4-AP-sensitive K+ channel in the IHC membrane should lead to a reduced contribution from the IHCs to the SP, because of an increase in basolateral membrane resistance. The increase in SP was found for stimulus conditions where the SP is assumed to depend mainly on contributions from basal turn OHCs. In this case the OHCs seemed to respond to blocking of the 4-AP-sensitive K+ channel in the basolateral membrane with an increased contribution to the nonlinearity of the transduction chain. Administration of 4-AP did not affect the endocochlear potential. Light microscopic examination revealed no apparent changes in morphology after 4-AP perfusion.

4-Aminopyridine↗
PubMed1991

The human auditory steady-state evoked potentials.

When auditory stimuli are presented at rates near 40/s, they evoke a steady-state middle latency response. This results from the super-position of the transient responses evoked by each of the rapidly presented stimuli. The steady-state evoked potentials are most appropriately analyzed using frequency-based techniques. The response is larger for stimuli of higher intensity and of lower tonal frequency. The amplitude of the response varies with the state of arousal of the subject. Sleep results in a decrease in the amplitude to between one third and one half of the amplitude during wakefulness. The response is even further attenuated by general anesthesia. This auditory steady-state evoked potential may therefore be helpful in monitoring the state of arousal of a patient undergoing anesthesia.

Adult↗
PubMed1997

Enhanced cochlear responses after sound exposure.

Alternating potentials produced in Hensen's cells of Mongolian gerbils by sinusoidal stimuli were enhanced or depressed after exposure to broad-band sound of moderately high intensity, depending on exposure- and stimulus intensities. Since Hensen's cell responses have been shown to be identical in phase and directly proportional in magnitude to outer hair cell (OHC) responses (Oesterle, E.C., Dallos, P., 1989, J. Acoust. Soc. Am. 86 (3), 1013-1032.; Zwislocki, J.J., Slepecky, N.B., Cefaratti, L., Smith, R.L., 1992, Hear. Res. 57, 175-194), it was assumed that these changes were reflections of changes in OHC receptor potentials, which were of main interest. The indirect method of intracellularly recording the Hensen's cell potentials rather than OHC potentials was used to minimize damage to the organ of Corti and reduce technical difficulties associated with repeated recordings from OHCs. Continuous magnitude and phase transfer functions (TFs) were obtained before and after the exposure over a range of sound pressure levels (SPLs) extending from 40-90 dB by using frequency sweeps ranging from 0.125-18 kHz. Cochlear microphonic (CM) TFs were also acquired over the same frequency and intensity ranges for monitoring purposes. The exposure stimuli were set at 80, 86, 90 or 100 dB SPL for periods ranging from 10-40 min. When response enhancement occurred, it was most clearly seen in the peak of the transfer function determined at 90 dB SPL. Enhancement ranged from approximately 12-230% of the original peak. In contrast, control Hensen's cell recordings obtained over periods of up to 130 min revealed great response stability. In all reliable recordings, response enhancement was associated with a phase lead or no phase change. The strongest exposure stimuli tended to produce sensitivity loss accompanied by phase lag at the lower SPLs, in agreement with previous work in this laboratory (Zhang and Zwislocki, 1995). In some preparations, both sensitivity loss at lower SPLs and enhancement at higher SPLs occurred simultaneously, suggesting involvement of two different mechanisms.

Acoustic Stimulation↗
PubMed2002

KCNJ10 (Kir4.1) potassium channel knockout abolishes endocochlear potential.

Stria vascularis of the cochlea generates the endocochlear potential and secretes K(+). K(+) is the main charge carrier and the endocochlear potential the main driving force for the sensory transduction that leads to hearing. Stria vascularis consists of two barriers, marginal cells that secrete potassium and basal cells that are coupled via gap junctions to intermediate cells. Mice lacking the KCNJ10 (Kir4.1) K(+) channel in strial intermediate cells did not generate an endocochlear potential. Endolymph volume and K(+) concentration ([K(+)]) were reduced. These studies establish that the KCNJ10 K(+) channel provides the molecular mechanism for generation of the endocochlear potential in concert with other transport pathways that establish the [K(+)] difference across the channel. KCNJ10 is also a limiting pathway for K(+) secretion.

Animals↗
PubMedDate not supplied

Alterations in oxygenation of cochlear endolymph during loud sound exposure.

The oxygen tension (pO2) of endolymph of the guinea pig cochlea was measured during exposure to loud sound (12 kHz or high-pass noise; 110 dB SPL up to 1 h duration). A small, but significant, steady decline in mean pO2 was observed after both pure tone and high-pass noise exposure. The extent of the change in pO2 varied from 0-50% in individual animals, compared with unexposed control animals. All exposed animals had an extensive loss of compound action potential (CAP) thresholds at frequencies of 8-30 kHz. However, there was no relationship between the extent of the change in pO2 of endolymph and CAP threshold loss.

Animals↗
PubMed1993

Effects of K(+)-channel blockers on cochlear potentials in the guinea pig.

The effects of different K+ channel blockers, 4-aminopyridine (4-AP), tetraethylammonium (TEA) and quinine, on the various cochlear potentials were observed by the means of perilymph infusion. Each of the three blockers depressed the compound action potential. However, they exerted quite different effects on other cochlear potentials, especially comparing 4-AP, a fast K(+)-channel blocker, with two other blockers. 4-AP induced a significant increase in the magnitude of summating potential, while TEA and quinine decreased it; 4-AP showed no effect on the general endocochlear potential (G-EP, the EP value recorded directly from the scala media, SM) and the negative EP component (N-EP), while TEA and Quinine increased G-EP and decreased the absolute value of N-EP. They also exerted different effects on the EP changes induced by exposure to intense noise. The results indicate the different roles of different K(+)-channels in the generation of cochlear potentials. The relationship of the two components of EP (positive and negative) and the G-EP was discussed.

4-Aminopyridine↗