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At least 1,207 records · Page 67Linked to original sources
PubMed1992

Electrophysiological responses of the cochlea to transient asphyxia are influenced by arachidonate metabolites.

The influence of a transient asphyxia on cochlear potentials, i.e. endolymphatic potential (EP), summating potential (SP) and cochlear microphonics (CM) was investigated in guinea pigs when pretreating the animals with various substances interacting with the arachidonic acid (AA) cascade at the level of thromboxane. The controls showed the well-known decline of the EP, CM and the SP increase. When infusing a thromboxane synthetase inhibitor (dazoxiben) or two different thromboxane receptor blockers (daltroban or sulotraban) before the 3-minutes' period of asphyxia was started, the electrophysiological responses of the inner ear (cochlea) could significantly be influenced. The results indicate that a shift of the thromboxane (TXA2)/prostacyclin (PGI2)-balance in favour of the last improve the metabolic conditions for a survival of the cochlea when it is challenged.

Analysis of Variance↗
PubMed2003

Myelin-deficiency in the cochlear nerve of the 'bt' mutant hamster.

In a previous report, we showed abnormal auditory evoked potentials in the mutant hamster, 'black tremor (bt)', with significantly prolonged wave latencies of auditory brainstem responses and prolonged N1 latencies of compound action potentials, but normal cochlear microphonics. In this report, we present the results of morphological studies supporting the results of our electrophysiological studies of the auditory pathway in bt. Observation by transmission electron microscopy revealed an abnormal myelin sheath surrounding the spiral ganglion cells, and a thinner compact myelin sheath surrounding the axons in bt than in normal hamsters. The bt hamster has a myelin deficiency not only in the brainstem, but also in the cochlear nerve.

Animals↗
PubMedDate not supplied

Blocking effect of radio-contrast media on cochlear depression.

Furosemide injection was used in a total of 72 guinea pigs to induce a cochlear dysfunction similar to the sensorineural loss associated with sudden deafness. Prior to the furosemide administration, 38 of the animals were treated with an injection of one of four radio-contrast media; methylglucamine and sodium diatrizoate, sodium iothalamate, methylglucamine and sodium iodamide, and methylglucamine diatrizoate. In the control animals, receiving only furosemide, both endocochlear potential (EP) and cochlear microphonic (CM) underwent a severe depression followed by recovery and subsequent secondary depression. Animals pretreated with one of the first three compounds showed little or no EP or CM depression. Animals pretreated with the fourth, methylglucamine diatrizoate, showed the same EP depression as the control animals. The possible mechanism for this blocking effect and its significance in the clinical treatment of sudden deafness is discussed.

Animals↗
PubMed1976

[Electrophysiologic characteristics of rapid auditory adaptation].

In 32 rabbits, dependence of character of fast auditory adaptation on frequency of the sound stimulation was shown. Specific features of the adaption in conditions of switching off of the inner ear receptors with streptomycine were revealed. The fast adaptation was concluded to have a peripheral mechanism. Methods of the adaptation studying with the acid of action potentials of the 8th nerve and microphone potentials of the cochlear were compared under conditions of sound overload, and differences in results of measuring the fast adaptation were explained from the standpoint of dependence upon intensity of sound simulation.

Action Potentials↗
PubMed1981

Potentiating effects of cisplatin and ethacrynic acid in ototoxicity.

Seven milligrams per kilogram of body weight of cisplatin and 50 mg/kg of body weight of ethacrynic acid were given intravenously to guinea pigs. The threshold for Preyer's reflex, the cochlear microphonics (CM), and the endocochlear dc potential (EP) were measured during a four-day period after the injection. The changes in Preyer's reflex audiometry and the CM were more severe than that of the EP. These changes are greater than those that occur with the administration of each agent independently. The ototoxic interaction seemingly has a greater effect on the hair cells than on the stria vascularis. Baseline and periodic audiometry should be performed when both of these drugs are administered clinically.

Animals↗
PubMed1993

The effects of low-frequency ultrasound on the inner ear: an electrophysiological study using the guinea pig cochlea.

By examining 218 albino guinea pigs, electrophysiological methods were used to investigate the effects of low frequency ultrasound at moderate sound pressure levels after long-term exposure to the inner ear. From 10 kHz to 28 kHz, low frequency ultrasound below 100 dB SPL induced significant changes in cochlear microphonics, elevated thresholds and decreased maximum output voltage of action potentials and decreased absolute values of negative potentials of the endocochlear potentials.

Acoustic Stimulation↗
PubMed1993

Effects of intra-cochlear perfusion of salicylates on cochlear microphonic and other auditory responses in the guinea pig.

The ototoxic action of salicylate was investigated in the guinea pig by perfusion of both salicylate and bromosalicylate through scala tympani. The results qualitatively confirmed experiments using intravenous administration in cats (Stypulkowski, 1990), showing dose-dependent elevations in compound action potential (CAP) thresholds, increases in cochlear microphonics (CM) and level-dependent reductions in 2f1-f2 acoustic distortion products. The endocochlear potential was not significantly affected and iontophoretic injection of salicylate into scala media had no measurable effect on CAP thresholds, consistent with an action on the basolateral walls of the hair cells. Perfusion with indomethacin produced effects similar to those of the salicylates, but at non-physiological doses. Together with the great effectiveness of 5-bromosalicylate, this suggests that salicylate does not act by inhibiting prostaglandin synthesis. The results are qualitatively consistent with the proposition that salicylates act on the basolateral walls of the outer hair cells. However, the magnitude of the CM increases, particularly at high drug concentrations, and the fact that salicylate reduced, but did not eliminate the effects of olivocochlear efferent stimulation on CM amplitude indicate that a simple explanation for salicylate effects based solely on a conductance increase in the outer hair cell membranes may be inadequate.

Acoustic Stimulation↗
PubMed1982

Comparison of the non-adrenergic action of phentolamine with that of vanadate on cochlear function.

Two drugs, which upon superficial examination appeared to be acting on common processes, have been found upon closer investigation to act by quite different means. Both act primarily at the organ of Corti, causing a pronounced increase of the endocochlear potential and a depression of the cochlear microphonic (CM). These effects are accompanied by the elimination of a negative component of the EP; however, it was found that these three effects are produced by phentolamine in scala media (or, more slowly, in scala tympani) but by vanadate only in scala tympani. This difference in locus of action isd manifested further by different changes of the summating potential (SP): phentolamine has little effect on the magnitude of SP-, while vanadate leads to an elevated SP-. In spite of this difference in the 'zeroth order harmonic', the second harmonic of the CM is depressed by both agents. It is argued that phentolamine may act either by blocking the acoustically-modulated ion channels in the luminal membranes of the hair cells or by inducing a large, non-selective, paracellular conductance in the organ of Corti. The present results, in conjunction with our previous results (Marcus, D.C., DeMott, J.E., Kobayashi, T., Ge, X.-X. and Thalmann, R. (1981): Hearing Res. 5, 231-243), are further interpreted as suggesting that vanadate may initially act by depolarizing the hair cells.

Adrenergic alpha-Antagonists↗
PubMed1983

Clinical implications of experiments on alteration of the labyrinthine fluid pressures.

Hearing is affected by changes in hydrostatic pressure of the perilymph, but very high pressures are required to produce a significant loss. Among the observed findings in cats are a rapidly reversible decrease in the sensitivity of the cochlear microphonic that is greater for low frequencies, harmonic distortion and reduction of dynamic range as measured by the input-output function for the cochlear microphonic, and a change in the summating potential from negative to positive. These changes are attributed to a temporary reduction in the size of the cochlear duct due to a shift of water molecules out of the cochlear duct into the blood until the resulting increase in osmotic pressure balances the increase in hydrostatic pressure. Consequently, the organ of Corti is biased "upward" away from the scala tympani. Increasing the hydrostatic pressure of the endolymph produces a "downward" biasing of the organ of Corti and has an opposite effect upon the summating potential. Presumably this is what happens in Meniere's disease. Because of the presence of the perilymphatic canaliculi, the locus of the hydrostatic pressure effect is assumed to be in the region of the reticular lamina. A theory has been developed to explain why cochlear function is very sensitive to relative differences between the hydrostatic pressures of the perilymph and the endolymph but is resistant to large variations in the absolute magnitudes of those pressures. Some of the clinical implications of this theory are discussed.

Animals↗
PubMed1999

Cochlear microphonics for hearing preservation in vestibular schwannoma surgery.

OBJECTIVES: To determine whether cochlear function is beneficial in decision-making concerning the selection of hearing preservation surgery for vestibular schwannoma. STUDY DESIGN: Retrospective review of 44 patients undergoing tumor resection with a middle fossa approach. METHODS: Cochlear microphonics in electrocochleography together with tumor size, pure-tone average (PTA), speech discrimination score (SDS), auditory brainstem response (ABR), and compound action potentials were examined. As acoustic stimuli, short tone-bursts with frequencies of 0.5, 1, and 2 kHz were employed to measure cochlear microphonics and a click was used to obtain compound action potentials. We determined detection thresholds of cochlear microphonics and action potentials. RESULTS: The overall rate of preservation of serviceable hearing was 59.1% (26/44). There were significant differences between patients with and without serviceable postoperative hearing in PTA, SDS, finding of ABR, compound action potential detection threshold, and mean cochlear microphonic detection threshold (at 0.5, 1, and 2 kHz). However, tumor size was unrelated to hearing outcome. Serviceable hearing was preserved in 23 (76.7%) of 30 patients, with a mean cochlear microphonic detection threshold of 40 dB nHL or less, suggesting normal or slightly impaired cochlear function. Hearing recovery was recognized in three patients, who also had a mean cochlear microphonic detection threshold of 40 dB nHL or less. Of the three patients, two had lower cochlear microphonic detection thresholds than audiometric thresholds, demonstrating the existence of a retrocochlear component in their hearing loss. CONCLUSIONS: The cochlear microphonic detection threshold predicts not only hearing preservation but also hearing improvement in patients with vestibular schwannomas.

Adult↗
PubMed1981

Longitudinal distribution of cochlear potentials and the K+ concentration in the endolymph after acoustic trauma.

Guinea pigs were exposed to 142 dB third-octave band of noise control at 1 kHz for 1 h. At different times after exposure the endocochlear potential (EP), the anoxic negative endocochlear potential (-EP), the concentration of K+ (K+e) and microphonic potentials were recorded in scala media in four cochlear turns. The remaining hair cells were counted in each animal. Immediately after the exposure, the EP and K+e decreased evenly in all four cochlear turns and gradually returned to normal physiological values in 5-20 days. When measured 20 days after the exposure, essentially normal EP and K+e values were observed, with an apicalwards decline, which was similar to that found along the cochlea in nonexposed animals. Abnormal increased EP was observed in some animals 20 days after the exposure in the first and second turns. In contrast to positive EP and K+e values, the anoxic negative EP attained less negative values in the second turn of exposed animals, i.e., in the turn where the narrow band noise exerted the major destructive effect. An almost normal distribution of hair cells and most negative EP values were found in the fourth turn. The distribution of persistent hair cells correlated positively with the values of the anoxic negative EP and amplitudes of the microphonic potentials. It is assumed that, in addition to the difference in K+ concentration between endolymph and perilymph, the anoxic negative EP is dependent upon the functional state of the organ of Corti.

Animals↗
PubMed1984

Auditory evoked potentials and audiological follow-up of subjects developing noise-induced permanent threshold shift.

Three examinations, including cochlear microphonics (CM) to 99/s 1-kHz tones and auditory brainstem evoked potentials (ABEP) to 10/s and 55/s clicks, as well as psychoacoustical tests, were performed on 31 normally hearing subjects, exposed to occupational noise for over a year. The results showed prolongation of the absolute latency of peaks I, III and V, without significant changes in interpeak latency differences (IPLD) or CM latency. The site affected by increasing stimulus rate, giving rise to increased IPLD, appears to be central rather than cochlear. The efficacy of increased stimulus rate in detecting noise-induced auditory changes was higher than achieved applying the 10/s click rate.

Adolescent↗
PubMed1986

Follow-up of auditory-evoked potentials and temporary threshold shift in subjects developing noise-induced permanent hearing loss.

The effects of auditory fatigue, using a temporary threshold shift (TTS) paradigm, on cochlear microphonics (CM) and on auditory brainstem-evoked potentials (ABEP), were studied in normal-hearing subjects during the development of permanent threshold shift (PTS). Behavioral threshold shifts were accompanied by different effects on CM and on ABEP, as PTS was gradually induced by occupational noise. Measures of the effect of increasing stimulus rate (ISR) on ABEP revealed decreased latency shifts during auditory fatigue. ABEP proved useful in early detection of changes in the auditory system, resulting from exposure to noise. In addition, this study further supports the suggestion that TTS acts as a peripheral attenuator of the effect of ISR on the central auditory pathway.

Adolescent↗
PubMed1990

Nimodipine, an L-channel Ca2+ antagonist, reverses the negative summating potential recorded from the guinea pig cochlea.

Nimodipine, an L-type Ca2+ channel antagonist, was tested using sound-evoked cochlear potentials in guinea pigs to investigate whether these channels are involved in cochlear function. Perilymph spaces of guinea pig cochleae were perfused with artificial perilymph solutions containing 0.1-10 microM nimodipine at a rate of 2.5 microliters/min for 10 min. The cochlear potentials evoked by 10 kHz tone bursts of varying intensities were recorded from the basal turn of the scala vestibuli. Cochlear perfusion of nimodipine resulted in reversible, dose-related suppression of the compound action potential of the auditory nerve (CAP; N1-P1), a prolongation of N1 latency at suprathreshold levels, an elevated CAP threshold, a decrease in N1 latency at a constant amplitude measured at CAP threshold, a reduction in cochlear microphonics (CM), and a reduction of the negative summating potential (SP) to a point where it became positive (i.e., a reversal of SP). The endocochlear potential (EP) was not affected. These results support the hypothesis that L-type Ca2+ channels are directly involved in the operation of the organ of Corti. We speculate that L-type Ca2+ channels are integrally involved in generation of a negative summating potential and the dc motion of the cochlear partition described by others.

Animals↗
PubMed2001

Effects of 4-aminopyridine on electrically evoked cochlear emissions and mechano-transduction in guinea pig outer hair cells.

Stimulation of the cochlea with alternating current produces sound in the ear canal. These electrically evoked oto-acoustic emissions (EEOAEs) are attributed to electro-motility of outer hair cells (OHCs). Earlier work suggested EEOAEs were sensitive to the open probability of OHC mechano-electrical transduction (MET) channels. They were attenuated by 4-aminopyridine (4-AP) and amplitude-modulated by low frequency sound, consistent with current gaining access to a motility source via the MET conductance. However, inconsistencies in the behaviour as well as physical considerations argued against this simple interpretation. In this study the behaviour of EEOAEs in the presence of 4-AP in scala media was examined along with OHC transfer functions derived from low frequency cochlear microphonic (CM) waveforms. Both the level and the modulation of the EEOAEs were reduced by 4-AP, but disproportionately more so than the 4-AP-induced loss of CM. In addition, the modulation as well as the level of the EEOAEs recovered more rapidly than the CM. Both these results indicated that 4-AP modified the process of EEOAE generation independently of its effect on the gross receptor current through the MET conductance. Changes in the derived OHC transfer functions, specifically shifts in the estimated operating bias of the MET channels, indicated the effects of 4-AP applied to the endolymphatic surface of OHCs were complex. It is suggested that both direct and indirect consequences of a 4-AP blockade may have contributed. 4-AP was ineffective when applied to scala tympani.

4-Aminopyridine↗
PubMed1980

Stimulation of efferents alters the cochlear microphonic and the sound-induced resistance changes measured in scale media of the guinea pig.

Electrical stimulation of the crossed olivo-cochlear bundle (COCB) increases both the cochlear microphonic and the acoustically synchronized changing resistance (CR) and it causes a decrease in the electrical impedance of scala media of the guinea pig. The similarity between the change in CR due to COCB stimulation and the change in CR due to negative d.c. polarization (Mountain, D.C., Hubbard, A.E. and Geisler, C.D. (1980): Hearing Res. 3, 215-229) suggests that the CR is dependent on the hair cell membrane potential measured with respect to scale tympani.

Acoustic Stimulation↗
PubMed1981

Alteration of aminoglycoside antibiotic ototoxicity by hyper- and hypohydration.

The ototoxicities of tobramycin sulfate and gentamicin sulfate were investigated in guinea pigs under conditions of normal, increased, and decreased hydration. Increased hydration was associated with no decline in the amplitude of the cochlear microphonics, a lesser decline in the eighth nerve action potentials and lesser damage to the organ of Corti. Decreased hydration was associated with an increase in the threshold of the cochlear microphonics and the eighth nerve action potentials, a decline in the amplitude of the cochlear microphonics, a greater decline in the eighth nerve action potentials, and greater damage to the organ of Corti. Tobramycin sulfate was substantially less toxic than gentamicin sulfate with normal, increased and decreased hydration. These findings suggest the preferential use of tobramycin sulfate for patients with normal renal function, and especially patients with renal impairment.

Action Potentials↗
PubMed1991

Absence of both auditory evoked potentials and auditory percepts dependent on timing cues.

An 11-yr-old girl had an absence of sensory components of auditory evoked potentials (brainstem, middle and long-latency) to click and tone burst stimuli that she could clearly hear. Psychoacoustic tests revealed a marked impairment of those auditory perceptions dependent on temporal cues, that is, lateralization of binaural clicks, change of binaural masked threshold with changes in signal phase, binaural beats, detection of paired monaural clicks, monaural detection of a silent gap in a sound, and monaural threshold elevation for short duration tones. In contrast, auditory functions reflecting intensity or frequency discriminations (difference limens) were only minimally impaired. Pure tone audiometry showed a moderate (50 dB) bilateral hearing loss with a disproportionate severe loss of word intelligibility. Those auditory evoked potentials that were preserved included (1) cochlear microphonics reflecting hair cell activity; (2) cortical sustained potentials reflecting processing of slowly changing signals; and (3) long-latency cognitive components (P300, processing negativity) reflecting endogenous auditory cognitive processes. Both the evoked potential and perceptual deficits are attributed to changes in temporal encoding of acoustic signals perhaps occurring at the synapse between hair cell and eighth nerve dendrites. The results from this patient are discussed in relation to previously published cases with absent auditory evoked potentials and preserved hearing.

Acoustic Stimulation↗