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At least 217 records · Page 12Linked to original sources
PubMed1985

Growth of suppression in the cochlear potentials.

Measurement of two-tone effects in the cochlear microphonic and summating potential indicates that the growth of suppression is different for these two cochlear potentials. Whereas the CM response to the fundamental is reduced 10 dB for each 10 dB increase in suppressor level, the SP decreases at a faster rate; approximately 20 dB per 10 dB increase. Slopes of functions for the CM response to the second harmonic are similar to those for the dc component. Since these results are consistent with the notion that suppression operates by attenuating the input to the CM generator, they are consonant with a mechanical origin of suppression.

Animals↗
PubMed1995

The effect of protein kinase C stimulator and inhibitor on cochlear potentials in the guinea pig.

To determine a possible role of protein kinase C (PKC) in the cochlear, the effects of a PKC stimulator (phorbol-12-myristate-13-acetate; PMA), an inactive analogue of PKC stimulator (4 alpha-phorbol-12,13-didecanoate; 4 alpha-PDD) and a PKC inhibitor (D-sphingosine) on cochlear potentials were examined in the guinea pig. The perilymphatic perfusion with PMA (3 x 10(-6) M) produced an increase in compound action potential (CAP) amplitude and no change in N1 latency, the amplitudes of negative summating potential (-SP), cochlear microphonics (CM) and endocochlear potential (EP). The perfusion with 4 alpha-PDD (3 x 10(-6) M) did not change the sound-evoked cochlear potentials and the EP. The perfusion with D-sphingosine (10(-5) M) produced a decrease in CAP amplitude and no change in N1 latency and the amplitudes of -SP, CM and EP. The results suggest that PKC may be involved in the mechanism underlying the CAP generation.

Acoustic Stimulation↗
PubMed1981

Comparative ototoxicity of chloramphenicol and kanamycin with ethacrynic acid.

Chloramphenicol is not ototoxic if administered for systemic effect, but topical applications of it to the middle ear produce severe cochlear toxic effects. Ethacrynic acid potentiates the ototoxicity of aminoglycosides. Guinea pigs were administered chloramphenicol or kanamycin sulfate with ethacrynic acid to compare the ototoxicity of chloramphenicol and ethacrynic acid with the ototoxicity of kanamycin and ethacrynic acid. Preyer's reflex audiometry and measurement of the endocochlear dc potential, the cochlear microphonics, and the negative potential of the organ of Corti indicate that ethacrynic acid does not potentiate the ototoxicity of chloramphenicol. There is not even indirect evidence that the blood-cochlear barrier for chloramphenicol is altered by ethacrynic acid. Assuming that the ototoxicity of chloramphenicol and ethacrynic acid are similar for man and guinea pig, the combination of the administration of chloramphenicol and ethacrynic acid of systemic effect in dosages commonly used clinically should not produce greater ototoxicity than either agent administered alone.

Animals↗
PubMed1975

Ethacrynic acid. Effects on the cochlear potentials in normal and high blood oxygen.

The effect of ethacrynic acid (EA) at different blood O(2) saturations on cochlear potentials of guinea pigs was investigated. All 18 young healthy guinea pigs received 50 mg/kg/h of EA intravenously and were divided into three groups: first group, normal (90.00+/-6.30-86.17+/-4.83 mm Hg); second group, lower Po(2) (78.00+/-4.74-70.00+/-4.42 mm Hg); and third group, high Po(2) (174.40+/-13.41-179.00+/-26.15 mm Hg). The partial pressure of oxygen (Po(2)), the partial pressure of carbon dioxide (Pco(2)), and the pH of the blood were measured before EA administration and at the end of the experiment (3 h later) by drawing blood samples from the contralateral carotid artery. Cochlear potentials-endocochlear potential (EP), cochlear microphonics (CM), and action potentials (AP)-were recorded by standard methods from the first turn of the cochlea. Experimental data seem to indicate that elevation of the Po(2) to 174-179 mm Hg during relatively high doses of EA treatment prevents the declines in cochlear potentials which were observed in the first and second groups (normal and lower Po(2)), and preserves active ion transport which is responsible for the generation of cochlear potentials. These data suggest a means by which to reduce the ototoxic effect of EA and possibly indicates a method of treatment for hearing loss which developed after the administration of EA.

Action Potentials↗
PubMed1984

Postnatal development of the brainstem auditory evoked potential and far-field cochlear microphonic in non-sedated rat pups.

Normal postnatal development of the scalp-recorded cochlear microphonic (CM) response and brainstem auditory evoked potential (BAEP) were studied in rat pups. BAEP latencies decreased and amplitudes increased as a function of maturation. These changes occurred rapidly between 14 and 23 days of age with gradual change occurring thereafter. The observed latency changes indicated that the auditory pathway matures in a sequential manner from the most peripheral to the most rostral structures. For example, CM latency stabilized (matured) by day 17 while BAEP wave I and II latencies stabilized by days 23 and 35, respectively. BAEP waves III and IV still showed significant latency decreases between days 42 and 70. The between-litter variability for CM and BAEP wave latencies also decreased with age. In contrast to peak latency measures, CM and BAEP amplitudes followed an independent time course of postnatal development. CM amplitude did not increase significantly after day 14. Amplitudes of all 4 BAEP components increased steadily from day 14 to 29, then stabilized. Unlike latency variability, amplitude variability was independent of age. There were no significant gender-dependent differences in amplitudes or latencies between the ages of 14 and 70 days.

Age Factors↗
PubMedDate not supplied

Evidence for intracochlear impedance changes following ethacrynic acid administration.

The effects of intra-arterial 30-, 40-, and 50-mg/kg doses of ethacrynic acid upon cochlear function in guinea pigs were studied for periods of three to five hours. Cochlear potentials recorded in the first turn included the endocochlear potential, whole nerve response, cochlear microphonics, and summating potentials in scala media, scala tympani, and scala vestibuli. Evidence of organ of Corti damage at 50 mg/kg was found in addition to electrical impedance changes in the cochlear membranes at all dose levels.

Animals↗
PubMedDate not supplied

Cerebellar actions on cochlear microphonics and on auditory nerve action potential.

The influence exerted by cerebellar stimulation upon cochlear microphonics (CM) and auditory nerve action potential (AP) has been analyzed in curarized guinea pigs. Round window recordings demonstrated that conditioning electrical stimulus trains delivered to the cerebellar cortex diminished the CM and AP amplitude at the same time and in a parallel fashion. On the other hand, cooling of the cerebellar cortex showed the opposite results of increased amplitudes. All pre-receptorial mechanisms were avoided. A PDP-12 computer performed parametric and non-parametric statistical analysis showing the differences to be significant for the shifts. Evidence of simultaneous inhibitory cerebellar action on both potentials has been demonstrated and a cerebello-olivo-cochlear pathway is proposed for such action upon the receptor cells and/or incoming fibers.

Acoustic Stimulation↗
PubMed1990

Augmented gentamicin ototoxicity induced by vancomycin in guinea pigs.

Vancomycin has been reported to be an ototoxic drug in the clinical literature. At best, this literature is confusing. There are no reports of ototoxicity of vancomycin in experimental animals, even when it is administered concurrently with ethacrynic acid, a drug known to augment the ototoxic effect of most other ototoxic drugs. In most of the cases of permanent ototoxicity that have been reported, the patient was treated with an aminoglycoside antibiotic as well as vancomycin. This study found no evidence of vancomycin ototoxicity in guinea pigs, but found that vancomycin greatly enhanced the ototoxicity of gentamicin.

Acoustic Stimulation↗
PubMed1991

Effect on cochlear potentials of lateral semicircular canal destruction.

Recording of the cochlear potentials was successfully performed during experimental labyrinthectomy in the guinea pig and in three patients with acoustic neuromas during translabyrinthine removal of the tumors. In the guinea pig, complete interruption of the duct of the lateral semicircular canal including the endolymphatic canal caused little change in the endocochlear DC potential of the first cochlear turn and input-output function curve of the N1 component of the compound action potential elicited by 8-kHz tone bursts. Further drilling of the vestibular labyrinth in the guinea pig caused decline of these potentials when the vestibular was opened. In patients with acoustic neuromas, the interruption of the duct of the lateral semicircular canal hardly altered the N1 input-output function curve and N1 input-latency function curve during the 1-hour observation period. Consistent preservation of cochlear function even after interruption of lateral semicircular canals suggests the possibility of partial surgical labryrinthectomy with preservation of hearing for lesions involving semicircular canals.

Acoustic Stimulation↗
PubMed1995

Tympanic electrocochleography for diagnosis of Menière's disease.

OBJECTIVE: Tympanic electrocochleography (ECOG) is a noninvasive technique for recording cochlear potentials with an electrode placed on the tympanic membrane. Electrocochleography is used clinically in the evaluation of patients for endolymphatic hydrops. This study was undertaken to obtain normative data for ECOG responses to clicks and tone bursts and to determine clinical indicators that result in high test specificities. DESIGN: Three cochlear potentials were measured; the eighth nerve compound action potential, the cochlear microphonic, and the summating potential. The subjects were 53 normal hearing adults with negative histories for symptoms of Menière's disease. The ECOG responses were measured with a silver wire-rayon wick electrode that was placed on the tympanic membrane under direct microscopic visualization. Stimuli were condensation, rarefaction, and alternating polarity clicks and 1- and 2-kHz tone bursts. RESULTS: Measures that appear to be useful in the evaluation of endolymphatic hydrops include the summating potential to action potential ratio, action potential latency difference to condensation and rarefaction clicks, and the tone-burst-evoked summating potential. Relationships among these measures were investigated, and abnormal criteria were determined that result in test specificities of 95%. CONCLUSIONS: Menière's disease is viewed as a progressive disease in which ECOG characteristics vary with the disease state. Cases are presented to illustrate ECOG responses in various stages of the disease. The normative data presented in this article are useful for the detection of Menière's disease in its early stages.

Adult↗
PubMed1987

Effects of carbon monoxide on cochlear electrophysiology and blood flow.

The belief that the cochlea is particularly vulnerable to a reduction in oxygen availability comes predominantly from studies reporting the disruption of electrophysiological measures, such as the compound action potential, endocochlear potential, inner hair cell intracellular potentials or afferent nerve fiber responses by asphyxiation. Because hypoxia has frequently been suggested as an underlying mechanism by which many ototoxic agents produce injury, and because such agents are not likely to completely disrupt oxygen delivery, we investigated the effects of graded hypoxia (using doses of carbon monoxide) on cochlear blood flow, the compound action potential (CAP) and the cochlear microphonic (CM). High doses of carbon monoxide injected intra-peritoneally yielded reversible loss of the CAP sensitivity for high frequency tone bursts, the extent of which was dose dependent. The loss was observed first at the highest frequency tested (50 kHz) and as carboxyhemoglobin levels increased, contiguous lower frequencies were influenced. Recovery progressed from low to high frequencies as carboxyhemoglobin levels declined. Carbon monoxide administration also produced a dose dependent elevation in the cochlear blood flow measured by a laser Doppler flow monitor. The data suggest that carbon monoxide administration disrupts cochlear function only under extremely severe exposure conditions. An elevation in cochlear blood flow may well serve as a protective mechanism which maintains cochlear function in the face of declining blood oxygen carrying capacity and delivery. While the site of action of carbon monoxide in the cochlea is uncertain, the data clearly indicate that elements involved in the generation of the CAP for high frequency tones are particularly vulnerable.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Tympanic electrocochleography for evaluation of endolymphatic hydrops.

There has been increased interest in electrocochleography for the diagnosis and intraoperative monitoring of patients with endolymphatic hydrops. Attention has been focused on the determination of the summating potential:action potential (SP:AP) ratio from alternating polarity clicks. Review of this technique at the University of Minnesota led to a reevaluation of the usual interpretation of these recordings. Separate examination of the rarefaction and condensation click recordings provides insight into abnormal response patterns. Cases are presented to illustrate a variety of normal and abnormal patterns including abnormal differences in the latency of condensation and rarefaction-click-generated action potentials, increased summating potential, uncanceled cochlear microphonic, and reduced action potential and summating potential amplitudes. These response categories may be useful in understanding the pathophysiology of Meniere's disease.

Acoustic Stimulation↗
PubMed1987

Time-related changes in cochlear potentials in guinea pigs with experimentally induced endolymphatic hydrops.

In order to examine the changes in cochlear function occurring in hydropic ears over time, endolymphatic hydrops was provoked by obliterating the endolymphatic sac in 62 albino guinea pigs. Cochlear potentials (EP, CM, SP and AP) were recorded in the 1st, 2nd, 4th and 12th postoperative weeks, respectively. A significant reduction in the level of EP was already observed in the 2nd week and the potential was further suppressed by the 4th week. There was no significant difference between the levels of the 4th and 12th weeks. The amplitudes of CM and AP decreased progressively as time elapsed after the surgery. In sharp contrast to the other potentials, the abnormality in SP was most frequently observed in the 1st week. These results are discussed in the light of the available literature.

Action Potentials↗
PubMed1980

CM tuning can be compatible with sharply tuned receptor potentials.

There is convincing evidence that cochlear microphonics (CM) arise primarily from outer hair cells and have a frequency distribution that is much broader than that measured in inner hair cells by Russel and Sellick [6,7]. The broad tuning results from the fact that CM generated at each location decays exponentially along the cochlear duct. This implies that the sources of CM (the outer hair cells) must be more sharply tuned than the CM itself. We modeled approximately the tuning of outer hairs on the assumption that it is proportional to the shear motion between the tectorial membrane and the reticular lamina. At each frequency the spatial distribution of CM is computed by convolving the shear distribution with an exponential decay function. The frequency dependence of CM at a given location can then be found by making a cut through a family of such frequency curves. The resulting CM tuning is much flatter than that of the modeled outer hair-cell receptor potentials and roughly parallels basilar-membrane tuning below the best frequency. Above the best frequency, the theoretical curves show a frequency-dependent plateau similar to that found in physiological CM measurements.

Basilar Membrane↗