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PubMed1992

Fine structure of the intracochlear potential field. II. Tone-evoked waveforms and cochlear microphonics.

1. Extracellular evoked potentials to low-frequency pure-tone stimuli were recorded in the second cochlear turn of the anesthetized guinea pig. Spatial variations of the field potentials were characterized by advancing and withdrawing micropipettes along radial tracks in scala tympani (ST) and scala vestibuli (SV). Compound action potentials (CAPs) and cochlear microphonics (CM) are the major components of the evoked responses to 50- to 1,600- Hz stimuli. The relative contribution of CM and CAP to the evoked potentials varies with cochlear scala and location within the scala as well as with stimulus frequency and intensity. 2. In the 50- to 800-Hz frequency range, the largest CM in the second turn was recorded from scala media (SM). Below 500 Hz the CM in SV is larger than in ST, whereas above 500 Hz a larger CM is present in ST. The CM in SV is nearly in phase with the CM in SM, although it is smaller by a factor of two to four. The CM diminishes by another factor of two over a 100-microns depth range as an electrode is withdrawn out of SV through the spiral ligament. While the electrode is in SV or in the fluid outside the spiral ligament, the CM magnitude does not change by greater than 10%. The shape of the radial CM magnitude profile along tracks in SV shows little or no dependence on intensity in the 65- to 105-dB SPL range or on frequency in the 50- to 800-Hz range. 3. Unlike the CM profiles in SV, the shape of the CM magnitude and phase profiles in ST are a complex function of frequency and intensity. Below 500 Hz, the CM goes through a 140-180 degree radial phase shift over a 100-microns distance near the spiral ligament bordering ST. Concomitant with the large radial phase shift is a local minimum of the CM magnitude. The location of this "virtual ground point" can shift radially by as much as 100 microns over a 30-dB intensity range. The CM magnitude deep in ST is always larger than the CM outside the spiral ligament bordering ST. However, the ratio of the CM magnitudes at these two locations can vary from 0.1 to 0.8, the ratio tending to increase with intensity in the 200- to 800-Hz range.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1983

Chronological changes of electrocochleogram in experimental endolymphatic hydrops. Special reference with AP output potential and hair cell cilia.

Chronological changes of the whole nerve action potential (AP), cochlear microphonics (CM) and summating potential (SP) in experimental endolymphatic hydrops in guinea pigs were studied during a period from 1 week to 13 months after the endolymphatic sac obliteration. Endolymphatic hydrops became extensive in month 3 and persisted thereafter. The threshold of AP increased with the lapse of time but good AP output potential was obtained, being maximum in month 3. The threshold of CM increased with the lapse of time. The CM output potential was the highest around week 3 when endolymphatic hydrops was slightly formed, and it decreased thereafter. SP responses at the frequencies of 8, 4, 1 and 0.5 kHz showed the reversed polarity of -SP in month 3 and changed towards potential 0 thereafter. In animals showing super-normal AP output potential, the cilia in the third row of outer hair cells were disarranged. This seems to be involved in recruitment.

Action Potentials↗

PubMed1984

Single unit responses in the cochlear nucleus of the deaf quivering mouse.

Mice homozygous for the autosomal recessive gene quivering do not have a classical Preyer reflex and appear to be deaf. Round window recordings including both cochlear microphonics and compound action potentials failed to reveal any abnormality. However, auditory-evoked potentials recorded from the inferior colliculus (IC) are small with long latencies, and the thresholds are at least 50 dB higher than those recorded in controls. This suggests that the auditory deficit arises in the auditory pathway between the cochlear nerve and IC and underlines the need for a description of the functioning of the cochlear nucleus (CN). Single units were recorded extracellularly from the CN in 9 mutants (qv/qv) and 11 control animals (+/qv, or +/+) in the age range 60-120 days. The spike response pattern in mutant animals was broadly similar to that in the controls: a sustained response with monotonic rate-intensity functions. In addition the mean Q10dB for units in the mutants was similar to that of the controls. However, in mutants the group mean threshold at the characteristic frequency was higher and the latency to the first evoked spike at 20 dB above threshold was longer than in controls. Some unit responses in the mutants were similar to those of the controls. Nevertheless, in the quivering mouse, evidence now exists of single unit dysfunction in the cochlear nucleus.

Acoustic Stimulation↗

PubMed1982

Cochlear potentials in the Bronx waltzer mutant mouse.

The Bronx waltzer mutant mouse has a unique cochlear abnormality in which the outer hair cells appear normal but the inner hair cells are absent. Potentials recorded from the round window indicate that the gross cochlear nerve action potential is very small or absent and cochlear microphonics are present but of small amplitude. Positive and negative summating potentials can both be recorded, indicating that mammalian outer hair cells are capable of producing both positive and negative DC potentials.

Animals↗

PubMed1983

Effect of xipamide and furosemide on guinea pig cochlear recorded potentials.

The effects of furosemide and xipamide on guinea pig cochlear potentials were studied under acute conditions. Auditory nerve action potentials (AP) and cochlear microphonics (CM) were depressed by both diuretics in a dose-related manner. Furosemide was more effective on AP than on CM. In contrast, the xipamide-induced reductions of AP and CM were similar. Our results suggest that the depressive effects of furosemide or xipamide may be related to a direct action on cochlear mechanisms.

Action Potentials↗

PubMed1986

Electrocochleographic study of low-tone hearing loss without vertigo.

Auditory nerve action potential (AP), cochlear microphonics (CM) and summating potential (SP) were recorded from 6 patients with low-tone hearing loss without vertigo. All these cases showed high AP and -SP amplitude and satisfactory CM response. These findings resembled the electrocochleographic findings of type 1, which is an early stage of Ménière's disease. Hearing returned to normal range in half of the cases but remained hardly changed in the other half. The difference between these two groups could not be clarified electrocochleographically. On the other hand, low-tone hearing loss due to retrolabyrinthine lesion and due to familial sensorineural deafness was shown to have a low AP amplitude.

Adolescent↗

PubMed1982

Electrocochleographic study of Ménière's disease.

Auditory nerve action potential (AP), cochlear microphonics (CM), and summating potential (SP) were recorded from 32 patients with Ménière's disease. Patients were classified into three groups according to the degree of their hearing impairment. The group of patients that had a mild to moderate hearing loss and whose hearing was reversible showed notably satisfactory responses for AP, CM, and negative SP (-SP), and also showed a high incidence of positive SP (+SP). Low responses for AP and CM with an increase of detection thresholds and a high -SP/AP ratio were obtained from patients with moderate hearing impairment, whose hearing fluctuated slightly. These electrocochleographic findings were suggestive of the pathophysiologic differences at the various stages of Ménière's disease.

Audiometry, Evoked Response↗

PubMed1992

Effects of various noise exposures on endocochlear potentials correlated with cochlear gross responses.

Changes in endocochlear potentials (EP), cochlear microphonics (CM), and compound action potentials (CAP) with noise exposure were investigated in guinea pigs. The animals were anesthetized and immobilized and exposed to white noise at intensities ranging from 105 to 125 dB. The negative EP (N-EP) was induced by anoxia and was investigated during and after noise exposure. It was found that the general EP (G-EP, the sum of both positive EP (P-EP) and N-EP) increased remarkably during exposure to 115 dB noise but decreased during exposure to 125 dB noise. A smaller absolute value of N-EP was encountered only during exposure to 125 dB noise. The results shed light on the relationship between EP and CM, CAP changes, and the potential mechanism of EP change and its significance in noise-induced hearing loss.

Acoustic Stimulation↗

PubMed1980

Meniere's disease: the selection and assessment of patients for surgery using electrocochleography.

Transtympanic electrocochleography has been used to measure the action potential (AP), summating potential (SP), and cochlear microphonic (CM) in patients with Menière's disease. In this condition the widening of the AP/SP complex is thought to be due to an enhanced negative SP which shows no adaptation and this may be the result of an increased asymmetry produced by endolymphatic hydrops. Measurements have also been made using two groups of agents -- those designed to increase the cochlear blood flow (the metabolic activator naftidrofuryl and inhalations of carbon dioxide) and those designed to reduce the hydrops "osmotically" (glycerol) or by diuresis. It was hoped that the "glycerol dehydration test" when assessed electrocochleographically would lead to a better selection of patients for surgical decompression of the saccus endolymphaticus. It was also hoped that it would lead to a fuller understanding of the electrophysiological changes which occur in Menière's disease. While it appeared that a decrease in the negative SP after glycerol may be a more sensitive indicator of the changes within the cochlea than either pure-tone audiometry or speech discrimination, no clearcut correlations between this change and the surgical result could be demonstrated. In many patients the AP/SP waveform remained unchanged after successful surgery, indicating perhaps that the pathological changes may have been checked but not reversed, while the hearing remained "pegged" at its preoperative level. Electrocochleography during operation failed to show any consistent change in the waveform or CM.

Acoustic Stimulation↗

PubMed1982

Acute perilymphatic perfusion of the guinea pig cochlea.

A method for the continuous perfusion of the perilymphatic space of the inner ear in the guinea pig is described. Artificial perilymph is supplied to the cochlea and drained away through a tubing system while flow rates from 10 microliters/min to 0.3 ml/min are established by gravity syphon pressure. Techniques are also presented which allow control over the temperature of the perfusate and over the level of dissolved oxygen in the perfusate. Alone with these variables, the pH of the artificial perilymph can be manipulated and various drugs can be added to the perfusate to test their effect on the inner ear. The function of the inner ear is monitored by continuous recording of the sound evoked bioelectric potentials, the cochlear microphonic and the compound action potential. The cochlear perfusion technique has many applications in the study of cochlear physiology and metabolism, and in testing the sensitivity of the inner ear to ototoxic drugs.

Animals↗

PubMed1983

Effects of trichloroethylene exposure on hearing. An investigation of cochlear microphonics and action potential of the guinea pig.

Four groups of guinea pigs with normal Preyer's reflex were exposed to trichloroethylene (TCE). Each group consisted of nine to 10 naive male albino Hartley guinea pigs of 9 weeks of age with a body weight of approximately 400 g. To test the suggestion that TCE causes damage to the cochlear system, a study was conducted involving four experiments. The results were as follows: No significant difference was observed between the intensity functions of the CM (4 kHz) and AP (7 kHz) potentials of the control groups and those of the TCE-exposed groups by analysis of variance. It was considered that there was no difference in the cochlear reaction to high frequency sound between guinea pig and man. It therefore might be suggested that acute exposure to TCE of a high concentration does not always induce dysfunction of the organ of Corti and the 8th nerve in man.

Action Potentials↗

PubMed1994

Time course of endolymph volume increase in experimental hydrops measured in vivo with an ionic volume marker.

A new method has been developed to measure the cross-sectional area (CSA) of scala media in the living cochlea. The method has some advantages over histological methods, in which tissues may shrink or move during processing. In the present study, scala media CSA was measured in the second turn of guinea-pig cochleas in which endolymphatic hydrops was induced surgically. The area measurement method used an iontophoretic injection of a volume marker into scala media, during which the concentration of marker in endolymph was monitored with an ion-selective microelectrode. The measured marker concentration was inversely proportional to the CSA of endolymph. The marker we used was the anion arsenic hexafluoride (AsF6-), which was almost ideal for the purpose as it was retained well in endolymph. Area was measured in normal animals and in hydropic animals at times from 4 days to 16 weeks after endolymphatic duct obstruction. The results showed that hydrops develops within days of ablation of the endolymphatic duct. The degree of hydrops was compared with electrophysiological measures of function, including the endocochlear potential, action potential thresholds and the amplitudes of the cochlear microphonic, summating potential and action potentials. In the initial stages of hydrops development, electrophysiological changes were small. In contrast, there were marked functional changes between 8 and 16 weeks, when endolymph volume was no longer increasing. If the same is true for dysfunction in the ears of patients with Ménière's Disease, then it may not be possible to restore normal function simply by alleviating the hydrops.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗

PubMed1981

Comparison between the effects of continuous and impact noise on cochlear potentials in guinea pigs.

Cochlear microphonics (CM), action potentials (AP), and endocochlear potential (EP) were recorded from anesthetized, immobilized guinea pigs during potential (EP) were recorded from anesthetized, immobilized guinea pigs during and following 20 min periods of noise exposure. Changes in cochlear potentials were compared in guinea pigs exposed to continuous broadband noise or mechanically generated impact noise of equal energy content. Over a range of continuous noise levels from 95 to 105 dB SPL it was found that continuous noise produced less suppression of CM and a greater suppression of AP than did impact noise of equal energy. A reduction of EP did not accompany CM suppression with either type of noise exposure. Suppression of CM and AP was also compared in guinea pigs with chronically implanted round window electrodes. In these preparations, AP was suppressed to a similar extent by impact and continuous noise of equal energy, but CM was suppressed to a significantly greater extent by impact noise. The data from both series of experiments indicate that the suppression of cochlear responses is not predicted by an "equal energy" rule when impact and continuous noise are compared.

Acoustics↗

PubMed1992

Sound induced displacement response of the guinea pig hearing organ and its relation to the cochlear potentials.

The sound induced motion of the cells within the fourth turn of the guinea pig organ of Corti was studied in an in vitro preparation (Ulfendahl et al. 1989). The cells were visualised by relief microscopy, achieved by an oblique illumination technique. The motion of the sensory cells was observed during the recording of the extracellular receptor potentials; the cochlear microphonics (CM) and the summating potential (SP). Our results show that the temporal bone preparation sustains an endocochlear potential and maintains the receptor potentials for 3-4 h. During the tone stimulus the outer hair cells were seen to elongate and the surface of the organ of Corti was displaced in the direction of scala vestibuli. The displacement response showed two frequency maxima, one at 150 and one at 300 Hz. The mechanical tuning of the sensory organ coincided with the tuning of the receptor potentials. Both the mechanical and the electrical responses at the 300 Hz peak were vulnerable to the administration of methylene blue suggesting cyclic GMP dependence, whereas the 150 Hz peak was unaffected. We conclude that the outer hair cells provide active tuning in the organ of Corti.

Acoustic Stimulation↗

PubMed1985

Corrective effects of thyroxine on cochlear abnormalities induced by congenital hypothyroidism in the rat. II. Electrophysiological study.

In order to study the corrective effects of thyroxine (T4) on functional abnormalities induced by congenital hypothyroidism, small doses of T4 were injected to propylthiouracil-treated (PTU-treated) rat pups for 2 consecutive days on selected periods of development (days 3 and 4, 6 and 7, 9 and 10, 12 and 13, 18 and 19). Some animals also received thyroid replacement therapy from days 12 to 17. The animals were tested electrophysiologically on day 30, by recording the compound action potential and the cochlear microphonic from the round window after click and tone burst stimulation. PTU-treated animals given T4 for 2 consecutive days demonstrated both AP and CM threshold shifts. On the contrary, PTU-treated animals given T4 from days 12 to 17 demonstrated a normal CM output of the cochlea, but still showed elevated AP thresholds. These results are discussed with previous data concerning the corrective effects of T4 on cochlear structures in PTU-treated rats previously described.

Animals↗

PubMed1989

[A study on the effect of infrasound].

In order to examine the influence of infrasound that is becoming topical in society, human beings and guinea pigs were exposed to infrasound. After exposure, the hearing level, vestibular functions and autonomic nervous functions of human beings were examined, and endocochlear potential (EP) and cochlear microphonics (CM) of guinea pigs were examined. Next, after guinea pigs were exposed to intense audible low frequency sound that was born secondarily from infrasound and/or vibration of whole body concerning about air pressure change of infrasound, their EP and CM were examined. The results obtained were as follows: 1) By exposure of infrasound 10-15Ha 130-135dB LSPL for 30min. to human beings, their hearing level, vestibular functions and autonomic nervous functions were not changed. 2) After exposure of infrasound 15Hz 135-140dB LSPL for 24hrs.-72hrs. to guinea pigs, their EP and CM remained normal. 3) After each exposure of audible low frequency sound 90Hz 120dB SPL for 72hrs., 150Hz 110dB SPL for 72hrs. and 200Hz 100dB SPL for 72hrs. to guinea pigs, their EP became abnormal though their CM remained normal. 4) After exposure of 15Hz 500 mu +/- 30 mu vibration for 72hrs. to guinea pigs, both EP and CM remained normal. 5) After exposure of both audible low frequency sound 150Hz 100dB SPL and vibration 15Hz 500 mu +/- 30 mu for 72hrs. to guinea pigs, their EP became abnormal though their CM remained normal.

Adult↗

PubMed1982

Corresponding effects of hypoxia on the cochlear microphonic and the compound action potential.

Mild hypoxia has an unexpected influence on the compound action potential (CAP) compared to its effect on the cochlear microphonic (CM). While the CM decreases in amplitude near threshold, the low-level CAP increases in amplitude by as much as 400% and decreases in latency and width. The magnitude of latency decrease is dependent on the center frequency of 1/3 octave band-filtered clicks used as stimuli. Below 13 500 Hz the latency is increasingly shortened at a rate of 0.073 ms/octave. At high intensities moderate hypoxia has no effect on either the CM or the CAP. However, with more severe hypoxia the high-level CM also begins to deteriorate. Correspondingly both the high- and low-intensity CAP decrease in magnitude and increase in latency relative to their control values. Assuming that the low-level CM is generated by outer hair cells, these results suggest that one relationship between outer hair cell function and auditory nerve function near function near threshold is that of inhibition. The fact that N1 latency is shortened suggests that this inhibition occurs in the basalward direction.

Acoustic Stimulation↗

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↗