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 325 records · Page 18Linked to original sources
PubMed1999

P2X receptor-mediated changes in cochlear potentials arising from exogenous adenosine 5'-triphosphate in endolymph.

Our previous studies have determined the presence of adenosine 5'-triphosphate (ATP) in the cochlear fluids and shown that extracellular ATP introduced into the endolymphatic compartment of the guinea pig cochlea has a significant dose-dependent suppressive effect on both endocochlear potential (EP) and cochlear microphonic (CM), which is mediated via P2 receptors. In the present study, the influence of P2 receptor agonists and antagonists on this suppressive effect was investigated to characterise the subtypes of P2 receptor mediating the ATP-induced effect on cochlear function. Using a double-barreled pipette attached to a pressure injector, small volumes (2-10 nl) of ATP (0.01-1 mM) and P2 receptor agonists or P2 receptor antagonists in artificial endolymph were introduced into the scala media of the first (basal) and third turns of the guinea pig cochlea, while the EP and CM were monitored. ATP and P2 receptor agonists (5x10(-14)-1x10(-11)cibacron blue. Neither adenosine nor uridine 5'-triphosphate (2x10(-13)-2x10(-11) moles) nor the P2 receptor antagonists on their own had any effect on EP and CM. The ATP effect on the potentials was greater at the third cochlear turn when compared to the first turn. These results provide evidence that in the endolymphatic compartment of the guinea pig, the extracellular ATP effect on cochlear function is likely mediated through an interaction with P2 receptors which assemble as ATP-gated ion channels.

Adenosine Triphosphate↗
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↗
PubMedDate not supplied

[A delay in the development of hearing and a shift in the leading afferentation in the early behavioral ontogeny of birds].

Development of auditory sensitivity was studied by recording microphonic component of cochlear potentials during the period of opening the eyes in 6 species of birds with different types of ontogeny (Anas plathyrynchos, Larus canus and L. argentatus, Sterna paradisaea, Coloeus monedula and Corvus frugeleus). The onset of opening the eyes is accompanied by a delay in development of auditory sensitivity and temporary decrease of upper frequency limit of the audible range. Before such a delay acoustic afferentation is leading in feeding behaviour or in response of following in nestlings or chicks. After the period of delay pure tones lose the efficacy in eliciting feeding and following reactions, and the correlation between the low-frequency range of increased sensitivity and the efficacy of pure tone signals disappears, while the new peak of sensitivity appears which fits the maximal energetic component of the parental acoustic signals. It seems possible that the delay may be the result of brain temperature decrease while eyes open the thermoregulation being unstable. Such a delay may facilitate also the substitution of acoustic afferentation for visual in the main behavioural responses in early ontogeny.

Acoustic Stimulation↗
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↗
PubMed1994

Cochlear function after selective inner hair cell degeneration induced by carboplatin.

The ototoxicity of carboplatin, a second generation anti-cancer agent, was examined using the chinchilla as an animal model. In animals treated with a clinical therapeutic dose (400 mg/m2), the dominant degenerative change is to inner hair cells (IHCs). This is in sharp contrast to most other ototoxic agents, which damage primarily the outer hair cells (OHCs). Functional changes to the cochlea have been evaluated in carboplatin treated subjects by recording cochlear action potentials (CAP) and cochlear microphonics (CM); cochlear lesions were evaluated using scanning electron microscopy. In carboplatin treated animals, CAP thresholds to tone-pip stimuli were elevated in proportion to IHC damage in corresponding cochlear regions. In contrast, CM amplitudes and 'thresholds' remained close to normal in most cases, reflecting the preservation of OHCs in the basal turn. These results indicate a high degree of independence between the inner and outer hair cell systems in the cochlear transduction mechanism. We suggest that this species-specific preparation with selective IHC loss will provide a valuable tool for studying, separately, the role of OHCs in both afferent and efferent cochlear function.

Acoustic Stimulation↗
PubMed2006

The influence of Er. YAG laser application in fenestration to the inner ear.

OBJECTIVE: Erbium (Er.) YAG laser may be usable for middle ear surgery because of its ability to ablate bony tissue. We investigated the inner ear damage caused by the fenestration to the inner ear with Er. YAG laser. DESIGN: We investigated the influence of Er. YAG laser on the inner ear using electrophysiological technique. RESULTS: Several cases had a decrease in endocochlear potential (EP) and cochlear microphonics (CM) after the fenestration to the inner ear. CONCLUSIONS: Er. YAG laser is safe if it is used for the small and superficial fenestration to the stapes footplate. However, a few extra pulses after fenestration are dangerous.

Acoustic Stimulation↗
PubMed2005

Simultaneous measurement of electrocochleography and cochlear blood flow during cochlear hypoxia in rabbits.

In this study, a new monitoring system is developed to measure cochlear blood flow (CBF) and electrocochleography (ECochG) during transient ischemic episodes of the cochlea. A newly designed otic probe was used for the simultaneous recordings of laser-Doppler CBF and ECochG directly from the round window (RW). The probe enabled the recording of high amplitude compound action potentials (CAP) and cochlear microphonics (CM) with few averages. Experiments were conducted on rabbits to generate episodes of cochlear ischemia by using timed compressions of the internal auditory artery (IAA). The computer monitoring system extracted and measured CAP and CM components from ECochG in real-time. Results indicate that CM and CAP generally followed CBF during compressions and releases of IAA. Both CBF values and CAP amplitudes showed an overshoot following the reperfusion. CAP amplitude measures were found to be very sensitive to ischemia showing very rapid amplitude, latency and morphological changes. CM amplitude decreased more slowly than the CAP and CBF. Simultaneous recordings of CBF and ECochG using the otic probe provide a valuable neuromonitoring tool to investigate the dynamic behavior of the cochlea during ischemia.

Acoustic Stimulation↗
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↗
PubMed2004

[Electrophysiologic examinations in low frequency hearing impairment: clinical and prognostic aspects].

INTRODUCTION: Low-frequency hearing impairment (LFHI) is mainly associated to endolymphatic hydrops and shows a high variety of possible outcomes. Electrophysiologic examinations are widely recommended in diagnostics of LFHI, wheras up to now no data exist about the prognostic value of these examinations in a conservative therapeutic regimen. METHODS: In a quality assessment, we retrospectively evaluated the records of 90 patients, and performed an audiometric follow-up for analysis of long-time hearing data. All patients had undergone diagnostic electrocochleographic examination (ECochG) and then had been treated with rheologic infusions, followed by dehydrating infusions in patients lacking complete remission. The results of both therapeutic strategies and of long-time results were correlated to electrophysiologic findings. RESULTS: The prognosis of LFHI is significantly reflected by pretherapeutic electrocochleographic data. All significant parameters were associated to compound action potential (CAP) whereas parameters associated to cochlear microphonics (CM) did not include any utilizable prognostic value. In patients with a good outcome, the latency of CAP complex was significantly shorter, and the width of CAP complex significantly smaller than in patients with poor hearing outcome after rheologic and after dehydrating therapy and in long time assessment. The relation of summating potential (SP) und CAP was significantly smaller when the outcome was sufficient or good for either therapy and in long time analysis. Steep CAP-input-output-curves were associated to insufficient outcome after rheologic therapy and in long time assessment, but not for dehydrating therapy. CONCLUSIONS: The results indicate that ECochG is of significant prognostic value concerning hearing outcome after conservative therapy in patients suffering from LFHI. It can help the physician to counsel the patient and perform an effective management of the disease. We conclude that ECochG should be performed before the onset of therapy, including collection of SP and CAP data whereas CM parameters may be omitted.

Action Potentials↗
PubMed1997

[Effects of increasing perilymph calcium levels on various cochlear potentials].

In the present study, we examined the effects of increasing perilymph calcium (12.20 mmol/L) on guinea pig cochlear functions. The results demonstrated that high calcium perilymphs suppressed the magnitude of compound action potential of auditory nerves (CAP) with a prolongation of N1-peak delay at a constant intensity (90 dB SPL), but not of cochlear microphonics (CM). High calcium perilymph didn't change general endocholear potential (G-EP), while reduced the rapid change of EP at on and off set of 115dB SPL white noise exposure. Furthermore the value of negative potential (N-EP) induced by anoxia was decreased because of high calcium perfusions. Machanisms of these effects were discussed.

Action Potentials↗
PubMed2001

Cochlear receptor (microphonic and summating potentials, otoacoustic emissions) and auditory pathway (auditory brain stem potentials) activity in auditory neuropathy.

OBJECTIVE: To define both auditory nerve and cochlear receptor functions in subjects with auditory neuropathy (AN). DESIGN: We tested 33 AN subjects (66 ears) and compared them with 21 healthy subjects (28 ears). In AN subjects, the average pure-tone (1, 2, and 4 kHz) threshold loss was 57 dB HL. Click stimuli were used to elicit transient evoked otoacoustic emissions (TEOAEs), cochlear microphonics (CMs), and auditory brain stem responses (ABRs). Both cochlear and ABR potentials were recorded from surface electrodes (vertex-ipsilateral mastoid) using averaging procedures. The amplitudes and latencies of CMs and ABRs and the amplitude of the TEOAEs were analyzed. RESULTS: CM amplitudes recorded from normal ears decreased as a function of subject age. CMs recorded from AN subjects fell within the normal age-adjusted range in 60% of the subjects and were >2 SEEs (standard error of estimate) above the age-adjusted normal regression in 40% of the subjects. TEOAEs were absent in 19 (30%) AN ears (bilaterally in eight, and unilaterally in three subjects) and were present in 44 ears. In AN subjects, correlations among CM amplitude, TEOAE amplitude, and pure-tone average thresholds were not significantly related. CM amplitudes were not significantly different whether TEOAEs or ABRs were present or absent. The ABR was present in 21% of AN subjects and consisted of a low-amplitude Wave V without a preceding Wave I. Measures of CM amplitude and PTA hearing loss were not significantly different in those AN ears with a preserved ABR compared with ears with absent ABRs. Summating potentials to transient click stimuli were of small amplitude (<0.1 microV) and detectable in approximately 50% of the AN and healthy control subjects limiting formal analysis of summating potentials. CONCLUSIONS: In a significant proportion of AN subjects, we found abnormalities of cochlear receptor function, including elevated CM amplitudes and absence of TEOAEs. These two abnormalities occurred independently of each other. A low amplitude Wave V of the ABR was found in approximately one-fifth of AN subjects, evidence that neural synchrony can be partially preserved in some subjects with this disorder.

Adolescent↗
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↗
PubMedDate not supplied

Effects of high-frequency sound on the guinea pig cochlea. Electrophysiological study using cochlear microphonics, action and endocochlear potential.

There are only a few studies investigating the effect of high-frequency sound on hearing. Authors investigated experimentally the effect of long exposure to high-frequency sound (19 and 25 kHz) below 100 dB (SPL) on guinea pig inner ear. Changes in cochlear microphonics (decrease of maximum output voltage) and especially in endocochlear potential (decrease of the absolute value of negative potential) were observed. The effects of high-frequency sound (10-30 kHz) on the inner ear were discussed.

Action Potentials↗
PubMed2000

Excitotoxic effect of kainic acid on chicken otoacoustic emissions and cochlear potentials.

Kainic acid (KA) is a potent glutamate analog that can temporarily or permanently damage glutamatergic neurons. The purpose of the present study was to determine the short- and long-term effects of KA on chicken otoacoustic emissions and cochlear potentials. A chronic electrode was used to record the compound action potential (CAP), cochlear microphonic (CM), and the slow, positive neural potential (SPNP), a predominantly dc response. The CM, CAP, SPNP, and distortion product otoacoustic emissions (DPOAEs) were recorded before and after infusing 10 microl of a low dose (KA-L, 0.3 mM) or high dose (KA-H, 5 mM) of KA into scala tympani. KA caused a rapid and large reduction in CAP and SPNP amplitude in both the KA-H and KA-L groups; however, the CM and DPOAEs were largely unchanged. The amplitude of the CAP and SPNP in the KA-L group began to recover around 1 week post-KA, but was approximately 50% below normal at 4 weeks post-KA. In contrast, the CAP and SPNP showed no signs of recovery in the KA-H group. The results suggest that KA has no effect on the CM and DPOAEs generated by the hair cells, but selectively damages the CAP generated by the cochlear ganglion neurons. The reduction in the avian SPNP suggests that the response originates in the cochlear afferent neurons, unlike the summating potential (SP) in mammals that is generated in hair cells.

Action Potentials↗