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PubMed1993

[Functional and morphological changes of the cochlea in guinea pigs during anoxia].

The influence to endocochlear potential (EP), cochlear microphonics (CM) and summating potential (SP), the ultrastructural changes of the cochlea and the survival time of hair cells in guinea pigs during anoxia and suffocation were investigated. We found that: 1) The stria vascularis was much more sensitive to anoxia than hair cells. 2) 85% CM was highly sensitive to anoxia, and 15% kept stable until the destruction of outer hair cells. 3) -SP turned into +SP after anoxia. 4) EP was related to the destruction of outer hair cells and the disappearance of CM.

Animals↗
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↗
PubMed1997

[Experimental study on the effect of nitric oxide on cochleas of guinea pigs].

The effects of nitric oxide (NO), 1-monoarginine (L-Arg), sodium nitroprusside (SNP) and N-methyl-1-monoarginine (NMLA) (which is an antagonist of nitric oxide synthase) on endocochlear potential, compound action potential(CAP) and cochlear microphonic(CM) of cochleas were studied by means of perilymphatic perfusion of the agents. The results showed that NMLA reduced EP, CAP and CM, L-Arg perilymphatic perfusion could reverse the change caused by NMLA. Continuous NO perilymphatic release restored the changes of EP, CAP and CM back to normal, sometimes above normal, followed by rapid reduction. After SNP perilymphatic perfusion, EP, CAP and CM went up transiently and then declined gradually and remained at a lower level. Addition of NMLA did not reverse the changes. The change of the latent period of CAP N1 and drift of CM was consistent with their amplitude changes. It was suggested that NO might help maintaining inner ear function under physiological condition and participate in controlling the micromechanical character and sensitivity of cochlear hair cells, undue expression of NO may cause toxicity to cochleas.

Action Potentials↗
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↗
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↗
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↗
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↗