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At least 217 records · Page 12Linked to original sources
PubMed1981

Effect of ethaverine hydrochloride on cochlear microcirculation.

The effect of ethaverine hydrochloride on cochlear microcirculation was observed in short-term experiments on 11 guinea pigs. In these experiments, the endocochlear PO2, endocochlear potential (EP), cochlear microphonic (CM) potential, and blood pressure (BP) were recorded. Endocochlear PO2 was measured polarographically by gold electrodes in the scala media. Ethaverine hydrochloride was administered by intravenous infusion for ten minutes in doses of 2, 5, and 10 mg/kg. These experiments demonstrated that ethaverine hydrochloride in doses of 5 and 10 mg/kg caused significant elevation of endocochlear PO2 for 35 to 90 minutes, even when the BP temporarily declined. At the same time, it was observed that this improvement of cochlear microcirculation coincided with an increase of the CM potential. Decrease of the EP is probably the result of BP decline and a direct action of ethaverine on EP generation.

Acoustic Stimulation↗
PubMed1978

Components of the frequency-following potential in man.

The scalp recorded frequency-following potentials (FFP) are a composite of several FFP's which may be distinguished by comparing simultaneously recorded waveforms from vertical and horizontal derivations in response to tones of very low frequently (below 350 Hz). The two most prominent FFP's were designated FFP1 and FFP2. FFP1 was recorded equally well in vertical and horizontal derivations and at a high stimulus intensities tended to be the predominant FFP. FFP2 followed FFP1 usually by about 1.7 msec and was optimally recorded in the vertical derivation. FFP2 threshold was about 10 dB lower than threshold for FFP1 and in several subjects, FFP2 was observed at 25 dB SL. Two other FFP's, a far-field recorded cochlear microphonic potential and a low-amplitude FFP, the latter presumably of neural origin, were also studied.

Acoustic Stimulation↗
PubMed1990

Cochlear threshold assessment using tone-derived action potentials.

An evoked-potential technique has been evaluated which detects whether the cochlea responds to a continuous, low level tone. The technique involves recording the cochlear action potential (AP) response to a suprathreshold probe tone, first in the absence and then in the presence of a continuous masking tone at the same frequency. Subtraction of the masked AP waveform from the unmasked AP yields a 'derived' potential, provided the continuous tone is above the threshold of cochlear sensitivity. Derived AP responses may be recorded with continuous masking tones over 10 dB below the threshold to the probe stimulus. In normally hearing guinea pigs, the mean best derived threshold using a 10-microV response criterion was 7.1 dB SPL, compared to 18.9 dB for conventional AP thresholds. The tone-derived response appears to provide a more sensitive and frequency-specific method for determining cochlear thresholds.

Animals↗
PubMed1982

Sectioning the efferent bundle decreases cochlear frequency selectivity.

Cochlear frequency selectivity was tested in rats and cats before and after sectioning the vestibular nerve which carries the efferent bundle to the cochlea. Compound action potential tuning curve were obtained by a simultaneous masking procedure. Transection of the efferent bundle resulted, in all group of animals, in an enlargement of the tip segment of the tuning curve. The Q10 dB value decreased by about 30% without any significant threshold change. These results taken together with previous developmental findings, suggest that efferents to outer hair cells could play a role in sharpening the frequency selectivity of the cochlea.

Animals↗
PubMed2004

Cochlear activation at low sound intensities by a fluid pathway.

In order to assess the mechanisms responsible for cochlear activation at low sound intensities, a semi-circular canal was fenestrated in fat sand rats, and in other experiments a hole was made in the bone over the scala vestibuli of the first turn of the guinea-pig cochlea. Such holes, which expose the cochlear fluids to air, provide a sound pathway out of the cochlea which is of lower impedance than that through the round window. This should attenuate the pressure difference across the cochlear partition and thereby reduce the driving force for the base-to-apex traveling wave along the basilar membrane. The thresholds of the auditory nerve brainstem evoked responses (ABR) and of the cochlear microphonic potentials were not affected in the fenestration experiments. In addition, holes in the scala vestibuli of the first turn did not cause ABR threshold elevations. These results contribute further evidence that at low sound intensities the outer hair cells are probably not activated by a base-to-apex traveling wave along the basilar membrane. Instead it is possible that they are excited directly by the alternating condensation/rarefaction fluid pressures induced by the vibrations of the stapes footplate. The activated outer hair cells would then cause the localized basilar membrane movement.

Acoustic Stimulation↗
PubMed1989

Auditory brain stem responses in preterm infants: evidence of peripheral maturity.

This study explored further the relationship between peripheral and central auditory maturation on the basis of the auditory brain stem response. Auditory brain stem responses were recorded in preterm infants and adults to rarefaction and condensation click stimuli transduced through insert Tubephones. Infant recordings presented a triphasic waveform preceding wave I similar to that of the cochlear receptor potentials seen with adults during electrocochleography. Wave I latency and amplitude were found to be equivalent to those of adult subjects. Moreover, neither latency nor amplitude variability among infant wave I responses was found to be any greater than adults. Latencies of waves III and V, however, exhibited the expected differences relative to the adult comparison group. When the indirect evidence of cochlear receptor potentials in the infant are viewed adjacent to the observations that their ABR wave I latency, amplitude, and variability were entirely consistent with those of young adults, the data lend strong support for peripheral auditory electromaturity. These data are discussed relative to previously published reports of prolonged wave I latency in the infant which was attributed either to middle ear effects or immaturity of the cochlea and first order VIIIth nerve neurons.

Adult↗
PubMed1982

Location-specific components of the gross cochlear action potential: an assessment of the validity of the high-pass masking technique by cochlear nerve fibre recording in the cat.

The auditory high-pass masking technique has been used in attempts to define the origin, along the cochlear partition, of the gross cochlear action potential (CAP) and the gross brain stem potential. Theoretically, the high-pass masking paradigm should be frequency and location specific at the cochlear level, and some indirect evidence does point to this specificity. However, this hypothesis has not yet been directly substantiated. In the present experiment, click-evoked cochlear nerve activity was recorded simultaneously from the round window and from single fibres of the cochlear nerve, with and without high-pass maskers spaced in octaves from 0.5 to 16 kHz, at three intensities, in the anaesthetized cat. The "derived' CAPs were computed and compared with the mapping of single cochlear fibre responses under the same conditions. With one main exception, the conclusions drawn on the origin of the frequency components of the "derived' potentials were found to be valid in the normal cat. The exception concerned fibres with characteristic frequencies below 1-2 kHz, where the substantial spread towards the high frequencies of their frequency threshold curves, and the effects of lateral suppression or of other "remote masking' phenomena rendered the high-pass masking less location specific. From these results and certain assumptions, we would predict the high-pass masking technique to be valid in electrophysiological investigations in normal humans for frequencies down to 0.5-1 kHz.

Animals↗
PubMed1988

Modulation of cochlear tuning by low-frequency sound.

An intense, low-frequency tone (about 30 Hz) modulates the sensitivity of the inner ear to high-frequency stimulation. This modulation is correlated with the displacement of the basilar membrane. The findings suggest that the modulation may also affect cochlear tuning. We have investigated modulation of cochlear tuning by low-frequency sound in the guinea pig. Applying indirect methods of measurement (narrow-band analysis of compound action potentials and compound-action-potential tuning curves), the results suggest a shift of the excitation pattern along the basilar membrane towards higher-frequency areas. The shift occurred for both scala tympani and scala vestibuli displacement of the cochlear partition. Tuning curves, obtained from single units in the cochlear nerve, show sensitivity loss and a tip shift towards lower frequencies. This was also found for both scala tympani displacement and scala vestibuli displacement. The shift of the tip of the tuning curve towards lower frequencies corresponds to the inferred high-frequency shift of the excitation pattern. The relationship of these phenomena with the pathophysiology of Ménière's disease and with possible active mechanisms in cochlear transduction is discussed.

Animals↗
PubMed1989

The combined effect of cisplatin and furosemide on hearing function in guinea pigs.

The effect of the combined administration of cisplatin and furosemide on the electrophysiological hearing thresholds and endocochlear DC potential (EP) was studied in guinea pigs. A lack of interaction was found in animals given repeated intraperitoneal injections of a low dose of cisplatin with a pharmacological dose of furosemide. An ototoxic interaction occurred when a moderately high dose of cisplatin was administered intravenously at a time when the strial function was most affected by a very high dose of furosemide. The interaction was seen both as a decreased EP and a pronounced shift of auditory thresholds. It is concluded that the stria vascularis plays a role in the ototoxic mechanism of cisplatin.

Animals↗
PubMed1984

Some otological differences between pigmented and albino-type guinea pigs.

Cochlear action potential thresholds across frequency (AP audiograms) and AP tuning curves were compared in albino (Dunkin-Hartley) guinea pigs and normal pigmented animals. AP audiograms were very similar; on average the albinos had AP thresholds 2-3 dB lower at 2 kHz and below compared with the pigmented guinea pig. AP tuning curves at 16 kHz were, on average, significantly less sharply tuned in the albino, but similar at 8, 4, and 2 kHz. Although we find only small differences in these measures of normal cochlear function, other evidence in the literature suggests that in auditory research the use of "albino" guinea pigs is best avoided.

Animals↗
PubMed1989

Thresholds of cat cochlear nucleus neurons to microwave pulses.

Action potentials of neurons in cat dorsal and posteroventral cochlear nuclei were recorded extracellularly with glass microelectrodes while the head of the cat was exposed to microwave pulses at 915 MHz using a diathermy applicator. Response thresholds to acoustic tones, acoustic clicks, and microwave pulses were determined for auditory units with characteristic frequencies (CFs) from 278 Hz to 39.2 kHz. Tests with pulsatile stimuli were performed for durations of 20-700 mus, principally 20, 70, and 200 mus. Brainstem midline specific absorption rate (SAR) threshold was as small as 11.1 mW/g per pulse, and specific absorption (SA) threshold was a small as 0.6 muJ/g per pulse. Microwave thresholds were generally lower for CF less than 9 kHz, as were most acoustic thresholds. However, microwave threshold was only weakly related to click threshold and CF-tone threshold of each unit.

Animals↗
PubMed1982

Ototoxic effects of salicylates on the responses of single cochlear nerve fibres and on cochlear potentials.

Anaesthetized cats were given 400 mg/kg sodium salicylate i.v. producing blood levels in excess of 300-400 mg/kg. Within 10 min of injection, thresholds of fibers had risen by values ranging from 13 to 21 dB. The elevation in thresholds progressed rapidly over the subsequent 5 or so hours, reaching a plateau in about 10 h. The Q10 dB values for tuning of the cochlear fibres decreased by a factor of 3-4 on average over the same period. Likewise, the dynamic range of response was significantly reduced. These effects on the cochlear fibres were reflected in the elevation of the gross cochlear action potential thresholds. In contrast to the findings with other types of cochlear pathology, the mean discharge rate of the subpopulation of cochlear fibres having discharge rates above 20 sp/s was significantly increased by an average of 10-20 sp/s. There was a tendency for this increase to be more marked for fibres with higher characteristic frequencies and to be inversely related to threshold. In addition, 63% of fibres had anomalous temporal patterns of spontaneous activity. In view of the relevance of these data on the ototoxic effects of salicylates for our understanding of tinnitus, the effects of direct electrical current stimulation via the round window have been studied. Positive currents up to at least 600 microA suppressed the spontaneous and evoked activity of all cochlear fibres studied in the normal cochlea. These findings are consistent with the effects of such current stimulation in patients with tinnitus of peripheral origin and support the hypothesis that the neural correlate of such tinnitus is hyperactivity at the cochlear nerve level.

Animals↗
PubMed2005

GATA3 haploinsufficiency causes a rapid deterioration of distortion product otoacoustic emissions (DPOAEs) in mice.

Human HDR (hypoparathyroidism, deafness and renal dysplasia)-syndrome is caused by haploinsufficiency of zinc-finger transcription factor GATA3. The hearing loss due to GATA3 haploinsufficiency has been shown to be peripheral in origin, but it is unclear to what extent potential aberrations in the outer hair cells (OHCs) contribute to this disorder. To further elucidate the pathophysiological mechanism underlying the hearing defect in HDR-syndrome, we investigated the OHCs in heterozygous Gata3-knockout mice at both the functional and morphological level. While the signal-to-noise ratios of distortion product otoacoustic emissions (DPOAE) in wild type mice did not change significantly during the first half-year of live, those in the heterozygous Gata3 mice decreased dramatically. In addition, both light microscopic and transmission electron microscopic analyses showed that the number of OHCs containing vacuoles was increased in the mutants. Together, these findings indicate that outer hair cell malfunctioning plays a major role in the hearing loss in HDR-syndrome.

Age Factors↗
PubMed1981

Electrophysiological study of the maturation of auditory responses from the inner ear of the chick.

Three electrophysiological functions of the chick basilar papilla were studied during development by recording the compound actin potential (AP) at the round window. The auditory thresholds showed a continuous maturation between the fifteenth day of incubation (E15) and the first post-hatching day (P1), when they attained adult values. Responses matured first to low frequencies and later to high frequency stimuli. The input-output (intensity-amplitude) functions matured regularly and never demonstrated the classical two slopes seen in mammals. The tuning properties, studied by tone-on-tone masking of the AP, achieved mature values before the thresholds; the Q10s reached adult values at E17 for a 500-Hz probe tone and at E19 for a 1000-Hz probe tone. The fact that a low-to-high frequency development trend was found with the embryonic middle ear cleared of fluids further suggests that this property of auditory ontogeny may be a function of changes in the transduction properties of the cochlea.

Aging↗
PubMed1992

Rapid disruption of cochlear function and structure by trimethyltin in the guinea pig.

Trimethyltin (TMT) is a potent ototoxicant which acutely disrupts generation of the action potential evoked by a broad range of tone frequencies and subsequently produces selective high frequency impairment and outer hair cell (OHC) damage in the extreme basal turn of the cochlea. We investigated the development of TMT ototoxicity in the guinea pig 6-48 h following treatment using the compound action potential (CAP), cochlear microphonic (CM), endocochlear potential (EP) and light and electron microscopic examinations. At all time intervals studied, TMT reduced CAP sensitivity and CM amplitude. The effect was relatively broad across test frequencies at 6 h and subsequently became restricted to higher frequencies. No disruption of the EP was observed between 6 and 24 h following TMT. OHC pathology in the basal turn of the cochlea 12 h following TMT consisted of vacuolization in the supranuclear region and disruption of the cuticular plate; some mitochondria exhibited dark inclusions. Type 1 spiral ganglion cells appeared swollen at 24 h with separation of myelin from the cell bodies. No pathological changes were observed in the inner hair cells (IHC). The present data identify the OHC as targets responsible for the loss of CM sensitivity after TMT as the EP was unaffected. These data suggest that CAP and CM recovery at low and middle frequencies following acute TMT administration is accompanied by recovery of neurotransmission at the IHC or Type 1 SGC level and OHC recovery at apical regions of the cochlea.

Action Potentials↗
PubMed1990

Electrically evoked whole-nerve action potentials: data from human cochlear implant users.

This study describes a method for recording the electrically evoked, whole-nerve action potential (EAP) in users of the Ineraid cochlear implant. The method is an adaptation of one originally used by Charlet de Sauvage et al. [J. Acoust. Soc. Am. 73, 615-627 (1983)] in guinea pigs. The response, recorded from 11 subjects, consists of a single negative peak that occurs with a latency of approximately 0.4 ms. EAP input/output functions are steeply sloping and monotonic. Response amplitudes ranging up to 160 micro V have been recorded. Slope of the EAP input/output function correlates modestly (approximately 0.6-0.69) with results of tests measuring word recognition skills. The refractory properties of the auditory nerve were also assessed. Differences across subjects were found in the rate of recovery from the refractory state. These findings imply that there may be difference across subjects in the accuracy with which rapid temporal cues can be coded at the level of the auditory nerve. Reasonably strong correlations (approximately 0.74-0.85) have been found between the magnitude of the slope of these recovery curves and performance on tests of word recognition.

Cochlear Implants↗
PubMed1979

Origins of the scalp recorded frequency-following response in the cat.

The frequency-following response (FFR) is a short-latency scalp-recorded evoked potential elicited by the presentation of low-frequency acoustic stimuli. It is thought to be the result of the synchronous electrical activity in brain stemauditory nuclei to each wave in the acoustic signal. The present investigation constitutes an attempt to determine the generators of the FFR in the cat by analysis of the response and by section of brain stem auditory nuclei and tracts. Among the results were the following: (1) the cochlear nuclei contribute approximately 50% of the amplitude of the scalp-recordedFFR in the cat. (2) The cochlea also makes a significant contribution, accounting for an average of nearly 25% of the response amplitude. (3) The superior olivary nuclei (and/or the nuclei of the lateral lemnisci) account for about 20% of the response amplitude. (4) The contributions from the inferior colliculi (contrary to earlier studies) were found to be relatively insignificant. (5) As a consequence of the existence of multiple generators, the FFR ample area of hair cell excitation for each stimulus frequency involved in the mediation of the FFR, suggestion that scalp-recorded FFRs could be used to ascertain low-frequency hearingsensitivity in uncooperative human subjects.

Animals↗
PubMed1990

Latency and amplitude tuning curves of the N1 and N2 components of the cochlear nerve compound action potential.

Compound action potential tuning curves (CAP TCs) generated by masking the N1 component of the CAP provide a means of assessing the ability of the cochlea to selectively tune to certain stimuli. This paper examines some of the factors which can influence this TC when a moderately intense (i.e. 40-80 dB SPL) probe stimulus is used. At these levels, each of the four corners of the trapezoidal stimulus envelope is capable of generating a CAP. Also, short stimulus rise times can merge the CAPs produced by the first two corners, but this does not appear to have a major effect on the CAP TC. It was shown that the N2 component of the CAP for the first corner of the stimulus is equally capable of producing a well-tuned TC. Another study has shown that, in addition to amplitude decrements, one can use latency increases as a criterion for CAP TCs. We have demonstrated that latency TCs are more finely tuned than amplitude TCs at high levels, especially when the stimulus rise time is short.

Animals↗