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PubMed1985

Structure and function of the adult inner ear in the mouse following prenatal irradiation.

The function and morphology of the vestibular and cochlear parts of the inner ear have been examined after prenatal irradiation on the 12th, 13th and 16th gestational days in the CBA/CBA mouse. Irradiation was performed with a 0.5, 1 or 2 Gy single dose, whole body irradiation of the pregnant female. The irradiated fetuses were born after full term pregnancies and reached maturity (were 1--2 months old) before inner ears were analyzed with regard to vestibular tests, auditory thresholds and morphology. Morphology was studied by light microscopy (LM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Auditory function was analyzed by frequency specific auditory brainstem response (ABR). Irradiation doses exceeding 2 Gy caused death to the pregnant female, abortion or malformed litters which were eaten by their mothers. Doses of 0.5, 1 and 2 Gy caused malformed cristae ampullares and maculae utriculi, in particular after exposure on the 12th or 13th gestational days. After those doses no abnormality of clinical behaviour of the animals was found. Ultrastructurally, type I hair cells (HC) of the vestibular part seemed more vulnerable to irradiation than the type II HC while the outer (OHC) and inner (IHC) hair cells appeared equally vulnerable. The ultrastructural changes of hair cells were predominantly localized to the hair cell surface showing a defect cuticle which was sometimes malformed and bulging. Sensory hair fusion occurred with a resulting poor maturation of sensory hair rootlets. The efferent nerve endings were estimated to be reduced in number but, if present, they had a normal ultrastructure. Otoconia showed severe morphological damage following irradiation particularly if exposed on the 16th gestational day. Malformed and fused otoconia were frequent having a disarrayed matrix. The irradiation induced morphological alterations in vivo could be reproduced in the in vitro systems. In addition, a retarded growth of the in vitro developing inner ear anlage was estimated to be the same for the vestibular and cochlear parts. The cochlear part of the inner ear showed a dose and age dependent hearing loss following irradiation. A shift of the ABR threshold was recorded in all exposed groups that were irradiated with 2 Gy. A correlation was found between the individual ABR-audiograms and the degree of morphological HC damage in the cochlea along the basilar membrane. The 12th gestational day inner ear anlage was most vulnerable to irradiation. The 13th gestational day inner ear was almost equally vulnerable and showed a dose-response relationship.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1999

Using mismatch negativity to measure auditory temporal resolution thresholds.

It has been hypothesized that poor auditory temporal resolution is related to language-learning problems in children as well as problems with speech perception in noise in the elderly. We show that the presence of occasional silent gaps between short tone pips elicits mismatch negativity (MMN) in young adults. We also measured gap-detection thresholds with MMN that agree well with behavioural thresholds. Near threshold, the MMN increases as the gap size increases millisecond by millisecond. The MMN methodology for measuring temporal resolution is not only robust, but can be applied identically across the life span as it does not require the attention of participants or a behavioural response. We are now in a position to examine temporal resolution in infancy.

Acoustic Stimulation↗

PubMed2000

Behavioral auditory assessment of young infants: methodological limitations or natural lack of auditory responsiveness?

The determination of auditory thresholds by means of behavioral techniques in young infants can be difficult. This could be the result of limitations in methodology, a lack of observable auditory responsiveness, or both. In the current study, 2- and 4-month old infants were tested under enhanced conditions for obtaining behavioral responses (i.e., salient auditory stimuli, reduced visual distractions, reinforced correct responses). A two-interval, forced-choice task with four intensity levels was used. Although a behavioral threshold was obtained for the 4-month-olds, threshold determination for the 2-month-olds remained elusive. In light of the current findings and previous studies of visual acuity of infants, these results suggest a lack of behavioral responsiveness to auditory stimuli for the younger infants rather than methodological limitations. With infants in the 2-month-old age range, clinical audiologists should expect few behavioral responses to auditory stimuli at intensity levels below those that elicit startle responses.

Attention↗

PubMed1998

The neuroethology of frequency preferences in the spring peeper.

We studied the relationship between auditory activity in the midbrain and selective phonotaxis in females of the treefrog, Pseudacris crucifer. Gravid females were tested in two-stimulus playback tests using synthetic advertisement calls of different frequencies (2600 versus 2875 Hz; 2800 versus 3500 Hz; 2600 versus 3500 Hz). Tests were conducted with and without a background of synthesized noise, which was filtered to resemble the spectrum of a chorus of spring peepers. There were no significant preferences for calls of any frequency in the absence of background noise. With background noise, females preferred calls of 3500 Hz to those of 2600 Hz. Multi-unit recordings of neural responses to synthetic sounds were made from the torus semicircularis of the same females following the tests of phonotaxis. We measured auditory threshold at 25 frequencies (1800-4200 Hz) as well as the magnitude of the neural response when stimulus amplitude was held constant and frequency was varied. This procedure yielded isointensity response contours, which we obtained at six amplitudes in the absence of noise and at the stimulus amplitude used during the phonotaxis tests with background noise. Individual differences in audiograms and isointensity responses were poorly correlated with behavioural data except for the test of 2600 Hz versus 3500 Hz calls in noise. The shape of the neural response contours changed with stimulus amplitude and in the presence of the simulated frog chorus. At 85 dB sound pressure level (SPL), the level at which females were tested, the contours of females were quite flat. The contours were more peaked at lower SPLs as well as during the broadcast of chorus noise and white noise at an equivalent spectrum level (45-46 dB/Hz). Peaks in the isointensity response plots of most females occurred at stimulus frequencies ranging from 3200 to 3400 Hz, frequencies close to the median best excitatory frequency (BEF) of 3357 Hz but higher than the mean of the mid-frequency of the male advertisement call (3011 Hz). Addition of background noise may cause a shift in the neural response-intensity level functions. Our results highlight the well-known nonlinearity of the auditory system and the danger inherent in focusing solely on threshold measures of auditory sensitivity when studying the proximate basis of female choice. The results also show an unexpected effect of the natural and noisy acoustic environment on behaviour and responses of the auditory system. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed2000

Succinate dehydrogenase (SDH) activity in hair cells: a correlate for permanent threshold elevations.

Hair cell loss is often used as a histological correlate of hearing loss. However, the histological and the physiological data are not always well correlated. This paper investigates the use of succinate dehydrogenase (SDH) activity in the hair cells as a marker of cellular dysfunction and so the loss of auditory sensitivity. In our previous studies, potentiation of noise-induced auditory threshold elevation by carbon monoxide (CO) was observed [Chen and Fechter, 1999; Chen et al., 1999]. However, its histological basis is still unclear. In this study, rats were exposed to 100-dB octave-band noise (center frequency=13.6 kHz, 2 h) or to the combination of the noise and CO (1200 ppm). Threshold elevation of compound action potential (CAP) and cochlear histological changes were assessed 4 weeks after exposure. The noise alone caused CAP threshold elevations with little if any or without hair cell loss. However, the SDH activity in the hair cells decreased after the exposure. The SDH reduction, especially in the inner hair cells, was well related to the loss of auditory sensitivity. The combined exposure to noise and CO caused more severe CAP threshold elevation and SDH activity reduction than did the noise alone and it also caused significant outer hair cell loss. However, across all the test frequencies, neither the hair cell loss nor the SDH reduction alone had good correlation to the reduction of the auditory sensitivity. Under this situation, CAP threshold elevation seemed to follow OHC loss at high frequencies and to follow SDH reductions in the IHCs at low frequencies, where no hair cell loss occurred.

Action Potentials↗

PubMedDate not supplied

Cisplatin ototoxicity involves organ of Corti, stria vascularis and spiral ganglion: modulation by alphaMSH and ORG 2766.

It has been shown that alphaMSH and the nonmelanotropic ACTH/MSH(4-9) analog ORG 2766 can ameliorate cisplatin-induced neurotoxicity and ototoxicity. Here, we investigated whether these peptides delay the occurrence of the cisplatin-induced shift in auditory threshold, and whether they affect the subsequent recovery of cochlear potentials. Chronically implanted round window electrodes were used to obtain daily recordings of auditory nerve compound action potentials (CAP) and cochlear microphonics at frequencies ranging from 2 to 16 kHz. Cisplatin (1.5 mg/kg i.p.) plus alphaMSH, ORG 2766 (75 mug/kg s.c.), or saline were injected daily until the 40-dB CAP threshold shift at 8 kHz was reached. Endocochlear potential (EP) was measured either 1-2 days or 28 days later, followed by morphometric analysis of the cochlea. Peptide cotreatment did not consistently delay the threshold shift; however, the CAP threshold recovered faster and to a greater extent, with the potency order being alphaMSH > ORG 2766 > saline. Significant recovery at the 2 highest frequencies was seen in the alphaMSH-treated animals only. CAP amplitude at high sound pressures, which depends more on nerve function than on outer hair cell (OHC) function, decreased severely in all groups but recovered significantly in the alphaMSH- and completely in the ORG-2766-cotreated group. EP was significantly lower in the first days after the threshold shift but had completely recovered at 28 days. Morphometric analysis of the spiral ganglion also indicated involvement of ganglion cells. OHC loss was most severe in the basal turn of saline-cotreated animals. These data suggest that the cisplatin-induced acute threshold shift might be due to reversible strial failure, whereas subsequent OHC survival determines the final degree of functional recovery. Both OHC loss and neuronal function were ameliorated by peptide cotreatment.

Adrenocorticotropic Hormone↗

PubMed1997

Synergestic effects of noise and aminoglycoside antibiotic (gentamicin) on auditory function in the gerbil.

Exposure to excessive noise can cause auditory impairment in people as well as in animals, which can be aggravated by many different ototoxic substances, such as aminoglycosides. In the present study, the gerbil was selected as the experimental animal because the gerbil has low-frequency auditory sensitivity that is similar to human beings. Auditory function in gerbils upon exposure to noise and/or gentamicin was evaluated from non-invasive records of brainstem auditory evoked potentials (BAEPs). Fifty mature male Mongolian gerbils were divided randomly into four groups. The control group was exposed neither to noise nor to gentamicin. The noise group was exposed to 100dBA noise ten hours a day for four weeks. The gentamicin group was treated with one dose of gentamicin, 75 mg/Kg i.m., daily for four weeks. The noise + gentamicin group was exposed concurrently to both noise and gentamicin treatment. BAEPs were recorded from all gerbils 24 hours before any experimental treatment, then every week for eight consecutive weeks. Long-term exposure to noise and/or gentamicin treatment was found to reduce gerbil's body weight. The increase in auditory threshold upon concurrent exposure to both noise and gentamicin treatment (evaluated from BAEPs) exceeded the sum of effects caused by exposure to noise alone and to gentamicin alone. Although differences of peak or interpeak latencies among the four groups were not statistically significant, large standard deviations were noted in the noise+gentamicin group. Thus the apparent threshold shifts in gerbils indicated a major noise and/or gentamicin induced auditory impairment to the cochlea, and the slight latency variations probably suggested a minor injury to the auditory pathways. We emphasize that noise and aminoglycoside antibiotic gentamicin can cause damage to the hearing ability at the frequency range vital to human speech recognition, and their effects are synergetic.

Animals↗

PubMed1990

The effect of tinnitus on ABR latencies.

Comparisons were made of the ABR latencies of tinnitus (T) and nontinnitus (NT) patient groups balanced for age and gender and matched for acoustic reflex threshold (ART)s, 1000 to 4000 Hz and 4000 Hz auditory thresholds, and normal hearing. In the ART match, prolongations of wave I [t(94) = 4.42, p less than 0.001], wave III [t(94) = 2.72, p less than 0.01], and wave V [t(94) = 3.32, p less than 0.01] and the III-V interval [t(94) = 2.48, p less than 0.02) were seen in T subjects. Wave I in 1 to 4 kHz matched [t(62) = 3.13, p less than 0.005] and normal-hearing subjects [t(30) = 2.58, p less than 0.01] was prolonged in T females. The utility of using wave I as a diagnostic indicator for tinnitus in females is discussed.

Adult↗

PubMedDate not supplied

Role of the efferent medial olivocochlear system in contralateral masking and binaural interactions: an electrophysiological study in guinea pigs.

Contralateral broadband noise (BBN) elevates ipsilateral auditory thresholds (central masking) and reduces the amplitude of ipsilateral brainstem auditory evoked potentials (BAEPs). Binaural interactions are complex psychophysical phenomena, but binaural interaction components are easily extracted from BAEPs to monaural versus binaural click stimulation. However, contralateral, or binaural, acoustical stimulation is known to activate simultaneously the crossed and uncrossed medial olivocochlear (MOC) efferent systems and decrease activity in both cochleas. Particularly, contralateral BBN stimulation suppresses in part ipsilateral peripheral activity. What is the role of such contralaterally induced peripheral suppression in the overall changes in central BAEPs observed during contralateral masking or binaural stimulation? Compound action potentials (CAPs) of the auditory nerve and BAEPs were recorded simultaneously in awake guinea pigs from electrodes chronically implanted on the round window of the cochlea and the surface of the brain. Peripheral and central measures of contralateral masking and binaural interactions were obtained from responses to monaural or binaural clicks, with or without contralateral BBN, recorded before, during, and after the reversible blockade of the MOC function following a single intramuscular injection of gentamicin. Contralateral BBN effectively reduced the amplitudes of CAP and of all BAEP peaks. CAP to ipsilateral click did not, however, change significantly from monaural to binaural click stimulation; still, normal binaural interaction components developed in the BAEPs. When the medial efferent function was blocked by gentamicin, the normal contralateral BBN suppression of CAP and of the earliest BAEP peak was lost; however, the later BAEP peaks were suppressed by contralateral BBN as before gentamicin, and the central binaural interaction components were unchanged. In these experimental conditions, the MOC efferent system seems to play little role in centrally recorded contralateral masking and binaural interactions.

Animals↗

PubMed2000

Abnormal positive potentials in round window electrocochleography.

OBJECTIVE: To describe an atypical waveform, termed an abnormal positive potential (APP), on round window electrocochleograms (RW ECochG) of children and to relate its occurrence to clinical history. STUDY DESIGN: APPs were identified prospectively, and a retrospective analysis was made of these patients' clinical histories, audiograms, and auditory outcomes (hearing aid, cochlear implant, or nonauditory communication) SETTING: Tertiary referral teaching hospital, day surgery and clinics. PATIENTS: All 431 children <110 months of age suspected of a severe to profound hearing loss who underwent RW ECochG from January 1993 to August 1997. INTERVENTION: Diagnostic RW ECochG for auditory threshold estimation. MAIN OUTCOME MEASURE: The presence on the RW ECochG of the APP: an early positive potential in the absence of a compound action potential (CAP). RESULTS: An APP was observed in 34 children. The APP was most marked in response to clicks and 8-kHz tones. The APP click threshold averaged 70 dB hearing loss. The brainstem evoked potential of these children showed an absence of waves, or a broad positive wave with no subsequent waves. Twenty-nine of 30 behavioral audiograms obtained were indicative of severe to profound hearing loss. Auditory outcomes were available from 26 children; 45% of them derived no help from a hearing aid, and 8 children received a cochlear implant. Clinical factors frequently associated with APP were prematurity in combination with kemicterus or hypoxia. CONCLUSIONS: APP thresholds were lower than neural thresholds or behavioral thresholds. Children with APP need close follow-up, because half of those studied needed nonauditory strategies to develop effective communication.

Audiometry, Evoked Response↗

PubMed2004

[Transforming and transmitting auditory information].

A mechanism of transforming and transmitting auditory information has been introduced taking into consideration the course of occurrences on molecular level in auditory cell itself. Physical energy of the sound wave is changed into bioelectric energy of the inside of the auditory cell owing to the generated electrochemical gradient. The change of the cell membrane potential which has been caused by the energy of the sound wave influences the change of the calcium level in the cell and at a further stage energetistic processes, enzymatic proteins activity and also it regulates the exocytosis of the mediator. The relationship between the generation of the transmitter and its secretion, and the stimulation of the auditory cell has been discussed. The role of afferent and efferent innervation in the generation of the fast and slow contraction of auditory cells has been noticed. Other phenomena accompanying the process of hearing have also been noticed. They are: Coding information, pre- and post-synaptic inhibition, facilitation of impulse transmission along nervous pathways, collateral inhibition, convergence and divergence. The mechanism of stimulating the receptors in the other senses has been described. A hypothesis has been put forward about the possibility of existence of a mechanism activating ionic canals of the cell membrane of auditory cells other than purely mechanical one connected with tip-links. The mechanism mentioned above may be based on inducing conformational changes of canal proteins, especially potassium canals, by the energy of the sound wave. There is a probability that there exist sound sensitive molecules in the ear as just as there exist light sensitive molecules in the organ of sight. The ability of basement membrane to transmit auditory information, especially on the verge of auditory threshold has been questioned.

Animals↗

PubMed1993

Auditory brainstem response thresholds to air and bone conducted clicks in neonates and adults.

Auditory brainstem response (ABR) thresholds to air and bone conducted clicks were investigated in 20 full-term neonates and 20 normal-hearing young adults. Results showed mean ABR thresholds to air and bone conducted clicks for neonates to be 3.75 dB nHL (40.75 peak SPL) and 1.25 dB nHL (36.25 dB peak re: 1 microN), respectively, and for adults 3.75 dB nHL (40.75 peak SPL) and 18.75 dB nHL (53.75 peak re: 1 microN), respectively. A significant difference was observed in mean ABR thresholds to bone conducted stimuli between neonates and adults (p < 0.0001) and among mean adult ABR thresholds to air and bone conducted stimuli (p < 0.0001). Nonsignificant differences were observed in mean ABR thresholds to air and bone conducted stimuli among neonates (p > 0.05) and in mean ABR thresholds to air conducted stimuli between neonates and adults (p = 1.00). It is speculated that the dissimilarity in the relationship of thresholds to air and bone conducted stimuli between neonates and adults reflects, in part, a difference in efficiency of signal delivery to the cochlea.

Acoustic Stimulation↗

PubMedDate not supplied

Effect of organophosphorus compound intoxication on auditory brainstem response in mini pigs.

Organophosphorus compounds (OPC) are widely used as insecticides and cause a high number of acute and chronic intoxications in man. Their toxicological properties lead among others to disturbances of the central nervous system. Hearing disturbances have been reported after chronic exposure to OPC, and changes in bioelectric brain activity have been observed during the acute state of intoxication. The EEG showed no characteristic alterations. We performed a threshold auditory brainstem response (ABR) in 12 mini pigs before, during and after paraoxon (a typical OPC) intoxication with a high dose of 27 mg/kg BW. During the application of paraoxon we saw a prolongation of the interpeak latencies Jewett I-V of approximately 1 ms. A threshold shift of 10-20 dB was seen in 8 animals. After the application, while the systemic effect of the paraoxon intoxication was still apparent, the threshold shift disappeared except for 2 animals and the prolongation of the interpeak latencies could not be observed any more. No characteristic signs of paraoxon intoxication could be seen in the ABR after the application was completed. Acute intoxication with an OPC only leads to temporary, limited hearing impairment and increased interpeak latency. We could not observe characteristic changes in the ABR corresponding to the state of intoxication.

Acute Disease↗

PubMed2004

[Inner ear damage due to leisure and broadband noise. An experimental study on initial and permanent functional and morphological damage].

The initial and permanent effects of leisure noise (toy pistols, rock music) compared to broadband noise were examined in 68 guinea pigs. Auditory threshold shifts at 1.5, 2, 3, 4, 6, 8, 12 und 16 kHz were registered before and immediately after exposure as well as on days 1, 2, 3, 5,7 and 21 post-exposure using the auditory brain stem response (ABR) technique. In order to examine cilia and hair cell damage in eight cochlear frequency regions (<0,4 kHz, 0,4-0,8 kHz, 0,8-1.5 kHz, 1.5-3 kHz, 3-5 kHz, 5-11.5 kHz, 11.5-26 kHz und >26 kHz), cytocochleograms were performed immediately after exposure and on days 1, 7 and 21.Frequency dependent functional or morphological damage was found which depended on the type of trauma tested. All results were highly significant ( P<0.001). The results show that partial recovery of hearing occurred within 3 days of acute acoustic trauma induced by toy pistols and within 1 day after exposure to rock music or broadband noise. There was no further recovery of hearing within the following 18 and 20 days, respectively. Furthermore, permanent threshold shifts after exposure to rock music or broadband noise were not associated with cilia and/or hair cell damage.

Acoustic Stimulation↗

PubMed1996

The neonatal chinchilla cochlea: morphological and functional study.

The developmental time scale of the cochlea varies from species to species. We investigate here the condition of the neonatal cochlea in the chinchilla, a species increasingly used in auditory research. We have examined the morphology of cochlear hair cells using scanning microscopy, and the development of auditory function during the first postnatal month by monitoring auditory brainstem evoked responses (ABR). We find that although there were some outer hair cell kinocilia present in middle and apical areas, the hair cells otherwise were mature at 24 hours after birth. Furthermore, cochlear auditory thresholds are adult-like at birth. However, whilst there was little change in ABR thresholds over one month, there is evidence of continued maturation of the central auditory system as shown by the shortening of the PI-P5 latency from 9.1 ms to 7.7 ms.

Animals↗

PubMed2004

On the development of low-level auditory discrimination and deficits in dyslexia.

Absolute auditory thresholds, frequency resolution and temporal resolution develop with age. It is still discussed whether low-level auditory performance is of clinical significance--specifically, for delayed maturation of central auditory processing. Recently, five new auditory tasks were used to study the development of low-level auditory discrimination. It was found that the development lasts up to the age of 16-18 years (on an average). Very similar tasks were now used with 432 controls and 250 dyslexic subjects in the age range of 7-22 years. For both groups the performance in one of the tasks was not related to the performance in another task indicating that the five tasks challenge independent subfunctions of auditory processing. Surprisingly high numbers of subjects were classified as low performers (LP), because they could not perform one or the other task at its easiest level and no threshold value could be assigned. For the dyslexics the incidence of LP was considerably increased in all tasks and age groups as compared with the age matched controls. The development of dynamic visual and optomotor functions and the corresponding deficits in dyslexia are discussed in relation to the auditory data presented here.

Adolescent↗

PubMed1999

Vestibular stimulation affects dichotic lexical decision performance.

We report an experimental attempt to shift, by vestibular stimulation, healthy subjects' right ear advantage (REA) in a dichotic listening (DL) task with words and nonwords as stimuli. Forty right-handed men performed the task under two different conditions, once while sitting in a stationary turning chair (baseline) and once during sinusoidal rotation. In this latter condition, every other stimulation was received during maximal left-to-right (i.e., clockwise), every other during maximal right-to-left (i.e., counterclockwise) acceleration. There was a reliable REA for lexical decision accuracy in the baseline and right-to-left trials but not during left-to-right rotation. While right ear performance was unaffected by rotation, there were more correct lexical decisions to left ear targets exclusively during left-to-right turns (one-tailed P = 0.05). Since there were no parallel shifts in auditory thresholds under the different conditions, this effect is not due to any hypothetical auditory-vestibular interactions on a primary sensory level. The improvement in left ear DL performance, although small in our study, is comparable to the symptom-alleviating effect of caloric vestibular stimulation in patients with left-sided hemispatial neglect and interpreted as a consequence of a rotation-induced attentional shift towards the left hemispace.

Adult↗

PubMed2002

Differential thresholds of local field potentials and unit discharges in rat auditory cortex.

Thresholds for responses to tone bursts in the primary auditory field of pentobarbital-anesthetized rat are significantly lower for local field potentials (5.60 dB+/-1.76 S.E.M.) than for multiple unit discharges (17.80 dB+/-3.17), recorded simultaneously from the same microelectrode. The characteristic frequencies (CFs) of local field potentials provide a good 'predictive' estimate of unit CFs at their higher thresholds. The findings are consistent with the view that local field potentials in the auditory cortex reflect summed synaptic potentials rather than cellular discharges.

Acoustic Stimulation↗