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PubMed1993

Auditory reflex thresholds elevated by stress-induced cortisol secretion.

To study steroid effects on auditory perception, 24 volunteers were unexpectedly confronted with a psychological stressor. Auditory reflexes to pure tones and noise were recorded before stress exposure, up to 100 min afterwards and in a second control session. Repeated measurements of cortisol and testosterone in saliva, as well as blood pressure, heart rate, and subjective feelings confirmed the stressful nature of the test. Following stress induction the auditory reflex of the contralateral ear needed significantly higher loudness (i.e. more decibels) to be elicited than at baseline or control measures. Two lines of evidence suggest that this stress-induced change may be specifically related to glucocorticoid actions: (1) In a previous study similar elevations in auditory reflex threshold had been obtained by the administration of exogenous glucocorticoids (hydrocortisone), and (2) in the present study the overall effect of stress induction on acoustic reflex described above was mainly observed in a subgroup of subjects, who responded to the stressor with a marked rise in free cortisol.

Acoustic Stimulation↗
PubMed1983

Physiological and behavioral effects of tilt-induced body fluid shifts.

This paper addresses the "fluid shift theory" of space motion sickness. The primary purpose of our research was the development of procedures to assess individual differences in response to rostral body fluid shifts on earth. Experiment I examined inner ear fluid pressure changes during head-down tilt in intact human beings. Tilt produced reliable changes. Differences among subjects and between ears within the same subject were observed. Experiment II examined auditory threshold changes during tilt. Tilt elicited increased auditory thresholds, suggesting that sensory depression may result from increased inner ear fluid pressure. Additional observations on rotation magnitude estimation during head-down tilt, which indicate that rostral fluid shifts may depress semicircular canal activity, are briefly described. The results of this research suggest that the inner ear pressure and auditory threshold shift procedures could be used to assess individual differences among astronauts prior to space flight. Results from the terrestrial observations could be related to reported incidence/severity of motion sickness in space and used to evaluate the fluid shift theory of space motion sickness.

Adolescent↗
PubMed1982

[Detection of auditory impairment in the offsprings caused by drug treatment of the dams].

To study the auditory impairment induced by prenatal administration of aminoglycosides in the offspring, the shuttle box method to measure the auditory threshold of rats (Kameyama et al., Folia pharmacol. japon. 77, 15, 1981) was employed. Four groups of pregnant rats were administered 200 mg/kg kanamycin sulfate (KM), 200 mg/kg dihydrostreptomycin sulfate (DHSM), 100 mg/kg neomycin sulfate (NM), or 1 ml/kg saline intramuscularly from the 10th to the 19th day of pregnancy. The auditory threshold of the offspring could be measured by the shuttle box method in about 90% of the live born rats at the age of 100 days. The auditory thresholds of the groups were as follows (mean +/- S.E.): saline group, 53.8 +/- 0.6 dB (N = 36); KM group, 63.8 +/- 1.1 dB (N = 34); DHSM group, 60.0 +/- 1.2 dB (N = 29); NM group, 62.4 +/- 1.2 dB (N = 24). Auditory thresholds of drug-treated groups were significantly higher than that of the saline group. However, no increase in the auditory threshold of the mother rat was detected after treatment with aminoglycosides. In addition, the experimental procedure of the shuttle box method is very easy, and the auditory threshold of a large number of rats could be measured in a short period. These findings suggest that this method is a very useful one for screening for auditory impairment induced by prenatal drug treatment in rat offspring.

Aminoglycosides↗
PubMed1996

Assessment of the discomfort threshold of command board operators in automated productions with respect to its application in professional selection.

The discomfort threshold problem is not yet clear from the audiological point of view. Its significance for work physiology and hygiene is not enough clarified. This paper discussed the results of a study of the discomfort threshold, performed including 385 operators from the State Company "Kremikovtzi", divided into 4 groups (3 groups according to length of service and one control group). The most prominent changes were found in operators with increased tonal auditory threshold up to 45 and over 50 dB with high confidential probability. The observed changes are distributed in 3 groups: 1. increased tonal auditory threshold (up to 30 dB) without decrease of the discomfort threshold; 2. decreased discomfort threshold (with about 15-20 dB) at increased tonal auditory threshold (up to 45 dB); 3. decreased discomfort threshold at increased (over 50 dB) tonal auditory threshold. The auditory scope of the operators, belonging to groups III and IV (with the longest length of service) is narrowed, being distorted for the latter. This pathophysiological phenomenon can be explained by an enhanced effect of sound irritation and the presence of a recruitment phenomenon with possible engagement of the central part of the auditory analyzer. It is concluded that the discomfort threshold is a sensitive indicator for the state of the individual norms for speech-sound-noise discomfort. The comparison of the discomfort threshold with the hygienic standards and the noise levels at each particular working place can be used as a criterion for the professional selection for work in conditions of masking noise effect and its tolerance with respect to achieving the individual discomfort level depending on the intensity of the speech-sound-noise signals at a particular working place.

Adult↗
PubMed1981

[Application of a shuttle avoidance schedule in rats to evaluate a drug-induced auditory impairment (author's transl)].

In attempts to study drug-induced auditory impairment we measured the auditory threshold in rats, using the shuttle box method. The auditory threshold with physical impairment of ears was also measured. The sensitivity of the rats to the auditory response was decreased to about 15dB in cotton-stuffed ears and to about 20dB in pierced eardrums. In this experiment, we used drugs known to be ototoxic; dihydrostreptomycin sulfate, kanamycin sulfate, neomycin sulfate and ethacrynic acid. With successive administration of each drug, the auditory sensitivity in rats decreased. This shuttle box method is easily facilitated and the auditory threshold of many rats can be measured over a short period. This approach may be a useful method for screening ototoxic drugs.

Aminoglycosides↗
PubMed1989

Distortion product emissions and sensorineural hearing loss.

Distortion product emissions (DPEs) are intimately linked to normal outer hair cell function. Outer hair cell function is itself intimately linked with normal auditory thresholds. We sought to correlate frequency-specific DPE measurements with auditory thresholds, in seven frequency regions from 700 Hz to 6 kHz, in each of 21 ears. Eleven of these ears had thresholds below 25 dB SPL at every test frequency, whereas 10 ears demonstrated some degree of purely sensorineural hearing loss. An analysis of the correlation between DPE measurements and sensory thresholds suggests that DPE measures can predict frequency-specific auditory thresholds to within 10 dB over a range of sensory thresholds from 0 dB SPL to 60 dB SPL. Distortion product emissions promise to provide an objective, non-invasive measure of sensory thresholds. The clinical value of DPE measurement is enhanced by that fact that it is brief and requires minimal subject participation. A clinical test based on the DPE measurement will not displace conventional audiometry or auditory brain stem response measurement. It promises to provide new information about cochlear function to both the clinician and auditory physiologist.

Acoustic Stimulation↗
PubMed2001

Relationship between the auditory brainstem response and auditory nerve thresholds in cats with hearing loss.

This study explored the relationship between the auditory brainstem response (ABR) and auditory nerve sensitivity in cats with normal hearing and with noise-induced permanent threshold shifts. A statistically significant linear correlation was found between each cat's ABR thresholds and the most sensitive single neuron thresholds at the same frequency. ABR thresholds were approximately 25 dB higher than the thresholds of the most sensitive neural responses in cats with normal hearing. The two measures produced equivalent thresholds at impaired frequencies in subjects with sensorineural hearing loss. Two factors may have contributed to this convergence of ABR and neural thresholds. First, our results suggest that the elevation of the most sensitive neural responses led to a compressed threshold distribution. Consequently, only a narrow range of sound levels separated stimulus conditions that activated relatively few fibers from those that were sufficient to evoke a robust population response. In addition, the threshold responses of impaired auditory nerve fibers may have been augmented by activity in the more sensitive 'off-frequency' regions that surrounded a discrete cochlear lesion. Across varying degrees of hearing loss, the ABR maintained a systematic relationship to auditory nerve fiber thresholds, and therefore has the potential to be used as a functional assay of cochlear pathology.

Action Potentials↗
PubMed1988

Screening for auditory dysfunction in infants by evoked oto-acoustic emissions.

Auditory threshold using auditory brain-stem responses (ABR) was determined in 30 ears from normally-hearing infants and 16 ears from infants with sensorineural deafness. In the same population, evoked oto-acoustic emissions (EOAEs) in response to a click of 20-dB hearing level were recorded. The presence of EOAEs was correlated with ABR thresholds. Evoked oto-acoustic emissions were always present when ABR wave V threshold was equal to or below 30-dB hearing level. On the contrary, infants with ABR thresholds higher than 40-dB hearing level never had EOAEs. As the recordings of EOAEs could be obtained more rapidly than ABR thresholds (average duration: five minutes vs 40 minutes), EOAEs could hold some promise as an objective, easy, and noninvasive test for screening auditory dysfunction in infants.

Brain Stem↗
PubMed2006

[Orientation of three lysosomal enzymes in the mouse inner ear and hearing loss in enzyme gene deficiency].

OBJECTIVE: To determine the distribution and influence of lysosomal neuraminidase (Neul), protective protein/cathepsin A (PPCA) and beta-galactosidase (beta-gal) in the inner ear of the mouse, and to observe their auditory alterations in enzyme deficiency. METHODS: Six wild type (2 months postnatal) (Neu1+/+, PPCA+/+ and beta-gal+/+) mice were used, and Neu1, PPCA and beta-gal homozygous (Neu1-/-, PPCA-/- and beta-gal-/-) mice at the same age used as control in this experiment. The auditory thresholds were examined through the auditory brainstem responses (ABR) to click, which tone pips were 8, 16, and 32 kHz. The mice were intracardically perfused with 4% paraformaldehyde. The bulla were further fixed in 4% paraformaldehyde, processed and sectioned with paraffin embedded method. Immunohistochemistry was used to determine the cellular localizations of Neu1, PP-CA, and beta gal in the inner ear. RESULTS: There was a similar distributive pattern of Neu1, PPCA and betagal in the inner ear. Neu1 intense staining was observed in the cochlear spiral ganglion cells, spiral limbus, spiral ligament, vestibular ganglion cells, cristae, maculae hair cells, and weak staining in inner hair cells, outer hair cells, supplying cells of the organ of Corti and stria vascularis. The intense staining of PPCA and beta-gal were observed in the spiral ganglion and vestibular ganglion cells, and weak staining in the spiral limbus, spiral ligament, stria vascularis and organ of Corti. The inner ear exhibited no staining when Neul, PPCA and beta-gal were deficient, respectively. A positive staining of PPCA and beta-gal was presented in Neu1-/- mice, and as well as Neu1 and PPCA in beta-gal-/- mice. However, the staining of Neu1 was not presented, and only very weak staining of beta-gal in PPCA-/- mice. The auditory thresholds of Neul, PPCA, and beta-gal mice were elevated for 60-69 dB, 40-48 dB, and 7-10 dB above those of wildtype littermates, respectively. CONCLUSION: Neu1 PPCA and beta-gal are distributed in the inner ear of mouse, and the three enzymes also form a lysosomal multi-enzyme complex in the inner ear. The respective enzyme deficiencies can induce the hearing the loss of different levels.

Animals↗
PubMed1996

Temporal and mean rate discharge patterns of single units in the dorsal cochlear nucleus of the anesthetized guinea pig.

1. We examined the temporal and mean rate discharge characteristics of 514 single units recorded extracellularly from the dorsal cochlear nucleus (DCN) of anesthetized guinea pigs. A mean rate response area (receptive field) was measured for the majority of units in this study. Each response area was placed in one of seven categories (type I to type V and the intermediate types I/III and IV-T) as defined by previous workers. The shape of the best frequency (BF) rate-level function has been used to aid in the distinction between type IV and type IV-T units, and the classification of type II units is based on their relative response to noise and tone bursts. 2. The threshold of single units was normalized to the cochlear action potential (CAP) threshold (a negative relative threshold indicates that the unit's threshold was more sensitive than the corresponding CAP threshold). There were significant differences (P < 0.05; 1-way analysis of variance--Duncan test) between the mean relative thresholds of type IV units (-12 dB) and those of type I (-6.52 dB), type II (-3 dB), and type I/III units (-4.25 dB). There were also significant differences between the relative thresholds of types III and IV-T and those of types I/III and II. 3. Rate-level functions at a unit's BF were divided into groups according to shape and degree of nonmonotonicity. Six units responded with a decrease in firing rate at all suprathreshold sound levels. However, most units increased their discharge rate over approximately the first 20 dB above BF threshold. Units were further subdivided by the change in slope 20 dB above BF threshold. The majority of units (60%) showed monotonic increases in discharge rate with sound level: some rate-level functions clearly resembled the sloping saturation rate-level functions observed in intermediate-threshold auditory nerve fibers. An unexpected finding was the relatively large number of nonmonotonic rate-level functions (40%). Among a relatively homogenous group of projection neurons (predominantly type IV and pause/build units) with nonmonotonic rate-level functions, the range of "best intensities" (the sound level evoking the highest discharge rate) was < 50 dB. This range of best intensities is narrower than found in higher auditory nuclei. 4. Units were also classified by their temporal activity pattern in response to suprathreshold BF tones. The most common pattern identified is the pause/build pattern (n = 294). This temporal activity pattern has been associated with the principal output neuron of the DCN, the fusiform cell. Our definition of pause/build units includes units with an almost constant steady-state discharge rate. Nonmonotonic rate-level functions were observed in 42% (99 of 233) of pause/build units. A measure of discharge regularity (the SD of the interspike interval/mean interspike interval: coefficient of variation, CV) revealed that the majority (82%) of units classified as pause/build and with steady-state discharge rates > 75 spikes/s (n = 142) were characterized by regular discharge patterns (CV = 0.41 +/- 0.15, mean +/- SD). 5. Units characterized by chopper or onset-type discharges were the next most frequently encountered units. The chopper units (n = 75) showed a regular discharge (CV = 0.39 +/- 0.17) similar to that found in recordings from the ventral division of the cochlear nucleus (VCN). One difference between many chopper units in the DCN compared with those recorded in the VCN was the relatively high value (> 5 ms) of the mean interspike interval (and thus the low steady-state discharge rate). The majority (44 of 59; 75%) of chopper units had monotonic rate-level functions. Onset units (n = 47) may represent several response types, linked by the predominance of discharges in response to stimulus onset, and the majority of onset units reported here bear little resemblance to onset units recorded in the VCN of the guinea pig. Approximately 10% of units did not fit easily into any of th

Acoustic Stimulation↗
PubMedDate not supplied

Use of the pinna reflex as a test of hearing in mutant mice.

Although it is a gross measure, the pinna reflex test is easily administered and is, therefore, incorporated as a general screening tool in mutagenesis programs. Our recent application of this approach indicated that mutant mice lacking one of the small Maf proteins, in this case MafG, failed to exhibit a pinna reflex. In contrast, littermate controls, with the same mixed 129/CD1 background, and including both wild type and heterozygous mutant animals, passed the test. Because previous studies indicate that mafG is expressed in both cochlear and vestibular parts of the mouse inner ear, the source of this 'presumed deafness' was further assessed by making round window recordings to determine compound action potential thresholds. Auditory brainstem responses were also acquired to assess function along portions of the central auditory pathway. In all cases, responses in homozygous mutants (-/-) were comparable to those obtained from littermate controls, either wild type (+/+) or heterozygous mutants (+/-). Gross anatomy of the organ of Corti was also found to be similar in all three groups of mice. Hence, the lack of a pinna reflex must relate to nonauditory causes.

Acoustic Stimulation↗
PubMed2005

[Morphological and functional alterations of ear in lysosomal neuraminidase gene deficient mouse].

OBJECTIVE: To observe the alterations of the auditory function and morphology of the ear in the mouse sialidosis models which has been generated by targeted deletion of lysosomal neuraminidase gene (Neul) and closely resembled the phenotypes in corresponding human conditions, and to explore pathophysiological mechanisms of hearing impairment. METHODS: Neul homozygous (Neul -/-) mice at 3 weeks, 2 and 4 months of age, and their wildtype littermates (Neu1 +/+) were examined for auditory thresholds through auditory brainstem responses (ABR) to click, 8, 16, and 32 kHz stimuli. Morphological analyses in ears were performed by series temporal bone section and light microscopy. RESULTS: Neul -/- mice at 3 weeks of age showed an elevated ABR threshold, 50-55 dB above those of Neul +/+ mice. Up to 2 and 4 months of age, their thresholds were further elevated for 60-68 dB. There were distinct pathological changes of middle and inner ear of 3 weeks of age in Neul -/- mice, especially at 2-4 months of age there were significant cerumen occlusion in the external auditory canal and severe otitis media. Vacuolation associated with lysosomal storage was observed within ossicles and cochlear bone cells, stria vascularis cells, spiral ganglion neurons and macrophages, spiral limbus, spiral prominence, Reissner's membrane cells, and the mesothelial cells of the perilymphatic scala and basilar membrane, but not within the organ of Corti. Vestibular ganglion neurons, hair cells and supporting cells in cristae and maculae also showed vacuolation. CONCLUSIONS: The deficiency of lysosomal neuraminidase may result in a serious hearing loss and morphological alterations of ear. The external auditory canal obstruction, otitis media and ossicle changes may cause conductive hearing loss, and the defects in lysosomal storage of neurons, stria vascularis, spiral limbus, Reissner's membrane and basilar membrane cells may contribute to sensorineural deafness.

Animals↗
PubMed2000

[Amelioration of nerve growth factor against noise-induced threshold shift: a transmission electron microscope observation].

OBJECTIVE: To study the protective effects of nerve growth factor(NGF) on noise-induced hearing damage in guinea pigs. METHODS: NGF injected Guinea pigs were consecutively exposed to white noise of 115 dB(A) for 6 days continually (45 min.d-1). Auditory thresholds were measured using auditory cortex evoked response to tone bursts in different post-exposure intervals (1 h, 1 d, 2 d, 3 d and 6 d). The ultrastructural changes within hair cells were also observed by a transmission electron microscope(TEM). RESULTS: The auditory threshold shifts in test group A(NGF:1,000 U.kg-1.d-1, i.m.), B(NGF:2,000 U.kg-1.d-1, i.m.) and C(NGF:3,000 U.kg-1.d-1, i.m.) were significantly fewer than that in the control group(Saline: 1 ml.kg-1.d-1, i.m.). Threshold shifts almost recovered in test group B and C 3 days after the exposure; while a threshold shift of (16.43 +/- 6.91) dB was present 6 days after the exposure in the control group. TEM showed that all three rows of the outer hair cells(OHCs) of the basal turn in the control group displayed significant pathological changes. Depolymerization of actin filiaments within stereocilia, swelling of submembraneous cistern and the efferent nerve-ending and slight edema of hair cells were evident. In test group A, the hair cells display slight pathological changes, which are confined in the third row of OHCs in a local position of the basal turn. In group B and C hair cells have nearly normal appearance. CONCLUSION: NGF is able to reduce threshold shift, and promote the recovery of auditory threshold in acoustic trauma. This factor can, to some extent, protect against noise-induced hearing damage.

Animals↗
PubMed2000

[Study on stepwise regression of risk factors in patients with sudden deafness].

OBJECTIVE: To explore the affected factors of sudden deafness. METHOD: To analyse the stepwise regression of various factors in age, systolic pressure/diastolic pressure, immunoglobulin G, A, M, KPTT, PT, Fbg, FDP, ELT and auditory threshold. RESULT: There was significant correlation (positive straightline relativity) between the auditory threshold and KPTT in patients with sudden hearing loss, and between the auditory threshold and PT in the analysis of coagulogram. CONCLUSION: The state of blood circulation didn't show hypercoagulability in some patients with sudden hearing loss. We must be very careful in therapy of anticoagulation and the increment of blood volume.

Adolescent↗
PubMed1986

Auditory field reduction in human following head trauma.

We measured the tonal auditory threshold for 500, 2000 and 4000 Hz, and made BAER recordings for both ears with unfiltered 125 dB SPL clicks, with 40 subjects between 18 and 23 years of age, 20 subjects having suffered minor cranial trauma during the preceding 48 hours and 20 being control subjects matched for age and sex. Compared to the control group, trauma patients showed a significantly higher auditory threshold: 19 dB SPL at 500 Hz, 9 dB SPL at 2000 and 4000 Hz. This threshold rise was bilateral. The head trauma patients showed, on average, one significantly earlier BAER wave I than did controls. This alteration was likewise bilateral. The latencies of waves II, III and V, the I-III, III-V, and I-V intervals, and the interaural wave latency and interval differences are comparable for trauma patients and control subjects. One to eight months after cranial trauma, 7 subjects manifested one sign of the subjective cranial trauma syndrome. Auditory threshold and BAER wave I earliness were not any greater for these subjects. Trauma patients seemed to show a reduction of the auditory field. They were hypersensitive to high stimulus intensities (shortening of BAER wave I) and less sensitive to low intensities (rise in tonal auditory threshold). This auditory alteration was bilateral. It can thus be thought that the trauma acts on the central nervous system to affect the operation of the cochlea via efferent pathways.

Adolescent↗