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PubMed2002

Use of DPOAEs for assessing hearing loss caused by styrene in the rat.

The study was carried out to test whether or not cubic distortion otoacoustic emissions were more sensitive than auditory-evoked potentials for assessing styrene-induced hearing losses in the Long-Evans rat. For the purposes of comparison, changes in cubic distortion product otoacoustic emissions (DeltaDPOAE), evoked potential permanent threshold shifts (PTS) and outer hair cell losses were measured in a population of styrene-treated rats. Each rat was exposed to either 650 or 750 ppm of styrene for 4 weeks, 5 days per week, 6 h per day. Only the 750 ppm exposure caused significant hearing losses. For this concentration, DPOAEs appeared as sensitive to styrene as the audiometry performed with evoked potentials, but not more. A high coefficient of correlation [0.84< or =r< or =0.91] between DeltaDPOAE and PTS was obtained across the styrene-induced effects for frequencies ranging from 5 to 12 kHz. This experiment demonstrates that DPOAEs can be used to monitor the ototoxicity induced by styrene even though they cannot be considered as a more sensitive index of cochlear pathology than the evoked potentials, at least under our experimental conditions. Likewise evoked potentials, normal DPOAEs may not guarantee a normal cochlear status and therefore results of DPOAE measurements should be interpreted cautiously. The use of both techniques and the determination of the ratio DeltaDPOAE/PTS may be useful in determining the cause of hearing loss: mechanical or chemical process. Moreover, because of its non-invasive and objective characteristics, the use of DPOAEs could play a greater role in a prevention policy.

Animals↗
PubMed1997

Taste- and odor-reactivity in heroin addicts.

Opiates in general, and heroin in particular, are known to induce compulsive drug-seeking and drug-taking behavior. Addiction is accompanied by psychobiological processes which may distort perception of sensory stimuli. Gustatory and olfactory stimuli are hedonically polarized and therefore most appropriate for the assessment of the organism's reactivity to "useful" and "harmful" chemosensory events. Previous studies revealed that psychophysical self-estimates and reflectory facial expressions mirror with comparable reliability the hedonics of the perceived taste and odor sensations. In the present study both cognitive verbal and reflectory facial expressions of a group of: a) heroin addicts were recorded and compared to those of a group of b) detoxified former addicts and to c) a group of matching controls. Results show that all three groups differentiate between pleasant, indifferent and aversive tastes and odors. Active addicts estimated sweet taste and savory smells as being somewhat more pleasant, and bitter and sour tastes and a putrid odor as less unpleasant than did the other two groups. The reflectory facial displays of addicts were less expressive and discriminative than those of the two other groups. Taste- and odor-induced facial displays are known to be controlled primarily by the brainstem. The findings indicate that heroin-addiction affects brain-mechanisms, which mirror taste- and odor-hedonics. Modulation of the phylogenetically ancient, sensory-motor coordinations was found to be of a different pattern than that of the cortically-controlled cognitive reactions.

Adult↗
PubMed1995

[Effect of contralateral noise exposure on otoacoustic distortion product emissions in man].

The influence of contralateral white noise with levels of 50 and 60 dBnHL on the amplitude of distortion-product otoacoustic emissions (DPOAE) was measured. Thirty ears of normally hearing adults (17 women, 13 men, mean age 26.5 +/- 5.3 years) were examined. Two representative DPOAE frequencies 2f1-f2 = 1342 Hz and 6341 Hz were compared. The lower DPOAE frequency was placed in the frequency region where middle-ear pressure has a strong influence on DPOAE amplitudes, the higher DPOAE frequency respectively in the region where lesser influence is exerted by middle-ear pressure. During the application of contralateral white noise a statistically significant total of 85% of DPOAE amplitudes was reduced, although there was some variation in the individual behaviour of DPOAE amplitudes. In general the higher DPOAE frequency (6341 Hz) was reduced distinctly less than the lower DPOAE frequency (1342 Hz). The reaction of DPOAE amplitude depended closely on the time course of the contralateral stimulus and amplitude reductions were present over 10 minutes without adaptation or fatigue. It is not possible to differentiate between middle-ear or inner-ear mediate effects but the middle ear is at least involved. Based on the presence of those DPOAE amplitude reductions over ten minutes without adaptation or fatigue and the fact that lower frequencies are influenced much more than higher frequencies a synergistic effect--middle-ear and efferent mediated--is suggested.

Adult↗
PubMed1991

[The clinical use of oto-acoustic emissions of cochlear distortion products].

Otoacoustic emissions of cochlear distortion products (DPOAEs) were measured in normally hearing and hearing-impaired human ears. A total of 133 subjects (231 ears) were tested. Two puretone stimuli f1 and f2 were delivered to a sound probe fixed in the outer ear canal. The frequencies of the two primaries were chosen so that their geometric mean represented pure-tone audiometric frequencies. The otoacoustic emission was measured at the distortion product frequency 2f1-f2 by spectral averaging. For 199 ears, the levels of the primaries were 73 dBHL for L1 and 67 dBHL for L2. Statistical analysis was carried out in 77 ears of 46 subjects with normal hearing (average hearing levels at pure-tone audiometric thresholds less than or equal to 10 dBHL) and 36 ears of 25 subjects exhibiting near-normal hearing (average hearing levels at pure-tone audiometric thresholds less than or equal to 20 dBHL). The mean DPOAE amplitudes were similar in these two groups of ears. In 111 of these 113 ears (98.2%), DPOAEs were detected at three or more of the six tested frequencies between 1 and 6 kHz. DPOAEs were measured in more than 75% of ears at each frequency between 1-6 kHz and in more than 86% between 1-4 kHz. Eighty-six hearing-impaired ears of 44 subjects with sensorineural hearing loss formed the patient group. A highly significant correlation between pure-tone audiometric thresholds and DPOAE amplitudes was demonstrated in the frequency range of 1-4 kHz. Percentiles of DPOAE amplitudes were calculated in 22 ears with a mean pure-tone threshold less than or equal to 5 dBHL and in 12 specially selected pathological ears.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1996

Maternal perception of children's weight in relation to eating disorders.

Abnormal perception of body weight in girls has been reported previously (1), and distorted perception of body shape is cited as one of the pathogenetic factors in eating disorders such as anorexia and bulimia nervosa (2,3). Parent-child relationships should also be considered as one of the factors possibly contributing to the onset of the eating disorders (3,4). In the present paper we shall examine whether mothers perceive the weight of their sons and daughters correctly or not, and we shall also compare the results with the perceptions of the children themselves, which we have reported previously in this journal (1). Five outline drawings (-20% to 20% overweight), used in the previous study (1), were shown to the mothers, who were asked to select the drawings which they considered to represent the body weight of their sons (n = 130) and daughters (n = 125), who were aged 6 to 18 years. The mean body weights of the boys and girls in the study sample were 6.0% and 6.6% overweight, respectively. The mothers perceived the weight of their sons to be significantly (P < 0.01) less than the actual weight of these boys. The mean difference between the perceived weight and the actual weight was 10.4%. The mothers' perception of their daughters' weight was also 7.9% less than the actual weight (P < 0.05) (Fig. 1).

Adolescent↗
PubMed2001

Temporary and permanent noise-induced changes in distortion product otoacoustic emissions in CBA/CaJ mice.

A number of studies have shown that the ear can be protected from sound over-exposure, either by activating the cochlear efferent system, or by sound 'conditioning' in which the role of the efferent system is less certain. To study more definitively the molecular basis of deliberately induced cochlear protection from excessive sounds, it is advantageous to determine, for an inbred mouse strain, a range of noise exposure parameters that effectively alter cochlear function. As an initial step towards this goal, young CBA/CaJ mice were exposed to a 105-dB SPL octave-band noise (OBN), centered at 10 kHz, for various lengths of time consisting of 10 min, or 0.5, 1, 3, or 6 h. Distortion product otoacoustic emissions (DPOAEs) at the 2f1-f2 frequency, in response to equilevel primary tones of low to moderate levels, were used to quantify the damaging effects of these sound over-exposures on cochlear function. In addition, staining for acetylcholinesterase (AChE) activity to assess for noise-induced changes in the pattern of efferent-nerve innervation to the cochlea was also performed in a subset of mice that were exposed to the longest-lasting 6-h OBN. The 10-min OBN resulted in only temporary reductions in DPOAE levels, which recovered to pre-exposure values within 5 days. Increasing the exposure to 0.5 h resulted in permanent DPOAE losses that, for low primary-tone levels, were still present at 31 days post-exposure. Additionally, the 1-h and longer exposures caused permanent reductions in DPOAEs for all test levels, which were measurable at 31 days following exposure. Light-microscopic observations restricted to the 11-18-kHz frequency region of the organ of Corti, for a subset of mice exposed to the 6-h OBN, uncovered a significant loss of outer hair cells (OHCs). However, despite the OHC loss in this region, the AChE activity associated with the related pattern of efferent innervation remained largely intact.

Acetylcholinesterase↗
PubMed1999

High-frequency hearing influences lower-frequency distortion-product otoacoustic emissions.

OBJECTIVES: The primary goal of this study was to test the ability of 2f1-f2 distortion-product otoacoustic emissions (DPOAEs) to detect reduced cochlear function in the presence of normal behavioral sensitivity. DESIGN: A prospective study was performed in normal-hearing young adults using simple and complex regression analyses to clarify the relationship between ultra-high frequency (UHF) hearing and DPOAE levels at lower frequencies, as well as the influence of hearing levels for frequencies within the conventional test range and subject age on this association. METHODS: Average DPOAE levels between 4 to 8 kHz, which were elicited by equilevel primary tones of low to moderate levels, were measured as level-frequency functions, or distortion-product (DP) grams, and related to the mean UHF hearing levels from 11.2 to 20 kHz. The median hearing level for the UHF hearing was used to separate subjects into good and poor UHF hearers. This distinction was then used to compare DPOAE levels from 4 to 8 kHz for the 2 groups to determine if UHF hearing status influenced DPOAE levels at lower frequencies. RESULTS: Simple regression analysis revealed that the 4-to 8-kHz DPOAE levels were significantly correlated with the pure-tone average (PTA) from 11.2 to 20 kHz. However, the PTA for 4 and 8 kHz was also significantly correlated with the PTA for UHF hearing. Further multiple regression analyses revealed that UHF hearing significantly and uniquely accounted for approximately 14% of the variance in DPOAE levels from 4 to 8 kHz for most of the primary-tone level combinations. In contrast, neither the PTA for the conventional hearing range nor subject age contributed significantly to the DPOAE variance. CONCLUSIONS: The findings suggest that UHF hearing influences DPOAEs at significantly lower frequencies because emissions are sensitive to subtle changes in outer hair cells not yet detected by pure-tone thresholds in this region or because alterations in the basal cochlea affect the generation of lower-frequency DPOAEs originating from more apical cochlear regions.

Adolescent↗
PubMed1996

Phase delay measurements of distortion product otoacoustic emissions at 2f1-f2 and 2f2-f1 in human ears.

The present study used distortion product otoacoustic emission (DPOAE) latency as a tool to provide information about the generation sites of 2f1-f2 and 2f2-f1 DPOAEs in humans. The DPOAE 2f1-f2 is supposed to be generated near the f2 site, but little is known about the 2f2-f1 DPOAE processing in humans. The present work sought to test several hypotheses as to the possible generation of 2f1-f2 at the f2 site and of 2f2-f1 at the 2f2-f1 site as well as their backward reflection site, by comparing latencies of the two DPOAEs, under appropriate frequency manipulation. The effect of stimulus level was also studied. The latency values were calculated as the phase-lag related to the frequency shift, using the ILO92 software. Amplitudes were lower and latencies shorter for 2f2-f1 than for 2f1-f2. As expected, 2f1-f2 and 2f2-f1 DPOAE latency decreased with increasing stimulus level and frequency. At 70 dB SPL, latencies of DPOAEs with primaries f1 and f2 or f*1 and f*2, chosen so as to obtain 2f*1-f*2 = 2f2 - f1, were identical, whereas at 55 dB SPL the similarities were less obvious, suggesting two different generation processes. The present study suggests that the comparison of several DPOAE components may produce useful information about their processing within the cochlea.

Adult↗
PubMed1995

[Distortion product of otoacoustic emissions in normal hearing and sensorineural hearing loss].

Based on a variety of experimental and clinical studies the diagnostic significance of transient evoked otoacoustic emissions (TEOAEs) is well established. This is also due to the availability of commercial hardware and software which is optimized for the recording of click-evoked OAEs. In cases with distortion product otoacoustic emissions (DPOAEs) the significance for clinical purposes is not yet clear. This study presents results obtained in normal hearing subjects and patients with sensorineural hearing losses (214 ears). The study focuses on three problems: 1. Incidence of DPOAEs in different groups of hearing loss. 2. Level of DPOAEs at various frequencies in each group of hearing loss. 3. Frequency-specific relationships between hearing loss and DPOAEs. Recording of DPOAEs was performed with the ILO92 system and standard configuration (primary tone level, 70 dB SPL). In normal hearing ears DPOAEs were observed at all frequencies above 1 kHz. In cases with moderate hearing loss the detection rate decreased to about 80%. With further increases in hearing loss the detection rate and level of DPOAEs decreased. At frequencies below 1500 Hz even in normal hearing subjects, the level of DPOAEs only slightly exceeded the noise level. The upper limit of hearing loss for which DPOAEs could be observed depended on frequency. In the low-frequency range DPOAEs were absent in ears with a sensorineural hearing loss greater than 35-45 dB; at frequencies between 4 and 6 kHz DPOAEs were observed even in ears with a hearing loss 65 dB.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Postnatal development of 2f1-f2 otoacoustic emissions in pigmented rat.

Distortion-product emissions at 2f1-f2 were measured in developing, pigmented rats to determine the characteristics of the functional onset and maturation of these emitted responses. Distortion-product testing was conducted on postnatal days 12, 14, 18, 21, 24, 28, and 51. The geometric-mean frequencies of the primaries were tested at one-half octave intervals, between 4 and 11.3 kHz. No emissions were detected on postnatal day 12; however, by day 14, emissions were measured at geometric-mean frequencies between 5.7 and 11.3 kHz, but not at 4 kHz. By the 18th postnatal day, all animals had measurable emissions at 4, 5, 7, 8, and 11.3 kHz. Both the functional onset and maturation of high- to midfrequency emissions developed before those elicited by lower-frequency primaries. Response/growth or input/output functions for the higher frequencies exhibited 'adult-like' properties that included an increase in maximum amplitude and 'saturation' at high levels of stimulation by the third to fourth postnatal week. Maturation of the lower-frequency responses progressed at a slower rate. These results differ somewhat from those reported previously for the neonatal albino rat. However, the present findings were based upon a wider frequency range of primary tones, lower levels of acoustic stimulation, and a measuring system with a significantly lower noise floor. These results are consistent with documented periods of the anatomical maturation of the rat outer hair-cell system and establish a functional 'baseline' for future studies utilizing agents that damage the developing cochlea.

Acoustic Stimulation↗
PubMed2000

The effects of maturation and stimulus parameters on the optimal f(2)/f(1) ratio of the 2f(1)-f(2) distortion product otoacoustic emission in neonates(1).

Distortion product otoacoustic emission (DPOAE) measurements are becoming popular in the clinical realm because they have been shown to reflect cochlear function. The primary tones used to evoke the DPOAE are important in determining the amplitude of the emission recorded in the ear canal. This study examined the ratio of the primaries necessary to determine the maximum amplitude emission as a function of development, stimulus level and frequency. Optimum f(2)/f(1) ratios were measured utilizing the f(1)-sweep technique from 105 neonates between 30-42 weeks conceptional age (CA) and 40 adults. No significant difference for optimum ratio was shown between the neonatal and the adult groups. Primary tone frequency had a significant effect on optimum ratio for both neonates and adults. Low f(2) frequencies (<4 kHz) were associated with higher optimum ratios than high f(2) frequencies (>4 kHz). The adult group was used to investigate the effect of stimulus level on the optimum f(2)/f(1) ratio for f(2) frequencies from 1.7 to 10 kHz. Regression analysis showed significant differences across levels of the primaries at all frequencies except for f(2)=3.4 and 7.0 kHz. These differences in f(2)/f(1) ratio across stimulus frequency and level may be attributed to the change in the shape of the excitation profiles along the basilar membrane.

Acoustic Stimulation↗
PubMed1996

Slopes of distortion-product otoacoustic emission growth curves corrected for noise-floor levels.

Distortion-product otoacoustic emission (DPE) input/output (I/O) curves were measured at 2f1-f2 frequencies with spectral-averaging and time-averaging procedures from ten normal-hearing ears. Stimuli were equal-level f1 and f2 primary tones with f2/f1 ratios of 1.2 and f2 frequencies at 1200, 2400, and 4800 Hz. Time-averaging procedures lowered noise-floor (NF) levels, compared to spectral averaging, so DPEs could be elicited by stimuli as low as 18 dB SPL in some ears. DPEs were corrected for power summation with NF levels and the resulting DPE I/O curves were fit with sixth-order polynomials. Slopes of fitted I/O curves were specified by the first derivative as a function of the level of the primary tones. Slopes of uncorrected spectrally averaged DPE I/O curves were strongly influenced by the NF level. Slopes of NF-corrected spectrally averaged DPE I/O curves were more representative of the true slope, specified as the slope of the corresponding time-averaged DPE I/O curve well above its NF. True DPE I/O slopes decreased with level from a mean slope near 1.0 dB/dB at 30 dB SPL and below for all three f2 frequencies. Nonmonotonicities in I/O curves were not seen at very low stimulus levels. At moderate stimulus levels and above, nonmonotonicities in individual DPE I/O curves reduced the slopes of individual I/O curves and reduced the average slopea cross ears.

Acoustic Stimulation↗
PubMed2001

Potentiation of noise-induced hearing loss by amikacin in guinea pigs.

Noise and aminoglycosides initially attack cochlear outer hair cells (OHCs). Distortion product otoacoustic emissions (DPOAEs) are used for the early diagnosis of damage to OHCs. The effects of sub-damaging doses of amikacin, an aminoglycoside antibiotic agent, on noise-induced hearing loss (NIHL) were examined in guinea pigs. Animals were grouped by gender and exposed to broadband noise at 105 dB SPL for 12 h and/or injected i.m. with either amikacin (100 mg/kg/day) or saline for 10 days. Auditory brainstem response (ABR) thresholds, along with DPOAE amplitudes, were measured serially before and after noise exposure. DPOAE amplitudes decreased and ABR thresholds elevated immediately after noise exposure and then gradually recovered. At all frequencies, the emission amplitudes recovered completely to pre-exposure baseline values by 4 days after noise exposure. There was no effect of amikacin on either the ABR threshold or DPOAE amplitudes, in animals treated with amikacin only. However, amikacin significantly prolonged the effect of noise exposure on DPOAE amplitude but not on the noise-induced temporary threshold shift (TTS) of the ABR. In animals treated with a combination of noise and amikacin, significant changes in DPOAE amplitudes were still observed at 4 weeks after cessation of noise exposure. No gender difference in the responses to noise and/or amikacin could be demonstrated. The present findings indicate that even sub-damaging dosages of amikacin might impair recovery from NIHL in guinea pigs.

Amikacin↗
PubMed1997

Fine structure of the 2 f1-f2 acoustic distortion products: effects of primary level and frequency ratios.

The fine structure of the 2 f1-f2 acoustic distortion product (ADP) was measured in humans with different primary level (L1/L2) and frequency (f2/f1, f2 > f1) ratios. The (L1/L2) ratio was varied under two conditions. In the first condition L1 was fixed at 50 dB SPL while L2 was varied from 30 to 75dB SPL in 5-dB steps. An upward frequency shift was observed in the ADP fine structure as L2 was increased. In the second condition, L2 was fixed at 50 dB SPL and L1 varied, and a downward frequency shift was observed. These opposing frequency shifts are predicted by a vector-sum model [Sun et al., J. Acoust., Soc. Am. 96, 2166-2174, 2175-2183 (1994)] and support the hypothesis that the ADP fine structure largely reflects place features of the area of overlap of the primary traveling waves. The mechanisms underlying the shifts in fine structure were further investigated by using three primary f2/f1 ratios: 1.11, 1.2, and 1.33. An orderly difference in the rate of fine-structure shift with level was observed as a function of f2/f1 ratio, with the largest rate of shift associated with the smallest frequency ratio. This observation, along with the fact that downward frequency shift (with L1 varied) is always at a larger rate than the upward shift (with L2 varied), suggests that ADP levels and fine structure are strongly influenced by the nonlinear compression present in the mechanics of the basilar membrane in the region of overlap between the primary traveling waves.

Adult↗
PubMed1997

[Increased amplitude of distortion product emissions in the human caused by contralateral low intensity acoustic stimulation].

Distortion product otoacoustic emissions (DPOAEs) are probably based on the motile properties of the cochlear outer hair cells (OHCs), which are richly innervated by medial olivo-cochlear efferent nerves (MOCs). DPOAEs provide a stimulating model for functional exploration of the efferent system. The influences of contralateral acoustic stimulation were studied on the amplitude of ipsilateral DPOAEs at the frequency 2f1-f2. Fifteen ears of adults with normal hearing (7 women, 8 men, mean age; 23.1 +/- 4.2 years) were examined. Sound stimulation consisted of exposure to 6 successive series of contralateral pure tones at frequencies between 0.5 and 4.0 kHz and low intensities of 30 dB HL. DP grams were registered with f2 ranging from 708 to 6165 Hz. Contralateral pure tones in the frequency range above 750 Hz and with intensities of 30 dB HL increased the ipsilaterally registered DPOAE amplitudes. The results showed that this increase was frequency specific, at least for frequencies at 1 and 2 kHz. The frequency specificity was especially marked when ipsilateral f2 was near 1 kHz. Contralateral frequencies of 3 and 4 kHz induced a significant, increasing effect, including ipsilateral frequencies around f2 = 3 kHz (or 4 kHz) and also lower frequencies around f2 = 1 kHz. Our results support the concept that the observed increase in DPOAE amplitudes is mediated by the medial olivo-cochlear efferent system. The rule of OHCs as a cochlear amplifier in the presence of contralateral low-intensity sound stimulation is discussed.

Acoustic Stimulation↗
PubMed2001

[Contralateral suppression of latency during distortion product otoacoustic emissions detection in guinea pigs].

OBJECTIVE: To investigate the cochlear micromechanics and the function of cochlear efferent system by detecting the distortion product otoacoustic emissions (DPOAE) with or without contralateral acoustic stimulation. METHODS: The DPOAE amplitude and latency of the cubic DPOAE (2f1-f2) were measured at f2 = 2, 4 and 6 kHz with or without 70 dB SPL broad-band noise contralateral stimulation in ears of 12 healthy pigmented guinea pigs, which were divided into two groups(A and B) and tested with different primary intensity level combinations. On the next day, an operation was made to open the acoustic bulla of right ear in Group A. Kainic Acid (KA, 1 microL of 60 mmol/L) was applied onto the round window membrane and wiped up carefully after three hours. The amplitude and latency of the cubic DPOAE from the left ear were measured after 6 hours of KA administration, with or without contralateral noise stimulation. RESULTS: Before the KA treatment, the amplitude of DPOAE induced by primaries of equal levels (L1 = L2) presented no significant change and the latency prolonged significantly during contralateral acoustic stimulation (Group A). But the amplitude at 2, 4 kHz of DPOAE induced by primaries of different levels (L1 > L2) decreased significantly and the latency also prolonged significantly (Group B). After KA administration in the contralateral ear of Group A, the contralateral acoustic stimulation had no significant effect on either amplitude or latency of DPOAE measured ipsilaterally. CONCLUSION: The result demonstrates that the latency is a sensitive index for the cochlear contralateral suppression. The efferent system may act as a negative feedback during the cochlear transduction.

Acoustic Stimulation↗
PubMed2002

Caffeine and ryanodine demonstrate a role for the ryanodine receptor in the organ of Corti.

The hypothesis that the release of Ca(2+) from ryanodine receptor activated Ca(2+) stores in vivo can affect the function of the cochlea was tested by examining the effects of caffeine (1-10 mM) and ryanodine (1-333 microM), two drugs that release Ca(2+) from these intracellular stores. The drugs were infused into the perilymph compartment of the guinea pig cochlea while sound (10 kHz) evoked cochlear potentials and distortion product otoacoustic emissions (DPOAEs; 2f(1)-f(2)=8 kHz, f(2)=12 kHz) were monitored. Caffeine significantly suppressed the compound action potential of the auditory nerve (CAP) at low intensity (56 dB SPL; 3.3 and 10 mM) and high intensity (92 dB SPL; 10 mM), increased N1 latency at high and low intensity (3 and 10 mM) and suppressed low intensity summating potential (SP; 10 mM) without an effect on high intensity SP. Ryanodine significantly suppressed the CAP at low intensity (100 and 333 microM) and at high intensity (333 microM), increased N1 latency at low intensity (33, 100 and 333 microM) and at high intensity (333 microM) and suppressed low intensity SP (100 and 333 microM) and increased high intensity SP (333 microM). The cochlear microphonic (CM) evoked by 10 kHz tone bursts was not affected by caffeine at high or low intensity, and ryanodine had no effect on it at low intensity but decreased it at high intensity (10, 33, 100 and 333 microM). In contrast, caffeine (10 mM) and ryanodine (33 and 100 microM) significantly increased CM evoked by l kHz tone bursts and recorded from the round window. Caffeine (10 mM) and ryanodine (100 microM) reversibly suppressed the cubic DPOAEs evoked by low intensity primaries. Overall, low intensity evoked responses were more sensitive and were suppressed to a greater extent by both drugs. This is consistent with the hypothesis that release of Ca(2+) from ryanodine receptor Ca(2+) stores, possibly in outer hair cells and supporting cells, affects the function of the cochlear amplifier.

Action Potentials↗
PubMed1995

Growth of the 2f1-f2 distortion product otoacoustic emission for low-level stimuli in human neonates.

Distortion product otoacoustic emissions (DPOAEs) for low stimulus levels (< 60 dB SPL) have been reported in adult humans under ideal conditions. In neonates, DPOAEs have been reported only for high-level stimuli. The purpose of this paper was to determine characteristics of the 2f1-f2 DPOAE for low-level stimuli in neonates and to assess the feasibility of obtaining such measures in a noisy environment. Subjects were 19 premature neonates presumed to have normal hearing based on systematic pneumatic otoscopy measures and evoked auditory brainstem responses. For stimuli centered at 2000 and 6000 Hz and presented over a range of 30 to 75 dB SPL, DPOAEs were measured employing linear time averaging for up to 128 time frames at each level. In quiescent subjects, the level of the noise floor was as low as that reported in cooperative adults under ideal conditions (approximately -30 dB SPL), and the functions were identical. That is, valid measures were obtained for very low stimulus levels (30 dB SPL), the rate of growth approached 1 dB/dB, and identical nonmonotonicities (saturation, plateaus, and notches) were observed as those reported for adults. When the noise floor was elevated due to subject activity, no valid data could be obtained for low-level stimuli even though the DPOAEs were at expected levels for high-level stimuli. These results have important implications for the use of such measures in this population because the DPOAEs associated with the metabolically active nonlinear cochlear processes at low stimulus levels may be contaminated with DPOAEs associated with other processes at high stimulus levels.

Acoustic Stimulation↗