The effect of quinine on psychoacoustic tuning curves, stapedius reflexes and evoked otoacoustic emissions in healthy volunteers

Twin study of neonatal transient-evoked otoacoustic emissions

Our knowledge of which physiological mechanisms shape transient evoked otoacoustic emissions (TEOAEs) is incomplete, although thousands of TEOAEs are recorded each day as part of universal newborn hearing-screening (UNHS). TEOAE heritability may explain some of the large TEOAE variability observed in neonates, and give insights into the TEOAE generators and modulators, and why TEOAEs are generally larger in females and right ears. The aim was to estimate TEOAE heritability and describe ear and sex effects in a consecutive subset of all twins that passed UNHS at the same occasion at two hospitals during a six-year period (more than 30 000 neonates screened in total). TEOAEs were studied and TEOAE level correlations compared in twin sets of same-sex (SS, 302 individual twins, 151 twin pairs) and opposite-sex (OS, 152 individual twins, 76 twin pairs). A mathematical model was used to estimate and compare monozygotic (MZ) and dizygotic (DZ) intra-twin pair TEOAE level correlations, based on the data from the SS and OS twin sets. For both SS and OS twin pairs TEOAE levels were significantly higher in right ears and females, compared to left ears and males, as previously demonstrated in young adult twins and large groups of neonates. Neonatal females in OS twin pairs did not demonstrate masculinized TEOAEs, as has been demonstrated for OAEs in young adult females in OS twin pairs. The within-twin pair TEOAE level correlations were higher for SS twin pairs than for OS twin pairs, whereas the within-pair correlation coefficients could not be distinguished from zero when twins were randomly paired. These results reflect heredity as a key factor in TEOAE level variability. Additionally, the estimated MZ within-twin pair TEOAE level correlations were higher than those for DZ twin pairs. The heritability estimates reached up to 100% TEOAE heritability, which is numerically larger than previous estimates of about 75% in young adult twins.

Concentration-Response Relationship of Hearing Impairment Caused by Quinine and Salicylate: Pharmacological Similarities but Different Molecular Mechanisms

This review has the purpose to summarize concentration-effect studies made with quinine and to compare the effects on hearing between quinine and salicylate. Quinine and salicylate have roles in experimental hearing research and may induce pronounced and reversible hearing impairment when administered in sizeable doses. The quinine-induced increase in hearing threshold and its recovery can be analysed according to 'the psychophysical power function'. The power function is a special case of the Hill equation when the stimulus (e.g. a drug concentration) is exceedingly small compared with the concentration that would elicit a half-maximum response. Quinine and salicylate induce sensorineural hearing impairment and tinnitus when given in higher dose ranges in man. The drugs influence the presence, magnitude, and quality of audiological responses, such as spontaneous and evoked otoacoustic emissions. Quinine reversibly reduces frequency selectivity and hearing sensitivity, whereas the self-attained most comfortable speech level and the acoustic stapedius reflex are not affected, that is the dynamic range of hearing is reversibly reduced. This observation supports the view that quinine acts on the outer hair cell of the cochlea. Both drugs share a protective effect against the permanent hearing damages caused by gentamicin. This action is interpreted as a request for functioning mechanoelectric transducer (MET) channels to elicit the ill effect of aminoglycosides. Both drugs may interfere with the cochlear amplifier through blocking MET channels and the motor protein prestin. This review finds considerable overlap between type and extent of pharmacological actions of quinine and salicylate, supposedly caused by partly shared mechanisms of action but performed with different molecular mechanisms.

Detecting incipient inner-ear damage from impulse noise with otoacoustic emissions

Audiometric thresholds and otoacoustic emissions (OAEs) were measured in 285 U.S. Marine Corps recruits before and three weeks after exposure to impulse-noise sources from weapons' fire and simulated artillery, and in 32 non-noise-exposed controls. At pre-test, audiometric thresholds for all ears were <or=25 dB HL from 0.5 to 3 kHz and <or=30 dB HL at 4 kHz. Ears with low-level or absent OAEs at pre-test were more likely to be classified with significant threshold shifts (STSs) at post-test. A subgroup of 60 noise-exposed volunteers with complete data sets for both ears showed significant decreases in OAE amplitude but no change in audiometric thresholds. STSs and significant emission shifts (SESs) between 2 and 4 kHz in individual ears were identified using criteria based on the standard error of measurement from the control group. There was essentially no association between the occurrence of STS and SES. There were more SESs than STSs, and the group of SES ears had more STS ears than the group of no-SES ears. The increased sensitivity of OAEs in comparison to audiometric thresholds was shown in all analyses, and low-level OAEs indicate an increased risk of future hearing loss by as much as ninefold.

Mefloquine neurotoxicity: a literature review

A literature review revealed that mefloquine neurotoxicity has been demonstrated at both the preclinical and clinical levels, with nausea, dizziness, sleep disturbances, anxiety and psychosis, amongst other adverse neuropsychiatric events, reported in users. Females and individuals of low body mass index (BMI) are at apparent greater risk. Mechanisms of possible neurotoxicity may include binding to neuroreceptors and cholinesterases, inhibition of sarcoendoplasmic reticulum ATPase (SERCA) and interference with cellular Ca(2+) homeostasis, accumulation in the CNS, and reductions in CNS efflux in individuals possessing certain MDR1 polymorphisms. It may be prudent to avoid mefloquine in females and low BMI individuals, and in combination with other potentially neurotoxic agents such as the artemisinin antimalarials.

Is there a close relationship between changes in amplitudes of distortion product otoacoustic emissions and hair cell damage after exposure to realistic industrial noise in guinea pigs?

In long-term experiments in awake guinea pigs (n = 12), distortion product otoacoustic emissions (DPOAEs) at various frequencies were measured repeatedly over 6-8 months. About 9 weeks after the first measurement, the animals were exposed to industrial noise (car industry, maximal intensity about 110 dB SPL) for 2 h. The amplitudes of DPOAE were measured prior to noise exposure and 10 min, 70 min, 1 day and 2 days after the noise exposure and then once every week. Three to four months after noise exposure, the animals were killed, and the cochleae were prepared for scanning electron microscopy. The row of inner hair cells (IHCs) was complete in all animals, while the rows of outer hair cells (OHCs) showed a considerable hair cell loss in some of the animals without a correlation to the change in amplitudes of DPOAE. However, a closer relationship between the decline of amplitudes of DPOAE and the number of missing and changed OHCs (fused stereocilia bundles, missing tip links) could be established. The number of lost OHC does not reflect the decline in DPOAE in all cases. This discrepancy must be considered when the degree of hearing loss needs to be established from changed DPOAE.

The effect of suppression on the periodicity of stimulus frequency otoacoustic emissions: experimental data

In a companion paper [Lineton and Lutman, J. Acoust. Soc. Am. 114, 859-870 (2003)], changes in the spectral period of stimulus frequency otoacoustic emissions (SFOAEs) during self-suppression and two-tone suppression were simulated using a nonlinear cochlear model based on the distributed roughness theory of otoacoustic emission generation [Zweig and Shera, J. Acoust. Soc. Am. 98, 2018-2047 (1995)1. The current paper presents the results of an experimental investigation of SFOAE suppression obtained from 20 human subjects. It was found that, in most subjects, the spectral period increased during self-suppression, but reduced during high-side two-tone suppression. This pattern of results is in close agreement with the predictions of the cochlear model, and therefore strongly supports the distributed roughness theory of Zweig and Shera. In addition, the results suggest that the SFOAE spectral period is sensitive to changes in the state of the cochlear amplifier.

Cisplatin-induced hyperactivity in the dorsal cochlear nucleus and its relation to outer hair cell loss: relevance to tinnitus

Cisplatin causes both acute and chronic forms of tinnitus as well as increases in spontaneous neural activity (hyperactivity) in the dorsal cochlear nucleus (DCN) of hamsters. It has been hypothesized that the induction of hyperactivity in the DCN may be a consequence of cisplatin's effects on cochlear outer hair cells (OHCs); however, systematic studies testing this hypothesis have yet to appear in the literature. In the present investigation, the relationship between hyperactivity and OHC loss, induced by cisplatin, was examined in detail. Hamsters received five treatments of cisplatin at doses ranging from 1.5 to 3 mg. kg(-1). day(-1), every other day. Beginning 1 mo after initiation of treatment, electrophysiological recordings were carried out on the surface of the DCN to measure spontaneous multiunit activity along a set of coordinates spanning the medial-lateral (tonotopic) axis of the DCN. After recordings, cochleas were removed and studied histologically using a scanning electron microscope. The results revealed that cisplatin-treated animals with little or no loss of OHCs displayed levels of activity similar to those seen in saline-treated controls. In contrast, the majority (75%) of cisplatin-treated animals with severe OHC loss displayed well-developed hyperactivity in the DCN. The induced hyperactivity was seen mainly in the medial (high-frequency) half of the DCN of treated animals. This pattern was consistent with the observation that OHC loss was distributed mainly in the basal half of the cochlea. In several of the animals with severe OHC loss and hyperactivity, there was no significant damage to IHC stereocilia nor any observable irregularities of the reticular lamina that might have interfered with normal IHC function. Hyperactivity was also observed in the DCN of animals showing severe losses of OHCs accompanied by damage to IHCs, although the degree of hyperactivity in these animals was less than in animals with severe OHC loss but intact IHCs. These results support the view that loss of OHC function may be a trigger of tinnitus-related hyperactivity in the DCN and suggest that this hyperactivity may be somewhat offset by damage to IHCs.

Quinine affects the response properties of compound action potentials elicited by periodic click trains

The effects of systemically applied quinine on the compound action potential (CAP) were investigated in 5 guinea pigs. A dose of 200 mg/kg body weight of quinine hydrochloride was administered intramuscularly, and CAPs were recorded at the round window before and after administration. The CAP thresholds of the animals were elevated by 5 to 25 dB approximately 30 minutes after administration, and thresholds recovered in some animals during the experimental session. The CAP waveform elicited by the click train stimulus was abnormal after administration of quinine. The amplitude of the CAPs elicited by the second click was larger than that of those elicited by the first click. These changes may be induced by an abnormally broadened N1 response to the first click in the click train following quinine administration. In contrast, the CAP waveforms elicited by the second click and by the following clicks in the click train appeared normal.

Otoacoustic emissions--an approach for monitoring aminoglycoside induced ototoxicity in children

OBJECTIVES

The early detection of hearing impairment caused by ototoxic drugs, such as aminoglycosides, has been the aim of research world-wide. Histopathological studies have shown that the outer hair cells are the most susceptible cochlear components to injury from ototoxic drugs like aminoglycosides. Otoacoustic emissions reflect the functional status of the outer hair cells and constitute the only non-invasive means of objective cochlear investigation. The aim of this study was to evaluate the potential of otoacoustic emissions in early identification of aminoglycoside-induced cochlear dysfunction. In addition, a comparison with pure-tone audiometry or auditory brainstem responses was performed in order to determine if this test might provide a more reliable method of monitoring early ototoxic insults to the cochlea.

METHODS

Twenty four children receiving gentamicin (4 mg/kg once daily) for 6-29 days were included in the study. Eleven children received gentamicin for up to 7 days (group A), while 13 underwent longer-term therapy lasting 8-29 days (group B). Hearing was serially monitored using transient evoked otoacoustic emissions and pure-tone audiometry (0.25-12 kHz) or auditory brainstem responses for younger or uncooperative children. Transient evoked otoacoustic emissions data were analysed in terms of emission amplitude and response reproducibility as a function of frequency.

RESULTS

All patients yielded a normal baseline audiometric assessment upon hospital admission. For group A patients no significant changes in hearing levels were observed either by pure-tone audiometry (P = 0.2), auditory brainstem responses (P = 0.3) or transient evoked otoacoustic emissions (mean response: P = 0.06, reproducibility by frequency: P > 0.05). For group B patients no significant changes in hearing levels measured by pure-tone audiometry (P = 0.1) or auditory brainstem responses (P = 0.4) were observed. Transient evoked otoacoustic emissions however revealed a statistically significant decrease in the mean response level (P = 0.017) and in the reproducibility over the whole frequency spectrum (1 kHz: P = 0.0057, 2 kHz: P = 0.0247, 3 kHz: P = 0.0134, 4 kHz: P = 0.0049, 5 kHz: P = 0.0019).

CONCLUSIONS

The findings suggest that transient evoked otoacoustic emissions are an extremely sensitive measure of the early effects of aminoglycoside-induced injury to the peripheral auditory system. Therefore, their use is recommended for regular monitoring of cochlear function, in the presence of potentially toxic factors, aiming at prevention of permanent damage.

The effects of quinine on cochlear nerve fibre activity in the guinea pig

The effect of quinine on single cochlear nerve fibre activity (n = 38) was measured in four pigmented guinea pigs, which were given 10-30 mg/kg of quinine intravenously. The frequency tuning curves of these fibres exhibited significant increases in the thresholds of both 'tip' and 'tails' regions of the frequency tuning curve, but these changes did not appear to be accompanied by significant changes in tuning, as measured by the Q'10'dB. In comparison with control fibres (n = 178) from 13 untreated animals, significant changes in the proportion of low:high spontaneous rates (SR) were also seen. Using a boundary criterion of 25 sp/s, this rate changed from 26:74% to 47:53% in control and quinine-poisoned fibres, respectively. Independent of changes in the spontaneous rate, significant increases in the mean absolute refractory period from 0.85 to 1 ms were measured following quinine administration. The absence of a significant effect on fibre tuning whilst threshold was elevated indicates that quinine does not affect the integrity of the cochlear amplifier, though appears to affect cochlear sensitivity.

Use of homeopathy in the treatment of tinnitus

Tinnitus is a prevalent condition which has no practical and effective pharmacological treatment. In the absence of relief by conventional routes, sufferers are increasingly turning to 'alternative' or 'complementary' medicine. This paper reports the evaluation of a homeopathic preparation 'Tinnitus' by a double-blind, placebo-controlled clinical trial. The remedy was taken in tablet form at a homeopathic D60 potency. Perceived intensity and intrusiveness of the tinnitus was assessed at four points during the trial by subjective procedures (visual analogue scales and questionnaires) and by a battery of audiological measurements. Although questionnaire responses indicated that the homeopathic preparation was preferred to placebo by 14 of the 28 subjects, an analysis of variance indicated that neither the VAS scores nor the audiological measures showed significant improvement in tinnitus symptoms in response to 'Tinnitus' versus the placebo. It was concluded that 'Tinnitus' could not be shown to be more effective than the matched placebo.

Effects of quinine on neural activity in cat primary auditory cortex

The effect of systemically applied quinine on single-unit firing activity in primary auditory cortex was investigated in seven cats. A dose of 100 or 200 mg/kg of quinine hydrochloride was administered intramuscularly and recordings from the same units were performed prior to application and continuously up to on average 5.5 h after administration. All animals showed 10-40 dB of threshold shift about 30 min after administration and some animals showed recovery during the course of the investigation. Significant increases were found in spontaneous firing rates for low-firing-rate units (initial firing rate < 1 spike/s). For high-firing-rate units (initial firing rate > 1 spike/s) no significant changes were observed. There were no significant changes in modal and mean interspike interval. The time-to-rebound peak in the autocorrelation function for spontaneous firings was not altered significantly. The rate of burst occurrence showed no significant change. The best modulation frequency in response to stimulation with periodic click trains decreased after administration, but the limiting rate did not change. Peak cross-correlation coefficients for the spontaneous firings of simultaneously recorded cells showed a significant increase and the correlogram's central peak was significantly narrower after quinine application. Dose effects were only present for cross-correlation results and temporal modulation transfer functions. The results for both spontaneous firing rate, peak width in the cross-correlogram and click stimulation were similar to those observed in salicylate-treated cats (Ochi and Eggermont, 1996). The other findings were different from those observed after salicylate. It is obvious that the effects of quinine on the auditory system are not the same as those of salicylate. The increased synchronization of the spontaneous firings across different neurons observed after application of both drugs may be related to tinnitus.

Reliability of transient-evoked otoacoustic emissions

OBJECTIVE

This investigation addressed four factors affecting transient-evoked otoacoustic emission (TEOAE) reliability: 1) The effect of evoking-stimulus level, 2) the effect of analyzing bandwidth, 3) the effect of slight-mild hearing loss, and 4) the effect of variability in the stimulus spectrum.

DESIGN

TEOAEs at 80, 74, 68, and 62 dB pSPL evoking-stimulus levels were measured in 25 ears spanning a range of hearing levels from normal to mild hearing loss for a minimum of 10 test sessions. Reliability was assessed for 1/6-, 1/3-, 1/2-, and 1-octave analyzing bandwidths.

RESULTS

Evoking-stimulus level, hearing loss, and center frequency did not significantly affect reliability. With decreasing analyzing bandwidth, reliability decreased. Intrasubject test-retest standard deviations were 1.2 dB for a broadband analyzing bandwidth and 1.4, 1.5, 1.6, and 1.8 dB for 1-, 1/2-, 1/3-, and 1/6-octave analyzing bandwidths, respectively. Stimulus variability within narrower bandwidths was of sufficient magnitude to influence test-retest reliability, and attempts to correct for the variations in stimulus spectrum were unsuccessful. Slopes of the input-output functions differed across frequencies, with shallower slopes at higher frequencies.

CONCLUSIONS

In general, TEOAE amplitude is highly reliable. For those individuals in this study who were more variable, the variability was at low frequencies or across the entire frequency spectrum. For clinical applications, the choice of analyzing bandwidth should be based on consideration of both frequency specificity (where narrow analyzing bandwidths are optimal) and reliability (where wide analyzing bandwidths are optimal).

Magnitude changes in transient evoked otoacoustic emissions and high-level 2f1-f2 distortion products in man during quinine administration

Quinine reversibly affects the outer hair cells (OHC). It is therefore an ideal drug for studying OHC-related phenomena, such as transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs). Pure-tone thresholds (PTTs), 1,000-4,000 Hz, TEOAEs, and DPOAEs were measured monaurally in 5 normal-hearing volunteers during quinine administration. DPOAE was evoked at 75 dB SPL (f2/f1 = 1.22) and analysed at 2f1-f2 with f2 at 6 frequencies (700-4,000 Hz), while TEOAE was obtained at 79 dB SPLp and analysed at the f2 frequencies (1/3 octave). The PTT-shift was flat, 10 dB, whereas the TEOAE-power and the global mean of the DPOAEs decreased 4.5 dB and 1.4 dB, respectively. No correlation was found between the intra-individual emission shifts. It is concluded that TEOAE is more sensitive than high-level DPOAE for identifying minor cochlear hearing losses. Support is given to the hypothesis that different sources are involved in generating DPOAEs at different evoking levels.

Clinical monitoring using otoacoustic emissions

Damaging influences to the cochlea are a leading cause of sensorineural hearing loss. Examples include acute or chronic noise exposure and cochleotoxic drugs such as aminoglycosides. Typically, once damage has occurred, the cochlea cannot recover. Therefore, prevention is critical. If damaging influences cannot be avoided, then secondary prevention or early detection of cochlear hearing loss becomes important. Ideally, methods for the detection of cochlear damage should be as specific and as sensitive as possible. Otoacoustic emissions satisfy these criteria and offer a means of testing aspects of cochlear function in a non-invasive and objective way. Evoked otoacoustic emissions measured either after transient stimuli or during two-tone stimulation (distortion-product otoacoustic emissions) are the types most commonly used for clinical purposes. They are stable over time within individual ears and their repeatability has been established under conditions of clinical testing using commercial equipment. Thus, they are well suited as an effective means of monitoring subtle changes in cochlear status. The possibility of making non-invasive repeated measures of cochlear function has led to the widespread use of otoacoustic emissions in animal experiments. Influences of development, anoxia, anaesthesia, noise, and drugs have been monitored. Preliminary studies in humans demonstrate that cochlear damage due to ototoxic drugs such as aminoglycosides or cisplatin and due to noise exposure can be detected using otoacoustic emissions. Comparison of such results to those available using pure-tone audiometry indicates a greater sensitivity of otoacoustic emissions for detecting early cochlear damage.(ABSTRACT TRUNCATED AT 250 WORDS)