Effect of contralateral auditory stimuli on active cochlear micro-mechanical properties in human subjects

The present study investigates the possibility that contralateral auditory stimulation along medial efferent system pathways may alter active cochlear micromechanics and hence affect evoked oto-acoustic emissions in humans. A first experiment, involving 21 healthy subjects showed reduction of oto-acoustic emission amplitude under low intensity contralateral white noise (from 30 dB SPL, 10 dB SL, upwards). The effect is found for intensities below the acoustic reflex threshold (85.2 dB HL). A second experiment, involving 10 of the above 21 subjects, sought to rule out any technical artefact. Recording was again carried out, but after sealing of the contralateral ear with a silicon putty plug. No contralateral intensity effect on oto-acoustic emission amplitude was found for contralateral intensities below 65 dB SPL. In subjective perception terms (dB SL) an effect was found under sealing when the sound reached or passed above the 10 dB SL level. These two findings confirm the preceding experiment. The third experiment investigated the role of transcranial transmission of the contralateral auditory stimulus. 16 subjects having total unilateral deafness and one healthy ear were tested by the same procedure as above. No fall-off in oto-acoustic emission amplitude was found for contralateral stimuli equal to or less than 80 dB SPL. There is thus a contralateral auditory stimulus effect on active cochlear micromechanics. The most appropriate explanation involves the medial cochlear efferent system, excited at brainstem level via the afferent auditory pathways. Alteration of active cochlear micromechanics seems promising at a basic level, pointing, as it does, to an interactive cochlear functioning which can be investigated by simple, non-intrusive, objective techniques which can be used with human subjects. We have here a model for functional exploration of the medial olivocochlear efferent system.

Contralateral auditory stimulation alters acoustic distortion products in humans

It is now generally accepted that otoacoustic emissions (OAE) represent the only objective and non-intrusive means of functional exploration of the active micromechanical characteristics of the outer hair cells of the organ of Corti. Previous studies showed a decrease of the transiently evoked otoacoustic emissions and spontaneous otoacoustic emissions in humans, during acoustic stimulation of the contralateral ear, and attributed this effect to the medial efferent system. Such an effect has been shown on acoustic distortion product otoacoustic distortion emissions (DPOAE) in guinea pigs, but has not been investigated for DPOAEs recorded in humans, although DPOAEs represent the easiest means of exploring active micromechanical cochlear properties both in humans and in laboratory animals. The present study sought to investigate the existence and characteristics of a contralateral auditory stimulation effect on DPOAEs recorded in humans. This study shows that contralateral broad-band noise (BBN) has a suppressive effect on DPOAEs recorded from 0.5 kHz to 5 kHz. This effect is not due to air conduction, as no change in the noise floor occurred under increasing contralateral stimulation, and as no reduction in DPOAE amplitude was obtained in subjects whose contralateral ear was sealed with a plastic ear plug. Moreover, cross-over attenuation by bone transmission has been ruled out, as no change in DPOAE amplitude was recorded in the healthy ear of total unilaterally deaf patients during acoustic stimulation of the deaf ear. The effect seen was not entirely due to the acoustic reflex, as it was found and could indeed be even greater in subjects with no acoustic reflex. Results presented here show that the contralateral BBN effect is greater at low levels of ipsilateral stimulation, which leads us to discuss the involvement of both passive and active mechanisms in DPOAE generation at high stimulation levels. The contralateral BBN effect seems to be greater in mid frequency cochlear regions. There is strong evidence that the medial efferent system is involved and that afferent and efferent inputs are, at least partly, integrated at a brainstem level in order to ensure cochlear interaction. DPOAEs provide an interesting model for functional exploration of the efferent system, since they seem to be the only type of otoacoustic emission that can be recorded in both humans and in the majority of animals, and since results are obtained in the same way from both animals and humans, which allows experimental animal models very close to the human model.

The temporal relationship between speech auditory brainstem responses and the acoustic pattern of the phoneme /ba/ in normal-hearing adults

OBJECTIVE

To investigate the temporal relationship between speech auditory brainstem responses and acoustic pattern of the phoneme /ba/.

METHODS

Speech elicited auditory brainstem responses (Speech ABR) to /ba/ were recorded in 23 normal-hearing subjects. Effect of stimulus intensity was assessed on Speech ABR components latencies in 11 subjects. The effect of different transducers on electromagnetic leakage was also measured.

RESULTS

Speech ABR showed a reproducible onset response (OR) 6ms after stimulus onset. The frequency following response (FFR) waveform mimicked the 500Hz low pass filtered temporal waveform of phoneme /ba/ with a latency shift of 14.6ms. In addition, the OR and FFR latencies decreased with increasing stimulus intensity, with a greater rate for FFR (-1.4ms/10dB) than for OR (-0.6ms/10dB).

CONCLUSIONS

A close relationship was found between the pattern of the acoustic stimulus and the FFR temporal structure. Furthermore, differences in latency behaviour suggest different generation mechanisms for FFR and OR.

SIGNIFICANCE

The results provided further insight into the temporal encoding of basic speech stimulus at the brainstem level in humans.

Interrelations between transiently evoked otoacoustic emissions, spontaneous otoacoustic emissions and acoustic distortion products in normally hearing subjects

Active cochlear mechanisms and especially outer hair cells seem to be involved in oto-acoustic emissions (OAEs) genesis. This study sought to investigate basic characteristics of spontaneous otoacoustic emissions (SOAEs), click-evoked otoacoustic emissions (TOAEs) and interrelations between SOAEs, TOAEs and 2f1-f2 and 2f2-f1 distortion product OAEs (DPOAEs) in 135 normally hearing subjects. A gender effect was shown on TOAEs and DPOAEs amplitude, and is attributed to the higher incidence of SOAEs in women (58%) than in men (22%). Moreover, SOAEs presence seems to mask the age effect found, especially at high frequency components, on TOAEs amplitude. A general influence of SOAEs on TOAEs and DPOAEs is shown, especially at frequencies ranging from 1 kHz to 3 kHz, collecting more than 66% of the SOAEs peaks recorded. Lastly, correlations between TOAEs frequency band amplitude and 2f1-f2 DPOAEs amplitude, shows frequency specificity, at least at low frequencies (i.e., from 0.5 to 2 kHz) in agreement with previous works suggesting that the 2f1-f2 DPOAEs generation site is at the geometric mean of the primaries. The same correlations calculated with 2f2-f1 DPOAEs amplitude show frequency specificity at low frequencies i.e., at 800 Hz and 1600 Hz. 2f2-f1 DPOAEs in humans are shown to be generated near the 2f2-f1 frequency region on the cochlear partition.

Effect of contralateral sound stimulation on the distortion product 2f1-f2 in humans: evidence of a frequency specificity

The frequency characteristics of the suppression by contralateral stimulations, of the cubic 2f1-f2 distortion products (DPOAEs), were studied during 63 sessions performed in 39 humans with normal hearing. Each session consisted of exposure to five successive series of randomized contralateral NBN frequencies centered between 0.25 and 8 kHz, while measuring 2f1-f2 set at one of the four studied frequencies, i.e., 1, 2, 3 or 5 kHz. For each value of 2f1-f2, analysis of variance and Student's t-test were used in order to indicate and, if necessary, to localize, a possible significant frequency specificity. Results showed that the suppression exerted on 2f1-f2 DPOAEs by contralateral sound stimulation, is frequency specific, at least for middle frequencies of 1 and 2 kHz. The frequency specificity is specially marked when 2f1-f2 = 1 kHz with contralateral NBN central frequencies around 1 kHz. When 2f1-f2 = 2 kHz, central frequencies which induced a significant suppressive effect include frequencies around 2 kHz and also lower frequencies around 1 kHz. These observations support the interpretation that the suppression of the DPOAE is mediated by the medial olivo-cochlear efferent system.

Inactivation of gastric and pancreatic lipases by diethyl p-nitrophenyl phosphate

Reacting gastric and pancreatic lipases with mixed diethyl p-nitrophenyl phosphate/bile salt micelles resulted in a stoichiometric inactivation of these enzymes as tested on emulsified tributyroylglycerol and trioleoylglycerol as substrates. Diethyl p-nitrophenyl phosphate treated gastric lipases were also inactive on water-soluble p-nitrophenyl acetate, whereas the modified pancreatic lipase was still able to hydrolyze this water-soluble substrate. The binding of diethyl p-nitrophenyl phosphate modified pancreatic and gastric lipases to tributyroylglycerol/water interface was comparable to that of native lipases. The essential free sulfhydryl group of gastric lipases underwent no chemical changes due to the reaction with micellar diethyl p-nitrophenyl phosphate. All in all, these results indicate that, in both gastric and pancreatic lipases, the essential serine residue which was stoichiometrically labeled by this organophosphorus reagent is involved in catalysis and not in lipid binding.

Is the test of medial efferent system function a relevant investigation in tinnitus?

The present results are drawn from preliminary observations made in 28 patients suffering from unilateral, permanent, non-pulsatile tinnitus, who were systematically submitted to an investigation of their otoacoustic emissions in both ears. Spontaneous otoemissions (SOAE) were carefully looked for, before recording of transient evoked otoemissions (TEOAE). The effectiveness of the medial olivo-cochlear efferent system (MOC) was also tested. The comparison between TEOAE input/output curves obtained with and without contralateral stimulation allowed a global assessment of the functioning of MOC. Additional information relating to the MOC functioning at the precise frequency of tinnitus and/or around it, was available from the comparison of analogous curves obtained using distortion product otoacoustic emissions (DPOAE) instead of TEOAEs. The results show that: (1) when the amplitude of otoacoustic emissions differs between the two ears, the tinnitus is generally lateralized on the side where amplitude was the lowest, which seems to be related to a greater hearing loss; (2) no general law concerning tinnitus can be drawn from the global testing of MOC functioning; the only result is that the slope of TEOAE input/output function appears as a deciding factor for efficiency of MOC, the least efficiency almost always occurring on the side where the slope is greater, and (3) even in the case of proved global effectiveness of MOC activation, there is, at least in the vicinity and in at least one ear, a part of the cochlea where its functioning is altered. A better comprehension of the mechanisms underlying this symptom will probably come from exhaustive exploration of individual cases rather than a rougher investigation of large samples in which different aetiologies are likely to be mixed.

Age-related changes in evoked otoacoustic emissions

Outer hair cells of the organ of Corti play an important part in the genesis of evoked otoacoustic emissions (EOAEs), which are related to cochlear biomechanics. The aim of this study was to investigate the age factor in relation to EOAEs in 166 ears of subjects between 6 weeks and 83 years of age. The results show that when age increases, the presence of EOAEs by age group and the frequency peak in spectral analysis decrease, and EOAE threshold increases. Thus, there is an effect of age upon EOAEs, and it seems linked with alteration of cochlear biomechanics and/or hair cell loss. Such an effect has to be taken into consideration when EOAEs are used in clinical applications, and limits the use of EOAEs in older subjects.

Evoked otoacoustic emissions and sensorineural hearing loss

Following Kemp's original studies, several others have confirmed the existence of otoacoustic emissions. Their clinical relevance remains, however, to be clarified. The various published studies have concerned small series. This study sought to specify otoacoustic emission characteristics in relation to sensorineural hearing loss (148 ears of 76 subjects). The results show that the presence of otoacoustic emissions drops as a function of hearing loss and that there is a highly statistically significant correlation between otoacoustic emission threshold and hearing loss at the 1000-Hz frequency. Otoacoustic emissions are never found when hearing loss at 1000 Hz exceeds 40 dB hearing level and when the mean audiometric hearing loss (at 500, 1000, 2000, and 4000 Hz) exceeds 45 dB hearing level. The main practical conclusion is that otoacoustic emission presence indicates middle frequency functional integrity of the outer hair cells of Corti's organ. Absence of otoacoustic emissions is harder to interpret.

Speech auditory brainstem response (speech ABR) characteristics depending on recording conditions, and hearing status: an experimental parametric study

Speech elicited auditory brainstem responses (Speech ABR) have been shown to be an objective measurement of speech processing in the brainstem. Given the simultaneous stimulation and recording, and the similarities between the recording and the speech stimulus envelope, there is a great risk of artefactual recordings. This study sought to systematically investigate the source of artefactual contamination in Speech ABR response. In a first part, we measured the sound level thresholds over which artefactual responses were obtained, for different types of transducers and experimental setup parameters. A watermelon model was used to model the human head susceptibility to electromagnetic artefact. It was found that impedances between the electrodes had a great effect on electromagnetic susceptibility and that the most prominent artefact is due to the transducer's electromagnetic leakage. The only artefact-free condition was obtained with insert-earphones shielded in a Faraday cage linked to common ground. In a second part of the study, using the previously defined artefact-free condition, we recorded speech ABR in unilateral deaf subjects and bilateral normal hearing subjects. In an additional control condition, Speech ABR was recorded with the insert-earphones used to deliver the stimulation, unplugged from the ears, so that the subjects did not perceive the stimulus. No responses were obtained from the deaf ear of unilaterally hearing impaired subjects, nor in the insert-out-of-the-ear condition in all the subjects, showing that Speech ABR reflects the functioning of the auditory pathways.

Distortion product otoacoustic emissions and sensorineural hearing loss

As other types of otoacoustic emissions, distortion product otoacoustic emissions (DPOAEs) allow the exploration of the active cochlear mechanisms known to take place in the outer hair cell system. Most authors consider that 2f1-f2 DPOAEs are generated in a cochlear region corresponding to the geometric mean (GM) of the primary frequencies. To verify the relevance of this hypothesis in clinical practice, DPOAEs were recorded at seven different frequencies, ranging from 0.5 to 4 kHz, in 81 hearing-impaired patients and in 24 normally hearing subjects. To test the hypothesis that DPOAEs reflect the hearing threshold at the frequency of the GM rather than at the 2f1-f2 frequency, this study compares the 2f1-f2 frequency and the GM of the primaries to the frequency of hearing loss. DPOAEs can be used to explore a large range of frequencies, especially at high frequencies, but responses at low frequencies are less reliable due to noise contamination. Secondly, DPOAEs can be recorded in ears that have a hearing threshold as high as 65 dB HL at the frequency corresponding to the GM of the primaries. Finally, DPOAE recordings show frequency specificity: i.e., hearing loss at a specific frequency correlates best with DPOAEs whose GM of primary frequencies corresponds to the frequency of the hearing loss. However, this frequency specificity is still unsatisfactory and decreases as the levels of primaries increase above 60 dB SPL. Moreover, DPOAE amplitude is too variable to predict hearing loss at a particular frequency, whereas DPOAE threshold allows a correct prediction of abnormal auditory threshold in more than 80% of the cases at frequencies above 1 kHz.

Otoacoustic Emissions and Persistent Tinnitus after Acute Acoustic Trauma

OBJECTIVES

To follow up the auditory status of military personnel after an acute acoustic trauma and to identify the possible predictive value of hearing thresholds and otoacoustic emissions during the first 24 hours after the acoustic trauma.

STUDY DESIGN

A group of 24 young military subjects, aged 22 +/- 2.3 years, without any otologic problem before the acoustic trauma, were examined at three time intervals after an accidental acoustic trauma caused by the discharge of a firearm: 24 hours, 72 hours, and 15 days.

METHODS

Each subject was submitted to medical examination and to a questionnaire detailing the circumstances of the acoustic trauma. Pure tone audiometry was performed from 1 to 8 kHz per half octave. Transiently evoked otoacoustic emissions were recorded in the nonlinear mode at 80 dB pSPL, and distortion product otoacoustic emissions were recorded from 1 to 6 kHz, using a distortion product-gram type procedure, at 65/55 dB SPL, with f2/f1 = 1.22. Two groups of subjects were defined: group 1 (n = 8) represented subjects with short-lasting tinnitus (<72 h) and group 2 (n = 16) subjects with long-lasting tinnitus (>72 h).

RESULTS

Hearing thresholds did not differ significantly between these two groups 24 hours after the acoustic trauma. However, otoacoustic emissions showed significantly lower amplitudes 24 hours after the acoustic trauma in subjects showing a longer lasting tinnitus.

CONCLUSION

Otoacoustic emissions appear to be a better predictor of the persistence of tinnitus than hearing thresholds alone 24 hours after an acute acoustic trauma.

Influence of spontaneous otoacoustic emissions (SOAE) on acoustic distortion product input/output functions: does the medial efferent system act differently in the vicinity of an SOAE?

Otoacoustic emission (OAE) generation mechanisms reside in the active micromechanical properties of the organ of Corti, and especially in the outer hair cells (OHCs). OHCs are strongly innervated by medial efferent olivo-cochlear fibres. Decrease of the intensity of transiently evoked otoacoustic emissions (TOAEs) and modification of spontaneous otoacoustic emissions (SOAEs) during acoustic stimulation of the contralateral ear have already been shown in humans. Similar results were obtained in guinea pigs with a decrease of 2F1-F2 acoustic distortion products (DPOAEs) and a suppression of the effect with sectioning of the floor of the fourth ventricle. The present study sought to investigate the influence of contralateral auditory stimulation on DPOAEs recorded in humans. It shows a decrease in DPOAE intensity for all frequencies, at levels above 45 dB SPL of contralateral broad band noise. This effect was found at levels of contralateral BBN well below the acoustic reflex threshold, and in subjects without acoustic reflex. Moreover, the influence of transcranial transmission could be ruled out since no effect was found when contralateral BBN applied to the altered ear of totally unilaterally deaf patients. Thus, the contralateral acoustic stimulation effect on DPOAEs provides a new means of functional exploration of the medial efferent system in humans. The effect obtained is more ample at low primary frequency levels. Moreover, as DPOAEs are known to be stronger and to show more irregular input/output function patterns in the vicinity of an SOAE, the influence of contralateral auditory stimulation was studied for DPOAEs recorded at 10 Hz, 50 Hz and 150 Hz from an SOAE frequency.

Multicomponent acoustic distortion product otoacoustic emission phase in humans. I. General characteristics

Phase characteristics and latency of 2f1-f2, 3f1-2f2, and 2f2-f1 acoustic distortion product otoacoustic emissions (DPOAEs) have been analyzed in 12 adults with normal hearing. Phase-versus-frequency functions (PFF) have been recorded at each of ten pairs of primary frequencies, by two methods, depending on which one of the primary frequencies f1 or f2 was swept in frequency. Whichever sweep method was used, local phase irregularities were found in the PFF and were shown to be independent of the phase variability due to the measured noise, to be reproducible and frequency specific. Phase irregularities were significantly greater in subjects exhibiting spontaneous otoacoustic emissions. The latency calculation was unaffected by phase irregularities provided that a suitably large range of f2/f1 ratio was used. The DPOAE latencies that were obtained at low ratios of primaries were significantly longer than those obtained at higher ratios. For all DPOAE components and sweep methods used, the latency decreased as frequency increased from 750 Hz to 6 kHz. Substantial intersubject differences were found. They might be due to two main factors: differences in middle ear acoustic properties and in cochlea mechanical characteristics. The influence of pressure in the outer ear canal increased the DPOAE latencies recorded with both the f1 and f2 sweep methods at low frequencies. Men showed significantly longer 2f2-f1 DPOAE latencies than women, especially at low frequencies, which can be attributed to the difference in length of the cochlea according to gender. Lastly, the latencies measured using the f2 sweep were consistently longer than the latencies obtained using an f1 sweep for lower sideband DPOAEs, but no difference was observed for upper sideband DPOAEs.

Lipases of the euphorbiaceae family: purification of a lipase from Euphorbia characias latex and structure-function relationships with the B chain of ricin

A lipase from the latex of Euphorbia characias was purified using a method involving extraction with apolar solvent and adsorption chromatography on silica gel. The lipase (specific activity, 1500 international units/mg of protein) was eluted from silica gel complexes with a lipid. The main protein fraction, which had a molecular mass of 38 kDa, was inactive when dissociated from the lipid fraction. When the lipid and protein fractions were reassociated, 72% of the lipolytic activity was recovered. This lipolytic activity was inhibited by diethyl p-nitrophenyl phosphate, which was shown to bind the lipase with a molar ratio of 0.75. High specific activities (1000 international units/mg) were measured for the lipase of E. characias on lipid extracts rich in galactosyl diacylglycerols. The apolipase was sequenced up to residue 23. The B chain of ricin has a strong homology (43.5%) with that sequence and cross-reacted with antibodies raised against the purified lipase from E. characias. The activity of the B chain of ricin was comparable (54 international units/mg) to that of the apolipase of E. characias (100 international units/mg) mixed with the same lipid cofactor complex. The primary structure (residues 68-72) of the B chain of ricin contains the lipase consensus sequence Gly-Xaa-Ser-Xaa-Gly. Its reactivity with diethyl p-nitrophenyl phosphate indicates the presence of an activated serine that, in addition to its well-documented lectin activity for galactosides, suggests that the B chain of ricin may be a galactosyl diacylglycerol lipase, closely analogous to the lipase from E. characias.

Effect of flavonoids from various Mediterranean plants on enzymatic activity of intestinal carboxylesterase

Flavonol compounds of three Mediterranean plants from the Algerian Atlas used traditionally in Arab folk medicine, Arenaria serpyllifolia, Rhamnus alaternus and Thapsia garganica, were found to inhibit the enzymatic activities of both rat intestine and purified porcine liver carboxylesterase in a concentration-dependent manner. Results indicate that the flavonol compounds from the aerial part of these plants lead to the inactivation of the CE pI = 5.1 with Ki of micromolar range. These results encourage us to perform further biological investigation.

Evoked and spontaneous otoacoustic emissions. A comparison of neonates and adults

Evoked otoacoustic emissions (EOAEs) and spontaneous otoacoustic emissions (SOAEs) were compared between neonates and adults. Several differences were seen for EOAEs: (i) the occurrence of EOAEs was significantly greater in adults than in neonates, and in neonates it increased with extra-uterine age; (ii) the high frequency EOAE intensity was greater in neonates than in adults; (iii) the EOAE intensity was significantly greater in neonates than in adults. No age-related differences for SOAEs were found: (i) age was not significantly related to the presence/absence of SOAEs in neonates or adults; (ii) the occurrence of SOAEs was, however, significantly greater in females than in males in both neonates and adults.

TEP1, the yeast homolog of the human tumor suppressor gene PTEN/MMAC1/TEP1, is linked to the phosphatidylinositol pathway and plays a role in the developmental process of sporulation

PTEN/MMAC1/TEP1 (PTEN, phosphatase deleted on chromosome ten; MMAC1, mutated in multiple advanced cancers; TEP1, tensin-like phosphatase) is a major human tumor suppressor gene whose suppressive activity operates on the phosphatidylinositol pathway. A single homologue of this gene, TEP1 (YNL128w), exists in the budding yeast Saccharomyces cerevisiae. Yeast strains deleted for TEP1 exhibit essentially no phenotype in haploids; however, diploids exhibit resistance to the phosphatidylinositol-3-phosphate kinase inhibitor wortmannin and to lithium ions. Although rates of cancer increase with age, neither tep1 haploids nor diploids have altered life spans. TEP1 RNA is present throughout the cell cycle, and levels are dramatically up-regulated during meiotic development. Although homozygous tep1 mutants initiate the meiotic program and form spores with wild-type kinetics, analysis of the spores produced in tep1 mutants indicates a specific defect in the trafficking or deposition of dityrosine, a major component of yeast spore walls, to the surface. Introduction of a common PTEN mutation found in human tumors into the analogous position in Tep1p produces a nonfunctional protein based on in vivo activity. These studies implicate Tep1p in a specific developmental trafficking or deposition event and suggest that Tep1p, like its mammalian counterpart, impinges on the phosphatidylinositol pathway.

Purification and molecular cloning of porcine intestinal glycerol-ester hydrolase--evidence for its identity with carboxylesterase

A glycerol-ester hydrolase was purified to homogeneity from porcine intestinal mucosa using a partial delipidation method and an eight-step purification procedure. The isolation scheme used gave a 483-fold purification, resulting in a pure enzyme with a specific activity on tributyrin of 290 micromol x min(-1) x mg(-1). The molecular mass of the enzyme was estimated at 240 kDa, based on the results of size-exclusion chromatography, and at 60 kDa, as determined by SDS/PAGE analysis. The isoelectric focusing data obtained indicated that only one isoform with a pI of 5.1 was present. Complete identity was found to exist between the N-terminal sequence of the first 25 amino acid residues and that of a porcine liver carboxylesterase. A full-length cDNA coding for the enzyme was isolated from pig small intestine. We observed that the corresponding protein originally named intestinal glycerol-ester hydrolase definitely belongs to the carboxylesterase family. The deduced amino acid sequence consisted of 565 residues and showed 97% identity with that of porcine liver carboxylesterase and more than 50% identity with those of other carboxylesterases from different mammalian species.

Spontaneous otoacoustic emissions and sensori-neural hearing loss

This study sought to clarify the clinical relevance of spontaneous otoacoustic emissions (SOAEs) and to define the hearing loss level (and frequency) at which absence of SOAE is found. Findings from 126 ears of patients with sensori-neural hearing loss showed an incidence of SOAEs in 18.25% of the cases (23 out of 126 ears). SOAEs were never found when hearing loss at 1,000 Hz exceeded 10 dB. The presence of SOAE seems to indicate a good cochlear functioning at least in the mid-frequencies. Although the incidence of SOAEs is markedly lower than that of evoked otoacoustic emissions (EOAEs), SOAE recording is shown to be a good test, rapid, non-invasive for audiological screening, the presence of SOAE confirming a hearing threshold of less than 10 dB at 1,000 Hz, the absence of SOAE being inconclusive.

V kappa gene family in (Glu60 Ala30 Tyr10)n (GAT)-specific antibodies that express CGAT (or pGAT) public idiotypic specificities. Protein and mRNA sequencing of eight monoclonal V kappa chains

A large proportion of (Glu60 Ala30 Tyr10)n (GAT)-specific antibodies expresses public idiotypic specificities, termed CGAT (or pGAT), that require the presence of both the heavy and the light chains in order to be expressed. We report in this paper the complete sequence of eight V kappa regions pertaining to eight anti-GAT monoclonal antibodies derived from three strains of mice: BALB/c, DBA/2, and C57BL/6. The methodology used a combination of NH2-terminal amino acid and mRNA nucleotide sequencing. All eight sequences analyzed, although highly homologous and all pertaining to the same V kappa 1 subgroup, allowed definition of three germline genes that are likely to be present in all three strains of mice and also in NZB. It seems likely, however, that any given strain may not necessarily use all three genes for making anti-GAT antibodies. The search for structural correlates of idiotypes could not be framed in a simple picture, but our data suggest that similar idiotopes may result from different interacting primary structures, leading to structural homologies that should be visualized at three-dimensional level.

Multicomponent acoustic distortion product otoacoustic emission phase in humans. II. Implications for distortion product otoacoustic emissions generation

Phase characteristics and latency of 2f1-f2, 3f1-2f2, and 2f2-f1 acoustic distortion product otoacoustic emissions (DPOAEs) recorded in normally hearing adults have been described in a companion paper [Moulin and Kemp, "Multicomponent acoustic distortion product otoacoustic emission phase in humans. I. General characteristics," J. Acoust. Soc. Am. 100, 1617-1639 (1996)]. Phase-versus-frequency functions (PFF) have been recorded using two methods, depending whether f1 or f2 was swept in frequency, defining, respectively, an "f1 sweep" and an "f2 sweep" method. The present study compares 2f1-f2, 3f1-2f2, 4f1-3f2, and 2f2-f1 DPOAEs phase characteristics, and latencies obtained by these two methods. For lower sideband DPOAEs, the f2 sweep gave consistently longer latencies than the f1 sweep method, whereas no difference was obtained for the 2f2-f1 DPOAE. This suggests that the lower sideband DPOAEs and the 2f2-f1 DPOAE do not come from the same aspect of the traveling wave. The longer delay obtained with an f2 sweep is suggested to be due to an additional delay added by the proximity of the peak of the f2 traveling wave. The place-fixed and the wave-fixed models of DPOAE generation are discussed, and an "intermediate" model of DPOAE generation is introduced to explain such additional delay and the existence of phase irregularities which were observed in the PFF. The ratio of the latencies obtained by the two sweep methods is frequency dependent and a relation to cochlear frequency selectivity is suggested. Finally, analysis of the differences in latency of the different lower sideband DPOAE components allowed an estimation of the return latency of DPOAEs.