摘要:

Forward masking of the auditory brainstem response (ABR) was achieved by increasing the time interval from 0 to 12 ms between the masker offset and the probe onset. The forward masking response demonstrated a near linear function with an approximate 3.0-dB increase in masking threshold for every millisecond interval increase in the control guinea pig. The slope of the masking curve at selected frequencies together with the quantification of hair cell loss through the analysis of cochlear surface morphology was studied before and after chemical insult. The intracochlear infusion of sodium salicylate caused an approximately 45-dB threshold shift of the ABR whereas the slope of the forward masking curve was not significantly different from the control values at the tested frequencies (1, 4, and 8 kHz). Systemic kanamycin administration (400 mg/kg body weight for 9 consecutive days) caused a permanent ABR threshold shift of 43–63 dB at 1, 4, and 8 kHz. The slope of the forward masking curve was not significantly different at 1 kHz despite significant outer hair cell loss. The slope of the forward masking curve at 4 and 8 kHz showed significant reductions at the time intervals between 0 and 4 ms. Analysis of the kanamycin-treated cochleae revealed not only significant outer hair cell loss throughout the cochlea but significant inner hair cell and inner pillar cell loss in the basal end of the cochlea. The results suggest that the outer hair cells are not needed for maintaining a normal forward masking curve, whereas the slope of the forward masking curve is sensitive to alterations induced to either the inner hair cells or the inner pillar cell

ISSN:1420-3030    

DOI:10.1159/000259215

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The goal of this study was to test the hypothesis that the inner hair cell complex (inner hair cell and dendritic contacts) is solely responsible for generating the slope of the forward masking curve. To test this hypothesis two experiments were performed. The first was to measure forward masking from the Bronx waltzing mouse, a mutant possessing an inner hair cell defect. The Bronx waltzing mouse demonstrated an approximately 60-dB auditory brainstem response (ABR) threshold shift compared to CBA/CBA mice at 8 and 12 kHz. The slope of the forward masking curve was significantly reduced compared to the control group, particularly at the early delay times between 0 and 4 ms. The second model employed kainic acid to affect the dendrites beneath the inner hair cell. After the intracochlear infusion of kainic acid, there was an approximately 47-dB ABR threshold shift at 4 and 8 kHz compared to pre-infusion thresholds. The slope of the forward masking curve from the kainic-acid group was significantly reduced compared to the artificial-perilymph group. Primarily the early delay times were affected by kainic acid (0-4 ms). Morphological analysis showed that there was extensive swelling of the afferent nerve radial dendrites under the inner hair cells. The results from the present study, as well as the preceding article, suggest that the analysis of the slope of the forward masking curve may be used for the detection of inner hair cell or radial dendrite damage, independent of outer hair cell damage. The present finding could provide a useful means of employing a clinical test for determining the function of the inner hair cell complex using a non-invasive measure of auditory function.

ISSN:1420-3030    

DOI:10.1159/000259216

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The forward masking curve of the auditory brainstem response (ABR) at selected frequencies together with the quantification of hair cell loss through the analysis of cochlear surface morphology was studied in guinea pigs before and after acoustic trauma resulting in either a temporary or a permanent threshold shift. In the presence of a noise-induced temporary threshold shift, the slope of the forward masking curve was not significantly different from the pre-exposure curve. In contrast, during the acute phase of the permanent threshold shift, the slope of the forward masking curve was significantly reduced compared to the pre-exposure value. After a recovery period of 2 weeks, the slope of the forward masking curve from the permanently damaged group returned to nearly normal values despite a persisting ABR threshold shift and significant loss of outer hair cells. The potential for analyzing the slope of the forward masking curve in order to distinguish between the acute phase of a permanent threshold shift and a temporary threshold shift is discussed.

ISSN:1420-3030    

DOI:10.1159/000259217

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

When anaesthetized animals are maintained over a long period, crossed-cochlear suppressive and enhancement-in-noise effects mediated by the olivocochlear bundle (OCB), as well as some OCB neuronal responses, show time-dependent variations. The present study determined if there were any such changes in OCB-mediated crossed-cochlear protection against compound action potential (CAP) threshold losses caused by a standard loud sound exposure at 11 kHz, presented under conditions either not evoking OCB-mediated protection (i.e. monaural exposure) or evoking protection (binaural exposure). Maintaining animals for periods up to ∼ 30 h from initial anaesthetization resulted in non-significant changes in pre-exposure CAP thresholds. There were also only small changes over select frequency ranges in threshold losses caused by the monaural or binaural loud sound, after a single exposure as well as when the testing of OCB function was extended to examine effects after dual successive exposures, the latter result being determined by application of a previously described additivity model. The features of OCB-mediated protection also showed good stability over the long maintenance. These results are discussed as providing further circumstantial evidence that protection is mediated by a different OCB subcomponent to that/those responsible for other OCB-mediated crossed-cochlear effects. In general, the results show that the barbiturate anaesthetic used here does not significantly modulate the crossed-cochlear OCB effect of protection, even though it has been shown elsewhere to significantly depress other crossed-cochlear OCB effect

ISSN:1420-3030    

DOI:10.1159/000259218

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

A new method for detecting the acoustic reflex that utilizes standard otoacoustic emissions recording techniques is introduced and discussed. Two successive identical tone bursts of 100 ms duration and 10 ms interstimulus interval are presented in the occluded ear canal at a repetition rate of one per second. If the acoustic reflex is elicited, the contraction of the stapedius muscle is delayed with respect to the onset of the first stimulus. Hence, the acoustic compliance in the ear canal decreases primarily during the second stimulus. The difference of the microphone signals produced by the two stimuli is computed and averaged across a certain number of repetitions of the sequence. The presentation level is increased until this difference is larger than -40 dB (with respect to the stimulus level) and if its signal-to-noise ratio exceeds 20 dB. For normal-hearing subjects, the acoustic reflex threshold measured with this method is on average 8 dB lower than in a standard clinical setup. In 5 out of the 10 tested hearing-impaired subjects, the new method could detect an acoustic reflex at one or more frequencies where no reflex was detected in the clinical setup.

ISSN:1420-3030    

DOI:10.1159/000259219

出版商:S. Karger AG    

年代:1996

数据来源: Karger

ISSN:1420-3030    

DOI:10.1159/000259220

出版商:S. Karger AG    

年代:1996

数据来源: Karger

ISSN:1420-3030    

DOI:10.1159/000259221

出版商:S. Karger AG    

年代:1996

数据来源: Karger

ISSN:1420-3030    

DOI:10.1159/000259222

出版商:S. Karger AG    

年代:1996

数据来源: Karger

ISSN:1420-3030    

DOI:10.1159/000259214

出版商:S. Karger AG    

年代:1996

数据来源: Karger