Physiological and Morphological Assessment of the Saccule in Guinea Pigs After Noise Exposure

ORIGINAL ARTICLE Physiological and Morphological Assessment of the Saccule in Guinea Pigs After Noise Exposure

Wei-Chung Hsu, MD, PhD; Jung-Der Wang, MD, PhD; June-Horng Lue, PhD; An-Shiou Day, MD; Yi-Ho Young, MD

Objective: To investigate whether the saccule exhibits threshold shifts recovered 2 and 4 days, respectively, af- temporary or permanent functional loss resembling ter short-term noise exposure, with an interval of 2 days threshold shifts in auditory brainstem response (ABR) earlier in the recovery of VEMPs than that of ABR thresh- of guinea pigs following noise exposure. olds. In contrast, in group B, 78% and 83% of the ears exhibited permanent VEMP loss and ABR threshold shifts, Design: Randomly bred guinea pigs were divided into respectively, 10 days following long-term noise expo- 3 groups: A (short-term noise exposure, 30 minutes, sure. In group C, all animals showed normal VEMPs and n=15), B (long-term noise exposure, 40 hours, n=9), and ABRs throughout the study period. Light and electron C (no noise exposure, n=5). microscopic studies confirmed that loss of VEMPs cor- related with saccular lesion. Setting: University hospital. Conclusions: The saccule can exhibit temporary or per- Main Outcome Measures: All animals underwent ves- manent functional loss resembling hearing threshold shifts tibular-evoked myogenic potential (VEMP) and ABR tests. in guinea pigs following noise exposure. Recovery of Chronological changes of VEMP and ABR responses fol- VEMP precedes restoration of hearing threshold after dam- lowing noise exposure were analyzed and compared. Af- age from short-term noise exposure. Conversely, perma- ter audiovestibular function testing, animals were killed for nent VEMP loss after long-term noise exposure may re- morphological study with light and electron microscopy. flect permanent hearing threshold shifts.

Results: In group A, temporary VEMP loss and ABR Arch Otolaryngol Head Neck Surg. 2008;134(10):1099-1106

XTREME NOISE CAN CLEARLY noise damages the hair cells of the cochlea damage hair cells in the and may also affect the saccular macula. cochlea, leading to tempo- Recently, the vestibular-evoked myo- rary or permanent thresh- genic potential (VEMP) has been vali- old shifts in hearing.1 How- dated to originate from the saccule and is ever,E the effect of noise on the vestibular easily recorded via the contracting neck part remains poorly understood.2,3 De- muscles using loud sound stimulation in hu- 9-11 spite numerous documented cases of bal- mans and experimental animals. The use ance disorders from noise-induced hear- of experimental animals, such as guinea pigs, ing loss, vestibular symptoms resulting facilitates the study of the mechanism of sac- from acoustic trauma have not been stud- cular disorders by recording VEMPs and confirming cell damage by morphological ied thoroughly. Furthermore, excessive ex- 12 posure to very loud music may also affect assessment. Hence, this study investi- gated whether VEMPs exhibit temporary or vestibular function. However, imbalance permanent loss resembling threshold shifts in noise-exposed workers or music- Author Affiliations: of the auditory brainstem response (ABR) exposed young people has not been ap- Department of Otolaryngology, in guinea pigs following noise exposure by National Taiwan University proved for compensation by insurance correlating the physiological results with Hospital, Taipei (Drs Hsu, Day, boards, possibly because vestibular dys- morphological changes. and Young); and Institute of function often recovers spontaneously via Occupational Medicine and central compensation.4 Industrial Hygiene, College of Phylogenically, the saccule in the lower METHODS Public Health (Drs Hsu and species such as amphibians and fish can act Wang) and Department of Anatomy and Cell Biology, as an acoustic receptor. Hence, intense ANIMAL PREPARATION College of Medicine (Dr Lue), sound and vibration may produce vestibu- National Taiwan University, lar reflexes, while the vestibular fibers can Randomly bred Hartley-strain guinea pigs Taipei. also respond to sound.5-8 Restated, loud weighing 250 to 300 g were housed at a mean

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©2008 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/02/2021 (SD) temperature of 23°C (2°C) and humidity of 55% (5%) and injection. Active and reference needle electrodes were in- fed a solid diet and tap water ad libitum. Fifteen animals re- serted in the vertex and ipsilateral retroauricular region, receiving 30 minutes of continuous exposure to loud noise were spectively, while a ground electrode was placed in the neck of classified as group A (short-term noise exposure). Group B con- the animal. Click stimuli (duration, 0.1 ms) were delivered via sisted of 15 animals subjected to continuous noise exposure a plastic tube inserted into the ear canal to record the ABR for 40 hours (long-term noise exposure). After excluding 6 ani- (Smart EP2), monaurally. The repetition rate was 20/s, with a mals with otitis media during the study period, group B com- mean of 400 sweeps. The stimulus intensity began from 100-dB prised 9 animals. Two noise exposure levels were chosen be- peak equivalent SPL, followed by 10-dB step decrements until cause the 30-minute exposure would only produce temporary waveforms I, III, and V disappeared, thus determining the ABR threshold shifts, while 40 hours of exposure was guaranteed threshold. to produce permanent threshold shifts. Another 5 animals with no noise exposure (group C) served as a control group. MORPHOLOGICAL ASSESSMENT All animals in group A underwent ABR and VEMP tests during the pre–noise exposure period and after noise exposure on Following deep anesthesia with intraperitoneal injection of pen- days 0, 1, 2, 3, 4, and 7. For animals in group B, ABR and VEMP tobarbital sodium (50 mg/kg), the animals were transcardially tests were performed during the pre–noise exposure period and perfused with isotonic sodium chloride solution, followed by after noise exposure on days 0, 3, 7, 10 and 30. Throughout a fixative containing glutaraldehyde, 2.5%, in 0.1M phosphate the study, each animal in group C underwent the same tests as buffer at pH 7.4. After complete fixation, the animals were de- those in groups A and B. capitated, and the temporal bones were harvested and placed This study was approved by the institutional review board in the same fixative for 24 hours and decalcified with 10% EDTA and was conducted in accordance with the guideline for the care containing glutaraldehyde, 2.5%, at pH 7.4 for 1 week. Tissue and use of laboratory animals by the Animal Research Commit- blocks were cut horizontally into 200-µm thick slices with a tee, College of Medicine, National Taiwan University, Taipei. vibratome and postfixed in 1% osmium tetroxide for 1 hour. The sections were dehydrated in ascending ethanol solution, NOISE EXPOSURE infiltrated with propylene oxide, and finally embedded in Araldite-Epon mixture (Electron Microscopy Science; Fort Each animal in the 2 noise exposure groups was placed in a cage Washington; Pennsylvania). Semi-thin (1-µm) sections were and allowed to move freely. The noise level was measured with a cut by a Leica Ultracut E ultramicrotome (Leica, Vienna, Aus- sound level meter (model NA-24; Rion, Tokyo, Japan). Continu- tria) and stained with toluidine blue for light microscopic study. ous broadband white noise at a mean (SD) intensity of 115 (5)-dB For electron microscopic study (Hitachi 7100; Hitachi, Tokyo, sound pressure level (SPL) was produced by an audiometer (GSI Japan), ultrathin sections (60-80 nm) of the specimen were cut 61; Grason-Stadler Inc, Milford, New Hampshire) connected to and stained with 1% lead citrate. loud speakers on both sides of the cage. STATISTICAL ANAYLSIS VEMP TEST The abnormal percentages of VEMP results following short- or All animals underwent VEMP tests without general or local an- long-term noise exposure were compared by the McNemar test. esthesia. Needle electrodes were placed in dorsal neck muscle Chronological changes in ABR threshold following short- or on both sides at the level of the third cervical vertebral bone. A long-term noise exposure were compared against pre–noise ex- reference electrode was placed in the occipital area at the mid- posure threshold by the paired t test. Moreover, abnormal per- line, and electromyographic activity was recorded (Smart EP2; centages of VEMP and ABR results were compared by the Intelligent Hearing Systems, Miami, Florida). During the re- McNemar test. Trends in recovery of VEMP responses and ABR cording, each animal was immobilized in a prone position with thresholds were analyzed by Kaplan-Meier survival analysis. its head elevated and neck hyperextended. Electromyo- Finally, the log-rank test was used to compare recovery curves graphic signals were amplified and band-pass filtered between between VEMP and ABR. PϽ.05 was considered to be statis- 30 and 3000 Hz. Click stimuli (130-dB peak equivalent [pe] tically significant. SPL; duration, 0.1 milliseconds [ms]) were delivered via an ear- phone connected through a short tube inserted into the ear ca- RESULTS nal and stimulated in each ear separately. The stimulation rate was 5 beats/s, the analysis time for each response was 24 ms, and 200 responses were averaged for each run.11 BEHAVIOR CHANGE The positive-negative polarity of biphasic waveform termed AFTER NOISE EXPOSURE as waves I and II was measured based on their respective la- tencies of approximately 7 and 9 ms, respectively. Each ani- During noise exposure, most animals appeared agi- mal underwent serial tests with initial stimulus intensities of tated, while other animals kept immobile at 1 corner of 130-dB pe SPL, followed by 10-dB decrements until the wave- the cage, usually the corner farthest from the noise source. form was absent, to confirm the reproducibility of peaks I and However, neither spontaneous nystagmus nor head tilt II. Conversely, VEMP responses were absent when reproducibility of the biphasic waveform at the latency of 6 to 9 ms was was observed in any animals after both short- and long- lacking. “Normal” VEMPs were defined as presence of bipha- term noise exposure. sic waveform at the 6- to 9-ms latency, with a peak-to-peak am- plitude of 5 to 20 µV. CLICK-EVOKED RESPONSES FOLLOWING GENERAL ANESTHESIA ABR TEST All guinea pigs in group C showed VEMP responses be- After the VEMP test, each animal underwent the ABR test after fore anesthesia. Following intraperitoneal administra- receiving an intraperitoneal pentobarbital sodium (35 mg/kg) tion of pentobarbital sodium (35 mg/kg), click-evoked

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Figure 1. Click-evoked myogenic potential test in a guinea pig after receiving general anesthesia reveals no evoked potentials at the 6- to 9-millisecond latency. A, Right side recording; B, left side recording (acoustic stimulation intensity from 130- to 70-dB peak equivalent sound pressure level). B (A) indicates bilateral stimulation with monaural recordings. ABR was observed at the 0.5- to 4.0-ms latency, which was consistent across SPLs. However, no animals dis- Table. Comparison of Abnormal Percentages of VEMP played evoked potentials on the neck at the 6- to 9-ms and ABR in Guinea Pigs After Short- and Long-term Noise Exposure latency (Figure 1). P Value SHORT-TERM NOISE EXPOSURE No. of (McNemar Ears VEMP, % ABR, % Test) Fifteen animals (group A, 30 ears) were subjected to After Short-term Noise Exposure (Group A) short-term noise exposure (30 minutes). The percent- Pre–noise exposure period 30 0 0 ages for absent VEMPs during the pre–noise exposure Day 0 30 70a 97a .02 period and after noise exposure on days 0, 1, 2, 3, 4, and Day 1 30 27a 70a .004 Day 2 30 10 67a Ͻ.001 7 were 0%, 70%, 27%, 10%, 0%, 0%, and 0%, respec- a tively, indicating absent VEMPs on post–noise expo- Day 3 30 0 30 .004 Ͻ Day 4 30 0 0 NS sure days 0 and 1 (P .01, McNemar test). However, Day 7 30 0 0 NS the percentage of normal VEMPs on post–noise exposure days 2 through 7 did not significantly differ from After Long-term Noise Exposure (Group B) Ն Pre–noise exposure period 18 0 0 the same pre–noise exposure period (P .05, McNemar Day 0 18 100b 100b NS test; Table). Figure 2 illustrates the absence of Day 3 18 94b 94b NS VEMPs in a guinea pig immediately following short- Day 7 18 83b 89b NS term noise exposure. On post–noise exposure day 2, Day 10 18 78b 83b NS VEMPs returned to normal. Day 30 18 78b 83b NS The mean (SD) ABR threshold for the pre–noise ex- Abbreviations: ABR, Auditory brainstem response; NS, nonsignificant posure period was 42.5 (5.4)-dB SPL, thus an ABR difference (PՆ.05); VEMP, vestibular-evoked myogenic potential. threshold exceeding 53.3-dB SPL (equal to mean a PϽ.01 when compared with the pre–noise exposure period ϩ2 SD) was defined as a threshold shift. Mean (SD) (McNemar test). ABR thresholds on post–noise exposure days 0, 1, 2, 3, b PϽ.001 when compared with the pre–noise exposure period (McNemar test). 4, and 7 were 71.2 (9.6)-, 58.5 (8.1)-, 54.0 (9.6)-, 46.7 (7.8)-, 45.8 (7.6)-, and 42.8 (6.0)-dB pe SPL, respectively, indicating temporary threshold shifts on post– group A were 97%, 70%, 67%, 30%, 0%, and 0% on noise exposure days 0 through 3 (PϽ.05, paired t test). post–noise exposure days 0, 1, 2, 3, 4, and 7, respec- Accordingly, percentages for ABR threshold shift in tively, indicating that recovery of ABR threshold oc-

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Figure 2. Vestibular-evoked myogenic potential (VEMP) recordings from the right ear of a guinea pig after short-term noise exposure. Absent VEMPs are noted immediately following noise exposure (day 0) (A), but normal VEMPs occur on post–noise exposure day 2 (B) (acoustic stimulation intensity from 130- to 90-dB peak equivalent sound pressure level: I, positive peak; II, negative peak). R (A) indicate right ear stimulation with monaural recordings.

curred on post–noise exposure day 4 (Table). Figure 3 65.0 (7.7)-, and 66.9 (7.1)-dB pe SPL, respectively, re- shows a guinea pig with an ABR threshold of 75-dB pe vealing permanent ABR threshold shifts on post–noise SPL immediately after short-term noise exposure, exposure days compared with the pre–noise exposure which returned to a threshold of 45-dB pe SPL on post– threshold (PϽ.001, paired t test). Thus, abnormal per- noise exposure day 4. centages for ABR in group B were 100%, 94%, 89%, 83%, Comparing the abnormal percentages between VEMP and 83% on post–noise exposure days 0, 3, 7, 10, and and ABR revealed statistically significant differences on 30, respectively. post–noise exposure days 0 through 3 (PϽ.05, McNemar Comparing the abnormal percentages between VEMP test). However, no statistically significant difference (100% and ABR in group B revealed no statistically significant vs 100%) was observed on post–noise exposure days 4 differences on post–noise exposure days 0 through 30 and7(PՆ.05, McNemar test; Table). Trends in recov- (PՆ.05, McNemar test; Table). The recovery curve of ery of VEMP responses and ABR thresholds demon- group B produced by the Kaplan-Meier survival analy- strated by a recovery curve from Kaplan-Meier survival sis method displayed a critical 10-day period for recov- analysis revealed that VEMP responses and ABR thresh- ery of VEMP responses and ABR thresholds. Notably, the olds recovered within 2 and 4 days, respectively, indi- recovery curves of VEMP responses and ABR thresholds cating a significant difference (PϽ.001, log-rank test; did not differ significantly (P Ն .05, log-rank test; Figure 4A). Figure 4B). Beyond 10 days following long-term noise exposure, absent VEMPs and permanent ABR threshold LONG-TERM NOISE EXPOSURE shifts were observed. In control group C, all animals showed normal VEMPs Absent percentages of VEMPs in group B (9 animals, 18 and ABRs throughout the study period. ears) during the pre–noise exposure period and on post– noise exposure days 0, 3, 7, 10, and 30, were 0%, 100%, MORPHOLOGICAL ASSESSMENT IN ANIMALS 94%, 83%, 78%, and 78%, respectively, showing statistically significant differences between the pre–noise ex- After Short-term Noise Exposure posure period and conditions on post–noise exposure days 0 through 30 (PϽ.001, McNemar test; Table). In addi- One week after short-term noise exposure, guinea pigs tion, mean (SD) ABR thresholds for the test animals af- in group A with normal VEMPs were killed for morpho- ter long-term noise exposure on post–noise exposure days logical assessment. On light microscopic examination, 0, 3, 7, 10, and 30 were 91.1 (8.0)-, 75.0 (9.9)-, 68.1 (7.9)-, hair and supporting cells of the saccular macula were in-

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Figure 3. Auditory brainstem response (ABR) from the right ear of a guinea pig at day 0 (A) and day 4 (B) after noise exposure. The ABR threshold is 75-dB peak equivalent (pe) sound pressure level on day 0 and 45-dB pe SPL on post–noise exposure day 4. R (A) indicates right ear stimulation with monaural recordings.

tact. Normal otolithic membrane with numerous small to occur in both humans and animals, relatively few stud- crystalline bodies (otoconia) was shown (Figure 5A). ies have examined similar phenomena in the vestibular Ultrastructurally, both flask-shaped type I and cylin- system, possibly because the semicircular canals are less drical type II hair cells of the saccular macula remained sensitive to impulse noise, even at very high intensi- intact. One kinocilium and many stereocilia were ob- ties.13 However, vestibulo-ocular reflex gain can be en- served on the top of the hair cells. Type I hair cells had a hanced by sound when the labyrinth is opened, eg, su- spherical nucleus and an afferent nerve chalice almost com- perior semicircular canal dehiscence, a condition termed pletely surrounding the entire cell. Type II hair cells had Tullio phenomenon. This designation is currently ap- buttonlike attachments of both afferent and efferent nerve plied to patients in whom there is evidence of vestibular endings. The supporting cells, basement membrane and activation in response to acoustic stimulation, mani- vestibular nerve fiber remained intact (Figure 6A). fested as vertigo, imbalance, or oscillopsia.14 Note that the auditory sensitivity of the saccule is mirrored by the After Long-term Noise Exposure sensitivity of the semicircular canals to sound: canal dehiscence is the most obvious example.15 One month after long-term noise exposure, group B ani- Excluding the Tullio phenomenon, vestibular symp- mals with absent VEMPs were killed for morphological toms in patients with acute acoustic trauma may be re- assessment. On light microscopic examination, the cell lated to functional impairment of the saccule. This is prob- bodies of the hair cells in the saccular macula showed ably due to the saccule retaining an ancestral acoustic signs of disruption and atrophy, eg, hair cells missing from sensitivity in humans; anatomical proximity of the sac- the neuroepithelium or lucent areas between hair cells. cule to the footplate of stapes also suggests that acoustic The supporting cells, otolithic membrane, and otoconia trauma may be associated with saccular damage.3 Fur- were normal (Figure 5B). thermore, the membrana limitans and trabecular mesh- Ultrastructurally, numerous vacuoles in the cyto- work act as a barrier, leading to differential sensitivity plasm or loss of nucleus were found in many type I hair of cochlear and vestibular sensory cells in the presence cells, but this was rarely seen in type II hair cells. The of noxious substances.16 Although the cochlear duct de- supporting cells, basement membrane, and vestibular velops from a comparatively large saccule, both coch- nerve fiber remained intact (Figure 6B). lear and saccular partitions display different neuronal cir- cuit routes, ie, the auditory brainstem system and COMMENT sacculocollic reflex system, respectively. Hence, this study applied both ABR and VEMP tests to assess how noise Although temporary or permanent threshold shifts in effects the peripheral auditory and vestibular systems of hearing following extreme noise exposure is well known guinea pigs.

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©2008 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/02/2021 Unlike well-known ABR studies in experimental ani- stimulation no animals displayed evoked potentials from mals, the VEMP test in alert guinea pigs is a recent pro- a neck muscle at the 6- to 9-ms latency after receiving cedure. To verify that recorded potentials are not con- general anesthesia (Figure 1) further supports the myo- taminated from ABR responses, animals have been genic origin of these biphasic responses. anesthetized with pentobarbital sodium intraperitone- Following short-term (30 minutes) noise exposure, ally. General anesthesia causes muscle relaxation, and re- 70% of the ears exhibited temporary VEMP loss. How- laxation of the neck muscles may abolish VEMPs en- ever, VEMPs recovered in 90% of the ears within 2 days tirely.9 In the present study, the fact that during acoustic (Table and Figure 2). Likewise, temporary threshold shifts in ABR were observed in 97% of the ears immediately after exposure, which resolved within 4 days (Table and 1.0 A Figure 3). Recovery of VEMPs preceded ABR thresholds returning to normal by 2 days in guinea pigs following 0.8 short-term noise exposure (Figure 4), indicating that a rest period of 48 to 96 hours following noise exposure 0.6 is effective for restoring both cochlear and saccular function in guinea pigs. 0.4 Because a single discharge from a high-powered rifle can result in as much damage as 40 hours of continuous 17 0.2 ABR exposure at 90 dB (A-weighted), animals in group B VEMP were subjected to long-term (40 hours) noise exposure. Permanent VEMP loss and ABR threshold shifts were 0.0 0 1 2 3 4 5 6 7 noted in 78% and 83% of the ears, respectively, 10 days following noise exposure (Table). Restated, beyond a 1.0 Ͼ B critical 10-day period, most ( 70%) ears exhibited ir- reversible changes in ABR thresholds and VEMPs 18 0.8 (Figure 4). Yamashita et al reported that reactive oxy- Probability for Normal Percentage gen species and reactive nitrogen species (as deter-

0.6 mined by 4-hydroxynonenal and nitrotyrosine immu- noreactivity) increased from post–noise exposure days 3 to 7, with maximum expression at days 7 to 10; ABR 0.4 threshold deficits and hair cell loss correspondingly plateaued at post–noise exposure days 7 to 10, which is 0.2 compatible with our results. Because intense noise exposure leads to a prolonged set of biochemical pro- 0.0 cesses that determine the final level of tissue damage, a 0 1 3 5 7 10 15 20 25 30 Days critical 10-day period of recovery could be a window of opportunity to treat the acoustic trauma with, for example, antioxidants or steroids. Figure 4. Recovery curves of vestibular-evoked myogenic potential (VEMP) 19 responses and auditory brainstem response (ABR) thresholds after McCabe and Lawrence observed damage to the oto- short-term (A) and long-term (B) noise exposure by the Kaplan-Meier lithic membrane and collapse of the saccule in a study survival analysis method. The interval between recovery of VEMP responses of animals exposed to a noise intensity of 136- to 150-dB and ABR thresholds is 2 days (median) (A). A critical 10-day period is required for recovery of both VEMP responses and ABR thresholds; beyond SPL for 20 minutes. However, in the present study, con- 10 days, neither VEMP nor ABR exhibits further significant change (B). tours of the saccule and otolithic membrane remained

A B

OM OM

Figure 5. Light microscopic photomicrographs of the saccule. A, Guinea pig with normal vestibular-evoked myogenic potentials (VEMPs) 1 week after short-term noise exposure. B, Guinea pig with absent VEMPs 1 month after long-term noise exposure. Note that the loss (black arrow) and disruption (white arrow) of hair cells in the saccular macula are only found in panel B but not in panel A. Otoconia (arrowheads) are normal in both A and B. OM indicates otolithic membrane. (Toluidine blue stain, scale bar=200 µm.)

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II II

I I

I c b

b S

Figure 6. Transmission electron photomicrographs of the saccule. A, Guinea pig with normal vestibular-evoked myogenic potentials (VEMPs) 1 week after short-term noise exposure. B, Guinea pig with absent VEMPs 1 month after long-term noise exposure. In panel A, type I (I) and type II (II) hair cells are surrounded by a nerve chalice (c) and several buttonlike endings (b), respectively. Both types of hair cells remain intact. In panel B, numerous vacuole formations (arrow) in the cytoplasm and loss of nucleus (asterisk) are detected in hair cells of saccular macula. S indicates supporting cells. (Lead citrate stain, scale bar=4 µm.)

intact after both short- and long-term noise exposure, pos- noise exposure may reflect permanent hearing thresh- sibly due to the lower noise intensity (mean [SD], 115 old shifts. [5]-dB SPL) applied. Nevertheless, in long-term noise- exposed guinea pigs with absent VEMPs, numerous vacuole formations were observed in type I hair cells of the Submitted for Publication: August 10, 2007; final revi- saccular macula (Figure 5B and Figure 6B). Curthoys et sion received November 3, 2007; accepted January 22, al20 reported that irregular primary otolithic afferent neu- 2008. rons of the guinea pigs are especially sensitive to bone Correspondence: Yi-Ho Young, MD, Department of conducted vibration. In addition, the physiological evi- Otolaryngology, National Taiwan University Hospital, dence showed that irregular afferents contact type I hair 1 Chang-Te St, Taipei, Taiwan ([email protected]). cells preferentially.21 Therefore, there are some grounds Author Contributions: Dr Young had full access to all for arguing that VEMPs are probably reflecting type I hair the data in the study and takes responsibility for the in- cell activity. tegrity of the data and the accuracy of the data analysis. Clinically, patients with acute acoustic trauma often Acquisition of data: Hsu, Lue, and Day. Analysis and in- express concern about hearing loss. Although distortion- terpretation of data: Wang and Young. Drafting of the manu- product otoacoustic emission can test the viability of the script: Hsu, Wang, and Lue. Critical revision of the manu- outer hair cells, it fails to predict the hearing outcome script for important intellectual content: Day and Young. when temporary threshold shifts greater than 70-dB hear- Statistical analysis: Hsu and Wang. Administrative, tech- ing level or cochlear damage is confined to the inner hair nical, and material support: Lue and Day. Study supervi- cells.22 Alternatively, the VEMP test may provide an- sion: Young. other clue for assessing the hearing outcome, as evi- Financial Disclosure: None reported. denced by a recent report that absent or delayed VEMPs Funding/Support: This study was supported by grant NSC in patients after acute acoustic trauma may indicate poor 96-2341-B002-135-MY3 from the National Science Coun- prognosis with respect to hearing improvement.23 Thus, cil, Taipei, Taiwan. clinical findings support our experimental results indicating that permanent saccular functional loss follow- REFERENCES ing noise exposure may reflect permanent threshold shifts in hearing. 1. Lim DJ. Effects of noise and ototoxic drugs at the cellular level in the cochlea: a In conclusion, the saccule can exhibit temporary or review. Am J Otolaryngol. 1986;7(2):73-99. permanent functional loss resembling hearing thresh- 2. Perez R, Freeman S, Cohen D, et al. Functional impairment of the vestibular end old shifts in guinea pigs following noise exposure. Re- organ resulting from impulse noise exposure. Laryngoscope. 2002;112(6): 1110-1114. covery of VEMP precedes restoration of hearing thresh- 3. Shupak A, Bar-El E, Podoshin L, et al. Vestibular findings associated with chronic old after damage from short-term noise exposure. noise induced hearing impairment. Acta Otolaryngol. 1994;114(6):579-585. Conversely, permanent VEMP loss after long-term 4. Ylikoski J, Juntunen J, Matikainen E, et al. Subclinical vestibular pathology in

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Correction

Error in Byline. In the Original Article by Otteson et al titled “Acute and Chronic Changes in the Subglottis Induced by Graded Carbon Dioxide Laser Injury in the Rabbit Airway,” published in the July 2008 issue of the Archives (2008;134[7]:694-702), the academic degree of one of the authors is incorrect. The author’s name and degree are Gregory M. DiSilvio, BS.

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