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   Table of Contents - Current issue
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September-October 2017
Volume 19 | Issue 90
Page Nos. 207-244

Online since Thursday, September 21, 2017

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ORIGINAL ARTICLES  

Sex bias in basic and preclinical noise-induced hearing loss research p. 207
Amanda Marie Lauer, Katrina Marie Schrode
DOI:10.4103/nah.NAH_12_17  PMID:28937014
Introduction: Sex differences in brain biochemistry, physiology, structure, and function have been gaining increasing attention in the scientific community. Males and females can have different responses to medications, diseases, and environmental variables. A small number of the approximately 7500 studies of noise-induced hearing loss (NIHL) have identified sex differences, but the mechanisms and characterization of these differences have not been thoroughly studied. The National Institutes of Health (NIH) issued a mandate in 2015 to include sex as a biological variable in all NIH-funded research beginning in January 2016. Materials and Methods: In the present study, the representation of sex as a biological variable in preclinical and basic studies of NIHL was quantified for a 5-year period from January 2011 to December 2015 prior to the implementation of the NIH mandate. Results: The analysis of 210 basic and preclinical studies showed that when sex is specified, experiments are predominantly performed on male animals. Discussion: This bias is present in studies completed in the United States and foreign institutions, and the proportion of studies using only male participants has actually increased over the 5-year period examined. Conclusion: These results underscore the need to invest resources in studying NIHL in both sexes to better understand how sex shapes the outcomes and to optimize treatment and prevention strategies.
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Chronic noise exposure in the spontaneously hypertensive rat p. 213
Anne T.M Konkle, Stephen E Keith, James P McNamee, David Michaud
DOI:10.4103/nah.NAH_15_17  PMID:28937015
Introduction: Epidemiological studies have suggested an association between the relative risk for developing cardiovascular disease (CVD) and long-term exposure to elevated levels of transportation noise. The contention is that this association is largely owing to an increase in stress-related biomarkers that are thought to be associated with CVD. Animal models have demonstrated that acute noise exposure is capable of triggering a stress response; however, similar studies using chronic noise models are less common. Materials and Methods: The current study assessed the effects of intermittent daily exposure to broadband 80 kHz bandwidth noise of 87.3 dBA for a period of 21 consecutive days in spontaneously hypertensive rats. Results: Twenty-one days of exposure to noise significantly reduced body weight relative to the sham and unhandled control groups; however, noise had no statistically significant impact on plasma adrenocorticotropic hormone (or adrenal gland weights). Noise was associated with a significant, albeit modest, increase in both corticosterone and aldosterone concentrations following the 21 days of exposure. Interleukin 1 and interleukin 6 levels were unchanged in the noise group, whereas both tumour necrosis factor alpha and C-reactive protein were significantly reduced in noise exposed rats. Tail blood sampling for corticosterone throughout the exposure period showed no appreciable difference between the noise and sham exposed animals, largely due to the sizeable variation for each group as well as the observed fluctuations over time. Discussion: The current pilot study provides only modest support that chronic noise may promote stress-related biological and/or developmental effects. More research is required to verify the current findings and resolve some of the unexpected observations.
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Impact of usage of personal music systems on oto-acoustic emissions among medical students p. 222
Prasanth G Narahari, Jayashree Bhat, Arivudai Nambi, Anshul Arora
DOI:10.4103/nah.NAH_75_16  PMID:28937016
Background: Intact hearing is essential for medical students and physicians for communicating with patients and appreciating internal sounds with a stethoscope. With the increased use of (PMSs), they are exposed to high sound levels and are at a risk of developing hearing loss. The effect of long term personal music system (PMS) usage on auditory sensitivity has been well established. Our study has reported the immediate and short term effect of PMS usage on hearing especially among medical professionals. Objective: To assess the effect of short term PMS usage on distortion product otoacoustic emissions (DPOAE) among medical professionals. Materials and Method: 34 medical students within the age range of 17–22 years who were regular users of PMS participated in the study. All participants had hearing thresholds <15 dBHL at audiometric octave frequencies. Baseline DPOAEs were measured in all participants after 18 h of non-usage of PMS. One week later DPOAEs were again measured after two hours of continuous listening to PMS. DPOAEs were measured within the frequency range of 2 to 12 kHz with a resolution of 12 points per octave. Output sound pressure level of the PMS of each participant was measured in HA-1 coupler and it was converted to free field SPL using the transformations of RECD and REUG. Results: Paired sample t test was used to investigate the main effect of short term music listening on DPOAE amplitudes. Analysis revealed no significant main effect of music listening on DPOAE amplitudes at the octave frequencies between 2 to 4 KHz (t67 = −1.02, P = 0.31) and 4 to 8 KHz (t67 = 0.24, P = 0.81). However, there was a small but statistically significant reduction in DPOAE amplitude (t67 = 2.10, P = 0.04) in the frequency range of 9 to 12 kHz following short term usage of PMS. The mean output sound pressure level of the PMS was 98.29. Conclusion: Short term exposure to music affects the DPOAE amplitude at high frequencies and this serves as an early indicator for noise induced hearing loss (NIHL). Analysis of output sound pressure level suggests that the PMSs of the participants have the capability to induce hearing loss if the individual listened to it at the maximum volume setting. Hence, the medical professionals need to be cautious while using PMS.
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The effects of repeated low-level blast exposure on hearing in marines p. 227
Lina R Kubli, Robin L Pinto, Holly L Burrows, Philip D Littlefield, Douglas S Brungart
DOI:10.4103/nah.NAH_58_16  PMID:28937017
Background: The study evaluates a group of Military Service Members specialized in blast explosive training called “Breachers” who are routinely exposed to multiple low-level blasts while teaching breaching at the U.S. Marine Corps in Quantico Virginia. The objective of this study was to determine if there are any acute or long-term auditory changes due to repeated low-level blast exposures used in training. The performance of the instructor group “Breachers” was compared to a control group, “Engineers”. Methods: A total of 11 Breachers and four engineers were evaluated in the study. The participants received comprehensive auditory tests, including pure-tone testing, speech-in-noise (SIN) measures, and central auditory behavioral and objective tests using early and late (P300) auditory evoked potentials over a period of 17 months. They also received shorter assessments immediately following the blast-exposure onsite at Quantico. Results: No acute or longitudinal effects were identified. However, there were some interesting baseline effects found in both groups. Contrary to the expected, the onsite hearing thresholds and distortion product otoacoustic emissions were slightly better at a few frequencies immediately after blast-exposure than measurements obtained with the same equipment weeks to months after each blast-exposure. Conclusions: To date, the current study is the most comprehensive study that evaluates the long-term effects of blast-exposure on hearing. Despite extensive testing to assess changes, the findings of this study suggest that the levels of current exposures used in this military training environment do not seem to have an obvious deleterious effect on hearing.
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Environmental noise exposure modifies astrocyte morphology in hippocampus of young male rats p. 239
Odelie Huet-Bello, Yaveth Ruvalcaba-Delgadillo, Alfredo Feria-Velasco, Rocío E González-Castañeda, Joaquín Garcia-Estrada, Miguel A Macias-Islas, Fernando Jauregui-Huerta, Sonia Luquin
DOI:10.4103/nah.NAH_97_16  PMID:28937018
Background: Chronic exposure to noise induces changes on the central nervous system of exposed animals. Those changes affect not only the auditory system but also other structures indirectly related to audition. The hippocampus of young animals represents a potential target for these effects because of its essential role in individuals’ adaptation to environmental challenges. Objective: The aim of the present study was to evaluate hippocampus vulnerability, assessing astrocytic morphology in an experimental model of environmental noise (EN) applied to rats in pre-pubescent stage. Materials and Methods: Weaned Wistar male rats were subjected to EN adapted to the rats’ audiogram for 15 days, 24 h daily. Once completed, plasmatic corticosterone (CORT) concentration was quantified, and immunohistochemistry for glial fibrillary acidic protein was taken in hippocampal DG, CA3, and CA1 subareas. Immunopositive cells and astrocyte arborizations were counted and compared between groups. Results: The rats subjected to noise exhibited enlarged length of astrocytes arborizations in all hippocampal subareas. Those changes were accompanied by a marked rise in serum CORT levels. Conclusions: These findings confirm hippocampal vulnerability to EN and suggest that glial cells may play an important role in the adaptation of developing the participants to noise exposure.
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