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Induction of enhanced acoustic startle response by noise exposure: dependence on exposure conditions and testing parameters and possible relevance to hyperacusis.

Salloum RH, Yurosko C, Santiago L, Sandridge SA, Kaltenbach JA - PLoS ONE (2014)

Bottom Line: In an effort to gain insight into these discrepancies, we conducted measures of acoustic startle responses (ASR) in animals exposed to different levels of sound, and repeated such measures on consecutive days using a range of different startle stimuli.Since many studies combine measures of acoustic startle with measures of gap detection, we also tested ASR in two different acoustic contexts, one in which the startle amplitudes were tested in isolation, the other in which startle amplitudes were measured in the context of the gap detection test.The results reveal that the emergence of chronic hyperacusis-like enhancements of startle following noise exposure is highly reproducible but is dependent on the post-exposure thresholds, the time when the measures are performed and the context in which the ASR measures are obtained.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurosciences, The Cleveland Clinic, Cleveland, Ohio, United States of America.

ABSTRACT
There has been a recent surge of interest in the development of animal models of hyperacusis, a condition in which tolerance to sounds of moderate and high intensities is diminished. The reasons for this decreased tolerance are likely multifactorial, but some major factors that contribute to hyperacusis are increased loudness perception and heightened sensitivity and/or responsiveness to sound. Increased sound sensitivity is a symptom that sometimes develops in human subjects after acoustic insult and has recently been demonstrated in animals as evidenced by enhancement of the acoustic startle reflex following acoustic over-exposure. However, different laboratories have obtained conflicting results in this regard, with some studies reporting enhanced startle, others reporting weakened startle, and still others reporting little, if any, change in the amplitude of the acoustic startle reflex following noise exposure. In an effort to gain insight into these discrepancies, we conducted measures of acoustic startle responses (ASR) in animals exposed to different levels of sound, and repeated such measures on consecutive days using a range of different startle stimuli. Since many studies combine measures of acoustic startle with measures of gap detection, we also tested ASR in two different acoustic contexts, one in which the startle amplitudes were tested in isolation, the other in which startle amplitudes were measured in the context of the gap detection test. The results reveal that the emergence of chronic hyperacusis-like enhancements of startle following noise exposure is highly reproducible but is dependent on the post-exposure thresholds, the time when the measures are performed and the context in which the ASR measures are obtained. These findings could explain many of the discrepancies that exist across studies and suggest guidelines for inducing in animals enhancements of the startle reflex that may be related to hyperacusis.

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Effect of increasing the level of exposure on ABR thresholds.The exposure sound was a continuous 10 kHz tone presented for 4 hours at a level of 110 dB SPL (A), 115 dB SPL (B) or 120 dB SPL (C). Each point represents the mean (±S.E.M.) of ABR thresholds measured in 5–8 animals, upon completion of the ASR testing period. Results from A, B and C are represented as threshold shifts in D, E and F, respectively. *: p<0.05, **: p<0.01, ***: p<0.001.
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pone-0111747-g002: Effect of increasing the level of exposure on ABR thresholds.The exposure sound was a continuous 10 kHz tone presented for 4 hours at a level of 110 dB SPL (A), 115 dB SPL (B) or 120 dB SPL (C). Each point represents the mean (±S.E.M.) of ABR thresholds measured in 5–8 animals, upon completion of the ASR testing period. Results from A, B and C are represented as threshold shifts in D, E and F, respectively. *: p<0.05, **: p<0.01, ***: p<0.001.

Mentions: In order to assess the impact of sound exposure on hearing function, we first compared mean ABR thresholds in animals exposed at each of the three levels of sound (110, 115 and 120 dB SPL) with those of control animals (Fig. 2A–C). Mean thresholds in control animals varied somewhat across frequencies but ranged between 18 and 33 dB SPL, which proved to be insignificant when comparing across the three control groups (F2,55 = 2.32, P = 0.11)(Fig. 2A–C, open circles). The mean threshold in exposed animals varied between 33 and 93 dB, increasing approximately linearly with the level of exposure at all frequencies (R = 0.72, P = 0.0007). The thresholds in exposed animals were significantly higher than those in their respective control groups in all three exposure level comparisons (F1,31 = 53.64, P<0.0001 for the 110 dB SPL exposure group, F1,35 = 50.08, P<0.0001 for the 115 dB SPL exposure group, and F1,51 = 165.3, P<0.001 for the 120 dB SPL exposure group). Maximal threshold shifts in exposed animals were consistently at 8 and 12 kHz and measured 36–38 dB, 49–52 dB and 60–76 dB for the 110, 115 and 120 dB SPL exposure groups, respectively (Fig. 2D–F). The number of frequencies at which significant threshold shifts occurred, as well as the extent of the shift, also increased with exposure level: 8 and 12 kHz in the 110 dB SPL group (P = 0.007 and 0.04, respectively), 8 and 12 kHz in the 115 dB SPL exposure group (P = 0.006 for both), and all four test frequencies (4, 8, 12 and 16 kHz) in the 120 dB SPL group (P values, 0.003, 0.0006, 0.0004 and 0.01, respectively). Thus, both the degree of threshold shift and the spectral range of these shifts increased with the level of exposure.


Induction of enhanced acoustic startle response by noise exposure: dependence on exposure conditions and testing parameters and possible relevance to hyperacusis.

Salloum RH, Yurosko C, Santiago L, Sandridge SA, Kaltenbach JA - PLoS ONE (2014)

Effect of increasing the level of exposure on ABR thresholds.The exposure sound was a continuous 10 kHz tone presented for 4 hours at a level of 110 dB SPL (A), 115 dB SPL (B) or 120 dB SPL (C). Each point represents the mean (±S.E.M.) of ABR thresholds measured in 5–8 animals, upon completion of the ASR testing period. Results from A, B and C are represented as threshold shifts in D, E and F, respectively. *: p<0.05, **: p<0.01, ***: p<0.001.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4216136&req=5

pone-0111747-g002: Effect of increasing the level of exposure on ABR thresholds.The exposure sound was a continuous 10 kHz tone presented for 4 hours at a level of 110 dB SPL (A), 115 dB SPL (B) or 120 dB SPL (C). Each point represents the mean (±S.E.M.) of ABR thresholds measured in 5–8 animals, upon completion of the ASR testing period. Results from A, B and C are represented as threshold shifts in D, E and F, respectively. *: p<0.05, **: p<0.01, ***: p<0.001.
Mentions: In order to assess the impact of sound exposure on hearing function, we first compared mean ABR thresholds in animals exposed at each of the three levels of sound (110, 115 and 120 dB SPL) with those of control animals (Fig. 2A–C). Mean thresholds in control animals varied somewhat across frequencies but ranged between 18 and 33 dB SPL, which proved to be insignificant when comparing across the three control groups (F2,55 = 2.32, P = 0.11)(Fig. 2A–C, open circles). The mean threshold in exposed animals varied between 33 and 93 dB, increasing approximately linearly with the level of exposure at all frequencies (R = 0.72, P = 0.0007). The thresholds in exposed animals were significantly higher than those in their respective control groups in all three exposure level comparisons (F1,31 = 53.64, P<0.0001 for the 110 dB SPL exposure group, F1,35 = 50.08, P<0.0001 for the 115 dB SPL exposure group, and F1,51 = 165.3, P<0.001 for the 120 dB SPL exposure group). Maximal threshold shifts in exposed animals were consistently at 8 and 12 kHz and measured 36–38 dB, 49–52 dB and 60–76 dB for the 110, 115 and 120 dB SPL exposure groups, respectively (Fig. 2D–F). The number of frequencies at which significant threshold shifts occurred, as well as the extent of the shift, also increased with exposure level: 8 and 12 kHz in the 110 dB SPL group (P = 0.007 and 0.04, respectively), 8 and 12 kHz in the 115 dB SPL exposure group (P = 0.006 for both), and all four test frequencies (4, 8, 12 and 16 kHz) in the 120 dB SPL group (P values, 0.003, 0.0006, 0.0004 and 0.01, respectively). Thus, both the degree of threshold shift and the spectral range of these shifts increased with the level of exposure.

Bottom Line: In an effort to gain insight into these discrepancies, we conducted measures of acoustic startle responses (ASR) in animals exposed to different levels of sound, and repeated such measures on consecutive days using a range of different startle stimuli.Since many studies combine measures of acoustic startle with measures of gap detection, we also tested ASR in two different acoustic contexts, one in which the startle amplitudes were tested in isolation, the other in which startle amplitudes were measured in the context of the gap detection test.The results reveal that the emergence of chronic hyperacusis-like enhancements of startle following noise exposure is highly reproducible but is dependent on the post-exposure thresholds, the time when the measures are performed and the context in which the ASR measures are obtained.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurosciences, The Cleveland Clinic, Cleveland, Ohio, United States of America.

ABSTRACT
There has been a recent surge of interest in the development of animal models of hyperacusis, a condition in which tolerance to sounds of moderate and high intensities is diminished. The reasons for this decreased tolerance are likely multifactorial, but some major factors that contribute to hyperacusis are increased loudness perception and heightened sensitivity and/or responsiveness to sound. Increased sound sensitivity is a symptom that sometimes develops in human subjects after acoustic insult and has recently been demonstrated in animals as evidenced by enhancement of the acoustic startle reflex following acoustic over-exposure. However, different laboratories have obtained conflicting results in this regard, with some studies reporting enhanced startle, others reporting weakened startle, and still others reporting little, if any, change in the amplitude of the acoustic startle reflex following noise exposure. In an effort to gain insight into these discrepancies, we conducted measures of acoustic startle responses (ASR) in animals exposed to different levels of sound, and repeated such measures on consecutive days using a range of different startle stimuli. Since many studies combine measures of acoustic startle with measures of gap detection, we also tested ASR in two different acoustic contexts, one in which the startle amplitudes were tested in isolation, the other in which startle amplitudes were measured in the context of the gap detection test. The results reveal that the emergence of chronic hyperacusis-like enhancements of startle following noise exposure is highly reproducible but is dependent on the post-exposure thresholds, the time when the measures are performed and the context in which the ASR measures are obtained. These findings could explain many of the discrepancies that exist across studies and suggest guidelines for inducing in animals enhancements of the startle reflex that may be related to hyperacusis.

Show MeSH
Related in: MedlinePlus