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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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Effects of exposure level on ASR growth curves for early (1–2 days) and late (7–9 days) post-exposure time frames.A–B. Data for animals exposed at 110 dB SPL. C–D. Data for animals exposed at 115 dB SPL. E–F. Data for animals exposed at 120 dB SPL. Each point represents the mean (±S.E.M.). Group sizes are indicated in the graphs. Asterisks indicate points where differences between exposed and control animals were statistically significant (p<0.05).
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pone-0111747-g004: Effects of exposure level on ASR growth curves for early (1–2 days) and late (7–9 days) post-exposure time frames.A–B. Data for animals exposed at 110 dB SPL. C–D. Data for animals exposed at 115 dB SPL. E–F. Data for animals exposed at 120 dB SPL. Each point represents the mean (±S.E.M.). Group sizes are indicated in the graphs. Asterisks indicate points where differences between exposed and control animals were statistically significant (p<0.05).

Mentions: ASR enhancements of the type shown in Fig. 3 were characteristic of most animals exposed at 115 dB SPL and some animals exposed at 110 dB SPL (Fig. 4, top and middle rows), although the precise details varied somewhat in the absolute amplitudes of startle and in the time course of the changes. When the data were averaged across animals on days 7–9 post-exposure, those exposed at 110 showed a trend suggestive of startle enhancements at high startle stimulus levels (≥105 dB SPL) (F3,72 = 6.21, P = 0.01), but the enhancement was significant only at a startle stimulus level of 110 dB SPL (T9 = 1.83, P = 0.05) (Fig. 4B). However, in the animals exposed at 115 dB SPL, the increases in ASR amplitude were highly significant at all stimulus levels from 105–120 dB SPL (Fig. 4D) (F3,80 = 38.57, P<0.0001) and followed an initial period when startle responses were decreased below control levels (Fig. 4C). Post hoc t tests yielded P values no higher than 0.01 ( = 2.55, P<0.01 at 105 dB SPL, T9 = 2.63, P<0.01 at 110 dB SPL, T9 = 3.38, P<0.005 at 115 dB SPL and T9 = 4.83, P<0.001 at 120 dB SPL).


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)

Effects of exposure level on ASR growth curves for early (1–2 days) and late (7–9 days) post-exposure time frames.A–B. Data for animals exposed at 110 dB SPL. C–D. Data for animals exposed at 115 dB SPL. E–F. Data for animals exposed at 120 dB SPL. Each point represents the mean (±S.E.M.). Group sizes are indicated in the graphs. Asterisks indicate points where differences between exposed and control animals were statistically significant (p<0.05).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0111747-g004: Effects of exposure level on ASR growth curves for early (1–2 days) and late (7–9 days) post-exposure time frames.A–B. Data for animals exposed at 110 dB SPL. C–D. Data for animals exposed at 115 dB SPL. E–F. Data for animals exposed at 120 dB SPL. Each point represents the mean (±S.E.M.). Group sizes are indicated in the graphs. Asterisks indicate points where differences between exposed and control animals were statistically significant (p<0.05).
Mentions: ASR enhancements of the type shown in Fig. 3 were characteristic of most animals exposed at 115 dB SPL and some animals exposed at 110 dB SPL (Fig. 4, top and middle rows), although the precise details varied somewhat in the absolute amplitudes of startle and in the time course of the changes. When the data were averaged across animals on days 7–9 post-exposure, those exposed at 110 showed a trend suggestive of startle enhancements at high startle stimulus levels (≥105 dB SPL) (F3,72 = 6.21, P = 0.01), but the enhancement was significant only at a startle stimulus level of 110 dB SPL (T9 = 1.83, P = 0.05) (Fig. 4B). However, in the animals exposed at 115 dB SPL, the increases in ASR amplitude were highly significant at all stimulus levels from 105–120 dB SPL (Fig. 4D) (F3,80 = 38.57, P<0.0001) and followed an initial period when startle responses were decreased below control levels (Fig. 4C). Post hoc t tests yielded P values no higher than 0.01 ( = 2.55, P<0.01 at 105 dB SPL, T9 = 2.63, P<0.01 at 110 dB SPL, T9 = 3.38, P<0.005 at 115 dB SPL and T9 = 4.83, P<0.001 at 120 dB SPL).

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