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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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Related in: MedlinePlus

Comparison of the ASR growth curves from control (n = 5) and exposed animals (n = 6) at each of the 7 post-exposure times indicated at the top of each graph (panels A–G).The data shows decrements in ASR in exposed animals during the first two days post-exposure, but by the fourth day, there is a suggestion of enhanced ASR at the highest startle stimulus levels. This enhancement was better established by the 8th day at all stimulus levels above 100 dB SPL and continued through the remainder of the 2 weeks of measurements, although the degree of enhancement varied over time.
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pone-0111747-g003: Comparison of the ASR growth curves from control (n = 5) and exposed animals (n = 6) at each of the 7 post-exposure times indicated at the top of each graph (panels A–G).The data shows decrements in ASR in exposed animals during the first two days post-exposure, but by the fourth day, there is a suggestion of enhanced ASR at the highest startle stimulus levels. This enhancement was better established by the 8th day at all stimulus levels above 100 dB SPL and continued through the remainder of the 2 weeks of measurements, although the degree of enhancement varied over time.

Mentions: Changes in the amplitudes of the ASR displayed considerable plasticity and rebound following tone exposure. The period of most dynamic change was the first few days following exposure, but additional quantitative changes continued through the remainder of the 3 or more weeks of measurements. The mean ASR growth curves for animals exposed at 115 dB SPL are shown in Fig. 3. Here, startle amplitudes can be seen to be either similar to or slightly diminished below control levels during the first 2 days following exposure (Fig. 3A–B). However, between 4 and 8 days post-exposure, a trend towards enhanced startle amplitudes were clearly evident at high levels of stimulation (Fig. 3C–D), and these enhancements continued to be apparent, albeit with some fluctuation, throughout the period of testing (Fig. 3E–G). The startle enhancements observed 1 week following exposure are similar to those described in our previous paper, which was based on a different set of animals [18], but the time series of Fig. 3 shows for the first time that the enhancement was a secondary effect that took several days to develop, suggesting the involvement of plastic mechanisms that are triggered by the initial insult.


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)

Comparison of the ASR growth curves from control (n = 5) and exposed animals (n = 6) at each of the 7 post-exposure times indicated at the top of each graph (panels A–G).The data shows decrements in ASR in exposed animals during the first two days post-exposure, but by the fourth day, there is a suggestion of enhanced ASR at the highest startle stimulus levels. This enhancement was better established by the 8th day at all stimulus levels above 100 dB SPL and continued through the remainder of the 2 weeks of measurements, although the degree of enhancement varied over time.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0111747-g003: Comparison of the ASR growth curves from control (n = 5) and exposed animals (n = 6) at each of the 7 post-exposure times indicated at the top of each graph (panels A–G).The data shows decrements in ASR in exposed animals during the first two days post-exposure, but by the fourth day, there is a suggestion of enhanced ASR at the highest startle stimulus levels. This enhancement was better established by the 8th day at all stimulus levels above 100 dB SPL and continued through the remainder of the 2 weeks of measurements, although the degree of enhancement varied over time.
Mentions: Changes in the amplitudes of the ASR displayed considerable plasticity and rebound following tone exposure. The period of most dynamic change was the first few days following exposure, but additional quantitative changes continued through the remainder of the 3 or more weeks of measurements. The mean ASR growth curves for animals exposed at 115 dB SPL are shown in Fig. 3. Here, startle amplitudes can be seen to be either similar to or slightly diminished below control levels during the first 2 days following exposure (Fig. 3A–B). However, between 4 and 8 days post-exposure, a trend towards enhanced startle amplitudes were clearly evident at high levels of stimulation (Fig. 3C–D), and these enhancements continued to be apparent, albeit with some fluctuation, throughout the period of testing (Fig. 3E–G). The startle enhancements observed 1 week following exposure are similar to those described in our previous paper, which was based on a different set of animals [18], but the time series of Fig. 3 shows for the first time that the enhancement was a secondary effect that took several days to develop, suggesting the involvement of plastic mechanisms that are triggered by the initial insult.

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