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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 context on startle amplitudes.A. Data for control animals. B. Data for exposed animals. In each graph, data from animals tested in the context of startle stimuli alone (context 1) are compared with data from animals tested using startle stimuli alone presented randomly in the context of the gap detection test (context 2). Note that in control animals, ASR amplitudes were generally weaker in context 2 than in context 1, but for the most part, the decreases were not significant. In exposed animals, ASRs measured in context 2 were consistently weaker than those measured in context 1, indicating an effect of context on startle suppression. C. Comparison of startle amplitudes of exposed animals tested in contexts 1 and 2 with startle amplitudes of controls tested in context 1, showing the loss of hyperresponsiveness when animals were tested in context 2. *: P<0.05 for comparison between exposed animals tested in the two contexts. Dot represents P<0.05 for comparison between exposed and controls tested in context 1.
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pone-0111747-g007: Effect of context on startle amplitudes.A. Data for control animals. B. Data for exposed animals. In each graph, data from animals tested in the context of startle stimuli alone (context 1) are compared with data from animals tested using startle stimuli alone presented randomly in the context of the gap detection test (context 2). Note that in control animals, ASR amplitudes were generally weaker in context 2 than in context 1, but for the most part, the decreases were not significant. In exposed animals, ASRs measured in context 2 were consistently weaker than those measured in context 1, indicating an effect of context on startle suppression. C. Comparison of startle amplitudes of exposed animals tested in contexts 1 and 2 with startle amplitudes of controls tested in context 1, showing the loss of hyperresponsiveness when animals were tested in context 2. *: P<0.05 for comparison between exposed animals tested in the two contexts. Dot represents P<0.05 for comparison between exposed and controls tested in context 1.

Mentions: The results of this experiment are shown in Fig. 7. Control animals showed context-dependent differences in startle amplitudes at the low and high startle stimulus levels (Fig. 7A). The exposed animals showed even more pronounced context-dependent differences, startle amplitudes being consistently lower in the context of the gap suppression test (context 2) than in the context of the startle growth curve test (context 1) (Fig. 7B); also, exposed animals showed a trend towards increasingly larger context-dependent differences with increases in stimulus level. Significantly weaker startle amplitudes were found in exposed animals at three of the four startle stimulus levels in context 2 than in context 1 (F2,16 = 5.34, P = 0.02 at 105 dB SPL, F2,16 = 10.44, P = 0.013 at 110 dB SPL and F = 13.03, P = 0.0004 at 115 dB SPL). Only in the condition where the startle stimulus level was 100 dB SPL were ASRs in exposed animals similar in the two contexts. Moreover, relative to controls, the significance of the enhancements of startle observed in exposed animals in context 1 (F1,64 = 27.02, P<0.0001), was not observed in context 2 (Fig. 7C). In fact, the ASR obtained in context 2 were consistently lower than those obtained from control animals tested in context 1 (F1,64 = 4.74, P<0.05). This indicates that the more complex stimulus battery of the gap detection test was suppressive of the ASR in both groups, although the suppression was more consistent and level dependent than in controls.


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 context on startle amplitudes.A. Data for control animals. B. Data for exposed animals. In each graph, data from animals tested in the context of startle stimuli alone (context 1) are compared with data from animals tested using startle stimuli alone presented randomly in the context of the gap detection test (context 2). Note that in control animals, ASR amplitudes were generally weaker in context 2 than in context 1, but for the most part, the decreases were not significant. In exposed animals, ASRs measured in context 2 were consistently weaker than those measured in context 1, indicating an effect of context on startle suppression. C. Comparison of startle amplitudes of exposed animals tested in contexts 1 and 2 with startle amplitudes of controls tested in context 1, showing the loss of hyperresponsiveness when animals were tested in context 2. *: P<0.05 for comparison between exposed animals tested in the two contexts. Dot represents P<0.05 for comparison between exposed and controls tested in context 1.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0111747-g007: Effect of context on startle amplitudes.A. Data for control animals. B. Data for exposed animals. In each graph, data from animals tested in the context of startle stimuli alone (context 1) are compared with data from animals tested using startle stimuli alone presented randomly in the context of the gap detection test (context 2). Note that in control animals, ASR amplitudes were generally weaker in context 2 than in context 1, but for the most part, the decreases were not significant. In exposed animals, ASRs measured in context 2 were consistently weaker than those measured in context 1, indicating an effect of context on startle suppression. C. Comparison of startle amplitudes of exposed animals tested in contexts 1 and 2 with startle amplitudes of controls tested in context 1, showing the loss of hyperresponsiveness when animals were tested in context 2. *: P<0.05 for comparison between exposed animals tested in the two contexts. Dot represents P<0.05 for comparison between exposed and controls tested in context 1.
Mentions: The results of this experiment are shown in Fig. 7. Control animals showed context-dependent differences in startle amplitudes at the low and high startle stimulus levels (Fig. 7A). The exposed animals showed even more pronounced context-dependent differences, startle amplitudes being consistently lower in the context of the gap suppression test (context 2) than in the context of the startle growth curve test (context 1) (Fig. 7B); also, exposed animals showed a trend towards increasingly larger context-dependent differences with increases in stimulus level. Significantly weaker startle amplitudes were found in exposed animals at three of the four startle stimulus levels in context 2 than in context 1 (F2,16 = 5.34, P = 0.02 at 105 dB SPL, F2,16 = 10.44, P = 0.013 at 110 dB SPL and F = 13.03, P = 0.0004 at 115 dB SPL). Only in the condition where the startle stimulus level was 100 dB SPL were ASRs in exposed animals similar in the two contexts. Moreover, relative to controls, the significance of the enhancements of startle observed in exposed animals in context 1 (F1,64 = 27.02, P<0.0001), was not observed in context 2 (Fig. 7C). In fact, the ASR obtained in context 2 were consistently lower than those obtained from control animals tested in context 1 (F1,64 = 4.74, P<0.05). This indicates that the more complex stimulus battery of the gap detection test was suppressive of the ASR in both groups, although the suppression was more consistent and level dependent than in controls.

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