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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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Dependence of enhancement of startle on threshold.The histogram depicts maximal ASR amplitudes with respect to thresholds for exposed animals. The dashed red line represents the mean maximal startle amplitude of control animals (thresholds for these animals ranged from 18 to 33 dB SPL). A–E: Representative ASR growth curves of exposed animals with different thresholds. When thresholds were less than 50 dB, startle amplitudes were similar to those of controls. For animals with thresholds of 50–70 dB, enhancements of startle were clearly apparent, but for animals with thresholds above 70 dB SPL, ASR amplitudes were in most cases reduced below control levels.
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pone-0111747-g006: Dependence of enhancement of startle on threshold.The histogram depicts maximal ASR amplitudes with respect to thresholds for exposed animals. The dashed red line represents the mean maximal startle amplitude of control animals (thresholds for these animals ranged from 18 to 33 dB SPL). A–E: Representative ASR growth curves of exposed animals with different thresholds. When thresholds were less than 50 dB, startle amplitudes were similar to those of controls. For animals with thresholds of 50–70 dB, enhancements of startle were clearly apparent, but for animals with thresholds above 70 dB SPL, ASR amplitudes were in most cases reduced below control levels.

Mentions: The data in Fig. 4 suggests a link between the magnitude of change in the ASR and exposure level, but they obscure the more important relationship of how the change in ASR relates to the post-exposure thresholds. To examine this relationship, we plotted the maximal ASR amplitude as a function of average threshold, irrespective of the level of sound to which the animals were exposed. The results in Fig. 6 show that the enhancement of startle was highly dependent on the loss in sound sensitivity, being limited to a narrow range of thresholds between 50 and 70 dB SPL. Below this range (30–50 dB SPL), startle amplitudes were comparable to control levels, but above this range (80–100 dB SPL), ASR amplitudes declined toward sub-control values with further increases in threshold. Thus, moderate threshold elevation restricted to a narrow range resulted in ASR enhancements, whereas severe threshold elevation resulted in a weakening of ASR.


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)

Dependence of enhancement of startle on threshold.The histogram depicts maximal ASR amplitudes with respect to thresholds for exposed animals. The dashed red line represents the mean maximal startle amplitude of control animals (thresholds for these animals ranged from 18 to 33 dB SPL). A–E: Representative ASR growth curves of exposed animals with different thresholds. When thresholds were less than 50 dB, startle amplitudes were similar to those of controls. For animals with thresholds of 50–70 dB, enhancements of startle were clearly apparent, but for animals with thresholds above 70 dB SPL, ASR amplitudes were in most cases reduced below control levels.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0111747-g006: Dependence of enhancement of startle on threshold.The histogram depicts maximal ASR amplitudes with respect to thresholds for exposed animals. The dashed red line represents the mean maximal startle amplitude of control animals (thresholds for these animals ranged from 18 to 33 dB SPL). A–E: Representative ASR growth curves of exposed animals with different thresholds. When thresholds were less than 50 dB, startle amplitudes were similar to those of controls. For animals with thresholds of 50–70 dB, enhancements of startle were clearly apparent, but for animals with thresholds above 70 dB SPL, ASR amplitudes were in most cases reduced below control levels.
Mentions: The data in Fig. 4 suggests a link between the magnitude of change in the ASR and exposure level, but they obscure the more important relationship of how the change in ASR relates to the post-exposure thresholds. To examine this relationship, we plotted the maximal ASR amplitude as a function of average threshold, irrespective of the level of sound to which the animals were exposed. The results in Fig. 6 show that the enhancement of startle was highly dependent on the loss in sound sensitivity, being limited to a narrow range of thresholds between 50 and 70 dB SPL. Below this range (30–50 dB SPL), startle amplitudes were comparable to control levels, but above this range (80–100 dB SPL), ASR amplitudes declined toward sub-control values with further increases in threshold. Thus, moderate threshold elevation restricted to a narrow range resulted in ASR enhancements, whereas severe threshold elevation resulted in a weakening of ASR.

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