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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

Representation of control and exposed animal weights, by group, from the beginning to the end of the ASR testing period.A. Weight averages on the first day of ASR testing, which is also the first day post-exposure. B. Weight averages on the last day of ASR testing. C. Weight averages over time through the entire ASR testing period. None of these measurements showed significant differences between exposed and control animals. (All P values >0.05, see text for exact values).
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pone-0111747-g005: Representation of control and exposed animal weights, by group, from the beginning to the end of the ASR testing period.A. Weight averages on the first day of ASR testing, which is also the first day post-exposure. B. Weight averages on the last day of ASR testing. C. Weight averages over time through the entire ASR testing period. None of these measurements showed significant differences between exposed and control animals. (All P values >0.05, see text for exact values).

Mentions: An altogether different pattern of change was observed in animals exposed at 120 dB SPL. In that group, both startle responses and the baseline level of activity below the startle threshold were below those of controls; moreover, the initial weakening of ASR amplitude observed above startle threshold on the first and second day after exposure (Fig. 4E) persisted and became even more pronounced when the same measures were performed 7–9 days after exposure (Fig. 4F). The decreases in ASR amplitude in this group of exposed animals were pronounced when tested by two-way ANOVA (F12,364 = 45.66, P<0.001), with significant differences found at all startle stimulus levels from 70 to 110 dB SPL (P values for points represented by asterisks in Fig. 4F ranged from 0.000007 at 93 dB SPL to 0.02 at 110 dB SPL). Thus, our results show that the effect of exposure on ASR growth curves is dependent not only on the level of the exposure but also on the intensity of the startle-eliciting stimulus and the time after exposure when the measures are performed. None of the changes in ASR amplitude could be attributed to difference in weight of the animals. As shown in Fig. 5, there were no significant differences between mean weights in exposed and control animals at the beginning (T4 = 1.05, P = 0.35 for the 110 dB SPL group, T5 = 1.81, P = 0.13 for the 115 dB SPL group, and T6 = 0.99, P = 0.36 for the 120 dB SPL group) and end (T4 = 1.02, P = 0.37 for the 110 dB SPL group, T5 = 1.13, P = 0.31 for the 115 dB SPL group, and T6 = 0.33, P = 0.75 for the 120 dB SPL group) of the ASR testing periods (Fig. 5A–B). Moreover, there was no significant difference between mean weights in exposed and control animals when averaged over time through the period of ASR testing (T4 = 0.85, P = 0.44 for the 110 dB SPL group, T5 = 1.17, P = 0.29 for the 115 dB SPL group, and T6 = 0.99, P = 0.36 for the 120 dB SPL group) (Fig. 5C).


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)

Representation of control and exposed animal weights, by group, from the beginning to the end of the ASR testing period.A. Weight averages on the first day of ASR testing, which is also the first day post-exposure. B. Weight averages on the last day of ASR testing. C. Weight averages over time through the entire ASR testing period. None of these measurements showed significant differences between exposed and control animals. (All P values >0.05, see text for exact values).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0111747-g005: Representation of control and exposed animal weights, by group, from the beginning to the end of the ASR testing period.A. Weight averages on the first day of ASR testing, which is also the first day post-exposure. B. Weight averages on the last day of ASR testing. C. Weight averages over time through the entire ASR testing period. None of these measurements showed significant differences between exposed and control animals. (All P values >0.05, see text for exact values).
Mentions: An altogether different pattern of change was observed in animals exposed at 120 dB SPL. In that group, both startle responses and the baseline level of activity below the startle threshold were below those of controls; moreover, the initial weakening of ASR amplitude observed above startle threshold on the first and second day after exposure (Fig. 4E) persisted and became even more pronounced when the same measures were performed 7–9 days after exposure (Fig. 4F). The decreases in ASR amplitude in this group of exposed animals were pronounced when tested by two-way ANOVA (F12,364 = 45.66, P<0.001), with significant differences found at all startle stimulus levels from 70 to 110 dB SPL (P values for points represented by asterisks in Fig. 4F ranged from 0.000007 at 93 dB SPL to 0.02 at 110 dB SPL). Thus, our results show that the effect of exposure on ASR growth curves is dependent not only on the level of the exposure but also on the intensity of the startle-eliciting stimulus and the time after exposure when the measures are performed. None of the changes in ASR amplitude could be attributed to difference in weight of the animals. As shown in Fig. 5, there were no significant differences between mean weights in exposed and control animals at the beginning (T4 = 1.05, P = 0.35 for the 110 dB SPL group, T5 = 1.81, P = 0.13 for the 115 dB SPL group, and T6 = 0.99, P = 0.36 for the 120 dB SPL group) and end (T4 = 1.02, P = 0.37 for the 110 dB SPL group, T5 = 1.13, P = 0.31 for the 115 dB SPL group, and T6 = 0.33, P = 0.75 for the 120 dB SPL group) of the ASR testing periods (Fig. 5A–B). Moreover, there was no significant difference between mean weights in exposed and control animals when averaged over time through the period of ASR testing (T4 = 0.85, P = 0.44 for the 110 dB SPL group, T5 = 1.17, P = 0.29 for the 115 dB SPL group, and T6 = 0.99, P = 0.36 for the 120 dB SPL group) (Fig. 5C).

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