ACOUSTIC STARTLE RESPONSE AFFECTED BY AGING AND CHOLINERGIC NEUROTRANSMITTERS

The acoustic startle response has been used to evaluate tinnitus and hyperacusis in animal models. Gap induced prepulse in- hibition of the acoustic startle reflex （gap-PPI） is affected by tinnitus and loudness changes. Since tinnitus and reduced sound tolerance are commonly seen in elderly, we measured gap-PPI in Fischer 344 rats, an aging related hearing loss model, at dif- ferent agcs： 3-5 months, 9-12 months, and 15-17 months. The startle response was induced by three different intensity of sound： 105, 95 and 85 dB SPL. Gap-PPI was induced by different duration of silent gaps from 1 to 100 ms. When thc startle was induced by 105 dB SPL sound intensity, the gap-PPI induced by 50 ms silent gap was significantly lower than those in- duced by 25 or 100 ms duration, showing a ＂notch＂ in the gap-PPI function. The ＂notch＂ disappeared with the reduction of startle sound, suggesting the ＂notch＂ may be related with hyper-sensitivity to loud sound. As the intensity of the stimulus de- creased, the appearance of the hyperacusis-like effect decreased more quickly for the youngest group of rats. We also tested scopolamine, a muscarinic acetylcholine receptor antagonist, and mecamylamine, a nicotinic acetylcholine receptor antago- nist, on the effect of gap-PPI. When scopolamine was administered, the results indicated no addition effect on the hyperacu- sis-like phenomenon in the two older groups. Mecamylamine, the nicotinic antagonist also showed effects on the appearance of hyperacusis on rats in different ages. The information derived from the study will be fundamental for the further research in determining the cause and treatment for hyperacusis.     

Dietary LC-PUFA in iron-deficient anaemic pregnant and lactating guinea pigs induce minor defects in the offsprings' auditory brainstem responses

Objectives: We previously demonstrated that a mild pre-natal/early post-natal iron-deficient anaemic (IDA) diet devoid of long-chain polyunsaturated fatty acids (LC-PUFA) affected development, neurophysiology, and cerebral lipid biochemistry of the guinea pigs' progeny. Impacts of dietary LC-PUFA on altered cerebral development resulting from pre-natal IDA are unknown. To address this health issue, impacts of mild gestational IDA in the presence of dietary LC-PUFA on the offsprings' neural maturation were studied in guinea pigs using auditory brainstem responses (ABRs) and assessments of brain fatty acids (FAs).

Methods: Female guinea pigs (n = 10/group) were fed an iron sufficient (IS) or IDA diet (146 and 12.7 mg iron/kg, respectively) with physiological amounts of LC-PUFA, during the gestation and lactation periods. From post-natal day (PNd) 9 onwards, the IS + PUFA diet was given to both groups of weaned offspring. Cerebral tissue and offsprings' ABR were collected on PNd24.

Results: There was no difference in peripheral and brainstem transmission times (BTTs) between IS + PUFA and IDA + PUFA siblings (n = 10/group); the neural synchrony was also similar in both groups. Despite the absence of differences in auditory thresholds, IDA + PUFA siblings demonstrated a sensorineural hearing loss in the extreme range of frequencies (32, 4, and 2 kHz), as well as modified brain FA profiles compared to the IS + PUFA siblings.

Discussion: The present study reveals that siblings born from dams exposed to a moderate IDA diet including balanced physiological LC-PUFA levels during pregnancy and lactation demonstrate minor impairments of ABR compared to the control siblings, particularly on the auditory acuity, but not on neural synchrony, auditory nerve velocity and BTT.     

The correlation between the hyperacusis questionnaire and uncomfortable loudness levels is dependent on emotional exhaustion

Abstract

Objective: To validate the hyperacusis questionnaire (HQ) in different strata of emotional exhaustion (EE). Design: HQ-scores and uncomfortable loudness levels (ULLs) were assessed in 348 individuals (140 men and 208 women) with low, intermediate, and high EE-levels. Results: Four individuals (1.1%) met the critical value for hyperacusis according to the HQ. An exploratory factor analysis extracted three factors from the HQ accounting for 57.6% of the variance. Internal consistency was acceptable for all subscales and for the total score, with Crohnbach's alpha ranging from 0.65 to 0.86. When controlling for hearing loss, significant correlations between the HQ and ULLs were found on both ears in those with intermediate (right: ?0.328; left: ?0.320) and high EE (right: ?0.349; left: ?0.393), but not with low EE (right: ?0.204; left: ?0.196). All correlations were negative, indicating that higher HQ-scores are correlated with lower ULLs. The strongest correlations were found for the social dimension, indicating that social aspects may correspond best to audiological parameters (ULLs) of hyperacusis. Conclusions: The results emphasize the need to take other factors, such as emotional exhaustion (long-term stress), into consideration when assessing hyperacusis with a questionnaire.     

Severity of hyperacusis predicts individual differences in speech perception in Williams Syndrome

Background Williams Syndrome (WS) is a neurodevelopmental disorder of genetic origin, characterised by relative proficiency in language in the face of serious impairment in several other domains. Individuals with WS display an unusual sensitivity to noise, known as hyperacusis. Methods In this study, we examined the extent to which hyperacusis interferes with the perception of speech in children and adults with WS. Participants were required to discriminate words which differed in one consonant of a cluster when these contrasts were embedded in a background of noise. Results Although the introduction of noise interfered with performance on a consonant cluster discrimination task equally in the WS and control groups, the severity of hyperacusis significantly predicted individual variability in speech perception within the WS group. Conclusions These results suggest that alterations in sensitivity to input mediate atypical pathways for language development in WS, where hyperacusis exerts an important influence together with other non‐auditory factors.     

Effect of sound generator on tinnitus and hyperacusis

Objective: Sound generator (SG) plays a role as effective sound therapy of tinnitus retaining therapy (TRT) in patients with severe tinnitus (Category 1) or hyperacusis (Category 3). This study was performed to evaluate the therapeutic effect of SGs.

Methods: A total of 120 tinnitus patients who visited our tinnitus clinic and were treated with SG along with TRT from January 2008 to December 2016 were included. The patients were divided into two groups by tinnitus category; 78 patients of category 1 and 42 patients of category 3. Their medical records including questionnaires regarding tinnitus severity were retrospectively reviewed to evaluate the therapeutic effect of SGs on tinnitus and hyperacusis.

Results: Category 3 patients included more female patients, were younger than category 1 patients (p?=?.001), and were prescribed SG earlier due to their severe symptom of hyperacusis. (p?=?.004) All patients showed significant improvements on all categories of tinnitus visual analogue scale (VAS) scores and tinnitus handicap inventory (THI) scores after six months use of SG (p?Conclusion: SG with TRT seems to be an effective treatment modality for all tinnitus patients, especially those with comorbid hyperacusis.     

Neural changes in the auditory cortex of awake guinea pigs after two tinnitus inducers: salicylate and acoustic trauma

Tinnitus, also called phantom auditory perception, is a major health problem in western countries. As such, a significant amount of effort has been devoted to understanding its mechanisms, including studies in animals wherein a supposed “tinnitus state” can be induced. Here, we studied on the same awake animals the effects of a high-dose of salicylate and of an acoustic trauma both at levels known to induce tinnitus. Recordings of cortical activity (local field potentials) from chronically implanted electrodes in the same animals under each condition allowed direct comparison of the effects of salicylate and trauma (noise trauma was carried out several days after full recovery from salicylate administration). Salicylate induced a systematic and reversible increase in amplitude of cortical responses evoked by tone bursts over a wide range of frequencies and intensities. The effects of noise trauma, though much more variable than those of salicylate, resulted in both increases and decreases in the amplitude of cortical responses. These alterations of cortical response amplitudes likely reflect associated hypoacusis and hyperacusis. The effects of salicylate administration and noise trauma on spontaneous activity were also studied. Fourier analysis did not reveal any increase in power within any given frequency band; rather, both treatments induced a decrease of power spectrum over a relatively broad frequency band (∼10–30 Hz). Entropy rate of spontaneous activity, a measure of complexity (temporal correlations), was found to decrease after salicylate but not after acoustic trauma. The present data on evoked potentials confirm salicylate effects at the cortical level and partially extend such effects to acoustic trauma. While the present study showed that both salicylate and noise trauma induced some changes of spontaneous activity in auditory cortex, none of these changes are interpretable in terms of potential neural correlate of tinnitus.     

Do extant elephants have superior canal dehiscence syndrome?

Conclusion: X-ray CT of an Asian elephant’s skull suggest that elephants do not have a labyrinthine 3^rd mobile window. This excludes the concept that elephants benefit from enhancement of bone conducted vibration by an extra opening of the labyrinth. This finding does not, however, exclude that elephants use bone conducted hearing for seismic detection, nor that other species may use an extra labyrinthine opening for improved detection of seismic signals. Objectives: In man, a pathologic extra opening of the bony labyrinth causes altered hearing with supranormal bone conduction. Theoretically, this variation in auditory performance could be advantageous for detection of seismic waves. Method: The skull of an adult Asian elephant was examined by X-ray computed tomography to investigate whether a natural ‘3^rd mobile window’ mechanism for enhanced sensitivity of body sounds exist in elephants. Results: Although the entire elephant’s skull was otherwise broadly aerated, the labyrinth areas were surrounded by dense bone.     

Age-Related Hearing Loss in C57BL/6J Mice has both Frequency-Specific and Non-Frequency-Specific Components that Produce a Hyperacusis-Like Exaggeration of the Acoustic Startle Reflex

Auditory brainstem-evoked response (ABR) thresholds were obtained in a longitudinal study of C57BL/6J mice between 10 and 53 weeks old, with repeated testing every 2 weeks. On alternate weeks, acoustic startle reflex (ASR) amplitudes were measured, elicited by tone pips with stimulus frequencies of 3, 6, 12, and 24 kHz, and intensities from subthreshold up to 110 dB sound pressure level. The increase in ABR thresholds for 3 and 6 kHz test stimuli followed a linear time course with increasing age from 10 to 53 weeks, with a slope of about 0.7 dB/week, and for 48 kHz a second linear time course, but beginning at 10 weeks with a slope of about 2.3 dB/week. ABR thresholds for 12, 24, and 32 kHz increased after one linear segment with a 0.7 dB slope, then after a variable delay related to the test frequency, shifted to a second segment having slopes of 3–5 dB/week. Hearing loss initially reduced the ASR for all eliciting stimuli, but at about 6 months of age, the response elicited by intense 3 and 6 kHz stimuli began to increase to reach values about three times above normal, and previously subthreshold stimuli came to elicit vigorous responses seen at first only for the intense stimuli. This hyperacusis-like effect appeared in all mice but was especially pronounced in mice with more serious hearing loss. These ABR data, together with a review of histopathological data in the C57BL/6 literature, suggest that the non-frequency-specific slow time course of hearing loss results from pathology in the lateral wall of the cochlea, whereas the stimulus-specific hearing loss with a rapid time course results from hair cell loss. Delayed exaggeration of the ASR with hearing loss reveals a deficit in centrifugal inhibitory control over the afferent reflex pathways after central neural reorganization, suggesting that this mouse may provide a useful model of age-related tinnitus and associated hyperacusis.