Does 5, 7-Dihydroxytryptamine injection into nucleus accumbens cause hyperacusis?

Molecular and behavioral effects of Acamprosate in male rats with sodium salicylate-induced tinnitus

BACKGROUND

Imbalance in inhibitory and excitatory neurotransmitters have been reported in tinnitus. Acamprosate modulates the excitatory and inhibitory neurotransmission in the nucleus accumbens (NAc). This study aims to assess the effect of Acamprosate on tinnitus, anxiety, depression, and molecular changes in nucleus accumbens (NAc), in Sodium-Salisylate (S-salicylate) model of tinnitus.

METHODS

Forty-four adult male wistar rats were used in this study. The study included Control, Saline, and S-salicylate groups during the first week, which then subdivided into five groups as Control, Saline, S-salicylate, Acamprosate, and S-salicylate+Acamprosate. Gap-in Noise (GIN) and pre-pulse inhibition (PPI) were used to assessment of tinnitus at baseline, day7 and day14. Anxiety and depression were evaluated on day 14, by elevated plus maze (EPM), open field (OF), and tail suspension (TST) tests. The protein expression of GABAAR-δ, NR1 and NR2B in NAc were also measured using western blot technique.

RESULTS

After seven days GIN reduced in S-salicylate compare to Control and Saline groups (P < 0.5), while PPI unchanged. After 14 days, GIN reduced in S-salicylate and S-salicylate+Acamprosate groups compare to Control; Saline; and Acamprosate groups (P < 0.5). Additionally, GIN was higher in S-salicylate+Acamprosate compare to S-salicylate group (P < 0.5). PPI was not changed after 14 days. Open arm time in EPM test was decreased in S-salicylate and S-salicylate+Acamprosate groups compare to Control; Saline; and Acamprosate groups (P < 0.5). Central Zone time in OF test was reduced in S-salicylate group compare to Control, Saline, Acamprosate, and S-salicylate+Acamprosate groups (P < 0.5). Immobility Time in TST was increased in S-salicylate group compare to Control, Saline, Acamprosate, and S-salicylate+Acamprosate groups (P < 0.5). GABAAR-δ was decreased in S-salicylate groups compare to Control, Saline, Acamprosate; and S-salicylate+Acamprosate groups (P < 0.5). NR1 and NR2B in NAc were increased in S-salicylate group compare to Control, Saline, Acamprosate, and S-salicylate+Acamprosate groups (P < 0.5).

CONCLUSION

S-salicylate can induce tinnitus-like behaviors in rat. Furthermore, S-salicylate induced depression/anxiety like behaviors, and changed the expression of GABAR and NMDAR subunits in NAc. Acamprosate partially reversed these changes. In conclusion, NAc may be involved in the pathophysiologic mechanisms of tinnitus.

Hyperexcitability of the Nucleus Accumbens Is Involved in Noise-Induced Hyperacusis

Reduced tolerance to sound stimuli (hyperacusis) is commonly seen in tinnitus patients. Dysfunction of limbic systems, such as the nucleus accumbens (NAc), may be involved in emotional reactions to the sound stimuli in tinnitus patients. To study the functional changes in the NAc in hyperacusis, we have examined the neural activity changes of the NAc using c-Fos staining in an animal model of hyperacusis. The c-Fos staining was also examined in the medial geniculate nucleus (MGN), a central auditory pathway which has neural projections to the NAc. Postnatal rats (14 days) were exposed to loud noise (115 dB SPL, 4 hours for two consecutive days) to induce hyperacusis (n = 4). Rats without noise exposure were used as the controls (n = 4). After P35, rats in both groups were put in a behavioral training for sound detection. After they were trained to detect sound stimuli, their reaction time to noise bursts centered at 2 kHz (40-110 dB SPL) was measured. Rats in the noise group showed a significantly shorter reaction time than those in the control group to the noise bursts at high intensities, suggesting the noise exposure induced hyperacusis behavior. The c-Fos expressions in the NAc and the MGNs of the noise group were significantly higher than those of the control group. Our results suggested that early-age noise exposure caused hyperactivity in the NAc and the MGNs which may induce the loudness increase in these rats.

The effect of insular cortex lesion on hyperacusis-like behavior in rats

Background and objectives: Hyperacusis is hypersensitivity and extreme response to the intensity of sound that is tolerable in normal subjects. The mechanisms underlying hyperacusis has not been well understood, specially the role of insular cortex. The aim of this study is to investigate the role of insular cortex in hyperacusis like behavior. Material and methods: The number of 33 male wistar rats weighting 170-250 gr were allocated randomly in three groups; control, sham, and insular lesion. Auditory startle responses (ASR) to different intensities of stimuli (70, 80, 90, 100, and110 dB without background noise as well as 110 dB in the presence of 70, 80 dB background noise) were measured before and up to four weeks after intervention. Results: Data analyses showed an increase in ASR to 100 dB stimulus without background noise one week after insular lesion, and increased responses to other intensities two weeks after lesion. Furthermore, there was a decrease in ASR to 110 dB stimulus with 80 dB background noise two weeks after insular lesion. However, no significant difference was observed in 70 dB background noise. The changes in ASR lasts at least four weeks.Conclusion: The findings indicated that there was an increase in ASR in the absence of background noise following cortical excititoxic lesion limited to insular cortex, while there was a decrease in responses in the presence of background noise which suggests possible increased sensitivity to sound loudness as a hyperacusis-like phenomenon. The study showed a significant relationship between insular cortex lesion and ASR in rats.

Identifying and prioritising unanswered research questions for people with hyperacusis: James Lind Alliance Hyperacusis Priority Setting Partnership

OBJECTIVE

To determine research priorities in hyperacusis that key stakeholders agree are the most important.

DESIGN/SETTING

A priority setting partnership using two international surveys, and a UK prioritisation workshop, adhering to the six-staged methodology outlined by the James Lind Alliance.

PARTICIPANTS

People with lived experience of hyperacusis, parents/carers, family and friends, educational professionals and healthcare professionals who support and/or treat adults and children who experience hyperacusis, including but not limited to surgeons, audiologists, psychologists and hearing therapists.

METHODS

The priority setting partnership was conducted from August 2017 to July 2018. An international identification survey asked respondents to submit any questions/uncertainties about hyperacusis. Uncertainties were categorised, refined and rephrased into representative indicative questions using thematic analysis techniques. These questions were verified as 'unanswered' through searches of current evidence. A second international survey asked respondents to vote for their top 10 priority questions. A shortlist of questions that represented votes from all stakeholder groups was prioritised into a top 10 at the final prioritisation workshop (UK).

RESULTS

In the identification survey, 312 respondents submitted 2730 uncertainties. Of those uncertainties, 593 were removed as out of scope, and the remaining were refined into 85 indicative questions. None of the indicative questions had already been answered in research. The second survey collected votes from 327 respondents, which resulted in a shortlist of 28 representative questions for the final workshop. Consensus was reached on the top 10 priorities for future research, including identifying causes and underlying mechanisms, effective management and training for healthcare professionals.

CONCLUSIONS

These priorities were identified and shaped by people with lived experience, parents/carers and healthcare professionals, and as such are an essential resource for directing future research in hyperacusis. Researchers and funders should focus on addressing these priorities.