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. 2010 Oct;120(10):2047-53.
doi: 10.1002/lary.21106.

Hearing Loss Alters Quantal Release at Cochlear Nucleus Stellate Cells

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Free PMC article

Hearing Loss Alters Quantal Release at Cochlear Nucleus Stellate Cells

Alexander W Rich et al. Laryngoscope. .
Free PMC article

Abstract

Objectives/hypothesis: Auditory nerve synapses in ventral cochlear nucleus end on two principal cell types, bushy and stellate cells. Although the effects of hearing loss on bushy cells have been well studied, little is known about the effects of hearing loss on synaptic input to the stellate cells. Based on prior observations in bushy cells, we hypothesized that noise-induced hearing loss (NIHL) would decrease quantal release onto stellate cells.

Study design: Prospective, randomized animal study.

Methods: CBA/CaJ mice were exposed for 2 hours to 98 dB sound pressure level (SPL) 8- to 16-kHz noise to produce a temporary threshold shift (TTS) or 114 dB SPL to produce a permanent threshold shift (PTS). Spontaneous miniature excitatory postsynaptic currents (mEPSCs) were then measured in stellate cells in brain slices of the cochlear nucleus.

Results: Click auditory brainstem evoked response thresholds were elevated by 35 dB in both TTS and PTS mice. Spontaneous mEPSC frequency was found to be five-fold higher than normal in stellate cells of TTS mice and three-fold higher in PTS mice. The mEPSC amplitude was also larger in PTS mice. The mEPSC time course was not different between experimental and control groups.

Conclusions: The dramatic increase in mEPSC frequency after NIHL was not expected. The increase in mEPSC amplitude in PTS mice suggests a postsynaptic remodeling process. Both of these effects could contribute to increased spontaneous firing in the cochlear nucleus in the absence of sound. Our results also suggest that hearing loss may have different effects at auditory nerve synapses on bushy and stellate cells in the VCN.

Conflict of interest statement

Conflict of Interest: The authors have no conflict of interest to disclose or declare with regards to this work.

Figures

FIG. 1
FIG. 1
Click ABR thresholds were significantly increased in TTS and PTS mice when compared to the control group (p<0.0001), but recovered to control group thresholds in the TTS group 10–14 days after noise exposure (p=0.0988).
FIG. 2
FIG. 2
Spontaneous mEPSC event frequency in anteroventral cochlear nucleus (AVCN) stellate cells was significantly increased in TTS and PTS animals. A: representative mESPC traces from AVCN stellate cells from each group. Cells were held near their resting membrane potentials at −70 mV. B: Spontaneous mEPSC frequency was significantly higher in TTS and PTS mice than in the control group.
FIG. 3
FIG. 3
Spontaneous mEPSC amplitudes were significantly increased in PTS mice vs. control (p=0.037). A: Representative distribution patterns of mEPSC amplitudes in individual cells from each group. B: Spontaneous mEPSC amplitudes were significantly increased in PTS mice vs control animals, but was not significantly different from the TTS group (p=0.10)
FIG. 4
FIG. 4
No significant difference in mEPSC time courses was noted between any of the experiment groups. A: No correlation in 10–90% rise time was seen between control, TTS, and PTS groups. B: No significant difference in mEPSC time constants was noted between any of the experiment groups.

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