Hearing loss alters quantal release at cochlear nucleus stellate cells.
OBJECTIVE
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.


METHODS
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.
Rich
Alexander W
AW
Department of Otolaryngology/Head and Neck Surgery, University of North Carolina, Chapel Hill, North Carolina 27599-7070, USA.
Xie
Ruili
R
Manis
Paul B
PB
D000704:Analysis of Variance; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D017626:Cochlear Nucleus / Q000166:cytology*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology*; D051379:Mice; D011446:Prospective Studies; D011897:Random Allocation
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