Objective: To investigate the changes of the potentials and structure of the guinea pig cochlear during whole cochlear perfusion with glutamate.
Methods: Cochlear microphonics (CM), compound action potential (CAP), distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) were measured to indicate the cochlear functional properties during whole cochlear perfusion. The morphology of the cochlear was monitored by transmission electron microscopy.
Results: There were no significant DPOAE changes before and after glutamate perfusion. CM I/O function maintained a nonlinear characteristic during infusion. After glutamate perfusion, ABR latencies were delayed. There was significant difference in CAP threshold before and after glutamate perfusion. The average CAP threshold was elevated 35 dB. The OHCs appeared normal, but IHCs and afferent dendrites showed cytoplasmic blebs after glutamate infusion.
Conclusions: Glutamate is thought to be a primary amino acid neurotransmitter at the synapses formed by cochlear hair cells and spiral ganglion neurons. However, the excessive glutamate is neurotoxic for cells, and it can destroy the IHCs and spiral ganglion neurons. The present method can also be built up as an animal model of auditory neuropathy.
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