Protection of auditory function against noise trauma with local caroverine administration in guinea pigs.

Glutamate is the most likely neurotransmitter at the synapse between the inner hair cell and its afferent neuron in the peripheral auditory system. Intense noise exposure may result in excessive glutamate release, binding to the post-synaptic receptors and leading to neuronal degeneration and hearing impairment. The present study investigated the protective effect of caroverine, an antagonist of two glutamate receptors, N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, on noise-induced hearing loss. Two different doses of caroverine were applied onto the round window membrane with gelfoam, followed by one-third-octave band noise centered at 6.3 kHz (110 dB SPL) for 1 h. Auditory brainstem responses were measured at regular time intervals afterwards. Caroverine was found to offer significant protection of the cochlear function against noise-induced hearing loss.