Glutamate neurotoxicity in the developing rat cochlea: physiological and morphological approaches

The neurotoxic effects of exogenous glutamate were studied in the rat cochlea. Glutamate-treated rats (4 g/kg/day i.p., postnatal days 2-9) exhibited electrophysiologically-measured elevations in high frequency thresholds usually associated with hair cell loss in the basal region of the cochlea. While surface preparations of the organ of Corti revealed no loss of hair cells, there was a dramatic and selective reduction of neurons in the basal, high frequency-related portion of the spiral ganglion. This sensitivity of developing spiral ganglion cells to the neurotoxicity of glutamate is consistent with the hypothesis that glutamate or a structurally related substance is a neurotransmitter at afferent synapses of cochlear hair cells.