Changes in neuronal structure after auditory deprivation in rat cochlea.

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Rats were deprivated the auditory function by administrating the Kanamycin for two weeks, which started immediately after the birth. Auditory brainstem response evaluated after 2 weeks of birth, showed no response. i) Immunohistochemical study confirmed no hair cells in the cochlea., decrease of neuronal cells in the inner ear and cochlear nucleus. ii) Expression of glutamate receptors were examined by both immunohistochemical study and by quantitative PCR technique. In control animals, glutamate receptors of Glu-R 2-5 (Kainic acid receptors) and NR 1 and 2 (NMDA receptors) were found in spiral ganglion cells and cochlear nucleus neurons. In deaf animals, there was a decrease in Glu-R 4 and NR 1, but a significant increase was found in Glu-R 2/3 and NR 2. The fact that the up-regulation of Glu-R 2/3 and NR 2 occurred in deafned rats reflected functional and structual changes in the cochlea. iii) Neurotrophic factor (HGF) was administered with chronocally embedded miniature pomp in deafned rats, and its protective effects was examined. The reslut showed that HGF had positive effects upon the number of spiral ganglion cells and expression in glutamate receptors. The importance of neurotrophic stimulation upon auditory system of deafned rats was stressed.