Study On Age-related Retrogression In Central Auditory System Of DBA/2Mice

Objective:To investigate age-related morphology changes and the pathogenesis in auditory cortex(AC),inferior colliculus(IC) and cochlear nuclear(CN) of DBA/2mice.Methods:DBA/2mice were divided into four groups as age, including3weeks group,8weeks group,12weeks group and8months group. The hearing threshold was tested by auditory brainstem response(ABR)at4kHz,8kHz,16kHz and32kHz. The morphology of central auditory system (cochlear nuclear,inferior colliculus and auditory cortex)was observed with hematoxylin and eosin stain(HE), Nissl’s staining and transmission electron microscope(TEM). Real-time PCR was used to quantify the mtDNA3873bp deletion and COX3gene deletion. Immunohistochemistry was performed to detect the express location of COX3in CN, IC and AC.Results:①The ABR threshold increased with the growing of the age.The threshold of32kHz was higher than that of other frequences at3weeks old. The thresholds of8kHz and16kHz increased obviously at8weeks old.At8months old, the thresholds at every frequences were over90db. The latent period of wave I, III, V and the interphase of Ⅰ-Ⅴ increased with the growing of the age. The wave form of32kHz is not clear at3weeks old and the amplitude of32kHz is little. Compared with8weeks age, the change of the latent period of all waves in4kHz and8kHz is not notable at12weeks age. All waves can not be elicited in all frequence at8months old.②Light microscope:With the growing of age, the neurons of central auditory system decreased in numbers and diminished in sizes and the numbers of colloid cells increased and Nissl’s bodies melt of CN, IC and AC.③TEM:With the growing of age, the decreasing of neurons transparence, pyknosis, bad integrality of karyotheca, dropsical mitochondrial,outstretched endoplasmic reticulum, increased lipofuscin and demyelination of myelinated nerve fiber were observed in CN, IC and AC.④The mtDNA3873bp deletion rate and COX3gene expression were not detected change with the growing of age.The rate of mtDNA3873bp deletion was10-4～10-5. Conclusion:DBA/2mice perform a age-related hearing loss and the morphology change of central auditory system.DBA/2mice could be used for presbycusis research. The relations of presbycusis of DBA/2mice to mtDNA3873bp deletion and to COX3gene deletion were not notable.