The Changes Of SOD, MDA And Apoptosis In The Auditory Cortex, The Cochlear Nuclei And The Cochlea Of The Rats With Age-related Hearing Loss

Objective: To explore the changes of superoxide dismutase (SOD), malondialdehyde (MDA) and apoptosis in the auditory cortex, the cochlear nuclei and the cochlea of the rats with age-related hearing loss, and understand the relationship between oxygen free radical (OFR), lipid peroxiclation and apoptosis with presbyacusis.Methods: Three-month-old rats (ABR 20±5 dB SPL ) and eighteen-month-old rats (ABR 55±10 dB SPL ) were used in the study. T-SOD activity was measured by xanthine oxidase (XO) method. MDA level was examined by thibabituric acid (TBA) method. Apoptosis was examined by Annexin V-FITC/PI staining with flow cytometry (FCM).Results: 1．The SOD activities (U/mgprot) in the auditory cortex, the cochlear nuclei and the cochlea of the eighteen-month-old rats were 170．33±16．15, 366．35±79．10, 382．56±88．10, and the levels of MDA (nmol/mgprot) were 1．79±0．17, 3．16±0．24, 1．66±0．24 respectively. However, the SOD activities (U/mgprot) in the auditory cortex, the cochlear nuclei and the cochlea of the three-month-old rats were 267．32±20．10, 483．97±60．25, 479．43±90．25, and the levels of MDA (nmol/mgprot) were 1．26±0．10, 2．42±0．31, 1．31±0．33 respectively. The SOD activities decreased and the MDA levels increased significantly in the auditory cortex, the cochlear nuclei and the cochlea of the eighteen-month-old rats (P<0．005) .2．The apoptosis rates (%) in the auditory cortex and the cochlear nuclei of the eighteen-month-old rats were 62．38±9．99, 27．81±24．31, and the apoptosis rates (%) in the auditory cortex and the cochlear nuclei of the three-month-old rats were 40．70±8．72,6．27±1．92 respectively. The apoptosis rates increased significantly in the auditory cortex and the cochlear nuclei of the eighteen-month-old rats (P<0．05) .Conclusions: The results showed that the SOD activities in the auditory cortex, the cochlear nuclei and the cochlea of the eighteen-month-old rats decreased significantly, and the MDA levels in the same tissues increased significantly. The apoptosis rates increased significantly in the auditory cortex and the cochlear nuclei with aging. It indicated that redundant oxygen free radical, lipid peroxiclation and the neuron apoptosis in the auditory cortex, the cochlear nuclei and the cochlea of the rats with age-related hearing loss were important in the development of presbyacusis.