Degenerative Changes Of Auditory Function, Hair Cells And Spiral Ganglion Neurons In Senescence Accelerated Dementia Mouse/Prone8

Objective To determine degenerative changes of auditory function,hair cells and spiral ganglion neurons in the senescence accelerated dementia mouse/prone 8.Methods The auditory thresholds and the morphological changes of the hair cells and the spiral ganglion neurons were studied in SAMP8 mice of 3,9 months. Normal aging senescence accelerated mouse/resistance 1 (SAMR1) mice served as the control groups. 8 kHz threshold of auditory brain-stem response (ABR) was determined to observe the binaural auditory function changes. Hair cells calculated on the left cochlear outer hair cells in the average loss rate was to observe the morphological changes of cochlea. Terminal deoxynucleotidyl transferase(TdT) dUTP nick end labeling(TUNEL) were used to observe the immunohistochemical changes in the cochlea.Results 1 Auditory function: The left ear's ABR threshold (dB SPL) of the experimental groups—3,9 months SAMP8 mice were 36.5±3.81,52.6±3.00, and the values of the control groups—3,9 months SAMR1 were 35.7±0.82,37.2±1.47 respectively. The right ear's ABR threshold (dB SPL) of the experimental groups—3,9 months SAMP8 mice were 37.6±3.40,54.1±4.27, and the values of the control groups—3,9 months SAMR1 mice were 34.5±1.05,36.3±2.07 respectively. Compared with the SAMR1 mice, SAMP8 mice of 9 months developed a progressive binaural hearing loss at 8kHz, which showed an age-related significant increase(P<0.01);compared with the SAMP8 mice of 3 months, SAMP8 mice of 9 months developed a progressive binaural hearing loss at 8kHz, which showed an age-related significant increase(P<0.01).2 The outer hair cells changes of cochlea: Compared with the SAMR1 mice, the SAMP8 mice suffered from age-related loss in the outer hair cells at basal gyrus. The average loss rate in the cochlear outer hair cells at basal gyrus in each group was: 3 months SAMP8 mice 2.5±0.91,3 months SAMR1 mice 1.6±0.80,9 months SAMP8 mice 19.5±3.73 and 9 months SAMR1 mice 2.7±1.11 respectively. Compared with the SAMR 1 mice, there was severe outer hair cell loss in the SAMP8 mice in 9 months, which showed a significant increase(P<0.01);compared with the SAMP8 mice of 3 months, there was severe outer hair cell loss in the SAMP8 mice in 9 months, which showed a significant increase(P<0.01).3 TUNEL observation: Compared with the SAMR1 mice, the SAMP8 mice showed age-related TUNEL dyeing deepening in cochlea spiral ganglion neuron. The percentage of positive reaction spiral ganglion neutron in TUNEL dyeing of each group was: 3 months SAMP8 mice 3.18±1.70,3 months SAMR1 mice 2.14±1.39,9 months SAMP8 mice 18.22±4.71 and 9 months SAMR1 mice 3.63±1.42 respectively. Compared with the SAMR 1 mice, there was severe spiral ganglion neutron apoptosis in the SAMP8 mice in 9 months, which showed a remarkable significant increase(P<0.01); compared with the SAMP8 mice of 3 months, there was severe spiral ganglion neutron apoptosis in the SAMP8 mice in 9 months, which showed a remarkable significant increase(P<0.01).Conclusions The results showed that there were degenerative changes——auditory function descending,hair cells damaging and spiral ganglion neutron apoptosis in the SAMP8 mice. And SAMP8 mice can be used for determining the correlativity between aging-related hearing loss and senile dementia.