Model Establishment Of Presbycusis By D-galactose And Pathological Changes In Auditory Cortex Of Presbycusis.

SectionⅠ【Objective】To find an ideal method for model establishment of presbycusis by D-galactose.【Methods】Fifty Wistar rats were randomly divided into five groups including one control group (CG) and four model groups(model group1,model group2,model group3 and model group4,MG1, MG2 ,MG3 and MG4) with different dosages of D-galoctose( 50 mg/kg,100 mg/kg,200 mg/kg,500 mg/kg).Then,we observed in each group the change in animal behavior (excitatory experiment),in ABR,and in the activity of SOD and the level of MDA in serum,as well as morphological and quantitative changes of neurons in auditory cortex.【Results】Compared with the control group,no visible change of tensity was observed while the ability of exploration obviously decreased in MG(P <0.05).The level of MDA and the activity of SOD in serum significantly changed(P <0.05)in four model groups when compared with the control group. Latency of wave I and III and threshold of ABR in MG4 were significantly delayed and elevated when compared with the control group and other model groups(P <0.05),but there was no visible change in MG1,MG2 and MG3(P>0.05). In addition,significant morphological changes in auditory cortex could also be seen in MG4,such as reduced number of neurons,swollen body of neurons,and reduced number of Nissl's bodies.【Conclusion】It is an effective method for the model establishment of presbycusis by intraperitoneally injection in Wistar rat by 500 mg/kg D-galactose every day for 10 weeks.SectionⅡ【Objective】To study the pathological changes in auditory cortex of presbycusis. 【Methods】Toluidine blue staining and immunohistochemistry were adopted to detect and compare the morphous and number of neurons and the content of two kinds of excitatory neurotransmitter–acetylcholine (ACh) and glutamic acid (Glu) and one inhibitory neurotransmitter–γ-aminobutyric acid (GABA) in auditory cortex among normal adult rats, aged rats with normal hearing (18 months old) and model rats of presbycusis established by D-galactose.【Results】1.Among the three groups,only in model rats of presbycusis, significant morphological changes could be seen in auditory cortex,such as reduced number of neurons,swollen body of neurons,and reduced number of Nissl's bodies. 2. Compared with normal adult rats and aged rats with normal hearing, the content of Ach and GABA in model rats of presbycusis was significantly decreased(P<0.01)but Glu significantly increased(P<0.01).However,there was no visible change between normal adult rats and aged rats with normal hearing(P>0.05).【Conclusion】Presbycusis may be related to reduced neurons number(P<0.05), morphological changes of neurons,decreased Ach and GABA content and increased Glu content in auditory cortex.