不同剂量白喉毒素对野生型听力成熟小鼠耳蜗结构及听功能的影响

目的 观察不同剂量白喉毒素对野生型听力成熟小鼠的耳蜗结构及听功能的影响,为建立白喉毒素受体介导的细胞敲除系统动物模型提供参考.方法 4周龄C57BL/6J小鼠30只随机分为50 ng/g组、100 ng/g组和对照组,每组10只;其中50 ng/g组和100 ng/g组小鼠分别单次腹腔注射白喉毒素50 ng/g、100 ng/g,对照组小鼠单次腹腔注射等量生理盐水,注射后7天观察两组动物的一般情况,并记录小鼠ABR反应阈,观察小鼠内外毛细胞、螺旋神经节神经元.结果 在白喉毒素注射后第7天,各组动物情况良好,无明显体重下降,中耳腔无积液.50 ng/g组小鼠2、8、32 kHz ABR反应阈分别为57.5±2.74、20.83±2.04、45.83±2.04 dB SPL,与对照组比较(分别为56.25±2.31、20.0±3.78、49.38±6.78 dB SPL)差异无统计学意义;内、外毛细胞损失率分别为0.8%±0.5%、1%±0.6%;对照组分别为0.3%±0.5%、0.4%±0.3%;螺旋神经节神经元SGN密度为39.45±3.65个/105 μm2、对照组为41.03±3.73个/105 μm2,均未见明显细胞缺失.100 ng/g组小鼠2、8、32 kHz ABR反应阈分别为85±3.54、63±4.47、90±0 dB SPL,较前两组显著升高(t=19.62,P<0.001),内、外毛细胞损失率分别为0.5%±0.1%、10.7%±0.3%,损伤严重,底、中、顶回缺失达10%(t=42.219, P<0.001);SGN密度为25.55±3.66个/105 μm2,平均减少38%,与对照组相比差异有显著统计学意义(t=10.985,P<0.001).结论 100 ng/g白喉毒素注射能引起听力成熟野生型C57BL/6J小鼠外毛细胞及螺旋神经元的损伤.

Effects of Different Doses of Diphtheria Toxin on the Cochlear Structure and AuditoryFunction in Wildtype Auditory-Mature Mice

Objective To investigate the effects of different doses of diphtheria toxin on cochlear structure and auditory function of adult wildtype mice.Methods The auditory-mature wild type C57BL/6J mice 4 weeks old were randomly devided into 50 ng/g group, 100 ng/g group and control group.C57BL/6J mice in the 50 ng/g or 100 ng/g group were injected 50 ng/g or 100 ng/g diphtheria toxin intraperitoneally for one time, respectively, and the control mice were injected equal volume of normal saline for one time.Then we investigated the ABR threshold change and morphological change of inner and outer hair cell and spiral ganglion neuron 7 days after the injection.Results At 7 day post diphtheria toxin injection compared with those of in control group, in the 50 ng/g group, there was no threshold elevation across frequencies(8 kHz ABR threshold was 20.0±3.78 and 20.83±2.04 dB SPL for 50 ng/g and control respectively), and no loss of inner and outer hair cells (for both groups, the HC loss rates were 0.3%~1%) or SGN (the SGN density was 39.45±3.65, 41.03±3.73/105 μm2, in 50 ng/g and control, respectively).However, the 100 ng/g group, compared with those of in control group, the ABR threshold (8 kHz ABR threshold was 63.0±4.47 dB SPL, respectively)was significantly elevated across each frequency(t=19.62,P<0.001), and there was significant loss of outer hair cell (the loss rate of IHC and OHC was 0.5%±0.1%, 10.7%±0.3%, respectively), which was 10% loss in the apical, middle and basal turn(t=42.219,P<0.001).And the loss of spiral ganglion neuron (the SGN density was 25.55±3.66/105 μm2) was 38%, which was significantly different from the control(t=10.985,P<0.001).Conclusion High dose injection of diphtheria toxin can cause loss of outer hair cell and spiral ganglion neuron in wild type auditory-mature C57BL/6J mice.