编码Na-K-2Cl的基因缺陷小鼠出现听觉和平衡功能障碍及内耳形态异常

目的： 培育突变型纯合子NKCC1^-/-、杂合子NKCC1^+/-及野生型NKCC1^+/+小鼠，将这3种基因型小鼠作为实验平台，研究NKCC1离子通道(Na-K-2Cl,co-transporter)在耳蜗听觉平衡功能中的作用，并观察不同基因型小鼠的内耳形态特征。方法： 利用同窝生各个基因型小鼠NKCC1^-/-（突变纯合子）、NKCC1^+/-（杂合子）和NKCC1^+/+（野生型）为实验对象，采用听觉脑干反应(ABR)和耳蜗内电位(EP)检测技术，对各基因型小鼠的听觉功能和EP进行检测；同时利用光学显微镜观察不同基因型小鼠的内耳形态变化。结果： NKCC1^+/+野生型小鼠听力正常，ABR检测的click短音阈值为［（23.13±3.78）dB,SPL］；EP为(98±16)mV。NKCC1^+/-杂合子小鼠听力低于同窝生的NKCC1^+/+野生型小鼠，ABR检测其Click短音阈值为［（38.49±12.29）dB,SPL］，EP为(78±7)mV。NKCC1^+/+和NKCC1^+/-小鼠ABR的阈值均值在各个频率的差异显著(P<0.01)；两者EP的均值差异也显著 (P<0.05)。NKCC1^-/-突变型纯合子小鼠呈现全聋，ABR各个频率在100 dB均无反应，其EP接近消失（4 mV±6 mV）。NKCC1^-/-突变型纯合子小鼠表现出听觉功能丧失和旋转为主的平衡失调。光镜下NKCC1^+/+野生型小鼠和NKCC1^+/-杂合子小鼠的耳蜗解剖结构无明显异常；NKCC1^-/-突变纯合子小鼠的耳蜗出现前庭膜塌陷、内淋巴腔缩小而致中阶完全消失，并有血管纹萎缩、Corti器缺失、螺旋神经节萎缩；且球囊和椭圆囊膜迷路失去正常结构并出现塌陷等病理改变。结论: NKCC1离子通道在内耳K⁺循环和维系内耳正常听觉平衡功能中起重要作用。NKCC1通道的缺失或功能受限，均可导致耳蜗内淋巴K⁺负荷水平，进而影响耳蜗的听觉平衡功能。     

［Ca2+］i对大鼠肺动脉平滑肌细胞膜钙激活氯离子通道的调节作用

目的： 探讨细胞浆内游离钙离子浓度（［Ca²⁺］_i）在常氧、急性和慢性低氧条件下对大鼠肺动脉平滑肌细胞(PASMCs)膜钙激活氯离子通道（Cl_Ca）的调节作用。 方法: 常规离体血管灌流法检测急性低氧时肺动脉环张力变化；钙荧光探针(Fura-2/AM)负载培养PASMCs，观察常氧和慢性低氧条件下［Ca²⁺］_i的变化并由此对Cl_Ca的影响；同时用四唑盐(MTT)比色法观察当［Ca²⁺］_i变化时Cl_Ca对PASMCs增殖的影响。 结果: (1) Cl_Ca阻断剂尼氟灭酸（NFA）和indaryloxyacetic acid (IAA-94)可以舒张急性低氧引起的肺动脉环收缩。(2) 慢性低氧时［Ca²⁺］_i升高：常氧状态下, PASMCs ［Ca²⁺］_i为(123.63±18.98)nmol/L，低氧时为(281.75±16.48)nmol/L (P<0.01)。(3) 常氧时，NFA和IAA-94对［Ca²⁺］_i 无明显影响(P>0.05)。(4) 慢性低氧时, NFA和IAA-94使PASMCs ［Ca²⁺］_i由(281.75±16.48)nmol/L降低到(117.66±15.36)nmol/L (P<0.01)。(5)MTT比色法中，慢性低氧状态下NFA和IAA-94引起升高的吸光度(A)值降低，由0.459±0.058到0.224±0.025 (P<0.01)。 结论: 低氧引起［Ca²⁺］_i升高，这可能激活Cl_Ca，对［Ca²⁺］_i起正反馈作用，Cl_Ca可能在低氧肺动脉高压中起作用；慢性低氧条件下Cl_Ca可能参与促进大鼠PASMCs的增殖。     

丹酚酸B对缺血小鼠脑能量代谢和脑水肿的影响

目的： 通过探讨丹酚酸B（SalB）对缺血小鼠脑能量代谢的影响，研究其对脑水肿的作用。方法：将NIH小鼠分为假手术组、缺血组、SalB治疗组和尼莫地平（Nim）治疗组，测定缺血30 min时脑组织能荷（EC）、磷酸肌酸（PCr）、ATP酶活性、兴奋性氨基酸（EAA）含量以及脑含水量。结果：SalB治疗组EC（0.520±0.034）和PCr［（98.344±13.249）μmol/g］的含量、Na⁺-K⁺-ATPase［（0.593±0.013）×10³ U/g］和Ca²⁺-ATPase［（0.484±0.053）×10³ U/g］的活性明显高于缺血组EC（0.465±0.037）、PCr［（81.614±9.919）μmol/g］的含量、Na+-K+-ATPase［（0.244±0.065）×10³ U/g］和Ca²⁺-ATPase［（0.321±0.086）×10³ U/g］ 的活性，2者相比显著差异（P<0.01）；而SalB治疗组Glu［（0.405±0.110）μmol/g］和Asp［（0.141±0.020）μmol/g］的含量和脑含水量［（38.1±0.1）%］ 则明显低于缺血组Glu［（0.550±0.140）μmol/g］、Asp［（0.287±0.050）μmol/g］的含量和脑含水量［（44.1±0.1）%］，2者比较亦有显著差异（P<0.05,P<0.01）。结论：增强脑组织能量代谢和ATP酶活性，并降低脑组织中兴奋性氨基酸的含量，可能是SalB减轻小鼠缺血性脑水肿的作用机制。     

维生素E对D-半乳糖诱致衰老小鼠脑抗氧化能力、钙稳态和线粒体DNA（mtDNA）损伤的影响

目的：探讨维生素E（Vit-E）对D-半乳糖诱致衰老小鼠脑抗氧化能力、胞浆游离Ca²⁺（［Ca²⁺］i）稳态和线粒体DNA（mtDNA）损伤的影响。方法:小鼠连续皮下注射（sc）D-半乳糖（1 000 mg·k^-1·d^-1）8周制备衰老模型，并于第3周开始给予维生素E（100 mg· kg^-1；250 mg· kg^-1）处理；8周后采用水迷宫测定小鼠学习记忆能力，并取脑组织测定谷胱甘肽过氧化物酶(GSH-Px)和琥珀酸脱氢酶（SDH）活性，测定一氧化氮（NO）含量和一氧化氮合酶（NOS）活性。Fura-2/AM负载法和PCR方法分别测定海马神经细胞［Ca²⁺］i浓度和mtDNA缺失突变。结果:维生素E处理能明显改善D-半乳糖诱致衰老小鼠学习记忆障碍，抑制脑组织NOS活性，降低NO含量，提高GSH-Px和SDH活性，降低［Ca²⁺］i水平（P＜0.01， P＜0.05），并防止mtDNA缺失突变的发生。结论:维生素E具有提高衰老小鼠脑抗氧化能力和调节［Ca²⁺］i稳态的作用，并抑制氧化应激引起的mtDNA损伤，从而改善衰老动物学习记忆障碍。     

硫化氢对体外大鼠肝星状细胞内Ca2+浓度变化及细胞增殖的影响

目的 研究硫化氢(H₂ S)对大鼠肝星状细胞-T6(HSC-T6) Ca²⁺浓度、细胞增殖的影响及其机制。 方法 活化HSC-T6用含10%小牛血清DMEM培养液制备为1×10⁵个肝星状细胞(HSC)悬液。钙离子荧光探针Fluo-3/AM负载细胞后，在不同刺激条件下，利用激光扫描共焦显微镜动态扫描HSC-T6细胞内Ca²⁺荧光强度（FI）变化，FI表示细胞内Ca²⁺浓度。四唑盐比色法，观察不同浓度H₂S供体——NaSH对HSC-T6细胞增殖的影响。 结果 低浓度H₂S（100μmol/L）明显降低HSC-T6细胞内Ca²⁺浓度（P<0.05)，而细胞增殖增加（增殖率为116%）；K_ATP通道阻断剂——格列本脲可阻断H2S的作用。高浓度H₂S（1mmol/L）刺激HSC-T6细胞内Ca₂₊浓度增加，但细胞增殖无明显变化(P＞0.05)。 结论 低浓度H₂S通过激活HSC-T6细胞K_ATP通道降低细胞内Ca²⁺浓度，可能通过调节细胞氧化应激促进细胞增殖；高浓度H2S刺激HSC-T6细胞内Ca₂₊浓度增加。提示H₂S在肝硬化门脉高压症的发生机制中具有双重作用。     

肝门阻断再灌注对脑兴奋性氨基酸及受体mRNA表达的影响

目的： 探讨无肝期后的再灌注对脑组织兴奋性氨基酸（EAAs）及其受体mRNA表达的影响。方法：分别采用血气分析、高效液相色谱荧光检测和半定量RT-PCR方法，研究大鼠肝门阻断和假手术组再灌注6 h、12 h和24 h后门静脉电解质和pH、脑组织Glu、Asp含量以及大脑皮层中NMDAR mRNA的相对含量表达的差异，观察无肝期后再灌注损伤对肝外远隔脏器脑EAAs及NMDA受体mRNA表达的的影响。结果：肝门阻断期间门静脉pH显著降低，［K⁺］升幅超过1倍，但开放后逐渐恢复；［Ca²⁺］于再灌注后持续下降至12 h；脑皮层中的Glu和Asp再灌注后分别在6 h、24 h出现2个高峰［Glu:(349±145) μg·g^-1wt,(456±203) μg·g^-1wt vs (238±24) μg·g^-1wt,(225±59) μg·g^-1wt;Asp: (134±50) μg·g^-1wt,(166±50) μg·g^-1wt vs (99±24) μg·g^-1wt,(71±20) μg·g^-1wt］；NMDAR亚单位NR1mRNA的表达在再灌注后显著升高后逐渐下降［(1.63±0.06) μg·g^-1wt vs (1.18±0.05) μg·g^-1wt;(1.73±0.06) μg·g^-1wt vs (1.17±0.03) μg·g^-1wt］,而NR2B mRNA在12 h升高(1.75±0.04 vs 1.18±0.05)，2者24 h时均恢复至对照组水平。结论：肝门阻断后肝和肠道再灌注过程可启动神经突触前Glu大量释放和重吸收抑制，引起脑皮层EAAs的堆积，同时刺激NMDARmRNA的表达，通过Glu - NMDAR途径可能引发脑损伤。     

神经鞘磷脂合成酶2基因敲除小鼠海马神经细胞自噬现象

目的 利用神经鞘磷脂合成酶2（SMS2）基因敲除小鼠探讨神经酰胺对海马神经细胞自噬现象的影响。方法 将SMS2杂合子（SMS2^+/- ）小鼠采用杂交、回交、互交的方法进行繁殖,用酚-氯仿提取法提取小鼠基因组DNA,PCR扩增目的基因,琼脂糖凝胶电泳对小鼠基因型作出鉴定,建立纯合子（SMS2^-/- ）小鼠模型;采用透射电子显微镜、免疫荧光染色及Western blotting技术观察生后第7天（P7）、P14和P30 SMS2^-/-小鼠海马CA1区神经细胞自噬的发生（每种方法每个时间点8只小鼠）。结果 1.SMS2^-/-小鼠海马CA1区神经细胞自噬现象：电子显微镜下,模型组海马神经元内出现较多自噬体或自噬溶酶体样结构。光镜下,模型组P7、P14和 P30 CA1区神经元自噬细胞数较对照组高(P ＜0.01）;2.自噬相关蛋白Beclin-1对于自噬的调节作用：Beclin-1在模型组与对照组间的表达规律与微管相关蛋白1轻链3（MAPLC3）基本一致,P7、P14、P30模型组Beclin-1阳性细胞数明显多于对照组(P ＜0.01）。Beclin-1与 MAPLC3两者在同一细胞中基本呈重叠表达; 3.Western blotting检测各组海马CA1区神经细胞MAPLC3蛋白的相对表达量与上述结果一致。结论SMS2-/-小鼠海马神经细胞内神经酰胺增高,神经酰胺不仅促进细胞凋亡,同时促进自噬,造成小鼠海马神经细胞自噬现象增强。     

卡托普利对缺氧/复氧乳鼠心室肌细胞游离钙的影响及其离子通道机制

目的：观察卡托普利晚期预处理对缺氧/复氧乳鼠心室肌细胞游离钙的影响及其离子通道机制。方法:建立培养乳鼠心肌细胞缺氧/复氧损伤模型。设正常对照组、缺氧/复氧组、缺氧预适应组和卡托普利组。经Flou-3/AM负载染色后，采用流式细胞分析技术，测定细胞内钙离子浓度(［Ca²⁺］i)；利用膜片钳技术，观察L-型钙通道和钠钙交换电流的变化。结果:（1）缺氧/复氧时，［Ca²⁺］i和Na⁺/Ca²⁺交换电流高于正常对照组（P<0.01），L-型钙电流（I_Ca-L）峰值下降，I-V曲线上移，半数失活电压(V_0.5)减小，ICa-L失活曲线左移。（2）晚期预处理和卡托普利使缺氧/复氧时［Ca²⁺］i低于缺氧/复氧组（P<0.01）；I_Ca-L增加，I-V曲线下移，V_0.5增大及稳态失活曲线右移；Na⁺/Ca²⁺ 交换电流减少；但［Ca²⁺］i和Na⁺/Ca²⁺交换电流高于对照组（P<0.05）。（3）卡托普利组与缺氧预适应组比较上述指标均无显著差异 。结论：心肌细胞缺氧/复氧，通过Na⁺/Ca²⁺交换电流的异常增加可引起［Ca²⁺］i的异常升高及其钙超载；卡托普利通过轻度增加Na⁺/Ca²⁺交换电流及其［Ca²⁺］i而触发晚期预处理，抑制后续缺氧/复氧引起的Na⁺/Ca²⁺交换电流及其［Ca²⁺］i的异常增加。     

类风湿关节炎CD4+CD28-T细胞与淋巴细胞凋亡的相关性研究

目的: 研究类风湿关节炎(RA)患者外周血CD4⁺CD28^-T细胞比例与淋巴细胞凋亡异常的相关性。方法: 采用流式细胞术三色分析法检测50例患者和50例健康志愿者的外周血淋巴细胞中CD4⁺CD28^-T细胞比例;通过加入PHA孵育检测RA病人外周淋巴细胞和正常对照的淋巴细胞对激活诱导细胞死亡(AICD)易感性差异;分析CD4⁺CD28^-T细胞比例与外周血淋巴细胞凋亡率的相关性。结果: RA组CD4⁺CD28^-T细胞比例的均数明显高于健康对照组(7.79%±3.52% vs 1.89%±1.78%,P<0.05)。RA组病人外周血淋巴细胞的AICD凋亡率低于健康对照组(11.38%±5.73% vs 19.46%±6.32%,P<0.05)。Spearman相关分析结果显示CD4⁺CD28^-T细胞比例与外周血淋巴细胞AICD凋亡率负相关(r=-0.433,P<0.01)。结论: RA患者外周血中CD4⁺CD28^-T细胞比例增多,活化淋巴细胞生存期延长,这可能参与RA的发病机制。     

慢性缺氧对大鼠肺动脉平滑肌细胞胞内钙的影响及其机制研究

目的:研究慢性缺氧对大鼠肺动脉平滑肌细胞(PASMCs)胞内钙浓度(［Ca²⁺］_i)的影响及L-型钙通道和胞内钙库的作用,为缺氧性肺动脉高压(HPH)发病机制的进一步研究提供理论依据。 方法:复制大鼠缺氧性肺动脉高压动物模型，利用Fura－2/AM钙离子成像方法测定PASMCs在不同钙离子浓度细胞外液及L-型钙通道阻滞剂nifedipine和IP3R钙通道抑制剂肝素干预前后 ［Ca²⁺］_i变化。 结果:(1)缺氧＋含钙外液组PASMCs ［Ca²⁺］_i 显著高于对照＋含钙外液组（P<0.05）。缺氧＋含钙外液组PASMCs ［Ca²⁺］_i显著高于缺氧＋无钙外液组（P<0.05）。(2)缺氧nifedipine组PASMCs［Ca²⁺］_i在加药前后无显著差异（P>0.05）。（3）缺氧未干预组与缺氧肝素组PASMCs ［Ca²⁺］_i无明显差异（P>0.05）。 结论:慢性缺氧可使PASMCs的［Ca²⁺］_i增加。慢性缺氧引起［Ca²⁺］_i增加可能与细胞外钙内流有关，L-型钙通道和IP3R钙通道在调节［Ca²⁺］_i的过程中可能不独立发挥作用。     

Esketamine may be an ideal substitute for ketamine during cochlear function measurement

The mixture of ketamine and xylazine is widely used for the auditory brainstem response (ABR) measurement. Esketamine is twice as potent as ketamine. Our objective was to assess the influence of esketamine in mice undergoing cochlear function measurement including ABR and distortion product otoacoustic emission (DPOAE) measurement. C57Bl/6J mice were treated with an equivalent dose of analgesia and received either a single intraperitoneal (ip) injection of 100 mg/kg ketamine and 25 mg/kg xylazine or 50 mg/kg esketamine and 25 mg/kg xylazine. Hearing thresholds, peak latencies of waves I and V, and DPOAE thresholds were recorded. Time to loss of righting and time to regain righting were also assessed. We found that hearing thresholds, the peak latencies of waves I and V, and DPOAE thresholds were similar between the two groups (all P>0.05). Time to regain righting was significantly shorter in the esketamine group (P<0.001) than in the ketamine group. We concluded that when using equivalent doses of analgesia, esketamine may be an ideal substitute for ketamine during cochlear function test.     

Detection and differentiation of sensorineural hearing loss in mice using auditory steady-state responses and transient auditory brainstem responses

Sensorineural hearing loss (SNHL) comprises hearing disorders with diverse pathologies of the inner ear and the auditory nerve. To date, an unambiguous phenotypical characterization of the specific pathologies in an affected individual remains impossible. Here, we evaluated the use of scalp-recorded auditory steady-state responses (ASSR) and transient auditory brainstem responses (ABR) for differentiating the disease mechanisms underlying sensorineural hearing loss in well-characterized mouse models. We first characterized the ASSR evoked by sinusoidally amplitude-modulated tones in wild-type mice. ASSR were robustly elicited within three ranges of modulation frequencies below 200 Hz, from 200 to 600 Hz and beyond 600 Hz in most recordings. Using phase information we estimated the apparent ASSR latency to be about 3 ms, suggesting generation in the auditory brainstem. Auditory thresholds obtained by automated and visual analysis of ASSR recordings were comparable to those found with tone-burst evoked ABR in the same mice. We then recorded ASSR and ABR from mouse mutants bearing defects of either outer hair cell amplification (KCNQ4-knockout) or inner hair cell synaptic transmission (Bassoon-mutant). Both mutants showed an increase of ASSR and ABR thresholds of approximately 40 dB versus wild-type when investigated at 8 weeks of age. Mice with defective amplification displayed a steep rise of ASSR and ABR amplitudes with increasing sound intensity, presumably reflecting a strong recruitment of synchronously activated neural elements beyond threshold. In contrast, the amplitudes of ASSR and ABR responses of mice with impaired synaptic transmission grew very little with sound intensity. In summary, ASSR allow for a rapid, objective and frequency-specific hearing assessment and together with ABR and otoacoustic emissions can contribute to the differential diagnosis of SNHL.     

Noise-induced aspartate and glutamate efflux in the guinea pig cochlea and hearing loss

Aspartate and glutamate were monitored in the scala tympani of the guinea pig cochlea using in vivo microdialysis before and during noise exposure. Moderate level broad band noise [105 dB sound pressure level (SPL), 30 min] neither altered the levels of aspartate or glutamate, nor auditory brainstem response (ABR) thresholds. High level noise exposure (135 dB SPL, 30 min) caused a large increase in aspartate (330%), a smaller increase in glutamate (150%), and a permanent ABR threshold shift of 60-75 dB between 2.0 and 12.5 kHz. Morphological analysis of the cochlea revealed a collapse of supporting structures, swelling of the afferent dendrites under the inner hair cells, and outer hair cell loss. Pretreatment with the NMDA antagonist, MK 801 (1 mg/kg body weight, i.p.) 1 h before noise exposure protected the afferent dendrites from swelling but did not protect the collapse of supporting structures, outer hair cell loss, or auditory thresholds. In conclusion, the noise-induced increase in aspartate and glutamate release in the cochlea and the protective effect of NMDA antagonism suggest that these two neurotransmitters are involved in noise-induced hearing loss.     

The Morphology and Electrophysiology of the Cochlea of the Miniature Pig

To report the cochlear morphology and electrophysiology of Chinese experimental miniature pigs. Twenty Chinese experimental miniature pigs were used in this study. Auditory brainstem responses (ABR), cochlear endolymphatic potentials (EP), and the potassium concentrations of cochlear endolymph were recorded. Hair cell morphology was examined using electron microscopy. The capsule of cochlea of the miniature pig has three and one‐half turns which contains a 39‐mm long membranous labyrinth. The organ of Corti in the labyrinth encompasses three rows of outer hair cells and one row of inner hair cells. The stereocilia of the hair cells in the apical turn of the cochlea were significantly longer than those in the basal turn. The vestibular apparatus consists of three semicircular canals and the otolith organs. The average threshold of the ABR was 35–45 dB SPL (n = 20) from 4 to 32 kHz. There was no significant difference in the threshold or latency of the ABR between 1‐day‐old and 30‐day‐old miniature pigs. The average EP value was 77.3 ± 14 mV (n = 9) and the average potassium concentration was 147.1 ± 13 mM (n = 5) recorded from the second turn of the cochlea. These studies on the cochlear morphology and electrophysiology of the miniature pigs help to establish the Chinese experimental miniature pig as an animal model for future studies in otology and audiology. Anat Rec, 298:494–500, 2015. © 2014 Wiley Periodicals, Inc.     

Ebselen prevents noise-induced excitotoxicity and temporary threshold shift

This investigation tested the hypothesis that a noise-induced temporary threshold shift (TTS) can be attenuated by a peroxynitrite scavenger, ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one). Guinea pigs received an oral dose of the vehicle or 10 mg/kg ebselen 1 h before exposure to 115 dB SPL 4-kHz octave band noise for 3 h. In controls, auditory brainstem response (ABR) thresholds increased by 25–45 dB immediately after noise and returned to pre-exposure baseline thresholds 7 days later. Ebselen eliminated this ABR threshold shift following noise exposure. In controls, swelling of the afferent dendrites beneath the inner hair cells was evident immediately after noise, whereas ebselen significantly reduced this pathology. These findings suggest that scavenging peroxynitrite can attenuate noise-induced excitotoxicity and, thereby, TTS.     

Hydrogen in drinking water attenuates noise-induced hearing loss in guinea pigs

It has been shown that molecular hydrogen acts as a therapeutic and preventive antioxidant by selectively reducing the hydroxyl radical, the most cytotoxic of the reactive oxygen species. In the present study, we tested the hypothesis that acoustic damage in guinea pigs can be attenuated by the consumption of molecular hydrogen. Guinea pigs received normal water or hydrogen-rich water for 14 days before they were exposed to 115 dB SPL 4-kHz octave band noise for 3h. Animals in each group underwent measurements for auditory brainstem response (ABR) or distortion-product otoacoustic emissions (DPOAEs) before the treatment (baseline) and immediately, 1, 3, 7, and 14 days after noise exposure. The ABR thresholds at 2 and 4 kHz were significantly better on post-noise days 1, 3, and 14 in hydrogen-treated animals when compared to the normal water-treated controls. Compared to the controls, the hydrogen-treated animals showed greater amplitude of DPOAE input/output growth functions during the recovery process, with statistical significance detected on post-noise days 3 and 7. These findings suggest that hydrogen can facilitate the recovery of hair cell function and attenuate noise-induced temporary hearing loss.     

Role of the tectorial membrane revealed by otoacoustic emissions recorded from wild-type and transgenic Tecta(deltaENT/deltaENT) mice

Distortion product otoacoustic emissions (DPOAE) were recorded from wild-type mice and mutant Tecta(deltaENT/deltaENT) mice with detached tectorial membranes (TM) under combined ketamine/xylaxine anesthesia. In Tecta(deltaENT/deltaENT) mice, DPOAEs could be detected above the noise floor only when the levels of the primary tones exceeded 65 dB SPL. DPOAE amplitude decreased with increasing frequency of the primaries in Tecta(deltaENT/deltaENT) mice. This was attributed to hair cell excitation via viscous coupling to the surrounding fluid and not by interaction with the TM as in the wild-type mice. Local minima and corresponding phase transitions in the DPOAE growth functions occurred at higher DPOAE levels in wild-type than in Tecta(deltaENT/deltaENT) mice. In less-sensitive Tecta(deltaENT/deltaENT) mice, the position of the local minima varied nonsystematically with frequency or no minima were observed. A bell-like dependence of the DPOAE amplitude on the ratio of the primaries was recorded in both wild-type and Tecta(deltaENT/deltaENT) mice. However, the pattern of this dependence was different in the wild-type and Tecta(deltaENT/deltaENT) mice, an indication that the bell-like shape of the DPOAE was produced by a combination of different mechanisms. A nonlinear low-frequency resonance, revealed by nonmonotonicity of the phase behavior, was seen in the wild-type but not in Tecta(deltaENT/deltaENT) mice.