耳蜗基底膜组织巨噬细胞对噪声的反应

目的观察强噪声暴露后耳蜗基底膜组织巨噬细胞形态的变化,探讨噪声性耳蜗损伤的免疫机制。方法将C57BL/6J小鼠接触持续噪声暴露(1-7k Hz,120d B SPL)1小时。应用电位反应测听仪,检测噪声暴露前和噪声暴露后10天不同频率短纯音(4、8、16和32 k Hz)诱发的动物双耳听性脑干反应阈值(ABR)。噪声暴露后1、4和10天处死动物,解剖取双侧耳蜗。采用鬼笔环肽(phalloidin)染色噪声暴露后10天毛细胞纤毛、表皮板的丝状肌动蛋白。白细胞共同抗原(CD45)荧光免疫抗体标记噪声暴露后1、4和10天耳蜗基底膜免疫细胞。以未接触噪声暴露动物耳蜗为对照,荧光显微镜下观察噪声暴露后小鼠耳蜗基底膜毛细胞和巨噬细胞形态变化,自耳蜗顶回到底回计数全耳蜗基底膜缺失的毛细胞和CD45荧光染色阳性细胞。结果噪声暴露后10天,不同频率短纯音诱发的ABR阈值均升高(F=1622.754,df=1,104,P<0.001;Tukey test,P<0.001)。耳蜗基底膜外毛细胞缺失数目明显多于正常对照组,底回缺失的外毛细胞数目多于顶回(F=92.484,df=1,40,P<0.001;Tukey test,P<0.001)。荧光显微镜下观察,生理条件下CD45阳性细胞主要为巨噬细胞,巨噬细胞分布于全耳蜗基底膜底面(鼓阶面)。细胞呈现多种形态,不同形态与其在耳蜗的不同部位相关。噪声暴露后1天,单核细胞渗入耳蜗基底膜,主要分布于耳蜗基底膜底回的上部。噪声暴露后4天,侵润的单核细胞转化为巨噬细胞,耳蜗基底膜CD45阳性细胞数目明显增加(F=15.205,df=3,46,P<0.001;Tukey test,P<0.001),耳蜗底回CD45阳性细胞数目多于顶回(P<0.05)。噪声暴露后10天,耳蜗基底膜CD45阳性细胞数目减少至噪声暴露前水平。结论免疫细胞参与了噪声性耳蜗损伤的反应,单核细胞的移入和转化可能在耳蜗细胞损伤和修复中起到重要的作用。     

骨髓神经组织定向干细胞移植修复听神经损伤模型大鼠的实验研究

目的 观察骨髓神经组织定向干细胞(NTCSCs)移植对听神经损伤大鼠的修复作用。方法将转染绿色荧光蛋白(EGFP)基因的骨髓NTCSCs移植至螺旋神经元特异性损伤模型大鼠左耳耳蜗蜗轴处(右耳作为自身对照,注射相同体积PBS溶液),同时设对照组(A组)、实验组(B～E组),所有组注射相同体积PBS溶液,HE染色观察耳蜗中轴切片,在荧光显微镜下观察感染EGFP的NTCSCs存活、分布部位及表达情况,注射后1周、2周、1个月时检测ABR阈值和DPOAE幅值等变化情况。结果 C组内耳耳蜗切片上发现转染EGFP基因的骨髓NTCSCs分散在鼓阶的腔隙内,D组发现转染EGFP基因的骨髓NTCSCs位置靠近基底膜和柯蒂氏器部位,E组发现转染EGFP基因的骨髓NTCSCs球团和两三个在一起的细胞聚集,并且位置靠近基底膜和柯蒂氏器部位,呈现良好的分布,类似有向基底膜和柯蒂氏器迁移行为;随着骨髓NTCSCs移植时间的延长,Nestin(+)细胞数量明显增多(P<0.05),而Myosin Ⅶa(+)细胞数量无明显变化(P>0.05);随着骨髓NTCSCs移植时间的延长,ABR阈值得到明显改善(P<0.05),DPOAE幅值明显上升(P<0.05)。结论 骨髓NTCSCs移植大鼠耳蜗后可逐渐分化成为螺旋神经节神经元(SGNs),进而起到改善听神经损伤大鼠听力的作用。     

TLR4基因敲除小鼠对噪声性耳蜗损伤的反应

目的揭示Toll样受体(Toll-like receptor,TLR)基因缺失对噪声性耳蜗感觉细胞损伤,听觉功能障碍和耳蜗免疫活力的影响作用,探讨噪声性耳蜗损伤的免疫炎性机制。方法将TLR4基因敲除(TLR4 KO)小鼠接触持续噪声暴露(1-7kHz,120dB SPL)1小时,以噪声暴露的野生型(WT)小鼠为对照,检测噪声暴露前和噪声暴露后25天四个频率短纯音(4 kHz、8 kHz、16 kHz和32 kHz)诱发的小鼠双耳ABR阈值。噪声暴露后1天,25天处死动物,解剖取双侧耳蜗。采用白细胞共同抗原(CD45)荧光免疫抗体标记噪声暴露前和噪声暴露后1天耳蜗基底膜免疫细胞,鬼笔环肽(phalloidin)染色噪声暴露前和噪声暴露后25天耳蜗基底膜毛细胞纤毛、表皮板的丝状肌动蛋白。荧光显微镜下观察噪声暴露后TLR4 KO小鼠和WT小鼠耳蜗基底膜组织的巨噬细胞、单核细胞和毛细胞形态变化,计数耳蜗基底膜外毛细胞的缺失数目。结果噪声暴露后1天,WT和TLR4 KO小鼠耳蜗基底膜均呈现单核细胞渗入。噪声暴露后25天,不同频率短纯音诱发的TLR4 KO小鼠ABR阈移和耳蜗基底膜外毛细胞缺失数目均低于WT小鼠(F=71.590, df=1,90, P<0.001; Tukey test, P<0.001),(F=8.996, df=1,17, P=0.008; Tukey test, P=0.008)。结论噪声暴露后TLR4基因缺失没有阻止单核细胞渗入耳蜗基底膜,但减轻噪声暴露后耳蜗感觉细胞和听功能损伤的程度。     

骨髓神经组织定向干细胞移植治疗大鼠听神经损伤的实验研究

目的观察骨髓神经组织定向干细胞（nerve tissue committed stem cells, NTCSCs）移植治疗大鼠听神经损伤的作用。方法 将60只SD大鼠按数字随机法分为5组,每组各12只,A组为对照组,在平静饲养环境下培养,另外4组（B、C、D、E组）构建感音神经性耳聋动物模型。B组大鼠断头后取出听泡组织行HE常规染色,详细观察耳蜗螺旋神经节神经元（spiral ganglion neurons, SGNs）损伤和内耳毛细胞存活情况,确认造模成功。将绿色荧光蛋白（green fluore scent protein, EGFP）基因表达阳性的骨髓NTCSCs注射至C、D、E 3组大鼠左耳耳蜗蜗轴处,SD大鼠右耳及A组作为对照;采用同一方法注射相同体积的0.1%PBS溶液。HE染色观察耳蜗中轴切片,在荧光显微镜下观察转染EGFP基因的NTCSCS存活、分布部位及表达情况。结果C组（移植后1周）内耳耳蜗切片上发现转染绿色荧光蛋白（green fluore scent protein, EGFP）基因的骨髓NTCSCs分散在鼓阶的腔隙内,D组（移植后2周）发现转染EGFP基因的骨髓NTCSCs位置靠近基底膜和柯蒂氏器部位,E组（移植后4周）发现转染EGFP基因的骨髓NTCSCs球团和多个在一起的细胞聚集,并且位置靠近基底膜和柯蒂氏器部位,呈现良好的分布,类似有向基底膜和柯蒂氏器迁移行为。随着骨髓NTCSCs移植时间的延长,Nestin（＋）细胞数量明显增多（P〈0.05）,而Myosin Ⅶa（＋）细胞数量无明显变化（P〉0.05）。结论骨髓NTCSCs移植大鼠耳蜗后可在一定程度上修复损伤听神经。     

胰岛素样生长因子1抑制小鼠耳蜗毛细胞凋亡

目的 利用耳蜗基底膜离体培养技术建立庆大霉素(gentamicin,GM)损伤模型,研究胰岛素样生长因子1(insulin-like growth factor-1,IGF-1)对小鼠耳蜗毛细胞(hair cell,HC)凋亡的影响及可能机制.方法 取新生小鼠耳蜗基底膜,在分别含有预先制备的培养液(A组),含有GM 0.5 mmol/L(B组),含有GM 0.5 mmol/L和IGF-1 1 ng/ml(C组),GM 0.5 mmol/L和IGF-1 10 ng/ml(D组),GM 0.5 mmol/L和IGF-1 50 ng/ml(E组),GM0.5 mmol/L和IGF-1 100 ng/ml(F组)的培养液中离体培养后制作耳蜗铺片.利用DNA末端转移酶介导的缺口末端标记法(terminal-deoxynucleotidyl transferase mediated nick end Iabeling,TUNEL)结合活性半胱氨酸蛋白酶-3抗体为标记物多重荧光免疫组织化学方法,激光共聚焦显微镜下观察各组耳蜗HC的凋亡情况.结果 耳蜗铺片观察显示A组各转及各组顶转未发现TUNEL染色阳性的凋亡HC.C、D、E、F各组耳蜗底转和中转HC的TUNEL染色阳性HC数较B组减少(P＜0.05),其中以D组减少最为明显.活性半胱氨酸蛋白酶-3抗体标记和TUNEL染色阳性的耳蜗HC凋亡的部位不完全重合.结论 GM可诱导离体培养的小鼠耳蜗HC凋亡的发生.应用IGF-1能够通过抑制其凋亡作用,在特定浓度达到最佳效果.半胱氨酸蛋白酶-3活化参与耳蜗HC凋亡过程.     

表没食子儿茶素没食子酸酯对噪声性耳蜗损伤的影响

目的 探讨表没食子儿茶素没食子酸酯(epigallocatechin-3-gallate,EGCG)对噪声性耳蜗损伤的影响.方法 45只豚鼠随机分为EGCG+噪声组、生理盐水+噪声组、正常对照组,每组15只.EGCG+噪声组和生理盐水+噪声组豚鼠在接受噪声暴露(120 dB SPL, 4 h)前一日及每次暴露前1 h分别腹腔注射EGCG(25 mg/1 000 g)和等量生理盐水,正常对照组不予任何处理.噪声暴露后即刻和第1、3、7、14天检测三组豚鼠听性脑干反应(ABR),第14天分离各组豚鼠耳蜗,行耳蜗基底膜、血管纹铺片及免疫组化染色,观察各组豚鼠耳蜗基底膜、血管纹细胞形态及外毛细胞运动蛋白(Prestin)、3-硝基酪氨酸(3-NT)分布的变化.结果 噪声暴露后,EGCG+噪声组各时间点的ABR反应阈均高于对照组,但低于生理盐水+噪声组,从第3天开始,与两组间ABR反应阈差异缩小,但差异仍有统计学意义(均为P<0.05).免疫组织化学染色显示,正常对照组Prestin蛋白显绿染的耳蜗三排外毛细胞排列整齐,无细胞缺失,3-NT主要分布于毛细胞胞质及表皮板;与生理盐水+噪声组相比,噪声暴露后,EGCG+噪声组豚鼠外毛细胞形态较好,Prestin染色清晰;基底膜、血管纹处损伤轻,细胞排列规则,3-NT分布减少.结论 预防性腹腔注射EGCG可减轻噪声引起的耳蜗损伤,对噪声性听力损伤有一定的防护作用.     

羊水干细胞拟胚体与耳蜗基底膜共培养向神经元分化的可行性

目的探讨人来源的羊水干细胞以拟胚体样结构与小鼠耳蜗基底膜组织共培养,分化为神经元的可行性。方法分离培养人来源的羊水干细胞,悬滴法培养,观察羊水干细胞拟胚体形成情况;免疫荧光检测拟胚体细胞干性标记物的表达;将拟胚体与小鼠基底膜组织共培养,不添加神经生长因子及神经元信号诱导因子,观察拟胚体向神经元分化情况。结果羊水干细胞经悬滴培养可形成拟胚体样结构,表达神经干细胞标记物Sox2、Nestin;与小鼠耳蜗基底膜组织共培养,拟胚体细胞有神经元标记物Tuj1表达,但无神经元形态特征。结论羊水干细胞体外悬滴后可形成形态均一且具有神经干性的拟胚体,与耳蜗基底膜组织共培养,不能诱导拟胚体细胞向形态典型的神经元分化。     

CBA小鼠内耳感觉上皮的参考数据

目的测量成年CBA小鼠耳蜗和前庭的有关数据,为内耳感受器定量分析提供参考依据。方法将6只出生后3个月左右的成年CBA小鼠(12耳)的耳蜗和前庭各终器取出并制备成全耳蜗基底膜铺片和全前庭终器铺片。测量全耳蜗基底膜的总长度,以及基底膜和Corti器在耳蜗不同部位的宽度。观察并记录全耳蜗毛细胞的总数和基底膜上不同区间的毛细胞密度。观察并记录椭圆囊斑和球囊斑毛细胞的总数及其微纹区和周边区的毛细胞密度,记录壶腹嵴上的毛细胞密度。结果正常成年CBA小鼠的耳蜗基底膜长度为(5.76±0.196)毫米(平均数±标准差,下同),基底膜的宽度在耳蜗底部距起始端约1.5毫米处为(339.1±9.87)微米,在耳蜗中部距起始端约3毫米处为(304.5±11.82)微米,在耳蜗顶部距起始端约5毫米处为(300.1±7.22)微米,说明小鼠耳蜗基底膜的宽度从底回到顶回逐渐变窄。Corti器的宽度在耳蜗底部距起始端1.5毫米处为(37.80±2.24)微米,在耳蜗中部距起始端约3毫米处为(45.00±2.67)微米,在耳蜗顶部距起始端约5毫米处为(52.20±3.16)微米,可见Corti器的宽度从底回到顶回逐渐变宽。CBA小鼠全耳蜗毛细胞的总数为(3116.41±151.91)个,其中内毛细胞总数为(680.67±17.50)个,而外毛细胞的总数是(2435.8±143.46)个。耳蜗内、外毛细胞的平均密度为(541.1±9.36)个/毫米,其中内毛细胞的平均密度为(118.3±2.68)个/毫米,外毛细胞的平均密度为(422.8±11.87)个/毫米,耳蜗毛细胞在耳蜗基底膜上不同区间的毛细胞密度无明显差异(P>0.05)。小鼠椭圆囊斑上的毛细胞总数为(3300±177.51)个,球囊斑上的毛细胞总数为(3045±361.57)个。前庭球囊斑和椭圆囊斑微纹区和周边区的毛细胞密度基本相同(P>0.05),两个囊斑微纹区的平均毛细胞密度为(40.2±6.59)个/0.0025mm2,两个囊斑周边区的平均毛细胞密度为(53.2±7.18)个/0.0025mm2,可见囊斑微纹区的毛细胞密度低于周边区。尽管小鼠上半规管和后半规管壶腹嵴的毛细胞区被位于嵴中央的上皮细胞分隔为两个区域,但三个壶腹嵴上的毛细胞密度基本相同,其平均密度为(44.7±7.15)个/0.0025mm2。结论本实验所得CBA小鼠耳蜗和前庭测量数据,为进一步定量观察CBA小鼠内耳病理学改变提供了重要的参考依据。     

听力学

20050684p27Kipl在不同时期大鼠耳蜗大上皮嵴的表达/汪学勇…//中华耳科学杂志·2005,3(1)·50~53目的:观察p27Kipl在不同时期大鼠耳蜗的大上皮嵴中的表达情况,探讨p27Kipl在毛细胞分化和再生过程中的作用。方法:对胚胎期12天、13天、14天、16天、18天、20天和出生后当天、2天、5天、7天、10天、14天等12个年龄段的大鼠耳蜗进行冰冻切片,然后以1:100抗p27Kipl小鼠单克隆抗体为一抗,1:900异硫氰酸荧光素标记山羊抗小鼠IgG为二抗,进行免疫荧光组织化学检查。结果:①胚胎期14天时,p27Kipl开始在蜗管表达,其表达限于原始柯蒂氏器。原始柯蒂氏…     

老年大鼠耳蜗毛细胞凋亡的信号通路

目的通过观察耳蜗基底膜毛细胞凋亡相关因子caspase-3、caspase-8和caspase-9表达的变化,揭示老年大鼠耳蜗毛细胞凋亡的信号通路。方法入选Fischer344大鼠27只,青年组12只,3～4月龄;老年组15只,20～27月龄。3种半胱氨酸天冬氨酸蛋白酶荧光标记青年大鼠耳蜗各8个,老年大鼠耳蜗各10个。应用电位反应测听仪检测不同频率短纯音(5、10、20和40kHz)诱发的青年和老年大鼠双侧听性脑干诱发电位反应阈值(ABR)。听觉功能测试后,用微量注射器分别将新鲜配制的3种半胱氨酸天冬氨酸蛋白酶荧光染色液缓慢注入动物内耳,耳蜗内灌注后1h,动物断头处死。采用细胞核DNA荧光染料碘化丙锭(PI)染色耳蜗基底膜细胞,荧光显微镜下观察不同月龄大鼠耳蜗基底膜毛细胞3种半胱氨酸天冬氨酸蛋白酶荧光染色的变化。结果老年大鼠的不同频率听性脑干反应阈值均高于青年对照组(P<0.05)。青年大鼠耳蜗毛细胞核周围未见3种半胱氨酸天冬氨酸蛋白酶阳性荧光标记物,老年大鼠耳蜗基底膜以核固缩为特征的凋亡外毛细胞核周围存在caspases-3和caspases-9绿色荧光标记物,未见caspases-8标记物。以核肿胀为特征的坏死外毛细胞核周围未见3种半胱氨酸天冬氨酸蛋白酶阳性荧光标记物。结论老年大鼠耳蜗毛细胞凋亡可能通过caspases-9相关的线粒体信号转导通路而不是cas-pases-8相关的死亡受体通路启动完成。     

Postnatal development of the organ of Corti in cats: a light microscopic morphometric study

This study quantitatively characterizes the development of the major morphological features of the organ of Corti during the first 2 weeks postnatal, the period when the cat auditory system makes the transition from being essentially non-functional to having nearly adult-like responses. Four groups of kittens (n=3) were studied at one day postnatal (P1), P5, P10, P15, and compared to adults. Measurements were made of the organ of Corti at 3 cochlear locations: 20%, 60% and 85% of basilar membrane length from the base – cochlear locations which in the adult correspond to best frequencies of ≈20 kHz, 2 kHz and 500 Hz, respectively. In addition, measurements of basilar membrane length and opening of the tunnel of Corti were made in 20 cochlear specimens from kittens aged P0–P6. Results indicate that: (i) at P0 the basilar membrane has attained adult length, and the tunnel of Corti is open over approximately the basal one-half of the cochlea; (ii) the initial opening of the tunnel of Corti occurs at a site about 4 mm from the cochlear base (best frequency of ≈25 kHz in the adult cochlea); (iii) the thickness of the tympanic cell layer decreases markedly at the basal 20-kHz location; (iv) the areas of the tunnel of Corti and space of Nuel and the angulation of the inner hair cells (IHC) relative to the basilar membrane all show marked postnatal increases at both the middle and apical locations; (v) IHC are nearly adult-like in length and shape at birth, whereas the OHC (at 2-kHz and 500-Hz locations) undergo marked postnatal changes; (vi) disappearance of the marginal pillars and maturation of the supporting cells are not yet complete by P15.     

Postnatal development of the organ of Corti in the wild house mouse, laboratory mouse, and their hybrid

Length of the basilar membrane, number and distribution of cochlear receptors, and the width of the triad of outer hair cells were analyzed in the course of the postnatal development and in adult individuals in wild and laboratory house mice and in hybrids of these species. While in newborn animals the triad of outer hair cells was wide at the base and narrow at the apex, the opposite was true for adult animals. The parameter decreased at the base and increased at the apex during postnatal development. The center of differentiation of (the reticular lamina of) the organ of Corti was localized at 40-50% of the basilar membrane length from the base and corresponded to the region with the maximum density of inner hair cells. The reticular lamina in the apical half of the cochlea matured earlier than in the basal half. Distribution of receptors did not change after birth. The shortest basilar membrane and the slowest rate of maturation were found in wild mice. Hybrids had the longest basilar membrane and the highest rate of maturation. These facts are considered an effect of heterosis.     

Differences in the distribution of F-actin in outer hair cells along the organ of Corti

There is evidence of differences in the structure, innervation and physiological responses between outer hair cells (OHCs) of the basal and apical turns of the mammalian cochlea. In this study we have used rhodamine-labelled phalloidin to investigate the differential distribution of F-actin in OHCs along the organ of Corti of the guinea pig. Isolated OHCs and surface preparations and cryosections of the organ of Corti were studied. F-actin was observed in stereocilia and the cuticular plate of all OHCs. In addition, some OHCs had a network of F-actin extending from the cuticular plate towards the nucleus. This infracuticular network was observed in most OHCs of the apical cochlear turns but was not seen in any OHCs of the basal turn. These microstructural differences between OHCs of the base and apex could be related to differences in OHC function between the apical and basal portions of the cochlea.     

Pathological findings in the human auditory system following long-standing gentamicin ototoxicity

Summary The clinical, audiovestibular and histopathological findings in a patient who suffered from a long-standing gentamicin-induced deafness are reported. In both temporal bones, the organ of Corti was completely absent, with only a few nerve fibres remaining in the apical part of the cochlea. Regenerative ingrowth of nerve fibers into the area of the degenerative organ of Corti was present apically in both ears. The stria vascularis exhibited considerable degeneration in all turns and loss of microvasculature was found in the basilar membrane. The spiral ganglion cells, the cochlear nerve and the central auditory pathways and nuclei appeared to be unaffected.     

Pathological findings in the human auditory system following long-standing gentamicin ototoxicity

The clinical, audiovestibular and histopathological findings in a patient who suffered from a long-standing gentamicin-induced deafness are reported. In both temporal bones, the organ of Corti was completely absent, with only a few nerve fibres remaining in the apical part of the cochlea. Regenerative ingrowth of nerve fibers into the area of the degenerative organ of Corti was present apically in both ears. The stria vascularis exhibited considerable degeneration in all turns and loss of microvasculature was found in the basilar membrane. The spiral ganglion cells, the cochlear nerve and the central auditory pathways and nuclei appeared to be unaffected.     

Hearing loss following exposure during development to polychlorinated biphenyls: a cochlear site of action

Maternal exposure to polyhalogenated hydrocarbons results in early postnatal hypothyroxenemia and a low-frequency hearing loss in adult offspring (Goldey et al., 1995a. Toxicol. Appl. Pharmacol. 135, 67-76; Herr et al., 1996. Fundam. Appl. Toxicol. 33, 120-128). The purpose of the present work was to determine whether the site-of-action of this auditory impairment was within the cochlea. Primiparous Long-Evans rats were given daily oral doses of corn oil (control) or 8 mg/kg of the commercial PCB mixture Aroclor 1254 (A1254) from gestation day (GD) 6 through postnatal day (PND) 21. Auditory thresholds for 1-, 4-, 16-, and 40-kHz tones were assessed using reflex modification audiometry in young adult offspring on postnatal days (PND) 92-110. Approximately 6 weeks after auditory assessments, a subset of animals (n=4 per group) were killed for histological assessment of the cochlea. Surface preparations of the organ of Corti were prepared from one cochlea per animal and modiolar sections were prepared from the opposite cochlea. Consistent with previous findings, auditory thresholds for 1-kHz tones were elevated by approximately 25 dB in the A1254-exposed animals. Thresholds for all higher frequencies were not different compared to controls. Surface preparations of the organ of Corti revealed a mild to moderate loss of outer hair cells in the upper-middle and apical turns. Inner hair cells were not affected. Modiolar sections failed to reveal alterations in any other cochlear structures. There was also no apparent loss of ganglion cells. These data clearly link the loss of low-frequency hearing caused by exposure during development to A1254 to a loss of outer hair cells in the organ of Corti. The mechanism that underlies this developmental ototoxicity remains to be determined. These data provide the first evidence of a structural deficit in the nervous system of adult animals exposed to PCBs during development.     

The organ of Corti in the bat Hipposideros bicolor

The bat Hipposideros bicolor (Hipposideridae, Microchiroptera) is the mammalian species with the highest upper limit of hearing in which the structure of the organ of Corti has been studied. H. bicolor emits pure tone echo-locating signals of 153 kHz, compensates for Doppler shifts in the echo and hears ultrasonic frequencies up to 200 kHz (Neuweiler et al., 1984). The organ of Corti was investigated qualitatively and quantitatively using the technique of semi-thin sectioning. Some complementary ultra-thin sections were also examined. Length, width and cross-sectional area of the basilar membrane, the tectorial membrane, the hair cells with their stereocilia and the organ of Corti were measured at equi-distant positions on the basilar membrane. The organ of Corti of H. bicolor is composed of elements similar to those found in the cochleae of other eutherian mammals studied. However, in H. bicolor some of these elements show species-specific differences when compared to auditorily unspecialized mammals. The most basal region of the cochlea is characterized by miniaturization and re-inforcement of macro- and micro-mechanically important elements. This is interpreted as an adaptation for hearing extremely high frequencies. Specialized structures as well as local maxima of 'normal' elements in the basal and middle cochlear region are associated with evaluation of the echos of emitted pure tones. Besides the basal specializations. Hipposideros also shows specializations in the apical, low frequency, region which can be correlated with passive acoustic orientation.     

Tubulin expression in the developing and adult gerbil organ of Corti

In the late stages of inner ear development, the relatively undifferentiated cells of Kollicker's organ are transformed into the elaborately specialized cell types of the organ of Corti. Microtubules are prominent features of adult cells in the organ of Corti, particularly supporting cells. To test the possible role of microtubules in organ of Corti development, the microtubule organization in the organ of Corti has been examined using indirect immunofluorescence to beta-tubulin in the developing gerbil cochlea. Tubulin first appears at post-natal day 0 (P0) as filamentous asters in inner hair cells and by P2, asters are also seen in outer hair cells. Tubulin appears at P3 in inner pillar cells in a tooth crown-like figure. By P6, tubulin expression is also evident in outer pillar cells and by P9, it is seen in Deiters cells. Elaboration of microtubules in pillar cells was observed to proceed from the reticular lamina towards the basilar membrane. The pattern of tubulin expression in the apical organ of Corti lags the base by about 3 days until P6, but by P9, apical and basal organ of Corti appear substantially the same.     

The ultrastructure of the basilar membrane in the cat

A detailed study of the feline basilar membrane was performed in 13 cochleae with light microscopy and in six with electron microscopy. The distribution of the mesothelial cells and homogeneous ground substance with the filaments was recorded and plotted as a function of length along the cochlear duct. The width, thickness and number of filaments were also measured. In the lower basal turn the basilar membrane was narrowest and its entire thickness was occupied by filaments. In the apical region the width was maximal and the filaments were fewer. The density of the filaments counted in the bundles showed no significant difference along the cochlear duct or across the width of the basilar membrane, but the number of filaments decreased markedly (approximately a ten-fold difference) from base to apex. The number of mesothelial cells increased towards the apex. These morphological characteristics may be related to the different motion pattern of the basilar membrane along the length of the cochlear duct. A discontinuity of the basement membrane was noted in the apical region in all cochleae studied. These gaps seemed to provide structural evidence for the permeability of the basilar membrane in this area. The vas spiralis was present as a blood vessel in two specimens and only in the apical region. Thus, its function as the sole nutritional source for the organ of Corti is doubtful.     

Adenylate cyclase and G-proteins as a signal transfer system in the guinea pig inner ear

In many eukaryotic cells G-proteins play a key role in signal transduction through outer cell membranes. To study this pathway in the auditory organ of mammals we examined tissue preparations from the stria vascularis and the organ of Corti from the guinea pig inner ear. The activity of adenylate cyclase was measured by stimulation at the site of the enzyme, the hormone receptors and the modulating G-proteins. In the organ of Corti we found a low enzyme activity in all cochlear turns. The stria vascularis, however, showed a constant high concentration of beta 2-adrenergic receptors and of stimulating G-proteins in all cochlear turns. In contrast, the activity of the enzyme increased from the apical to the basal turn. Adenylate cyclase could be stimulated or inhibited in a concentration-dependent manner by drugs selectively effecting the G-proteins. Our results suggest a structure of the adenylate cyclase complex in the inner ear similar to other organs. Pathophysiological correlations to hearing loss associated with pseudohypoparathyroidism are discussed.