Bistability in Ephaptic Coupling as a Possible Memory Element Explored through a Colloid Interptation of Stereocilia Bistability

When the processes of neurons are in close proximity they effectively couple to each other in a process termed Ephaptic coupling. This coupling occurs without the membranes touching when the space between them is some tens of nanometers. If the intra-membrane spacing has a mechanical bistability, which moves the membranes closer and further apart, the Ephaptic coupling will be turned on and off allowing one neuron to read, or not read the content of the other. This paper explores the possibilities of bistable ephaptic memory element by a study of an analogous system that operates at a much larger scale, the Stereocilia of the hair cell. Published measurement of hair cell Stereocilia force/displacement function shows both a negative slope region in the displacement function and tendency to express bistability. We show here how this negative slope region can arise through the exigency of colloid forces. An explanation of Colloid Theory, presented in a graphic form, shows how a colloid force function can be modified to match the measured hair cell cilia force function. The colloid force function is modified by a limiting function resulting from Stereocilia side links, structural details that tie together the hair cell Stereocilia clusters. Understanding how a limited, simple behavior such as Stereocilia bistability functions may point to a more general understanding of how bistability may underlie other areas of living organisms such as memory and computation.

Tprn is essential for the integrity of stereociliary rootlet in cochlear hair cells in mice

Tprn encodes the taperin protein,which is concentrated in the tapered region of hair cell stereocilia in the inner ear.In humans,TPRN mutations cause autosomal recessive nonsyndromic deafness(DFNB79)by an unknown mechanism.To determine the role of Tprn in hearing,we generated Tprn-null mice by clustered regularly interspaced short palindromic repeat/Cas9 genome-editing technology from a CBA/CaJ background.We observed significant hearing loss and progressive degeneration of stereocilia in the outer hair cells of Tprn-null mice starting from postnatal day 30.Transmission electron microscopy images of stereociliary bundles in the mutant mice showed some stereociliary rootlets with curved shafts.The central cores of the stereociliary rootlets possessed hollow structures with surrounding loose peripheral dense rings.Radixin,a protein expressed at stereocilia tapering,was abnormally dispersed along the stereocilia shafts in Tprn-null mice.The expression levels of radixin andβ-actin significantly decreased.We propose that Tprn is critical to the retention of the integrity of the stereociliary rootlet.Loss of Tprn in Tprn-null mice caused the disruption of the stereociliary rootlet,which resulted in damage to stereociliary bundles and hearing impairments.The generated Tprn-null mice are ideal models of human hereditary deafness DFNB79.

Characteristics of echolocating bats’auditory stereocilia length, compared with other mammals

The stereocilia of the Organ of Corti in 4 different echolocating bats, Myotis adversus, Murina leuco-gaster, Nyctalus plancyi (Nyctalus velutinus), and Rhinolophus ferrumequinum were observed by using scanning electron microscopy (SEM). Stereocilia lengths were estimated for comparison with those of non-echolocating mammals. The specialized lengths of outer hair cells (OHC) stereocilia in echolocating bats were shorter than those of non-echolocating mammals. The specialized lengths of inner hair cells (IHC) stereocilia were longer than those of outer hair cells stereocilia in the Organ of Corti of echolocating bats. These characteristics of the auditory stereocilia length of echolocating bats represent the fine architecture of the electromotility process, helping to adapt to high frequency sound and echolocation.

Myosin XVA:dancing at the tips of the stereocilia

Myosins comprise a large superfamily of adenosine triphosphatases(ATPases)that interact with actin filaments to generate motility or force.Unconventional myosins are implicated in diverse cellular processes including organelle trafficking,F-actin organization and cell movement.The unconventional myosin,myosin XVA(MYO15A),is localized at the tips of stereocilia in the inner ear hair cells and plays important roles in the development and maintenance of stereocilia.Mutations in MYO15A/Myo15a genes are responsible for hearing loss DFNB3 and shaker-2 in human and mice,respectively.In the present review,we will discuss the expression and alternative splicing of the MYO15A gene,the biochemical properties of the MYO15A protein and the association of MYO15A mutations with hearing loss.We will also discuss the recent investigations into the mechanism of how MYO15A regulates stereocilia development and maintenance.At present we are just beginning to appreciate the important roles of MYO15A in stereocilia,and further investigations are warranted to fully understand them.

The role of Rho GTPase family in cochlear hair cells and hearing

Rho GTPases are essential regulators of the actin cytoskeleton.They are involved in various physiological and biochemical processes such as the regulation of cytoskeleton dynamics,development,proliferation,survival,and regeneration.During the development of cochlear hair cells,Rho GTPases are activated by various extracellular signals through membrane receptors to further stimulate multiple downstream effectors.Specifically,RhoA,Cdc42,and Rac1,members of the classical subfamily of the Rho GTPase family,regulate the development and maintenance of cilia by inducing the polymerization of actin monomers and stabilizing actin filaments.In addition,they also regulate the normal morphology orientation of ciliary bundles in auditory hair cells,which is an important element of cell polarity regulation.Moreover,the actin-related pathways mediated by RhoA,Cdc42,and Rac1 also play a role in the motility of outer hair cells,indicating that the function of Rho GTPases is crucial in the highly polar auditory sensory system.In this review,we focus on the expression of RhoA,Cdc42,and Rac1 in cochlear hair cells and how these small molecules participate in ciliary bundle morphogenesis and cochlear hair cell movement.We also discuss the progress of current research investigating the use of these small molecules as drug targets for deafness treatment.

盖膜与内毛细胞静纤毛相互作用的生物力学分析

目的探讨在Corti器振动过程中盖膜与内毛细胞静纤毛的相互作用关系;进一步阐明感音传导过程中,内耳Corti器微观结构可能的存在状态。方法以豚鼠耳蜗底回Corti器的电镜图像为原型,建立盖膜与内毛细胞最长静纤毛接触和不接触的两种二维计算模型各一个,并作力学分析比较。结果模拟Corti器振动过程,在相同剪切流的压力作用下,静纤毛在不接触盖膜时表现偏移度较大;两种模型均表现在静纤毛顶连接及小根基部应力较高、固有频率近似。结论静纤毛在不与盖膜直接接触时更容易受兴奋性刺激。

豚鼠耳蜗毛细胞静纤毛的扫描电镜观察

目的 了解耳蜗毛细胞正常和变异静纤毛的形态特征。 方法 用扫描电镜观察了 2 5 4只豚鼠的耳蜗。 结果 豚鼠耳蜗毛细胞静纤毛正常和几种变异的形态特征为 :1.外毛细胞静纤毛排列不规则及静纤毛的自然缺失 ;2 .外毛细胞静纤毛束转位 ;3.外毛细胞静纤毛副毛与列外内毛细胞。 结论 外毛细胞静纤毛排列不规则和静纤毛的自然缺失不是病理变化。外毛细胞静纤毛束转位 ,静纤毛副毛与列外内毛细胞是遗传变异引起的。

出生后大鼠听毛细胞纤毛发育过程

目的观察新生大鼠(P1、P7、P14、P21)耳蜗Corti器的形态结构及排列方式,以便了解听毛细胞纤毛发育的过程。方法取新生SD大鼠四个阶段的耳蜗,采用扫描电镜对出生后大鼠耳蜗Corti器形态结构进行系统观察。结果发现这四个阶段在体大鼠耳蜗毛细胞从出生至毛细胞完全发育成熟,绝大部分都是以一排内毛细胞和三排外毛细胞的方式排列的,只有少部分在局部发现多出几个外毛细胞形成第四排。毛细胞的形态结构及排列方式随着时间的改变逐渐发育成熟。P14这个阶段是个重要的时期,Corti器表面柱细胞头板增宽,表面的微绒毛减少,Deiter细胞表面微绒毛也减少,动纤毛从底圈至顶圈逐渐退化已经基本结束,P14这个阶段Corti器各个部分发育已经完全成熟。结论出生后14天之内,大鼠听毛细胞静纤毛和动纤毛与听器其他细胞形态结构仍不同程度地处于由不成熟到成熟的逐渐发育过程,为研究大鼠出生后Corti器的发育、听觉功能的建立和完善提供了比较可靠的形态学证据。

蝙蝠耳蜗Corti器的电子显微镜观察

目的研究蝙蝠耳蜗基底膜毛细胞及静纤毛的特化现象。方法扫描电镜和透射电镜观察三种蝙蝠耳蜗毛细胞及静纤毛的表面亚显微结构形态。结果外毛细胞静纤毛特别的短,外毛细胞体呈瓶状或哑铃状,外毛细胞体被Deiters细胞的杯状膜包裹。结论我们观察到三种蝙蝠耳蜗外毛细胞体基本呈烧瓶状和哑铃状,明显有别于其他哺乳类耳蜗外毛细胞呈圆柱型的形态。这种毛细胞体的独特形态,可能是蝙蝠为适应高频回声定位的需要出现的特化现象。

豚鼠耳蜗盖膜的扫描电镜观察

目的为了更好地理解耳蜗盖膜在听觉产生过程中的作用。方法用扫描电子显微镜观察豚鼠耳蜗盖膜的超微结构。结果在盖膜上表面观察到许多纤维网,相应与内毛细胞静纤毛顶部接触的部位有一条带状结构,在耳蜗的基底圈盖膜的下面观察到外毛细胞静纤毛的压迹,外毛细胞静纤毛的W型印在盖膜下面也形成W型的压迹。结论根据扫描电镜观察的结果讨论了盖膜与内、外毛细胞之间的接触在听力形成的作用。

人Corti's器扫描电镜观察

目的 了解正常人Corti’s器的超微结构特征。方法 用扫描电镜观察成年人和胎儿的Corti’s器。结果成人和胎儿Corti’s器基底圈内、外毛细胞排列规则,中圈和顶圈毛细胞排列不规则,内毛细胞以一排,外毛细胞以三排排列。可观察到列外的内、外毛细胞,四排排列和自然缺失的外毛细胞。外毛细胞粗大的静纤毛以及由于固定不及时引起的外毛细胞静纤毛气球样改变。结论 用扫描电镜观察成人和胎儿Corti’s器的精细结构,发现了毛细胞排列的基本规律和一些异常的形态。及时固定是保存Corti’s器结构完好的必要条件。

鸡卡那霉素耳中毒后听功能恢复不全的形态基础

目的 探讨鸡卡那霉素耳中毒后听功能恢复不全的形态基础。方法 将 3天龄罗曼鸡按 2 0 0mg·kg-1·d-1连续肌注卡那霉素 10天 ,分别于施药第 8天、停药后 1、7、15、30、6 0天时处死 ,对照组动物不给予任何药物。动物处死前先用半正弦波 (40 0 0Hz)刺激行ABR检查 ,完毕后取颞骨 ,行扫描电镜标本制作及观察。结果 鸡ABR阈移于施药完毕时达到极限 ,停药后即开始恢复 ,停药后 7天时 ,ABR阈值有明显恢复 ,停药后 15天时 ,其ABR阈值已接近正常 ,但直至停药后 2个月时 ,ABR阈值仍有 15dBSPL未能完全恢复。扫描电镜所见 ,施药完毕时 ,鸡基底乳头近端 4 0 %区域内毛细胞完全破坏消失 ,并见毛细胞再生修复现象 ,停药后 7天时 ,毛细胞形态有成熟 ,其表皮板增大 ,表面静纤毛丛排列成阶梯样 ,停药后 15天时 ,基底乳头损伤区域已基本修复 ,大多数再生毛细胞已基本成熟 ,但直至停药后 2月时其静纤毛丛极向仍未完全恢复正常。结论 鸡卡那霉素耳中毒后 。

LOWER DOSE OF AMINOGLYCOSIDE OTOTOXIC EXPOSURE CAUSES PRESYNAPTIC ALTERATIONS ASSOICATED WITH HEARING LOSS

Objective To study presynaptic alternations of cochlear ribbons arising from aminoglycoside ototoxic stimuli in C57BL/6J mice. Methods Animals were injected with low dose gentamicin (100 mg/kg/day) for 14 days, From the 14th to 28th days, the mice were maintained free of gentamicin treatment. Immunohisto-chemistry labeling was employed to trace RIBEYE, a major presynaptic componment of ribbon synapses. RIBEYE/CtBP2 expression levels were assessed and compared with hearing threshold shifts. Auditory func-tion was assessed by auditory brainstem responses. The stereocilia of outer hair cells (OHCs) and IHCs was examined by scanning electron microscopy (SEM). Results Hearing thresholds were elevated with peak hearing loss observed on the 7th day after gentamicin exposure, followed by improvement after the 7th day. RIBEYE/CtBP2 expression directly correlated with observed hearing threshold shifts. Strikingly, we did not see any obvious changes in stereocilia in both OHCs and IHCs until the 28th day. Mild changes in stereocil-ia were only observed in OHCs on the 28th day. Conclusions These findings indicate that presynapse co-chlear ribbons, rather than stereocilia, may be sensitive to aminoglycoside ototoxic exposure in mice cochle-ae. A pattern of RIBEYE/CtBP2 expression changes seems to parallel hearing threshold shifts and suggests presynaptic response properties to lower dosage of aminoglycoside ototoxic stimuli.

耳蜗毛细胞静纤毛束生后发育的实验研究

本文对一系列生后不同年龄小白鼠耳蜗毛细胞静纤毛束发育进行形态学观察、发现其发育过程基本呈现4个阶段、各阶段都伴数量、长度及交联结构等方面的变化,本结果有助于对哺乳动物毛细胞静纤毛形态发育及此过程中结构-功能关系的进一步理解。

回声定位蝙蝠耳蜗听黄斑区毛细胞形态研究

目的观察蝙蝠耳蜗听黄斑毛细胞的特化形态结构,以探讨听黄斑区毛细胞对蝙蝠回声定位回声频率的敏锐调谐、放大和频率选择的作用。方法选用听力正常的蹄蝠(22只)、菊头蝠(64只)和犬吻蝠(10只),分别检测其ABR各频率反应阈,对耳蜗基底膜毛细胞进行扫描电镜和透射电镜观察。结果三种蝙蝠ABR反应阈值除最佳频率外,均在35 dB SPL以上,菊头蝠、蹄蝠、犬吻蝠反应幅值最大及最敏锐调谐频率分别为83～86、60～62、20～28 kHz。回声定位蝙蝠耳蜗听黄斑区外毛细胞胞体(OHC)呈纺锤形或烧瓶形,明显不同于非回声定位哺乳动物的长圆柱形外毛细胞形态。结论回声定位蝙蝠耳蜗听黄斑OHC的形态特化特征支持其OHC作为耳蜗阻尼机制的结论,OHC的这种形态特化与其他耳蜗微机械结构的匹配有利于耳蜗前行波的传导。

豚鼠耳蜗盖膜下面的超微结构

目的利用扫描电镜技术详细地观察豚鼠盖膜下的超微结构,为耳蜗的感音机制提供新的认识。方法用S-4800型超高分辨率扫描电子显微镜观察了6只豚鼠12只耳蜗的盖膜。结果 (1)耳蜗各圈盖膜下面均可观察到外毛细胞静纤毛压迹,这种压迹多半与静纤毛最高排的形态一致,第一圈呈"W"型,由基底圈到顶圈,逐渐由"W"型渐变为"V"型及不规则的簇状。压迹为一排圆形的小凹,将盖膜下表面表层辐射状纤维断开,只有最高排的静纤毛才与盖膜接触形成压迹,压迹排列呈串珠一样。(2)盖膜下内毛细胞相应的位置有一条较深的波浪状沟槽,呈线性结构,沟槽比外毛细胞静纤毛的压迹浅而宽,由耳蜗的基底圈到顶圈这种压迹逐渐呈带状。(3)盖膜下的纤维由盖膜的外缘到盖膜与内毛细胞静纤毛压迹之间以蜗轴呈辐射状排列,但在外毛细胞静纤毛压迹的位置被这些压迹所阻断,而总的辐射方向和纤维走行并没有改变,纤维非常的精细,每根纤维之间又相互交错相连。内、外毛细胞压迹之间,柱细胞顶部的盖膜纤维很细,均匀呈细丝状。而内毛细胞与螺旋缘之间,即内沟上方的盖膜下方的纤维更加细长。结论通过对盖膜超微结构的观察,盖膜下内外毛细胞静纤毛的压迹充分说明毛细胞静纤毛与盖膜的接触。盖膜下的纤维由盖膜的外缘到柱细胞和柱细胞到盖膜下内毛细胞静纤毛带状压迹之间也就是内、外毛细胞压迹之间,柱细胞顶部的盖膜的纤维与内毛细胞顶部盖膜带状结构到螺旋缘之间的纤维的粗细都不一样。这种纤维的分布特点,可能与盖膜在声音调谐方面所起的作用有一定的关系。

耳蜗中tip-link张力与静纤毛运动动力学研究

诠释耳蜗的主动感音放大机制一直是未解的医学难题.这种机制与耳蜗中外毛细胞顶端的静纤毛运动密切相关,静纤毛运动又受到tip-link张力与淋巴液流体力的调节.因此,研究静纤毛运动过程中tip-link张力是诠释耳蜗的主动感音放大机制的重要环节.本文把静纤毛视为变形体,基于泊肃叶流动理论并结合分布参数模型,推导了静纤毛运动的解析解.研究了盖膜剪切荷载作用下静纤毛和淋巴液相互作用的动力响应以及tip-link张力的变化规律.研究发现:当静纤毛的杨氏模量减小时,在小于峰值频率的区域,tip-link张力显著增大,f_(2)的峰值频率减小.以往的研究将静纤毛作为刚体,势必导致低频声音信号作用减弱.当系数c=0(无黏性阻力)时,f_(2)频率选择特性存在;当μ=0(无压力)时,f_(2)频率选择特性消失,因此淋巴液可能是通过在静纤毛间产生压强的方式来调节毛束的频率特性的.另外,盖膜剪切荷载频率越高,静纤毛轴弯曲越明显,发束内外域的压强差也越大.

Mechanical model of organ of Corti

According to the vibration characteristics of the organ of Corti （OC）, seven hypotheses are made to simplify the structure of the model, and a mechanical OC model is established. Using the variational principle, a displacement analytical expression is solved under a certain pressure. The results are in good agreement with experimental data, showing the validity of the formula. Combined with the damage caused by noise in clinic, it is found that the hardening of outer hair cells and outer stereocilia can lead to loss of hearing and generation of threshold shift. In addition, the results show that high frequency resonance occurs at the bottom of the basilar membrane （BM）, and low frequency resonance occurs at the top of the BM. This confirms the frequency selective characteristics of the BM. Further, using this formula can avoid interference of the envi- ronment and the technical level of the test personnel, and can evaluate performance of the OC objectively.

PTPRQ基因的内耳功能及突变致聋机制的研究进展

受体型蛋白酪氨酸磷酸酶Q(Receptor type protein tyrosine phosphatase Q,PTPRQ)作为一种蛋白酪氨酸磷酸酶,能催化不同的底物,参与多种细胞内的功能。PTPRQ基因突变可导致常染色体隐性和显性非综合征性耳聋DFNB84A型和DFNA73型耳聋的发生,两型耳聋的临床表型差异提示了其致病机制的不同。在内耳,PTPRQ主要位于前庭及耳蜗毛细胞纤毛基底部,参与耳蜗毛细胞纤毛束的成熟,对维持纤毛的形态和功能具有重要作用。目前世界上报道的与PTPRQ突变相关的耳聋家系有14个,多数隐性突变是因截短或缺失而影响了PTPRQ的酶结构域的功能,但是PTPRQ的显性突变致病机理仍不清楚。有关该基因显、隐性突变致病机制的更深入研究可为相关病例的针对性干预提供理论依据。

DBA/2J小鼠耳蜗毛细胞静纤毛早期的形态结构变化

目的:观察低周龄DBA/2J小鼠耳蜗毛细胞静纤毛形态结构的变化,探讨DBA/2J小鼠早期听力受损的原因。方法:检测DBA/2J小鼠2、4周龄和8周龄听觉脑干反应,扫描电镜下观察耳蜗底回毛细胞静纤毛的形态结构特征。结果:听觉脑干反应显示DBA/2J小鼠在4周龄后表现为渐进性的听力受损。扫描电镜可见2周龄时高倍镜下纤毛束融合并伴有纤毛束软化,4周龄时纤毛束融合、软化和倒伏更为严重,8周龄低倍镜下纤毛束缺失数目较多,尚存纤毛融合倒伏更为严重。结论:DBA/2J小鼠耳蜗毛细胞静纤毛出现纤毛束融合、软化、弯曲、倒伏甚至缺失,可能是导致其早发性听力受损的主要原因。