Glycerol effect on the guinea pig tectorial membrane

Summary The tectorial membrane (Tm) of guinea pigs has been found to have an altered organization of its matrix fibers in response to intravenously administered glycerol. Following treatment, the Tm middle zone shows an increase in waviness and clumping of fibers in nonhydropic and several hydropic ears in contrast to nontreated control ears. Residue of the internal sulcus cells occasionally fills the subtectorial space. In the present study, additional investigations were performed with scanning electron microscopy in order to study the relationship between the Tm and the organ of Corti, as well as the relationship between Hensen's stripe and the inner hair cell. Present findings provide evidence for a connection between the inner hair cell stereocilia and Hensen's stripe which may be the molecular basis for the modulation of hearing during the glycerol test in a patient with Meniere's disease. Correspondence to: A. M. Meyer zum Gottesberge     

Regeneration of the tectorial membrane in the chick cochlea following severe acoustic trauma

Damage to the tectorial membrane caused by acoustic trauma was examined with scanning and transmission electron microscopy immediately after exposure and at selected time points over a 10 day recovery period. At 0 h of recovery the structure of the tectorial membrane overlying the region of hair cell damage was severely disrupted and connections between the membrane and the basilar papilla were lost. By 24 h of recovery, regeneration of the tectorial membrane was evident in the secretion of new matrix materials by the supporting cells of the basilar papilla. By 10 days of recovery a new honeycomb-like matrix had replaced the segment of damaged tectorial membrane, re-established connections with hair cell stereocilia and become fused with adjacent regions of undamaged tectorial membrane. However, the regenerated segment included only the honeycomb-like structure of the lower layer of the normal tectorial membrane. The laterally-oriented fibers which form the upper layer of the membrane were not regenerated over the damaged region. These findings indicate that the tectorial membrane is regenerated in parallel with the hair cells during recovery from acoustic trauma but the full extent of this recovery and its effect on cochlear function are not yet clear.     

Secretion of a new basal layer of tectorial membrane following gentamicin-induced hair cell loss

Scanning electron microscopy (SEM) and video-enhanced DIC light microscopy were used to assess morphological changes in the chick tectorial membrane (TM) following gentamicin-induced hair cell loss. Gentamicin was administered (100 mg/kg/day for 3 days) and isolated and in-situ TMs were examined in both fixed and unfixed preparations at days 5 and 10 after the initial injection. Although this protocol induced hair cell damage extending up to 75% of the length of the basilar papilla, there was no apparent damage to the TM itself. However, the ejection of damaged hair cells appeared to sever the filamentous attachments between the TM and the apical surface of the basilar papilla. In SEM preparations this detachment caused the TM to shrink back toward the superior edge. Interestingly, despite the lack of TM damage, gentamicin treatment did reveal the secretion of a new basal layer of TM. Secretion of this new basal layer had begun by day 5 and it was well organized by day 10. This new layer formed attachments to both the recovering basilar papilla and the overlying original TM, a step thought to be necessary for the restoration of auditory function in the regenerating cochlea.     

Contact between the tectorial membrane and the cochlear sensory hairs in the human and the monkey

European Archives of Oto-Rhino-Laryngology - The surface structure of the organ of Corti and the overlying tectorial membrane were studied in human and monkey cochleas under a scanning electron...     

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.     

鸡内耳盖膜的超微结构观察

为了解鸟纲内耳盖膜的超微结构及其与毛细胞、支持细胞的关系，应用扫描电镜和透射电镜对鸡内耳盖膜的超微结构进行观察。发现：扫描电镜下盖膜横断面呈三角形，内有许多空洞，内淋巴面呈网状；透射电镜下见盖膜由微丝及肢状基质构成，听毛细胞的最高排静纤毛及动纤毛插入盖腹中，支持细胞的微绒毛通过絮状细丝与盖膜呈锚状连接。这种连接既有弹性又十分牢固，可在一定范围内限制盖膜运动。由此推测鸟纲内耳与哺乳纲内耳在感受声刺激的方式上有所不同。     

Iontophoresis with an adrenergic alpha-blocker in acoustic overstimulation

Summary To study the influence of sympathetic innervation on the amount of threshold shift (TS) induced by sound overstimulation, iontophoresis with phentolamine, a known adrenergic alpha-blocker, was performed on awake guinea pigs. The sound exposure following this induced a significantly lesser degree of TS when compared with the control group. These findings indicate that iontophoresis may be of great help in transporting specific ionized chemical compounds through the intact cochlear walls in a completely non-invasive manner for studying cochlear physiology.     

Hereditary deafness in the cat: An electron-microscopic study of the tectorial membrane

Summary The tectorial membrane is affected at an early stage of the cochlear degeneration in the hereditarily deaf white cat. The membrane first descends towards the organ of Corti with obliteration of the intervening sub-tectorial space in the basal coil during the second post-natal week. Both the microvilli of supporting and Hensen's cells, and the hair cell stereocilia make deep indentations on the under-surface of the membrane. Cells are found insinuated between the tectorial membrane and Corti's organ, and numerous cellular processes occur within the former. A phagocytic function would appear probable for these cells, which seem to originate from the internal sulcus region. The membrane is retracted into the latter around the 2-month stage. At all ages, small spherical structures, which may represent altered interdental cell secretions, are found within the membrane, these becoming calcified in older animals.This investigation has been supported by the Norwegian Research Conncil for Science and the Humanities through grant C.37.59-1     

Ultrastructural organization of proteoglycans and fibrillar matrix of the tectorial membrane

The molecular and supramolecular structure of the tectorial membrane (TM) was studied by transmission electron microscopy (TEM). Collagen (type A) fibrils in the TM were found associated with proteoglycans (PGs) and type B fibrils. Most PGs were orthogonally oriented and attached D-periodically to collagen fibrils. Computer averaged projections of PG particles and linear aggregates of PGs in crystalline arrays, stained with Cuprolinic blue, showed an elongated, electron-dense structure 50–65 nm in length and 10 nm in width. Image analysis of type B fibrils showed that they are constructed of globular domains arranged with a periodicity of 12–14 nm. Each globular domain contains two thin ‘arms', extended in opposite directions, which contact the ‘arms' of adjacent fibrils. Numerous type B fibrils were found between collagen fibrils. They are attached to adjacent collagen fibrils by the ‘arms' of their globular domains. An association of type B fibrils and PGs with collagen seems to result in the local ordered arrangement of the TM matrix. A hypothetical model of the TM matrix supramolecular structure is presented.     

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.     

Localization of the marginal zone of the tectorial membrane in situ,unfixed, and with in vivo-like ionic milieu

Summary In order to determine the normal positional relationship between the tectorial membrane and the organ of Corti, a preparation method was developed which made it possible to study the unfixed tectorial membrane in its normal position in relation to the cochlea and with in vivo-like ionic conditions. With this method, post-mortem changes visible with the light microscope were detectable after 60 to 90 min instead of the normal 30 min.When endolymph or artificial endolymph are present in the scala media, the marginal zone lies in close contact with the surface of the organ of Corti. If the endolymph is replaced by artificial perilymph, first the marginal zone of the tectorial membrane, and later the whole membrane shrinks. At this stage, latex particles suspended in the perilymph are free to enter the subtectorial space.This work was carried out in the Sonderforschungsbereich 50 Kybernetik München, which is supported by the Deutsche Forschungsgemeinschaft.     

Static material properties of the tectorial membrane: a summary

The tectorial membrane (TM) is a polyelectrolyte gel. Hence, its chemical, electrical, mechanical, and osmotic properties are inextricably linked. We review, integrate, and interpret recent findings on these properties in isolated TM preparations. The dimensions of the TM in alligator lizard, chick, and mouse are sensitive to bath ion concentrations of constituents normally present in the cochlear fluids – an increase in calcium concentration shrinks the TM, and an increase in sodium concentration swells the TM in a manner that depends competitively on the calcium concentration. The sodium-induced swelling is specific; it does not occur with other alkali metal cations. We interpret these findings as due to competitive binding of sodium and calcium to TM macromolecules which causes a change in their conformation that leads to a change in mechanical properties. In mouse TM, decreasing the bath pH below 6 or increasing it above 7 results in swelling of the TM. Electric potential measurements are consistent with the notion that the swelling is caused by a pH-driven increase in positive fixed charge at low pH and an increase in the magnitude of the negative fixed charge at high pH which is consistent with the known protonation pattern of TM macromolecules. Increasing the osmotic pressure of the bathing solution with polyethylene glycol shrinks the TM and decreasing the ionic strength of the bathing solution swells the TM. Both results are qualitatively consistent with predictions of a polyelectrolyte gel model of the TM.     

Observations of the sensing and the tectorial membrane in bullfrog amphibian papilla: Their possible functional roles

Three dimensional reconstructions of the amphibian papilla were performed with light microscopic observations, mainly for the sensing membrane (SM). In horizontal sections of the papilla, the anteromedial end of the SM, which makes contact with the massive anterior portion of the tectorial membrane (TM), is several times thicker than the posterolateral end close to the column of the innervating nerves. This gradient of thickness is observed in all the sections from the dorsal portion attached to the TM to the ventral floor of the papilla. The SM connects to the TM in a topological manner; the anteromedial portion of the TM relates to the anterior end of the SM and the anterolateral and the middle portions of the TM correspond to the sites shifting posteriorly on the SM. The morphology of the SM and its manner of connection to the TM suggest that the SM plays important roles in the occurrence of frequency selectivity and of tonotopic organization of the amphibian papilla.     

A comparison of initial and permanent surface changes to guinea pig hair cells after acoustic overstimulation

Summary Groups of pigmented guinea pigs were exposed unilaterally to a 15 kHz pure tone at 133 dB SPL for 7.5 min. The inner ears of one group were examined by light microscopy to count damaged hair cells 3 weeks after exposure. Four other groups were investigated using scanning electron microscopy to assess the progression of initial surface changes after sound exposure. Hair cells were examined at 0, 10 and 30 min and compared with those seen at 3 weeks. Drastic stereociliary disturbances were present immediately after this short sound stimulation. Changes initially affected the first row of outer hair cells, followed by the inner hair cell row, and then spread to all rows at the centre of a damaged area. These changes appeared more advanced in specimens from the later groups. At 3 weeks, primarily phalangeal scars were seen at the main damaged area, with partially degenerating cells at the periphery. The latter still showed stereociliary disturbances, but the types predominating were different from those seen initially. However, no differences were found in the extents of damage when the various exposure groups were compared. No changes due to overstimulation were present in the contralateral ears.     

The tectorial membrane of mammals

Cochlear damage immediately following exposure to continuous pure tones of varying intensity and duration was assessed in anaesthetized guinea pigs. Indices of damage used were elevation of N₁ thresholds and severity of swelling of the afferent dendrites beneath the inner hair cell. The results were not wholly consistent with the assumptions of the equal energy principle. Longer duration exposures resulted in greater N₁ threshold elevation and more severe swelling of dendrites than short exposures of the same total energy.     

The surface morphology of the avian tectorial membrane

The structure of the tectorial membrane of the chick was evaluated by scanning electron microscopy (SEM), using standard techniques, and, for the first time, by studying unfixed tectorial membranes with video-enhanced light microscopy techniques (AVEC-DIC). The SEM pictures show a widely varying morphology, ranging from a fully perforated tectorial membrane to a completely closed upper boundary, with a smooth surface. Based on several indicators, it is concluded that the latter presents the more natural state. This was confirmed by the results of the AVEC-DIC technique, which show a highly homogeneous structure. In contrast to the bulk of the tectorial membrane, its lower surface shows discrete structures, especially regularly oriented fibril bundles.     

Donnan equilibrium in the tectorial membrane

Basic properties of the isolated tectorial membrane were investigated. Pieces of the membrane were equilibrated in various bathing fluids and the potential difference between the matrix of the membrane and the bathing fluid was measured, using micropipette electrodes. A negative potential was recorded within the membrane, and the magnitude of the potential was dependent upon the pH and ionic strength of the bathing fluid. These observations suggest that a Donnan equilibrium is established under these experimental conditions, and demonstrate that the tectorial membrane acts as a separate phase in vitro. It may not be valid, therefore, to assume that the membrane is electrically and ionically transparent in vivo.     

Development of the embryonic chick's tectorial membrane

The nascent tectorial membrane (TM) is identifiable as early as stage 33 (7th day) as thin, wispy material. By stage 37 (11th day), the dense mesh of the immature TM and fibrous webs (subtectorial threads) that attach the TM to the basilar papilla are distinct but scanty. The TM condenses slightly in its upper face. The growth of the columnar cells and basilar papilla during the following days pulls the TM, lifting it upward, and resembling the cables on a suspension bridge in cross-section. As a result, a large hollow wedge forms. During stages 40-44 (14th-18th days), the columnar cells secrete large amounts of fibrous material, which fills the hollow wedge and condenses into the dense meshes. The honeycombed patterns appear at this time. The supporting cells secrete the fibrous webs. Their secretory activity closely corresponds to that of the columnar cells. The secretory material from both cell types remains attached to the apical ends of their respective cells after secretory activity ends. By hatching (stage 46-21 days), the columnar cells have filled with fibrous material and their cytoplasmic organelles are restricted to the apices. The cytoplasm of supporting cells is relatively clear, with few cytoplasmic remnants of their intense secretory activity earlier.     

直流电脉冲刺激豚鼠耳蜗基底膜振动研究

为了在活体上研究哺乳类动物耳蜗基底膜的电－机械特性，将一对铂－铱电极分别置于３０只豚鼠耳蜗底回的前庭阶和鼓阶。用矩形直流脉冲电刺激蜗管，用激光多普勒测速仪测定电刺激诱发的耳蜗基底膜振动的幅度和速度。结果表明，在听敏度正常豚鼠的耳蜗，电刺激可诱发基底膜向正电极方向位移，其位移波形类似于电脉冲的矩形波。在矩形脉冲的起始沿和结束沿，由于外毛细胞的瞬态反应，可诱发与该部位特征频率一致的共振运动。据分析，这一共振运动是外毛细胞的主动耗能过程，并由耳蜗放大器参与。在听力受损的耳蜗，直流电刺激仍能引起基底膜的位移，但振铃运动明显减少或消失。这可能是受损毛细胞的能量代谢障碍所致。直流电刺激诱发的基底膜振动与声波一样，可通过行波沿基底膜向其它部位传输，这一特性奠定了电听觉和耳声发射的生理基础。     

Damage of the basilar membrane by acoustic stimulation

Summary Sound exposures of more than 130 dB lead to typical tears in the basilar membrane in the area of maximal damage. The position, size, and number of these tears are evaluated.