Incorporation of palmitic acid in the organ of Corti as revealed by autoradiography

The sites of incorporation of [3H]palmitic acid perfused through the scala tympani of the guinea pig cochlea were localized autoradiographically. The most active incorporation occurred in the lipid globules of Hensen's cells, followed by the hair cells, myelin of the cochlear nerve and other cells. It is speculated that the lipid globules of Hensen's cells act as a reservoir of the vitamin A esterified by fatty acids.     

Wheat germ agglutinin and Helix pomatia agglutinin lectin binding on cochlear hair cells

The fluorescein labelled lectins FITC-WGA and FITC-HPA were used to identify specific carbohydrates in cochlear hair cells. Wheat germ agglutinin (WGA) bound with the cell coat of both inner and outer hair cells (IHC and OHC) suggesting the presence of either N-acetyl-D-glucosamine or sialic acid. In contrast, glycoconjugates with terminal N-acetyl-D-galactosamine residues that bind with Helix pomatia agglutinin (HPA), were demonstrated inside the plasma membrane of outer hair cells. WGA and HPA lectin binding implies the presence of anionic glycoconjugates that furnish added negative charge on the membranes to which they are fixed. The presence of sialic acid or N-acetyl-D-glucosamine on the extracellular surface of cochlear hair cell plasma membrane is consistent with the normal distribution of these glycoconjugates in the cell coat. The presence of the membrane associated oligosaccharide N-acetyl-D-galactosamine within the outer hair cell is inconsistent with the distribution of glycoproteins in internal membrane systems of other cell types.     

卡那霉素在耳蜗毛细胞中的积聚部位

为进一步探讨卡那霉素的耳中毒机理，应用放射自显影和电镜技术观察了３Ｈ标记卡那霉素在５只豚鼠耳蜗毛细胞中的积聚部位。发现卡那霉素主要积聚在线粒体、质细胞膜和静纤毛。卡那霉素积聚在线粒体的原因可能是由于线粒体具有与细菌相同的蛋白质合成方式，卡那霉素可以其杀菌的相同方式抑制线粒体的蛋白质合成。卡那霉素积聚在质膜的原因可能由于这里是药物进入细胞的途径。而药物积聚在静纤毛的原因可能与卡那霉素对糖萼的化学亲和力有关。     

卡那霉素在耳蜗毛细胞中的积聚部位

为进一步探讨卡那霉素的耳中毒机理，应用放射自显影和电镜技术观察了＾３Ｈ标记卡那霉素在５只豚鼠耳蜗毛细胞中的积聚部位。发现卡那霉素主要积聚在线粒体、质细胞膜和静纤毛。卡那霉素积聚在线粒体的原因可能是由于线粒体具有与细菌相同的蛋白质合成方式，卡那霉素可以其杀菌的相同方式抑制线粒体的蛋白质合成。卡那霉素积聚在质膜的原因可能由于这里是药物进入细菌的途径。而药物积聚在静纤毛的原因可能与卡那霉素对糖萼的化学样     

Cell-surface glycoconjugate layer in the tubotympanic mucosa of the guinea pig as revealed by wheat germ agglutinin/gold labelling

To evaluate the protective function of the mucous blanket (MB) against lectin substances, we examined at the ultrastructural level whether intraluminal colloidal gold-labelled wheat germ agglutinin (WGA) could enter the MB-covered epithelial cell surface of the guinea pig tubotympanic mucosa. Post-embedding staining with WGA/gold on thin tissue sections was done in parallel for comparison. The cell surface glycoconjugate of the eustachian tubal and transitional epithelium had a typical bilayered structure: the outer MB and the microvilli-associated glycocalyx (MAG), which were interposed by the interciliary fluid zone. In squamous epithelium of the distal middle ear, the MB adhered to the MAG, thereby forming a monolayered coat of glycoconjugates at the cell surface. In the pre-embedding staining, WGA/gold did not bind with the MB and MAG in the eustachian tube, and exclusively bound with MB in the transitional area. Direct binding was also found with MAG and the apical plasmic membrane in the squamous epithelium. These findings indicate that MAG is occluded by MB lined with the interciliary fluid zone for luminal access of lectin at the proximal lumina of the tubotympanic epithelium. It is also suggested that MB existing at two sites possesses a different WGA-binding capacity: shielding as a dust cover in the eustachian tube and entrapping as a flypaper against lectin in the transitional area of the middle ear.     

Gentamicin-induced alterations of succinic dehydrogenase activity in the organ of Corti as revealed by non-decalcified frozen sections of the guinea pig's cochlea

Summary The distribution of succinic dehydrogenase (SDH) activity and the changes of SDH activity after injection of gentamicin (GM) were observed in the organ of Corti using non-decalcified frozen sections of the guinea pig's cochlea. The distribution of SDH activity was found to increase from the apex to the basal turn. At each turn, SDH activity of the inner hair cells, the inner supporting cells and the nerve endings surrounding the supporting cell and on the hair cells presented a greater activity than that found in the outer hair cells, adjacent Deiter's cells and associated nerve endings. It was further observed that GM had a greater effect on SDH activity in the basal turn than the other turns. At each turn, a more sensitive area of response to GM was found on the nerve endings one each hair cell, especially on the outer hair cells of the basal turn.The experimental part of this study was completed at the Laboratory of Autoradiography, Beijing Medical University, Beijing, People's Republic of China     

Fine structure of the guinea pig organ of Corti revealed by a quick-freeze, freeze-substitution method]

A quick-freeze, freeze-substitution method was applied to the guinea pig organ of Corti. Many similarities were apparent between the conventionally fixed samples and the freeze-substituted samples, including the lateral membrane system of the cochlear outer hair cells consisting of the lateral plasma membrane, pillars, cytoskeletal lattice and subsurface cysternae. However, some ultrastructural differences were found in the cells prepared by the freeze-substitution method. Electron-dense mosaic structures were found in the lumen of the tubules of the subsurface cysternae. Tangential sections of the tubules of the subsurface cysternae showed spirally wound parallel rows of electron-dense materials. In a rectangularly cut membrane with a trilaminar structure, the electron-dense materials appeared to be triangular protrusions from the outer leaflet of the unit membrane. These structures suggest that the subsurface cysternae may play an important role in the contraction of cochlear outer hair cells.     

Hydrops of the organ of Corti

Objectives: The authors would like to confirm a fluid pathway from the scala tympani to the organ of Corti, and to observe its morphological changes.

Methods: A staining solution for succinic dehydrogenase was perfused with phenazine methosulfate in the scala tympani of living guinea pigs (n?=?5) under deep anesthesia. After fixation, the cochleas were eventually embedded in epon. Sections were observed under a light microscope.

Results: Blue-stained tissue is indicative of the pathway taken by the solution. The staining solution entered the organ of Corti through Hensen-Deiters’ slit. The slit widened and Hensen’s cells were pushed laterally. A new space was formed medial to Hensen’s cells. Cortilymphatic hydrops developed.

Conclusion: The Hensen-Deiters’ slit is a pathway of a certain staining solution from the scala tympani to inside the organ of Corti of the guinea pig. The influx of the fluid pushes Hensen’s cells laterally and upward, resulting in a formation of hydrops of the organ of Corti or cortilymphatic hydrops. The hydrops is observed in animals with experimental perilymphatic fistula and with viral labyrinthitis. At the end stage of the hydrops, only the surface of the organ of Corti remains as a thin layer without any cellular elements.     

Cupulogenesis and glycoconjugates in the labyrinthine ampulla as revealed by WGA-gold labeling

Summary We studied the distribution of wheat germ agglutinin (WGA)-bindable glycoconjugates in the vestibular ampulla of mongolian gerbils. WGA was conjugated with gold particles and applied to Lowicryl K4M sections of the ampulla. WGA-binding sites were found on the cupula and some of the secretory granules and Golgi apparatuses in the supporting cells of the sensory epithelia. The granules were seen to secrete into the endolymphatic space through reticular membrane. It is likely, therefore, that glycoconjugates are glycosylated at the Golgi apparatus in the supporting cells, stored in the granules, and secreted through the reticular membrane into the endolymphatic space to be used as a component of the cupula. The cell membranes of various cells, connective tissue filaments in the perilymphatic space and the cytoplasm of melanocytes were also labeled with WGA-gold.     

Cupulogenesis and glycoconjugates in the labyrinthine ampulla as revealed by WGA-gold labeling

We studied the distribution of wheat germ agglutinin (WGA)-bindable glycoconjugates in the vestibular ampulla of mongolian gerbils. WGA was conjugated with gold particles and applied to Lowicryl K4M sections of the ampulla. WGA-binding sites were found on the cupula and some of the secretory granules and Golgi apparatuses in the supporting cells of the sensory epithelia. The granules were seen to secrete into the endolymphatic space through reticular membrane. It is likely, therefore, that glycoconjugates are glycosylated at the Golgi apparatus in the supporting cells, stored in the granules, and secreted through the reticular membrane into the endolymphatic space to be used as a component of the cupula. The cell membranes of various cells, connective tissue filaments in the perilymphatic space and the cytoplasm of melanocytes were also labeled with WGA-gold.     

Membrane specializations in the human organ of Corti

The human organ of Corti was investigated with the freeze fracturing technique with the purpose of analysing membrane specializations. Tight junctions were found on hair cells as well as on supporting cells. Inner and outer hair cells were coupled to the supporting cells by rather extensive tight junctions. The tight junctions between the Deiter's cells were comparable to those of the hair cells, while the tight junctions between the Hensen's cells were considerably less extensive. Gap junctions were present coupling all supporting elements in the organ of Corti, small ones preferably in the apical regions of the cells and large ones in the basal region.     

Serotonergic innervation of the organ of Corti

The olivocochlear efferent system of the mammalian cochlea, which is divided into two lateral and medial bundles, contains numerous neuroactive substances (acetylcholine, GABA, dopamine, enkephalins, dynorphins and CGRP). These have been located at the brainstem in neurons belonging to the lateral superior olive (lateral efferent system) or in neurons of the periolivary region around the medial superior olive and the trapezoid body (medial efferent system). All of these substances were found in well-characterized projections corresponding to lateral and medial nerve fibres and terminals which connect to the type I afferent dendrites and the outer hair cells, respectively. All could be involved in the modulation of the auditory process, as is suggested by the cochlear turnover increases observed in some of them (i.e. enkephalins or dopamine) induced by sound stimulation. Recently, the presence and distribution of serotonin-containing fibres has been included in the long list of cochlear neuroactive substances. However, its highly particular peripheral pattern of distribution together with the lack of response to sound stimulation could suggest that serotonergic fibres constitute a previously unknown cochlear innervation.