Early postmortem changes in the Organ of Corti (guinea pig)

Summary Early post mortem changes in the Organ of Corti are described. 15 minutes after death, when kept at room temperature, 20° C (63° F), an oedematous swelling is observed within the cytoplasm of hair cells and nerve endings, the latter being more severe affected. After 30 minutes post mortem the mitochondria of the hair cells have also become significantly swollen. Three hours post mortem the general character of the hair cells is still recognizable, but most of the nerve endings have been completely destroyed. Acknowledgement. We wish to express our appreciation of the skilful technical assistance of Mrs. B. Flock, Miss A.-M. Lundberg, Miss Sonja Löfvenius, Mr. G. Bornholm and Mr. Rune Ragnefjell.This work was supported by grants from the Swedish Medical Research Council, the National Institute of Health grant (no NB 03956-02), the Therese and Johan Anderssons minne, the Gustav and Tyra Svenssons fund and the King Gustav V Research Fund.     

Age-related changes of hypocretin in basal forebrain of guinea pig

Hypocretin-1 (hcrt-1) and hypocretin-2 (hcrt-2) have been implicated in a wide variety of functions including sleep and wakefulness as well as related behaviors. Many of these functions of the hypocretins involve the activation of cholinergic neurons in the basal forebrain (BF). These neurons have been shown to exhibit age-related changes in a variety of species. In the present experiment, in adult and aged guinea pigs, we compared hypocretin immunoreactivity in regions of the BF that include the medial septal nucleus (MS), the vertical and horizontal limbs of the diagonal band of Broca (VDB and HDB) and the magocellular preoptic nucleus (MCPO). In adult guinea pigs (3–5 months of age), all of the preceding BF regions contained dense hypocretin fibers with varicosities. On the contrary, in old guinea pigs (27–28 months), although the MS exhibited a similar intensity of hypocretin immunoreactivity compared with the adult guinea pig, there was a significant decrease in the intensity of immunoreactivity of hypocretinergic fibers in the VDB, HDB and MCPO. These data indicate that the hypocretinergic innervation of specific nuclei of the BF is compromised during the aging process. We suggest that the reduction in hypocretinergic innervation of the BF nuclei may contribute to the age-related changes in the states of sleep and wakefulness as well as deficits in related systems that occur in old age.     

基于原子力显微镜测量内耳螺旋器的弹性特征

应用原子力显微镜分析内耳螺旋器(Corti器)不同部位的弹性特征。采用豚鼠内耳基底膜底回新鲜标本,用原子力显微镜在液相接触式测量,获得不同部位力曲线。经计算,对应Corti器相当于Hensen细胞、外毛细胞、柱细胞、内毛细胞、内指细胞、盖膜的部位及基底膜底面局部,其杨氏模量均值分别为46±1.7、59±0.9、250±31、140±2.8、430±29.9、210±7.2和230±8.8 kPa。结果表明,基底膜径向排列的组织结构不同,杨氏模量存在明显差异,在整块基底膜标本上测量Corti器各结构的杨氏模量能更准确地反映它们在生理状态下的弹性特征。     

Comparative histochemical investigation of the organ of Corti in the kangaroo rat, gerbil, and guinea pig

The distribution of carbohydrates, proteins, and lipids was studied in the cochleae of kangaroo rat, gerbil, and guinea pig using both fixed paraffin sections and fresh-frozen cryostat sections. Enzyme distribution in the cochleae of the three speices was studied with both EDTA-decalcified and undecalcified fresh-frozen cryostat sections. Although the cochleae of the three species are morphologically different, their distributions of proteins, carbohydrates, and lipids are similar. The zona pectinata of the basilar membrane—which is hypertrophied in the kangaroo rat and gerbil but normal in the guinea pig—stains the same in all three species. The unique, flaskshaped Hensen cells of the kangaroo rat contain more protein than do the normal Hensen cells of the gerbil and guinea pig. At least some of the protein in the kangaroo rat Hensen cells is in the form of carboxylic esterases which are not affected by 10^?4 M eserine, but are inhibited by 10^?2 M eserine and 10^?6 M E600. More than one population of carboxylic esterases is indicated by this reaction to inhibitors and by the results of enzyme distribution tests which used different substrates. A high concentration of malate dehydrogenase in the kangaroo rat Hensen cells may be related to the synthesis of carboxylic esterases. The possible role of these esterases in cochlear functioning is discussed.     

A freeze-fracture study of afferent and efferent synapses of hair cells in the sensory epithelium of the organ of Corti in the guinea pig

Summary Afferent and efferent synapses of hair cells in the organ of Corti of the guinea pig have been examined in freeze-fracture replicas.Afferent synapse In the inner hair cells, intramembranous particles 10 nm in diameter are aggregated on the ridge on the P-face of the presynaptic membrane directly beneath the synaptic rod. In the outer hair cells, in which the synaptic rod is located in the presynaptic cytoplasm underneath the presynaptic membrane, small aggregations of intramembranous particles 10 nm in diameter can be found on the P-face of the presynaptic membrane corresponding to the site of the presynaptic dense projection. Intramembranous particles 10 nm in diameter are also densely aggregated on the P-face of the postsynaptic membrane of the outer hair cells.Efferent synapse of the outer hair cells Large intramembranous particles 13 nm in diameter are distributed in clusters composed of four to ten particles on the P-face of the presynaptic membrane. In the P-face of the postsynaptic membrane, disc-like aggregations of intramembranous particles 9 nm in diameter are found. The subsynaptic cistern covers the cytoplasmic surface of the postsynaptic membrane of the efferent synapse; it may cover more than one postsynaptic membrane when several efferent synapses are in close proximity to one another.     

An ultrastructural study of the development of afferent and efferent synapses on outer hair cells of the guinea pig organ of Corti

The guinea pig organ of Corti was studied using transmission electron microscopy, the second turn of the cochlea being examined at various ages between 20 days before birth and 30 days postnatal. Outer hair cells were examined at each of these ages. At all ages studied, the efferent (presynaptic) terminals are large and are packed with synaptic vesicles, whereas the afferent (postsynaptic) terminals are generally smaller, with a relatively small number of vesicles. During development, the subsynaptic cistern changes from a fragmented, diffuse profile extending over 50-70% of the length of the efferent contact zones, to a continuous, compact structure spanning neighbouring synapses. Synaptic vesicles in the efferent terminals are predominantly rounded in early development, flattened vesicles appearing postnatally. The synaptic bodies at afferent synapses do not change noticeably during development. Quantitative analysis revealed that the area of efferent terminals and the length of their active zone increase with increasing age, the same parameters decreasing in afferent terminals. Synaptic vesicles in the efferent terminals decrease in diameter, but remain constant in afferent terminals, with increasing age. The number of hair cell membrane invaginations decreases as development proceeds.     

Dye coupling in the organ of Corti

Summary Dye-coupling in an in vitro preparation of the supporting cells of the guinea-pig organ of Corti was evaluated by use of the fluorescent dyes, Lucifer Yellow, fluorescein and 6 carboxyfluorescein. Despite the presence of good electrical coupling in Hensen cells (coupling ratios >0.6) the spread of Lucifer yellow was inconsistent. Hensen cells are very susceptible to photoinactivation, i.e., cell injury upon illumination of intracellular dye; and this in conjunction with Lucifer Yellow's charge and K+-induced precipitability may account for its variability of spread. Fluorescein and 6 carboxyfluorescein, on the other hand, spread more readily and to a greater extent than Lucifer Yellow, often spreading to cell types other than those of Hensen. Dye spread is rapid, occurring within a few minutes. These results suggest that molecules of metabolic importance also may be shared by the supporting cells of the organ of Corti.     

Innovar-Vet-induced pathologic changes in the guinea pig.

High doses of Innovar-Vet administered im induced pathologic changes in tissues at the site of drug deposition. The onset and extent of the changes were dose related. Distal self-mutilation occurred coincidentally to the peak of pathologic changes in the ischiatic nerve.     

Three-dimensional motion of the organ of Corti

The vibration of the organ of Corti, a three-dimensional micromechanical structure that incorporates the sensory cells of the hearing organ, was measured in three mutually orthogonal directions. This was achieved by coupling the light of a laser Doppler vibrometer into the side arm of an epifluorescence microscope to measure velocity along the optical axis of the microscope, called the transversal direction. Displacements were measured in the plane orthogonal to the transverse direction with a differential photodiode mounted on the microscope in the focal plane. Vibration responses were measured in the fourth turn of a temporal-bone preparation of the guinea-pig cochlea. Responses were corrected for a "fast" wave component caused by the presence of the hole in the cochlear wall, made to view the structures. The frequency responses of the basilar membrane and the reticular lamina were similar, with little phase differences between the vibration components. Their motion was rectilinear and vertical to the surface of their membranes. The organ of Corti rotated about a point near the edge of the inner limbus. A second vibration mode was detected in the motion of the tectorial membrane. This vibration mode was directed parallel to the reticular lamina and became apparent for frequencies above approximately 0.5 oct below the characteristic frequency. This radial vibration mode presumably controls the shearing action of the hair bundles of the outer hair cells.     

Kanamycin-induced changes in cochlear hair cells of the guinea pig

Summary Electron-microscopical studies on the organ of Corti in kanamycin-intoxicated guinea pigs showed that progressive changes occurred in the cochlear hair cells. The changes appeared first in the basal turn of the organ of Corti, and affected primarily the outer hair-cells. During the later stages of intoxication, degeneration spread from the basal turn upwards, in the direction of the apex of the cochlea and, finally, affected all the external hair-cells.The early changes caused clumping of the chromatin in the nucleus, swelling of the nuclear membrane, damage in the mitochondria, with vesiculation of the mitochondrial cristae, and the formation of lamellated structures. The lysosomes were converted into dense bodies exhibiting various degeneration patterns. The ribosomes disappeared at an early stage from the cytoplasm.Even in cells where severe changes had occurred the hairs and cuticle seemed to be intact.During the final stages the plasma membrane, as well as the hairs and cuticle, was destroyed, and only remnants of these structures remained.Even after the disappearance of the sensory cells and the afferent nerve endings, some efferent nerve endings were still present in the organ of Corti.The action of kanamycin seems to differ slightly from that of streptomycin, since the changes caused by kanamycin in the plasma membrane are a fairly late effect, whereas the earliest changes occur apparently in the RNA protein-synthesis system and in the mitochondria of the external hair-cells.

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Zusammenfassung Elektronenmikroskopische Untersuchungen am Cortischen Organ von Meerschweinchen mit Kanamycinintoxikation ergaben eine fortschreitende Schädigung der cochlearen Haarzellen. Die Veränderungen begannen in der basalen Schneckenwindung und betrafen vorwiegend die äußeren Haarzellen. In späteren Intoxikationsstadien breitete sich die Degeneration von der Basalwindung nach aufwärts bis in die Schneckenspitze aus und wurde schließlich an allen äußeren Haarzellen gesehen.Die früheren Veränderungen manifestierten sich am Kern mit Chromatinverklumpung, Schwellen der Kernmembran, Schädigung der Mitochondrion mit vesikulären Cristae mitochondriales und Bildung von Lamellenstrukturen. Die Lysosomen waren in dichte Körper verwandelt und wiesen verschiedene Degenerationsmuster auf. Die Ribosomen verschwanden früh aus dem Cytoplasma. Sogar in schwer geschädigten Zellen erschienen Haare und Cuticula intakt.In den Endstadien waren Plasmamembran, Haare und Cuticula bis auf Reste zerstört. Einige efferente Nervenendigungen waren selbst nach dem Verschwinden der Haarzellen und der afferenten Endigungen noch anzutreffen.Die Wirkung von Kanamycin ist offenbar etwas anders als die von Streptomycin, da die Veränderungen an der Plasmamembran ziemlich spät auftreten, während sich die frühesten Schäden im System der RNA-Proteinsynthese und in den Mitochondrien der äußeren Haarzellen zu manifestieren scheinen.

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This investigation was supported by Grant No. NB 3956-03 from the US Public Health Service, the Swedish Medical Research Council, and Stiftelsen Therese and Johan Anderssons Minne. The skillful technical assistance of Miss Cathrine Lindholm, Miss Ann-Marie Lundberg, Miss Sonja Löfvenius, and Miss Gunilla Wiman is gratefully acknowledged. The kanamycin was kindly supplied by AB H. Lundbeck & Co.     

Developmental changes in the adenine nucleotide translocase in the guinea pig

Investigations of developmental changes in energy metabolism in guinea pig liver mitochondria showed that mitochondria from the newborn were well coupled, with respiratory control ratios and membrane energy potentials similar to those obtained with mitochondria from the 1-day-old and the adult. In contrast, there was a 3-fold increase in the rate of mitochondrial respiration and a 2-fold increase in adenine nucleotide content during the first 24 h of extrauterine life. There was no significant change in the ATP/ADP ratio and only a 30% increase in the uncoupled rate of respiration during this same time period. Titrations of the adenine nucleotide translocase with the specific inhibitor, carboxyatractyloside, showed that the newborn had only 50% of the adenine nucleotide translocase activity of the adult. Furthermore, by applying flux control theory to these inhibitor titrations, it was possible to demonstrate that the adenine nucleotide translocase exerted greater control over respiration in the newborn than in the adult, and at maximal rates of coupled respiration the translocase had a control strength of 0.98. The consequences of this finding on cellular energy metabolism are discussed in relation to adaptation of the newborn to extrauterine life.     

Cellular commitment and differentiation in the organ of Corti

The organ of Corti, the sensory epithelium of the mammalian cochlea, develops from a subset of cells located along the dorsal side (referred to as the floor) of the cochlear duct. Over the course of embryonic development, cells within the developing organ of Corti become committed to develop as each of the unique cell types within the organ, including inner and outer hair cells, and at least four different types of supporting cells. Moreover, these different cell types are subsequently arranged into a highly rigorous cellular mosaic that includes the formation of ordered rows of both hair cells and supporting cells. The events that regulate both the location of the organ of Corti within the cochlear duct, the specification of each cell type and cellular patterning remain poorly understood. However, recent results have significantly improved our understanding of the molecular, genetic and cellular factors that mediate some of the decisions required for the development of this structure. In this review I will present an overview of cochlear development and then discuss some of the most recent and enlightening results regarding the molecular mechanism underlying the formation of this remarkable structure.     

Hearing and glycoconjugates: localization of Ley, Lex and sialosyl-Lex in guinea pig cochlea, particularly at the tectorial membrane and sensory epithelia of the organ of Corti

Immunohistological examination of guinea pig cochleas was performedusing a panel of 25 monoclonal antibodies directed to variouslacto-, ganglio- and globo-series carbohydrate epitopes as wellas mucin-type epitopes. Lacto-series structures were found tobe localized at specific sites of the tectorial membrane (TM)and Corti's organ, i.e. 13 fucosyl type 2 chain (Le^x) at Kimura'smembrane, marginal band and covering net of TM; 12, 13 difucosyltype 2 chain (Le^y) at covering net; and sialosyl-Le^x and sialosyl-iat Kimura's membrane and sensory epithelia, particularly sensorytips of hair cells of Corti's organ. In striking contrast, ganglio-seriesstructures (GM3, GD3, GD2, 9-O-Ac-GD3) were detected at spiralganglion cells, neuronal fibres and stria vascularis, but werecompletely absent from Corti's organ and most of the TM. Otherepitope structures defined by various antibodies were not detectableat any location. The functional roles of lacto-series carbohydrateepitopes expressed at TM and Corti's organ remain unknown. However,the expression of Le^y (but not other structures) in associationwith developmental deficiency of TM induced by 6-N-propyI-2-thio-uracilin rats suggests that Le^y plays some role in normal TM development.The presence of Le^x at Kimura's membrane and sialosyl-Le^x athair cell sensory tips of Corti's organ suggests the intriguingpossibility that these fucosylated/sialosylated carbohydratestructures play some role in interactions (either attractiveor repulsive) of these inner ear components, which have beenimplicated in the physiology of hearing, i.e. the conversionof sound waves to nerve impulses. cochlea Corti's organ glycoconjugate sialosyl fucosyl type 2 chain tectorial membrane