The cochlea of the spontaneously diabetic mouse

Summary We used transmission electron microscopy to examine the cochleae of non-obese diabetic mice as animal models for human type I or non-insulin-dependent diabetes mellitus. Pathological changes were observed in the organ of Corti of the basal turn and in the stria vascularis of each turn. Major findings in the stria vascularis were protrusion or condensation of marginal cells, swelling of intermediate cells, and widening of the intercellular spaces. Principal findings in the organ of Corti involved degenerative changes of the outer and inner hair cells and replacement of hair cells by supporting cells. No prominent pathological changes were observed in the capillaries. The possible mechanism of diabetic involvement in cochlear pathology is discussed.     

Experimental mumps labyrinthitis in monkeys (Macaca irus)--immunohistochemical and ultrastructural studies

Three monkeys (Macaca irus) were inoculated with mumps virus into unilateral cochleas and their inner ear were examined by immunofluorescent microscopy and transmission electronmicroscopy. The temporal bones were removed after survival period of 14 days when serological tests disclosed elevation of anti-mumps antibody titers. Immunofluorescent microscopy revealed that the viral antigen was positive in the stria vascularis. The ultrastructural study revealed that the pathologic changes in the cochleas were marked in the organ of Corti and stria vascularis. The outer hair cells were more susceptible to the infection than the inner hair cells. In the stria vascularis, both marginal and intermediate cells were affected. It was possible to find some of marginal cells in the basal turn shedding a large number of mature virions into the endolymph. These pathologic changes observed in the cochleas of the monkeys were similar to those previously revealed in the guinea pig cochleas and thus were considered as the specific features of acute mumps labyrinthitis.     

Results of an ultrastructural study comparing stria vascularis with organ of Corti in guinea pigs treated with kanamycin

Ultrastructural study of ototoxicity is well documented with two points of interest: organ of Corti for aminoglycosides and stria vascularis for loop diuretics. As a previous study suggested initial lesions of stria vascularis, an attempt of comparison and of chronological study was made between the organ of Corti and stria vascularis lesions by kanamycin intoxication. The method was devised by J. M. ARAN, with electrophysiological control. We failed to find in the stria vascularis a radial or longitudinal pattern of lesions. We could not discern a chronological injury between the organ of Corti and stria vascularis because both were damaged even in the less deafened animals. Nevertheless, two facts were clarified: hair cell lesions are lysosomial as for the kidney lesions, while stria vascularis lesions are mitochondrial, melanine granulations play a part in drug metabolism (increased number, secretory aspect) and deserve further study.     

Degeneration of the organ of Corti following intravenous administration of cisplatin.

The development of acute morphological changes in the cochlea was studied in guinea pigs given one intravenous high-dose injection of cisplatin. In the light microscope three major stages of degeneration in the organ of Corti could be recognized: 1) an initial swelling of the Hensen's cells and protrusion of the Deiters' cells into the space of Nuel enclosing the outer hair cells, 2) a gradual degeneration of the outer hair cells together with a vacuolization in the region of the base of the inner hair cells, 3) a collapse of the Reissner's membrane and the entire organ of Corti with different degrees of damage to the inner hair cells. Sporadic bulging of the marginal cells of the stria vascularis into the endolymphatic space could be observed 4 days after injection.     

Electron microscopic study on inner ear barotrauma: with emphasis on the cochlear damage

In order to investigate inner ear barotrauma, guinea pigs were subjected to rapid decompression between 2 absolute pressure (ATA) and 1 ATA in a chamber. After pressure loading and observation for absence of Preyer's reflex, they were sacrificed immediately, 1 day, 1 week and 1 month later, respectively. Then, morphological changes of the organ of Corti and stria vascularis were studied under TEM and SEM. The immediate features noted were fracture of stereocilia with minimal intracellular changes. One day later, there was marked degeneration of outer hair cells and expansion of supporting cells. The damage to stereocilia clearly preceded morphological alterations within hair cell bodies and cannot be interpreted as arising secondary to hair cell degeneration. Most of outer hair cells eventually disappeared and were replaced by supporting cells. Inner hair cells degenerated slowly; 1 month later, some of them remained almost intact, despite disappearance of stereocilia. The continuity of reticular lamina was maintained not only immediately but also through the period of hair cell degeneration, thus preventing any leakage of endolymph into the organ of Corti. There was reversible dendritic swelling of inner hair cells immediately following the trauma. No changes of stria vascularis were observed over passage of time. The mechanism of hair cell damage due to inner ear barotrauma is presumed to be a deformity of the organ of Corti caused by pressure discrepancy between perilymph and endolymph resulting in an injury to stereocilia.     

Electron microscopic temporal bone histopathology in experimental pneumococcal meningitis.

Bacterial meningitis is one of the most common causes of acquired profound sensorineural deafness in children. Measurement of hearing and examination of the cochlea is limited in patients suffering from acute meningitis. A rabbit model of pneumococcal meningitis was developed to identify the temporal bone histopathologic changes that occur in meningogenic labyrinthitis caused by Streptococcus pneumoniae. Light microscopy was previously performed on temporal bones from acutely meningitic rabbits with profound hearing loss as determined electrophysiologically. Extensive inflammation of the cochlea with endolymphatic hydrops was observed. The organ of Corti, however, showed preserved architecture in the majority of these animals. In order to further investigate these findings, a protocol was used to create meningitic rabbits with hearing loss ranging from early high-frequency loss to profound deafness. The temporal bones from 7 rabbits were examined by transmission electron microscopy. In cases of mild hearing loss, partial degeneration of the inner row of outer hair cells, as well as edema of efferent cochlear nerve endings and marginal cells of the stria vascularis, was seen. With increasing degrees of hearing loss, the remainder of the organ of Corti and intermediate cells of the stria showed ultrastructural abnormalities. Spiral ganglion cells and basal cells of the stria vascularis remained intact in all subjects. This study provides unique information regarding the histology and pathophysiology of meningogenic deafness. The clinical implications of these findings are discussed, with an emphasis on potentially reversible changes and therapeutic intervention.     

川芎嗪对庆大霉素耳中毒耳蜗外毛细胞和血管纹的保护作用

目的：探讨在庆大霉素（gentamycin，GM）耳中毒情况下，川芎嗪（tetramethylpyrazine，TMP）对豚鼠耳蜗外毛细胞和血管纹边缘细胞的保护作用。方法：12只豚鼠随机分为GM组、联合用药组、TMP组及对照组，用药十天后处死，采用透射电镜观察耳蜗外毛细胞及血管纹边缘细胞超微结构，扫描电镜观察血管纹边缘细胞表面形态。结果：透射和扫描电镜显示，联合用药组外毛细胞及血管纹边缘细胞超微及表面结构破坏不均明显轻于庆大霉素组，特别是其中的线粒体结构破坏与数目减少更显著轻于庆大霉素组。结论：川芎嗪具有保护庆大霉素耳中毒耳蜗外毛细胞和血管纹结构的作用，从而拮抗庆大霉素耳毒性。     

Cochleosaccular dysplasia: a morphometric and histopathologic study in a series of temporal bones.

OBJECTIVE: The objective of this study was to perform a morphometric analysis of a series of temporal bones with cochleosaccular dysplasia to clarify the extent of inner ear changes in this disease. STUDY DESIGN: This human temporal bone histopathologic study of a series of deaf-mute cases involves morphometric analysis, including stria vascularis and spiral ligament area measurements and spiral ganglion and hair cells counts. SUBJECTS: Thirteen temporal bones were selected from 35 with deaf mutism based on the histopathologic findings described by Scheibe. Twenty normal age-matched control subjects were used for comparisons. RESULTS: All temporal bones had the main histopathologic findings described by Scheibe, as well as severe affected stria vascularis. Seven temporal bones had cystic areas in the stria and three had concretions. Cross-sectional strial areas in temporal bones with cochleosaccular dysplasia were smaller than normal in all cochlear turns; however, no difference was found in spiral ligament cross-sectional areas. Reissner's membrane was hydropic in three temporal bones and the organ of Corti was absent in at least one cochlear turn in five. Concretions were present in the macula of seven temporal bones. Twelve temporal bones showed some level of spiral ganglion cell loss. No hair cells were observed in any temporal bone. A familial history of deafness was found in three cases. CONCLUSION: Pathologic findings were variable and limited to the saccule and scala media. The variation, perhaps, reflects the different etiologies involved in the origin of cochleosaccular dysplasia.     

Immunohistochemical detection of platinated DNA in the cochlea of cisplatin-treated guinea pigs

Cisplatin-induced ototoxicity is correlated with functional and morphological changes in the organ of Corti, the stria vascularis and the spiral ganglion. However, the cochlear sites of cisplatin uptake and accumulation have not been properly identified. Therefore, we have developed an immunohistochemical method to, indirectly, detect cisplatin in semithin cryosections of the guinea pig cochlea (basal turn) using an antiserum containing antibodies against cisplatin-DNA adducts. Platinated DNA was present in the nuclei of most cells in the organ of Corti and the lateral wall after cisplatin administration. Nuclear immunostaining was most pronounced in the outer hair cells, the marginal cells and the spiral ligament fibrocytes. This study is the first to demonstrate the presence of cisplatin in histological sections of the cochlea.     

Scanning electron microscopy of the normal human cochlea

Preservation of the fine structures of the human cochlea has been achieved by perfusing the cochlea with fixative shortly after death. Following the dissection of the temporal bone the surface of the organ of Corti and stria vascularis has been examined in the scanning electron microscope. The surfaces of the inner and outer hair cells can be seen and the stereocilia projecting from their surfaces closely examined. The number and length of the stereocilia of the outer hair cells changes linearly with distance along the cochlear duct. The surface of the stria vascularis is similar to that seen in other animals.     

Expression pattern of adenylyl cyclase isoforms in the inner ear of the rat by RT-PCR and immunochemical localization of calcineurin in the organ of Corti.

Most studies concerning adenylyl cyclases in the inner ear were carried out before the advent of molecular biology. In a PCR approach using cDNAs of six inner ear tissues (stria vascularis, endolymphatic sac, organ of Corti, vestibulum, cochlear and vestibular nerve) we found tissue specific expression of adenylyl cyclase isoforms. Adenylyl cyclases types 2 and 4 are predominant in the fluid controlling tissues, i.e. in the stria vascularis and endolymphatic sac. In the organ of Corti and vestibulum the Ca2+-modulated isoforms types 1, 6 and 9 were expressed. The regulation of adenylyl cyclase 9, which is the major isoform expressed in the organ of Corti, proceeds via the Ca2+-activated protein phosphatase 2B (calcineurin, PPP3). PCR with specific primers for calcineurin demonstrated its abundant expression in the organ of Corti. Using a monoclonal antibody we localized calcineurin immunochemically to the cochlear nerve, the nerve fibers and the inner hair cells. In the cochlear and vestibular nerves a characteristic neuronal expression pattern of adenylyl cyclase isoforms was observed, i.e. adenylyl cyclases types 2, 3 and 8. The functional consequences of the adenylyl cyclase expression pattern in the inner ear are discussed in conjunction with its unique sensory performance.     

Ultrastructural and physiological defects in the cochlea of the Mpv17 mouse strain. A comparison between young and old adult animals

Ultrastructural investigations were performed in young (approximately 2 months) and old (7 months) Mpv17-negative and wild-type mice. The onset, the severity and the pattern of the degeneration significantly differed between both mice strains. In the wild-type mouse strain the degenerative changes of the cochlear structures were similar to the aging pattern described for other species. In contrast, the Mpv17 mutants showed degenerative changes of the cochlear structures already at the age of 2 months. The degenerative changes were patchy arranged throughout the entire length of the cochlea and involved the organ of Corti as well as the stria vascularis epithelia with alterations of the basement membrane of the capillaries. The severe sensorineural hearing loss and degenerative changes of the cochlear structures indicate that cochlear structures, especially the outer hair cells and the intermediate cells of the stria vascularis, are vulnerable to the missing Mpv17 gene product.     

High resolution scanning electron microscopy of the human organ of Corti. A study using freshly fixed surgical specimens

Scanning electron microscopy on immediately fixed human cochleae obtained during surgery for life-threatening petro-clival meningioma showed excellently preserved morphology. We compared the morphological findings with those from transmission electron microscopic sections of well preserved human and animal tissue. The characteristics of neural innervation, the pathways of the nerves through the organ of Corti and the intimate relation of nerves to supporting cells along their route could be studied in detail. The lateral membranes of Hensen and Claudius cells were folded creating a surface enlargement. Marginal pillars extended the distal end of the tectorial membrane and correspond to the marginal net or "randfasernetz" described earlier. Stereocilia imprints at the undersurface of the tectorial membrane go as far as to the distal end of the marginal pillars. The presence of an irregularly distributed fourth row of outer hair cell, attached to the marginal pillars, raises questions about differences in the excitation of the last row of outer hair cells. The complex nature of many supporting cells, stria vascularis and Reissner's membrane, intracellular complexities as well as surface features are described. Supernumerary inner hair cells were observed and the different arrangement of outer spiral fibres in contrast to findings in animals and variations of nerve fibres within the organ of Corti between apex and base are discussed.     

Inner ear pathology in the Palmerston North autoimmune strain mouse.

The Palmerston North autoimmune strain mouse is a model for spontaneous systemic lupus erythematosus. Inner ear structure and function were examined during the onset and progression of systemic autoimmune disease to identify potentially correlated auditory system pathology. The onset of systemic disease occurred at 4 to 5 months of age and was characterized by elevated serum immune complexes, cryoglobulins, and antinuclear antibodies. Coincident with the onset of autoimmune disease was degeneration of the apical turn stria vascularis and outer hair cells. These cochlear changes progressed basalward. At 10 months of age, auditory brainstem response thresholds were elevated and the stria vascularis area was measurably smaller throughout the cochlea. Immunohistochemical staining showed immunoglobulin G deposits within the organ of Corti, the vas spirale of the basilar membrane, the scala tympani, and marrow cavities of the bony otic capsule. These results suggest that cochlear pathology may be immune mediated in this mouse, which would make the strain suitable for the study of the mechanisms relating inner ear abnormalities and autoimmune disease.     

Cisplatin-induced apoptotic cell death in Mongolian gerbil cochlea

Cisplatin is well known to cause cochleotoxicity. In order to determine the underlying mechanisms of cisplatin-induced cell death in the cochlea, we investigated the apoptotic changes and the expression of bcl-2 family proteins controlling apoptosis. Mongolian gerbils were administered 4 mg/kg/day cisplatin consecutively for 5 days. The cisplatin-treated animals showed a significant deterioration in the responses of both distortion product otoacoustic emissions and the endocochlear potential as compared with those of the age-matched controls, suggesting outer hair cell and stria vascularis dysfunction. The presence of DNA fragmentation revealed by a terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling method was recognized in the organ of Corti, the spiral ganglion, and the stria vascularis in the cisplatin-treated animals whereas almost negative results were obtained in the control animals. The nuclear morphology obtained by Hoechst 33342 staining revealed pyknotic and condensed nuclei, confirming the presence of the characteristic features of apoptosis. A significant increase and reduction in the number of bax- and bcl-2-positive cells, respectively, following cisplatin treatment was observed in the cells of the organ of Corti, the spiral ganglion, and the lateral wall. These findings suggest a critical role for bcl-2 family proteins in the regulation of apoptotic cell death induced by cisplatin. The underlying mechanisms of the cisplatin-induced cell death are discussed.     

Inner ear damage due to lipoid nephrosis

Summary Inner ear pathology was studied in adult rats with lipoid nephrosis induced by puromycin aminonucleoside. Although no abnormality was observed in auditory brain-stem responses, significant changes were noted in the stria vascularis. The most striking observation was that intermediate cells were markedly swelled, there-by pressing adjacent marginal cells. Severely affected marginal cells have vacuoles and increased lysosomes and protruded toward the endolymphatic space. The organ of Corti remained virtually intact. Although the vestibular maculae were relatively normal, type I hair cells in the semicircular canal underwent a conspicuous vaculolization. These findings support a postulate that the inner ear is liable to damage in lipoid nephrosis. Correspondence to: H. Yamane     

Effects of type 2 diabetes mellitus on cochlear structure in humans

OBJECTIVE: To evaluate the effects of type 2 diabetes mellitus on cochlear elements in humans. DESIGN: Comparative study of the histopathologic characteristics of human temporal bones. SETTING: Otopathology laboratory in a tertiary academic medical center. PATIENTS: Temporal bones from 18 patients with type 2 diabetes mellitus were divided into 2 groups according to the method of management of diabetes: insulin in 11 patients (mean age, 51.9 years; age range, 44-65 years) and oral hypoglycemic agents in 7 patients (mean age, 54.4 years; age range, 45-64 years). The diabetic groups and 26 age-matched controls (mean age, 52.9 years) were examined using light microscopy, and the cochlear changes were compared between groups. MAIN OUTCOME MEASURES: Morphometric measurements of vessel wall thickness in the basilar membrane and stria vascularis were made in all turns of the cochlea at the midmodiolar level. Area measurements of the stria vascularis were made in all turns of the cochlea at the midmodiolar level. Cochlear reconstructions and standard cytocochleograms were prepared using an oil immersion objective. The number of spiral ganglion cells was determined for each segment of the cochlea. Comparisons were made in each segment between diabetic and control groups. RESULTS: In the insulin group, walls of the vessels of the basilar membrane and stria vascularis in all turns were significantly thicker than those of controls. Walls of the vessels of the stria vascularis in the basal turn were also significantly thicker in the oral hypoglycemic group than in controls. Atrophy of the stria vascularis in most turns of the insulin group and the lower middle turn of the oral hypoglycemic group was significantly greater than in the controls. Loss of cochlear outer hair cells was significantly greater in the lower and upper basal turns in both diabetic groups. No significant difference was found in the number of spiral ganglion cells or inner hair cells between groups. CONCLUSION: This study demonstrates that cochlear microangiopathy and degeneration of the stria vascularis and cochlear outer hair cells are found in patients with type 2 diabetes mellitus.     

Cisplatin ototoxicity in guinea pigs with special reference to toxic effects in the stria vascularis

The toxic effects of cisplatin (cis-diamminedichloroplatinum [II]) on the organ of Corti are well established. Few and conflicting data on this drug's effects on the stria vascularis exist. The present study presents animal experiments on the toxic effects of cisplatin in the stria vascularis and in the organ of Corti. Cisplatin-induced toxicity in albino and pigmented guinea pigs was evaluated morphologically and functionally, using light and transmission electron microscopy as well as auditory brainstem-evoked potentials on the organ of Corti and the stria vascularis. The results showed variability in hearing thresholds, ranging from no change to hearing loss of 30 dB, and prominent damage in the organ of Corti and in the stria vascularis. The toxic effects to both the organ of Corti and the stria vascularis should be considered when cisplatin is used in chemotherapy.     

Ototoxic effect of nitromin and some congenital deaf animal cochlea. An electron microscopical study

Summary The ototoxic action of nitromin on guinea pigs and mice was studied, Shaker-l-mice and Hedlund white mink cochlea were also studied with the comparison of nitromin intoxicated cochlea.Nitromin was found to be more toxic than kanamycin, streptomycin and gentamicin with regard to their dosages. Toxic reactions were mainly observed in the cochlear sensory epithelia. Degeneration appeared first in the outer hair cells in the basal turn of the cochlea starting with the formation of whorls and proliferation of smooth endoplasmic reticula and ending with the complete degeneration of the sensory cells, but the stria vascularis showed little change. Even after the disappearance of the hair cells, some efferent nerve endings were still present in the organ of Corti.Shaker mice have a fairly normal stria vascularis with normal filling of scaly media but show severe degeneration of organ of Corti. This cochlea shows pathological changes somewhat similar to those of ototoxic antibiotics intoxicated cochlea. On the other hand, Hedlund white mink showed the degeneration of the organ of Corti caused by severe degeneration of the stria vascularis and collapse of scaly media.We have demonstrated similar final cochlear degeneration following different pathological pathways in three species of animals.

---

Zusammenfassung Die ototoxische Wirkung von Nitromin wurde an Mäusen und Meerschweinchen studiert and die toxischen Veränderungen den morphologischen Bildern der Cochlea von Shaker-Mäusen und Hedlund-Nerzen gegenüber gestellt.Es wurde festgestellt, daß die toxische Wirkung von Nitromin größer ist als die von Streptomycin and Kanamycin — bezogen auf die verabfolgte Dosis.Toxische Veränderungen fanden sick hauptsächlich im Sinnesepithel der Cochlea. Zuerst kam es zum Untergang von äußeren Haarzellen in der basalen Schneckenwindung beginnend mit der Bildung von Wirbeln and der Proliferation des glatten endoplasmatischen Reticulums und endend mit der kompletten Degeneration der Sinneszellen, jedoch nur mit geringen Veränderungen in der Stria vascularis. Gleich nach dem Verschwinden der Haarzellen waxen immer noch einige efferente Nervenendungen im Corti-Organ vorhanden.Die Shaker-Maus hat eine völlig normale Stria vascularis mit normaler Ausfüllung der Scaly media, abet One schwere Degeneration des Corti-Organs. Die Cochlea zeigt pathologische Veränderungen etwas ähnlich der durch ototoxische Antibiotica geschädigten Cochlea.Auf der anderen Seite fmdet man bei Hedlund-Nerzen eine Degeneration des Cortischen Organs, hervorgerufen durch schwere Degeneration der Stria vascularis und durch Kollaps der Scala media.Wir haben also ähnliche Formen von Cochlea-Degeneration bei drei Sorten von Versuchstieren gezeigt, die auf unterschiedlichen pathologischen Wegen zustande kommen.