Penetration of the cochlear endost by the fibrous component of the otosclerotic focus

Human otosclerotic bone-derived peptide decreases the gain of the electromotility in isolated outer hair cells

An otosclerotic peptide (OP) (Sziklai et al., 1985a.b) was purified from perilymph and stapes footplate of otosclerotic patients by Sephadex G-25 gel column chromatography and subsequent isotachophoretic (ITP) separation. The transfer function of the electromotility was measured by inserting the isolated outer hair cells (OHC) into a partitioning microchamber (Evans et al., 1991) and applying a series of pairs of brief square-pulse stimuli with opposite polarity and with increasing magnitude. Somatic length changes of the inserted part of the OHCs were measured by an optoelectronic system. The isotachophoretically homogeneous peptide exerted a gain and magnitude decreasing effect on the transfer function of electromotility of isolated OHCs of the guinea pig, in vitro. The operating point of the electromotility did not change due to the effect of the peptide. The peptide decreased the electromotile performance within a minute and bath exchange to normal saline did not completely restore the transfer curve to baseline. Application of caffeine to the cells already under the effect of the otosclerotic peptide produced an opposite effect: gain and magnitude increase. Simultaneous application of acetylcholine (ACh) did not antagonize the effect of OP. The underlying mechanism of the action of OP on the transfer function of electromotility of OHCs is postulated to involve the modulation of intracellular Ca2- concentration.

Early bone formation in the human fetal otic capsule. A methodological approach

The present study was concentrated on the use of energy-dispersive X-ray analysis and backscattered electron imaging as practical tools for advanced autopsy of human fetuses when diagnostic evaluation of ear pathology is required. These methods were used to revisit the primary calcification front of the fetal otic capsule between 18 and 36 weeks' gestational age. Energy-dispersive X-ray analysis indicates an equal Ca/P ratio in all the three layers of the otic capsule. These results are discussed in view of calcium homeostasis and inner ear function.

Early ossification within the human fetal otic capsule: morphological and microanalytical findings

Besides the use of conventional techniques such as light and polarization microscopy, the present paper proposes the combined use of transmission electron microscopy, secondary and backscattered electron imaging, energy dispersive X-ray analysis and computed tomography for the diagnostic evaluation of ear pathology in the human fetus. These methods were used to revisit the primary calcification front of the fetal otic capsule between 16 and 23 weeks gestational age. Ultramicroscopic evaluation demonstrates similar fetal bone formation to that found in other bones of the human fetus. The formation of the endosteal and periosteal layers is a typical example of early intra-membranous ossification. The enchondral layer is made up of fibrillar bone, laid down around the calcified cartilage remnants. Microchemical analysis indicates a significantly higher Ca/P ratio in the endochondral layer with respect to the endosteum and periosteum. The consequences of a lower Ca/P ratio in the endosteal layer are discussed in view of calcium homeostasis and inner ear function.

Fine morphology of bony dysplasia of the murine ear: comparisons with otosclerosis

Dysplastic bony lesions that bear certain similarities to otosclerosis occur spontaneously in LP/J inbred mice. These lesions develop after the fifth week of life and progressively enlarge; they are present in 90% of animals by 90 weeks of age. In the present study, the fine morphology of these lesions was investigated. Dysplastic lesions in the middle ear of LP/J mice appeared to begin as subperiosteal accumulations of amorphous material. These accumulations occurred adjacent to the bone surface below the epithelium of the middle ear. This amorphous material was often associated with macrophages on the adjacent epithelial surface. The material appeared to be replaced with collagen fibers in a disorganized manner, forming a homogeneous base (osteoid) on which calcification occurred. The fine morphology and periodicity of the collagen appeared normal. The lesions then calcified by forming calcospherites that became confluent. During this period, transformed fibroblasts (osteoblasts) appeared in the calcifying matrix, resulting in a lesion made of bone. These lesions could sometimes be seen replacing normal bony contours but most often were exophytic. The lesions at all stages of development may be associated with macrophages and effusions in the middle ear. The lesions in the middle ear of LP/J mice appeared to develop by an active process of bone formation; in contrast, otosclerosis is an active process of bone resorption and formation.