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At least 469 records · Page 26Linked to original sources
PubMed1997

Relationship between the development of outer hair cell electromotility and efferent innervation: a study in cultured organ of corti of neonatal gerbils.

Outer hair cell (OHC) electromotility, which powers the cochlear amplifier, develops at a later stage of hearing ontogeny. There has been speculation whether efferents play a necessary role in directing or achieving OHC maturation in mammals. In this study, we examine whether the development of OHC motility depends on the establishment of efferent innervation of the cells' synaptic pole by measuring electromotility of OHCs grown in cultures, deprived of efferent innervation. Tissue cultures of the organ of Corti were prepared from the cochleas of newborn gerbils. Solitary OHCs were obtained from 4- to 15-d-old cultures by enzymatic digestion and mechanical trituration. Length changes evoked by transcellular electrical stimulation were detected and measured with a photodiode sensor. Results show that OHCs develop electromotility between 6 and 13 d in culture without the presence of efferent innervation. The timetable for the onset of OHC electromotility is comparable with that in vivo. This demonstrates that the ontogeny of OHC electromotility is an intrinsic process that does not require the influence of efferent innervation.

Animals↗
PubMed2000

Microglia-like cells in rat organ of Corti following aminoglycoside ototoxicity.

The repair process of neomycin induced cochlear damage in the postnatal developing rat was investigated in the present study. The results showed that electron dense atypical cells with a cluster of microvilli on their apical surface, resembling early stage of embryonic hair cell, were observed in the former hair cell region. The striking finding was that microglia-like cells appeared and replaced OHCs in the injured auditory sensory epithelium. Using Brdu immunohistochemistry, cell proliferation was found in the area of inner and outer spiral sulcus but not in the hair cells and supporting cells. It is proposed that microglia-like cells play a role in eliminating waste products from the organ of Corti and may participate in direct structural repair.

Animals↗
PubMed2000

Experimental studies of vibratory trauma of Corti's organ. I: Electrophysiological measurements.

In the present-day environment, vibration concomitant with noise is most frequently observed, but even though it is regarded as only a weak, additional traumatic factor affecting the organ of hearing. This opinion is contrary to a number of reports on the damage of the hearing organ caused by vibration in workers of various branches of industry. As experiments on humans are rather difficult, the harmful effect of vibration is usually examined on laboratory animals. In the majority of studies dealing with this problem the presence of noise (purposely or casually) was found in most cases. The aim of this study was to determine the effect of isolated long-term whole-body vibration and vertical sinusoidal shaking (10 Hz frequency, 5 mm amplitude, and 2 g acceleration) on Corti's organ. The study was carried out on young guinea pigs of both sexes. Eighty four animals (30 control and 54 experimental) with Preyer's reflex and without otoscopically detectable changes were used. A group of 18 animals was subjected to vibration in noiseless shaking apparatus for 30, 90 and 180 days. After a one-month rest, cochlear microphonics were performed under urethane anaesthesia. Our modification of the phase-sensitive detection method was used. Cochlear microphonics at frequencies of 260 Hz, 500 Hz, 1 kHz and 2 kHz was recorded from the apex of the cochlea and for 4 kHz and 8 kHz from the region of the round window. As the cochlear microphonics values showed significant individual differences, all experimental samples were examined by means of non-parametric tests. The outcome of the study demonstrated a gradual but considerable cochlear microphonics voltage decrease in the range to 2 kHz. This result pointed to the generation of vibration-induced damage in outer hair cells of the fourth and third turnings of the cochlea in the guinea pigs under study.

Animals↗
PubMed2000

Perilymphatic fluid compartments and intercellular spaces of the inner ear and the organ of Corti.

An in vitro preparation of the inner ear cochlea has been used to visualize the structural relationships of unfixed, living sensory cells and structural components within the intact hearing organ. By perfusing perilymphatic compartments of the cochlea with fluorochrome-conjugated dextran, the extracellular spaces were clearly outlined. The staining pattern illustrated the large fluid compartments formed by the tunnel of Corti, the space of Nuel, and the outer tunnel. The dextran solution also indicated the spaces between the outer hair cell rows, the inner hair cells, and the surrounding supporting cells. The staining pattern demonstrates that the organ of Corti has a loose structure, suggesting a weak mechanical coupling between the cells. Moreover, it is evident that substances applied to the perilymph (e.g., therapeutic drugs) will readily reach all the cells of the hearing organ. In addition to the intraorgan fluid compartments, the spiral limbus was shown to contain significant volumes of perilymph within the intercellular spaces forming the so-called teeth of Huschke between the interdental cells. An extensive system of bundles following the teeth of Huschke was shown to be completely immersed in perilymph. The bundles were stained by a potentiometric dye, which in the inner ear primarily stains nerve fibers and sensory cells, which may indicate a nervous control of cells in this region.

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