No abstract available.
Noise* ; Organ of Corti*

Inner ear is an important organ that is responsible for balance and hearing. It is composed of two complicated major subunits, vestibular organ and cochlea. During development, both functional units require complex genetic interactions to achieve proper patterning and morphology as its purpose. This review comprises three parts. In the first part, general information about technical tools in studying mouse ear development is introduced. In the second part, it is shown how semicircular canals are formed and what genetic interaction is involved in canal formation. In the last part, genetic interactions required for proper development of cochlea are elaborated, focusing on the length of cochlea and morphology of organ of Corti. The study about development of mutant mice provides us useful information about genetic interaction involved in the formation of structures for hearing and balance. The data acquired in the development field could provide a breakthrough to hair cell regeneration and stem cell therapy fields in stuck, which are directly applicable to human.
Animals ; Cochlea ; Ear ; Ear, Inner ; Hair ; Hearing ; Humans ; Mice ; Organ of Corti ; Regeneration ; Semicircular Canals ; Stem Cells

BACKGROUND AND OBJECTIVES: It has been known that the motility of the outer hair cell controls the physiological characteristics of the organ of Corti. Motility can be divided into two different types: fast and slow motility. Slow motility can be induced by high concentration of KCl and increase of intracellular Ca2+ concentration. In this study, authors aimed to define the effect of acetylcholine, one of the efferent neurotransmitters, on the slow motility of the outer hair cells of guinea pig. MATERIALS AND METHOD: Outer hair cells were isolated from guinea pigs by enzymatic and mechanical dissociation. The length of the hair cells was recorded by CCD camera equipped on an inverted microscope. Slow motility was induced by 10 (micro)M of ionomycin and 150 mM of KCl. Carbamylcholine (1 mM), a non-hydrolyzable derivative of acetylcholine, was used to observe the effect of acetylcholine and choline chloride (1 mM) was used as control. RESULTS: The length of outer hair cell was decreased after adding 150 mM of KCl and increased after adding 10 (micro)M of ionomycin. Stimulation of carbamylcholine (1 mM) did not induce the length change of the outer hair cells. Preincubation of 1 mM of carbamylcholine also did not affect the length change induced by ionomycin or KCl in outer hair cells. CONCLUSION: We could suggest that carbamylcholine does not have an effect on the slow motility of outer hair cell induced by the change of osmotic pressure which was elicited by high potassium, or intracellular Ca2+ increase.
Acetylcholine ; Animals ; Calcium* ; Carbachol ; Choline ; Guinea Pigs ; Hair* ; Ionomycin ; Neurons, Efferent ; Neurotransmitter Agents ; Organ of Corti ; Osmotic Pressure ; Potassium Chloride ; Potassium*

Noise-induced hearing loss could be caused by mechanical destruction of the delicate membranes of the inner ear, hair cells and supporting structures of the organ of Corti, and by intense metabolic activity, which increases free radical formation in the cochlea. When exposure is continuous, injury is a consequence of the total amount of energy to which cochlear tissues are exposed and a hearing conservation program is essential including hearing protection devices. Several therapeutic trials including antioxidant agents have been shown at least partially effective in prevention of hearing loss and hair cell death.
Cell Death ; Cochlea ; Ear, Inner ; Hair ; Hearing ; Hearing Loss* ; Hearing Loss, Noise-Induced ; Membranes ; Noise* ; Organ of Corti

Deiters' cells are the supporting cells in organ of Corti and are suggested to play an important role in biochemical and mechanical modulation of outer hair cells. We successfully isolated functionally different K+ currents from Deiters' cells of guinea pig using whole cell patch clamp technique. With high K+ pipette solution, depolarizing step pulses activated strongly outward rectifying currents which were dose-dependently blocked by clofilium, a class III anti-arrhythmic K+ channel blocker. The remaining outward current was transient in time course whereas the clofilium-sensitive outward current showed slow inactivation and delayed rectification. Addition of 5 mM tetraethylammonium (TEA) further blocked the remaining current leaving a very fast inactivating transient outward current. Therefore, at least three different types of K+ current were identified in Deiters' cells, such as fast activating and fast inactivating current, fast activating slow inactivating current, and very fast inactivating transient outward current. Physiological role of them needs to be established.
Animals ; Ear, Inner ; Guinea Pigs* ; Guinea* ; Hair ; Hearing ; Organ of Corti ; Pharmacology ; Potassium Channels ; Potassium* ; Quaternary Ammonium Compounds ; Tetraethylammonium

BACKGROUND AND OBJECTIVES: Organotypic culture of organ of Corti maintains the basic organization of the spiral lamina and can conserve several factors responsible for the neuronal growth of the nervous components. The explant culture technique has been widely used in organ culture system, however, the floating drop method using collagen gel was also developed as a simple and reliable method. In order to study the effect of growth factors on the regenerative and protective ability of cochlear hair cells, we first had to establish an in vitro model of the inner ear. MATERIALS AND METHODS: Organ of Corti was obtained from newborn rats and cultured with the floating drop method using collagen gel. Immunohistochemical staining was used to visualize the stereocilia and scanning electron microscopic study was also carried out. RESULTS: Explants were maintained up to 10 days without contamination. Morphologically, immunofluorescent staining with phalloidin showed well preserved outer and inner hair cells with stereocilia on the second day of culture. On the tenth day of culture, the staining result showed inner and outer hair cells, although the stereocilia were poorly stained. In scanning electron microscopic examination, an explant on the tenth day of culture showed preserved outer and inner hair cells and stereocilia, although damaged hair cells and stereocilia were also observed. CONCLUSION: The floating drop method was an appropriate method for maintaining the organ of Corti in vitro with the advantage being the easiness in its manual manipulation.
Animals ; Collagen ; Culture Techniques ; Ear, Inner ; Hair ; Humans ; Infant, Newborn* ; Intercellular Signaling Peptides and Proteins ; Neurons ; Organ Culture Techniques ; Organ of Corti* ; Phalloidine ; Rats* ; Spiral Lamina ; Stereocilia

OBJECTIVETo determine weather or not the mtDNA(4568) deletions in guinea-pig contribute to the development of presbycusis.

METHODSForty-four guinea-pigs were divided into 2 groups: group A (young control group, normal hearing, 22 guineas) and group B (aged group). The group B was subdivided into group B(1) (old normal hearing, 6 guineas) and group B(2) (old hearing loss, 16 guineas). First the guineas were tested by auditory brainstem response (ABR), and then the Cortis's tissues, auditory nerve tissues, brain and blood were harvested and the total DNA was extracted. The mtDNA(4568) deletion was analyzed by PCR.

RESULTSHearing loss was occurred with age. The mtDNA(4568) deletion incidence of aged group in all tissues was significant higher than that of young control group (P< 0.05). The incidence of mtDNA deletion in Cortis's and auditory nerve with presbycusis (B(2) group) were significant higher than that of aged normal hearing group (B(1) group) (P< 0.05). The incidence of mtDNA deletion in brain and blood was not significantly different between presbycusis and aged normal hearing group (P> 0.05).

CONCLUSIONmtDNA(4568) deletion of guinea-pig possibly contributes to aging and mtDNA(4568) deletion in Cortis's and auditory nerve tissues of guinea-pig may be associated with presbycusis. There is no enough evidence to prove that the mtDNA(4568) deletions in brain and blood are related with presbycusis.

Age Factors ; Animals ; Base Sequence ; Cochlear Nerve ; metabolism ; physiopathology ; DNA, Mitochondrial ; genetics ; Evoked Potentials, Auditory, Brain Stem ; Guinea Pigs ; Organ of Corti ; metabolism ; physiopathology ; Presbycusis ; genetics ; physiopathology ; Sequence Deletion

OBJECTIVES: Apoptosis may play an important role in the mechanism underlying the GJB2 gene conditional knockout (cCx26) mice cochlear cell death. The objective of this study was to explore the the damage mode of the outer hair cells (OHCs) and its real time point of apoptosis and provide information to further explore the role of apoptosis in the happening of hearing loss in cCx26 mice. METHODS: Cochleae from mice at various developmental stages (P8, P12, and P21) were dissected out and first used to be observed under the scanning electron microscope (SEM). Basilar membranes from mice at P8, P14, P18, and P21 were stained by fluorescein isothiocyanate-conjugated phalloidin and propidium iodide (PI) and examined under confocal microscope. RESULTS: The loss of OHCs of cCx26 knockout mice was first set between P12 and P21 under SEM. Whole mount phalloidin and PI staining revealed that obvious apoptotic appearance of the OHCs surface morphology was observed at P18. CONCLUSION: Typical apoptotic morphology was found in the OHCs in the organ of Corti of the cCx26 mice at P18. This may provide information to further study the role of apoptosis in the occurrence of hearing loss of cCx26 mice.
Animals ; Apoptosis ; Basilar Membrane ; Cell Death ; Cochlea ; Connexins ; Electrons ; Fluorescein ; Hair ; Hair Cells, Auditory, Outer ; Hearing Loss ; Hearing Loss, Sensorineural ; Mice ; Mice, Knockout ; Organ of Corti ; Phalloidine ; Propidium

OBJECTIVES: Morphological studies on presbycusis, or age-related hearing loss, have been performed in several different strains of mice that demonstrate hearing loss with auditory pathology. The C57BL/6 (C57) mouse is a known model of early onset presbycusis, while the CBA mouse is characterized by relatively late onset hearing loss. We performed this study to further understand how early onset hearing loss is related with the aging process of the cochlea. METHODS: We compared C57 cochlear pathology and its accompanying apoptotic processes to those in CBA mice. Hearing thresholds and outer hair cell functions have been evaluated by auditory brainstem response (ABR) recordings and distortion product otoacoustic emission (DPOAE). RESULTS: ABR recordings and DPOAE studies demonstrated high frequency hearing loss in C57 mice at P3mo of age. Cochlear morphologic studies of P1mo C57 and CBA mice did not show differences in the organ of Corti, spiral ganglion, or stria vascularis. However, from P3mo and onwards, a predominant early outer hair cell degeneration at the basal turn of the cochlea in C57 mice without definitive degeneration of spiral ganglion cells and stria vascularis/spiral ligament, compared with CBA mice, was observed. Additionally, apoptotic processes in the C57 mice also demonstrated an earlier progression. CONCLUSION: These data suggest that the C57 mouse could be an excellent animal model for early onset 'sensory' presbycusis in their young age until P6mo. Further studies to investigate the intrinsic or extrinsic etiologic factors that lead to the early degeneration of organ of Corti, especially in the high frequency region, in C57 mice may provide a possible pathological mechanism of early onset hearing loss.
Aging ; Animals ; Apoptosis ; Cochlea ; Evoked Potentials, Auditory, Brain Stem ; Hair ; Hearing ; Hearing Loss ; Ligaments ; Mice ; Mice, Inbred CBA ; Models, Animal ; Organ of Corti ; Presbycusis ; Spiral Ganglion ; Stria Vascularis

BACKGROUNDModern research has provided new insights into the biological mechanisms of noise-induced hearing loss, and a number of studies showed the appearance of increased reactive oxygen species (ROS) and reactive nitrogen species (RNS) during and after noise exposure. This study was designed to investigate the noise exposure induced nitrotyrosine change and the mechanism of outer hair cells death in guinea pig cochlea.

METHODThirty guinea pigs were used in this study. The experimental animals were either exposed for 4 hours per day to broadband noise at 122 dB SPL (A-weighted) for 2 consecutive days or perfused cochleae with 5 mg/ml of the SIN1 solutions, an exogenous NO and superoxide donor, for 30 minutes. Then the cochleae of the animals were dissected. Propidium iodide (PI), a DNA intercalating fluorescent probe, was used to trace morphological changes in OHC nuclei. The distribution of nitrotyrosine (NT) in the organ of Corti and the cochlear lateral wall tissue from the guinea pigs were examined using fluorescence immunohistochemistry method. Whole mounts of organ of Corti were prepared. Morphological and fluorescent changes were examined under a confocal microscope.

RESULTSEither after noise exposure or after SIN1 perfusion, outer hair cells (OHCs) death with characteristics of both apoptotic and necrotic degradation appeared. Nitrotyrosine immunolabeling could be observed in the OHCs from the control animals. After noise exposure, NT immunostaining became much greater than the control animals in OHCs. The apoptotic OHC has significant increase of nitrotyrosine in and around the nucleus following noise exposure. In the normal later wall of cochleae, relatively weak nitrotyrosine immunolabeling could be observed. After noise exposure, nitrotyrosine immunoactivity became stronger in stria vascularis.

CONCLUSIONNoise exposure induced increase of nitrotyrosine production is associated with OHCs death suggesting reactive nitrogen species participation in the cochlear pathophysiology of noise-induced hearing loss.

Animals ; Cell Death ; Cochlea ; chemistry ; pathology ; Female ; Guinea Pigs ; Hair Cells, Auditory, Outer ; pathology ; Immunohistochemistry ; Male ; Noise ; adverse effects ; Organ of Corti ; chemistry ; pathology ; Tyrosine ; analogs & derivatives ; analysis