BACKGROUND AND OBJECTIVES: Endolymphatic hydrops has been considered as an important histologic substrate of Meniere's disease. A permanent displacement of basilar membrane (BM) by increased endolymphatic pressure has been thought to be an explanation for hearing change. Direct observation of histological sections of temporal bones, however, suggested that stereocilia and tectorial membrane decoupling is more associated with pressure induced by mechanical deformation of the organ of Corti rather than with the displacement of BM. METERIALS AND METHOD: 26 cochleae from 13 female pigmented ginea pigs were harvested. One cochlea per each animal was injected with artificial perilymph. The other one was used as control. After fixation, followed by embedding and mid-modiolar sectionning, specimens were observed with a microscope. Morphometric parameters of each row and turn of the organ of Corti were measured and quantified. RESULTS: The average area and height of the organ of Corti were significantly smaller in the apical turn of the experimental group (p<0.05). The lengths of outer hair cell and Deiters cell in the apical turn were also significantly reduced in the experimental group (p<0.05). The angle between the outer hair cell and Deiters cell was smaller in the apex and in the 3rd turn of the experimental group (p<0.05). CONCLUSION: Results show that compression and deformation of the organ of Corti, especially in the apical turn, is a prominent feature in the acute endolymphatic hydrops model. We suggest that the deformation of organ of Corti is the primary cause of hydrops that induce the decoupling of tectorial membrane and stereocilia rather than the displacement of BM.
Animals ; Basilar Membrane ; Cochlea ; Edema ; Endolymphatic Hydrops* ; Female ; Guinea Pigs ; Hair ; Hearing ; Humans ; Meniere Disease ; Organ of Corti* ; Perilymph ; Stereocilia ; Swine ; Tectorial Membrane ; Temporal Bone

Noise-induced hearing loss (NIHL) is the second most common cause of permanent hearing impairment after age-related hearing loss. NIHL is influenced by environmental and genetic factors and the effects of noise can be exacerbated by the administration of ototoxic drugs or exposure to chemicals. The pathophysiology of NIHL is classified as either mechanical injury or metabolic (or biochemical) injury. Exposure of cochleae to intense sounds has been found to disrupt the stereocilia on the hair cells by separating the tip links and to depolymerize actin filaments, resulting in a disturbance in signal transduction. Major mechanisms of metabolic injuries include accumulation of reactive oxygen species enhanced by oxidative stress, cochlear ischemia followed by reperfusion injury, and excitotoxicity to auditory neuron induced by excessive release of the cochlear afferent neurotransmitter, glutamate. Many studies involving therapeutic or preventive trial with antioxidants, JNK inhibitors, and NMDA antagonists have shown partial effectiveness. However, protection from noise before cochlear injury occurs is very important because damaged hair cells and auditory neurons in the mammalian cochleae are unable to regenerate.
Actin Cytoskeleton ; Antioxidants ; Apoptosis ; Cochlea ; Glutamic Acid ; Hair ; Hair Cells, Auditory ; Hearing Loss ; Hearing Loss, Noise-Induced* ; Ischemia ; N-Methylaspartate ; Neurons ; Neurotransmitter Agents ; Noise ; Oxidative Stress ; Reactive Oxygen Species ; Reperfusion Injury ; Signal Transduction ; Stereocilia

Smoking has been positively associated with hearing loss in human. However, its effect on the cochlea has not been previously evaluated. Aim of work is to investigate the effect of nicotine, which is the primary pharmacological component of tobacco, on the structure of the cochlea of adult male guinea pigs. Fifteen male guinea pigs were classified into two groups: group I (control) and group II (nicotine treated group). Group II was further subdivided into two subgroups; IIA and IIB according to the dose of nicotine (3 mg/kg and 6 mg/kg, respectively). The cochlea was harvested and processed for light microscopy, transmission electron microscopy and scanning electron microscopy. Nicotine administration induced damage of outer hair cells which were distorted in shape with vacuolated cytoplasm and heterochromatic nuclei. Topography revealed damage of the stereocilia which included disorganization, bent and limp or complete loss and expansion of the surrounding supporting cells. These changes were more pronounced in the basal turn of the cochlea and mainly involved the outer hair cells. High dose induced more damage and resulted in protrusion of the apical poles of hair cells (blebing), particularly the outer two rows. Nicotine is proved to be harmful to the cells of the cochlea, particularly the outer hair cells of the basal turn. High doses induce blebing of hair cells.
Adult ; Animals ; Cochlea* ; Cytoplasm ; Guinea Pigs* ; Hair ; Hearing Loss ; Humans ; Male ; Microscopy ; Microscopy, Electron, Scanning ; Microscopy, Electron, Transmission ; Nicotine* ; Smoke ; Smoking ; Stereocilia ; Tobacco

OBJECTIVES: Gentamicin (GM) is a commonly used aminoglycoside antibiotic that generates free oxygen radicals within the inner ear, which can cause vestibulo-cochlear toxicity and permanent damage to the sensory hair cells and neurons. Piper longum L. (PL) is a well-known spice and traditional medicine in Asia and Pacific islands, which has been reported to exhibit a wide spectrum of activity, including antioxidant activity. In this study, we evaluated the effect of hexane:ethanol (2:8) PL extract (subfraction of PL [SPL] extract) on GM-induced hair cell loss in basal, middle and apical regions in a neonatal cochlea cultures. METHODS: The protective effects of SPL extract were measured by phalloidin staining of cultures from postnatal day 2-3 mice with GM-induced hair cell loss. The anti-apoptosis activity of SPL extract was measured using double labeling by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and myosin-7a staining. The radical-scavenging activity of SPL extract was assessed using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. RESULTS: SPL extract at a concentration of 1 microg/mL significantly inhibited GM-induced hair cell loss at basal and middle region of cochlea, while 5 microg/mL was effective against apical region hair cell loss. The protective effect of SPL extract was concentration dependent and hair cells retained their stereocilia in explants treated with SPL extract prior to treatment with 0.3 mM GM. SPL extract decreased GM-induced apoptosis of hair cells as assessed by TUNEL staining. The outer hair and inner hair counts were not decreased in SPL extract treated groups in compare to GM treated explants. Additionally, SPL extract showed concentration dependent radical scavenging activity in a DPPH assay. CONCLUSION: An anti-apoptosis effect and potent radical scavenger activity of SPL extract protects from GM-induced hair cell loss at basal, middle and apical regions in neonatal cochlea cultures.
Animals ; Apoptosis ; Asia ; Cochlea ; DNA Nucleotidylexotransferase ; Ear, Inner ; Ethanol* ; Gentamicins ; Hair* ; In Situ Nick-End Labeling ; Medicine, Traditional ; Mice ; Neurons ; Pacific Islands ; Phalloidine ; Piper* ; Reactive Oxygen Species ; Spices ; Stereocilia

BACKGROUND AND OBJECTIVES: The study was designed to investigate the changes in the expression of hypoxia inducible factor-1alpha (HIF-1alpha) according to time after being exposed to noise trauma and find out the effect of HIF-1 alpha in the prevention of noiseinduced hearing loss by pre-treatment with cobalt chloride (CoCl2). SUBJECTS AND METHOD: BALB/c hybrid mice with 25 dB HL or less ABR were used in this study. In the study group, subjects were exposed to 120 dB SPL broad white band noise for 3 hours per day for 3 days. The changes in their hearing were documented before and after 1, 2, 3, 4, and 9 days of the first noise exposure. CoCl2 was injected into the peritoneum 2 hours prior to each noise exposure to see the effect of induced HIF-1alpha on noise-induced hearing loss. For the control, injection with distilled water was performed and hearing thresholds were measured in the same manner. Cochlea from each group was obtained in order to observe the morphological changes in the inner ear and the expression of the HIF-1alpha using immunohistochemial staining and immuno-fluorescein staining along with quantification of the hair cell loss. RESULTS: Mice exposed to the noise for 3 days, showed permanent threshold shift and the expression of HIF-1alpha was increased. When HIF-1alpha was induced by pre-treatment of CoCl2 prior to the noise exposure, however, hearing recovery was observed to some degree. And hair cell survival rate was also higher when treated with CoCl2 compared to the distilled water treated group. CONCLUSION: When pre-treated with CoCl2, inducing HIF-1alpha before the noise trauma, it allowed for a less stereocilia loss in the hair cells in the organ of Corti. HIF-1alpha may play an important role in the prevention of noise-induced hearing loss.
Animals ; Anoxia ; Cell Survival ; Cobalt ; Cochlea ; Ear, Inner ; Hair ; Hearing ; Hearing Loss ; Hearing Loss, Noise-Induced* ; Hypoxia-Inducible Factor 1 ; Mice ; Noise ; Organ of Corti ; Peritoneum ; Stereocilia ; Water

BACKGROUND AND OBJECTIVES: Mechanism of inner ear hair cell distortion after noise exposure has been well described. The present study was designed to determine the response to the auditory system of a genetically well-defined laboratory mouse in preparation for examining the effect of noise on mice with specific genetic mutations. So it is important to recognize the relationship between noise exposure duration and hair cell morphological changes. We try to reveal the hearing loss and inner ear hair cell morphological changes after applying the noise protocol. SUBJECTS AND METHOD: The mice were BALB/c hybrids and aged 8 weeks. Six mice served as non-noise-exposed controls and 8 mice were exposed for 3 hours per day to white band noise with a center frequency from 0.2 kHz to 70 kHz and a sound pressure level of 120 dB. And we divided the noise exposure group into 3 subgroups(1 day, 3 day, 5 day noise exposure group). We checked the photographs of FITC phalloidin stain and scanning electron microscopy of cochlea after noise exposure. RESULTS: The hearing level of mice decreased after noise exposure. We could see the stereocilia damage in cochlea after FITC phalloidin stain in cochlea and sterocilia loss was more severe in basal turn. In scanning electron microscopy, morphological changes of stereocilia were observed to be more severe in the cochlear basal turn than other area. Significant hair cell loss in the cochlear basal turn could be calculated using cochleocytogram. CONCLUSION: 120dB broad white band noise can damage the hair cell of cochlea in mice. These changes were especially severe in the cochlear basal turn. Noise exposure duration is the other important factor in damaging cochlear hair cells. Therefore, we can guess that harmful noise level and noise exposure duration are the main risk factors that injure the inner ear hair cell.
Animals ; Cochlea ; Ear, Inner* ; Fluorescein-5-isothiocyanate ; Hair* ; Hearing ; Hearing Loss ; Mice* ; Microscopy, Electron, Scanning ; Noise* ; Phalloidine ; Risk Factors ; Stereocilia

BACKGROUND AND OBJECTIVES: Cisplatin (CP), an antitumor agent widely used in the treatment of head and neck cancers, has side effects such as ototoxicity and nephrotoxicity. These side effects are closely related to oxidative stress. In the present study, we attempted to suppress CP-induced ototoxicity in rats by administering melatonin, an antioxidant. MATERIALS AND METHOD: Male Sprague-Dawley rats were divided into different groups and were treated as follows: 1) saline control, 2) CP (16 mg/kg, i.p.), 3) CP plus melatonin (10 mg/kg, i.p.). The rats were sacrificed at the 6th day after CP treatment. RESULTS: CP-treated rats showed increase in cochlear malondialdehyde, hydrogen peroxide, glutathione peroxidase and glutathione reductase levels, and the decrease in cochlear superoxide dismutase (SOD) and catalase levels. CP-treated rats showed markedly decreased in the number of stereocilia on the inner hair cells and mildly decreased in the number of outer hair cells in organ of Corti under the light and scanning electron microscopic examination. Light and electron microscopic findings, and cochlear hydrogen peroxide, malondialdehyde, SOD, catalase, glutathione peroxidase and glutathione reductase levels were restored in the rats injected with CP plus melatonin than those with CP alone. CONCLUSION: These results suggest that melatonin suppresses CP-induced ototoxicity via the suppression of the increased production of reactive oxygen species.
Animals ; Catalase ; Cisplatin* ; Glutathione Peroxidase ; Glutathione Reductase ; Hair ; Head ; Humans ; Hydrogen Peroxide ; Male ; Malondialdehyde ; Melatonin* ; Neck ; Organ of Corti ; Oxidative Stress ; Rats* ; Rats, Sprague-Dawley ; Reactive Oxygen Species ; Stereocilia ; Superoxide Dismutase

BACKGROUND AND OBJECTIVES: The Deiters' cell is one of the supporting cells in the organ of Corti and is known to possibly regulate the signal transduction pathway in the organ of Corti. The signal transduction process can be modulated by ATP and acetylcholine, the so-called neurotransmitters, in Deiters' cells. Intracellular Ca2+ concentration can be also increased by these neurotransmitters and the control mechanism on the organ of Corti is highly suggested in Deiters' cells. Potassium ion (K+) is known to be important both in hair cells and supporting cells. Through K+ channel, the membrane potential may be controlled and the signal transduction pathway can be regulated. Furthermore, the motility of outer hair cell and the signal transduction from the apical stereocilia are considered to be regulated by this channel. The aim of this study is to record the K+ current in the isolated Deiters' cells from guinea pig cochlea. MATERIALS AND METHODS: Deiters' cells were isolated from the organ of Corti of guinea pig by using collagenase and a pipet. A whole cell patch clamp was performed under the inverted microscope and the current was measured with List-7 amplifier and pClamp 8.0.2 software. RESULTS: The resting membrane potential was -15.02+/-2.66 mV (n=6). When the cell membrane was hyperpolarized into -110 mV from the -40 mV holding potential, the peak current was -227+/-39.9 pA (n=15). After having depolarized to the maximum, (50 mV), the peak current was 7123+/-737 pA, and the reversal potentials of different external K+ concentration changed in the K+-dependent manner. About 80% of this current was inhibited by TEA. When K+ was substituted by Cs+, the peak current was 1788+/-231 pA at 50 mV step pulse. Activation curve of this outward current showed two different Vh (half activation voltage) and K (slope factor). CONCLUSION: Outward rectifying K+ channels exist in Deiters' cells and they can be inhibited by TEA and permeable to Cs+. More than two types of K+ current can exist and they may play a role in the recovery of membrane potential after depolarization,
Acetylcholine ; Adenosine Triphosphate ; Animals ; Cell Membrane ; Cochlea* ; Collagenases ; Guinea Pigs* ; Guinea* ; Hair ; Labyrinth Supporting Cells ; Membrane Potentials ; Neurotransmitter Agents ; Organ of Corti ; Patch-Clamp Techniques ; Potassium ; Potassium Channels ; Signal Transduction ; Stereocilia ; Tea

BACKGROUND AND OBJECTIVES: The mechanism of the noise damage to the cochlea is not fully understood in spite of many studies. The morphological changes in a noise stimulated model show various features relating to the duration of the exposure and sound intensity. Until now there had been a lot of the morphological studies on noise induced hearing loss models, but only a few reports of single blast injury of more than 150 dB. MATERIALS AND METHOD: We observed with a transmission electron microscope by using the microslicing technique for minimizing the tissue injury and successful hair cell counting in resin embedded cochlea of the guinea pig, stimulated by a 178 dB single blast wave. RESULTS: The area of hair cell damage in L.M. showed stereocilia bending at 24 hours, proliferation of Hensen's body, subsurface cistern in outer hair cell and mitochondria proliferation in inner hair cell within 2wks. The area of no hair cell damage in L.M. showed minimal changes in E.M., as well. CONCLUSION: These results suggest that the 178 dB single blast wave injury may not cause severe distortion of the organ of Corti in the guinea pig and thus the compensation process can be advanced gradually.
Animals ; Blast Injuries ; Cell Count ; Cochlea* ; Compensation and Redress ; Guinea Pigs* ; Guinea* ; Hair ; Hearing Loss ; Microscopy, Electron ; Mitochondria ; Noise ; Organ of Corti ; Stereocilia

BACKGROUND AND OBJECTIVES: Nitric oxide has been suggested to play an important role in the pathogenesis of cisplatin ototoxicity. L-NAME (NG-Nitroarginine Methyl Ester) is an inhibitor of nitric oxide synthase. MK-801 (Dizocilpine Maleate) is a NMDA receptor antagonist. To evaluate a role of nitric oxide in cisplatin ototoxicity, we investigated whether L-NAME and MK-801 can block the cisplatin ototoxicity in guinea pigs. MATERIALS AND METHOD: In the Group 1, normal saline was injected intraperitoneally as a control group. Group 2, 3, 4, and 5 were injected intraperitoneally as described in the following: Group 2, cisplatin only; Group 3, L-NAME+isplatin; Group 4, MK-801+cisplatin; Group 5, L-NAME+K-801+cisplatin. Using an auditory brainstem response, hearing threshold was tested before cisplatin administration and 5 days after cisplatin injection in each group. The morphological changes of the cochlea were observed by scanning electron microscopy. RESULTS: In the Group 2, a significant hearing loss was observed comparing to Group 1. In contrast , Group 3, 4, and 5 did not demonstrate any significant hearing loss compared to Group 1. In the scanning electron microscopy, the Group 2 showed distorsion and loss of stereocilia of the hair cells. However, the Group 1, 3, 4, and 5 demonstrated well preserved cochlear hair cell morphology. CONCLUSION: Hearing loss induced by ototoxicity of cisplatin was prevented by L-NAME and MK-801. This study suggests that NO may mediate cisplatin ototoxicity.
Animals ; Cisplatin* ; Cochlea ; Dizocilpine Maleate* ; Evoked Potentials, Auditory, Brain Stem ; Guinea Pigs* ; Guinea* ; Hair ; Hearing ; Hearing Loss ; Microscopy, Electron, Scanning ; N-Methylaspartate ; NG-Nitroarginine Methyl Ester* ; Nitric Oxide ; Nitric Oxide Synthase ; Stereocilia