Downregulation of inwardly rectifying potassium channel 5.1 expression in C57BL/6J cochlear lateral wall / 华中科技大学学报（医学）（英德文版）

Age-related hearing loss (AHL) is one of the most common sensory disorders among elderly persons. The inwardly rectifying potassium channel 5.1 (Kir5.1) plays a vital role in regulating cochlear K(+) circulation which is necessary for normal hearing. The distribution of Kir5.1 in C57BL/6J mice cochleae, and the relationship between the expression of Kir5.1 and the etiology of AHL were investigated. Forty C57BL/6J mice were randomly divided into four groups at 4, 12, 24 and 52 weeks of age respectively. The location of Kir5.1 was detected by immunofluorescence technique. The mRNA and protein expression of Kir5.1 was evaluated in mice cochleae using real-time polymerase-chain reactions (RT-PCR) and Western blotting respectively. Kir5.1 was detected in the type II and IV fibrocytes of the spiral ligament in the cochlear lateral wall of C57BL/6J mice. The expression levels of Kir5.1 mRNA and protein in the cochleae of aging C57BL/6J mice were down-regulated. It was suggested that the age-related decreased expression of Kir5.1 in the lateral wall of C57BL/6J mice was associated with hearing loss. Our results indicated that Kir5.1 may play an important role in the pathogenesis of AHL.

Expression Changes of Endothelin-1, Endothelin Receptor A and B in the Cochlea after Noise Exposure / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: There are several evidences of reduced cochlea blood flow after noise exposure in the cochlea. However, the pathophysiology of blood flow change is still obscure, and endothelins, proteins that constrict blood vessels and play a key role in vascular homeostasis using its receptors may have importance in this respect. In this study, we investigated the expression changes of endothelin-1 (ET-1), endothelin receptor A (ETAR) and B (ETBR) according to auditory threshold change after noise exposure. MATERIALS AND METHOD: Mice were exposed to different noise to generate transient (group 2) and permanent threshold shift (group 3), respectively. Auditory threshold shifts were evaluated with auditory brainstem response and expression changes of ET-1, ETAR and ETBR after noise exposure were evaluated by immunohistochemistry and real time RT-PCR. RESULTS: After noise exposure, the increased ET-1, ETAR and ETBR immunoreactivities were observe in stria vascularis, spiral ligament and spiral ganglion neuron. ET-1 mRNA expressions increased after noise exposure in both group 2 and group 3 compared to those of the control group. At 2 weeks after noise exposure, however, the ET-1 mRNA expressions in group 3 increased compared to that of the control but decreased compared to that of group 2. On the other hand, ETAR mRNA expression increased at 2 weeks after noise exposure in both groups, just after noise exposure in group 2 and at 2 weeks after noise exposure in group 3. CONCLUSION: These results suggest that expression changes of ET-1, ETAR and ETBR might be associated with hearing threshold shift and recovery after noise exposure in the cochlea.

Expression of Aquaporin-2 in the Inner Ear of Water-Deprived Guinea Pigs / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Although the role of aquaporin-2 (AQP2) in the kidney has been well defined, its role in the inner ear remains to be determined. The present study was to investigate the effect of water deprivation on the expression of AQP2 in the inner ear. MATERIALS AND METHOD: Healthy male guinea pigs weighing 250 g were used. The experimental group underwent water restriction and the control underwent water loading with sucrose-containing water for 3 days. Concentrations of plasma arginine-vasopressin (AVP) were determined and electrocochleography (ECoG) recordings were made. An RT-PCR, real-time PCR and Westernblotting analysis were used for quantitative analysis of AQP2 mRNA and AQP2 protein expression. Immunohistochemistry was also used to evaluate the distribution of AQP2 water channel proteins in the inner ear. RESULTS: AQP2 was mainly expressed in the epithelium of endolymphatic sac, spiral limbus, spiral ligament and stria vascularis of scala media. The concentrations of plasma AVP were 9.2+/- 0.8 pg/mL in the experimental group and 0.78+/-0.3 pg/mL in the control. The summation potential/ action potential (SP/AP) ratio in ECoG was markedly increased in the experimental group (0.55 in the experimental and 0.29 in the control). RT-PCR and real time PCR as well as Western blot analysis showed that the level of AQP2 mRNA and protein in the cochlea and endolymphactic sac of the water-deprived group was significantly higher than those in the control group. CONCLUSION: These data suggest that AQP2 is one of the important water channels in fluid homeostasis in the inner ear. Moreover, the volume of endolymphatic space can be increased via AVP-AQP2 system in response to water deprivation.

Expression Patterns of KCNJ10 K+ Channel in the Cochlear Lateral Wall After Acoustic Trauma / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: It is well known that noise exposure leads to the sensory hair cell loss and other neuronal damage in the cochlea. But recently it has been reported that noise exposure could also damage lateral wall of cochlea such as stria vascularis and spiral ligament. K+ is the major cation in endolymph and important to maintain homeostasis within the cochlea. We have investigated the expression patterns of KCNJ10 K+ channel in noise induced cochlear damage. MATERIALS AND METHOD: Twenty adult male guinea pigs (300-350 g) were included in this study. In experimental group (n=16), acoustic trauma was induced by continuous broad band noise for 2 hr to 115 dB SPL and broad band noise for 6 hr to 120 dB SPL with 3 consecutive days. After noise exposure, auditory brainstem response threshold shift and hair cell loss were evaluated. A study for KCNJ10 K+ channel expression was examined by immunohistochemical staining. RESULTS: After noise exposure, auditory brainstem response showed transient threshold shift (TTS) and permanent threshold shift (PTS) in accordance with noise exposure. The expression patterns of CKNJ10 K+ channel were changeable in TTS group. But there were no change of expression patterns in PTS group. CONCLUSION: In the cochlear lateral wall, KCNJ10 K+ channel expressions were affected with noise exposure and these changes might be associated with the regulation of homeostasis in the cochlea lateral wall.

Regional Distribution of 5-HT 1A, 1B, and 1D Receptors in Rat Vestibular Nuclei (Vn) and Inner Ear

Migraine and anxiety disorders are frequently co-morbid with balance disorders. Potential mechanisms for migrainous vertigo include sites of action of 5-HT (serotonin) 1B and 1D receptor agonists such as rizatriptan, which attenuate motion sickness in migraineurs. Selective serotonin reuptake inhibitors (SSRIs) are also known to be efficacious in the treatment of vertigo. Relative distribution of the 5-HT receptor subtypes and their functional roles in the vestibular nuclei and inner ear is still unknown. Using 5-HT1A, 1B, AND 1D receptors-specific antibody, we have demonstrated a differential distribution of these receptor subtypes within the rat vestibular nuclei and inner ear. For 5-HT receptor subtypes expression in the vestibular and auditory periphery, most ganglion cells in the vestibular ganglion showed immunoreactivity for 5-HT1A, 5-HT1B and 5-HT1D receptors. In addition, 5-HT1B and 1D receptors immunopositive reactivities were associated with endothelial cells of small blood vessels in the vestibular ganglion and nerve, endothelial cells in both the spiral ligament deep to the spiral prominence and stria vascularis and endothelial cells on blood vessels along the margins of the spiral ganglion. For 5-HT receptor subtypes expression in the vestibular nuclei (VN), the 5-HT1A, 1B and 1D receptors were expressed differentially in the VN. Fine varicose axons in the periventricular plexus showed intense 5-HT1A receptor expression in the medial VN (MVN) and extended into the superior VN (SVN). By contrast, 5-HT1B receptors were not expressed the ventricular plexus axons. Rather, 5-HT1B and 1D receptors immunopositive cell bodies and neuronal processes were dense in rostral MVN, dorsal SVN, lateral VN (LVN) and ventral aspect of nucleus prepositus hypoglossi (NPH). In the present study, inner ear and vestibular nuclei showed distinct distributions of 5- HT1A, 1B and 1D receptors expressions that are parallel to their distribution in peripheral and central nociceptive pathways. These differentially distributed 5-HT receptor subtypes are potential targets to explain the efficacy of SSRIs and triptans in treating migraine and migrainous vertigo.

Expression of Protein Kinase C Isotypes in the Albino Guniea Pig Cochlea / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Protein kinase plays an important role in transmembrane signalling, which is modulated by cellular transduction by second messengers such as inositol-1, 4, 5-triphosphate (IP3), Diacylglycerol (DG), cAMP, to express biological activity by stimulation of hormones, neurotransmitters, antigens, growth factors. Protein kinase Cs participate in signal transduction of cell, secretion of neurotransmitter, regulation of ion conduction, exocytosis, gene expression and cellular proliferation. Also, it raises slow motility by Na+-H+ exchange (NHE) and Ca2+ channel in the outer hair cells. It may also be involved in mechanical transduction, cellular proliferation and reproduction in supporting cells, and in producing endolymphs using the KCNE1 and Na+/K+-ATPase in the lateral wall of cochlea. MATERIALS AND METHOD: We investigated the immunoreactivities of the PKC (alpha, beta, gamma, delta) via paraffin section and surface preparation of the cochlea of albino guinea pigs. RESULTS: PKC alpha immunoreactivities were shown in the outer and inner hair cell cytoplasm and delta was revealed in the type II fibrocytes and suprastrial cells in the basal turn of the spiral ligament. But beta, gamma were not shown. CONCLUSION: We suggest that PKC alpha may induce the slow motility and depolarization to mediate the ion conductance in the hair cells. Also, PKC delta may participate in the production of endolymph. We thus conclude that PKC alpha and delta play an important role in the cochlear signal transduction.

Expression of Tonicity-Responsive Enhancer Binding Protein (TonEBP) in the Rat Cochlea: An Immunohistochemical Study / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The inner ear is an organ used for hearing and balance. For its normal function, the inner ear fluid homeostasis is required. There has been controversy over the regulatory mechanisms of maintaining inner ear fluid balance, and they have not yet been clearly defined. TonEBP is the protein that binds tonicity-responsive enhancer elements in the osmoprotective gene, which elevates the compatible osmolytes, which in turn induces cell survival in hypertonic condition. The aim of this study was to elucidate if there is an osmoregulatory mechanism in cochlea. Material and Method: The localization of TonEBP in the cochlea of male Sprague-Dawley rats was studied by immunohistochemistry with an anti rabbit polyclonal anti-rat TonEBP antibody. RESULTS: TonEBP was expressed at outer hair cells, Deiter cells, spiral ligaments, sprial limbus connective tissues, and epithelial lining of basilar membrane facing scala tympani. CONCLUSION: TonEBP in cochlea is one of the proteins involved in elucidating cell survival in changed tonicity during inner ear homeostasis.

Noise Induced Changes of Glucocorticoid Receptors in Rat Cocohlea / 대한이비인후과학회지

It has been suggested that glucocorticoid receptors are present in inner ear tissues and may act in stress related mechanism of cochlea. The purpose of this study was to determine whether stress to auditory system could change glucocorticoid receptors(GR) in the cochlear tissues and to hypothesize the relationship between heat shock protein and glucococorticoid receptors which may involve in stress related mechanism of cochlea. Sprague-Dawley rats were exposed to intense broad band noise(110dB SPL) as a stressful condition to auditory system and immunohistochemical and western blot analyses were used to compare the expression patterns of glucocorticoid receptors between noise exposed and normal rat cochlea. In western blot analysis, immunoreactive bands of noise exposed cochlear tissues were weaker than those of normal non-noise exposed cochlear tissues. In immunohistochemistry, GR immunostaining was observed in spiral ligament, stria vascularis, and outer hair cells of both noise exposed and normal cochlear tissues. Density of immunoreactive staining was decreased after noise exposure. With these results was could hypothesize the relationship between glucocorticoid receptor and heat shock proteins under stressful condition in the cochlea. If the cochlea is exposed to stress such as noise trauma, glucocorticoid hormone would be released and enter the cell to bind to glucocorticoid receptors with dissociation of heat shock proteins from the DNA binding sites. Then the levels of glucocorticoid receptors in the cytoplasm would be decreased and resultant increased expression of heat shock proteins may occur. This study suggest that glucocorticoid receptors may participate in stress response of the cochlea alone or in conjunction with heat shock proteins.