Association between sleep duration and hearing threshold shifts of adults in the United States: National Health and Nutrition Examination Survey, 2015-2016.

BACKGROUND: Obstructive sleep apnea (OSA) is linked to hearing loss (HL). Another sleep characteristics, sleep duration might also be associated with HL, but prior evidence is limited. This study is aimed to investigate the association between sleep duration and hearing level in the adult US population. METHODS: In total, a sample of 2777 individuals aged 20-69 years from the 2015-2016 National Health and Nutrition Examination Survey cycle (NHANES, 2015-2016) were investigated in this study. Self-reported sleep duration data was classified into the short-sleep (< 7 h), normal-sleep (7-9 h), and long-sleep (> 9 h) group. Multivariable linear regression models between sleep duration and hearing threshold shifts were estimated. Interactions between sleep duration and age, gender, race, OSA were also considered, and the study population was stratified by age, gender, race, and OSA to analyze the potential disparities among adults in different subgroups. RESULTS: Long-sleep duration was positively associated with speech- and high-frequency pure-tone average (PTA) thresholds with statistical significance (ß = 1.31, 95%CI: 0.10, 2.53, P = 0.0347, and ß = 2.71, 95%CI: 0.69, 4.74, P = 0.0087, respectively). When stratified by age, short sleep duration was positively associated with low-, and speech-frequency PTAs (P = 0.0140 and 0.0225, respectively) for adults aged 40-59 years, and long-sleep duration was positively associated with low-, and speech-frequency PTAs (P = 0.0495 and 0.0142, respectively) for adults aged 60-69 years with statistical significance. There was statistically significant interaction between OSA and sleep duration on speech-frequency PTA, but no significant interaction between either gender or race with sleep duration on hearing thresholds among US adults. CONCLUSION: Short/long sleep durations are associated with worse hearing level comparing to sleep 7-9 h in the American adults. Nonoptimal sleep duration may be a potential risk factor for HL.

Effects of Functional Rhinoplasty on Nasal Obstruction: A Meta-Analysis.

BACKGROUND: Functional rhinoplasty (FRP) is used to improve nasal ventilation by correcting problems with the nasal valves. It has not been systematically reviewed on a large scale. METHODS: A comprehensive literature search was conducted in the PubMed, EMBASE, and Cochrane Library databases to identify studies evaluating nasal obstruction before and after functional rhinoplasty in patients with nasal valve problems. RESULTS: A total of 57 cohorts from 43 studies involving 2024 patients were included in the current meta-analysis. The Nasal Obstruction Symptom Evaluation (NOSE) scores indicated significant improvement in nasal obstruction at the 1-month follow-up (WMD = 38.12; 95% CI, 29.15-47.10; I2 = 83.6%; P = 0.00), 3-month follow-up (WMD = 48.40; 95% CI, 43.16-53.64; I2 = 69.1%; P = 0.00), 6-month follow-up (WMD = 44.35; 95% CI, 36.65-52.04; I2 = 96.6%; P = 0.00), 12-month follow-up (WMD=43.07; 95% CI, 26.56-59.58; I2 = 97.9%; P = 0.00), and the last follow-up (WMD = 46.90; 95% CI, 43.92-49.88; I2 = 95.9%; P = 0.00) with respect to the preoperative baseline. The Visual Analogue Scale (VAS) scores indicated a similar trend at the 1-month follow-up (WMD = 4.68; 95% CI, 3.79-5.57; I2 = 86.8%; P = 0.00), 3-month follow-up (WMD = 4.46; 95% CI, 3.19-5.74; I2 = 93.3%; P = 0.00), 6-month follow-up (WMD = 4.91; 95% CI, 4.04-5.78; I2 = 88%; P = 0.00) and last follow-up (WMD = 4.22; 95% CI, 3.12-5.32; I2 = 97.1%; P = 0.00). Nasal obstruction was obviously relieved through rhinomanometry (SMD=0.56; 95% CI, 0.27-0.84; I2 = 0.0%; P = 0.00) but not through peak nasal inspiratory flow (PNIF) (SMD=-1.51; 95% CI, -3.10 to 0.07; I2 = 98.9%; P = 0.09). CONCLUSION: FRP may have a positive effect on nasal obstruction caused by nasal valve problems. Broader and well-designed studies are needed to shed more light on the relationships in this area. LEVEL OF EVIDENCE III: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

[Effect of the NF-κB/iNOS Signaling Pathway on Spiral Ganglion in Mouse Model of Sensorineural Hearing Loss].

Objective: To explore the effect of changes in the expression level of necorsis factor (NF)-κB/inducible nitric oxide synthase (iNOS) signaling pathway on hearing loss in a mouse model of sensorineural hearing loss (SNHL) induced by 3-nitropropionic acid (3-NP). Methods: The animal model was established by tympanic injection. C57BL/6 male mice were divided into three groups, 3-NP group receiving tympanic injection of 3-NP solution, 3-NP+EVP4593 group receiving tympanic injection of 3-NP solution and intraperitoneal injection of EVP4593 solution, and a control group receiving tympanic injection of phosphate buffered saline (PBS). Auditory brainstem response (ABR) was tested before and after injection. After 4 weeks, the cochlea was harvested and immunohistochemistry and qRT-PCR of NF-κB p65, RelB, iNOS, and Caspase-3 were conducted accordingly. Results: The hearing thresholds of the 3-NP group were higher than those of the control group and the 3-NP+EVP4593 group ( P<0.05), and the hearing thresholds of the 3-NP+EVP4593 group were also higher than those of the control group ( P<0.05). Immunofluorescence staining and qRT-PCR results showed that 3-NP exposure caused an increase in the expressions of NF-κB p65, RelB, and iNOS in the spiral ganglion in comparison with those of the control group ( P<0.05), and their expressions decreased with the administration of EVP4593 ( P<0.05). The expression of Caspase-3 in the spiral ganglion cells in the 3-NP group was higher than that in the control group, while in the 3-NP+EVP4593 group, it was lower than that in the 3-NP group ( P<0.05). Conclusion: This study found that, by activating the NF-κB/iNOS signaling pathway, 3-NP may cause inflammation in the spiral ganglion of the cochlear in the SNHL model mice, which may play an important role in the pathogenesis of SNHL.

[Effect of Connexin on Cochlear Blood-Labyrinth Barrier in a Mouse Model of Endolymphatic Hydrops].

Objective: To examine the expression of tight-junction connexin ZO-1 in the stria vascularis tissue of the cochlea by using spontaneous endolymphatic hydrops animal model constructed with PHEX gene mutant mice, and to analyze the dynamic changes of the gene mutant mice in pathology, imaging, and hearing function. Methods: Male Hyp-Duk/Y mice with PHEX gene mutation were selected as the experimental group at three time points, 21 days post birth (P21), 90 days post birth (P90) and 120 days post birth (P120), and wild-type male mice of the same ages were selected as the control groups. The cochlear sections were HE-stained in order to observe whether endolymphatic hydrops was present or absent and to assess its severity. The expression of connexin ZO-1 in both groups was evaluated through immunohistochemical staining of cochlear sections. Auditory-evoked brainstem response (ABR) was induced in both groups at P90 and gadolinium-enhanced MRI was conducted in vivo to observe the middle-order endolymphatic dilatation of cochlea in experimental and control mice aged P21, P90 and P120. Results: HE staining of pathological sections of PHEX Hyp-Duk/Y mice aged P90 and P120 showed increased endolymphatic hydronephrosis. The level of striae ZO-1 in PHEX Hyp-Duk/Y mice aged P90 and P120 was significantly lower than that of the controls of the same age (P<0.05). The expression level of ZO-1 was significantly negatively correlated with the degree of endolymphatic hydronephrosis (r=-0.939, P<0.01). The bilateral ABR threshold of PHEX Hyp-Duk/Y mice aged P90 was higher than that of the wild-type mice of the same age, and the mutant mice showed asymmetric hearing loss on both sides. Severe endolymphatic hydronephrosis was observed in PHEX Hyp-Duk/Y mice aged P90 and P120 through in vivo MRI gadolinium imaging. Conclusion: PHEX Hyp-Duk/Y can be used as a sound model for basic research of Ménière's disease. Compared with wild-type mice, PHEX Hyp-Duk/Y mice showed decreased expression of connexin protein ZO-1, which damaged the function of the blood-labyrinth barrier in stria vascularis, and was involved in the formation of endolymphatic hydrops. 7.0 T MRI gadolinium imaging can be used to observe the changes of severe endolymphatic hydrops in mice in vivo, providing imaging basis for the diagnosis of Ménière's disease.

Olfactory changes after endoscopic sinus surgery for chronic rhinosinusitis: A meta-analysis.

BACKGROUND: Endoscopic sinus surgery (ESS) is an important treatment modality for chronic rhinosinusitis (CRS). However, its effect on olfaction remains controversial. OBJECTIVE OF REVIEW: To assess the olfactory impact of ESS in patients with CRS. TYPE OF REVIEW: A meta-analysis. SEARCH STRATEGY: A systematic literature search in the PubMed, EMBASE and Cochrane Library databases was conducted to identify studies that assessed change in olfaction after ESS in patients with CRS. Search terms were related to paranasal sinus diseases, smell and endoscopy. EVALUATION METHOD: The extracted data included authors, publication year, study type, age, sex, diagnostic criteria, surgical mode, sample size, follow-up time, olfaction measurement tool and outcome. We analysed the olfactory changes as continuous variables. RESULTS: Thirty-five studies including 3164 patients with CRS were eligible for the meta-analysis. Among patients having CRS with nasal polyps, olfactory dysfunction improved, as assessed by the Sniffin' Sticks total score (P = .000), Sniffin' Sticks discrimination score (P = .023), Sniffin' Sticks identification score (P = .005), University of Pennsylvania Smell Identification Test (P = .046) and Visual Analogue Scale (P = .000). However, the threshold score of the Sniffin' Sticks test did not improve significantly (P = .361). Olfactory dysfunction did not improve in patients having CRS without nasal polyps according to the University of Pennsylvania Smell Identification Test (P = .404). In non-classified CRS patients, improvement in olfactory dysfunction was observed according to the University of Pennsylvania Smell Identification Test (P = .000), Visual Analogue Scale (P = .001) and Questionnaire of Olfactory Disorders-Negative Statements (P = .001). However, there were no significant improvements according to the Brief Smell Identification Test (P = .325), Sniffin' Sticks threshold score (P = .160) and Sniffin' Sticks identification score (P = .079). CONCLUSION: Endoscopic sinus surgery may be beneficial for improvement in olfactory conditions in patients with CRS. Further thorough and comprehensive studies need to be conducted.

Case presentation of an intranasal ectopic tooth in a pediatric patient.

An ectopic tooth in the nasal cavity is a rare phenomenon, especially on the inferior turbinate. In most of the reported cases, no etiological explanation of the intranasal teeth has been suggested or found. In children, intranasal ectopic teeth are usually associated with cleft lip and alveolus. Here, we report a rare case of a pediatric patient with unilateral nasal obstruction due to an intranasal ectopic tooth originating from the inferior turbinate without any facial and dental deformities. This case is unique due to the unusual location of the ectopic tooth and its presentation in a child without facial and dental deformities.

5-HT1A receptor-mediated activation of outward potassium current by serotonin in mouse cultured spiral ganglion neurons.

Cochlear spiral ganglion neurons provide the only pathway for transmitting sound evoked activity from the hair cells to the central auditory system. Serotonin plays a role in the response properties of central auditory neurons. However, knowledge about the role of serotonin in the peripheral auditory nervous system remains limited. In the current study, we investigated the influence of serotonin on outward potassium current in mouse cultured spiral ganglion neurons using whole-cell patch clamp technique. The cell capacitance was 4.03 ± 0.18 pF (n = 54). Application of serotonin caused an increase of outward potassium currents within seconds, whereas treatment with WAY100635, a selective 5-HT1A receptor antagonist, counteracted the increase effect of serotonin. These results suggest that serotonin increases outward potassium currents in cultured spiral ganglion neurons through the activation of 5-HT1A receptor. Serotonin may play an important role in sound transmission.

Urinary pyrethroid metabolite and hearing threshold shifts of adults in the United States: A cross-sectional study.

Hearing loss (HL) is a global health problem with a high prevalence and profound socioeconomic impact. Pyrethroids are one of the most commonly used insecticides. Although previous studies have reported the relationship between pyrethroids and neurotoxicity, little is known about the effect of pyrethroid exposure on the auditory system among the general population. This study is aimed to investigate the association of pyrethroid exposure with hearing threshold shifts of adults in the United States. A total of 726 adults, aged from 20 to 69 years from the 2011-2012 National Health and Nutrition Examination Survey (NHANES) data were included in the study. Urinary 3-phenoxybenzoic acid (3-PBA), a general pyrethroid metabolite, was used as a biomarker for pyrethroid exposure. HL was defined as a pure-tone average (PTA) at 0.5, 1, 2, 4 kHz ≥ 20 dB in the better ear. Analyses by using multivariate linear regressions were conducted to explore the associations of urinary 3-PBA with PTA hearing threshold shifts. There were no statistically significant correlations between Ln-transformed 3-PBA and either low-frequency or high-frequency hearing thresholds after adjusting for age, gender, race/ethnicity, education level, firearm noise exposure, occupational noise exposure, recreational noise exposure, serum cotinine, BMI, hypertension, and diabetes. However, associations of 3-PBA with both low-frequency and high-frequency hearing thresholds depended on age (P interaction < 0.0396 and 0.0017, respectively). Positive associations between Ln-transformed 3-PBA and both low-frequency and high-frequency hearing thresholds were observed in participants aged 20-39 years after adjusting confounders (ß = 1.53, 95% CI: 0.04-3.01, and ß = 3.14, 95% CI: 0.99-5.29, respectively) with the highest tertile (≥ 0.884 µg/g creatinine) of 3-PBA compared with the lowest tertile (< 0.407 µg/g creatinine). The possibility of interaction between 3-PBA and age on the hearing threshold shifts indicated that pyrethroid insecticides were prone to be more toxic to auditory system in younger adults than in older ones. Further studies will be required to confirm these findings.

Assessing the Quality of Hearing Aids-Related Videos on TikTok.

Hearing aids are effective at improving listening ability and health-related quality of life. Recently, we observed that there are many hearing aids-related videos published on TikTok. However, the quality of the information they offer remains unstudied. This study aimed to evaluate the information quality of hearing aids videos on TikTok. We collected a sample of 155 hearing aids-related videos in Chinese and extracted the basic information. First, we identified the source of each video. Two independent raters assessed the quality of the information in the videos, using the PEMAT-A/V tool and DISCERN instrument. Regarding content, the results showed that the video contents on TikTok mainly about features, functionalities, and suggestions of purchase or fitting of hearing aids, while the information about the disadvantages and complications of hearing aids was limited. The overall quality of the hearing aids-related videos was acceptable on average, although the quality varies greatly depending on the type of source. Patients should be cautious in obtaining information about hearing aids on TikTok.

Urine caffeine metabolites and hearing threshold shifts in US adults: a cross-sectional study.

Previous studies have reported the relationship between effect of caffeine and many diseases. However, studies to evaluate the association between caffeine and hearing loss are contradictory. To examine the relationship of urinary caffeine metabolites with the hearing threshold in US adults, a total of 849 adults aged 20-69 years who participated in the National Health and Nutrition Examination Survey (NHANES, 2011-2012) were enrolled in this study. Urinary caffeine and its 14 metabolites were applied as biomarkers to assess caffeine exposure. Hearing loss was defined as mean pure tone averages > 25 dB HL at 500, 1000, and 2000 Hz in both ears (low frequency); and 3000, 4000, and 6000 Hz in both ears (high frequency). Univariate and multivariate linear regression analyses were conducted to examine the associations of urinary caffeine metabolites with low- and high-frequency hearing thresholds, respectively. Low-frequency hearing loss were 5.08% and 6.10% in male and female participants, respectively; and high-frequency hearing loss were 31.81% and 15.14% in male and female participants, respectively. In the unadjusted model, the P value for trend shows that urinary caffeine metabolites 137X and AAMU were significantly associated with low-frequency PTA, and that 17X, 137X, AAMU were significantly associated with high-frequency PTA, but when the model was adjusted for sex, age, education level, firearm noise exposure, occupational noise exposure, recreational noise exposure, serum cotinine, body mass index, diabetes, hypertension, these were no longer statistically significant. In conclusion, urinary caffeine metabolites were not associated with the hearing threshold shifts in US adults.

The expression of atrial natriuretic peptide receptor in the mouse inner ear labyrinth.

OBJECTIVE: To compare the relative expression levels of NPR-A mRNA in the stria vascularis (StV), nonstrial tissue of the cochlear lateral wall (NSt) and vestibula in the mouse inner ear to determine the potential contribution of ANP signaling in different parts to inner ear fluid homeostasis. SETTING: Atrial natriuretic peptide (ANP) is a cardiac hormone known to be involved in the regulation of body fluid homeostasis. It is assumed that ANP might also participate in the regulation of inner ear fluid dynamics. ANP selectively binds with atrial natriuretic peptide receptor (NPR-A) to exert its physiological function. We have previously shown the presence of NPR-A transcripts in the mouse stria vascularis as well as in the nonstrial tissue of the cochlear lateral wall and vestibular organ by polymerase-chain reaction. METHODS: Total RNA of samples of stria vascularis, nonstrial tissue of the cochlear lateral wall and vestibular organ tissue from ears of 10 adult mice was isolated, amplified by the real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) using consensus primers flanking a region of 127 bp at the target sequences. The brain of mice known to contain NPR-A was used as a positive control. The one-way analysis of variance, ANOVA and Student-Newman-Keuls method were performed to analyze the data. RESULTS: NPR-A mRNA expression was found in tissue samples of all the three areas. The mRNA expression level of NPR-A in the StV was higher than that in the NSt and vestibula (p<0.05). The difference of NPR-A mRNA expression level in the NSt and vestibula was not statistically significant (p>0.05). CONCLUSIONS: Our results suggest that the StV may be the most important place for ANP to regulate endolymph fluid balance via NPR-A.

[The distribution of perivascular-resident cells in blood-labyrinth barrier observed with two-photon fluorescence microscope and Imaris deconvolution].

Objective:To determine the cell types composing blood-labyrinth barrier in stira vascularis of cochlear lateral wall, analyze the distribution of these composing cells in blood-labyrinth barrier, and to investigate the relationship between perivascular-resident macrophages （PVMs）, endothelial cells and pericytes in blood-labyrinth barrier. Method:Cochlear lateral wall tissues were harvested from adult GFP-transgenic mice（C57BL/6）. Then the isolated whole stria vascularis tissue was scanned at 0.5 um intervals on the Z axis by two-photon confocal microscope and a 3D-structure of stria vascularis was reconstructed to observe the distribution of capillaries in blood-labyrinth barrier. Cochlear stria vascularis isolated from Balb/c mice was stained by mulit-immunofluorescence and then 3D real time deconvolution of stria vascularis was performed by Imaris software to investigate the distribution of PVMs and pericytes, and their contacting with basement membrane of capillaries was also observed. The ultrastructure of endothelial cells, pericytes and PVMs in blood-labyrinth barrier was observed using transmission electron microscope. Result:The vessels in stria vascularis are parallel to modiolus, distinct from that in spiral ligament which are perpendicular to modiolus. Numerous pericyts in stria vascularis are ensheathed by a vascular basement membrane shared with endothelial cells and closely attaching to the lateral wall of endothelial cells, while PVMs are located outside basement membrane of capillaries. Unlike pericytes that surround one capillary, PVMs branch to connect with more than one capillary. Conclusion:Serial layers on the Z axis scanned by two-photon confocal microscope and a 3D-structure reconstructed by Imaris 3D deconvolution helps to display the micro structure of capillaries in cochlear lateral wall clearly, which could be applied to analyze the 3D structure and function of blood-labyrinth barrier. PVMs in stria vascularis contact with more than one vessel through cytoplasmic processes, suggesting that PVMs may play a more significant role than pericytes in the integrity of blood-labyrinth barrier.

Lipopolysaccharide disrupts the cochlear blood-labyrinth barrier by activating perivascular resident macrophages and up-regulating MMP-9.

OBJECTIVE: To determine the distribution of perivascularresident macrophages (PVMs) in BLB and their relationship with capillaries, and to explore the possible mechanisms responsible for lipopolysaccharide (LPS)-induced activation of PVMs and the breakdown of BLB. METHODS: Adult Balb/c mice were either trans-tympanically injected with LPS, or mock-treated. Auditory brainstem response was tested before and 48 h after treatments. Distribution of pericytes, PVMs and capillaries was analyzed by immunohistochemical staining, and BLB permeability was estimated by FITC-dextran leakage assay. Ultrastructure of stria vascularis was examined by transmission electron microscope. Protein and mRNA level of matrix metallopeptidase 9 (MMP-9), zona occludens-1 (ZO-1), interleukin-33 (IL-33) and its receptor suppression of tumorigenicity 2 (ST2) was measured by IHC and qRT-PCR. RESULTS: Unlike pericytes that surround one capillary, PVMs branched to connect with more than one capillary. LPS caused hearing loss in mice. Following LPS challenge, cochleae showed vascular leakage in stria vascularis, and PVMs presented morphological changes including reduced contact with capillaries. TEM revealed a reduced number of tight junction contact points between endothelial cells and a wider space between PVMs, pericytes and endothelial cells. The mRNA and protein levels of MMP-9 and ST2 in stria vascularis were up-regulated, while ZO-1 were down-regulated after exposure to LPS. CONCLUSIONS: Our results suggest that PVMs may play a more significant role than pericytes in maintaining the integrity of BLB. Our findings also reveal a possible mechanism contributing to LPS-induced activation of PVMs, breakdown of BLB and hearing loss.

FMRFamide modulates outward potassium currents in mouse olfactory sensory neurons.

1. The olfactory system can detect the presence of low concentrations of odourant molecules and discriminate even slight differences among molecules with a very similar chemical structure. The detection and discrimination of odourants are correlated with the electrophysiology of the olfactory sensory neurons. To get a better understanding of the molecular mechanisms of olfactory transduction, it is therefore of considerable importance to obtain electrophysiological recordings of olfactory sensory neurons. FMRFamide (Phe-Met-Arg-Phe-NH(2)), secreted from the nerve terminals of the nasal cavity, has been suggested to act as a neurotransmitter or neuromodulator, playing an important role in modulating the activity of olfactory receptor neurons. Its effects on voltage-dependent potassium currents in the mouse olfactory sensory neurons were investigated in the present study using the whole-cell patch-clamp technique. 2. Olfactory sensory neurons were isolated from the Kunming Mouse (KM) mouse olfactory epithelium. Different protocols were applied to obtain delayed-rectifier potassium current (I(K)) and fast transient potassium current (I(A)). The effects of FMRFamide on the outward potassium currents, including I(K) and I(A), in mouse olfactory sensory neurons were investigated. 3. We found that FMRFamide (5 micromol/L) increased the magnitude of I(K). However no effect on I(A) was observed. The activation dynamics of both currents were not changed by FMRFamide. 4. In conclusion, FMRFamide may play a role in the modulation of peripheral olfactory signals by regulating I(K). This modulation may shorten the phase of the fast repolarization of the action potential in mouse olfactory sensory neurons and increase the excitability of the neuronal membrane.

Expression and significance of endothelin 1 in spiral ganglion cells of guinea pig.

OBJECTIVES: Endothelin 1 has many biological activities including actions in the nervous system. This study aimed to investigate the expression of the endothelin 1 in spiral ganglion cells of guinea pig and its significance in the auditory transmission. METHODS: Healthy guinea pigs were sacrificed and cardiac perfused with saline followed by 4% paraformaldehyde. Temporal bones were removed and fixed, decalcified in 10% EDTA, embedded in paraffin block and serially sectioned in 5 microm thick slice. Rabbit anti-endothelin 1 polyclonal antibody was used as primary antibody to examine the expression of endothelin 1 in the spiral ganglion by immunohistochemistry. RESULTS: Endothelin 1 expression was detected in spiral ganglion cells from the basal turn to the apical turn of the cochlea. CONCLUSIONS: The endothelin 1 presents in spiral ganglions cells of the guinea pig and might play a role in the auditory transmission.

Detection of atrial natriuretic peptide receptor in the labyrinth of the mouse inner ear.

OBJECTIVES: To examine whether the atrial natriuretic peptide receptor (NPR-A) is present in the secretory regions of the membrane labyrinth of the adult mouse inner ear. SETTING: Recent studies have implied that the homeostasis of endolymph fluid in the inner ear may be regulated by receptor-mediated mechanisms. Several studies have identified the presence of atrial natriuretic peptide receptors in the inner ear of guinea pig and rat. As a member of the natriuretic peptide receptor family, which also includes B-type natriuretic peptide receptor (NPR-B) and C-type natriuretic peptide receptor (NPR-C), NPR-A may be involved in the regulation of fluid homeostasis in the inner ear. METHODS: In this study, samples of stria vascularis, nonstrial tissue of the cochlear lateral wall and vestibular organ tissue from the ears of 6 adult mice were obtained by immediate excision of bony labyrinth under operating microscope after decapitation. Total RNA was isolated and mRNA was amplified by the reverse transcription-polymerase chain reaction (RT-PCR) using consensus primers flanking a region of 127 bp at the target sequence. Mouse renal cortex known to contain NPR-A was used as a positive control. RESULTS: We demonstrated that NPR-A was expressed in the mouse stria vascularis as well as in the nonstrial tissue of the cochlear lateral wall and vestibular organ. CONCLUSION: These results suggest that natriuretic peptides may play an important role in maintaining the fluid homeostasis of inner ear endolymph via interaction with NPR-A.

Distribution of serotonin immunoreactivity in the spiral ganglion neurons of mouse cochlea.

OBJECTIVE: Serotonin (5-hydroxytryptamine, 5-HT) is a neuromodulator/neurotransmitter with multiple biological functions. Spiral ganglion cells in the cochlea are the primary neurons of the afferent system in the auditory transmission. In this study, we used the immunohistochemical technique to investigate the distribution of serotonin in the spiral ganglion of mouse cochlea. MATERIALS AND METHODS: The cochlea tissue of four adult mice was dissected and fixed. The immunohistochemical staining was applied by using goat anti-serotonin polyclonal antibody as primary antibody. Tissue sections were treated with biotin-labeled rabbit anti-goat immunoglobulin G, followed by adding streptavidin-biotin-peroxidase complex. Finally, the sections were stained with 3,3-diaminobenzidine (DAB) solution. RESULTS: The spiral ganglion exhibited pronounced immunoreactivity for serotonin. Specifically, serotonin immunoreactivity was detected in the cytoplasma of spiral ganglion neurons located in Rosenthal's canal of the bony modiolus of mouse cochlea. CONCLUSIONS: Since spiral ganglion neurons are the afferent neurons to the auditory sense organ, our result strongly suggests that serotonin molecule may function as a neuromodulator/neurotransmitter in the peripheral auditory processing.

Distribution of Tryptophan Hydroxylase Immunoreactivity in the Spiral Ganglion Neurons of Mouse Cochlea.

Serotonin, also known as 5-hydroxytryptamine, is an important neurotransmitter and neuromodulator in the nervous system. Spiral ganglion neurons (SGNs) are the first station of the peripheral afferent auditory nervous system. We have previously demonstrated positive serotonin immunoreactivity in mouse SGNs. Whether serotonin in the SGNs is absorbed from the circumstances, or is synthesized by the neurons themselves is unknown. The purpose of this study was to find out the source of serotonin in the SGNs. Tryptophan hydroxylase is the rate-limiting enzyme in the process of serotonin biosynthesis. We detected tryptophan hydroxylase in the mouse SGNs using immunohistochemistry. The positive immunostaining of tryptophan hydroxylase was observed in the cytoplasm of SGNs. The cytoplasm of the SGNs was not get stained in the negative control group. Our results suggest that SGNs can synthesize serotonin themselves, and they may serve as an additional source of serotonin in the cochlea. The SGNs are serotonergic neurons. The receptors of serotonin on the membrane of SGNs interact with serotonin as auto-receptors. Serotonin in these neurons plays its physiological role in an autocrine/paracrine way.

The expression of endothelin type A and B receptors in the lateral wall of the mouse cochlea.

Endothelin (ET), originally characterized as a vasoconstrictive peptide, has been found to have many different biological functions, including acting as a local hormonal regulator of pressure, fluid, ions and neurotransmitters in the inner ear. The objective of this study was to examine and quantify the mRNA expression of the endothelin type A and B receptors (ETAR and ETBR) in the strial vascularies (StV) and non-strial tissues (NSt) of the cochlear lateral wall using the real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) technique. The mouse tissue samples were harvested and RNA was extracted. RT was performed to obtain cDNA, and then the mRNA expression of each gene was measured via real-time PCR. We found that both receptor subtypes were expressed in the cochlear lateral wall, with a predominance of ETAR over ETBR. We showed that the mRNA expression of the two receptor subtypes was higher in the StV with a 1.8 times higher level of ETAR and an 8.1 times higher level of ETBR mRNAs than in the adjacent NSt of the lateral wall tissue. This study shows the existence and the quantity of ET receptor subtypes in the StV and NSt of the mouse cochlea. Our results suggest that an endothelin-mediated response via two different receptors, ETAR and ETBR, may play an important role in the physiological functions of the cochlear lateral wall by maintaining the homeostatic environment of the cochlea.