From hidden hearing loss to supranormal auditory processing by neurotrophin 3-mediated modulation of inner hair cell synapse density.

Loss of synapses between spiral ganglion neurons and inner hair cells (IHC synaptopathy) leads to an auditory neuropathy called hidden hearing loss (HHL) characterized by normal auditory thresholds but reduced amplitude of sound-evoked auditory potentials. It has been proposed that synaptopathy and HHL result in poor performance in challenging hearing tasks despite a normal audiogram. However, this has only been tested in animals after exposure to noise or ototoxic drugs, which can cause deficits beyond synaptopathy. Furthermore, the impact of supernumerary synapses on auditory processing has not been evaluated. Here, we studied mice in which IHC synapse counts were increased or decreased by altering neurotrophin 3 (Ntf3) expression in IHC supporting cells. As we previously showed, postnatal Ntf3 knockdown or overexpression reduces or increases, respectively, IHC synapse density and suprathreshold amplitude of sound-evoked auditory potentials without changing cochlear thresholds. We now show that IHC synapse density does not influence the magnitude of the acoustic startle reflex or its prepulse inhibition. In contrast, gap-prepulse inhibition, a behavioral test for auditory temporal processing, is reduced or enhanced according to Ntf3 expression levels. These results indicate that IHC synaptopathy causes temporal processing deficits predicted in HHL. Furthermore, the improvement in temporal acuity achieved by increasing Ntf3 expression and synapse density suggests a therapeutic strategy for improving hearing in noise for individuals with synaptopathy of various etiologies.

Hidden hearing loss in hereditary demyelinating neuropathies: insights from Charcot-Marie-Tooth mouse models.

Hidden hearing loss (HHL) is a recently described auditory neuropathy characterized by normal audiometric thresholds but reduced sound-evoked potentials. It has been proposed that HHL contributes to hearing difficulty in noisy environments in people with normal audiometric thresholds, a widespread complaint. While most studies on HHL pathogenesis have focused on inner hair cell (IHC) synaptopathy, recent research suggests that transient auditory nerve (AN) demyelination may also cause HHL. To test the impact of myelinopathy in a clinically relevant model, we studied a mouse model of Charcot-Marie-Tooth type 1A (CMT1A), the most prevalent hereditary peripheral neuropathy in humans. CMT1A mice exhibit the functional hallmarks of HHL, together with disorganization of AN heminodes near the IHCs with minor loss of AN fibers. Our results support the hypothesis that mild disruptions of AN myelination can cause HHL, and that heminodal defects contribute to the alterations in action potential amplitudes and latencies seen in these models. Also, these findings suggest that patients with CMT1A or other mild peripheral neuropathies are likely to suffer from HHL. Furthermore, these results suggest that studies of hearing in CMT1A patients might help develop robust clinical tests for HHL, which are currently lacking.

Electrical nerve stimulation for sensory-neural pathway reconstruction in upper-limb amputees.

Introduction: The loss of the neural sensory function pathways between the stump limbs and the brain greatly impacts the rehabilitation of limb function and the daily lives of amputees. Non-invasive physical stressors, such as mechanical pressure and transcutaneous electrical nerve stimulation (TENS), could be potential solutions for recovering somatic sensations in amputees. Previous studies have shown that stimulating the residual or regenerated nerves in the stumps of some amputees can produce phantom hand sensations. However, the results are inconclusive due to unstable physiological responses caused by inaccurate stimulus parameters and positions. Methods: In this study, we developed an optimal TENS strategy by mapping the distribution of the nerves in the stump skin that elicitsphantom sensations known as a "phantom hand map." We evaluated the effectiveness and stability of the confirmed stimulus configuration in a long-term experiment using single- and multi-stimulus paradigms. Additionally, we evaluated the evoked sensations by recording electroencephalograms (EEG) and analyzing brain activities. Results: The results demonstrated that various types of intuitive sensations for amputees could be stably induced by adjusting TENS frequencies, particularly at 5 and 50 Hz. At these frequencies, 100% stability of sensory types was achieved when the stimuli were applied to two specific locations on the stump skin. Furthermore, at these locations, the stability of sensory positions was 100% across different days. Moreover, the evoked sensations were objectively supported by specific patterns of event-related potentials in brain responses. Discussion: This study provides an effective method for developing and evaluating physical stressor stimulus strategies, which could play an important role in the somatosensory rehabilitation of amputees and other patients suffering from somatomotor sensory dysfunction. The paradigm developed in this study can provide effective guidelines for stimulus parameters in physical and electrical nerve stimulation treatments for a variety of symptoms related to neurological disorders.

Cochlear Neurotrophin-3 overexpression at mid-life prevents age-related inner hair cell synaptopathy and slows age-related hearing loss.

Age-related hearing loss (ARHL) is the most prevalent sensory deficit in the elderly. This progressive pathology often has psychological and medical comorbidities, including social isolation, depression, and cognitive decline. Despite ARHL's enormous societal and economic impact, no therapies to prevent or slow its progression exist. Loss of synapses between inner hair cells (IHCs) and spiral ganglion neurons (SGNs), a.k.a. IHC synaptopathy, is an early event in cochlear aging, preceding neuronal and hair cell loss. To determine if age-related IHC synaptopathy can be prevented, and if this impacts the time-course of ARHL, we tested the effects of cochlear overexpression of neurotrophin-3 (Ntf3) starting at middle age. We chose Ntf3 because this neurotrophin regulates the formation of IHC-SGN synapses in the neonatal period. We now show that triggering Ntf3 overexpression by IHC supporting cells starting in middle age rapidly increases the amplitude of sound-evoked neural potentials compared with age-matched controls, indicating that Ntf3 produces a positive effect on cochlear function when the pathology is minimal. Furthermore, near the end of their lifespan, Ntf3-overexpressing mice have milder ARHL, with larger sound-evoked potentials along the ascending auditory pathway and reduced IHC synaptopathy compared with age-matched controls. Our results also provide evidence that an age-related decrease in cochlear Ntf3 expression contributes to ARHL and that Ntf3 supplementation could serve as a therapeutic for this prevalent disorder. Furthermore, these findings suggest that factors that regulate synaptogenesis during development could prevent age-related synaptopathy in the brain, a process involved in several central nervous system degenerative disorders.

Axon-glia interactions in the ascending auditory system.

The auditory system detects and encodes sound information with high precision to provide a high-fidelity representation of the environment and communication. In mammals, detection occurs in the peripheral sensory organ (the cochlea) containing specialized mechanosensory cells (hair cells) that initiate the conversion of sound-generated vibrations into action potentials in the auditory nerve. Neural activity in the auditory nerve encodes information regarding the intensity and frequency of sound stimuli, which is transmitted to the auditory cortex through the ascending neural pathways. Glial cells are critical for precise control of neural conduction and synaptic transmission throughout the pathway, allowing for the precise detection of the timing, frequency, and intensity of sound signals, including the sub-millisecond temporal fidelity is necessary for tasks such as sound localization, and in humans, for processing complex sounds including speech and music. In this review, we focus on glia and glia-like cells that interact with hair cells and neurons in the ascending auditory pathway and contribute to the development, maintenance, and modulation of neural circuits and transmission in the auditory system. We also discuss the molecular mechanisms of these interactions, their impact on hearing and on auditory dysfunction associated with pathologies of each cell type.

Comparison of frequency-specific hearing outcomes after endoscopic and microscopic tympanoplasty.

BACKGROUND: Hearing results of endoscopic and microscopic tympanoplasty have been compared using the average pure tone threshold which could conceal subtle differences at a specific frequency. OBJECTIVES: To compare frequency-specific hearing outcomes of endoscopic and microscopic tympanoplasty. MATERIAL AND METHODS: The study included 42 patients who underwent endoscopic or microscopic type I tympanoplasty. The medical charts of these patients were reviewed retrospectively. We evaluated the pure tone audiometry at 250, 500, 1000, 2000 and 4000 Hz, including bone conduction (BC), air conduction (AC) and air-bone gap (ABG) before and after the surgery. The main outcome measures were frequency-specific pre- and post-operative hearing thresholds and the corresponding changes. We also assessed the graft success rate and surgical complications. RESULTS: BC revealed a significant aggravation at 4000 Hz in microscopic tympanoplasty group, but no significant differences between the two groups at any frequencies. Both groups showed improvements in AC and ABG at all frequencies, without significant differences between the two groups at any single frequency. The maximum improvement of AC and ABG was found at 250 Hz. The graft success rate and operative complications were also similar. CONCLUSIONS AND SIGNIFICANCE: The frequency-specific hearing outcomes of endoscopic and microscopic tympanoplasty are similar.

Protection from noise-induced cochlear synaptopathy by virally mediated overexpression of NT3.

Noise exposures causing only transient threshold shifts can destroy auditory-nerve synapses without damaging hair cells. Here, we asked whether virally mediated neurotrophin3 (NT3) overexpression can repair this damage. CBA/CaJ mice at 6 wks were injected unilaterally with adeno-associated virus (AAV) containing either NT3 or GFP genes, via the posterior semicircular canal, 3 wks prior to, or 5 hrs after, noise exposure. Controls included exposed animals receiving vehicle only, and unexposed animals receiving virus. Thresholds were measured 2 wks post-exposure, just before cochleas were harvested for histological analysis. In separate virus-injected animals, unexposed cochleas were extracted for qRT-PCR. The GFP reporter showed that inner hair cells (IHCs) were transfected throughout the cochlea, and outer hair cells mainly in the apex. qRT-PCR showed 4- to 10-fold overexpression of NT3 from 1-21 days post-injection, and 1.7-fold overexpression at 40 days. AAV-NT3 delivered prior to noise exposure produced a dose-dependent reduction of synaptopathy, with nearly complete rescue at some cochlear locations. In unexposed ears, NT3 overexpression did not affect thresholds, however GFP overexpression caused IHC loss. In exposed ears, NT3 overexpression increased permanent threshold shifts. Thus, although NT3 overexpression can minimize noise-induced synaptic damage, the forced overexpression may be harmful to hair cells themselves during cochlear overstimulation.

Synaptopathy as a Mechanism for Age-Related Vestibular Dysfunction in Mice.

Age-related decline of inner ear function contributes to both hearing loss and balance disorders, which lead to impaired quality of life and falls that can result in injury and even death. The cellular mechanisms responsible for the ear's functional decline have been controversial, but hair cell loss has been considered the key cause for a long time. However, recent studies showed that in the cochlea, loss of inner hair cell (IHC) synapses precedes hair cell or neuronal loss, and this synaptopathy is an early step in the functional decline. Whether a similar process occurs in the vestibular organ, its timing and its relationship to organ dysfunction remained unknown. We compared the time course of age-related deterioration in vestibular and cochlear functions in mice as well as characterized the age-associated changes in their utricles at the histological level. We found that in the mouse, as in humans, age-related decline in vestibular evoked potentials (VsEPs) occurs later than hearing loss. As in the cochlea, deterioration of VsEPs correlates with the loss of utricular ribbon synapses but not hair cells or neuronal cell bodies. Furthermore, the age-related synaptic loss is restricted to calyceal innervations in the utricular extrastriolar region. Hence, our findings suggest that loss of extrastriolar calyceal synapses has a key role in age-related vestibular dysfunction (ARVD).

Auditory metabolomics, an approach to identify acute molecular effects of noise trauma.

Animal-based studies have provided important insights into the structural and functional consequences of noise exposure on the cochlea. Yet, less is known about the molecular mechanisms by which noise induces cochlear damage, particularly at relatively low exposure levels. While there is ample evidence that noise exposure leads to changes in inner ear metabolism, the specific effects of noise exposure on the cochlear metabolome are poorly understood. In this study we applied liquid chromatography-coupled tandem mass spectrometry (LC-MS/MS)-based metabolomics to analyze the effects of noise on the mouse inner ear. Mice were exposed to noise that induces temporary threshold shifts, synaptopathy and permanent hidden hearing loss. Inner ears were harvested immediately after exposure and analyzed by targeted metabolomics for the relative abundance of 220 metabolites across the major metabolic pathways in central carbon metabolism. We identified 40 metabolites differentially affected by noise. Our approach detected novel noise-modulated metabolites and pathways, as well as some already linked to noise exposure or cochlear function such as neurotransmission and oxidative stress. Furthermore, it showed that metabolic effects of noise on the inner ear depend on the intensity and duration of exposure. Collectively, our results illustrate that metabolomics provides a powerful approach for the characterization of inner ear metabolites affected by auditory trauma. This type of information could lead to the identification of drug targets and novel therapies for noise-induced hearing loss.

PlexinA2 Forward Signaling through Rap1 GTPases Regulates Dentate Gyrus Development and Schizophrenia-like Behaviors.

Dentate gyrus (DG) development requires specification of granule cell (GC) progenitors in the hippocampal neuroepithelium, as well as their proliferation and migration into the primordial DG. We identify the Plexin family members Plxna2 and Plxna4 as important regulators of DG development. Distribution of immature GCs is regulated by Sema5A signaling through PlxnA2 and requires a functional PlxnA2 GTPase-activating protein (GAP) domain and Rap1 small GTPases. In adult Plxna2-/- but not Plxna2-GAP-deficient mice, the dentate GC layer is severely malformed, neurogenesis is compromised, and mossy fibers form aberrant synaptic boutons within CA3. Behavioral studies with Plxna2-/- mice revealed deficits in associative learning, sociability, and sensorimotor gating-traits commonly observed in neuropsychiatric disorder. Remarkably, while morphological defects are minimal in Plxna2-GAP-deficient brains, defects in fear memory and sensorimotor gating persist. Since allelic variants of human PLXNA2 and RAP1 associate with schizophrenia, our studies identify a biochemical pathway important for brain development and mental health.

Aging and the peripheral vestibular system.

Whereas much has been learned about age-related auditory changes in the inner ear, relatively little is known about the aging effects on the vestibular part of the inner ear-the peripheral vestibular system. Here we review relevant literature with regard to the prevalence of vestibular dysfunction, vestibular functional and structural changes in the elderly. The prevalence of vestibular dysfunction increases with age. Functionally, as age increases, VEMP amplitudes decrease, VEMP thresholds increase, VOR gain of HIT decreases. Due to the complexity of the vestibular system, variations in subject age and measurement techniques, findings in VEMP latency and caloric tests are conflicting. To address this, a direct measure of the peripheral vestibular system should be applied. Structurally, age-related loss in vestibular ganglion and otoconia have been noted; hair cell changes are not well defined; while subcellular changes remain to be explored. Defining how the onset of vestibular dysfunction correlates with structural degeneration will offer insights into the mechanisms underlying vestibular aging.

Normal values of nasal NO and exhaled NO in young Chinese people aged 9 - 22 years.

OBJECTIVE: To assess the normal levels of nasal nitric oxide (NNO) and fractional exhaled nitric oxide (FENO) in healthy Chinese young people, and to determine whether the obtained values were associated with age, sex, height, weight, BMI (body mass index) or BSA (body surface area). METHODS: One hundred and twenty healthy people were selected from a total of 436 Chinese young people based on their answers to a questionnaire. An electrochemical analyzer (NIOX MINO system) was used to measure NNO and FENO. The relationship between NNO, FENO and age, sex, height, weight, BMI, BSA was analyzed using SPSS software. RESULTS: The values of NNO were normal distributed (mean 273.5 ppb; SD 112.3). The values of FENO were non-normally (Skewed) distributed (median: 14.00 ppb; interquartile range: 7.00 ppb). The obtained NNO values were independent of age, sex, height, weight, BMI and BSA, but were positively correlated to lnFENO (FENO log base e); lnFENO values were also independent of age, height, weight, BMI and BSA, but correlated with NNO and sex. CONCLUSIONS: NNO values positively correlate with lnFENO in healthy people and the levels of each may be predicted by the other. The results of this study are expected to serve as a reference for future studies in China.

[Causes analysis of misdiagnosis in patients with familial nasal bleeding].

OBJECTIVE: To analyze the causes of misdiagnosis in patients with familial nasal bleeding and to improve the level of diagnosis and treatment. METHOD: The clinical characteristics of 7 families with nose blood were analyzed retrospectively and 2 typical cases were reported, including their treatment and misdiagnosis in consulting, out-patient and in-patient. RESULT: Typical case 1 was misdiagnosed and mistreated for 42 years, misdiagnosed as blood disease so that the patient was biopsied in bone marrow, misdiagnosed as endometriosis so that the patient was performed uterus resection. Typical case 2 was misdiagnosed and mistreated for 17 years, misdiagnosed as upper digestive tract hemorrhage so that the patient was performed endoscopic sleeve ligation, misdiagnosed as inferior turbinate hemangioma so that the patient was performed nasal endoscopic surgery. CONCLUSION: Neglect of family history and the typical signs are the causes of misdiagnosis. So asking about the family history and checking for the typical signs in patients with nose blood can avoid misdiagnosis.

[Diagnosis and clinical characteristics of patients with non-allergic rhinitis].

OBJECTIVE: To explore a step-by-step exclusive diagnosis and analyze the clinical characters of non-allergic rhinitis (NAR). METHODS: Patients with symptoms (nasal itching, sneezing, rhinorrhea, nasal congestion) were selected to take four-step exclusive diagnosis for NAR and we tried to eliminate the false NAR and retain the true NAR. First step was to exclude the patients who were not suitable for skin prick test (SPT, such as during pregnancy, breastfeeding, asthma, oral antihistamine medication in 7 day, severe skin diseases). The second step was to exclude the patients with positive SPT and the third step was to exclude the patients with 1 level or above of specific sero-immunoglobulin E (sIgE). The fourth step was to exclude the patients with infection rhinitis, clear abnormal nasal structure, drug-induced rhinitis, nasal neoplasm. The remained patients were finally diagnosed as NAR and who were further differential diagnosed as vasomotor rhinitis (VMR) or non-allergic rhinitis with eosinophilia syndrome (NARES) according to the eosinophilia counts in nasal secretion and venous blood. The common characters of patients with NAR were analyzed and their symptoms and quality of life were evaluated by visual analogue scale (VAS) and rhino-conjunctivitis quality of life questionnaire (RQLQ) separately. RESULTS: One thousand four hundred and thirty-seven patients were included after first step exclusion and 735 cases with negative SPT were remained after second step exclusion. Of 735 patients, 302 were tested in vitro for sIgE and 93 cases with 0 level of sIgE and total IgE were remained after third step exclusion. Sixty-two patients were finally diagnosed as NAR after fourth step exclusion. The NAR diagnosis rate was 51.15% (735/1 437) with negative SPT alone and the NAR diagnosis rate was 29.06% (93/302) with combination of negative SPT and sIgE. Of 62 patients with NAR, 47 patients (75.81%) were diagnosed as VMR and 15 cases (24.19%) as NARES. There were 23 males and 39 females in the 62 patients aged 11 - 77 years. The history was 11-47 months. The biggest numbers of patients with VMR or NARES were among 41-50 years. Their onset ages were among 21-30 years in both two groups. VAS scores of nasal congestion in VMR patients were the highest with significant difference among nasal symptoms (F = 3.958 0, P = 0.009 1). VAS scores of sneezing in NARES patients were the highest but without significant difference among nasal symptoms. There were no difference in seven domain scores of RQLQ and the total mean scores between VMR group and NARES group but the nasal symptoms got the highest scores with significant difference among the seven domains in each group (VMR group, F = 9.771 2, P = 0.000 0;NRAES group, F = 3.226 9, P = 0.006 2). CONCLUSIONS: SPT combined with sIgE may exclude much more patients with AR. Females with NAR are much more than males. Patients with NAR aged 21-30 years. The characters of NAR are helpful to improve our knowledge about NAR. VAS and RQLQ may be a suitable tool in assessment of NAR.

[Noninvasive measurement of nasal NO and fractional exhaled NO in healthy people and patients with allergic rhinitis].

OBJECTIVE: To measure the nasal nitric oxide (NNO) and fractional exhaled nitric oxide (FENO) in healthy people and patients with allergic rhinitis (AR), and to discuss the clinical significance of the results. METHODS: Ninety-six healthy volunteers and 51 patients with moderate-severe persistent AR, but without asthma, were enrolled. NNO and FENO concentrations were measured noninvasively by using of NIOX MINO (Aerocrine AB, Solna, Sweden).SPSS 13.0 software was used to analyze the data. RESULTS: The concentration of NNO in healthy people was 245.0 [189.8;331.3] ppb (median [25th percentile; 75th percentile], the followings were same as). The concentration of FENO was 14.0 [10.0; 18.0] ppb. The concentration of NNO in patients with AR was 304.0[179.5; 397.5]ppb. The concentration of FENO was 21.0 [16.0; 40.5] ppb. The concentration of NNO in the AR patients was higher than that in the healthy persons, but the difference did not reach statistical significance (Z = 1.349, P = 0.177).On the other hand, FENO concentrations were significantly increased in patients compared with concentrations in healthy persons (Z = 5.555, P = 0.000). CONCLUSIONS: FENO concentrations of patients with moderate-severe persistent AR are increased significantly even though the patients do not have typical symptoms of asthma. This finding suggests that AR patients should be treated actively in order to prevent asthma from developing in them.

[Clinical characteristics of primary ciliary dyskinesia].

OBJECTIVE: To analyze the clinical characteristics of primary ciliary dyskinesia(PCD) so as to improve the diagnostic level of this rarely seen disease. METHODS: Ten patients with PCD were retrospectively reviewed, the medical history, symptoms, signs, lung CT or chest X-ray, rhino-sinus CT scan, nasal nitric oxide (NO) levels, nasal ciliary ultrastructure, DNAH5 and DNAH11 genetic mutation, as well as treatment outcome were analyzed. RESULTS: All 10 patients had recurrent chronic sinusitis, otitis media, bronchitis/bronchiectasis since childhood. Nine cases with translocation of heart and big vessels were diagnosed as Kartagener syndrome. One woman was suffering from barrenness and one man sterility after marriage for long time without birth control. Nasal NO levels were significantly lower in 2 patients with PCD but it was almost normal in one patient. Ciliary ultrastructure investigated by transmission electron microscope were almost normal in 4 cases without missing of inner or outer dynein arms. Two cases taking exome capture sequencing showed that mutations happened in DNAH5 and DNAH11. Five subjects underwenting sanger sequencing on 6 common exon fragments of DNAH5 and DNAH11 did not show any abnormality. Ten cases took medication therapy, while 5 patients once underwent functional endoscope sinus surgery. All of the 10 patients had improvement of their symptoms and signs after treatment. CONCLUSIONS: The PCD is so rare in clinic that it is easily misdiagnosed. Clinical characteristics, nasal NO levels, ciliary ultrastructure and genetic testing are significant for clinical diagnosis.

Frequency of tuberculosis among diabetic patients in the People's Republic of China.

The People's Republic of China has nearly the highest incidence of both diabetes mellitus (DM) and tuberculosis (TB) worldwide. DM increases the risk of TB by two to three times and adversely affects TB treatment outcomes. The increasing epidemic of DM in the People's Republic of China is due to decreased physical activity, unhealthy diet, and obesity. Over the last 20 years, the excellent free China National Tuberculosis Program has been set up, and the "DOTS" (directly observed treatment + short-course chemotherapy) model for TB control has successfully reduced the burden of TB, but the disease is still a considerable problem. Given the high burden of TB and DM in the People's Republic of China and the relationship between the two diseases, it is sensible to screen DM patients for TB. A bidirectional screening of the two diseases was conducted in the People's Republic of China from 2011 to 2012, which identified a TB incidence in patients with DM of about 958 per 100,000. Here, we report the findings of our recent study on the incidence of TB among diabetic patients in the People's Republic of China. The data agree with those of previous reports.

[Early genetic diagnosis in patients with HHT induced severe nosebleed].

OBJECTIVE: To study the early gene diagnosis of hereditary hemorrhagic telangiectasia (HHT) induced severe nosebleed. METHOD: Clinical features of 23 family members in two HHT pedigrees were examined. Genomic DNA was extracted from peripheral blood samples. PCR amplification was conducted to screen ENG and ACVRL-1 genes with their specific primers. Direct sequencing was performed to detect the mutation. Mutation analysis was carried out to evaluate its significance. RESULT: A heterozygous c. 263A > G mutation was identified in exon 3 of ACVRL-1 in 6 out of 11 members in NMG-1 pedigree. In GD-2 pedigree, 5 of 11 members carried c. 199C > G mutation. Mutation detection rate was 100% in subjects with nosebleed history and 25% in family members without epistaxis. CONCLUSION: Gene diagnosis characterized by high sensitivity and specificity is of great practi-cal significance and early genetic screening should be a clinical routine test for HHT induced severe nosebleed.