Mapping of estrogen receptors alpha and beta in the inner ear of mouse and rat

Loss of calcitonin gene-related peptide (αCGRP) and use of a vestibular challenge highlight balance deficiencies in aging mice

Aging impacts the vestibular system and contributes to imbalance. In fact, imbalance precedes changes in cognition in the elderly. However, research is limited in assessing aging mouse models that are deficient in crucial neuromodulators like Calcitonin Gene-Related Peptide (CGRP). We studied the loss of CGRP and its effects in the aging mouse, namely its effect on both static and dynamic imbalances. Postural sway and rotarod testing were performed before and after a vestibular challenge (VC) in the 129S wild type and the αCGRP (-/-) null mice. Four age groups were tested that correspond to young adulthood, late adulthood, middle age, and senescence in humans. Our results suggest wild type mice experience a decline in rotarod ability due to aging after they reach their prime performance at 6-10 months of age, while the αCGRP (-/-) null mice perform poorly on rotarod early in life but improve with age as they get older, potentially due to vestibular compensation. Our postural sway study suggests that a vestibular challenge can lead to significantly reduced CoP ellipse areas (freezing behaviors) in older mice, and this change occurs earlier in the αCGRP (-/-) null but requires future studies to evaluate anxiety effects. These results indicate that αCGRP is an important component of proper balance and that the loss of αCGRP can contribute to balance complications that may compound with aging.

Expression profiling of cochlear genes uncovers sex-based cellular function in mouse cochleae

Sex is a pivotal biological factor that significantly impacts tissue homeostasis and disease susceptibility. In the auditory system, sex differences have been observed in cochlear physiology and responses to pathological conditions. However, the underlying molecular mechanisms responsible for these differences remain elusive. The current research explores the differences in gene expression profiles in the cochlea between male and female mice, aiming to understand the functional implication of sex-biased gene expression in each sex. Using RNA-sequencing analysis on cochlear tissues obtained from male and female mice, we identified a significant number of genes exhibiting sex-biased expression differences. While some of these differentially expressed genes are located on sex chromosomes, most are found on autosomal chromosomes. Further bioinformatic analysis revealed that these genes are involved in several key cellular functions. In males, these genes are notably linked to oxidative phosphorylation and RNA synthesis and processing, suggesting their involvement in mitochondrial energy production and regulatory control of gene expression. In contrast, sex-biased genes are associated with mechano-transduction and synaptic transmission within female cochleae. Collectively, our study provides valuable insights into the molecular differences between the sexes and emphasizes the need for future research to uncover their functional implications and relevance to auditory health and disease development.

Loss of Esr1 Does Not Affect Hearing and Balance

Although estrogen affects the structure and function of the nervous system and brain and has a number of effects on cognition, its roles in the auditory and vestibular systems remain unclear. The actions of estrogen are mediated predominately through two classical nuclear estrogen receptors, estrogen receptor 1 (ESR1) and estrogen receptor 2 (ESR2). In the current study, we investigated the roles of ESR1 in normal auditory function and balance performance using 3-month-old wild-type (WT) and Esr1 knockout (KO) mice on a CBA/CaJ background, a normal-hearing strain. As expected, body weight of Esr1 KO females was lower than that of Esr1 KO males. Body weight of Esr1 KO females was higher than that of WT females, while there was no difference in body weight between WT and Esr1 KO males. Similarly, head diameter was higher in Esr1 KO vs. WT females. Contrary to our expectations, there were no differences in auditory brainstem response (ABR) thresholds, ABR waves I-V amplitudes and ABR waves I-V latencies at 8, 16, 32, and 48 kHz, distortion product otoacoustic emission (DPOAE) thresholds and amplitudes at 8, 16, and 32 kHz, and rotarod balance performance (latency to fall) between WT and Esr1 KO mice. Furthermore, there were no sex differences in ABRs, DPOAEs, and rotarod balance performance in Esr1 KO mice. Taken together, our findings show that Esr1 deficiency does not affect auditory function or balance performance in normal hearing mice, and suggest that loss of Esr1 is likely compensated by ESR2 or other estrogen receptors to maintain the structure and function of the auditory and vestibular systems under normal physiological conditions.

Early-Onset Hearing Loss in Mouse Models of Alzheimer's Disease and Increased DNA Damage in the Cochlea

There is considerable interest in whether sensory deficiency is associated with the development of Alzheimer's disease (AD). Notably, the relationship between hearing impairment and AD is of high relevance but still poorly understood. In this study, we found early-onset hearing loss in two AD mouse models, 3xTgAD and 3xTgAD/Polβ+/-. The 3xTgAD/Polβ+/- mouse is DNA repair deficient and has more humanized AD features than the 3xTgAD. Both AD mouse models showed increased auditory brainstem response (ABR) thresholds between 16 and 32 kHz at 4 weeks of age, much earlier than any AD cognitive and behavioral changes. The ABR thresholds were significantly higher in 3xTgAD/Polβ+/- mice than in 3xTgAD mice at 16 kHz, and distortion product otoacoustic emission signals were reduced, indicating that DNA damage may be a factor underlying early hearing impairment in AD. Poly ADP-ribosylation and protein expression levels of DNA damage markers increased significantly in the cochlea of the AD mice but not in the adjacent auditory cortex. Phosphoglycerate mutase 2 levels and the number of synaptic ribbons in the presynaptic zones of inner hair cells were decreased in the cochlea of the AD mice. Furthermore, the activity of sirtuin 3 was downregulated in the cochlea of these mice, indicative of impaired mitochondrial function. Taken together, these findings provide new insights into potential mechanisms for hearing dysfunction in AD and suggest that DNA damage in the cochlea might contribute to the development of early hearing loss in AD.

The impact of menopausal status on auditory brainstem responses

OBJECTIVE

To determine the effect of decreased estrogen levels due to menopause on auditory brainstem response measurements (ABR).

STUDY DESIGN

Retrospective chart review.

SETTING

Academic.

PATIENTS

Pre- and post-menopausal females (pre-M, post-M) and age-matched males.

METHODS

ABR measurements of wave I, III, and V latencies, and interpeak latencies; amplitudes of waves I, III, V, and V/I ratio.

OUTCOME MEASURE

Differences in ABR measurements between pre-M and post-M.

RESULTS

164 subjects (101 female and 64 male) were included. Post-M had significantly greater latencies (msec) than pre-M of wave V. Post-M had a significantly smaller wave I amplitude (uV) than pre-M. Post-M had a significantly higher wave V/I amplitude ratio than pre-M. Pre-M had significantly shorter latencies than young males for wave III, and wave V. Post-M had significantly shorter latencies than older males at wave III, and wave V. A two-way ANOVA revealed a significant interaction between the effects of age category and gender on V/I amplitude.

CONCLUSION

Post-M group showed a significant drop in wave I amplitude compared with pre-M group, even in the absence of hearing loss, suggesting that the gender differences in hearing are related to estrogen signaling along the auditory pathway. If wave I amplitude changes between older and younger groups resulted from decreased peripheral hearing sensitivity, we would expect larger drops in amplitude in males since rates of presbycusis are higher. We observed much larger drops in wave I amplitude in females, which cannot be attributed to peripheral hearing loss. These results may assist in understanding gender differences in presbycusis and a possible protective effect of estrogen on the auditory system. Knowledge of gender differences in wave I may be important when ABR is used to assess possible synaptopathy.

Sex differences and the effect of female sex hormones on auditory function: a systematic review

Aims

First, to discuss sex differences in auditory function between women and men, and whether cyclic fluctuations in levels of female sex hormones (i.e., estradiol and progesterone) affect auditory function in pre-menopausal and post-menopausal women. Second, to systematically review the literature concerning the discussed patterns in order to give an overview of the methodologies used in research. Last, to identify the gap in knowledge and to make recommendations for future work.

Methods for the systematic review

Population, Exposure, Control, Outcome and Study design (PECOS) criteria were used in developing the review questions. The review protocol follows the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and was pre-registered in the Prospective Register of Systematic Reviews (PROSPERO; CRD42020201480). Data Sources: EMBASE, PubMed, MEDLINE (Ovid), PsycINFO, ComDisDome, CINAHL, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL) via Cochrane Library, and scanning reference lists of relevant studies, and internet resources (i.e., Mendeley) were used. Only studies published between 1999 and 2022, in English, or in English translation, were included. The quality of evidence was assessed using the Newcastle-Ottawa Scale (NOS).

Results

Sex differences: Women had more sensitive hearing (measured at the level of peripheral and central auditory system) than men. Cyclic fluctuations: Auditory function in women fluctuated during the menstrual cycle, while no such fluctuations in men over the same time period were reported. Hearing sensitivity improved in women during the late follicular phase, and decrease during the luteal phase, implying an effect of female sex hormones, although the specific effects of estradiol and progesterone fluctuations on the central auditory system remain unclear. Hearing sensitivity in women declined rapidly at the onset of menopause.

Conclusion

The review has shown the following. Consistent sex differences exist in auditory function across the auditory pathway with pre-menopausal women often showing better function than age-matched men. Moreover, pre-menopausal women show fluctuations in hearing function across the menstrual cycle with a better function during the peak of estradiol or when the ratio of estradiol to progesterone is high. Third, menopause marks the onset of hearing loss in women, characterized by a rapid decline in hearing sensitivity and a more pronounced loss than in age-matched men. Finally, the systematic review highlights the need for well-designed and -controlled studies to evaluate the influence of estradiol and progesterone on hearing by consistently including control groups (e.g., age-matched man), using objective tests to measure hormonal levels (e.g., in saliva or blood), and by testing participants at different points across the menstrual cycle.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020201480, identifier CRD42020201480.

Sex differences in glutamate AMPA receptor subunits mRNA with fast gating kinetics in the mouse cochlea

Evidence shows that females have increased supra-threshold peripheral auditory processing compared to males. This is indicated by larger auditory brainstem responses (ABR) wave I amplitude, which measures afferent spiral ganglion neuron (SGN)-auditory nerve synchrony. However, the underlying molecular mechanisms of this sex difference are mostly unknown. We sought to elucidate sex differences in ABR wave I amplitude by examining molecular markers known to affect synaptic transmission kinetics. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) mediate fast excitatory transmission in mature SGN afferent synapses. Each AMPAR channel is a tetramer composed of GluA2, 3, and 4 subunits (Gria2, 3, and 4 genes), and those lacking GluA2 subunits have larger currents, are calcium-permeable, and have faster gating kinetics. Moreover, alternatively spliced flip and flop isoforms of each AMPAR subunit affect channel kinetics, having faster kinetics those AMPARs containing Gria3 and Gria4 flop isoforms. We hypothesized that SGNs of females have more fast-gating AMPAR subunit mRNA than males, which could contribute to more temporally precise synaptic transmission and increased SGN synchrony. Our data show that the index of Gria3 relative to Gria2 transcripts on SGN was higher in females than males (females: 48%; males: 43%), suggesting that females have more SGNs with higher Gria3 mRNA relative to Gria2. Analysis of the relative abundance of the flip and flop alternatively spliced isoforms showed that females have a 2-fold increase in fast-gating Gria3 flop mRNA, while males have more slow-gating (2.5-fold) of the flip. We propose that Gria3 may in part mediate greater SGN synchrony in females. Significance Statement: Females of multiple vertebrate species, including fish and mammals, have been reported to have enhanced sound-evoked synchrony of afferents in the auditory nerve. However, the underlying molecular mediators of this physiologic sex difference are unknown. Elucidating potential molecular mechanisms related to sex differences in auditory processing is important for maintaining healthy ears and developing potential treatments for hearing loss in both sexes. This study found that females have a 2-fold increase in Gria3 flop mRNA, a fast-gating AMPA-type glutamate receptor subunit. This difference may contribute to greater neural synchrony in the auditory nerve of female mice compared to males, and this sex difference may be conserved in all vertebrates.

Vestibular Disorders and Hormonal Dysregulations: State of the Art and Clinical Perspectives

The interaction between endocrine and vestibular systems remains poorly documented so far, despite numerous observations in humans and animals revealing direct links between the two systems. For example, dizziness or vestibular instabilities often accompany the menstrual cycle and are highly associated with the pre-menopause period, while sex hormones, together with their specific receptors, are expressed at key places of the vestibular sensory network. Similarly, other hormones may be associated with vestibular disorders either as causal/inductive factors or as correlates of the pathology. This review was carried out according to the PRISMA method, covering the last two decades and using the MEDLINE and COCHRANE databases in order to identify studies associating the terms vestibular system and/or vestibular pathologies and hormones. Our literature search identified 646 articles, 67 of which referred directly to vestibular dysfunction associated with hormonal variations. While we noted specific hormonal profiles depending on the pathology considered, very few clinical studies attempted to establish a direct link between the expression of the vestibular syndrome and the level of circulating hormones. This review also proposes different approaches to shed new light on the link between hormones and vestibular disorders, and to improve both the diagnosis and the therapeutic management of dizzy patients.

Sex-Linked Biology and Gender-Related Research Is Essential to Advancing Hearing Health

There is robust evidence that sex (biological) and gender (behavioral/social) differences influence hearing loss risk and outcomes. These differences are noted for animals and humans-in the occurrence of hearing loss, hearing loss progression, and response to interventions. Nevertheless, many studies have not reported or disaggregated data by sex or gender. This article describes the influence of sex-linked biology (specifically sex-linked hormones) and gender on hearing and hearing interventions, including the role of sex-linked biology and gender in modifying the association between risk factors and hearing loss, and the effects of hearing loss on quality of life and functioning. Most prevalence studies indicate that hearing loss begins earlier and is more common and severe among men than women. Intrinsic sex-linked biological differences in the auditory system may account, in part, for the predominance of hearing loss in males. Sex- and gender-related differences in the effects of noise exposure or cardiovascular disease on the auditory system may help explain some of these differences in the prevalence of hearing loss. Further still, differences in hearing aid use and uptake, and the effects of hearing loss on health may also vary by sex and gender. Recognizing that sex-linked biology and gender are key determinants of hearing health, the present review concludes by emphasizing the importance of a well-developed research platform that proactively measures and assesses sex- and gender-related differences in hearing, including in understudied populations. Such research focus is necessary to advance the field of hearing science and benefit all members of society.

Hormones and Vestibular Disorders: The Quest for Biomarkers

The vestibular system exerts control over various functions through neural pathways that are not yet fully mapped. Functional dysregulations or tissue lesions at different levels of the peripheral and the central vestibular networks can alter these different functions, causing a wide variety of symptoms, ranging from posturo-locomotor alterations to psychiatric syndromes such as PPPD, including the deregulation of the main biological functions. These different symptoms differ by their expression kinetics (they each appear and regress with their own kinetics) by the targets affected (muscles, organs, and brain areas) and by the sensitivity specific to each individual. Vestibular pathologies thus cover a mosaic of distinct effects, and they involve various effectors—which constitute the many markers of their different types and stages. It is therefore crucial, to predict the onset of a vertigo syndrome, to follow its temporal course, or to monitor the impact of therapeutic approaches, and to have specific and reliable biomarkers. Hormonal variations are among the possible sources of biomarkers for neurotology. We know that specific hormonal profiles can promote the appearance of vestibular disorders. We also know that the expression of vertigo syndrome is accompanied by measurable hormonal variations. The link between endocrine deregulation and vestibular alterations therefore no longer needs to be proven. However, there are still few data on their precise correlations with the vertigo syndrome. This study was undertaken with the aim to deliver an extensive review of the hormonal alterations linked to vestibular disorders. A review of the literature covering the last two decades was carried out using the MEDLINE and COCHRANE databases in order to identify studies associating the terms vestibular system or vestibular pathologies and hormones. Bibliographic data provides several outcomes in terms of therapeutic innovation in the diagnosis and therapeutic follow-up of vestibular pathologies.

Estradiol Protects against Noise-Induced Hearing Loss and Modulates Auditory Physiology in Female Mice

Recent studies have identified sex-differences in auditory physiology and in the susceptibility to noise-induced hearing loss (NIHL). We hypothesize that 17β-estradiol (E2), a known modulator of auditory physiology, may underpin sex-differences in the response to noise trauma. Here, we gonadectomized B6CBAF1/J mice and used a combination of electrophysiological and histological techniques to study the effects of estrogen replacement on peripheral auditory physiology in the absence of noise exposure and on protection from NIHL. Functional analysis of auditory physiology in gonadectomized female mice revealed that E2-treatment modulated the peripheral response to sound in the absence of changes to the endocochlear potential compared to vehicle-treatment. E2-replacement in gonadectomized female mice protected against hearing loss following permanent threshold shift (PTS)- and temporary threshold shift (TTS)-inducing noise exposures. Histological analysis of the cochlear tissue revealed that E2-replacement mitigated outer hair cell loss and cochlear synaptopathy following noise exposure compared to vehicle-treatment. Lastly, using fluorescent in situ hybridization, we demonstrate co-localization of estrogen receptor-2 with type-1C, high threshold spiral ganglion neurons, suggesting that the observed protection from cochlear synaptopathy may occur through E2-mediated preservation of these neurons. Taken together, these data indicate the estrogen signaling pathways may be harnessed for the prevention and treatment of NIHL.

Gender differentiates effects of acoustic stimulation in patients with tinnitus

Gender constitutes a major factor to consider when tailoring subtype-based therapies for tinnitus. Previous reports showed important differences between men and women concerning basic perceptual tinnitus characteristics (i.e., laterality, frequency, tinnitus loudness) as well as psychological reactions linked to this condition. Therapeutic approaches based on acoustic stimulation involve processes beyond a pure masking effect and consist of sound presentation temporarily altering or alleviating tinnitus perception via residual and/or lateral inhibition mechanisms. Presented stimuli may include pure tones, noise, and music adjusted to or modulated to filter out tinnitus pitch and therefore trigger reparative functional and structural changes in the auditory system. Furthermore, recent findings suggest that in tonal tinnitus, the presentation of pitch-adjusted sounds which were altered by a 10Hz modulation of amplitude was more efficient than unmodulated stimulation. In this paper, we investigate sex differences in the outcome of different variants of acoustic stimulation, looking for factors revealing predictive value in the efficiency of tinnitus relief.

Sex differences in the auditory functions of rodents

BACKGROUND

In humans, it is well known that females have better hearing than males. The mechanism of this influence of sex on auditory function in humans is not well understood. Testing the hypothesis of underlying mechanisms often relies on preclinical research, a field in which sex bias still exists unconsciously. Rodents are popular research models in hearing, thus it is crucial to understand the sex differences in these rodent models when studying health and disease in humans.

OBJECTIVES

This review aims to summarize the existing sex differences in the auditory functions of rodent species including mouse, rat, Guinea pig, Mongolian gerbil, and chinchilla. In addition, a concise summary of the hearing characteristics and the advantages and the drawbacks of conducting auditory experiments in each rodent species is provided.

DESIGNS

Manuscripts were identified in PubMed and Ovid Medline for the queries "Rodent", "Sex Characteristics", and "Hearing or Auditory Function". Manuscripts were included if they were original research, written in English, and use rodents. The content of each manuscript was screened for the sex of the rodents and the discussion of sex-based results.

CONCLUSIONS

The sex differences in auditory function of rodents are prevalent and influenced by multiple factors including physiological mechanisms, sex-based anatomical variations, and stimuli from the external environment. Such differences may play a role in understanding and explaining sex differences in hearing of humans and need to be taken into consideration for developing clinical therapies aim to improve auditory performances.

Sex-based Differences in Hearing Loss: Perspectives From Non-clinical Research to Clinical Outcomess

INTRODUCTION

It is estimated over 466 million people worldwide have disabling hearing loss, and untreated hearing loss is associated with poorer health outcomes. The influence of sex as a biological variable on hearing loss is not well understood, especially for differences in underlying mechanisms which are typically elucidated through non-clinical research. Although the inclusion of sex as a biological variable in clinical studies has been required since 1993, sex reporting has only been recently mandated in National Institutes of Health funded non-clinical studies.

OBJECTIVE

This article reviews the literature on recent non-clinical and clinical research concerning sex-based differences in hearing loss primarily since 1993, and discusses implications for knowledge gaps in the translation from non-clinical to clinical realms.

CONCLUSIONS

The disparity between sex-based requirements for non-clinical versus clinical research may inhibit a comprehensive understanding of sex-based mechanistic differences. Such disparities may play a role in understanding and explaining clinically significant sex differences and are likely necessary for developing robust clinical treatment options.

Benign Paroxysmal Positional Vertigo Risk Factors Unique to Perimenopausal Women

Many investigations have found common occurrences of benign paroxysmal positional vertigo (BPPV) in women, and clinical experience has shown that BPPV can develop due to increased hormonal fluctuations, especially during menopause. Therefore, knowledge about neurochemicals and their involvement with BPPV is imperative for the management of neurological issues in women. This review will discuss appropriate gender-based considerations of BPPV based on experimental and clinical evidence. The studies describe 2 lines of evidence regarding the association of perimenopause in women and the development of BPPV: (1) experimental evidence: the existence of estrogen receptors in the inner ear, otoconial malformations in osteopenic/osteoporotic rats, changes in otoconin 90 caused by hormone replacement therapy, and impaired calcium absorption following estrogen deprivation corrected by estrogen replacement therapy and (2) clinical evidence: epidemiological aspects, osteoporosis and estrogen deficiency. Future studies are necessary to validate the effects of hormonal replacement therapy and phytoestrogen in women with recurrent BPPV.

Age-related hearing loss: Why we need to think about sex as a biological variable

It has long been known that age-related hearing loss (ARHL) is more common, more severe, and with an earlier onset in men compared to women. Even in the absence of confounding factors such as noise exposure, these sexdifferences in susceptibility to ARHL remain. In the last decade, insight into the pleiotrophic nature by which estrogen signaling can impact multiple signaling mechanisms to mediate downstream changes in gene expression and/or elicit rapid changes in cellular function has rapidly gathered pace, and a role for estrogen signaling in the biological pathways that confer neuroprotection is becoming undeniable. Here I review the evidence why we need to consider sex as a biological variable (SABV) when investigating the etiology of ARHL. Loss of auditory function with aging is frequency-specific and modulated by SABV. Evidence also suggests that differences in cochlear physiology between women and men are already present from birth. Understanding the molecular basis of these sex differences in ARHL will accelerate the development of precision medicine therapies for ARHL.

Understanding hormone and hormone therapies' impact on the auditory system

Hormones such as estrogen, progesterone, and aldosterone all demonstrate vital roles in sustaining auditory function through either the maintenance of cochlear neurons, up/down regulation of critical molecules (i.e., IGF-1, BDNF, etc.), or generation of the endocochlear potential. With disease and/or age, hormone expression begins to decline drastically, which ultimately affects cochlear structures and the integrity of cochlear cells. The following review explores the latest findings as well as realistic outcomes for hormone therapy treatment in the auditory system. This information could serve as a potential guide for patients considering hormone therapy as a medicinal choice to alleviate the signs of onset of presbycusis-age-related hearing loss. Additional scientific investigations could also be carried out to further enhance recent findings.

Postnatal Effects of Sex Hormones on Click-Evoked Otoacoustic Emissions: A Study of Adolescents with Gender Dysphoria

Click-evoked otoacoustic emissions (CEOAEs) are echo-like sounds, generated by the inner ear in response to click-stimuli. A sex difference in emission strength is observed in neonates and adults, with weaker CEOAE amplitudes in males. These differences are assumed to originate from testosterone influences during prenatal male sexual differentiation and to remain stable throughout life. However, recent studies suggested activational, postnatal effects of sex hormones on CEOAEs. Adolescents diagnosed with gender dysphoria (GD) may receive gonadotropin-releasing hormone analogs (GnRHa) in order to suppress endogenous sex hormones and, therefore, pubertal maturation, followed by cross-sex hormone (CSH) treatment. Using a cross-sectional design, we examined whether hormonal interventions in adolescents diagnosed with GD (62 trans boys, assigned female at birth, self-identifying as male; 43 trans girls, assigned male at birth, self-identifying as female), affected their CEOAEs compared to age- and sex-matched controls (44 boys, 37 girls). Sex-typical differences in CEOAE amplitude were observed among cisgender controls and treatment-naïve trans boys but not in other groups with GD. Treatment-naïve trans girls tended to have more female-typical CEOAEs, suggesting hypomasculinized early sexual differentiation, in support of a prominent hypothesis on the etiology of GD. In line with the predicted suppressive effects of androgens, trans boys receiving CSH treatment, i.e., testosterone plus GnRHa, showed significantly weaker right-ear CEOAEs compared with control girls. A similar trend was seen in trans boys treated with GnRHa only. Unexpectedly, trans girls showed CEOAE masculinization with addition of estradiol. Our findings show that CEOAEs may not be used as an unequivocal measure of prenatal androgen exposure as they can be modulated postnatally by sex hormones, in the form of hormonal treatment.

Auditory function and dysfunction: estrogen makes a difference

Estrogen is the major female hormone involved in reproductive functions, but it also exerts a variety of additional roles in non-reproductive organs. In this review, we highlight the preclinical and clinical studies that have pointed out sex differences and estrogenic influence on audition. We also describe the experimental evidences supporting a protective role of estrogen towards acquired forms of hearing loss. Although a high level of endogenous estrogen is associated with a better hearing function, hormonal treatments at menopause have provided contradictory outcomes. The various factors that are likely to explain these discrepancies include the treatment regimen as well as the hormonal status and responsiveness of the patients. The complexity of estrogen signaling is being untangled and many downstream effectors of its genomic and non-genomic actions have been identified in other systems. Based on these advances and on the common physio-pathological events that underlie age-related, drug or noise-induced hearing loss, we discuss potential mechanisms for their protective actions in the cochlea.

Sex differences in hearing: Probing the role of estrogen signaling

Hearing loss is the most common form of sensory impairment in humans, with an anticipated rise in incidence as the result of recreational noise exposures. Hearing loss is also the second most common health issue afflicting military veterans. Currently, there are no approved therapeutics to treat sensorineural hearing loss in humans. While hearing loss affects both men and women, sexual dimorphism is documented with respect to peripheral and central auditory physiology, as well as susceptibility to age-related and noise-induced hearing loss. Physiological differences between the sexes are often hormone-driven, and an increasing body of literature demonstrates that the hormone estrogen and its related signaling pathways may in part, modulate the aforementioned differences in hearing. From a mechanistic perspective, understanding the underpinnings of the hormonal modulation of hearing may lead to the development of therapeutics for age related and noise induced hearing loss. Here the authors review a number of studies that range from human populations to animal models, which have begun to provide a framework for understanding the functional role of estrogen signaling in hearing, particularly in normal and aberrant peripheral auditory physiology.

Clinical update on sensorineural hearing loss in Turner syndrome and the X-chromosome

Hearing loss is one of the major medical concerns in girls and women with Turner syndrome (TS) and has a negative effect on well-being and quality of everyday life. Sensorineural hearing loss is the most common type of hearing loss, affecting more than half of adults with TS. Karyotypes with a loss of the short p-arm on the X-chromosome are more prone to ear and hearing problems. The importance of detecting, investigating, and treating hearing loss with hearing aids cannot be emphasized enough. The pathophysiology of the sensorineural hearing loss in TS is not known, but theories regarding estrogen deficiency, the cell cycle delay hypothesis, IGF-1 deficiency and the possible role of the KDM6A gene are discussed. Due to the diversity of symptoms and conditions within the same karyotype, a combination of genetic factors altered by epigenetic and/or hormonal effects is probable. Further research is needed regarding the pathophysiology of ear and hearing problems in TS to develop new treatment methods.

Menopause and postmenopausal hormone therapy and risk of hearing loss

OBJECTIVE

Menopause may be a risk factor for hearing loss, and postmenopausal hormone therapy (HT) has been proposed to slow hearing decline; however, there are no large prospective studies. We prospectively examined the independent relations between menopause and postmenopausal HT and risk of self-reported hearing loss.

METHODS

Prospective cohort study among 80,972 women in the Nurses' Health Study II, baseline age 27 to 44 years, followed from 1991 to 2013. Baseline and updated information was obtained from detailed validated biennial questionnaires. Cox proportional-hazards regression models were used to examine independent associations between menopausal status and postmenopausal HT and risk of hearing loss.

RESULTS

After 1,410,928 person-years of follow-up, 18,558 cases of hearing loss were reported. There was no significant overall association between menopausal status, natural or surgical, and risk of hearing loss. Older age at natural menopause was associated with higher risk. The multivariable-adjusted relative risk of hearing loss among women who underwent natural menopause at age 50+ years compared with those aged less than 50 years was 1.10 (95% confidence interval [CI] 1.03, 1.17). Among postmenopausal women, oral HT (estrogen therapy or estrogen plus progestogen therapy) was associated with higher risk of hearing loss, and longer duration of use was associated with higher risk (P trend < 0.001). Compared with women who never used HT, the multivariable-adjusted relative risk of hearing loss among women who used oral HT for 5 to 9.9 years was 1.15 (95% CI 1.06, 1.24) and for 10+ years was 1.21 (95% CI 1.07, 1.37).

CONCLUSIONS

Older age at menopause and longer duration of postmenopausal HT are associated with higher risk of hearing loss.

ZENK induction in the zebra finch brain by song: Relationship to hemisphere, rhythm, oestradiol and sex

Oestradiol is abundant in the zebra finch auditory forebrain and has the capacity to modulate neural responses to auditory stimuli with specificity as a result of both hemisphere and sex. Arrhythmic song induces greater ZENK expression than rhythmic song in the caudomedial nidopallium (NCM), caudomedial mesopallium (CMM) and nucleus taeniae (Tn) of adult zebra finches. The increases in the auditory regions (i.e. NCM and CMM) may result from detection of errors in the arrhythmic song relative to the learned template. In the present study, zebra finches were treated with oestradiol, the aromatase inhibitor fadrozole or a control and then exposed to rhythmic or arrhythmic song to assess the effect of oestradiol availability on neural responses to auditory rhythms. ZENK mRNA was significantly greater in the left hemisphere within the NCM, CMM and Tn. Main effects of sex were detected in both auditory regions, with increased ZENK in males in the NCM and in females in the CMM. In the CMM, an effect of hormone treatment also existed. Although no pairwise comparison was statistically significant, the pattern suggested greater ZENK expression in control compared to both fadrozole- and oestradiol-treated birds. In the NCM, an interaction between sex and hormone treatment suggested that the sex effect was restricted to control animals. An additional interaction in the NCM among sex, stimulus rhythmicity and hemisphere indicated that the strongest effect of laterality was present in males exposed to arrhythmic song. The hormone effects suggest that an optimal level of oestradiol may exist for processing rhythmicity of auditory stimuli. The overall pattern for left lateralisation parallels the left lateralisation of language processing in humans and may suggest that this hemisphere is specialised for processing conspecific vocalisations. The reversed sex differences in the NCM and CMM suggest that males and females differentially rely on components of the auditory forebrain for processing conspecific song.

The effects of aging and sex on detection of ultrasonic vocalizations by adult CBA/CaJ mice (Mus musculus)

Mice are frequently used as animal models for human hearing research, yet their auditory capabilities have not been fully explored. Previous studies have established auditory threshold sensitivities for pure tone stimuli in CBA/CaJ mice using ABR and behavioral methodologies. Little is known about how they perceive their own ultrasonic vocalizations (USVs), and nothing is known about how aging influences this perception. The aim of the present study was to establish auditory threshold sensitivity for several USV types, as well as to track these thresholds across the mouse's lifespan. In order to determine how well mice detect these complex communication stimuli, several CBA/CaJ mice were trained and tested at various ages on a detection task using operant conditioning procedures. Results showed that mice were able to detect USVs into old age. Not surprisingly, thresholds differed for the different USV types. Male mice suffered greater hearing loss than females for all calls but not for 42 kHz tones. In conclusion, the results highlight the importance of studying complex signals across the lifespan.

Preliminary Report on the Investigation of the Association Between BPPV and Osteoporosis Using Biomarkers

OBJECTIVE

To test the hypothesis that levels of a BPPV biomarker, otolin-1, correlate with those of osteoporosis markers, aminoterminal propeptide of protocollagen type I (P1NP), and aminoterminal telopeptides of collagen (NTX), thus further supporting a link between the two diseases.

STUDY DESIGN

Prospective pilot clinical trial (Level of Evidence: 2b).

PATIENTS

Postmenopausal women with BPPV.

INTERVENTIONS

Diagnostic.

MAIN OUTCOME MEASURES

Serum levels of otolin-1, P1NP, NTX, vitamin D, and calcium were examined in relation to each other, age, and DEXA scan T-scores.

RESULTS

There was a strong, negative correlation between T-scores and otolin-1 levels. Although P1NP and NTX levels were strongly correlated, neither had statistical correlations with otolin-1.

CONCLUSIONS

Despite a strong correlation between DEXA scan results and otolin-1 levels, there were no significant correlations between otolin-1 and P1NP or NTX. This suggests that the association between osteoporosis and BPPV is complex, but not likely to be causal. Although more work is needed to elucidate these relationships, this preliminary finding has important practical implications for BPPV in that proactive management of osteoporosis, per se, would not be expected to have benefits in management of BPPV.

Estrogen Blockade Reduces Auditory Feedback in CBA Mice

OBJECTIVE: To examine the effects of estrogen suppression on age-related changes in distortion product otoacoustic emissions (DPOAEs) and contralateral suppression (CS) of DPOAEs in CBA mice.

STUDY DESIGN AND SETTING: Young CBA mice received a slow-release shoulder implantation of either tamoxifen or placebo. Serial DPOAEs and CS of DPOAEs were obtained at 3-week intervals over a period of 9 weeks.

RESULTS: Although DPOAEs were maintained over the study interval, CS of DPOAEs decreased significantly with age in the experimental group. No such declines were observed in either the control animals or the untreated male mice.

CONCLUSIONS: Estrogen suppression negatively affects the MOC efferent feedback system.

SIGNIFICANCE: Our results support the hypothesis that estrogen plays an important role in the maintenance of auditory integrity. Additionally, our findings raise intriguing questions about auditory effects of hormonal shifts in humans resulting from menopause, hormone supplements such as oral contraceptives, and hormone replacement therapy as well as antiestrogens.

Early expression of aromatase and the membrane estrogen receptor GPER in neuromasts reveals a role for estrogens in the development of the frog lateral line system

Estrogens and their receptors are present at very early stages of vertebrate embryogenesis before gonadal tissues are formed. However, the cellular source and the function of estrogens in embryogenesis remain major questions in developmental endocrinology. We demonstrate the presence of estrogen-synthesizing enzyme aromatase and G protein-coupled estrogen receptor (GPER) proteins throughout early embryogenesis in the model organism, Silurana tropicalis. We provide the first evidence of aromatase in the vertebrate lateral line. High levels of aromatase were detected in the mantle cells of neuromasts, the mechanosensory units of the lateral line, which persisted throughout the course of development (Nieuwkoop and Faber stages 34-47). We show that GPER is expressed in both the accessory and hair cells. Pharmacological activation of GPER with the agonist G-1 disrupted neuromast development and migration. Future study of this novel estrogen system in the amphibian lateral line may shed light on similar systems such as the mammalian inner ear.

Sexual attractiveness of male chemicals and vocalizations in mice

Male-female interaction is important for finding a suitable mating partner and for ensuring reproductive success. Male sexual signals such as pheromones transmit information and social and sexual status to females, and exert powerful effects on the mate preference and reproductive biology of females. Likewise, male vocalizations are attractive to females and enhance reproductive function in many animals. Interestingly, females' preference for male pheromones and vocalizations is associated with their genetic background, to avoid inbreeding. Moreover, based on acoustic cues, olfactory signals have significant effects on mate choice in mice, suggesting mate choice involves multisensory integration. In this review, we synopsize the effects of both olfactory and auditory cues on female behavior and neuroendocrine functions. We also discuss how these male signals are integrated and processed in the brain to regulate behavior and reproductive function.

Hearing loss in adult women with Turner's syndrome and other congenital hypogonadisms

OBJECTIVES

To define the patterns and causes of hearing decline associated to Turner's syndrome (TS).

METHODS

An observational study with three cohorts was designed: 31 TS patients, 15 women with other congenital hypogonadims (OCH) and 41 healthy age-matched women taking contraception. Microotoscopy, standard pure-tone audiometry brain auditory evoked potentials (BAEP) were performed to study hearing function.

RESULTS

Up to 87% of TS subjects suffered from some degree of hearing loss (HL) in the audiograms, compared with 20% OCH and 27% controls. Sensorineural hearing loss (SNHL) was the most frequent type of hypoacusia found in TS group. BAEP study demonstrated that 61% of TS women showed HL compared to 20% in OCH patients. No significant differences in latencies, amplitudes, and interpeaks of waves I, III and V were found between TS and OCH, nor when compared to reference population. Worse results were observed among the oldest TS patients, those with pure monosomy or isochromosome, and those with a history of recurrent otitis.

CONCLUSIONS

More than a half of TS females presented HL. SNHL is the most frequent pattern among middle-aged women with TS. Old age, karyotype and recurrent otitis are predisposition factors to produce HL, while oestrogens play a minor role.

No direct nuclear effect of progesterone in the inner ear: other possible pathways

CONCLUSION

No nuclear progesterone receptors were found in human or rat stria vascularis, organ of Corti or spiral ganglion with immunohistochemistry or polymerase chain reaction (PCR). Progesterone receptor B (PR-B) was found with Western blot in the cochlea, probably representing the staining in the cochlear bone. The effect of progesterone on hearing is therefore most likely not due to a direct action on the inner ear.

OBJECTIVES

Studies suggest that progesterone as a component in hormone replacement therapy has a negative effect on hearing thresholds and otoacoustic emissions in pre- and postmenopausal women and mice. This study was designed to examine the presence of PRs in the cochlea of humans and rats.

METHODS

Immunohistochemical staining of PR protein in humans and rats, PCR of PR-B mRNA expression, and Western blot of PR-A and PR-B protein in rats was performed.

RESULTS

No nuclear staining could be found for any PR in human or rat inner ear except the PR-B staining in the cochlear bone. No mRNA expression was detected by PCR. PR-B could be detected in Western blot performed on the whole cochlea including bone.

Polymorphisms in genes encoding aquaporins 4 and 5 and estrogen receptor α in patients with Ménière's disease and sudden sensorineural hearing loss

AIMS

The etiologies of Ménière's disease and idiopathic sudden sensorineural hearing loss (SSNHL) remain unclear. The homeostasis of the water and blood circulation in the inner ear is essential for maintaining its hearing and equilibrium functions, and aquaporins and estrogen are involved in the fluid or ion balance in the inner ear. We investigated the associations between genetic polymorphisms in aquaporin 4 (AQP4, rs2075575), aquaporin 5 (AQP5, rs3736309), and estrogen receptor α (ERα1, rs2234693; ERα2, rs9340799) and susceptibility to Ménière's disease or SSNHL.

MAIN METHODS

We compared 86 patients affected by Ménière's disease, 85 patients affected by SSNHL, and 2136 adults who were participants in a comprehensive longitudinal study of aging.

KEY FINDINGS

With the AQP5 polymorphism, the odds ratio for Ménière's disease was 0.676 (95% confidence interval: 0.477-0.957) after adjustment for age and sex, when an additive genetic model was used. The AQP5 polymorphism entailed no significant risk of SSNHL and the polymorphisms of AQP4, ERα1, and ERα2 entailed no significant risk of Ménière's disease or SSNHL in the additive genetic model, regardless of adjustments for age and sex.

SIGNIFICANCE

Our study suggests that the variant G allele of AQP5 polymorphism rs3736309 reduces the risk of Ménière's disease.

Estradiol treatment and hormonal fluctuations during the estrous cycle modulate the expression of estrogen receptors in the auditory system and the prepulse inhibition of acoustic startle response

Estrogens' effects on hearing are documented across species, but the responsible molecular mechanisms remain unknown. The presence of estrogen receptors (ER) throughout the auditory system offers a potential pathway of direct estrogenic effects on auditory function, but little is known about how each ER's expression is regulated by the overall hormonal status of the body. In the present study, we determined the effects of ovariectomy and chronic 17β-estradiol treatment on mRNA and protein expression of ERα and ERβ in peripheral (cochlea) and central (inferior colliculus) auditory structures of mice, as well as on auditory-related behavior using the acoustic startle response (ASR), prepulse inhibition (PPI), and habituation of the startle response. 17β-Estradiol treatment down-regulated ERα but not ERβ and increased PPI and latency of the ASR. Neither the magnitude nor the habituation of ASR was affected. Furthermore, ER's mRNA and protein expression in the inner ear were analyzed throughout the estrous cycle (proestrus, estrus, metestrus, and diestrus), revealing a negative correlation of circulating estrogens with ERα expression, whereas ERβ was stable. Our findings show that ER not only are present in both the peripheral and central auditory system but also that circulating estrogen levels down-regulate ERα expression in the auditory system and affect PPI and the latency of ASR, suggesting a key role of ERα as a hormone-induced modulator of the auditory system and behavior.

Screen of FDA-approved drug library reveals compounds that protect hair cells from aminoglycosides and cisplatin

Loss of mechanosensory hair cells in the inner ear accounts for many hearing loss and balance disorders. Several beneficial pharmaceutical drugs cause hair cell death as a side effect. These include aminoglycoside antibiotics, such as neomycin, kanamycin and gentamicin, and several cancer chemotherapy drugs, such as cisplatin. Discovering new compounds that protect mammalian hair cells from toxic insults is experimentally difficult because of the inaccessibility of the inner ear. We used the zebrafish lateral line sensory system as an in vivo screening platform to survey a library of FDA-approved pharmaceuticals for compounds that protect hair cells from neomycin, gentamicin, kanamycin and cisplatin. Ten compounds were identified that provide protection from at least two of the four toxins. The resulting compounds fall into several drug classes, including serotonin and dopamine-modulating drugs, adrenergic receptor ligands, and estrogen receptor modulators. The protective compounds show different effects against the different toxins, supporting the idea that each toxin causes hair cell death by distinct, but partially overlapping, mechanisms. Furthermore, some compounds from the same drug classes had different protective properties, suggesting that they might not prevent hair cell death by their known target mechanisms. Some protective compounds blocked gentamicin uptake into hair cells, suggesting that they may block mechanotransduction or other routes of entry. The protective compounds identified in our screen will provide a starting point for studies in mammals as well as further research discovering the cellular signaling pathways that trigger hair cell death.

Effects of neuroactive steroids on cochlear hair cell death induced by gentamicin

As neuroactive steroids, sex steroid hormones have non-reproductive effects. We previously reported that 17β-estradiol (βE2) had protective effects against gentamicin (GM) ototoxicity in the cochlea. In the present study, we examined whether the protective action of βE2 on GM ototoxicity is mediated by the estrogen receptor (ER) and whether other estrogens (17α-estradiol (αE2), estrone (E1), and estriol (E3)) and other neuroactive steroids, dehydroepiandrosterone (DHEA) and progesterone (P), have similar protective effects. The basal turn of the organ of Corti was dissected from Sprague-Dawley rats and cultured in a medium containing 100 μM GM for 48h. The effects of βE2 and ICI 182,780, a selective ER antagonist, were examined. In addition, the effects of other estrogens, DHEA and P were tested using this culture system. Loss of outer hair cells induced by GM exposure was compared among groups. βE2 exhibited a protective effect against GM ototoxicity, but its protective effect was antagonized by ICI 182,780. αE2, E1, and E3 also protected hair cells against gentamicin ototoxicity. DHEA showed a protective effect; however, the addition of ICI 182,780 did not affect hair cell loss. P did not have any effect on GM-induced outer hair cell death. The present findings suggest that estrogens and DHEA are protective agents against GM ototoxicity. The results of the ER antagonist study also suggest that the protective action of βE2 is mediated via ER but that of DHEA is not related to its conversion to estrogen and binding to ER. Further studies on neuroactive steroids may lead to new insights regarding cochlear protection.

Estradiol-dependent modulation of auditory processing and selectivity in songbirds

The steroid hormone estradiol plays an important role in reproductive development and behavior and modulates a wide array of physiological and cognitive processes. Recently, reports from several research groups have converged to show that estradiol also powerfully modulates sensory processing, specifically, the physiology of central auditory circuits in songbirds. These investigators have discovered that (1) behaviorally-relevant auditory experience rapidly increases estradiol levels in the auditory forebrain; (2) estradiol instantaneously enhances the responsiveness and coding efficiency of auditory neurons; (3) these changes are mediated by a non-genomic effect of brain-generated estradiol on the strength of inhibitory neurotransmission; and (4) estradiol regulates biochemical cascades that induce the expression of genes involved in synaptic plasticity. Together, these findings have established estradiol as a central regulator of auditory function and intensified the need to consider brain-based mechanisms, in addition to peripheral organ dysfunction, in hearing pathologies associated with estrogen deficiency.

Seasonal plasticity of auditory hair cell frequency sensitivity correlates with plasma steroid levels in vocal fish

Vertebrates displaying seasonal shifts in reproductive behavior provide the opportunity to investigate bidirectional plasticity in sensory function. The midshipman teleost fish exhibits steroid-dependent plasticity in frequency encoding by eighth nerve auditory afferents. In this study, evoked potentials were recorded in vivo from the saccule, the main auditory division of the inner ear of most teleosts, to test the hypothesis that males and females exhibit seasonal changes in hair cell physiology in relation to seasonal changes in plasma levels of steroids. Thresholds across the predominant frequency range of natural vocalizations were significantly less in both sexes in reproductive compared with non-reproductive conditions, with differences greatest at frequencies corresponding to call upper harmonics. A subset of non-reproductive males exhibiting an intermediate saccular phenotype had elevated testosterone levels, supporting the hypothesis that rising steroid levels induce non-reproductive to reproductive transitions in saccular physiology. We propose that elevated levels of steroids act via long-term (days to weeks) signaling pathways to upregulate ion channel expression generating higher resonant frequencies characteristic of non-mammalian auditory hair cells, thereby lowering acoustic thresholds.

Discrepancy in improvement of hearing loss between left and right ears after postmenopausal hormone therapy

Physiological levels of estrogen would seem to have a possible protective effect on hearing function and estrogen replacement therapy may delay hearing loss in menopausal women. Treatment of healthy menopausal women with Tibolone for 6 months resulted in improvement in audiometry results at low frequencies which was more prominent on the right side. The reason of better improvement on the right side is not known. There might be some other factors modifying the condition or effect of the drug such as laterality. There might be hearing lateralization in menopausal women. Especially significant improvement on right ear might be explained by differences in distribution of estrogen receptor (ER) in the ear, in another words lateralization of ER concentration. ER-α and -β might be more dense in the right ear, so give better response to estrogen treatment. Another reason might be difference in bone mineral density of sides of body which is lower on the right side. Similarly lower bone mineral density right ear bones would cause better response to estrogen therapy and better improvement in audiometry results on that side.

Peripheral auditory processing changes seasonally in Gambel's white-crowned sparrow

Song in oscine birds is a learned behavior that plays important roles in breeding. Pronounced seasonal differences in song behavior and in the morphology and physiology of the neural circuit underlying song production are well documented in many songbird species. Androgenic and estrogenic hormones largely mediate these seasonal changes. Although much work has focused on the hormonal mechanisms underlying seasonal plasticity in songbird vocal production, relatively less work has investigated seasonal and hormonal effects on songbird auditory processing, particularly at a peripheral level. We addressed this issue in Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii), a highly seasonal breeder. Photoperiod and hormone levels were manipulated in the laboratory to simulate natural breeding and non-breeding conditions. Peripheral auditory function was assessed by measuring the auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAEs) of males and females in both conditions. Birds exposed to breeding-like conditions demonstrated elevated thresholds and prolonged peak latencies when compared with birds housed under non-breeding-like conditions. There were no changes in DPOAEs, however, which indicates that the seasonal differences in ABRs do not arise from changes in hair cell function. These results suggest that seasons and hormones impact auditory processing as well as vocal production in wild songbirds.

Sex differences in auditory filters of brown-headed cowbirds (Molothrus ater)

Receiver sensory abilities can be influenced by a number of factors, including habitat, phylogeny and the selective pressure to acquire information about conspecifics or heterospecifics. It has been hypothesized that brood-parasitic brown-headed cowbird (Molothrus ater) females may locate or determine the quality of potential hosts by eavesdropping on their sexual signals. This is expected to produce different sex-specific pressures on the auditory system to detect conspecific and heterospecific acoustic signals. Here, we examined auditory filter shape and efficiency, which influence the ability to resolve spectral and temporal information, in males and females at center frequencies of 2, 3 and 4 kHz. We found that overall, cowbirds had relatively wide filters (lsmean +/- SE: 619.8 +/- 41.6 Hz). Moreover, females had narrower filters (females: 491.4 +/- 66.8, males: 713.8 +/- 67.3 Hz) and greater filter efficiency (females: 59.0 +/- 2.0, males: 69.8 +/- 1.9 dB) than males. Our results suggest that the filters of female cowbirds may allow them to extract spectral information from heterospecific vocalizations. The broader auditory filters of males may reflect limited spectral energy in conspecific vocalizations in this frequency range, and hence, weaker selection for high resolution of frequency in the range of 2-4 kHz.

c-Fos induction by a 14 T magnetic field in visceral and vestibular relays of the female rat brainstem is modulated by estradiol

There is increasing evidence that high magnetic fields interact with the vestibular system of humans and rodents. In rats, exposure to high magnetic fields of 7 T or above induces locomotor circling and leads to a conditioned taste aversion if paired with a novel taste. Sex differences in the behavioral responses to magnetic field exposure have been found, such that female rats show more locomotor circling and enhanced conditioned taste aversion compared to male rats. To determine if estrogen modulates the neural response to high magnetic fields, c-Fos expression after 14 T magnetic field exposure was compared in ovariectomized rats and ovariectomized rats with estradiol replacement. Compared to sham exposure, magnetic field exposure induced significantly more c-Fos positive cells in the nucleus of the solitary tract and the parabrachial, medial vestibular, prepositus, and supragenualis nuclei. Furthermore, there was a significant asymmetry in c-Fos induction between sides of the brainstem in several regions. In ovariectomized rats, there was more c-Fos expressed in the right side compared to left side in the locus coeruleus and parabrachial, superior vestibular, and supragenualis nuclei; less expression in the right compared to left side of the medial vestibular; and no asymmetry in the prepositus nucleus and the nucleus of the solitary tract. Chronic estradiol treatment modulated the neural response in some regions: less c-Fos was induced in the superior vestibular nucleus and locus coeruleus after estradiol replacement; estradiol treatment eliminated the asymmetry of c-Fos expression in the locus coeruleus and supragenualis nucleus, created an asymmetry in the prepositus nucleus and reversed the asymmetry in the parabrachial nucleus. These results suggest that ovarian steroids may mediate sex differences in the behavioral responses to magnetic field exposure at the level of visceral and vestibular nuclei of the brainstem.

Effects of age and sex on the expression of estrogen receptor alpha and beta in the mouse inner ear

CONCLUSION

Estrogen receptor (ER) alpha and beta were expressed in the inner ear, and expression decreased with increasing age. ERalpha may alter cochlear and vestibular sensory transduction, and ERbeta may have a neuroprotective function in the inner ear.

OBJECTIVE

Expression of ERalpha and ERbeta in the mouse inner ear and its alterations with sex and aging were analyzed.

MATERIALS AND METHODS

Male and female CBA/J mice aged 8 weeks and 24 months were used. The localization and the intensity of ERalpha and ERbeta immunoreactivity in the inner ear of young and old mice of both sexes were investigated by immunohistochemistry.

RESULTS

ERalpha and ERbeta were co-expressed in the inner ear, i.e. in the nuclei of stria vascularis, outer and inner hair cells, spiral ganglion cells and vestibular ganglion cells, vestibular dark cells and endolymphatic sac. Strial marginal cells, outer hair cells and type II ganglion cells showed less expression of ERalpha. No gender- or age-related difference was noted in the expression pattern of ERalpha or ERbeta, but fluorescence intensity of ERalpha was stronger in young female mice than in young male mice. In contrast, ERbeta revealed no significant difference. In the old mice, fluorescence intensities of both ERalpha and ERbeta were significantly decreased in both sexes.

Estrogen receptors in the inner ear during different stages of pregnancy and development in the rat

CONCLUSION

ERalpha and ERbeta are present in the inner ear and are up- and down-regulated depending on the stage of maturation, development and pregnancy, suggesting that estrogen may have an effect on the cochlea during various stages of life. No estrogen receptors (ERs) were found in the cochlea of the developing fetus, which suggests that estrogen does not have an effect on the cochlea during gestation.

OBJECTIVE

To investigate the distribution of ERs in the cochlea during pregnancy, maturation and development in a female rat model.

MATERIALS AND METHODS

The cochleas of 24 rats in 4 groups in different time periods of maturation (21 and 56 days old) and pregnancy (day 8 and 18 of pregnancy) and 16 fetuses at gestational ages of 8 and 18 days were collected. All specimens were stained for ERs using standard immunohistochemical techniques.

RESULTS

ERs are present in the cochlea of the rat and vary during maturation and pregnancy. No ERs were found in the fetal cochleas. Of the non-fetal time points measured, the expression levels of ERs in the rat cochlea were highest at the postnatal age of 21 days and were lowest during late pregnancy (day 18).

Cellular targets of estrogen signaling in regeneration of inner ear sensory epithelia

Estrogen signaling in auditory and vestibular sensory epithelia is a newly emerging focus propelled by the role of estrogen signaling in many other proliferative systems. Understanding the pathways with which estrogen interacts can provide a means to identify how estrogen may modulate proliferative signaling in inner ear sensory epithelia. Reviewed herein are two signaling families, EGF and TGFbeta. Both pathways are involved in regulating proliferation of supporting cells in mature vestibular sensory epithelia and have well characterized interactions with estrogen signaling in other systems. It is becoming increasingly clear that elucidating the complexity of signaling in regeneration will be necessary for development of therapeutics that can initiate regeneration and prevent progression to a pathogenic state.