Development of cochlear active mechanisms in humans differs between gender (original) (raw)
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Sexual Dimorphism in the Functional Development of the Cochlear Amplifier in Humans
2021
Objectives: Otoacoustic emissions, a byproduct of active cochlear mechanisms, exhibit a higher magnitude in females than in males. The relatively higher levels of androgen exposure in the male fetus are thought to cause this difference. Postnatally, the onset of puberty is also associated with the androgen surge in males. In this study, we investigated sexual dimorphism in age-related changes in stimulus-frequency otoacoustic emissions for children. Design: In a retrospective design, stimulus-frequency otoacoustic emissions were analyzed from a cross-sectional sample of 170 normal-hearing children (4 to 12 years) and 67 young adults. Wideband acoustic immittance and efferent inhibition measures were analyzed to determine the extent to which middle ear transmission and efferent inhibition can account for potential sex differences in stimulus-frequency otoacoustic emissions. Results: Male children showed a significant reduction in otoacoustic emission magnitudes with age, whereas fema...
Sex hormones and hearing: A pioneering area of enquiry
Hearing Research, 2009
Sensory neuroscience and biomedical research in general, have become extremely specialized. Most fields and subfields, for one attempting to enter them as a cutting-edge researcher, or as an investigator in a related field who wants to gain mastery of another area; it can take much time and effort to attain a useful, comfortable level of knowledge. Sometimes, this learning task is so daunting, few venture to undertake it, particularly as we advance professionally. The influence of sex hormones on the auditory system is one of those rare areas of investigation, where mastering what has been discovered to date, is actually feasible. This special issue of Hearing Research is a very effective introduction and summary of what is currently known about how sex hormones can effect hearing, and how in some cases, alterations in natural levels of sex hormones can lead to hearing impairment or deafness. Not surprisingly, the neonatal nature of this developing area of enquiry can be both satisfying and unsettling. Being able to master most of what is known about this sub-field of hearing research and auditory neuroscience, in real-time, is quite rewarding. However, from a mechanistic and clinical interventional point of view, it can be very frustrating. Delineation of mechanisms below the systems level, including working out of cellular and molecular pathways and biomarkers, a requirement of clinical translational innovations and drug discovery, is still a lengthy task. Some believe that one key mark of good science is that for every question that is answered, many more questions and hypotheses are generated from the experiments carried out. This is certainly the state-of-the-art stage we find ourselves in regarding what we know, and what further necessary experimentation is needed about how sex hormones can influence hearing and their involvement in hearing loss.
Prenatal Masculinization of the Auditory System in Infants: The MIREC-ID Study
Psychoneuroendocrinology, 2019
Prenatal androgen exposure is thought to impact early cochlear development Physical indices, e.g. penile length, provide a proxy for fetal androgen exposure We find that scrotal pigmentation is inversely associated with inner ear function We find that penile length is inversely associated with inner ear function These findings are reported for the first time in a sample of human infants ABSTRACT Sex differences in inner-ear function are detectable in infants, notably through the measurement of otoacoustic emissions (OAEs). Prevailing theories posit that prenatal exposure to high levels of androgens in boys may weaken OAEs, and that this phenomenon may predominantly affect the right ear/left hemisphere (Geschwind-Galaburda (GG) hypothesis). Yet, actual tests of these models have been difficult to implement in humans. Here we examined the relationship between markers of fetal androgen exposure collected at birth (anogenital distances (AGD); penile length/width, areolar/scrotal/vulvar pigmentation) and at 6 months of age (2 nd to 4 th digit ratio (2D:4D)) with two types of OAEs, click-evoked OAEs (CEOAEs) and distortionproduct OAEs (DPOAEs) (n=49; 25 boys; 24 girls). We found that, in boys, scrotal pigmentation was inversely associated with the amplitude and reproducibility of CEOAEs in the right ear at 4 kHz, with trends also present in the same ear for mean CEOAE amplitude and CEOAE amplitude at 2 kHz. Penile length was inversely associated with the mean amplitude of DPOAEs in both the right and left ears, as well as with DPOAE amplitude in the right ear at 2 kHz and the reproducibility of CEOAEs in the left ear at 2.8 kHz. Finally, AGD-scrotum in boys was positively associated in boys with the amplitude of DPOAEs in the left ear at 2.8 kHz. Unexpectedly, there were no sex differences in the amplitude or reproducibility of OAEs, nor, in girls, any associations between androgenic markers and auditory function. Nonetheless, these findings, reported for
Hearing Research, 2012
Brief tones of 1.0 and 8.0 kHz were used to evoke auditory brainstem responses (ABRs), and the differences between the wave-V latencies for those two frequencies were used as a proxy for cochlear length. The tone bursts (8 ms in duration including 2-ms rise/fall times, and 82 dB in level) were, or were not, accompanied by a continuous, moderately intense noise band, highpass filtered immediately above the tone. The proxy values for length were compared with various measures of otoacoustic emissions (OAEs) obtained from the same ears. All the correlations were low, suggesting that cochlear length, as measured by this proxy at least, is not strongly related to the various group and individual differences that exist in OAEs. Female latencies did not differ across the menstrual cycle, and the proxy length measure exhibited no sex difference (either for menses females vs. males or midluteal females vs. males) when the highpass noises were used. However, when the subjects were partitioned into Whites and Non-Whites, a substantial sex difference in cochlear length did emerge for the White group, although the correlations with OAEs remained low. Head size was not highly correlated with any of the ABR measures.
Frontiers in Aging Neuroscience
Fischer 344 (F344) rats represent a strain that is frequently used as a model for fast aging. In this study, we systematically compare the hearing function during aging in male and female F344 rats, by recording auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs). In addition to this, the functional parameters are correlated with the cochlear histology. The parameters of the hearing function were not different in the young (3-month-old) male and female F344 rats; the gender differences occurred only in adult and aged animals. In 8-24-month-old males, the ABR thresholds were higher and the ABR amplitudes were smaller than those measured in females of the same age. There were no gender differences in the neural adaptation tested by recording ABRs, elicited by a series of clicks with varying inter-click interval (ICI). Amplitudes of DPOAEs in both the males and females decreased with age, but in the males, the decrease of DPOAE amplitudes was faster. In males older than 20 months, the DPOAEs were practically absent, whereas in 20-24-month-old females, the DPOAEs were still measurable. There were no gender differences in the number of surviving outer hair cells (OHC) and the number of inner hair cell ribbon synapses in aged animals. The main difference was found in the stria vascularis (SV). Whereas the SV was well preserved in females up to the age of 24 months, in most of the age-matched males the SV was evidently deteriorated. The results demonstrate more pronounced age-related changes in the cochlear morphology, hearing thresholds, ABR amplitudes and DPOAE amplitudes in F344 males compared with females.
Early Fetal Development of the Human Cochlea
The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 2011
The cochlear scalas are differentiated from a single tube with a lining by the tall epithelium, that is, the cochlear duct. However, we have no information about the mechanism involved in the formation of the scalas. We evaluated histological sections taken from 20 fetuses: eight each at 8-9 weeks [early stage; 28-45 mm crown-rump length (CRL)] and 11-12 weeks (middle stage; 52-74 mm CRL), and four at 14-15 weeks (late stage; 90-110 mm CRL) of gestation. In four of eight early-stage and in all eight middle-stage specimens, we observed irregular perilymphatic spaces and their fusion; these spaces tended to be larger in the future scala tympani than in the future scala vestibuli. The cochlear duct epithelium was positive for cytokeratin 19 in contrast to the other parts of the cochlea. The tectorial membrane appeared in two of eight middle-stage and all four late-stage specimens. After 16 weeks, mesothelial lining of the scala may follow the development of aquaporin-positive thin blood vessels along the scala wall. Notably, gap formation of the cochlear duct epithelium at a site facing the scala tympani consistently occurred before the development of S100 protein-negative organ of Corti. This gap is likely to correspond to a site occupied finally by Hensen's cells. All these steps likely started in the basal coil and extended to the apical side of the cochlea. These findings suggest that leakage through the epithelial gap of endolymph, with a high concentration of potassium ions, causes mesenchymal cell death, leading to the coalescence of vacuoles containing low potassium perilymph.
Differences in otoacoustic emissions in infants and adults with normal hearing
HVM Bioflux, 2015
Introduction There has been an increasing interest in studying OAE in order to understand and investigate the cochlear function both in adults and infants, since the first description of OAE by Kemp in 1978. There still is no complete description of the most basic aspects of audition although studies of ear development were performed even before 1970 (Abdala 2000). It is believed that the study of OAE in human beings can serve as good criterion to investigate the physiological events of cochlear maturation, because OAE provide a glimpse into the human cochlea during the earliest segments of perinatal and postnatal life. The maturational processes underlying the acoustical and mechanical functioning of the human ear and the detectable functional differences in OAE responses represent a challenging and interesting scientific problem. There is evidence that OAE (TEOAE or/and DPOAE) differ in newborn compared to older children and adults with normal hearing (Norton et al 1990; Kok et al...
Sex differences in hearing: Probing the role of estrogen signaling
Journal of the Acoustical Society of America, 2019
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.