Presence of aromatase and estrogen receptor alpha in the inner ear of zebra finches.
Noirot, Isabelle ; ; Cornil, Charlotte et al
in Hearing Research (2009)
Sex differences in song behavior and in the neural system controlling song in songbirds are well documented but relatively little is known about sex differences in hearing. We recently demonstrated the ... [more ▼]
Sex differences in song behavior and in the neural system controlling song in songbirds are well documented but relatively little is known about sex differences in hearing. We recently demonstrated the existence of sex differences in auditory brainstem responses in a songbird species, the zebra finch (Taeniopygia guttata). Many sex differences are regulated by sex steroid hormone action either during ontogeny or in adulthood. As a first step to test the possible implication of sex steroids in the control of sex differences in the zebra finch auditory system, we evaluated via immunocytochemistry whether estrogens are produced and act in the zebra finch inner ear. Specifically we examined the distribution of aromatase, the enzyme converting testosterone into an estrogen, and of estrogen receptors of the alpha subtype (ERalpha) in adult zebra finch inner ears. The anatomy of the basilar papillae was visualized by fluorescein-phalloidin, which delineated the actin structure of hair cells and supporting cells at their apical surface. Whole mount preparations of basilar papillae stained by immunocytochemistry revealed in both males and females an abundant aromatase distribution in the cytoplasm of hair cells, while ERalpha was identified in the nuclei of hair cells and of underlying supporting cells. Double labeled preparations confirmed the extensive co-localization of aromatase and ERalpha in the vast majority of the hair cells. These results are consistent with studies on non-avian species, suggesting a role for estrogens in auditory function. These findings are also consistent with the notion that estrogens may contribute to a sex difference in hearing. To our knowledge, this is the first demonstration of the presence of aromatase and of the co-localization of aromatase and ERalpha in the sensory epithelium of the inner ear in any animal model. [less ▲]Detailed reference viewed: 83 (11 ULg)
Strategies to Regenerate Hair Cells: Identification of Progenitors and Critical Genes
Breuskin, Ingrid ; Bodson, Morgan ; Thelen, Nicolas et al
in Hearing Research (2008), 236(1-2), 1-10
Deafness commonly results from a lesion of the sensory cells and/or of the neurons of the auditory part of the inner ear. There are currently no treatments designed to halt or reverse the progression of ... [more ▼]
Deafness commonly results from a lesion of the sensory cells and/or of the neurons of the auditory part of the inner ear. There are currently no treatments designed to halt or reverse the progression of hearing loss. A key goal in developing therapy for sensorineural deafness is the identification of strategies to replace lost hair cells. In amphibians and birds, a spontaneous post-injury regeneration of all inner ear sensory hair cells occurs. In contrast, in the mammalian cochlea, hair cells are only produced during embryogenesis. Many studies have been carried out in order to demonstrate the persistence of endogenous progenitors. The present review is first focused on the occurrence of spontaneous supernumerary hair cells and on nestin positive precursors found in the organ of Corti. A second approach to regenerating hair cells would be to find genes essential for their differentiation. This review will also focus on critical genes for embryonic hair cell formation such as the cell cycle related proteins, the Atoh1 gene and the Notch signaling pathway. Understanding mechanisms that underlie hair cell production is an essential prerequisite to defining therapeutic strategies to regenerate hair cells in the mature inner ear. [less ▲]Detailed reference viewed: 95 (32 ULg)
Effects of systemic versus local gentamicin on the inner ear in the Atlantic cod, Gadus morhua (L.), relevance for fish hearing investigations.
Faucher, Karine ; ; et al
in Hearing Research (2008), 240(1-2), 12-21
Fish models are increasingly being used for hearing research investigations. Aminoglycoside antibiotics that are used for damaging the inner ear hair cells can have systemic side effects leading to death ... [more ▼]
Fish models are increasingly being used for hearing research investigations. Aminoglycoside antibiotics that are used for damaging the inner ear hair cells can have systemic side effects leading to death of study animals. This study aimed to compare two methods: (i) systemic (intravenous) and (ii) local (intrasaccular) gentamicin administration for induction of inner ear hair cell damage in the Atlantic cod, Gadus morhua (L.). Hair cell damage was assessed using scanning electron microscopy; hair cell density, prevalence of immature hair cells and kinocilia length were measured. Gentamicin-treated fish were compared with control and sham fish. Intravenous gentamicin led to dose-dependent mortality caused by nephrotoxicity. The only visible effect after treatment was more immature hair cells and shorter kinocilia, the effect on hair cell density was equivocal. Following intrasaccular gentamicin treatment, fish mortality was negligible, and hair cells were damaged regardless of dose. Here, we observed decreased hair cell density, high prevalence of immature hair cells, and significantly shortened kinocilia. Conclusion: intrasaccular injection is preferable to intravenous injection of gentamicin for the study of ototoxicity in the Atlantic cod. [less ▲]Detailed reference viewed: 34 (3 ULg)
Identification of factors that maintain mammalian outer hair cells in adult organ of Corti explants
Malgrange, Brigitte ; ; et al
in Hearing Research (2002), 170(1-2), 48-58
Both outer hair cells (OHCs) and inner hair cells (IHCs) survive and mature in 3 days old rat organ of Corti explants cultured for I month in a minimal essential medium. In contrast. under the same ... [more ▼]
Both outer hair cells (OHCs) and inner hair cells (IHCs) survive and mature in 3 days old rat organ of Corti explants cultured for I month in a minimal essential medium. In contrast. under the same culture conditions, only IHCs survive in explants from adult guinea pig organ of Corti while many of the OHCs are lost within the first 48 It. Hair cell Count,, show OHCs loss to be greater in the lower portion (i.e. middle turn) of the cochlea than Lit the apex. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) indicates that there is DNA damage in adult OHCs, within 8 h of explantation. Treatment of the adult organ of Corti explants with either actinomycin D (10(-7) M) or cycloheximide (10(-6) M) prevents most OHC losses . According to these results apoptosis may be the mechanism of OHC loss in adult organ of Corti explants, Stable membrane potentials recorded from the OHCs in both uncultured and actinomycin D-treated organ of Corti explants cultured for 72 h demonstrate the functional integrity of these hair cells. OHC losses in the adult guinea pig, organ of Corti cultures can also be prevented by treatment with several of the growth factors tested. i.e. acidic fibroblast growth factor (aFGF), insulin-like growth factor-1 (IGF-1), epidermal growth factor (EGF), transforming growth factor-beta1 (TGF-beta1). and glial cell-derived neurotrophic factor (GDNF). The results of this study suggest that growth factor therapy may be applicable to the treatment of some hearing disorders. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]Detailed reference viewed: 75 (6 ULg)
Peripheral and central target-derived trophic factor(s) effects on auditory neurons.
Lefèbvre, Philippe ; ; et al
in Hearing Research (1992), 58(2), 185-92
In the developing inner ear, a naturally occurring programmed cell death of cochleovestibular ganglion (CVG) neurons as well as peripheral and central target-derived trophic effects on survival of ... [more ▼]
In the developing inner ear, a naturally occurring programmed cell death of cochleovestibular ganglion (CVG) neurons as well as peripheral and central target-derived trophic effects on survival of embryonic CVG neurons are known. To further analyze these target derived trophic interactions, spiral ganglion explants obtained from 5 day postpartum (P5) rat pups were cultured with an intact organ of Corti and in the absence of Corti's organ. Both neuronal survival and neurite extension were influenced by the presence of this peripheral target tissue. Local destruction of Corti's organ caused both neuritic retraction and neuronal cell death to occur in a corresponding portion of the spiral ganglion. This peripheral target-derived neurotrophic effect may be mediated by a diffusible factor(s) since organ of Corti conditioned medium also had a neurotrophic effect on the survival of auditory neurons in cell cultures of dissociated spiral ganglia from P5 rat pups. A component of central target tissue, i.e. astrocytes, was also shown to release a diffusible factor(s) that supported the survival of dissociated P5 rat spiral ganglion neurons. The neurotrophic effects on the in vitro survival of spiral ganglion neurons by both of these conditioned medium factors were concentration dependent. [less ▲]Detailed reference viewed: 11 (1 ULg)
Potassium-Induced Release of an Endogenous Toxic Activity for Outer Hair Cells and Auditory Neurons in the Cochlea: A New Pathophysiological Mechanism in Meniere's Disease?
Lefebvre, Philippe ; ; et al
in Hearing Research (1990), 47(1-2), 83-93
In Meniere's disease, the increase of extracellular potassium concentration in the perilymph is thought to play a key role in determining the progressive loss of cochlear hair cells. In this paper, we ... [more ▼]
In Meniere's disease, the increase of extracellular potassium concentration in the perilymph is thought to play a key role in determining the progressive loss of cochlear hair cells. In this paper, we describe a serum-free culture preparation of hair cells from 5 day-old rat and report the release by the cochlea, in response to an increase of extracellular potassium concentration, of a cytotoxic activity active on hair cells and auditory neurons. The toxic activity is associated with low molecular weight (less than 10,000 Dalton) molecule(s) as revealed by ultrafiltration. Morphological studies performed on the organ of Corti incubated during 24 h in the presence of the cochlea-derived toxic activity (CTA), show that this factor is toxic for hair cells and not for supporting or surrounding cells. The release of CTA occurs both in the spiral ganglion and in the organ of Corti. We suggest that this cochlea-derived toxic activity may play an important role in the pathophysiology of the hearing loss that occurs during the progression of Meniere's disease. [less ▲]Detailed reference viewed: 16 (0 ULg)