111 research outputs found
Vestibular role of KCNQ4 and KCNQ5 K+ channels revealed by mouse models
The function of sensory hair cells of the cochlea and vestibular organs depends on an influx of K+ through apical mechanosensitive ion channels and its subsequent removal over their basolateral membrane. The KCNQ4 (Kv7.4) K+ channel, which is mutated in DFNA2 human hearing loss, is expressed in the basal membrane of cochlear outer hair cells (OHCs) where it may mediate K+ efflux. Like the related K+ channel KCNQ5 (Kv7.5), KCNQ4 is also found at calyx terminals ensheathing type I vestibular hair cells where it may be localized pre- or postsynaptically. Making use of Kcnq4-/- mice lacking KCNQ4, as well as Kcnq4dn/dn and Kcnq5dn/dn mice expressing dominant negative channel mutants, we now show unambiguously that in adult mice both channels reside in postsynaptic calyx-forming neurons, but cannot be detected in the innervated hair cells. Accordingly whole-cell currents of vestibular hair cells did not differ between genotypes. Neither Kcnq4-/-, Kcnq5dn/dn nor Kcnq4-/-/Kcnq5dn/dn double mutant mice displayed circling behavior found with severe vestibular impairment. However, a milder form of vestibular dysfunction was apparent from altered vestibulo-ocular reflexes in Kcnq4-/-/Kcnq5dn/dn and Kcnq4-/- mice. The larger impact of KCNQ4 may result from its preferential expression in central zones of maculae and cristae, which are innervated by phasic neurons that are more sensitive than the tonic neurons predominantly present in the surrounding peripheral zones where KCNQ5 is found. The impact of postsynaptic KCNQ4 on vestibular function may be related to K+ removal and modulation of synaptic transmission.Fil: Spitzmaul, Guillermo Federico. Leibniz Institut Fur Molekulare Pharmakologie; Alemania. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico BahĂa Blanca. Instituto de Investigaciones BioquĂmicas BahĂa Blanca (i); ArgentinaFil: Tolosa, Leonardo. Netherlands Institute For Neuroscience; PaĂses BajosFil: Winkelman, Beerend H. J.. Netherlands Institute For Neuroscience; PaĂses BajosFil: Heidenreich, Matthias. Leibniz_Institut Fur Molekulare Pharmakologie (Fmp) ; AlemaniaFil: Frens, Maartens. Department Of Neurosciences, Erasmus; PaĂses BajosFil: Chabbert, Christian. Institut Des Neurosciences De Montpellier; FranciaFil: de Zeeuw, Chris I.. Netherlands Institute For Neuroscience; PaĂses BajosFil: Jentsch, Thomas J.. CharitĂ©-UniversitĂ€tsmedizin. Cluster of Excellence NeuroCure; Alemani
Vestibular role of KCNQ4 and KCNQ5 K+ channels revealed by mouse models
The function of sensory hair cells of the cochlea and vestibular organs depends on an influx of K+ through apical mechanosensitive ion channels and its subsequent removal over their basolateral membrane. The KCNQ4 (Kv7.4) K+ channel, which is mutated in DFNA2 human hearing loss, is expressed in the basal membrane of cochlear outer hair cells (OHCs) where it may mediate K+ efflux. Like the related K+ channel KCNQ5 (Kv7.5), KCNQ4 is also found at calyx terminals ensheathing type I vestibular hair cells where it may be localized pre- or postsynaptically. Making use of Kcnq4-/- mice lacking KCNQ4, as well as Kcnq4dn/dn and Kcnq5dn/dn mice expressing dominant negative channel mutants, we now show unambiguously that in adult mice both channels reside in postsynaptic calyx-forming neurons, but cannot be detected in the innervated hair cells. Accordingly whole-cell currents of vestibular hair cells did not differ between genotypes. Neither Kcnq4-/-, Kcnq5dn/dn nor Kcnq4-/-/Kcnq5dn/dn double mutant mice displayed circling behavior found with severe vestibular impairment. However, a milder form of vestibular dysfunction was apparent from altered vestibulo-ocular reflexes in Kcnq4-/-/Kcnq5dn/dn and Kcnq4-/- mice. The larger impact of KCNQ4 may result from its preferential expression in central zones of maculae and cristae, which are innervated by phasic neurons that are more sensitive than the tonic neurons predominantly present in the surrounding peripheral zones where KCNQ5 is found. The impact of postsynaptic KCNQ4 on vestibular function may be related to K+ removal and modulation of synaptic transmission.Fil: Spitzmaul, Guillermo Federico. Leibniz Institut Fur Molekulare Pharmakologie; Alemania. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico BahĂa Blanca. Instituto de Investigaciones BioquĂmicas BahĂa Blanca (i); ArgentinaFil: Tolosa, Leonardo. Netherlands Institute For Neuroscience; PaĂses BajosFil: Winkelman, Beerend H. J.. Netherlands Institute For Neuroscience; PaĂses BajosFil: Heidenreich, Matthias. Leibniz_Institut Fur Molekulare Pharmakologie (Fmp) ; AlemaniaFil: Frens, Maartens. Department Of Neurosciences, Erasmus; PaĂses BajosFil: Chabbert, Christian. Institut Des Neurosciences De Montpellier; FranciaFil: de Zeeuw, Chris I.. Netherlands Institute For Neuroscience; PaĂses BajosFil: Jentsch, Thomas J.. CharitĂ©-UniversitĂ€tsmedizin. Cluster of Excellence NeuroCure; Alemani
E-Biothon: an experimental platform for BioInformatics
International audienceThe E-Biothon platform is an experimental Cloud platform to help speed up and advance research in biology, health and environment. It is based on a Blue Gene/P system and a web portal that allow members of the bioinformatics community to easily launch their scientific applications. We describe in this paper the technical capacities of the platform, the different applications supported and finally a set of user experiences on the platform
Allylnitrile metabolism by CYP2E1 and other CYPs leads to distinct lethal and vestibulotoxic effects in the mouse
This study addressed the hypothesis that the vestibular or lethal toxicities of allylnitrile depend on CYP2E1-mediated bioactivation. Wild-type (129S1) and CYP2E1-null male mice were exposed to allylnitrile at doses of 0, 0.5, 0.75, or 1.0 mmol/kg (po), following exposure to drinking water with 0 or 1% acetone, which induces CYP2E1 expression. Induction of CYP2E1 activity by acetone in 129S1 mice and lack of activity in null mice was confirmed in liver microsomes. Vestibular toxicity was assessed using a behavioral test battery and illustrated by scanning electron microscopy observation of the sensory epithelia. In parallel groups, concentrations of allylnitrile and cyanide were assessed in blood after exposure to 0.75 mmol/kg of allylnitrile. Following allylnitrile exposure, mortality was lower in CYP2E1-null than in 129S1 mice, and increased after acetone pretreatment only in 129S1 mice. This increase was associated with higher blood concentrations of cyanide. In contrast, no consistent differences were recorded in vestibular toxicity between 129S1 and CYP2E1-null mice, and between animals pretreated with acetone or not. Additional experiments evaluated the effect on the toxicity of 1.0 mmol/kg allylnitrile of the nonselective P450 inhibitor, 1-aminobenzotriazole, the CYP2E1-inhibitor, diallylsulfide, and the CYP2A5 inhibitor, methoxsalen. In 129S1 mice, aminobenzotriazole decreased both mortality and vestibular toxicity, whereas diallylsulfide decreased mortality only. In CYP2E1-null mice, aminobenzotriazole and methoxsalen, but not diallylsulfide, blocked allylnitrile-induced vestibular toxicity. We conclude that CYP2E1-mediated metabolism of allylnitrile leads to cyanide release and acute mortality, probably through α-carbon hydroxylation, and hypothesize that epoxidation of the ÎČ-Îł double bond by CYP2A5 mediates vestibular toxicity
Vestibulotoxic properties of potential metabolites of allylnitrile
This study addressed the hypothesis that epoxidation of the double bond in allylnitrile mediates its vestibular toxicity, directly or after subsequent metabolism by epoxide hydrolases. The potential metabolites 3,4-epoxybutyronitrile and 3,4-dihydroxybutyronitrile were synthesized and characterized. In aqueous solutions containing sodium or potassium ions, 3,4-epoxybutyronitrile rearranged to 4-hydroxybut-2-enenitrile, and this compound was also isolated for study. Male adult Long-Evans rats were exposed to allylnitrile or 3,4-epoxybutyronitrile by bilateral transtympanic injection, and vestibular toxicity was assessed using a behavioral test battery and scanning electron microscopy (SEM) observation of the sensory epithelia. Overt vestibular toxicity was caused by 3,4-epoxybutyronitrile at 0.125 mmol/ear and by allylnitrile in some animals at 0.25 mmol/ear. Additional rats were exposed by unilateral transtympanic injection. In these studies, behavioral evidences and SEM observations demonstrated unilateral vestibular toxicity after 0.125 mmol of 3,4-epoxybutyronitrile and bilateral vestibular toxicity after 0.50 mmol of allylnitrile. However, 0.25 mmol of allylnitrile did not cause vestibular toxicity. Unilateral administration of 0.50 mmol of 3,4-dihydroxybutyronitrile or 4-hydroxybut-2-enenitrile caused no vestibular toxicity. The four compounds were also evaluated in the mouse utricle explant culture model. In 8-h exposure experiments, hair cells completely disappeared after 3,4-epoxybutyronitrile at concentrations of 325 or 450ÎŒM but not at concentrations of 150ÎŒM or lower. In contrast, no difference from controls was recorded in utricles exposed to 450ÎŒM or 1.5mM of allylnitrile, 3,4-dihydroxybutyronitrile, or 4-hydroxybut-2-enenitrile. Taken together, the present data support the hypothesis that 3,4-epoxybutyronitrile is the active metabolite of allylnitrile for vestibular toxicity
The kisspeptin-GnRH pathway in human reproductive health and disease
BACKGROUND: The discovery of kisspeptin as key central regulator of GnRH secretion has led to a new level of understanding of the neuroendocrine regulation of human reproduction. The related discovery of the kisspeptin-neurokinin B-dynorphin (KNDy) pathway in the last decade has further strengthened our understanding of the modulation of GnRH secretion by endocrine, metabolic and environmental inputs. In this review, we summarize current understanding of the physiological roles of these novel neuropeptides, and discuss the clinical relevance of these discoveries and their potential translational applications. METHODS: A systematic literature search was performed using PUBMED for all English language articles up to January 2014. In addition, the reference lists of all relevant original research articles and reviews were examined. This review focuses mainly on published human studies but also draws on relevant animal data. RESULTS: Kisspeptin is a principal regulator of the secretion of gonadotrophins, and through this key role it is critical for the onset of puberty, the regulation of sex steroid-mediated feedback and the control of adult fertility. Although there is some sexual dimorphism, both neuroanatomically and functionally, these functions are apparent in both men and women. Kisspeptin acts upstream of GnRH and, following paracrine stimulatory and inhibitory inputs from neurokinin B and dynorphin (KNDy neuropeptides), signals directly to GnRH neurones to control pulsatile GnRH release. When administered to humans in different isoforms, routes and doses, kisspeptin robustly stimulates LH secretion and LH pulse frequency. Manipulation of the KNDy system is currently the focus of translational research with the possibility of future clinical application to regulate LH pulsatility, increasing gonadal sex steroid secretion in reproductive disorders characterized by decreased LH pulsatility, including hypothalamic amenorrhoea and hypogonadotropic hypogonadism. Conversely there may be scope to reduce the activity of the KNDy system to reduce LH secretion where hypersecretion of LH adds to the phenotype, such as in polycystic ovary syndrome. CONCLUSIONS: Kisspeptin is a recently discovered neuromodulator that controls GnRH secretion mediating endocrine and metabolic inputs to the regulation of human reproduction. Manipulation of kisspeptin signalling has the potential for novel therapies in patients with pathologically low or high LH pulsatility
Pathophysiological mechanisms at the sources of the endolymphatic hydrops, and possible consequences
International audienceThe mechanisms of ion exchanges and water fluxes underlying the endolymphatic hydrops phenomenon, remain indeterminate so far. This review intends to reposition the physical environment of the endolymphatic compartment within the inner ear, as well as to recall the molecular effectors present in the membranous labyrinth and that could be at the source of the hydrops
Homéostasie glutamatergique des synapses en calice de l'appareil vestibulaire (implication de plusieurs transporteurs du glutamate de la famille des EAAT)
L'homĂ©ostasie glutamatergique dans les fentes synaptiques rĂ©gule la neurotransmission et prĂ©serve de l'excitotoxicitĂ©. Cela est particuliĂšrement important dans l'oreille interne oĂč il y a une libĂ©ration soutenue de neurotransmetteur. Pour la plupart des cellules ciliĂ©es cochlĂ©aires et vestibulaires, la clairance du glutamate est assurĂ©e par les transporteurs du glutamate EAAT1 (GLAST) exprimĂ©s par les cellules de soutien. Un tel mĂ©canisme n'est pas possible pour les cellules ciliĂ©es vestibulaires de type I car leur terminaison synaptique en calice empĂȘche tout accĂšs Ă la fente synaptique. Nous avons donc postulĂ© qu'un ou plusieurs transporteurs du glutamate devaient ĂȘtre prĂ©sents au niveau des cellules ciliĂ©es de type I ou du calice ou des deux.GrĂące Ă des enregistrements Ă©lectrophysiologiques, nous avons dĂ©montrĂ© qu'un courant anionique induit par le glutamate et bloquĂ© par le DL-TBOA est prĂ©sent dans les cellules ciliĂ©es de type I. Les techniques d'hybridation in situ et d'immunohistochimie ont rĂ©vĂ©lĂ© la prĂ©sence d'EAAT4 et EAAT5. Ces deux transporteurs du glutamate, qui pourraient ĂȘtres Ă l'origine des courants enregistrĂ©s, sont exprimĂ©s par les cellules ciliĂ©es de type I et de type II. De plus, des expĂ©riences de RT-PCR et de microscopie Ă©lectronique ont confirmĂ© ces rĂ©sultats et suggĂ©rĂ© que ces transporteurs pourraient aussi ĂȘtre exprimĂ©s postsynaptiquement par le calice. Ces travaux de thĂšse montrent qu'EAAT4 et EAAT5, considĂ©rĂ©s respectivement comme spĂ©cifiques des tissus cĂ©rĂ©belleux et rĂ©tiniens, ont une distribution plus large. Ces rĂ©sultats posent la question des rĂŽles potentiels de ces transporteurs dans l'homĂ©ostasie glutamatergique vestibulaire.Glutamate homeostasis in synaptic clefts shape neurotransmission and prevent excitotoxicity. This may be particularly important in the inner ear where there is a continually high rate of neurotransmitter release. In the case of most cochlear and vestibular hair cells, clearance involves the diffusion of glutamate to supporting cells, where it is taken up by EAAT1 (GLAST), a glial glutamate transporter. A similar mechanism is unlikely to work in vestibular type I hair cells because the presence of calyx endings separates supporting cells from the synaptic zone. Based on this arrangement, we postulated that a glutamate transporter must be present in the type I hair cell, the calyx ending, or both. Using whole-cell patch-clamp recordings, we demonstrated that a glutamate-activated anion current blocked by DL-TBOA is expressed in type I hair cells. In situ hybridization and immunohistochemistry revealed that EAAT4 and EAAT5, two glutamate transporters that could support the anion current, are expressed in both type I and type II hair cells. Furthermore, RT-PCR and immunogold investigations confirmed those results and added that although preferentially expressed presynaptically, the transporters may also be present in the postsynaptic calyx membrane. Previously thought to be exclusively expressed in the cerebellum and retina respectively, this thesis work shows that EAAT4 and EAAT5 have a wider distribution. The potential role of these transporters in the glutamatergic homeostasis of the calyx synapse is then discussed.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF
Proceedings of the GDR Vertige 2019 annual meeting devoted to endolymphatic hydrops
International audienceThe GDR Vertige is a federative research group gathering the different components of the French neuro-otology community. The annual meeting of the GDR Vertige is an opportunity for interactive exchanges between scientists, clinicians and industrialists, on basic issues related to vestibular function, as well as translational questions regarding the management of vestibular disorders. For its fifth edition, the annual meeting of the GDR Vertige, which took place in September 2019 in Marseille (France), was devoted to one of the most peculiar phenomena of neuro-otology: endolymphatic hydrops. For two days, international scientists and clinicians presented the most recent advances regarding the biophysical correlates of endolymphatic hydrops, the genetic and endocrine tableaux that favor its manifestation, new methods of clinical imaging, and current and upcoming therapeutic strategies to overcome the associated clinical manifestations. This special issue of the Journal of Vestibular Research aims at providing the proceedings of this meeting
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