Système auditif

Résumé

Le système auditif est le système sensoriel du sens de l'ouïe. Il est composé de deux systèmes: le système auditif périphérique et le système auditif central. Dans le système auditif périphérique, on retrouve l’oreille externe, moyenne et interne. Le système auditif central comprend le nerf auditif jusqu’au cortex auditif. Système auditif périphérique Le long de son trajet de l'extérieur jusqu'au cerveau antérieur, l'information sonore est conservée et en même temps modifiée de diverses manières. Celle-ci change deux fois de support, passant d'abord de l'air à un liquide, puis de ce liquide à des potentiels d'action. Aperçu du système vignette|Structures de l'oreille L'oreille externe achemine les vibrations sonores vers le tympan, ce qui augmente la pression acoustique dans la gamme des fréquences moyennes. Les osselets (marteau, enclume, étrier) de l'oreille moyenne amplifient encore la pression vibratoire environ 20 fois et transmet cette énergie vers l’oreil

Source officielle

https://fr.wikipedia.org/wiki/Syst%C3%A8me_auditif

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Identification of Signaling Mechanisms Determining the Development of Large Excitatory Synapses in the Lower Auditory System

Le Xiao

In the brainstem auditory circuit of mammals and birds, excitatory synapses with extraordinarily large size have evolved, which ensure fast membrane potential signaling mediated by large, multiquantal excitatory postsynaptic currents (EPSCs). The so-called "calyx of Held" synapses are formed by the globular bushy cells (GBCs) in the ventral cochlear nucleus (VCN) onto the contralateral medial nucleus of the trapezoid body (MNTB) neurons. One the other hand, the spherical bushy cells (SBCs) in the VCN project to the lateral superior olive (LSO), where they form small bouton-like synapses. Therefore, the lower auditory brainstem circuits constitute an example of synapse-specificity, in which presynaptic neuron pools are connected through highly specific synapses to their postsynaptic partner neurons. Calyx of Held synapses are formed at postnatal day 2 - 4 in rodents in a target-cell specific manner and prior to the onset of hearing. The molecular signaling pathways which drive the formation of these synapses are unknown. Here we identify bone morphogenetic protein (BMP) signaling as an essential signaling pathway in the development of calyces of Held. Through unbiased genome-wide transcriptome analyses in rats and mice, BMPs were identified as candidates for diffusible signaling molecules which are expressed at a higher level in the MNTB (the target area of calyces of Held), as compared to the LSO. The microarray analysis was validated by quantitative PCR (qPCR) and in-situ hybridisation. A conditional knock-out (KO) of BMP-receptor 1a (BMPR1a) in the lower auditory system, in the genetic background of a conventional KO of BMP-receptor 1b (BMPR1b), was then used to address the role of BMP-receptor signaling for calyx of Held formation in vivo. Genetically knocking out BMPR1a/1b activity in the auditory brainstem led to a drastic deficit at the calyx of Held synapses both morphologically and functionally, as well as to the persistence of multiple innervation of MNTB neurons. This study therefore shows that BMP signaling drives the development of the large calyx of Held synapses. The study offers a possible mechanism for the specificity of a large excitatory synapse formation in the central nervous systems (CNS). In addition, the study shows a novel function of BMP signaling in synaptogenesis in the mammalian CNS.

EPFL2011

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During the formation of neuronal circuits, axon pathfinding decisions specify the location of synapses on the correct brain side and in correct target areas. We investigated a possible link between axon midline crossing and the subsequent development of output synapses formed by these axons. Conditional knockout of Robo3 in the auditory system forced a large commissural synapse, the calyx of Held, to be exclusively formed on the wrong, ipsilateral side. lpsilateral calyx of Held synapses showed strong transmission defects, with reduced and desynchronized transmitter release, fewer fast-releasable vesicles, and smaller and more variable presynaptic Ca2+ currents. Transmission defects were not observed in a downstream inhibitory synapse, and some defects persisted into adulthood. These results suggest that axon midline crossing conditions functional maturation of commissural synapses, thereby minimizing the impact of mislocalized synapses on information processing. This mechanism might be relevant to human disease caused by mutations in the ROBO3 gene.

Elsevier2013

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BMP signaling specifies the development of a large and fast CNS synapse

Enida Gjoni, Graham Knott, Elin Kristina Kronander, Ralf Schneggenburger, Le Xiao

excitatory synapses with multiple active zones ensure reliable and fast information transfer at specific points in neuronal circuits. However, the mechanisms that determine synapse size in CNS circuits are largely unknown. Here we use the calyx of Held synapse, a major relay in the auditory system, to identify and study signaling pathways that specify large nerve terminal size and fast synaptic transmission. Using genome-wide screening, we identified bone morphogenetic proteins (BMPs) as candidate signaling molecules in the area of calyx synapses. Conditional deletion of BMP receptors in the auditory system of mice led to aberrations of synapse morphology and function specifically at the calyx of Held, with impaired nerve terminal growth, loss of monoinnervation and less mature transmitter release properties. Thus, BMP signaling specifies large and fast-transmitting synapses in the auditory system in a process that shares homologies with, but also extends beyond, retrograde BMP signaling at Drosophila neuromuscular synapses.

Nature Publishing Group2013

Chargement

Identification of Signaling Mechanisms Determining the Development of Large Excitatory Synapses in the Lower Auditory System

Le Xiao

EPFL2011