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Nouvelle méthode d'exploration fonctionnelle du nerf auditif

Abstract : Background: The synchronous activation of the auditory nerve fibers (ANFs), is commonly studied through the compound action potential (CAP), or the auditory brainstem responses (ABR), to probe deafness in experimental and clinical settings. Recent studies have shown that substantial ANF loss can coexist with normal hearing threshold, and even unchanged CAP amplitude, making the detection of auditory neuropathies difficult. In this study, we took advantage of the round window neural noise (RWNN) to probe ANF loss in a physiologically-relevant model of neuropathy.Material and methods: ANF loss was induced by the application of ouabain onto the round window niche. CAP and RWNN of the gerbil's cochlea were recorded through an electrode placed onto the round window niche, 6 days after the ouabain application. Afferent synapse counts and single-unit recordings were carried-out to determine the degree and the nature of ANF loss, respectively. Results: Application of a low ouabain-dose into the gerbil RW niche elicits a specific degeneration of low spontaneous rate (SR) fibers, as shown by single-unit recordings. Simultaneous recordings (CAP/single-unit) demonstrate that low-SR fibers have a weak contribution to the CAP amplitude because of their delayed and broad first spike latency distribution. However, the RWNN amplitude decreases with the degree of synaptic loss. The RWNN method is therefore more sensitive than CAP to detect low-SR fiber loss, most probably because it reflects the sustained discharge rate of ANFs. Based on these data, we proposed a far-field method (Peri-stimulus time response-PSTR) to assess the fast, slow, and sustain vesicular release at the first auditory synapse.Conclusion: The round window neural noise is a faithful proxy to probe the degree and the SR-based nature of fiber loss. This method could be translated into the clinic to probe hidden hearing loss and orient the practitioner toward synaptopathy and/or neuropathy.Key words: Cochlea, auditory nerve, compound action potential, round window neural noise, single fiber recording, ouabain-induced neuropathy
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Charlène Batrel. Nouvelle méthode d'exploration fonctionnelle du nerf auditif. Médecine humaine et pathologie. Université Montpellier I, 2014. Français. ⟨NNT : 2014MON13520⟩. ⟨tel-01197159⟩

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