Update zur Physiologie und Pathophysiologie des Innenohrs

Abstract

Hearing impairment is the most common form of human sensory deficit. The most frequent form, sensorineural hearing loss (SNHL), which accounts for approximately 70% of cases, encompasses various pathologies in both the inner ear and the auditory nerve. The individual hearing impairment and its outcome following aiding with hearing devices critically depend on the underlying disorder. Here recent progress in our understanding of the cellular mechanisms of SNHL in genetically engineered mouse models is reviewed. First, insights gained from models for specific defects in cochlear sound amplification and ion homeostasis are discussed followed by a focus on disorders of the inner hair cell synapses (auditory synaptopathy) and the auditory nerve (auditory neuropathy). Both nosological entities have also attracted substantial clinical interest in recent years and share an impaired temporal processing of auditory stimuli. This results in poor speech recognition, often out of proportion to the pure tone threshold. Hearing loss can range from mild variants with exclusive deficits of temporal processing to complete deafness. At least initially, signs of normal outer hair cell function such as evoked otoacoustic emissions can be found. In summary, well-characterized animal models allow us to refine our pathophysiological understanding of SNHL and offer invaluable help in defining toolboxes for investigating the mechanism(s) underlying the SNHL of affected individuals. Together, this will contribute to custom-tailored diagnostics and rehabilitation of SNHL patients.

Association between Ocular Pseudoexfoliation and Sensorineural Hearing Loss

“…Hearing threshold of 21 dB or more in any one ear is considered as hearing impairment in that ear [6]. Sensorineural hearing loss (SNHL) is the most common form of human sensory deficit and accounts for approximately 70% of cases while encompassing various pathologies in both the inner ear and the auditory nerve [7]. …”

Auditorische Synaptopathie/Neuropathie

“…Als mögliche Ursachen der AS/AN kommen erworbene oder genetisch bedingte Störungen der Reizverarbeitung an den IHC, der Erregungsübertragung an den Bändersynapsen der IHC oder der neuronalen Verarbeitung im Bereich der Spiralganglienzellen und Axone des Hörnervs in Betracht [13,15,26] …”

“…Neuropathien Mischformen entstehen, die zu progredienten Haarzellverlusten führen und damit den Verlust der OAE erklären[15]. Auch aus Tiermodellen konnten wertvolle Erkenntnisse zur Pathophysiologie erworbener und genetisch bedingter Formen der AS/AN gewonnen werden, die selektive Störungen an den IHC, den Bändersynapsen und der neuralen Kodierung und Weiterleitung zeigen und in ihrer phänotypischen Ausprägung den menschlichen Verlaufsformen der AS/AN gleichen[9,15,26].Diedifferenzierte Diagnose der AS/AN erfolgt mehrstufig und orientiert sich am Alter und dem individuellen Entwicklungsstand des Patienten (. Tab.…”

Molecular biology of hearing

“…Auditory brainstem potentials can be evoked in the DFNB9 mouse model, so that cochlear implantation is indicated in DFNB9 [103], [104]. Both in the Ca V 1.3 knockout and in the otoferlin knockout, the result is almost complete blockage of synaptic transmission with severe hearing impairment, and a pattern of auditory neuropathy or synaptopathy [105]. There are also acquired auditory synaptopathies, such as in hyperbilirubin anaemia and hypoxia in premature infants [105], [106].…”

“…Both in the Ca V 1.3 knockout and in the otoferlin knockout, the result is almost complete blockage of synaptic transmission with severe hearing impairment, and a pattern of auditory neuropathy or synaptopathy [105]. There are also acquired auditory synaptopathies, such as in hyperbilirubin anaemia and hypoxia in premature infants [105], [106]. Selective damage to the inner hair cells can be triggered by platinum-containing chemotherapeutic agents [107] and by noise trauma [108].…”