Characterization of the Sheep Round Window Membrane
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JARO (2020) DOI: 10.1007/s10162-020-00778-9 D 2020 Association for Research in Otolaryngology
Research Article
Journal of the Association for Research in Otolaryngology
Characterization of the Sheep Round Window Membrane S. HAN,1,2 H. SUZUKI-KERR,1,2 M. SUWANTIKA,1,2 R.S. TELANG,1,2 D. A. GERNEKE,3 P. V. ANEKAL,4 P. BIRD,2,5,6 S. M. VLAJKOVIC,1,2,7 AND P. R. THORNE1,2,7,8 1
Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand Eisdell Moore Centre, University of Auckland, Auckland, New Zealand
2 3
Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
4
Biomedical Imaging Research Unit (BIRU), School of Medical Sciences, University of Auckland, Auckland, New Zealand Department of Surgery, University of Otago, Dunedin, New Zealand
5 6
Department of Otolaryngology, Head and Neck Surgery, Christchurch Hospital, Christchurch, New Zealand Brain Research New Zealand (BRNZ), University of Auckland, Auckland, New Zealand
7 8
Department of Audiology, School of Population Health, University of Auckland, Private Bag 92014, Auckland, 1142, New Zealand Received: 10 August 2020; Accepted: 19 October 2020
ABSTRACT Intratympanic injection is a clinically used approach to locally deliver therapeutic molecules to the inner ear. Drug diffusion, at least in part, is presumed to occur through the round window membrane (RWM), one of the two openings to the inner ear. Previous studies in human temporal bones have identified a three-layered structure of the RWM with a thickness of 70–100 μm. This is considerably thicker than the RWM in rodents, which are mostly used to model RWM permeability and assess drug uptake. The sheep has been suggested as a large animal model for inner ear research given the similarities in structure and frequency range for hearing. Here, we report the structure of the sheep RWM. The RWM is anchored within the round window niche (average vertical diameter of 2.1 ± 0.3 mm and horizontal diameter of 2.3 ± 0.4 mm) and has a curvature that leans towards the scala tympani. The centre of the RWM is the thinnest (55–71 μm), with increasing thickness towards the edges (G 171 μm), where the RWM forms tight attachments to the surrounding bony niche. The S. Han and H. Suzuki-Kerr shared first authorship. Correspondence to: P. R. Thorne & Department of Audiology, School of Population Health & University of Auckland & Private Bag 92014, Auckland, 1142, New Zealand. email: [email protected]
layered RWM structure, including an outer epithelial layer, middle connective tissue and inner epithelial layer, was identified with cellular features such as wavy fibre bundles, melanocytes and blood vessels. An attached “meshwork structure” which extends over the cochlear aqueduct was seen, as in humans. The striking anatomical similarities between sheep and human RWM suggest that sheep may be evaluated as a more appropriate system to predict RWM permeability and drug delivery in humans than rodent models. Keywords: temporal bone, cochlea, sheep, r
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