Ultrastructural characteristics of the round window membrane during pneumococcal otitis media in rat
Yong-Joo Yoon1, Sten Hellstrom
1Department of Otorhinolaryngology, Chonbuk National University Hospital, Chonju, Korea. yjyoon@moak.chonbuk.ac.kr
Abstract:
To understand better the pathogenesis of inner ear (IE) damage caused by otitis media (OM), the round window membrane(RWM) structure was investigated in a rat model for pneumococcal otitis media (POM). The RWM of 25 rats were evaluated light and electron microscopically on 1 day, 3 days, 6 days, 10 days, and 20 days after the unilateral inoculation of type 3 pneumococcus suspension into their middle ear cavities. The thickness of the RWM increased in various stages of the pneumococcus-evoked otitis media, compared with that of the normal. The thickening was most pronounced on day 1, being about 4 to 5 times greater than that of the normal RWM. All layers of the RWM were affected by the pneumococcal infection, but the major changes were confined to the subepithelial space close to the basement membrane (BM). Together with alterations to the BM, the most distinct pathological features were characterized by an increase and hypertrophy of fibroblasts in association with abundant collagen fibers. Elastic fibers observed close to the inner mesothelial layer under a high power magnification also increased during the experiment. These results will be relevant to a better understanding of the histologic implication of RWM in stages of acute otitis media involving pneumococcus-evoked otitis media.
Insights
Pneumococcal otitis media (POM) causes significant thickening of the round window membrane (RWM) in rats, primarily due to fibroblast and collagen proliferation in the subepithelial space. These changes offer insights into inner ear damage mechanisms.
Area of Science:
- Otolaryngology
- Pathology
- Microbiology
Background:
- Otitis media (OM) is a common infection that can lead to inner ear (IE) damage.
- The round window membrane (RWM) is a critical structure separating the middle and inner ear, potentially vulnerable to OM pathogenesis.
- Understanding RWM changes during OM is crucial for elucidating IE damage mechanisms.
Purpose of the Study:
- To investigate the structural and pathological changes in the RWM during pneumococcal otitis media (POM).
- To analyze the temporal progression of RWM alterations following pneumococcal inoculation.
Main Methods:
- A rat model of POM was established using unilateral middle ear inoculation of type 3 pneumococcus.
- Round window membranes (RWMs) were examined using light and electron microscopy at multiple time points (1, 3, 6, 10, and 20 days post-inoculation).
- Histological analysis focused on RWM thickness, cellular changes, and extracellular matrix components.
Main Results:
- Significant RWM thickening was observed in POM rats compared to controls, peaking around day 1 (4-5 times normal thickness).
- Pathological changes affected all RWM layers, with major alterations in the subepithelial space near the basement membrane (BM).
- Increased and hypertrophied fibroblasts, abundant collagen fibers, and increased elastic fibers were prominent features.
Conclusions:
- Pneumococcal otitis media induces substantial structural changes in the RWM, characterized by edema and connective tissue proliferation.
- These RWM alterations, particularly fibroblast and collagen changes, are key histological implications in acute POM and may contribute to inner ear damage.
