Round Window Cochlear Microphonic and Atrophy of Short and Middle Stereocilia on Outer Hair Cells in Hydropic Cochleas in Guinea Pigs
Endolymphatic hydrops of the inner ear in man is a major pathology but since the etiology is not known treatment of the disease remains obscure. Induction of endolymphatic hydrops in animals is an experimental manipulation which has been employed for the past 60 years (Portmann, 1927) with the aim of providing an animal model for the investigation of hydrops. Despite the fact that hydrops can be surgically induced (Kimura, 1967) with almost 100% success in the guinea pig, the model has, in general, failed to reveal any specific characteristics and indeed instead of providing an insight to the disease the model itself has remained poorly understood. Despite this rather disconcerting appraisal there has recently been a renewed wave of interest in the model. In the past couple of years a considerable amount of data on the histopathology of experimental hydrops has been published including outer hair cell loss (Kimura, 1967) as well as progressive loss of inner hair cells (Aran et al., 1984; Albers, et al, 1987) towards the apex which can account well for the elevation of thresholds. However the physiological basis for the most characteristic and intriguing symptom of the disease — that of fluctuant thresholds — is still at the stage of hypotheses which are discussed by us elsewhere (Horner et al., 1988). Clearly, whilst the thresholds remain fluctuant we can consider that the sensory hair cells are still present and functional to some degree at least intermittently. Indeed by employing chronically implanted guinea pigs (Horner and Cazals, 1987) it has been shown that the early stage in experimental hydrops is indeed associated with fluctuant thresholds and in particular for the lower frequencies. Whilst hair cell loss can account for sensitivity loss, fluctuant aggravation of the sensitivity loss can be more fully explained by a perturbation of the remaining hair cells. Indeed we have recently pin-pointed a specific stereocilia pathology which could represent a candidate to explain the physiological data.
KeywordsHair Cell Outer Hair Cell Harmonic Distortion Hair Cell Loss Sensitivity Loss
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