Microslicing of the resin-embedded cochlea in comparison with the surface preparation technique for analysis of hair cell number and morphology.

The surface preparation technique for hair cell counting is frequently used for the analysis of cochlear pathology in relation to hearing impairment. To overcome problems encountered with standard surface preparation methods, a new combination of resin embedding and microslicing has been applied to the mammalian cochlea, to permit hair cell counting to be followed by electron microscopic analysis. Partial removal of the cochlear shell is followed by resin infiltration under vacuum prior to polymerization. The cochlea is then subdivided into hemicoils using a mounted annular diamond blade. Embedding before microslicing ensures that both apical and basal regions of the cochlea are preserved equally well with an evenly distributed and therefore predictable 10% hair cell loss. By comparison, the standard surface preparation method often produces distortion of remaining organ of Corti and unpredictable losses of hair cells, for example, up to 17%. The damage tends to be greatest towards the base of the cochlea, an area which shows particular susceptibility to ototoxic agents such as the aminoglycoside antibiotics. Thus, for assessment of pathology caused by ototoxic agents, this method has considerable advantages over the surface preparation technique.