Endocochlear Potential Measures, Local Drug Application, and Perilymph Sampling in the Mouse Inner Ear

Abstract

Functionally and anatomically, the laboratory mouse inner ear is comparable to other mammals, except that it is considerably smaller and operates over a higher acoustic frequency range. Other than miniaturization of methods that might be applied to the inner ears of guinea pigs, gerbils, or chinchillas, the major difference lies in fewer points of access, due both to small number of cochlear turns $\left(2\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$4$}\right.\right)$ and reduced access to cochlear scalae in any single turn. These features do not particularly complicate auditory brainstem, compound action potential, or distortion product emission recording. Due to the close proximity to generators, these responses can be quite large in mice. Instead, they present challenges for endocochlear potential (EP) measurement and for manipulations and measurements of inner ear fluids. Without appropriate modifications, considerable technical challenges and potential pitfalls can render such measurements uninterpretable in mice. This chapter outlines experimental techniques for targeting inner ear fluid manipulations and fluid measures in mice. We specifically consider methods for EP measurement, perilymph sampling, and introduction of chemical agents into the middle or inner ear.