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Van Dijk, P., Narins, P.M. & Mason, M.J. (2003) Physiological vulnerability of distortion product otoacoustic emissions from the amphibian ear. Journal of the Acoustical Society of America 114: 2044-2048.
Following our earlier discovery that distortion product otoacoustic emissions (DPOAEs) can be recorded from some frog species, including the leopard frog Rana pipiens (van Dijk et al., 2002), we sought to find out more about the nature of these emissions in frogs. In principle, DPOAEs can be elicited either "actively" from movements of living cells (such as the outer hair cells of the mammalian cochlea), or passively, due to non-linearities in the response of the inner ear to loud sounds. In this study, we demonstrated that DPOAEs in response to low-amplitude input tones (<75 dB SPL) disappeared within minutes post mortem, suggesting that an active mechanism might be involved in their generation: the nature of this is unknown. Basilar papilla DPOAEs were found to be less vulnerable than those from the amphibian papilla, suggesting that there may be important functional differences between the mechanisms of these inner ear hearing organs in frogs. By contrast, DPOAEs in response to higher amplitude tones persisted for at least three days post mortem, showing that the presence of DPOAEs in vertebrates does not necessarily imply that the inner ear is functioning normally.
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