Morell, M., Lenoir, M., Puel, J., Jauniaux, T., Dabin, W., Ferreira, M., Maestre, I., Degollada, E., Cazevieille, C., Fortuño, J., André, M. Scanning and Transmission Electron Microscopy Imaging of Odontocete Cochlea Proceedings of the 34th annual midwinter research meeting of the Association for Research in Otolaryngology, Baltimore, Maryland, USA, p.202-203, Feb 2011 Resum: The morphological study of the Odontocete organ of Corti as well as possible alterations associated to sound exposure represent a key conservation issue to assess the effects of acoustic pollution on marine ecosystems. In addition, since odontocetes produce species-specific acoustic signals at various frequency ranges, morphological differences in the cochlea may be expected among species. Through the collaboration with stranding networks and rehabilitation centres from several European countries that followed an ear extraction and fixation protocol (defined at the Necropsy Workshop 2009 in Liège, Belgium), 117 ears from 13 species of Odontocetes that stranded in the Mediterranean Sea, North Atlantic and North Sea were processed. Due to technical and experimental constraints, all the cochlea were chemically fixed post-mortem, at least 6 hours after death. Here, we present scanning and transmission electron microscopy images of several cochlea structures: e.g. inner (IHC) and outer hair cell (OHC) stereociliary bundles, supporting cells, spiral ganglion neurons and OHC stereocilia imprints in the undersurface of the tectorial membrane of common dolphin (Delphinus delphis), harbour porpoise (Phocoena phocoena), striped dolphin (Stenella coeruleoalba) and bottlenose whale (Hyperoodon ampullatus). By contrast with the rapid decomposition process of the sensory epithelium after death, spiral ganglion neurons and tectorial membrane appeared to be more resistant to postmortem autolysis. Interestingly, the tectorial membrane structure still remains in acceptable condition for analysis when the cochlea was fixed more than 20h post-mortem. The analysis of the stereocilia imprints on the tectorial membrane is allowing gaining insights in odontocete hair cell stereocilia organization and detecting possible ultrastructural alterations. Projecte: eCREM, Effects and Control of Anthropogenic Noise in Marine Ecosystems