Attempt at hair cell neodifferentiation in developing and adult amikacin intoxicated rat cochleae

Recent studies have shown that an attempt at auditory hair cell neodifferen tiation occurs in vivo in the rat organ of Corti after amikacin intoxicatio n during the last stages of cochlear maturation. Atypical cells, with morph ological characteristics reminiscent of very immature sensory hair cells, w ere transiently observed after outer hair cell losses. The aim of the prese nt study was to assess (i) if this attempt at hair cell neodifferentiation was related to the degree of maturity of the organ of Corti and (ii) to cha racterise morphological and molecular changes in the scarring epithelium. W e therefore investigated, using electron and confocal microscopy, morpholog ical and molecular changes in cochleae from rats treated with amikacin at t wo different periods: from post natal day (PND) 1 to PND 8, when the organ of Corti is very immature; and from PND 30 to 37, when the organ of Corti i s morphologically and functionally mature. In both groups, transient atypic al cells were observed, attesting that the attempt at hair cell neodifferen tiation is not strictly related to the immaturity of the cochlea. The resul ts also suggest that Deiters cells are involved in the appearance of atypic al cells, possibly through a transdifferentiation process. Finally, it appe ars that non-sensory epithelial cells from the outer spiral sulcus progress ively colonize the region of pre-existing outer hair cells. (C) 1998 Elsevi er Science B.V. All rights reserved.