Topographical and drug specific sensitivity of hair cells of the zebrafish larvae to aminoglycoside-induced toxicity

The hair cells of the lateral line system of fishes are morphologically and physiologically similar to the hair cells of the mammalian inner ear, also sharing its molecular characteristics. For this reason, it has been used as a powerful animal model to analyze in vivo ototoxicity. In this work, we examined the dose-dependent effects of two potent ototoxic aminoglycosides, neomycin and gentamicin, on the hair cells of two selected neuromasts (L1 and T1, the first of the trunk and the terminal located in the fin, respectively) of the lateral line in the ET4 transgenic zebrafish line. The hair cells of this strain selectively and constitutively display fluorescence. The fish were treated for 24 h at different doses (1, 2.5, 5, 10 and 100 μM levels) of both aminoglycosides. Immediately after treatment the morphology and the number of cells in L1 and T were analyzed under a fluorescence microscope. The results show that neomycin and gentamicin have different effects on the hair cell death at the same concentration, showing also different toxicity in L1 and T1 neuromasts. The toxicity observed in the hair cells of T1 neuromast was less than in L1 especially for the gentamicin treatment. These results demonstrate different sensitivity of hair cells of the lateral line to ototoxic drugs according to topographical localization and suggest the in vivo assay of the L1 neuromast of zebrafish larva and low doses of neomycin as an ideal model to study ototoxicity induced by aminoglycosides.