Reevaluating the use of aminoglycoside antibiotics in behavioral studies of the lateral line

Van Trump et al. (2010) recently demonstrated that the aminoglycoside antibiotic gentamicin, previously thought to be selectively toxic to hair cells of the canal neuromasts (CN) of the fish lateral line system, is additionally toxic to hair cells of the superficial neuromasts (SN). The authors used the fluorescent vital dyes DASPEI (2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide) and FM1-43 ((n-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide) to visualize by fluorescence microscopy the survival of hair cells in the CN and SN of zebrafish (Danio rerio) and Mexican blind cave fish (Astyanax fasciatus) treated in a solution of 0.001% gentamicin sulfate for 24h. Extensive hair cell death was observed in populations of CN and SN of gentamicin-treated animals of both species compared to control animals. On the basis of this result, the authors concluded, (p. 49), “(1) That hair cells in the SNs of the lateral line can no longer be regarded as functionally resistant to gentamicin toxicity, (2) that this drug should therefore no longer be used as a pharmacological tool for selective blocking of CN, but not SN hair cells, and (3) that the conclusions of some previous studies need to be reevaluated.” Using an alternative approach to themselves reevaluate a 15-year-old assumption in the literature drawn from SEM imaging (e.g., Song et al., 1995), Van Trump et al. (2010) convincingly demonstrated that gentamicin in fact damages a high proportion of both SN and CN, similar in effect to another commonly used aminoglycoside, streptomycin (e.g., Kaus, 1987; Blaxter and Fuiman, 1989; Montgomery et al., 1997; Montgomery et al., 2003). Toward further caution in the interpretation of lateral line behavioral studies that have used aminoglycoside antibiotics to chemically ablate SN and/or CN without rigorous verification of treatment efficacy, we are inspired to share our own recent observations on limitations in the efficacy of both gentamicin and streptomycin in damaging the lateral line systems of three fish species.