Ototoxin-induced cellular damage in neuromasts disrupts lateral line function in larval zebrafish

The ototoxicity of a number of marketed drugs is well documented, and there is an absence of convenient techniques to identify and eliminate this unwanted effect at a pre-clinical stage. We have assessed the validity of the larval zebrafish, or more specifically its lateral line neuromast hair cells, as a microplate-scale in vivo surrogate model of mammalian inner ear hair cell responses to ototoxin exposure. Here we describe an investigation of the pathological and functional consequences of hair cell loss in lateral line neuromasts of larval zebrafish after exposure to a range of well known human and non-human mammalian ototoxins. Using a previously described histological assay, we show that hair cell damage occurs in a concentration-dependent fashion following exposure to representatives from a range of drug classes, including the aminoglycoside antibiotics, salicylates and platinum-based chemotherapeutics, as well as a heavy metal. Furthermore, we detail the optimisation of a semi-automated method to analyse the stereotypical startle response in larval zebrafish, and use this to assess the impact of hair cell damage on hearing function in these animals. Functional assessment revealed robust and significant attenuation of the innate startle, rheotactic and avoidance responses of 5 day old zebrafish larvae after treatment with a number of compounds previously shown to induce hair cell damage and loss. Interestingly, a startle reflex (albeit reduced) was still present even after the apparent complete loss of lateral line hair cell fluorescence, suggesting some involvement of the inner ear as well as the lateral line neuromast hair cells in this reflex response. Collectively, these data provide evidence to support the use of the zebrafish as a pre-clinical indicator of drug-induced histological and functional ototoxicity.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (176 K)Download as PowerPoint slideHighlights► The functional effects of known ototoxins were studied in the zebrafish lateral line. ► Ototoxins cause cellular damage to hair cells present in lateral line neuromasts. ► Consequences of the damage are attenuated startle, rheotactic and avoidance reflexes. ► The zebrafish ear may contribute to initiating the noise-evoked startle reflex. ► When combined, zebrafish assays are sensitive pre-clinical detectors of ototoxicity.