Abstract
Zebrafish (Danio rerio) larvae are widely used to study otic functions because they possess all five typical vertebrate senses including hearing and balance. Powerful genetic tools and the transparent body of the embryo and larva also make zebrafish a unique vertebrate model to study otic development. Due to its small larval size and moisture requirement during experiments, accurately acquiring the vestibulo-ocular reflex (VOR) of zebrafish larva is challenging. In this report, a new VOR testing device has been developed for quantifying linear VOR (LVOR) in zebrafish larva, evoked by the head motion about the earth horizontal axis. The system has a newly designed larva-shaped chamber, by which live fish can be steadily held without anesthesia, and the system is more compact and easier to use than its predecessors. To demonstrate the efficacy of the system, the LVORs in wild-type (WT), dlx3b and dlx4b morphant zebrafish larvae were measured and the results showed that LVOR amplitudes were consistent with the morphological changes of otoliths induced by morpholino oligonucleotides (MO). Our study represents an important advance to obtain VOR and predict the vestibular conditions in zebrafish.
Highlights
Vestibular dysfunction, due to aging, genetic diseases, injury, or medical conditions is common today, but a direct measurement or observation of inner ear defects is not feasible
Because zebrafish larvae are a few millimeters in length and live in water, methods to evaluate the vestibular function in human or adult zebrafish are not applicable to assess the vestibular function in fish larva (Kenyon et al, 1998; Trapani and Nicolson, 2010)
Both WT and dlx4b morphant larvae had robust eye movements rotated about the A-P axis
Summary
Vestibular dysfunction, due to aging, genetic diseases, injury, or medical conditions is common today, but a direct measurement or observation of inner ear defects is not feasible. The vestibulo-ocular reflex (VOR) of the eyes, which refers to a reflex caused by tilting the patient’s head, has been conventionally used in the clinics for assessment of vestibular function. Zebrafish (Danio rerio) has been popularly used to study the inner ear, in which both auditory and vestibular end-organs are physically situated. To assess inner ear functions in zebrafish larvae is largely relied on the behavioral observation and evaluation (Mo et al, 2010; Cameron et al, 2013). The unconditioned orienting response of zebrafish larvae to the water currents is used to assess hearing function, yet the visual, vestibular, hydro-mechanical, and proprioceptive cues are all known interfering factors (Platto et al, 2014; Niihori et al, 2015)
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