Direct exposure to tricaine methanesulfonate (MS-222) alters zebrafish visual response properties.

Tricaine methanesulfonate (MS-222) is a commonly used amphibian and fish anesthetic that blocks voltage-gated sodium channels. There are documented deleterious effects of MS-222 on visual response properties in newts, frogs and humans. Yet, the impact of MS-222 on the amplitudes and kinetics of visual responses in the zebrafish (Danio rerio) retina remains unresolved. Here, we use ex vivo electroretinogram (ERG) recordings from zebrafish retinae to investigate the effects of brief exposure and prolonged exposure to MS-222 on photoreceptor and bipolar cell response properties. Zebrafish were anesthetized in either an ice-cooling bath or MS-222 until surgical-grade anesthesia was achieved (30 seconds - 2 minutes), before isolating the retinae for ex vivo recordings. This brief exposure to MS-222 did not significantly alter response amplitudes or kinetics, however, synaptic transfer analysis suggested a non-significant trend toward reduced retinal gain. Prolonged bath application of MS-222 to isolated retinae altered ERG a-wave amplitudes, b-wave recovery dynamics, and response latencies. Recovery from bath application of MS-222 was also hindered, as we observed small a-wave responses even after a 30-min washout recovery process, although response kinetics were observed to return to similar values as control during recovery. These findings demonstrate that prolonged direct MS-222 exposure alters retinal function in zebrafish, and suggests that anesthesia should be considered as an experimental variable in zebrafish visual physiology studies where prolonged anesthetic exposure may confound visual response measurements.