LAUSR

MS-222 has been widely used as an anaesthetic in fish, thus, raising the need to infer about its toxicological safety during development. In this study, MS-222 toxicity in zebrafish embryos was evaluated after a 20-min exposure at different stages of development. Embryos exposed during the 256-cell stage displayed an increase in mortality, associated with defective early developmental pathways. Following exposure during the 50% epiboly stage, an increase in mortality and abnormal cartilage development, as well as changes in noggin expression were observed. Locomotor deficits were detected and associated with changes in early signalling pathways through the involvement of noggin. When exposed at the 1-4 somites stage, zebrafish were phenotypically normal, although presenting changes in the expression pattern of developmental genes. These findings indicate a teratogenic impact, independent of sodium channels that should be taken into consideration when MS-222 toxicity is discussed.