Exposure to aflatoxin B₁ interferes with locomotion and neural development in zebrafish embryos and larvae

Aflatoxin B₁ (AFB₁) is the major mycotoxin that contaminates aquafeeds and regarded as a causative agent in illnesses and the mortality of aquacultural species. However, the effects of AFB₁ on developing fish and associated toxic mechanism are still unknown. This study examines the behavioral changes, neuronal morphology and gene expression in zebrafish embryos and larvae upon exposure to aflatoxin solutions. Treatment of 6 h post fertilization (hpf) embryos with AFB₁ at 15-75 ng/mL significantly changed the swimming patterns of seven days post-fertilization (dpf) zebrafish larvae. Larvae in the 15 ng/mL group demonstrated a hypolocomotor activity in free swimming, but hyperlocomotion was observed in the larvae exposed to 30-75 ng/mL AFB₁. AFB₁ at 75 ng/mL also significantly reduced the startle response of 7 dpf larvae after tapping stimulus. Exposure to AFB₁ resulted in an aberrant morphology of trigeminal ganglion and hindbrain neurons in transgenic embryos (HuC:eGFP); this finding was supported by acetylated alpha-tubulin staining in wild-type fish. Additionally, AFB₁ altered the levels of neurotoxic markers, including gfap and huC. The transcriptomic profile of AFB₁-treated embryos revealed several differentially expressed genes that are related to neuroactivity and neurogenesis. PCR analysis verified that AFB₁ significantly down-regulated the expression of ngfa and atp1b1b genes and increased that of prtga gene. The results herein indicate the toxicological impacts of AFB₁ on the behaviors and neurodevelopment of fish in the early embryonic stage. Disruption of neural formation and synapse dysfunction may be responsible for the behavioral alteration.