Schmitt_2019_Neurotoxicol.Teratol_73_67

Organophosphates insecticides (OPs) are common surface water contaminants in both urban and agricultural landscapes. Neurobehavioral effects on larval fish are known to occur at concentrations higher than those reported in the environment. The aim of this study was to perform a comparative analysis of neurobehavioral, molecular, and biochemical responses of four OPs (diazinon, dichlorvos, malathion, methyl-parathion) via the following endpoint measurements: distance traveled, velocity, gene expression (AChE, c-Fos, LINGO-1B, GRIN-1B), enzymatic acetylcholinesterase (AChE) activity, and carboxylesterase (CES) activity. OP exposures (5 hpf - 120 dpf) on embryo-larval zebrafish (Danio rerio) were assessed using a larval zebrafish behavior assay at concentrations: 0.01, 0.1, 10, and 100mug/L. Individual OPs had varying degrees of neurotoxicity. Significant hypoactivity was observed in the 100mug/L treatments for diazinon and malathion (p<0.05) as compared to the controls. Diazinon-exposed larvae exhibited a 26% locomotor decrease, and hypoactivity was observed in malathion-exposed larvae at a reduction of 22% and 29% for distance traveled and velocity, respectively. Gene regulation and enzymatic activity changes were measured for both 0.1 and 100mug/L exposures across OP treatments. Increased CES activity was observed for the 0.1mug/L treatments of diazinon and methyl-parathion as well as the 100mug/L treatment of dichlorvos; meanwhile, decreased CES activity was observed for 100mug/L treatments of diazinon and malathion. Relative enzymatic activity of AChE was inhibited as compared to the control for the 0.1mug/L diazinon. No other treatment group exhibited a significant effect on biochemical AChE activity; however, AChE upregulation was observed in the 0.1mug/L exposure for diazinon, dichlorvos, and malathion. Methyl-parathion was observed to downregulate c-Fos at 0.1mug/L exposure. Malathion upregulated LINGO-1B at 100mug/L, a gene associated with neuronal regeneration; meanwhile, downregulation of LINGO-1B was observed for 0.1mug/L exposure of methyl-parathion. Additional downregulation was observed for GRIN-1B in the 100mug/L diazinon, 100mug/L dichlorvos, and 0.1mug/L methyl-parathion treatments. Exposure of ZF embryos to independent concentrations of 100mug/L concentrations of diazinon and malathion resulted in hypoactivity and decreased CES activity at 5 dfp. No changes in swimming behavior were observed for either the 0.1mug/L or 100mug/L dichlorvos or methyl-parathion treatments. Observations from this study indicate that AChE inhibition may not be the most sensitive biomarker of OP pesticide exposure in zebrafish. Rather, the enzyme CES demonstrated higher sensitivity as a biomarker of OP toxicity.