Developmental exposure of zebrafish to neonicotinoid pesticides: Long-term effects on neurobehavioral function

Neonicotinoid compounds are commonly used insecticides which have become increasingly used as re-placements of older generations of insecticides, such as organophosphates. Given the established neurotoxicity of cholinergic toxicants, developmental neurotoxicity studies are needed to identify in vertebrate species the po-tential toxicity of these insecticides which act on nicotinic cholinergic receptors. Previously, developmental exposure to a neonicotinoid insecticide imidacloprid was shown to cause persisting neurobehavioral toxicity in zebrafish. The current study evaluated neurobehavioral effects of embryonic exposure to two other neonicotinoid insecticides, clothianidin (1-100 mu M) and dinotefuran (1-100 mu M) in zebrafish (5-120 h post-fertilization), concentrations below the threshold for increased lethality and overt dysmorphogenesis. Neurobehavioral tests were conducted at larval (6 days), adolescent (10 weeks) and adult (8 months) ages. Both compounds caused short-term behavioral effects on larval motility, although these effects were distinct from one another. At a lower concentration (1 mu M) clothianidin increased dark-induced locomotor stimulation the second time the lights turned off, while a higher concentration (100 mu M) reduced activity in the dark at its second presentation. By contrast, dinotefuran (10-100 mu M) caused a general decrease in locomotion. Specific longer-term neuro-behavioral toxicity after early developmental exposure was also seen. clothianidin (100 mu M) reduced locomotor activity in the novel tank in adolescence and adulthood, as well as reduced baseline activity in the tap startle test (1-100 mu M) and reduced activity early (1-10 mu M) or throughout the predator avoidance test session (100 mu M). In addition to locomotor effects, clothianidin altered the diving response in a dose-, age-and time-block-dependent manner (1 mu M, 100 mu M), causing fish to remain further away from a fast predator cue (100 mu M) relative to controls. Dinotefuran produced comparatively fewer effects, increasing the diving response in adulthood (10 mu M), but not adolescence, and suppressing initial locomotor activity in the predator avoidance test (1-10 mu M). These data indicate that neonicotinoid insecticides may carry some of the same risks for vertebrates posed by other classes of insecticides, and that these adverse behavioral consequences of early developmental exposure are evident well into adulthood.

Automated summary

This study evaluated the neurobehavioral effects of two neonicotinoid insecticides on zebrafish during embryonic exposure. The results showed that low concentrations of these insecticides affected the locomotion of larvae, while higher concentrations affected the activity and predator avoidance ability of adult fish. These effects were persistent and continued into adulthood.