A peripheral irritant motor response (PIMR) assay to identify chemical-induced locomotor deficits in larval zebrafish (Danio rerio)

Abstract

Zebrafish (Danio rerio) behavioral assays provide valuable insights into the effects of environmental chemicals on the developing nervous system, primarily through motor responses triggered by stimuli-induced CNS activation. However, as these responses rely on the locomotor integrity of larval zebrafish, chemical-induced impairments to their locomotor capacity could obscure behavioral observations and confound findings concerning the developmental neurotoxicity of the tested chemicals. This limitation emphasizes the need for supporting assays designed to specifically evaluate the locomotor capacity of larval zebrafish. In the present study, we evaluated the use of peripheral irritant-elicited motor responses as a method to identify chemical-induced locomotor deficits. The motor activity of 120 hours post-fertilization (hpf) zebrafish larvae exposed to different concentrations of two peripheral stimulants—mustard oil and cinnamon oil—was evaluated. Subsequently, we assessed changes to central (visual and acoustic) and peripheral (irritant) motor responses after tricaine-s (MS-222; neurodepressant) and tubocurarine (neuromuscular blocker) exposures. Additional investigations were also carried out to assess the central and peripheral motor activity of larvae after developmental exposures (114 h) to lead (Pb) and cadmium (Cd)—two suggested developmental neurotoxic environmental contaminants. Our observations revealed that exposure to mustard oil (12.5 µM) elicits the strongest motor response. Larvae exposed to MS-222 showed decreases in motor responses to visual and acoustic stimuli, but the same exposure induced limited effects on motor responses elicited by the peripheral irritant. Exposure to tubocurarine depressed all motor responses examined. Finally, both Pb and Cd exposures induced hypoactivation of central motor responses, but only Cd showed a significant depression in the peripheral irritant motor response (PIMR) in both intact and developmentally deformed larvae. This finding suggests that loss of locomotor capacity might be confounding the behavioral observations associated with Cd exposures. This research underscores the utility of this zebrafish-based PIMR assay in elucidating locomotor impairments induced by chemicals, which may obscure the behavioral findings of motor response assays designed to evaluate developmental neurotoxicity.