Developmental lead exposure causes startle response deficits in zebrafish

Lead (Pb2+) exposure continues to be an important concern for fish populations. Research is required to assess the long-term behavioral effects of low-level concentrations of Pb2+ and the physiological mechanisms that control those behaviors. Newly fertilized zebrafish embryos (<2 h post fertilization; hpf) were exposed to one of three concentrations of lead (as PbCl2): 0, 10, or 30 nM until 24 hpf. (1) Response to a mechanosensory stimulus: Individual larvae (168 hpf) were tested for response to a directional, mechanical stimulus. The tap frequency was adjusted to either 1 or 4 taps/s. Startle response was recorded at 1000 fps. Larvae responded in a concentration-dependent pattern for latency to reaction, maximum turn velocity, time to reach Vmax and escape time. With increasing exposure concentrations, a larger number of larvae failed to respond to even the initial tap and, for those that did respond, ceased responding earlier than control larvae. These differences were more pronounced at a frequency of 4 taps/s. (2) Response to a visual stimulus: Fish, exposed as embryos (2–24 hpf) to Pb2+ (0–10 μM) were tested as adults under low light conditions (∼60 μW/m2) for visual responses to a rotating black bar. Visual responses were significantly degraded at Pb2+ concentrations of 30 nM. These data suggest that zebrafish are viable models for short- and long-term sensorimotor deficits induced by acute, low-level developmental Pb2+ exposures.

► Time to respond, maximum velocity and escape swim duration are affected by low developmental Pb2+.
► Escape swim at chamber center for embryo Pb2+-exposure larvae; control larvae swim at periphery.
► Low developmental Pb2+ reduces response rate to visual stimuli in adult zebrafish.