Developmental lead exposure causes startle response deficits in zebrafish

Abstract

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 hours 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/sec. 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/sec. 2) Response to a visual stimulus. Fish, exposed as embryos (2–24 hpf) to Pb2+ (0–10 uM) 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.

Examining the effects of lead on the life of larval zebrafish (1-7 days old)

“…Specifically, the survival rate of larvae was decreased 0.810 times (equivalent 19%, 95% confidence interval, change in the range from 12.9% to 24.7%) by cultured everyday (from 63.75% on the first day to 21.25% on the 7th day, see [12]. According that, when embryo stages were exposed to low concentrations of Pb2+, they were not affected the activites and behaviors of fish later.…”

“…Four replicates (n = 4), each of which containing 20 embryos in a 60-mm diameter glass Petri dishes, were cultured in glass beaker with a volume of 200ml embryo Hank medium with supplemen tation of Pb2+ at examined concentrations (to tally 80 embryos for every concentration). After hatching, larvae were transferred to larval Hank medium with supplementation of Pb2+ at corre sponding concentrations [2, 3,5,12].…”

Zebrafish as a Model for Developmental Neurotoxicity Assessment: The Application of the Zebrafish in Defining the Effects of Arsenic, Methylmercury, or Lead on Early Neurodevelopment

“…The behavioral changes of the zebrafish were evaluated on several parameters reflecting altered movement in response to different frequencies of tapping stimulation (i.e., one tap/s or four taps/s), showing that zebrafish developmentally treated with 30 nM of Pb exhibited altered responses under both the one and four taps/second frequency stimulation [131]. Rice et al [131] also provided a probable mechanistic interpretation of the behavioral changes including altered sensitivity of mechanosensory neuromasts, function of neurons involved in signal integration, or neurotransmitter signaling, albeit inclusive. In another study Chen et al [132] treated zebrafish with up to 1 mg/L (≈5 µM) Pb acetate from 6-8 hpf and monitored spontaneous movement from 20 until 30 hpf, showing that spontaneous activity of embryos exposed to 1 mg/L of Pb significantly decreased at most of the tested time points.…”

“…In Rice et al [131], embryos were treated with up to 30 nM of Pb chloride through 24 hpf and then subjected to a neurobehavioral test at 168 hpf. The behavioral changes of the zebrafish were evaluated on several parameters reflecting altered movement in response to different frequencies of tapping stimulation (i.e., one tap/s or four taps/s), showing that zebrafish developmentally treated with 30 nM of Pb exhibited altered responses under both the one and four taps/second frequency stimulation [131].…”

“…In Rice et al [131], embryos were treated with up to 30 nM of Pb chloride through 24 hpf and then subjected to a neurobehavioral test at 168 hpf. The behavioral changes of the zebrafish were evaluated on several parameters reflecting altered movement in response to different frequencies of tapping stimulation (i.e., one tap/s or four taps/s), showing that zebrafish developmentally treated with 30 nM of Pb exhibited altered responses under both the one and four taps/second frequency stimulation [131]. Rice et al [131] also provided a probable mechanistic interpretation of the behavioral changes including altered sensitivity of mechanosensory neuromasts, function of neurons involved in signal integration, or neurotransmitter signaling, albeit inclusive.…”