Effects of embryonic exposure to polychlorinated biphenyls (PCBs) on anxiety-related behaviors in larval zebrafish

Abstract

The zebrafish (Danio rerio) is an excellent model system for assessing the effects of toxicant exposure on behavior and neurodevelopment. In the present study, we examined the effects of sub-chronic embryonic exposure to polychlorinated biphenyls (PCBs), a ubiquitous anthropogenic pollutant, on anxiety-related behaviors. We found that exposure to the PCB mixture, Aroclor (A) 1254, from 2 to 26h post-fertilization (hpf) induced two statistically significant behavioral defects in larvae at 7 days post-fertilization (dpf). First, during 135min of free swimming, larvae that had been exposed to 2ppm, 5ppm or 10ppm A1254 exhibited enhanced thigmotaxis (edge preference) relative to control larvae. Second, during the immediately ensuing 15-min visual startle assay, the 5ppm and 10ppm PCB-exposed larvae reacted differently to a visual threat, a red 'bouncing' disk, relative to control larvae. These results are consistent with the anxiogenic and attention-disrupting effects of PCB exposure documented in children, monkeys and rodents and merit further investigation.

Keywords: Attention; Behavior; Polychlorinated biphenyls; Startle; Thigmotaxis; Zebrafish.

Fig. 1

Effect of embryonic PCB exposure on edge preference at 7 dpf. Mean (± SEM) percent thigmotaxis in the 135-min period of free swimming on a uniform white background with no visual stimulus (phase 1) shown separately for the combined controls (EW and DMSO) and the three PCB-exposure concentrations (2 ppm, 5 ppm and 10 ppm). Asterisks denote statistically significant differences between the control and the PCB exposed larvae (p = .035 for 2 ppm, p = .006 for 5 ppm, and p = .003 for 10 ppm, Dunnett’s two tailed tests).

Fig. 2

Effect of embryonic PCB exposure on activity measures at 7 dpf. A) Mean (± SEM) swim speed (mm/min); B) mean (± SEM) percent still. For both panels, data are plotted in 15-min blocks for the 135-min period of free swimming on a uniform white background with no visual stimulus (phase 1) and shown separately for the three PCB-exposure concentrations (2 ppm, 5ppm and 10 ppm) and the combined controls (EW and DMSO).

Fig. 3

Effect of embryonic PCB exposure on transitional swim speed at 7 dpf. Mean (± SEM) swim speed (mm/min) between the last pretest image and the first test image in the VSA shown separately for the controls (EW and DMSO combined) and the three PCB-exposure concentrations (2 ppm, 5 ppm and 10 ppm). Asterisks denote statistically significant differences between the control and the PCB exposed larvae (p <.001 for 5 ppm and p < .05 for 10 ppm, Dunnett’s two tailed tests).

Fig. 4

Effect of embryonic PCB exposure on VSA behavior at 7 dpf. A) Mean (± SEM) percent avoidance; B) mean (± SEM) percent thigmotaxis; C) mean (± SEM) swim speed (mm/min); D) mean (± SEM) percent still. For all panels, data are shown separately for each of the three 5-min periods corresponding to pretest (Pre), test with the red ‘bouncing’ disk (Test) and posttest (Post) and for the combined controls (EW and DMSO) and the three PCB-exposure concentrations (2 ppm, 5 ppm and 10 ppm). Asterisks denote statistically significant differences between the control and the PCB exposed larvae (p < .05 for 5 ppm, Dunnett’s two tailed test). The letter ‘a’ above a bar indicates a significant difference between that mean and the corresponding mean in the test with the red ‘bouncing’ disk (Test, ps < .05, repeated measures ANOVAs).