Neurotoxicity of FireMaster 550® in zebrafish (Danio rerio): Chronic developmental and acute adolescent exposures

Abstract

Background: FireMaster® 550 (FM 550) is the second most commonly used flame retardant (FR) product in consumer goods and has been detected in household dust samples. However, neurobehavioral effects associated with exposure have not been characterized in detail. We investigated the behavioral effects of FM 550 in zebrafish to facilitate the integration of the cellular and molecular effects of FM 550 with its behavioral consequences. The effects of developmental FM 550 exposure on zebrafish larvae swimming shortly after the end of exposure as well as the persisting effects of this exposure on adolescent behavior were studied. In addition, the acute effects of FM 550 on behavior with exposure during adolescence in zebrafish were studied.

Methods: Developmental exposure to 0, 0.01, 0.1 or 1 mg/L of FM 550 via immersion spanned 0-5 days post fertilization, with larval testing on day 6 and adolescent testing on days 40-45. Acute adolescent (45 dpf) exposure was to 0, 1.0 or 3.0 mg/L of FM 550 via immersion, for 24 h, with testing 2 h or 1 week later. The vehicle condition was colony tank water with .0004% (developmental) or .0012% (adolescent) DMSO. Zebrafish behavior was characterized across several domains including learning, social affiliation, sensorimotor function, predator escape, and novel environment exploration.

Results: Persisting effects of developmental FM 550 exposure included a significant (p<0.01) reduction in social behavior among all dose groups. Acute FM 550 exposure during adolescence caused hypoactivity and reduced social behavior (p's<0.05) when the fish were tested 2 h after exposure. These effects were attenuated at the 1 week post exposure testing point

Discussion: Taken together, these data indicate that FM 550 may cause persisting neurobehavioral alterations to social behavior in the absence of perturbations along other behavioral domains and that developmental exposure is more costly to the organism than acute adolescent exposure.

Keywords: Acute; Behavior; Cognition; Developmental; FireMaster 550; Flame retardant; Zebrafish.

Figure 1. Developmental Exposure, Larval Testing: Motility

Swimming activity in alternating 10-min blocks of light and dark. Dotted line denotes phase change. FM 550 exposure groups are plotted with open symbols, the control group is plotted with filled circles, each data point corresponds to a 1-min average of activity. The rectangular blocks along the x-axis indicate illumination condition (filled=dark, open=light). Error bars represent standard error of the mean.

Figure 2. Developmental Exposure, Adolescent Testing: Tank exploration and habituation to a startle

Results from the neurobehavioral test battery are plotted for the developmental (0–6 dpf) exposure group. Panels A–B represent distance from the floor (A) or total distance traveled (B) during the novel tank exploration assay. Each bar represents 1-min of the session, exposure group is plotted along the x-axis. Panels C–D represent distance traveled before (C) and after (D) the presentation of a tap stimulus during the startle habituation assay. Each bar represents the average distance traveled for each 2-tap block during the session, with exposure group plotted along the x-axis. All error bars (A–D) represent standard error of the mean and “*” denotes difference from control.

Figure 3. Developmental Exposure, Adolescent Testing: Shoaling

Results from the neurobehavioral test battery are plotted for the developmental (0–6 dpf) exposure group. Panels A and C correspond to baseline behavioral during the shoaling procedure, B and D represent behavior in the presence of shoaling conspecifics (video). Distance to the shoal (A–B) and total distance traveled (C–D) are plotted by exposure group. All error bars represent standard error of the mean and “*” denotes difference from control.

Figure 4. Developmental Exposure, Adolescent Testing: Predator escape/avoidance

Results from the neurobehavioral test battery are plotted for the developmental (0–6 dpf) exposure group. Behavior during the predator escape/avoidance procedure is shown during baseline (A & D), in the presence of the predator stimulus (B & E) and in its absence (C & F). The top row (A–C) plots distance from the predator (cm) stimulus by exposure condition and the bottom row (D–F) plots total distance traveled (cm) by exposure condition. Error bars represent standard error of the mean.

Figure 5. Acute Exposure, Adolescent Testing 2-hr Following Exposure: Exploration, habituation to a startle and motility

Results from the neurobehavioral test battery are plotted for the acute (24 hr) exposure group, tested 2 hr after exposure. Panels A–B correspond to distance from the floor (A) and total distance traveled (B) during the novel tank exploration assay, each bar represents the mean for one min of the trial. Panel C shows distance traveled following the tap presentation during the startle habituation assay, each bar represents the average of two consecutive tap presentations. Panel D plots swimming during the light/dark adolescent motility assay, the filled bars correspond to swimming in a dark environment and the open bars to swimming in a brightly lit environment. Exposure condition is plotted along the x-axis. All error bars represent standard error of the mean and “*” denotes difference from control.

Figure 6. Acute Exposure, Adolescent Testing 2-hr Following Exposure: Shoaling

Results from the neurobehavioral test battery are plotted for the acute (24 hr) exposure group, tested 2 hr after exposure. Distance to the active shoal (A) and total distance traveled (B) in the presence of the conspecifics is plotted by exposure group. Error bars represent standard error of the mean and “*” denotes difference from control.