Abstract:

Objective To study the neurotoxicity of niclosamide (NIC) on juvenile zebrafish. Methods Taking the model animal zebrafish as the research object, 7 200 fertilized zebrafish eggs were randomly divided into 6 groups with each four replicates and exposed in water containing 0, 5, 10, 20, 40 and 80 μg/L of NIC, respectively, for 120 hours. The rates of survival, malformation, hatchingand and body mass of juvenile zebrafish were measured. The acetylcholinesterase (AChE) activity of each group of fish was determined using an AChE Activity Kit. The average moving speed of juvenile zebrafish was monitored using a ZebraLab monitor system. The mRNA relative expression of mircroglobulin precursor (mbp) and α-tubulin in fish exposed to different concentration of NIC was determined by qRT-PCR. The results were statistically analyzed using one-way ANOVA followed by Tukey’s multiple comparison using SPSS 16.0. Results The survival of zebrafish were significantly reduced when exposed in water containing 40 μg/L NIC [(81.9 ± 0.8)%] and 80 μg/L NIC [(80.5 ± 0.9)%] compared to the water without NIC [(86.8 ± 0.2)%] (P < 0.05, P < 0.01, respectively). The malformation were significantly increased in water containing 40 and 80 μg/L NIC [(5.7 ± 0.6)% and (6.0 ± 0.4)%], respectively compared to water with 0 μg/L NIC [(3.2 ± 0.3)%] (P < 0.05, P < 0.01, respectively). The hatching and body mass of zebrafish were not significantly altered in all NIC exposure groups compared to 0 μg/L NIC exposure group [(92.2 ± 2.2) % and (472 ± 45 ) ng] (P > 0.05). The AChE activity in zebrafish exposed to 40 and 80 μg/L NIC was significantly increased [1 048.6 and 1 202.4 nmol/(mg·min), respectively] compared to fish in water without NIC[838.4 nmol/(mg·min)] (P < 0.05, P < 0.01, respectively). The moving speed of zebrafish in dark environment was significantly decreased in water containing 40 μg/L NIC [(2.3 ± 0.2) mm/s] and 80 μg/L NIC [(2.1 ± 0.2) mm/s] compared to water without NIC [(2.7 ± 0.2) mm/s]. In the bright environment the moving speed of zebrafish was also significantly decreased when exposed to 40 and 80 μg/L NIC water [(1.5 ± 0.1) mm/s, (1.4 ± 0.1) mm/s, respectively] compared to fish in water with 0 μg/L NIC [(1.9 ± 0.1) mm/s] (P < 0.05, P < 0.01, respectively). Compared to the fish in water without NIC (1.0 ± 0.0), the mRNA relative expression of mbp and α-tubulin were significantly down-regulated in fish exposed to 40 and 80 μg/L NIC (0.8 ± 0.1, 0.7 ± 0.1 and 0.7 ± 0.1, 0.6 ± 0.1, respectively) (P < 0.05, P < 0.01). Conclusion Exposure to 40 and 80 μg/L NIC could cause significant toxicity to zebrafish indicated by the decreased survival, moving speed and mbp and α-tubulin mRNA expression, and increased malformation and AChE activity.

Key words: Niclosamide, Juvenile zebrafish, Neurotoxicity, Environmental related concentration