Mechanism of TiO2 nanoparticle‐induced neurotoxicity in zebrafish (Danio rerio)

Zebrafish (Danio rerio) has been used historically for evaluating the toxicity of environmental and aqueous toxicants, and there is an emerging literature reporting toxic effects of manufactured nanoparticles (NPs) in zebrafish embryos. Few researches, however, are focused on the neurotoxicity on adult zebrafish after subchronic exposure to TiO₂ NPs. This study was designed to evaluate the morphological changes, alterations of neurochemical contents, and expressions of memory behavior‐related genes in zebrafish brains caused by exposures to 5, 10, 20, and 40 μg/L TiO₂ NPs for 45 consecutive days. Our data indicated that spatial recognition memory and levels of norepinephrine, dopamine, and 5‐hydroxytryptamine were significantly decreased and NO levels were markedly elevated, and over proliferation of glial cells, neuron apoptosis, and TiO₂ NP aggregation were observed after low dose exposures of TiO₂ NPs. Furthermore, the low dose exposures of TiO₂ NPs significantly activated expressions of C‐fos, C‐jun, and BDNF genes, and suppressed expressions of p38, NGF, CREB, NR1, NR2ab, and GluR2 genes. These findings imply that low dose exposures of TiO₂ NPs may result in the brain damages in zebrafish, provide a developmental basis for evaluating the neurotoxicity of subchronic exposure, and raise the caution of aquatic application of TiO₂ NPs. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 163–175, 2016.