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.
Exposure to titanium dioxide nanoparticles (TiO2 NPs) has been demonstrated to decrease learning and memory of animals. However, whether the impacts of these NPs on the recognition function are involved in hippocamal neuron damages is poorly understood. In this study, primary cultured hippocampal neurons from one-day-old fetal Sprague-Dawley rats were exposed to 5, 15, or 30 µg/mL TiO2 NPs for 24 h, we investigated cell viability, ultrastructure, and mitochondrial membrane potential (MMP), calcium homeostasis, oxidative stress, antioxidant capacity, apoptotic signaling pathway associated with the primary cultured hippocamal neuron apoptosis. Our findings showed that TiO2 NP treatment resulted in reduction of cell viability, promoted lactate dehydrogenase release, apoptosis, and increased neuron apoptotic rate in a dose-dependent manner. Furthermore, TiO2 NPs led to [Ca(2+)]i elevation, and MMP reduction, up-regulated protein expression of cytochrome c, Bax, caspase-3, glucose-regulated protein 78, C/EBP homologous protein and caspase-12, and down-regulated bcl-2 expression in the primary cultured hippocampal neurons. These findings suggested that hippocampal neuron apoptosis caused by TiO2 NPs may be associated with mitochondria-mediated signal pathway and endoplasmic reticulum-mediated signal pathway.
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