Toxic Effects of CdTe Quantum Dots on Locomotor Behavior, Neurodevelopment, and Axon Growth in Zebrafish Larvae

The nervous system is very sensitive to CdTe quantum dots (CdTe QDs), and an understanding of the effects of CdTe QDs on the nervous system is indispensable for their use in biomedical applications, especially in clinical medicine. This research explored the possible neurotoxic effects of CdTe QDs on the peripheral nervous system of zebrafish, including motor neuron damage, altered mobility and motor behavior of zebrafish larvae. The mechanism of peripheral neurotoxicity induced by CdTe QDs was also investigated by qRT-PCR in this study. The experimental results showed that 100 nM and above quantum dot exposure induced shortening of axon length of motor neurons and reduced the length and number of neurogenesis as well as motor nerve branching in 24-120-hpf zebrafish. The toxic effects of 100 nM and above CdTe QDs on motor neurons were further manifested as a decrease in the overall activity level of the 144-hpf zebrafish larvae including decreased locomotor velocity and shortened movement time. The average swimming velocity and total movement time of zebrafish in the 400-nM CdTe QDs-treated group were 24.7% and 17.1% of those of the control group, respectively. Molecular toxicology studies showed that genes related to neurogenesis (nrd) and axonal growth (mbp, gfap, and gap43) were significantly affected by CdTe QDs exposure. Their expressions all tended to decrease in zebrafish larvae at 72 hpf after exposure to 400-nM CdTe QDs. In conclusion, the present study demonstrates that exposure of zebrafish to CdTe QDs at early life stages leads to adverse neural outcomes through inhibition of neural development and motor neuron axon growth.