Graphene quantum dots (GQDs) induce thigmotactic effect in zebrafish larvae via modulating key genes and metabolites related to synaptic plasticity

Graphene quantum dots (GQDs) recently gain much attention for its medicinal values in treating diseases such as neurodegeneration and inflammations. However, owing to the high permeability of GQDs across the blood-brain barrier, whether its retention in the central nervous system (CNS) perturbs neurobehaviors remains less reported. In the study, the locomotion of zebrafish larvae (Danio rerio) was fully evaluated when administrated by two GQDs in a concentration gradient, respectively as reduced-GQDs (R-GQDs): 150, 300, 600, 1200, and 2400 g/L, and graphene oxide QDs (GOQDs): 60, 120, 240, 480, and 960 g/L. After exposure, the larvae were kept for locomotion analysis within one week's depuration. Substantial data showed that the basal locomotor activity of zebrafish larvae was not significantly changed by both two GQDs at low concentrations while weakened greatly with the increase of concentrations, and the total ATP levels of zebrafish larvae were also found to decrease significantly when exposed to the highest concentrations of GQDs. Next, the thigmotactic effect was observed to be remarkably induced in larvae by both two GQDs at any concentrations during exposure, and remained strong in larvae treated by high concentrations of R-GQDs after 7 days' depuration. To be noted, we found that GQDs affected the synaptic plasticity via downregulating the mRNA levels of NMDA and AMPA receptor family members as well as the total glutamine levels in zebrafish larvae. Together, our study presented robust data underlying the locomotor abnormalities aroused by GQDs in zebrafish larvae and indicated the potential adverse effects of GQDs on synaptic plasticity.