Unmasking aminated graphene quantum dots neurotoxicity in freshwater planarian: Dopaminergic disruption and reversible motor dysfunction at sublethal doses.

Despite their favorable biocompatibility profile, the neurotoxic potential of aminated graphene quantum dots (A-GQDs) remains poorly characterized, especially concerning their environmental impact. Utilizing the planarian Dugesia japonica, a freshwater invertebrate model with a vertebrate-like, highly conserved central nervous system (CNS) and regenerative capacity, we systematically evaluated A-GQDs neurotoxicity. The results demonstrated that sublethal doses (≤80 µg/mL) of A-GQDs selectively accumulated within cephalic ganglia and ventral nerve cords, inducing pronounced, dose- and time-dependent locomotor deficits. Crucially, this neurobehavioral toxicity was reversible upon A-GQDs removal. Mechanistically, A-GQDs exposure significantly disrupted neurotransmitter homeostasis, decreasing dopamine (DA) and 5-hydroxytryptamine (5-HT) levels and suppressing acetylcholinesterase (AChE) activity. Exogenous DA supplementation uniquely rescued locomotor impairment, implicating dopaminergic dysfunction as a primary mechanism. Transcriptional analysis revealed consistent downregulation of synaptic genes (synapsin, Djsyt) alongside upregulation of DA synthesis (Djth) and adhesion (Djdscam) genes. Whole-mount immunofluorescence confirmed dose-dependent neural damage, evidenced by diminished SYNAPSIN signal intensity and structural clarity. Neoblast marker piwiA upregulation indicated triggering regenerative responses post-exposure. To our knowledge, this is the first study to provide comprehensive in vivo evidence of A-GQDs-induced neurotoxicity in a freshwater planarian model, highlighting significant sublethal risks to aquatic ecosystems upon its environmental discharge. These findings revealed that A-GQDs, as "low-toxicity" nanomaterials, despite perceived safety, provoked significant sublethal neurotoxic risks via dopaminergic disruption and synaptic impairment, challenging their unqualified use in biomedical applications and underling the urgent need to regulate their environmental discharge to protect aquatic ecosystems.