Micro/nano-plastics cause neurobehavioral toxicity in discus fish (Symphysodon aequifasciatus): Insight from brain-gut-microbiota axis

Numerous studies have investigated neurobehavioral toxicity of microplastics, but no studies have illustrated mechanism via brain-gut axis. Here, juvenile discus fish (Symphysodon aequifasciatus) were exposed for 96 h to microfibers (900 mu m, fiber, MFs) or nanoplastics (similar to 88 nm, bead, NPs) with three concentrations (0, 20 and 200 mu g/L). Accumulation in fish gut was independent of plastics type and concentration. MFs reduced growth per-formance while NPs weakened swimming and predatory performance of post-exposed discus. For brain cholinesterase activity, acetylcholinesterase was activated by NPs while NPs/MFs exposure inhibited butyr-ylcholinesterase. Concentrations of neurotransmitters (acetylcholine, dopamine and gamma-aminobutyric acid) increased in brain but decreased in gut after NPs or MFs exposure. For gut microbiota, increased richness under MFs exposure was observed. At phylum level, Proteobacteria proportion was lower in NPs but higher in MFs. Abundance of Clostridia and Fusobacteriia (Bacillus), potentially secreting neurotransmitters, increased in NPs but decreased in MFs. Brain transcriptomics revealed seven upregulated and four downregulated genes concerning neural-activities. Pathways of neuroactive ligand-receptor interaction and serotonergic synapse were enriched in both MFs and NPs, but dopaminergic synapse pathway was enriched only in MFs. These results established a novel mechanism by which microplastics might cause behavioral toxicities via brain-gut-microbiota axis.

Automated summary

Numerous studies have investigated the neurobehavioral toxicity of microplastics, and this study reveals a novel mechanism by which microplastics may cause behavioral toxicities via the brain-gut-microbiota axis. Results showed that exposure to different types and concentrations of microplastics had varying effects on the growth, swimming, and predatory performance of juvenile discus fish, as well as on neurotransmitter concentrations in the brain and gut. Additionally, the study found changes in gut microbiota richness and composition, as well as alterations in gene expression related to neural activities and enrichment of specific neuroactive pathways in both types of microplastics.