Unraveling the mechanism of brain damage in Carassius auratus by polypropylene microplastics and oxytetracycline via the brain-gut-microbiota axis

Microplastics (MPs) and antibiotic residues are widespread coexistence and pose a greater threat in aquatic environments, but the neurotoxic effects of co-exposure on aquatic animals remain poorly understood. This study investigated the mechanisms of MPs and oxytetracycline (OTC) on the brain-gut-microbiota axis of Carassius auratus at environmentally realistic levels. The carrier effect of MPs resulted in OTC accumulation levels of 221.84 ng/g and 2524.61 ng/g in the brain and intestine of the combined exposure, respectively, and aggravated infectious inflammation in the brain and intestinal dissolution and necrosis. MPs and OTC raised the abundance of Actinobacteriota, and markedly reduced the content of acetic acid and propionic acid by 41.86 % and 75.52 %, respectively. Moreover, combined exposure had a synergistic effect, with inhibition rates of 52.57 % and 61.99 % for AChE and BChE, respectively, further leading to a decrease in 5-hydroxytryptamine and dopamine levels. Transcriptomics further revealed that the toxic effects of co-exposure might induce nervous system disorders through synaptic vesicle recycle and GABAergic synaptic pathway, which were influenced by gut microbiota and neuroactive molecules. In summary, MPs and antibiotics trigger various physiological changes by disrupting the fish brain-gut-microbiota axis, which provides scientific information to understand the co-exposure risks of MPs and associated contaminants in aquatic ecosystems.