Oral exposure to polystyrene nanoplastics induces anxiety-like behavior and cognitive deficit accompanied with alteration of neuroimmune markers in rats

Microplastic (MP) pollution has become a global environmental issue, but its potential health effect remains unknown. We aimed to investigate the effect of oral administration of polystyrene nanoplastics (PSNPs) on brain functions and behaviors. Five-week-old Sprague Dawley male rats were given 50 nm PSNPs orally at doses of 10 or 50 mg/kg thrice per week for four weeks. At 9-week-old after completion of oral exposure, novel object recognition test and open field test were performed. The hippocampus from each rat was collected to detect neurological, immunological, and antioxidative stress markers using ELISA, real-time RT-PCR and immunohistochemical analyses. High-dose PSNP-treated rats showed decreased exploration time with a novel object, and reduced entry time and time spent in the center. Increased glutamate concentration, decreased glutamate receptor NMDA subunits (NR1, NR2B) and transcription factors CREB1 and CaMKIV mRNAs and increased cFos and early growth response 1, reduced postsynaptic density protein-95, synaptophysin mRNAs, were observed in high-dose PSNP-treated rats. Moreover, antioxidative stress markers such as superoxide dismutase and catalase were significantly decreased whereas inflammatory cytokines (interleukin 1β, tumor necrosis factor-α) and microglial marker (ionized calcium-binding adapter molecule 1) were significantly higher in high-dose PSNP-treated rats. Our results indicate oral exposure to PSNPs induced anxiety-like behavior and learning, memory impairment by altering neuron-glia-immune cells interaction at synaptic regions in the rat hippocampus. This study would be helpful to understand the association between MP pollution and increasing neurological disorders like dementia, anxiety, and Alzheimer's disease in humans.