Manifestation of polystyrene microplastic accumulation in tissues of vital organs including brain with histological and behaviour analysis on Swiss albino mice

Abstract Plastic waste is persistent environmental pollutant, produced every year and cause unwanted ecological side effects. Microplastic (MPs) are small sized plastics found in cosmetics or those derived from degradation of larger plastic. MPs have shown harmful effects on both terrestrial and marine ecosystem. However, their effects on mammalian behaviour are scarcely studied. Recent reports indicated that toxic effects exhibited by MPs may vary with type, size, dosage, and duration of exposure. Specifically, how these MPs accumulate in vital organs including brain and affect behaviour of mice with different time period of exposure and dosage still needs to be investigated. Present study aimed to evaluate whether behavioural effects of polystyrene microplastic (PS-MPs) exposure varies with different time period and doses in adult male Swiss albino mice. Animals were orally exposed to 0.1mg/ml and 1mg/ml PS-MPs (of diameter 2 µm) for acute (15 days) and sub-chronic (30 and 60 days) time period. After the exposure period animals were subjected to behavioural test for accessing general locomotor behaviour (open field test), anxiety related behaviour (elevated plus maze) and learning behaviour (Morris water maze). Results showed that PS-MPs exposed animals exhibited behavioural changes like decreased exploration in open field, increased number of entries and time spent in closed arms of elevated plus maze as compared to control animals; giving indications of anxiety like effects due to PS-MPs. Treatment to PS-MPs also altered cognitive behaviour of mice, as treated mice spent more time in locating the hidden platform in Morris water maze. We demonstrated that exposure to PS-MPs can induce anxiety and impair learning just after 15 days of low dose exposure, however effects became more pronounced with increase in dose and time period of exposure. Further histological observation revealed that PS-MPs were found to be accumulated in gut, liver, kidney, and brain. To better understand pathology behind the behavioural and neurologic findings of the present study we further analysed histological structures of PS MPs exposed mice brain areas i.e., cortex, hippocampus, amygdala, and hypothalamus. PS MPs exposure caused decrease in hippocampal pyramidal cells and affected neuronal architecture of brain areas (cortex, hypothalamus, and amygdala), related with cognition and anxiety like-behaviour of mice. Our study provides novel insight into how accumulation and exposure at various time periods and dosage of microplastic particle cause histological and morphometric changes in different brain areas like i.e., cortex, hippocampus, amygdala, and hypothalamus which further lead to change in general and cognitive behaviour of mice.