Extreme low-temperature exacerbates polystyrene microplastic-induced neuroendocrine and behavioral dysfunctions in female mice

Despite the growing recognition of the impacts of microplastics (MPs) and the intensification of extreme weather events, recent investigations have focused mainly on the consequences of global warming, while overlooking the potential impacts of extreme low-temperature (ELT) events and their interaction with these pollutants. Accordingly, the aim of this study was to assess the integrated effects of co-exposure to environmentally aged polystyrene microplastics (PS-MPs) and ELTs on behavioral, neuroendocrine, metabolic, and histomorphometric biomarkers in female Swiss mice. To this end, animals were orally exposed to environmentally aged PS-MPs (10 mg/kg/day) and maintained in a climate-controlled chamber at 4 °C for 21 days, whereas control groups were kept at 25 °C. In the behavioral domain, co-exposed animals exhibited increased locomotor disorganization, anxiety-like behavior, reduced exploratory efficiency, and impairments in memory and social discrimination, associated with neuroendocrine alterations involving dopamine, serotonin, epinephrine, and corticosterone, depending on the response evaluated. The retention of PS-MPs in the interscapular brown adipose tissue (iBAT) was confirmed by epifluorescence microscopy. It was associated with oxidative stress, decreased antioxidant defenses, and metabolic dysfunction in iBAT, effects exacerbated by ELT exposure. Multivariate analyses, including principal component analysis (PCA), Random Forest, and structural equation modeling (PLS-PM), revealed distinct phenotypic patterns among groups, as well as integrated causal trajectories linking neuroendocrine dysfunction to systemic phenotypic alterations. In conclusion, our study confirms the initial hypothesis by demonstrating that the combination of ELT and PS-MP ingestion amplifies systemic physiological dysfunctions beyond the effects of each individual stressor, highlighting the vulnerability of homeothermic mammals under multiple environmental pressures, and opening new perspectives for ecotoxicology to consider not only the impacts of global warming, but also the deleterious effects of ELTs in interaction with emerging pollutants.