Polystyrene microplastics induce anxiety-like behavior via lateral amygdala excitatory–inhibitory imbalance and glia–neuron crosstalk

Polystyrene microplastics (PS–MPs) are emerging environmental pollutants with growing evidence of neurotoxic effects. This study examined how particle size and surface charge influence PS–MPs-induced neurotoxicity in male mice. Chronic exposure to 5000 nm PS–MPs disrupted excitatory–inhibitory balance in the basolateral amygdala, marked by upregulation of excitatory markers (VGLUT2, GLUA1) and downregulation of inhibitory markers (GAD65 + 67, GABABR1). These synaptic alterations were accompanied by glial activation, neuroinflammation, and microglial polarization toward a pro-inflammatory M1 state (CD86/CD206). In vitro co-culture and conditioned media experiments confirmed that microglial activation contributes to astrocytic and neuronal injury independent of direct PS–MPs internalization. Statistical modeling encompassing principal component analysis and multiple linear regression identified surface charge (zeta potential) as a stronger predictor than particle size for neuroinflammatory and behavioral outcomes, although size more directly influenced glial activation. Contrary to the assumption that smaller particles are inherently more toxic due to greater uptake, 5000 nm PS–MPs induced more severe neurotoxic effects, likely through microenvironmental disruption rather than cellular internalization. These findings underscore that PS–MPs neurotoxicity is driven by a complex interplay between particle size and surface charge, with surface charge emerging as the dominant factor in driving microglial-mediated inflammation and behavioral changes. Overall, the study reveals that PS–MPs exposure disrupts neural signaling, triggers neuroinflammation, and promotes anxiety-like behaviors through glial activation and excitatory-inhibitory imbalance. These findings underscore the distinct and complementary roles of size and surface charge in PS–MPs neurotoxicity and highlight the importance of glial-mediated mechanisms in driving behavioral and neural circuit disruptions. Not applicable.