Investigation of Anxiety and Depression Patterns in an In Vivo Model Following Chronic Exposure to Polyethylene Microplastic

Abstract

Microplastic pollution has emerged as a critical environmental issue with growing evidence of its biological toxicity in aquatic organisms. This study investigated the neurobehavioral and biochemical effects of chronic polyethylene (PE) microplastic exposure in zebrafish larvae. Behavioral assays, including locomotion tracking, light/dark preference, and T-maze tests, were conducted alongside acetylcholinesterase (AChE) enzymatic activity measurements to assess the impact of PE at two concentrations (10 µg/mL and 100 µg/mL). Locomotion analysis revealed that control larvae displayed normal exploratory swimming patterns, while PE-exposed groups exhibited dose-dependent reductions in distance travelled and average velocity, with the 100 µg/mL group showing restricted movement confined to limited zones. In the light/dark preference assay, control larvae maintained a natural preference for the dark zone, whereas PE exposure disrupted this behaviour. Larvae exposed to 10 µg/mL showed equal distribution of time in both zones, and at 100 µg/mL, they predominantly remained in the light zone, reflecting abnormal anxiety-like responses. T-maze testing further demonstrated impaired exploratory and cognitive behaviour, with significantly reduced exploration of the reward zone in PE-treated groups compared to controls. Biochemical analysis revealed marked inhibition of AChE activity in the head region of exposed larvae, suggesting impaired cholinergic neurotransmission due to excessive acetylcholine accumulation. Collectively, these findings highlight that chronic PE exposure disrupts locomotor activity, anxiety related behaviour, cognitive function, and cholinergic signalling in zebrafish larvae in a concentration-dependent manner. This study underscores the neurotoxic potential of microplastics and emphasizes the urgent need to evaluate their ecological and health risks in aquatic environments.