Chronic exposure to PM₁₀ induces anxiety-like behavior via exacerbating hippocampal oxidative stress

As one of the most environmental concerns, inhaled particulate matter (PM₁₀) causes numerous health problems. However, the associations between anxiety behavior and toxicity caused by PM₁₀ have rarely been reported so far. To investigate the changes of behavior after PM₁₀ exposure and to identify the potential mechanisms of toxicity, PM₁₀ samples (with doses of 15 mg/kg and 30 mg/kg) were intratracheally instilled into rats to simulate inhalation of polluted air by the lungs. After instillation for eight weeks, anxiety-like behavior was evaluated, levels of oxidative stress and morphological changes of hippocampus were measured. The behavioral results indicated that PM₁₀ exposure induced obvious anxiety-like behavior in the open field and elevated plus maze tests. Both PM₁₀ concentrations tested could increase whole blood viscosity and trigger hippocampal neuronal damage and oxidative stress by increasing superoxide dismutase (SOD) activities and malondialdehyde levels, and decreasing the expressions of antioxidant-related proteins (e.g., nuclear factor erythroid 2-related factor 2 (Nrf2), SOD1 and heme oxygenase 1). Furthermore, through collecting and analyzing questionnaires, the data showed that the participants experienced obvious anxiety-related emotions and negative somatic responses under heavily polluted environments, especially PM₁₀ being the main pollutant. These results show that PM₁₀ exposure induces anxiety-like behavior, which may be related to suppressing the Nrf2/Keap1-SOD1 pathway.