Dim light at night modulates neuroimmune and clock gene responses to burn pit emission inhalation exposure in mice

Many U.S. soldiers and support personnel stationed in the Middle East and Southwest Asia are exposed to hazardous combustion byproducts from military burn pits, which may produce chronic health effects. In addition, prolonged and irregular work schedules increase susceptibility to circadian rhythm disruption, worsening adverse health outcomes. This study aimed to examine the interaction between light at night and burn pit exposure and their effects on neuroinflammatory and behavioral outcomes in mice. Thirty-two male Swiss Webster mice were housed either in dark nights (LD) or dim light at night (DLAN) condition. During week 4, mice from each group were exposed to either filtered air (FA) or burn pit emissions (BPE) for 4 hr/ day over 6 days. For the BPE‑exposed mice, the average exposure concentrations were 6.9 mg/m³ (mass) and 4.03E⁶ #/cc (particle counts). The mice housed in LD conditions and exposed to FA served as an experimental control group. Behavioral testing conducted 24 hr after the last exposure resulted in no significant differences in distance traveled, spatial working memory, or anxiety-like behavior in open field, y-maze, and elevated plus maze. However, DLAN-FA mice exhibited reduced average speed in comparison to LD-FA. qRT-PCR analysis revealed decreased expression of proinflammatory cytokine genes in hippocampus (Il6, Tnfα, and Il1β) and cortex (Il6) of LD-BPE mice. Significant changes in gene expression were not observed in lungs and liver. Reduced Bmal1 expression was noted in hippocampus of LD-BPE mice, whereas DLAN-FA group increased Bmal1 and Cry1 expression in cortex. Our data demonstrate that light at night modulates neuroimmune and circadian responses following repeated BPE exposures.