Chronic pulmonary exposure to traffic-related fine particulate matter causes brain impairment in adult rats

BACKGROUND: Effects of air pollution on neurotoxicity and behavioral alterations have been reported. The objective of this study was to investigate the pathophysiology caused by particulate matter (PM) in the brain. We examined the effects of traffic-related particulate matter with an aerodynamic diameter of < 1 μm (PM(1)), high-efficiency particulate air (HEPA)-filtered air, and clean air on the brain structure, behavioral changes, brainwaves, and bioreactivity of the brain (cortex, cerebellum, and hippocampus), olfactory bulb, and serum after 3 and 6 months of whole-body exposure in 6-month-old Sprague Dawley rats. RESULTS: The rats were exposed to 16.3 ± 8.2 (4.7~ 68.8) μg/m(3) of PM(1) during the study period. An MRI analysis showed that whole-brain and hippocampal volumes increased with 3 and 6 months of PM(1) exposure. A short-term memory deficiency occurred with 3 months of exposure to PM(1) as determined by a novel object recognition (NOR) task, but there were no significant changes in motor functions. There were no changes in frequency bands or multiscale entropy of brainwaves. Exposure to 3 months of PM(1) increased 8-isoporstance in the cortex, cerebellum, and hippocampus as well as hippocampal inflammation (interleukin (IL)-6), but not in the olfactory bulb. Systemic CCL11 (at 3 and 6 months) and IL-4 (at 6 months) increased after PM(1) exposure. Light chain 3 (LC3) expression increased in the hippocampus after 6 months of exposure. Spongiosis and neuronal shrinkage were observed in the cortex, cerebellum, and hippocampus (neuronal shrinkage) after exposure to air pollution. Additionally, microabscesses were observed in the cortex after 6 months of PM(1) exposure. CONCLUSIONS: Our study first observed cerebral edema and brain impairment in adult rats after chronic exposure to traffic-related air pollution. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12989-018-0281-1) contains supplementary material, which is available to authorized users.