Air pollution exposure as well as physical activity was found to have different effects on the brain. At first, air pollution is believed to evoke neuroinflammation which might induce neurodegeneration. Second, physical activity benefits brain function by supporting neuroprotective effects and neurogenesis. Previously, we found exercise induced up regulation of Brain-Derived Neurotrophic Factor (BDNF). BDNF is a neurotrophine important for neurogenesis and neuroprotection. The purpose of this study was to examine the acute and short-term effects of both exercise and air pollution on the brain, using gene expression analysis and whether these effects translate to the blood. The gene expression of inflammatory markers (NFE2L2, IL1α, IL1β, IL6, TNFα, NOS1, NOS2, NOS3 and COX2), neurotrophic growth factors (VEGFa, IGF1) and synaptic proteins (SYN1, SYP) were analyzed in two different animal studies. At first, twenty C57BL6 mice were divided into four groups of five mice and placed into the Craeybeckxtunnel with or without filter cap (Antwerp) for five days. Two control groups were placed outside the tunnel. Brain samples of olfactory bulb and hippocampus were collected twenty-four hours after the exposure to analyze changes in gene expression of inflammatory genes and brain plasticity related genes. Second, twenty-four male, albino, Wistar rats were allocated into four groups to investigate the effects of exposure to ultrafine particles (UFP) during a single bout of physical activity. The animals were exposed for 90 minutes to one of the following regimes: Ambient air/Rest, Ambient air/Exercise, UFP/Rest and UFP/Exercise. Analysis of changes in gene expression of inflammatory and brain plasticity related genes was performed by qPCR. Previous analysis revealed an increased expression of inflammatory genes (COX2, NOS2, NOS3, NFE2L2) in the hippocampus of the mice due to air pollution exposure. In this study, an increased NOS1 expression was found due to air pollution in the mice hippocampus. The previously decreased expression of BDNF did not reflect to the other brain plasticity related genes (VEGFa and IGF1). The rat study previously revealed an up regulation of Brain-Derived Neurotrophic Factor (BDNF). In this sequel, synapsin 1 (SYN1) follows the same pattern as BDNF but without a significant increase due to exercise and with significant decrease due to UFP, regardless of physical activity. The gene expression pattern in the brain did not seem to translate to the blood. In addition to the previous findings demonstrating a negative effect of UFP exposure on BDNF gene expression, this study shows a negative effect of UFP exposure on the gene expression of SYN1 and VEGFa. This finding suggests that a short exposure to air pollution decreases neurotrophic support and synaptic plasticity. Keywords Particulate matter (PM), brain-derived neurotrophic factor (BDNF), inflammation, hippocampus, olfactory bulb, prefrontal cortex, blood, brain plasticity related genes.

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