Subchronic exposure to ambient PM2.5impairs novelty recognition and spatial memory

Abstract

AbstractAir pollution remains a great challenge for public health, with the detrimental effects of air pollution on cardiovascular, rhinosinusitis, and pulmonary health increasingly well understood. Recent epidemiological associations point to the adverse effects of air pollution on cognitive decline and neurodegenerative diseases. Mouse models of subchronic exposure to PM2.5(ambient air particulate matter < 2.5 µm) provide an opportunity to demonstrate the causality of target diseases. Here, we subchronically exposed mice to concentrated ambient PM2.5for 7 weeks (5 days/week; 8h/day) and assessed its effect on behavior using standard tests measuring cognition or anxiety-like behaviors. Average daily PM2.5concentration was 200 µg/m3in the PM2.5group and 10 µg/m3in the filtered air group. The novel object recognition (NOR) test was used to assess the effect of PM2.5exposure on recognition memory. The increase in exploration time for a novel object versus a familiarized object was lower for PM2.5-exposed mice (42% increase) compared to the filtered air (FA) control group (110% increase). In addition, the calculated discrimination index for novel object recognition was significantly higher in FA mice (67 %) compared to PM2.5exposed mice (57.3%). The object location test (OLT) was used to examine the effect of PM2.5exposure on spatial memory. In contrast to the FA-exposed control mice, the PM2.5exposed mice exhibited no significant increase in their exploration time between novel location versus familiarized location indicating their deficit in spatial memory. Furthermore, the discrimination index for novel location was significantly higher in FA mice (62.6%) compared to PM2.5exposed mice (51%). Overall, our results demonstrate that subchronic exposure to higher levels of PM2.5in mice causes impairment of novelty recognition and spatial memory.