Study On The Effects Of Prenatal And Postnatal Exposure To PM2.5 On The Learning And Memory Ability Of Rats And Its Mechanism

Objective:The animal model of PM2.5 exposure during pregnancy and lactation was used to observe the changes of learning and memory ability of rats at postnatal day 60(PND60).To study the effects of PM2.5 exposure on the learning and memory ability of rats in prenatal and postnatal,and to explore the possible mechanism.Methods:1.Establishment of animal models(1)PM2.5 exposurePregnant rats were randomly divided into three groups,including prenatal exposure group(GD0.5-GD16.5 inhalation exposure concentrated PM2.5)and exposure group(GD0.5-GD16.5 and PND1-PND21 inhalation exposure concentrated PM2.5),control group(always kept in the animal room with air cleaner).The exposure time was 6 hours a day.(2)Particle size distribution analysis and concentration monitoring of PM2.5The aerodynamic particle size spectrometer was used to detect the distribution of particle size in the exposed chamber of the atmospheric online enrichment system.The aerosol particle detector was used to monitor the concentration of PM2.5 in concentrated atmospheric PM2.5,clean air and the outside atmosphere in real time.2.Effects of PM2.5 exposure on learning and memory ability in ratsMorris water maze was used to detect learning and memory.3.Effects of PM2.5 exposure on hippocampal morphology in ratsThe pathological changes of hippocampus were observed by HE staining.The morphology of hippocampal neurons was observed by Nissl staining and the number of intact neurons was counted.The expression of microglia marker Iba-1 was detected by immunohistochemistry.4.Effects of PM2.5 exposure on oxidative stress in hippocampusThe level of reactive oxygen species in hippocampus was detected by flow cytometry.The content of malondialdehyde and the activity of glutathione peroxidase and superoxide dismutase were detected by biological kit.5.Effect of PM2.5 exposure on AKT/GSK-3β/CREB signaling pathwayWestern blot was used to detect the expression of AKT,p-AKT,GSK-3β,p-GSK-3β,CREB and p-CREB in hippocampus.Results:1.Particle size distribution and concentration change of PM2.5 exposedPM2.5(particle size<2.50μm)in the exposed chamber accounted for92.17%of the total mass concentration,accounting for 99.80%of the total particles.During the whole exposure period,the average concentration of PM2.5 in the outside atmosphere was 72.55±37.97μg/m~3,the concentrated atmosphere was 535.24±392.95μg/m~3,and the clean atmosphere was6.85±3.09μg/m~3.2.Effect of PM2.5 exposure on learning and memory ability in ratsThe escape latency of the exposed rats in the first three days was slightly higher than that of the control group,but there was no significant difference(P>0.05).There was no significant difference between the prenatal exposure group and the control group(P>0.05).There was no significant difference in the target quadrant activity time and number of crossing platforms between the prenatal exposure group and the control group(P>0.05).The exposed group was significantly lower than the control group and prenatal exposure group(P<0.05).3.Effect of PM2.5 exposure on hippocampal morphology(1)HE stainingThe number of neurons in the hippocampus of the exposed group was significantly decreased,the number of cell layers was declined,the cell volume was reduced,the nuclei were deeply stained,and nuclear pyknosis appeared.(2)Nissl stainingIn the exposed group,the intact neurons were reduced,and a large number of incomplete neurons with irregular contours,deep nucleolus staining and nuclear membrane disappeared were observed.(3)Effect of PM2.5 on the expression of microglia marker Iba-1The average optical density of Iba-1 positive cells was not significantly different between the prenatal exposed group and the control group(P>0.05).The exposed group was significantly higher than the control group and the prenatal exposure group(P<0.05).4.Effects of PM2.5 exposure on oxidative stress in hippocampusThere was no significant difference in ROS level and MDA content between the prenatal exposed group and the control group(P>0.05).The exposed group was significantly higher than the control group and the prenatal exposure group(P<0.05).The activities of GSH-Px and SOD in the prenatal exposed group and the exposed group were significantly lower than those in the control group(P<0.05).5.Effect of PM2.5 exposure on AKT/GSK-3β/CREB signaling pathwayThe expression levels of p-AKT/AKT,p-GSK-3β/GSK-3β,and p-CREB/CREB in the prenatal exposed group were not significantly different from those in the control group(P>0.05);The exposed group was significantly lower than the control group and the prenatal exposure group(P<0.05).Conclusions:1.Prenatal and postnatal exposure to PM2.5 caused a certain decline in the learning and memory ability of rats in adulthood.2.However,the effect of prenatal exposure to PM2.5 in the learning and memory ability in rats was not observed.3.Prenatal and postnatal exposure to PM2.5 caused a decrease in the learning and memory ability in rats,which may be related to pathological damage of hippocampus,oxidative damage and changes in AKT/GSK-3β/CREB signaling pathway.