Effects Of Acute Paraquat Poisoning On Learning And Memory Ability And Microglial Polarization In Rats

Objective: The rat model of acute paraquat（PQ）exposure was est ablished to observe the changes of learning and memory ability of rats,pathological changes and microglia polarization phenotype changes in different parts on the 8^th,30^th and 60^th days after exposure.Further to explore the role of microglial in the effect of acute PQ poisoning on long-term learning and memory in rats.Methods:1.Animal model establishedThirty-nine adult female Wistar rats were randomly divided into three groups: control group（normal saline）,low-dose group（PQ was exposed with 25mg/kg）,and high-dose group（PQ was exposed with 45mg/kg）.Single-exposure was performed on each group of experimental animals through oral administration.The rats in the low and high-dose groups who died after PQ poisoning were enrolled with same administration.2.Effect of acute PQ poisoning on learning and memory ability in rats.Morris water maze and step-down test was used to detect learning and memory ability.3.Pathological changes hippocampus,striatum and SN after acute PQ exposure.HE staining was used to observe the damage of neurons in hippocampus,striatum and substantia nigra（SN）.4.The number and morphology of microglia in hippocampus,striatum and SN after acute PQ poisoning.Immunohistochemical was used to label microglial with Iba-1 in hippocampus,striatum and SN,and analyzed the morphology of microgliausing Image J.5.Effect of acute PQ exposure on microglia polarized phenotype.Immunofluorescence double staining was used to label M1 phenotype with iba-1 and i NOS,M2 phenotype with iba-1 and Arg-1 in hippocampus,striatum and SN to observe the microglia polarization phenotype changes after acute PQ exposure.Results:1.The rats wight of high-dose group was lower than control group on the 3th,4^th,5th and 6th days after exposure（P<0.05）.After one week,the weight recovered to the pre-infection level,and there was no significant difference between the exposure group and the control group at the end of the observation period（P>0.05）;2.There was no significant difference between the low and high-dose groups with the control group in the escape incubation period of the training period on the 8^th day of poisoning（P>0.05）.On the 30^th day of poisoning,the latency to escape of the high-dose group on the 4^th day of training was significantly higher than that of the low-dose group and the control group（F=10.131,P<0.05）.On the 60^th day of poisoning,the latency to escape of each group during the training period were no significant difference（P>0.05）,there was no significant difference in the latency to escape between the first day,second day and third day of training in the low-dose group（P>0.05）,the latency to escape in the fourth day of training was lower than the first day of training（F=1.392,P<0.05）.On days 8^th,30^th and 60^th of poisoning,there was no significant difference in the number of platform crossing of each group and percent time in target quadrant（P>0.05）.After PQ acute poisoning,the step down latency of the low-dose group was lower than that of the control group,but there was no statistically significant difference between each groups（P>0.05）.The error times of low-dose group was higher than the control group on the 8^th,30^th and 60^th days of poisoning,and the difference was statistically significant on the 60^th day of poisoning（F=3.947,P<0.05）;3.The neurons in the hippocampus were loosely arranged after acute PQ exposure.The nuclear pyknosis,edema and neuronophagocytosis were observed in the hippocampus and SN after acute PQ exposure.The number of neurons in the compact part of the SN increased in the low-dose group and decreased in the high-dose group;4.The number of Iba-1 positive cells in the hippocampus and striatum of the high-dose group increased on the 8^th day of acute PQ exposure.The number of Iba-1 positive cells in the hippocampus of the lowdose group on the 60^th day and the high-dose group on the 30^th day decreased（P<0.05）.The number of Iba-1 positive cells in the SN of the high-dose group increased on the 30^th and 60^th days.The average endpoints and process length of Iba-1 positive cells in the hippocampus of the high-dose group on the 8^th day of poisoning were lower than the control group,and the average process length of the low-dose group was lower than the control group（P<0.05）.The average process length in the hippocampus of the low and high-dose groups on the 60^th day of poisoning were lower than the control group（P<0.05）.The average process length in the high-dose group was lower than the control group（P<0.05）.The average endpoints of Iba-1 positive cells in the striatum of the low and high-dose groups on the 30^th day of poisoning were lower than the control group（P<0.05）.The average endpoints and process length of the high-dose group on the 60^th day of poisoning were lower than the control group,and the average process length of the low-dose group was lower than the control group（P<0.05）.The average process length in the SN of the low and high-dose groups on the 8^th day of poisoning were lower thanthe control group（P<0.05）.The average endpoints and process length in the SN of the low-dose group on the 30^th day of poisoning were lower than the control group,and the average process length of the high-dose group was lower than the control group（P<0.05）.The average endpoints and process length in the SN of the low-dose group on the 60^th day of poisoning were higher than the control and high-dose group（P<0.05）.5.On the 8^th day after acute PQ exposure,the Arg-1 expression in the hippocampus of the high-dose group and the i NOS expression in the low-dose group were no significant difference with the control group（P>0.05）.On the 30^th day of exposure,the expression of Arg-1 in the hippocampus of the high-dose group was lower than the control and low-dose groups,and the expression of i NOS in the low-dose group was lower than the control group（P<0.05）.On the 60^th day of exposure,the expressions of Arg-1 and i NOS in the hippocampus of the low and high-dose groups were not significantly different from the control group（P>0.05）.The expression of Arg-1 in the striatum of the high-dose group was higher than the control and low-dose group on the 8^th day of poisoning（P<0.05）.The expression of Arg-1 in the striatum of the low-dose groups was higher than the control and high-dose groups on the 30^th day of poisoning（P<0.05）.The expression of i NOS in the low and high-dose groups were not significantly different from the control group（P>0.05）.The expression of Arg-1 in the striatum of the low and highdose groups were lower than the control group on the 60^th day of poisoning（P<0.05）.The expression of Arg-1 in the SN of the high-dose group was higher than the control and low-dose group on the 8^th day of poisoning（P<0.05）.The expression of Arg-1 in the SN of the low-dose group was higher than the control and high-dose groups on the 30^th day of poisoning（P<0.05）.The expression of i NOS in the SN of the high-dose group was higher than the low-dose group on the 30^th day of poisoning（P<0.05）.The expression of Arg-1 and i NOS in the SN of the high-dose group on the 60^th day of poisoning were higher than the control and low-dose groups（P<0.05）.Conclusions:1.Acute PQ poisoning may damage the learning and memory ability of rats.2.Acute PQ poisoning can cause nuclear shrinkage,edema,and neuron-phasing in neurons of the hippocampus,striatum,and substantia nigra in the rat brain.3.After acute PQ poisoning,microglia in hippocampus,striatum and substantia nigra were proliferated and activated,and polarization phenotypes were changed.