The Effect Of MTOR Pathway Mediated Kappa Opioid Receptor Agonists On PND In Rats After Cardiopulmonary Bypass

Objective:To observe the effects of κ-opioid receptor(KORs)agonists on cognitive function and mTOR pathway after cardiopulmonary bypass(CPB)in rats,and to explore possible protective mechanisms of kappa opioid receptor agonists on brain and cognitive function.Methods:40 adult male SD rats weighing 350 to 400g were randomly divided into four groups by random number table:sham operation group(group S),cardiopulmonary bypass group(group C).cardiopulmonary bypass+KORs ago?nists U50488H group(group U).cardiopulmonary bypass+KORs antagonist Nor-BNI+U50488H group(group N).Before operation.rats in each group were given water maze training for 5 days,four times a day.The aim was to unde-rstand the preoperative swimming and cognitive status of rats in each group a-nd to exclude the differences in preoperative cognitive function of rats in each group.In group S,only arteriovenous catheterization was performed without cardiopulmonary bypass.In group C,arteriovenous catheterization was performed with cardiopulmonary bypass for 1 hour.In group U.U50488H 1.5mg/kg was intravenously injected 30 minutes before CPB,the rest were same to group C.In group N,Nor-BNI 2mg/kg was intravenously injected 1 hour before CPB,the same as in group U.On the 3rd day after the successful establishment of the model.Morris water maze test was used to detect the cognitive function of rats.After deep anesthesia,rats were killed by bloodletting and hippocampus tissue was taken off on ice.TUNEL staining was used to observe the apopto-sis of hippocampal cells.ELISA was used to detect the content of Aβ.Western blot was used to detect the expression of p-mTOR.p-p70s6k and p-tau.Real-timePCR was used to detect the expression of mTOR.p70s6k and tau.SPSS 20.0 software was used for statistical analysis.The experimental data were ex-pressed as mean±standard deviation(x±s),Single factor analysis of variance was used for comparison between groups.and the differencewas statistically significant with P<0.05Result:1.Comparison of the results of water maze test in each group of rats after operation(1)Hidden platform training experimentCompared with group S.the average latency of finding hidden platform in group C.group U and group N was longer.and the difference was statistically significant(P<0.05).Compared with group C.the average latency of finding hidden platform in group U was significantly shorter(P<0.05).There was no significant difference in swimming speed between group N and group C(P>0.05).(2)Space exploration experimentsCompared with group S.the number of rats crossing the original platform of the targel quadrant in group C.U and N was significantly reduced.at the same time.the swimming distance and residence time were significantly shortened(P<0.05)Compared with group C.the number of rats crossing the original platform of the target quadrant in group U was increased.and the swimming distance and residence time of the target quadrant were also prolonged.The diference was statistically significant(P<0.05).but there was no significant difference between group N and group C(P>0.05)2.Comparison of p-tau expression and Aβ content in hippocampus tissue of rats in each groupCompared with group S.the expression of p-tau and the content of Aβ of hippocampus in group C_U and N increased significantly and the difference was statistically significant(P<0.05):compared with group C.the expression of p-tau and the content of Aβ in group U decreased and the difference was statistically significant(P<0.05),while there was no significant difference between group N and group C(P>0.05).3.Comparison of p-mTOR and p-p70s6k protein expression in hippocampus tissue of rats in each groupCompared with group S.the expression of p-mTOR and p-p70s6k of hippocampus in group C,U and N increased significantly and the difference was statistically significant(P<0.05).Compared with group C.the expression of p-mTOR and p-p70s6k in group U decreased significantly and the difference was statisticall)significant(P<0.05).while there was no significant difference between group N and group C(P>0.05)4.The comparison of mTORmRNA.p70S6kmRNA and taumRNA in hippocampus tissue of rats in each groupCompared with group S.the expression of mTORmRNA.p70S6kmRNA and taumRNA of hippocampus in group C,U and N increased significant]),and the difference was statistically significant(P<0.05).Compared with group C,the expression of mTOR,p70S6k and tau in group U decreased significantly and the difference was statistically significant(P<0.05).while there was no significant difference between group N and group C.(P>0.05)5.Comparison of TUNEL staining results of rats in each group hippocampus tissue Compared with group S.the hippocampal cell apoptosis of group C,U and N increased significantly and the difference was statistically significant(P<0.05)Compared with group C,the hippocampal cell apoptosis of group U decreased significantly and the difference was statistically significant(P<0.05).while there was no significant difference between group N and group C(P>0.05)Conclusion:1.Kappa opioid receptor agonists can improve PND in rats after CPB to a certain degree.2.Kappa opioid receptor agonists may play a protective role in cognitive function after CPB by inhibiting the mTOR signaling pathway and reducing the expression of tau and Aβ proteins in hippocampus.