| Objectives This study was designed to investigate the effects of propofol and low-dose ketamine on spatial learning and memory,long-term potentiation（LTP）,LTP induction threshold,N-methyl-D-aspartic acid receptor（NMDAR）mediated field excitatory postsynaptic potential(fEPSPNMDAR)and NMDAR I/O relation in depressive rats receiving electroconvulsive shock（ECS）,aiming to illuminate the mechanism of learning and memory impairment induced by ECS and neuroprotection of anesthetics based on the inner regulation of synaptic plasticity.MethodsPart IMale Sprague Dawley（SD）rats,aged 23 months,weigh 180250 g were used,and chronic unpredictable mild stress（CUMS）procedure was used to conducted a model of depressive rats.80 depressive rats were randomly divided into 5 groups（n=16）:group D,DE,DPE,DKE and DPKE.Another 16 healthy rats were regarded as group C.Group C were healthy rats without any treatment.Group D were treated with sham ECS combined with saline（8 ml/kg,intraperitoneally,（i.p.））.Group DE were treated with saline（8 ml/kg,i.p.）and then subjected to ECS.Group DPE were received propofol（80 mg/kg,i.p.）and then suffered ECS.Group DKE were given ketamine（10mg/kg,i.p.）and then treated with ECS.Group DPKE were treated with propofol（80 mg/kg,i.p.）combined with ketamine（10mg/kg,i.p.）and then subjected to ECS.The aforementioned treatments were conducted once daily for 7 days.Depressive behavior and spatial learning and memory were assessed by sucrose preference test and Morris water maze;field excitatory postsynaptic potential（fEPSP）and LTP induced by high-frequency stimulation in Schaffer collaterals-CA1 pathway synapses were also detectedPart IISD rats,aged 23 months,weigh 180250 g were used,and CUMS procedure was used to conducted a model of depressive rats.The groups and treatment in each group were the same as those in Part I.Expression of p-Thr305/306-CaMKⅡαin hippocampus were assessed by western-blot（n=6）;LTD and LTP induced by different frequency stimulation（more than 8slices for each stimulation protocol）and PTP in Schaffer collaterals-CA1pathway synapses（n=6）were also recorded.Part IIISD rats,aged 23 months,weigh 180250 g were used,and CUMS procedure was used to conducted a model of depressive rats.The hippocampal slices from 6 depressive rats were made and fEPSPNMDARMDAR were tested with different intensity of electrical stimulation.The hippocampal slices from 30 depressive rats were made and perfused with different agents under 0.4 mA electrical stimulation simulated ECS:with propofol perfusion（n=6）;with intralipid perfusion（n=6）;with propofol combined with bicuculline perfusion（n=6）;low-dose ketamine perfusion（n=6）;low-dose ketamine combined with propofol perfusion（n=6）.The fEPSPNMDAR before,during and after perfusion in the aforementioned groups were detected.Another hippocampal slices from 30 depressive rats were divided into 5groups:D,De,Dpe,Dke and Dpke.6 hippocampal slices from healthy rats were regarded as group C.Group C and D indicated healthy and depressive slice,respectively.Group De indicated depressive slice were treated with preconditioning（an analog of ECS in slice）;group Dpe indicated depressive slice were treated with preconditioning with propofol perfusion;group Dke indicated depressive slice were treated with preconditioning with low-dose ketamine perfusion;group Dpke indicated depressive slice were treated with preconditioning with propofol and low-dose ketamine perfusion.NMDAR input/output relation were assessed after agents elution.ResultsPart I（1）Compared with group C,SPP of group D,DE,DPE,DKE and DPKE were lower after CUMS（P<0.05）.Compared with group D,SPP of group DE,DPE,DKE and DPKE were higher after ECS（P<0.05）.SPP of group DPE was lower than that of group DE（P<0.05）.Compared with group DPE,SPP of group DKE and DPKE were higher（P<0.05）.There was no statistical difference in the comparison of SPP among group DE,DKE and DPKE（P>0.05）.（2）No difference of swimming speed was observed（P>0.05）.Compared with group C,all groups after CUMS exhibited longer escape latency and shorter space exploration time（P<0.05）.Compared with group D,escape latency was longer and space exploration time was shorter in group DE,DPE and DKE（P<0.05）.Compared with group DE,escape latency was shorter and space exploration time was longer in group DPE,DKE and DPKE（P<0.05）.No difference was found in the comparison of escape latency and space exploration time between group DPE and DKE（P>0.05）.Escape latency and space exploration time of group DPKE was shorter and longer than those of group DPE and DKE,respectively（P<0.05）.No interaction was found for the neuroprotection of propofol and ketamine（P>0.05）.（3）Compared with group D,baseline fEPSP of group DE,DPE,DKE and DPKE was higher（P<0.05）.Baseline fEPSP of group DE was higher than that of group DPE（P<0.05）.No difference was observed in the comparison of baseline fEPSP among the group DE,DKE and DPKE（P>0.05）.（4）Compared with group C,LTP of all groups after CUMS were decreased（P<0.05）.Compared with group D,LTP of group DE,DPE and DKE were decreased（P<0.05）.Compared with group DE,LTP of group DPE,DKE,DPKE were increased（P<0.05）.LTP of group DPKE was higher than that of group DPE and DKE（P<0.05）.Part II（1）Compared with group C,expression of p-Thr305/306-CaMKⅡαin hippocampus of all groups after CUMS were higher（P<0.05）.Compared with group D,expression of p-Thr305/306-CaMKⅡαin hippocampus of group DE,DPE and DKE were higher（P<0.05）.Compared with group DE,expression of p-Thr305/306-CaMKⅡαin hippocampus of group DPE,DKE and DPKE were lower（P<0.05）.Expression of p-Thr305/306-CaMKⅡαin hippocampus of group DPKE was lower than that of group DPE and DKE（P<0.05）,however,no difference was found when compared with group D（P>0.05）.（2）LTP induction threshold point were 1020 Hz,around 20 Hz,5080Hz,4050 Hz,4050 Hz,2040 Hz for group C,D,DE,DP,DK and DPKE,respectively.（3）Compared with group C,PTP of all groups after CUMS was decreased（P<0.05）.Compared with group D,PTP of group DE,DPE and DKE were decreased（P<0.05）.Compared with group DE,PTP of group DPE,DKE and DPKE was increased（P<0.05）.PTP of group DPKE was higher than that of group DPE and DKE（P<0.05）,however,no difference was found when compared with group D（P>0.05）.Part III（1）The slope of fEPSPNMDAR was gradually increased with the increase of intensity of electrical stimulation,fEPSPNMDAR could be successfully evoked when the intensity was set as 0.4 mA for the slice.10%intralipid perfusion had no influence on fEPSPNMDAR（P>0.05）.fEPSPNMDAR induced by 0.4 mA current was inhibited partly by propofol perfusion with 20μM（P<0.05）,however,bicuculline（50μM）almost reversed the inhibitory effect of propofol on fEPSPNMDAR（P>0.05）.Besides,fEPSPNMDAR induced by 0.4mA current was inhibited partly by ketamine perfusion with 10μM（P<0.05）.Further,fEPSPNMDAR was nearly vanished with propofol combined ketamine perfusion（P<0.05）.No interaction was found for the inhibition of fEPSPNMDARMDAR of propofol and ketamine（P>0.05）.（2）In the model of ECS for slice,NMDAR I/O of other groups were decreased when compared with group C（P<0.05）.Compared with group D,NMDAR I/O of group De,Dpe,Dke were decreased（P<0.05）.Compared with group De,NMDAR I/O of group Dpe,Dke and Dpke were increased（P<0.05）.NMDAR I/O of group Dpke was higher than that of group Dpe and Dke（P<0.05）,however,no difference was found when compared with group D（P>0.05）.Conclusions（1）Propofol and low-dose ketamine can regulate metaplasticity,and make a difference to synaptic plasticity,so as to alleviating LTP and learning and memory impairment.（2）The neuroprotection of propofol and ketamine is mediated by up-regulating NMDAR function consist with LTP induction threshold decrease due to partial inhibition on NMDAR activation.Further,the inhibitory effect of propofol on NMDAR activation is conducted via activating GABAAR.（3）Propofol combined with low-dose ketamine conducts the best neuroprotective performance because of the complete inhibition on NMDAR activation induced by ECS. |
