The Role Of Glu/GABA-Gln Metabolic Cycle In The Mechanism Of The Synergistic Effects Of Low-Dose Ketamine Combined With Propofol On The Antidepressant Efficacy Of ECT

Objective Electroconvulsive therapy (ECT) is one of the mosteffective treatments in severe or drug-resistant depression. However, itsremission rate is still lower than expected. In the present study, weevaluated a possible improvement effect of low-dose ketamine combinedwith propofol on the therapeutic effectiveness of electroconvulsivestimulation (ECS, an animal model of electroconvulsive therapy) in ratsunderwent chronic unpredictable mild stress (CUMS, an animal model ofdepression), and investigated the effects of low-dose ketamine combinedwith propofol on the expression of GAD65, GAD67and GS in theprefrontal cortex of CUMS-exposure rats receiving ECS.Methods The present study includes two parts.Part I Fifty male Sprague-Dawley (SD) rats (aged7weeks),weighing220±20g, were randomly divided into5groups (n=10for eachgroup): the control group (no intervention), the propofol+depressiongroup (group PD), the ketamine+propofol+depression group (group KPD), the ketamine+propofol+depression+ECS group (group KPDE),and the propofol+depression+ECS group (group PDE). The depressionmodel was established by chronic unpredictable mild stress (CUMS) ingroups PD, KPD, KPDE and PDE. Following28d of CUMS exposure,groups PD and KPD received mock ECS after intraperitoneal propofol100mg/kg and ketamine10mg/kg+propofol80mg/kg respectively,andgroups KPDE and PDE received ECS after intraperitoneal injection ofketamine10mg/kg+propofol80mg/kg and propofol100mg/kgrespectively once a day for7consecutive days. Depressive behaviors wereassessed by a sucrose preference test on days1,37and52and an openfield test on days2,38and53. Learning and memory were evaluated by aMorris water maze test on days3,39and54.Part II Seventy five male SD rats (aged7weeks), weighing22020g, were randomly divided into5groups (n=15for each group): thecontrol group (no intervention), the propofol+depression group (groupPD), the ketamine+propofol+depression group (group KPD), theketamine+propofol+depression+ECS group (group KPDE), and thepropofol+depression+ECS group (group PDE). The intervention protocolof Part II was same as Part I, and conducted simultaneous. The meandensity of GAD65and GAD67in the prefrontal cortex was detected byimmunofluorescence staining. The mean density of GS in the prefrontalcortex was detected by immunohistochemistry. The expression of GAD65, GAD67and GS mRNAs in prefrontal cortex was assessed throughRT-PCR.ResultsPart ISucrose preference test Compared with the control group, asignificant difference in SCP of groups PD, KPD, KPDE and PDE wasfound at different time (P <0.05). No significant difference in SCP amongall groups was observed on day1(P>0.05). CUMS was found to induce asignificant decrease in SCP of groups PD, KPD, KPDE and PDE on day37following28day of CUMS exposure compared with the control group (P <0.05). On day52, a significant increase in SCP of groups KPDE and PDEwas found compared with the group PD or KPD (P <0.05). At the sametime, the animals of group KPDE showed SCP levels higher than theanimals of group PDE, but lower than control group ones (P <0.05).Open field test Compared with the control group, a significantdifference in total distance traveled and rearing scores of groups PD, KPD,KPDE and PDE was found at different time (P <0.05). No significantdifference in total distance traveled and rearing scores was observed amongall five groups on day2(P>0.05). Compared with the control group,CUMS exposure significantly decreased total distance traveled and rearingscores in groups PD, KPD, KPDE and PDE on day38following28d ofCUMS exposure (P <0.05). On day53, a significant increase in total distance traveled and rearing scores of groups KPDE and PDE was foundcompared with group PD or KPD (P <0.05). At the same time, the animalsof group KPDE showed significant increases in total distance traveled andrearing scores compared with the ones of group PDE (P <0.05); however,these remained lower than those of the control group (P <0.05).Morris water maze test Compared with the control group, asignificant difference in the escape latency and the duration of targetquadrant (staying at the original platform quadrant) of groups PD, KPD,KPDE and PDE was found at different time (P <0.05). No significantdifference in escape latency and duration of target quadrant was observedamong all five groups on day3(P>0.05). Compared with the controlgroup, the escape latency of groups PD, KPD, KPDE and PDE wasprolonged on day39following28d of CUMS exposure (P <0.05).However, there was no significant deference in duration of target quadrantamong all five groups at the same time. On day54, a significant increase inescape latency and a significant decrease in duration of target quadrant ingroups KPDE and PDE were found compared with group PD or KPD (P <0.05). At the same time, the animals of group KPDE showed a significantdecrease in the escape latency and a significant increase in duration oftarget quadrant compared with the ones of group PDE (P <0.05).Part IIImmunofluorescence Compared with the control group, a significant decrease in the mean density of GAD65and GAD67in theprefrontal cortex was determined in groups PD, KPD, KPDE and PDE (P <0.05). Compared with group PD or KPD, a significant increase in the meandensity of GAD65and GAD67was found in groups KPDE and PDE (P <0.05). The animals of group KPDE showed a significant increase in themean density of GAD65compared with the ones of group PDE (P <0.05).However, there was no significant deference in the mean density of GAD67beween groups KPDE and PDE (P>0.05).Immunohistochemistry Compared with the control group, asignificant decrease in the mean density of GS in the prefrontal cortex wasdetermined in groups PD, KPD, KPDE and PDE (P <0.05). Comparedwith group PD or KPD, a significant increase in the mean density of GSwas found in group KPDE (P <0.05). The animals of group KPDE showeda significant increase in the mean density of GS compared with the ones ofgroup PDE (P <0.05). However, there was no significant deference in themean density of GS among groups PD, KPD and PDE (P>0.05)RT-PCR Compared with the control group, a significant decrease inthe mRNA levels of GAD65, GAD67and GS in the prefrontal cortex wasdetermined in groups PD, KPD, KPDE and PDE (P <0.05). Comparedwith group PD or KPD, significant increases in the mRNA levels ofGAD65and GAD67in groups KPDE and PDE and the mRNA level of GSin group KPDE were found (P <0.05). The animals of group KPDE showed significant increases in the mRNA levels of GAD65and GScompared with the ones of group PDE (P <0.05). However, there was nosignificant deference in the mRNA level of GAD67beween groups KPDEand PDE (P>0.05).Conclusions(1) CUMS can induce distinctive depressive behaviors, that is, deficitsin tests measuring anhedonia and loss of interest. In addition, CUMSimpaires learning ability but does not affect memory ability.(2) Anesthesia of low-dose ketamine combined with propofol in ECScould provide a highly potent synergistic antidepressant effects, as well asimprove the impairment of learning and memory induced by ECScompared with propofol anesthesia.(3) The depressive behaviors induced by CUMS may be associatedwith decreases in the expression of neuronal GAD65, GAD67and glial GSin the prefrontal cortex. These deficits in Glu/GABA-Gln cycle could causemetabolic imbalance between Glu and GABA, which result in neuralexcitotoxicity and abnormalities in neuroplasticity.(4) Low-dose ketamine combined with propofol can increase theexpression of GAD65and GS in the prefrontal cortex, and normalize themetabolic imbalance between Glu and GABA as a result, which isimplicated in its mechanisms of enhancing the efficacy of ECS.