| Background:Major depressive disorder(MDD)is a devastating mental disorder.Clinical antidepressant drugs used presently have many setbacks such as low efficiency and high relapse.MDD patients need new antidepressant drugs with high efficiency and rapid onset,which is satisfied by the emerging of metabotropic glutamate receptors 2/3(mGluR2/3)antagonists which are believed to have rapid antidepressant effect.However,its underlying mechanism is still under reseaech and the clinical researches are still in progress.Clinical research found the increase expression of mGluR2/3 in the frontal cortex of depression patients.It was also found the increase expression of mGluR2/3 with depression-like behavior in the PFC and hippocampus in depressive mouse model,however later application of mGluR2/3 antagonist could reverse the depression-like behavior.Preclinical research found that mGluR2/3 antagonists such as MGS0039 and LY341495 have been found to have a rapid and long-lasting antidepressant action.Also,the underlying rapid antidepressant mechanism of mGluR2/3 antagonists may similar to that of ketamine and scopolamine,however it under clear and need to be further studied.Clinical research also found that in the anterior cingulate cortex(ACC)the number of the interneurons expressing somatostatin(SST)was reduced,decreased SST m RNA levels and GABA(Gamma-amino-butyric Acid)concentration.Additionally,the concentration of GABA could be recovered after antidepressant treatment with the ease of depression behavior.There are numerous expression of GABAergic interneurons and mGluR2/3.Therefore,we hypothesize that the underlying rapid antidepressant mechanism of mGluR2/3 antagonists may exerted by regulating activity of GABAergic interneurons of the ACC region,especially the SST interneurons.In this work,polymerase chain reaction(PCR),patch clamp,Immunohistochemistry and forced swimming test were used to study the effect of mGluR2/3 agonist(DCG-IV)and mGluR2/3 antagonist(LY341495)on the excitatory and inhibitory synaptic transmission in SST interneurons and PV interneurons.Our study provide insight into how mGluR2/3 activity affects the synaptic activities in interneurons in the ACC,which is crucial to understand the underlying mechanism of the rapid antidepressant action.Methods:1.The SST-cre or PV-cre mice were crossed with Ai9-RFP mice to obtain transgenic mice that SST or PV interneurons express red fluorescent(SST-RFP mice and PV-RFP mice).Also,we used immunostaining methods to further confirm coexpression of the RFP+ neurons with SST and PV antibodies.2.Whole-cell recordings were used to study the electrophysiological properties of SST interneurons and PV interneurons in the ACC region.3.Forced swimming test(FST)was used to test the drug effect of mGluR2/3antagonist LY341495 on behavior study.In this trial,the forced swim test was performed in four groups of male mice,adolescent C57BL/6J mice(P35-P50),adult C57BL/6J mice(P70),adolescent SST-RFP and PV-RFP transgenic mice(P35-P50).The change of immobile time was recorded after intraperitoneally(i.p.)administrated of LY341494(3 mg/kg).4.Whole-cell recordings were performed to record the synaptic transmission in SST interneurons and PV interneurons such as sEPSCs,mEPSCs,eEPSCs,sIPSCs,mIPSCs and eIPSCs.In this study,mGluR2/3 agonist DCG-IV(4 μM)and antagonist LY341495(2 μM)were used.Results:1.Immunohistochemical results showed that 80% neurons from RFP-expressing neurons in the ACC region of SST-RFP transgenic mice were co-expressed with SST antibody,and 81% neurons from RFP-expressing neurons in the ACC region of PVRFP transgenic mice were co-expressed with PV antibody.2.Compared to the control groups,30 min after i.p.administration of LY341495(3 mg/Kg)significantly reduced the immobility time in both adolescent(p < 0.0001,n= 11)and adult C57BL/6J mice(p < 0.0001,n = 10).Similar results were seen in SSTRFP(p = 0.0016,n = 8)and PV-RFP mice(p = 0.0006,n = 9).3.Bath application of DCG-IV which activate mGluR2/3 significantly reduced the frequency of sEPSCs and mEPSCs in SST interneurons(sEPSCs: p<0.04;mEPSCs:p = 0.046);mEPSCs: p = 0.75).Subsequent addition of LY341495 reversed the effect of DCG-IV on sEPSCs and mEPSCs.(sEPSCs: p<0.49;mEPSCs: p = 0.27).Moreover,DCG-IV reduced the amplitude of evoked EPSCs in SST interneurons(p < 0.0001),which was accomplished with a significant increase in the paired-pulse facilitation(p =0.028).Bath application of DCG-IV significantly reduced the frequency of sEPSCs and mEPSCs in PV interneurons(sEPSCs: p = 0.037;mEPSCs: p = 0.001).Subsequent addition of LY341495 reversed the effect of DCG-IV on sEPSCs and mEPSCs(sEPSCs:p = 0.58;mEPSCs: p = 0.27).Moreover,DCG-IV reduced the amplitude of evoked EPSCs in PV interneurons(p = 0.0002),which was accomplished with a significant increase in the paired-pulse facilitation(p = 0.028).Bath application of LY341495 which inactivate mGluR2/3 didn’t significantly affect the frequency and amplitude of sEPSCs and mEPSCs of SST interneurons.However,LY341495 significantly increased the amplitude of evoked EPSCs of SST interneurons(p = 0.005).The paired-pulse ratio was not significantly affected(p =0.083).Bath application of LY341495 didn’t significantly affect the frequency and amplitude of sEPSCs and mEPSCs of PV interneurons.However,LY341495 significantly increased the amplitude of evoked EPSCs of PV interneurons(p = 0.024).The paired-pulse ratio was not significantly affected(p = 0.35).4.In SST interneurons,bath application of DCG-IV had no significant effect on the frequency and amplitude of sIPSCs and mIPSCs.It also had no effect on eIPSCs and PPR.In PV interneurons,bath application of DCG-IV had no significant effect on the frequency and amplitude of sIPSCs and mIPSCs,also the amplitude of eIPSCs and PPR.Bath application of LY341495 didn’t affect the frequency and amplitude of sIPSCs in SST interneurons,but it had marginal significance after application of LY341495(p= 0.046)in mIPSCs,without affecting the amplitude.Also,it also had no effect on eIPSCs and PPR.In PV interneurons,bath application LY341495 had no effect on the frequency and amplitude of sIPSCs and mIPSCs.Also,it also had no effect on eIPSCs and PPR.Conclusion:1.We confirmed the effect of LY341495 on immobility time in the FST on our hands and it was consistent with previous reports.2.In SST interneurons and PV interneurons of the ACC regions,mGluR2/3agonist DCG-IV attenuated excitatory synaptic transmission.About the evoked synaptic transmission,it had also been decreased by DCG-IV with the increasing of PPR.mGluR2/3 antagonist LY341495 did not affect the excitatory synaptic transmission in both interneurons.However,about the evoked synaptic transmission in SST interneurons and PV interneurons,it could be enhanced by antagonism of mGluR2/3 without affecting the PPR.3.In SST interneurons and PV interneurons of the ACC regions,mGluR2/3agonist DCG-IV could not affect the inhibitory synaptic transmission.Also,mGluR2/3antagonist LY341495 did not impact the inhibitory synaptic transmission in both type of interneurons.4.Our results indicated that activity of mGluR2/3 primarily regulates the excitatory synapses in cortical SST interneurons and PV interneurons in the ACC,but the aim to understand the rapid antidepressant mechanism of LY341495 still needs further study. |
PDF Full Text Request