The Exploration On The Rapid Antidepressant Action Of Ifenprodil: A NR2B-subunit Containing NMDA Receptor Antagonist

[Background and Objective] Mood disorders,particularly depression,are the most prevalent and costly mental diseases in modern societies.The number of patients suffering from depression is constantly growing,and the classic antidepressants that modulate monoaminergic systems are not sufficiently effective and require long systematic application.Recent studies suggest that substances that modulate glutamatergic system in CNS may produce antidepressant effects which are not only faster but also more sustained.Hence,a steady accumulation of evidence supporting a role for the excitatory amino acid neurotransmitter glutamate and its receptors in the treatment of depression have been reported in the recently years.Stress and depression are associated with neuronal atrophy,as well as decreased synaptic connections in the prefrontal cortex and limbic brain regions.Excitatory amino acid and monoamine neurotransmitter are extensively colocalized in brain nucleus relevant for depressive psychopathology.Glutamate induced over-activation of extra-synaptic NMDA receptors in the hippocampus plays an important role in the etiology of depression and high levels of glutamate may be responsible for the high incidence of comorbid depression.In 2000,reports from the robust and long lasting antidepressant effects of ketamine had launched investigations into a variety of agents that target at glutamatergic system in treatment major depressive disorder(MDD).In 2018,a research team from Zhejiang University reported that ketamine reduced neuronal bursting by blocking N-methyl-D-aspartate receptors(NMDARs)in the ‘anti-reward center’,lateral habenular(LHb),and then,relieved the suppression break onto the “reward center” to combat depression.This research which has been published by ‘nature’,represented the highest achievement in the field of antidepressant mechanisms of ketamine.However,the mechanisms underpin the potent antidepressant efficacy of ketamine is still under debate.In spite of that,emerging evidences indicated that N-methyl-D-aspartic acid receptor(NMDAR)antagonists andα-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor(AMPAR)agonists have antidepressant properties.It has been discussed that subtype selective,rather than pan blockers of the NMDA receptors,could maintain the efficacious profile and minimize the adverse effects during blocking this receptor.Previous studies showed that antagonists which selectively target at NR2 B subunit exerted anti-depressive behavioral effects in certain depression animal model,such as the chronic variable stress mouse model and chronic social defeat stress mouse model.In this regard,NR2B-contaning NMDA receptors have attracted greater attention.Therefore,in this study,we explored the potential rapid antidepressant mechanisms of ifenprodil: a selective NR2B-contaning NMDA receptor antagonist.[Methods and results]1.Evaluate the depressive-like behaviors of Chronic unpredictable mild stress(CUMS)rats after ifenprodil administration.After identification of CUMS rat model,ifenprodil were administrated intraperitoneally(3mg/kg)and behavioral tests were conducted at 2 hours,6 hours and 24 hours postadministration respectively.The results indicated that ifenprodil rapidly ameliorated depressive-like behaviors.2.Test the glutamate levels in the hippocampus,detect alterations of downstream cellular signaling and synaptic plasticity associated molecules after ifenprodil treatment.1)Test the glutamate levels of hippocampus by microdialysis.The result indicated that glutamate level increased after CUMS paradigm.2)Detect the changes of m TOR signaling,as well as the expression of BDNF and activated e EF2 via immunoprecipitation.The results indicated that ifenprodil rapidly activated m TOR pathway,promoted the expression of BDNF and activated e EF2.3.Explore the regulatory effect of ifenprodil on the CUMS-induced inflammatory response via analyzing pro-inflammatory cytokines.1)Observe the CUMS-induced morphological changes of microglia via immunohistochemistry,and detect levels of pro-inflammatory cytokines by ELISA.The result indicated that CUMS over-activated microglia cells,which represented by increase in microglia numbers,enlargement of the soma and shortened processes.The levels of hippocampal pro-inflammatory cytokines increased in CUMS rats.2)Detect the influence on pro-inflammatory cytokines by ifenprodil administration.The results showed that ifenprodil down regulated levels of IL-1β、IL-6 and TNF-α in CUMS rats hippocampus.Ifenprodil may regulated those cytokines via enhancing the expression of CX3CL1.[Main conclusions]1.Selective NR2 B subunit antagonist ifenprodil rapidly ameliorated depressive-like behaviors in CUMS rats.2.Ifenprodil rapidly activated m TOR pathway and promoted the expression of synaptic plasticity associated proteins in hippocampus of CUMS rats.3.Ifenprodil down regulated levels of hippocampal IL-1β,IL-6 and TNF-α in hippocampus of CUMS rats possibly through enhance chemokine CX3CL1 expression.