Fluoxetine Exerts Anxiolytic And Antidepressive Effects Via Down-regulating NNOS-CAPON Coupling In The Hippocampus

Anxiety and depression are highly prevalent neuropsychiatric diseases which have serious social harmfulness on individual physical and mental health.Numerous reports showed that aggravated anxiety and depression contribute to suicide attempt and suicidal ideation.The selective serotonin reuptake inhibitors（SSRIs）of antidepressants,especially fluoxetine（FLX）,are the most commonly prescribed drug for the treatment of anxiety and depression.It exerts its therapeutic effects through inhibiting serotonin reuptake transporters（SERT）on presynaptic neurons which leads to an enhanced serotonergic neurotransmission.However,clinical reports indicate that its efficacy is incomplete and variable for less than 60%of patients show a significant response.Besides,anxiolytic and antidepressive effects of FLX occur several weeks after treatment.Although many authors explained the molecular and cellular mechanisms underlying the anxiolytic and antidepressive effects of fluoxetine,more research is needed.nNOS（neuronal Nitric Oxide Synthase）is the major nitric oxide synthase of central nervous system.Series of studies of our research group have shown that nNOS plays an important role in the regulation of anxiety and depression.As an important attached protein of nNOS,CAPON was identified to contribute to many psychiatric illnesses,including PTSD（Post-traumatic Stress Disorder）,bipolar disorder and schizophrenia.Increased CAPON expression was observed in the prefrontal cortex of patients with schizophrenia and bipolar disorder,which suggesting a probable role of CAPON in neuropsychiatric diseases.Our previous results showed that hippocampal nNOS-CAPON coupling can be used as a target for developing new anxiolytics.Augmenting nNOS-CAPON interaction produced anxiolytic effects,while dissociating CAPON from nNOS can reverse chronic stress-induced anxiogenic behaviors.What’s more,hippocampal synaptic plasticity and Dexras1-p-ERK signaling play a crucial role in nNOS-CAPON binding regulating anxiety-related behaviors.There are studies showing that 5-HT modulating the expression of nNOS via 5-HT1AR.On the basis of the above research,the project intends to explore whether FLX exerts anxiolytic and antidepressive effects by regulating nNOS-CAPON coupling in hippocampus.Firstly,mice were subjected to chronic mild stress and chronic CORT exposure to induce anxiogenic-like and depressive-like phenotype.Meantime,we intraperitoneally administered FLX to mice at a dose of10mg kg^-1 d^-1 for 28d.We found that mice treated with FLX displayed anxiolytic and antidepressive behaviors.And increasing expression and association of nNOS and CAPON in hippocampus reduced by CMS can be markedly reversed.Consistent with previous reports,FLX remarkably increased 5-HT level in the hippocampus of mice exposed to CMS.Furthermore,we used 5-HT,selective 5-HT1AR agonist（8-OH-DPAT）and selective 5-HT1AR antagonist（NAN-190）to observe the regulation of serotonin system on the expression and coupling of nNOS and CAPON in vivo and in vitro.We found that 5-HT and 8-OH-DPAT dramatically down-regulated the expression and interaction of nNOS and CAPON in vivo and in vitro,while NAN-190 exerts notably up-regulated effects.Moreover,NAN-190 reversed uncoupler-induced interaction of nNOS with CAPON in the hippocampus and behavioral modifications.Finally,we explored the molecular mechanisms of FLX reversing nNOS-CAPON expression and interaction reduced by chronic sress.More importantly,we found that FLX reversed chronic stress-induced NF-κB signalling activation.In sum,our data highlight the importance of 5-HT1AR in mediating the regulation of FLX on the expression and interaction of nNOS and CAPON in hippocampus,and FLX exerts anxiolytic and antidepressive effects via down-regulating nNOS-CAPON coupling in the hippocampus.