Glycine site N-methyl-D-aspartate receptor antagonist 7-CTKA produces rapid antidepressant-like effects in male rats

Dynamic regulation of phosphorylation of NMDA receptor GluN2B subunit tyrosine residues mediates ketamine rapid antidepressant effects

The rapid antidepressant effects of ketamine depend on the N-methyl-D-aspartate (NMDA) receptor containing 2B subunit (NR2B), whose function is influenced by its phosphorylated regulation and distribution within and outside synapses. It remains unclear if ketamine's rapid onset of antidepressant effects relies on the dynamic phosphorylated regulation of NR2B within and outside synapses. Here, we show that ketamine rapidlyalleviated depression-like behaviors and normalized abnormal expression of pTyr1472NR2B and striatal-enriched protein tyrosine phosphatase (STEP) 61 within and outside synapses in the medial prefrontal cortex (mPFC) induced by chronic unpredictable stress (CUS) and conditional knockdown of STEP 61, a key phosphatase of NR2B, within 1 hour after administration Together, our results delineate the rapid initiation of ketamine's antidepressant effects results from the restoration of NR2B phosphorylation homeostasis within and outside synapses. The dynamic regulation of phosphorylation of NR2B provides a new perspective for developing new antidepressant strategies.

Sex- and suicide-specific alterations in the kynurenine pathway in the anterior cingulate cortex in major depression

Major depressive disorder (MDD) is a serious psychiatric disorder that in extreme cases can lead to suicide. Evidence suggests that alterations in the kynurenine pathway (KP) contribute to the pathology of MDD. Activation of the KP leads to the formation of neuroactive metabolites, including kynurenic acid (KYNA) and quinolinic acid (QUIN). To test for changes in the KP, postmortem anterior cingulate cortex (ACC) was obtained from the National Institute of Health NeuroBioBank. Gene expression of KP enzymes and relevant neuroinflammatory markers were investigated via RT-qPCR (Fluidigm) and KP metabolites were measured using liquid chromatography-mass spectrometry in tissue from individuals with MDD (n = 44) and matched nonpsychiatric controls (n = 36). We report increased IL6 and IL1B mRNA in MDD. Subgroup analysis found that female MDD subjects had significantly decreased KYNA and a trend decrease in the KYNA/QUIN ratio compared to female controls. In addition, MDD subjects that died by suicide had significantly decreased KYNA in comparison to controls and MDD subjects that did not die by suicide, while subjects that did not die by suicide had increased KYAT2 mRNA, which we hypothesise may protect against a decrease in KYNA. Overall, we found sex- and suicide-specific alterations in the KP in the ACC in MDD. This is the first molecular evidence in the brain of subgroup specific changes in the KP in MDD, which not only suggests that treatments aimed at upregulation of the KYNA arm in the brain may be favourable for female MDD sufferers but also might assist managing suicidal behaviour.

Anxiolytic and antidepressant like effects of Zamzam water in STZ-induced diabetic rats, targeting oxidative stress, neuroinflammation, BDNF/ERK/CREP pathway with modulation of hypothalamo-pituitary-adrenal axis

Introduction

Recent studies have reported a strong relationship between diabetes and anxiety- and depression-like behaviors; however, there is a lack of information on the underlying pathophysiology. Alkaline Zamzam water (ZW), which is rich in several trace elements, has neuroprotective properties. This study aimed to investigate the anxiolytic and antidepressant effects of ZW against diabetes-induced behavioral changes and shed light on the possible underlying mechanisms.

Methods

Forty-eight rats were divided into four experimental groups (n = 12): group I (control group), group II (Zamzam water group), group III (diabetic group), and group IV (diabetic + Zamzam water group). Diabetes was induced by an intraperitoneal injection of 60 mg/kg streptozotocin (STZ). At the end of the experiment, the forced swimming test (FST) was used to assess depression-like effects. The elevated plus maze test (EPMT) and open field test (OFT) were performed to evaluate anxiety-like behavior. Blood levels of the hypothalamic-pituitary-adrenal (HPA) axis were measured, and prefrontal cortex and hippocampal tissue samples were removed for histological, immunohistochemical, ELISA, and Q-PCR analyses.

Results

ZW significantly decreased the immobility time in the FST, indicating an antidepressant effect (p < 0.001). Additionally, ZW significantly improved the OFT and open field entry (OFE) percentages in the EPMT, increasing center crossing and decreasing grooming and fecal boli in the OFT. This indicated an anxiolytic-like effect in diabetic rats with histological improvement. Interestingly, ZW significantly increased prefrontal cortical and hippocampal levels of antioxidant enzymes and the Nrf2/HO-1 pathway. It also modulated the HPA axis by increasing cortisol and corticotropin-releasing hormone (CRH) levels, with a decrease in ACTH and an increase in monoamine neurotransmitters. Furthermore, diabetic rats that received ZW showed a decrease in the inflammatory markers TNF-α and GFAP by immunohistochemistry and in the mRNA levels of NFκB, IL-1β, and IL6. In addition, ZW downregulated the expression of the BDNF/ERK2/CREP pathway.

Conclusion

Our results suggested a neuroprotective effect of ZW against diabetes-induced anxiety- and depression-like behaviors and explored the underlying mechanisms. These findings suggest a promising therapeutic strategy for patients with diabetes who experience anxiety and depression.

Fast-onset effects of Pseudospondias microcarpa (A. Rich) Engl. (Anacardiaceae) hydroethanolic leaf extract on behavioral alterations induced by chronic mild stress in mice

INTRODUCTION

Pseudospondias microcarpa (Anacardiaceae) is a plant widely used traditionally for treating various central nervous system disorders. A previous study in our laboratory confirmed that the hydroethanolic leaf extract (PME) of the plant produces an antidepressant-like effect in rodent models of behavioral despair. However, its effect on depressive-like behavior induced by chronic mild stress (CMS) and its time course of action are still unknown. In this context, the long-term effects of PME on cognitive function and depressive- and anxiety-like behavior caused by CMS were assessed.

METHODS

Male ICR mice were exposed to CMS for nine weeks and anhedonia was evaluated by monitoring sucrose intake (SIT) weekly. PME (30, 100, or 300 mg kg-1) or fluoxetine (FLX) (3, 10, or 30 mg kg-1) was administered to the mice during the last six weeks of CMS. Behavioral tests-coat state, splash test, forced swimming test (FST), tail suspension test (TST), elevated plus maze (EPM), open field test (OFT), novelty suppressed feeding (NSF), EPM transfer latency, and Morris water maze (MWM)-were performed after the nine-week CMS period.

RESULTS

When the mice were exposed to CMS, their SIT and grooming behavior reduced (splash test), their coat status was poor, they became more immobile (FST and TST), more anxious (OFT, EPM, and NSF), and their cognitive function was compromised (EPM transfer latency and MWM tests). Chronic PME treatment, however, was able to counteract these effects. Additionally, following two (2) weeks of treatment, PME significantly boosted SIT in stressed mice (30 mg kg-1, P<0.05; 100 mg kg-1, P<0.05; and 300 mg kg-1, P<0.001), as compared to four (4) weeks of treatment with FLX.

CONCLUSION

The present findings demonstrate that PME produces a rapid and sustained antidepressant-like action and reverses behavioral changes induced by chronic exposure to mild stressors.

Antidepressants in the post-ketamine Era: Pharmacological approaches targeting the glutamatergic system

The efficacy of currently available medications for depression is unsatisfactory, and that has spurred the development of novel antidepressants based on a hypothesis other than the monoamine hypothesis. Recent studies have revealed the importance of the glutamatergic system as a drug target for depression, and the validity of this hypothesis has been underpinned by the discovery of the antidepressant effects of ketamine, leading to the market launch of Spravato® nasal spray which delivers (S)-ketamine (esketamine). However, both ketamine and esketamine have unwanted adverse effects that hinder their routine use in daily practice. Extensive studies have elucidated the mechanisms underlying the antidepressant effects of ketamine, and that has encouraged numerous drug discovery activities to search for agents that retain a ketamine-like antidepressant profile but with lesser adverse effect liabilities. The discovery activities have included attempts to identify 1) the active substance(s) in the circulation after ketamine administration and 2) agents that act on the proposed mechanisms of action of ketamine. Clinical trials of agents discovered in the course of these activities are underway, and in 2022, AUVELITY™ (AXS-05; dextromethorphan with bupropion) was approved by the United States Food and Drug Administration. Drug development of post-ketamine agents should provide novel antidepressants that are safer, but as potent and rapidly acting as ketamine.

L-4-Fluorophenylglycine produces antidepressant-like effects and enhances resilience to stress in mice

D-serine has attracted increasing attention for its possible role in depression. L-4-Fluorophenylglycine (L-4FPG), an inhibitor of the neutral amino acid transporter ASCT1/2, has been shown to regulate extracellular D-serine levels. The present study aimed to explore the potential antidepressant effects of L-4FPG. First, the acute effects of L-4FPG on the forced swimming test, elevated plus maze test, and novelty-suppressed feeding test were examined. L-4FPG showed antidepressant-like effects, which could be reversed by rapamycin, a mammalian target of rapamycin (mTOR) inhibitor, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor antagonist. The phosphorylation levels of mTOR and GluR1 in the hippocampus were also increased after L-4FPG treatment. Next, the therapeutic effects of L-4FPG were examined in a chronic social defeat stress (CSDS) model of depression. L-4FPG ameliorated depression-like behaviors in mice subjected to CSDS. Furthermore, treatment with L-4FPG prior to each social defeat stress session not only decreased defensive behaviors but also prevented CSDS-induced social avoidance and anxiety-like and depression-like behaviors. These findings suggest that L-4FPG may be useful not only in alleviating depression but also in protecting against chronic stress-related psychiatric disorders.

The trilateral interactions between mammalian target of rapamycin (mTOR) signaling, the circadian clock, and psychiatric disorders: an emerging model

Circadian (~24 h) rhythms in physiology and behavior are evolutionarily conserved and found in almost all living organisms. The rhythms are endogenously driven by daily oscillatory activities of so-called "clock genes/proteins", which are widely distributed throughout the mammalian brain. Mammalian (mechanistic) target of rapamycin (mTOR) signaling is a fundamental intracellular signal transduction cascade that controls important neuronal processes including neurodevelopment, synaptic plasticity, metabolism, and aging. Dysregulation of the mTOR pathway is associated with psychiatric disorders including autism spectrum disorders (ASD) and mood disorders (MD), in which patients often exhibit disrupted daily physiological rhythms and abnormal circadian gene expression in the brain. Recent work has found that the activities of mTOR signaling are temporally controlled by the circadian clock and exhibit robust circadian oscillations in multiple systems. In the meantime, mTOR signaling regulates fundamental properties of the central and peripheral circadian clocks, including period length, entrainment, and synchronization. Whereas the underlying mechanisms remain to be fully elucidated, increasing clinical and preclinical evidence support significant crosstalk between mTOR signaling, the circadian clock, and psychiatric disorders. Here, we review recent progress in understanding the trilateral interactions and propose an "interaction triangle" model between mTOR signaling, the circadian clock, and psychiatric disorders (focusing on ASD and MD).

GluN2A-ERK-mTOR pathway confers a vulnerability to LPS-induced depressive-like behaviour

Inflammation plays a key role in the pathogenesis of the major depressive disorder. Namely, neuroinflammation can induce the production of neuroactive metabolites that interfere with N-methyl-D-aspartate receptors (NMDAR)-mediated glutamatergic neurotransmission and contribute to depressive-like behaviour. On the other hand, mammalian target of rapamycin (mTOR) activity with synaptogenic effects is the main mediator of antidepressant effects of several potent NMDAR antagonists. In this study, we investigated the specific role of GluN2A subunits of NMDAR on the activity of mTOR signaling and behaviour in lipopolysaccharide (LPS)-induces model of depression. The results showed that mice lacking GluN2A subunit did not display depressive-like behavior after the immune challenge, opposite to LPS-treated wild-type mice. Specifically, in GluN2A knockout mice, we estimated the activity of the mTOR pathway in the hippocampus and prefrontal cortex (PFC) by measuring synaptic levels of upstream regulators (p-Akt, p-ERK, and p-GSK3β) and downstream effectors (p-mTOR, and p-p70S6K) of mTOR activity. In addition, we assessed the changes in the levels of two important synaptic markers, GluA1 and PSD-95. Contrary to downregulated mTOR signaling and decreased synaptic markers in LPS-treated wild-type animals, the resilience of GluN2A KO mice to depressive-like behaviour was paralleled with sustained mTOR signaling activity synaptic stability in hippocampus and PFC. Finally, we disclosed that resistance of GluN2A knockouts to LPS-induced depressive-like behavior was ERK-dependent. These findings demonstrate that GluN2A-ERK-mTOR signaling is a vulnerability factor of inflammation-related depressive behaviour, making this signaling pathway the promising target for developing novel antidepressants.

Phencynonate hydrochloride exerts antidepressant effects by regulating the dendritic spine density and altering glutamate receptor expression

Phencynonate hydrochloride (PCH) is a drug that crosses the blood-brain barrier. Cellular experiments confirmed that PCH protects against glutamate toxicity and causes only weak central inhibition and limited side effects. As shown in our previous studies, PCH alleviates depression-like behaviours induced by chronic unpredictable mild stress (CUMS). Here we administered PCH at three different doses (4, 8 and 16 mg/kg) to male rats for two continuous days after CUMS and conducted behavioural tests to assess the dose-dependent antidepressant effects of PCH and its effects on the neuroplasticity in the hippocampus and medial prefrontal cortex (mPFC). Meanwhile, we measured the spine density and expression of related proteins to illustrate the mechanism of PCH. PCH treatment (8 mg/kg) significantly alleviated depression-like behaviours induced by CUMS. All doses of PCH treatment reversed the spine loss in prelimbic and CA3 regions induced by CUMS. Kalirin-7 expression was decreased in the hippocampus and mPFC of the CUMS group. The expression of the NR1 and NR2B subunits in the hippocampus, and NR2B in mPFC are increased by CUMS. PCH treatment (8 and 16 mg/kg) reversed all of these changes of Kalirin-7 in PFC and hippocampus, as well as NR1 and NR2B expression in the hippocampus. PCH is expected to be developed as a new type of rapid antidepressant. Its antidepressant effect may be closely related to the modulation of dendritic spine density in the prelimbic and CA3 regions and the regulation of Kalilin-7 and N-methyl-D-aspartic acid receptor levels in the hippocampus.

Electroacupuncture Ameliorates Depression-Like Behaviour in Rats by Enhancing Synaptic Plasticity via the GluN2B/CaMKII/CREB Signalling Pathway

Background

Hippocampal synaptic plasticity during the pathological process of depression has received increasing attention. Hippocampal neuron atrophy and the reduction in synaptic density induced by chronic stress are important pathological mechanisms of depression. Electroacupuncture (EA) exerts beneficial effects on depression, but the mechanism is unclear. This study explored the effect of EA on synaptic plasticity and the potential mechanism.

Methods

Forty-eight SD rats were randomly divided into the control, chronic unpredictable mild stress (CUMS), EA, and fluoxetine (FLX) groups, and each group consisted of 12 rats. The sucrose preference test, open field test, and forced swimming test were used for the evaluation of depression-like behaviour, and Golgi and Nissl staining were used for the assessment of synaptic plasticity. Western blotting and immunofluorescence were conducted to detect proteins related to synaptic plasticity and to determine their effects on signalling pathways.

Results

We found that CUMS led to depression-like behaviours, including a reduced preference for sucrose, a prolonged immobility time, and reduced exploration activity. The dendritic spine densities and neuron numbers and the protein levels of MAP-2, PSD-95, and SYN were decreased in the hippocampi of rats with CUMS-induced depression, and these trends were reversed by EA. The molecular mechanism regulating this plasticity may involve the GluN2B/CaMKII/CREB signalling pathway.

Conclusion

These results suggest that EA can improve depression-like behaviour and hippocampal plasticity induced by CUMS, and the mechanism may be related to the GluN2B/CaMKII/CREB pathway.

Novel rapid-acting glutamatergic modulators: Targeting the synaptic plasticity in depression

Major depressive disorder (MDD) is severely prevalent, and conventional monoaminergic antidepressants gradually exhibit low therapeutic efficiency, especially for patients with treatment-resistant depression. A neuroplasticity hypothesis is an emerging advancement in the mechanism of depression, mainly expressed in the glutamate system, e.g., glutamate receptors and signaling. Dysfunctional glutamatergic neurotransmission is currently considered to be closely associated with the pathophysiology of MDD. Biological function, pharmacological action, and signal attributes in the glutamate system both regulate the neural process. Specific functional subunits could be therapeutic targets to explore the novel glutamatergic modulators, which have fast-acting, and relatively sustained antidepressant effects. Here, the present review summarizes the pathophysiology of MDD found in the glutamate system, exploring the role of glutamate receptors and their downstream effects. These convergent mechanisms have prompted the development of other modulators targeting on glutamate system, including N-methyl-d-aspartate receptor antagonists, selective GluN2B-specific antagonists, glycine binding site agents, and regulators of metabotropic glutamate receptors. Relevant researches underly the putative mechanisms of these drugs, which reverse the damage of depression by regulating glutamatergic neurotransmission. It also provides further insight into the mechanism of depression and exploring potential targets for novel agent development.

Glycine/NMDA Receptor Pathway Mediates the Rapid-onset Antidepressant Effect of Alkaloids From Trichilia Monadelpha

INTRODUCTION

Major depressive disorder is often associated with suicidal tendencies, and this condition accentuates the need for rapid-acting antidepressants. We previously reported that Alkaloids (ALK) from Trichilia monadelpha possess antidepressant action in acute animal models of depression and that this effect is mediated through the monoamine and L-arginine-NO-cGMP pathways. This study investigated the possible rapid-onset antidepressant effect of ALK from T. monadelpha and its connection with the glycine/NMDA receptor pathway.

METHODS

The onset of ALK action from T. monadelpha was evaluated using the Open Space Swim Test (OSST), a chronic model of depression. The modified forced swimming and tail suspension tests were used to assess the effect of the ALK on the glycine/NMDA receptor pathway. The Instutute of Cancer Research (ICR) mice were treated with either ALK (30-300 mg/kg, orally [PO]), imipramine (3-30 mg/kg, PO), fluoxetine (3-30 mg/kg, PO), or saline. To identify the role of glycine/NMDA receptor pathway in the effect of ALK, we pretreated mice with a partial agonist of the glycine/NMDA receptor, D-cycloserine (2.5 mg/kg, intraperitoneally [IP]), and an agonist of glycine/NMDA receptor, D-serine (600 mg/kg, IP), before ALK administration.

RESULTS

ALK reversed immobility in mice after the second day of drug treatment in the OSST. In contrast, there was a delay in the effects induced by fluoxetine and imipramine. ALK also increased mean swimming and climbing scores in mice. ALK was more efficacious than imipramine and fluoxetine in reducing immobility and increasing distance traveled. It is noteworthy that ALK was less potent than fluoxetine and imipramine. D-cycloserine potentiated mobility observed in the ALK- and fluoxetine-treated mice. In contrast, D-serine decreased mobility in the ALK-treated mice.

CONCLUSION

The study results suggest that ALK from T. monadelpha exhibits rapid antidepressant action in mice, and the glycine/NMDA receptor pathway possibly mediates the observed effect.

Photobiomodulation Therapy Ameliorates Glutamatergic Dysfunction in Mice with Chronic Unpredictable Mild Stress-Induced Depression

Accumulating evidence indicates that dysfunction of the glutamatergic neurotransmission has been widely involved in the pathophysiology and treatment of depression. Photobiomodulation therapy (PBMT) has been demonstrated to regulate neuronal function both in vitro and in vivo. Herein, we aim to investigate whether the antidepressant phenotype of PBMT is associated with the improvement of glutamatergic dysfunction and to explore the mechanisms involved. Results showed that PBMT decreased extracellular glutamate levels via upregulation of glutamate transporter-1 (GLT-1) and rescued astrocyte loss in the cerebral cortex and hippocampus, which also alleviated dendritic atrophy and upregulated the expression of AMPA receptors on the postsynaptic membrane, ultimately exhibiting behaviorally significant antidepressant effects in mice exposed to chronic unpredictable mild stress (CUMS). Notably, PBMT also obtained similar antidepressant effects in a depressive mouse model subcutaneously injected with corticosterone (CORT). Evidence from in vitro mechanistic experiments demonstrated that PBMT treatment significantly increased both the GLT-1 mRNA and protein levels via the Akt/NF-κB signaling pathway. NF-κB-regulated transcription was in an Akt-dependent manner, while inhibition of Akt attenuated the DNA-binding efficiency of NF-κB to the GLT-1 promoter. Importantly, in vitro, we further found that PKA activation was responsible for phosphorylation and surface levels of AMPA receptors induced by PBMT, which is likely to rescue excitatory synaptic transmission. Taken together, our research suggests that PBMT as a feasible therapeutic approach has great potential value to control the progression of depression.

Epilepsy Associated Depression: An Update on Current Scenario, Suggested Mechanisms, and Opportunities

Depression is one of the most frequent psychiatric comorbidities associated with epilepsy having a major impact on the patient's quality of life. Several screening tools are available to identify and follow up psychiatric disorders in epilepsy. Out of various psychiatric disorders, people with epilepsy (PWE) are at greater risk of developing depression. This bidirectional relationship further hinders pharmacotherapy of comorbid depression in PWE as some antiepileptic drugs (AEDs) worsen associated depression and coadministration of existing antidepressants (ADs) to alleviate comorbid depression has been reported to worsen seizures. Selective serotonin reuptake inhibitors (SSRIs) and selective serotonin and norepinephrine reuptake inhibitors (SNRIs) are first choice of ADs and are considered safe in PWE, but there are no high-quality evidences. Similar to observations in people with depression, PWE also showed pharmacoresistant to available SSRI/SNRIs, which further complicates the disease prognosis. Randomized double-blind placebo-controlled clinical trials are necessary to report efficacy and safety of available ADs in PWE. We should also move beyond ADs, and therefore, we reviewed common pathological mechanisms such as neuroinflammation, dysregulated hypothalamus pituitary adrenal (HPA) axis, altered neurogenesis, and altered tryptophan metabolism responsible for coexistent relationship of epilepsy and depression. Based on these common pertinent pathways involved in the genesis of epilepsy and depression, we suggested novel targets and therapeutic approaches for safe management of comorbid depression in epilepsy.

Probenecid Increases the Concentration of 7-Chlorokynurenic Acid Derived from the Prodrug 4-Chlorokynurenine within the Prefrontal Cortex

Recent advances in the understanding of depression have led to increasing interest in ketamine and the role that N-methyl-d-aspartate (NMDA) receptor inhibition plays in depression. l-4-Chlorokynurenine (4-Cl-KYN, AV-101), a prodrug, has shown promise as an antidepressant in preclinical studies, but this promise has not been realized in recent clinical trials. We sought to determine if transporters in the CNS could be playing a role in this clinical response. We used radiolabeled uptake assays and microdialysis studies to determine how 4-Cl-KYN and its active metabolite, 7-chlorokynurenic acid (7-Cl-KYNA), cross the blood-brain barrier (BBB) to access the brain and its extracellular fluid compartment. Our data indicates that 4-Cl-KYN crosses the blood-brain barrier via the amino acid transporter LAT1 (SLC7A5) after which the 7-Cl-KYNA metabolite leaves the brain extracellular fluid via probenecid-sensitive organic anion transporters OAT1/3 (SLC22A6 and SLC22A8) and MRP4 (ABCC4). Microdialysis studies further validated our in vitro data, indicating that probenecid may be used to boost the bioavailability of 7-Cl-KYNA. Indeed, we found that coadministration of 4-Cl-KYN with probenecid caused a dose-dependent increase by as much as an 885-fold increase in 7-Cl-KYNA concentration in the prefrontal cortex. In summary, our data show that 4-Cl-KYN crosses the BBB using LAT1, while its active metabolite, 7-Cl-KYNA, is rapidly transported out of the brain via OAT1/3 and MRP4. We also identify a hitherto unreported mechanism by which the brain extracellular concentration of 7-Cl-KYNA may be increased to produce significant boosting of the drug concentration at its site of action that could potentially lead to an increased therapeutic effect.

Systemic immunization with altered myelin basic protein peptide produces sustained antidepressant-like effects

Immune dysregulation, specifically of inflammatory processes, has been linked to behavioral symptoms of depression in both human and rodent studies. Here, we evaluated the antidepressant effects of immunization with altered peptide ligands of myelin basic protein (MBP)-MBP_87-99[A⁹¹, A⁹⁶], MBP_87-99[A⁹¹], and MBP_87-99[R⁹¹, A⁹⁶]-in different models of depression and examined the mechanism by which these peptides protect against stress-induced depression. We found that a single dose of subcutaneously administered MBP_87-99[A⁹¹, A⁹⁶] produced antidepressant-like effects by decreasing immobility in the forced swim test and by reducing the escape latency and escape failures in the learned helplessness paradigm. Moreover, immunization with MBP_87-99[A⁹¹, A⁹⁶] prevented and reversed depressive-like and anxiety-like behaviors that were induced by chronic unpredictable stress (CUS). However, MBP_87-99[R⁹¹, A⁹⁶] tended to aggravate CUS-induced anxiety-like behavior. Chronic stress increased the production of peripheral and central proinflammatory cytokines and induced the activation of microglia in the prelimbic cortex (PrL), which was blocked by MBP_87-99[A⁹¹, A⁹⁶]. Immunization with MBP-derived altered peptide ligands also rescued chronic stress-induced deficits in p11, phosphorylated cyclic adenosine monophosphate response element binding protein, and brain-derived neurotrophic factor expression. Moreover, microinjections of recombinant proinflammatory cytokines and the knockdown of p11 in the PrL blunted the antidepressant-like behavioral response to MBP_87-99[A⁹¹, A⁹⁶]. Altogether, these findings indicate that immunization with altered MBP peptide produces prolonged antidepressant-like effects in rats, and the behavioral response is mediated by inflammatory factors (particularly interleukin-6), and p11 signaling in the PrL. Immune-neural interactions may impact central nervous system function and alter an individual's response to stress.

Ifenprodil rapidly ameliorates depressive-like behaviors, activates mTOR signaling and modulates proinflammatory cytokines in the hippocampus of CUMS rats

RATIONALE

The rapid-onset and long-lasting antidepressant properties of ketamine have prompted investigations into a variety of agents that target N-methyl-D-aspartate receptors (NMDARs) for the treatment of major depressive disorder (MDD). According to the literature, ifenprodil (a GluN2B-containing NMDAR antagonist) can potentiate the antidepressant-like effects of certain antidepressant drugs in mice. Here, we report that a single injection of ifenprodil (3 mg/kg, intraperitoneally (i.p.)) was sufficient to provoke rapid antidepressant-like effects in chronic unpredictable mild stress (CUMS) rats. Moreover, ifenprodil activated mTOR signaling and reversed the CUMS-induced elevation of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in the hippocampus after acute administration. Unfortunately, in our study, ifenprodil had no influence on corticosterone levels in the plasma. Our data indicate that ifenprodil per se might exert antidepressant-like effects by modulating neuroplasticity and inflammatory processes rather than the typical hormonal factors affected by stressors.

OBJECTIVES

To explore the potential rapid antidepressant-like effects and mechanisms of ifenprodil, a GluN2B subunit-selective NMDAR antagonist.

METHODS

Male Sprague-Dawley rats were used in 3 separate experiments. In experiment 1, we used the forced swim test (FST) and sucrose preference test (SPT) to identify the rapid antidepressant-like effects of ifenprodil in chronic unpredictable mild stress (CUMS) rats after acute administration. In experiment 2, we assessed neurochemical changes involved in synaptic plasticity within the hippocampus of CUMS rats. In experiment 3, we assessed the levels of corticosterone in the plasma and proinflammatory cytokines in the hippocampus in CUMS rats after ifenprodil treatment.

RESULTS

Ifenprodil rapidly ameliorated depressive-like behaviors in the FST and SPT, activated mTOR signaling, dephosphorylated eukaryotic elongation factor 2, enhanced BDNF expression, and promoted the synthesis of the synaptic protein GluA1 synthesis after acute administration. Moreover, ifenprodil reversed the CUMS-induced elevation of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in the hippocampus after acute administration. Unfortunately, ifenprodil had no influence on corticosterone levels in the plasma in our study.

CONCLUSIONS

Our data indicate that ifenprodil per se might exert antidepressant-like effects through its effects on neuroplasticity and inflammatory processes rather than the typical hormonal factors affected by stressors.

The antidepressant-like effects of fluvoxamine in mice involve the mTOR signaling in the hippocampus and prefrontal cortex

Recent studies have suggested that activation of the mammalian target of rapamycin (mTOR) signaling may be related to antidepressant actions. Although thought as a selective serotonin reuptake inhibitor (SSRI), the antidepressant mechanisms of fluvoxamine remain elusive. Therefore, this study aims to evaluate whether mTOR underlies the antidepressant-like effects of fluvoxamine. Male C57BL/6 J mice were subjected to 8 weeks of chronic unpredictable mild stress (CUMS) with fluvoxamine administered during the last 2 weeks. Western blotting analyses were then used to assess the expression of the mTOR signaling cascade in the hippocampus and prefrontal cortex (PFC) among all groups. The selective inhibitor of mTOR, rapamycin, was further used. It was found that fluvoxamine treatment fully reversed the effects of CUMS on the mTOR signaling in the hippocampus and PFC, and the usage of rapamycin significantly prevented the antidepressant-like effects of fluvoxamine in the CUMS model of depression. Taken together, the mTOR system is involved in the antidepressant mechanisms of fluvoxamine.

Beyond Ketamine: New Approaches to the Development of Safer Antidepressants

Background:

Ketamine has been reported to exert rapid and sustained antidepressant effects in patients with depression, including patients with treatment-resistant depression. However, ketamine has several drawbacks such as psychotomimetic/dissociative symptoms, abuse potential and neurotoxicity, all of which prevent its routine use in daily clinical practice.

Methods:

Therefore, development of novel agents with fewer safety and usage concerns for the treatment of depression has been actively investigated. From this standpoint, searching for active substances (stereoisomers and metabolites) and agents acting on the N-methyl-D-aspartate (NMDA) receptor have recently gained much attention.

Results:

The first approach includes stereoisomers of ketamine, (R)-ketamine and (S)-ketamine. Although (S)-ketamine has been considered as the active stereoisomer of racemic ketamine, recently, (R)-ketamine has been demonstrated to exert even more prolonged antidepressant effects in animal models than (S)-ketamine. Moreover, ketamine is rapidly metabolized into several metabolites, and some metabolites are speculated as being active substances exerting antidepressant effects. Of such metabolites, one in particular, namely, (2R,6R)-hydroxynorketamine, has been reported to be responsible for the antidepressant effects of ketamine. The second approach includes agents acting on the NMDA receptor, such as glycine site modulators and GluN2B subunit-selective antagonists. These agents have been tested in patients with treatment-resistant depression, and have been found to exhibit rapid antidepressant effects like ketamine.

Conclusion:

The above approaches may be useful to overcome the drawbacks of ketamine. Elucidation of the mechanisms of action of ketamine may pave the way for the development of antidepressant that are safer, but as potent and rapidly acting as ketamine.

Urinary Metabolomic Study of Chlorogenic Acid in a Rat Model of Chronic Sleep Deprivation Using Gas Chromatography-Mass Spectrometry

The urinary metabolomic study based on gas chromatography-mass spectrometry (GC-MS) had been developed to investigate the possible antidepressant mechanism of chlorogenic acid (CGA) in a rat model of sleep deprivation (SD). According to pattern recognition analysis, there was a clear separation among big platform group (BP), sleep deprivation group (SD), and the CGA (model + CGA), and CGA group was much closer to the BP group by showing a tendency of recovering towards BP group. Thirty-six significantly changed metabolites related to antidepressant by CGA were identified and used to explore the potential mechanism. Combined with the result of the classic behavioral tests and biochemical indices, CGA has significant antidepressant effects in a rat model of SD, suggesting that the mechanism of action of CGA might be involved in regulating the abnormal pathway of nicotinate and nicotinamide metabolism; glyoxylate and dicarboxylate metabolism; glycine, serine, and threonine metabolism; and arginine and proline metabolism. Our results also show that metabolomics analysis based on GC-MS is a useful tool for exploring biomarkers involved in depression and elucidating the potential therapeutic mechanisms of Chinese medicine.

Convergent Mechanisms Underlying Rapid Antidepressant Action

Traditional pharmacological treatments for depression have a delayed therapeutic onset, ranging from several weeks to months, and there is a high percentage of individuals who never respond to treatment. In contrast, ketamine produces rapid-onset antidepressant, anti-suicidal, and anti-anhedonic actions following a single administration to patients with depression. Proposed mechanisms of the antidepressant action of ketamine include N-methyl-D-aspartate receptor (NMDAR) modulation, gamma aminobutyric acid (GABA)-ergic interneuron disinhibition, and direct actions of its hydroxynorketamine (HNK) metabolites. Downstream actions include activation of the mechanistic target of rapamycin (mTOR), deactivation of glycogen synthase kinase-3 and eukaryotic elongation factor 2 (eEF2), enhanced brain-derived neurotrophic factor (BDNF) signaling, and activation of α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptors (AMPARs). These putative mechanisms of ketamine action are not mutually exclusive and may complement each other to induce potentiation of excitatory synapses in affective-regulating brain circuits, which results in amelioration of depression symptoms. We review these proposed mechanisms of ketamine action in the context of how such mechanisms are informing the development of novel putative rapid-acting antidepressant drugs. Such drugs that have undergone pre-clinical, and in some cases clinical, testing include the muscarinic acetylcholine receptor antagonist scopolamine, GluN2B-NMDAR antagonists (i.e., CP-101,606, MK-0657), (2R,6R)-HNK, NMDAR glycine site modulators (i.e., 4-chlorokynurenine, pro-drug of the glycineB NMDAR antagonist 7-chlorokynurenic acid), NMDAR agonists [i.e., GLYX-13 (rapastinel)], metabotropic glutamate receptor 2/3 (mGluR2/3) antagonists, GABAA receptor modulators, and drugs acting on various serotonin receptor subtypes. These ongoing studies suggest that the future acute treatment of depression will typically occur within hours, rather than months, of treatment initiation.

Uncoupling DAPK1 from NMDA receptor GluN2B subunit exerts rapid antidepressant-like effects

Several preclinical studies have reported the rapid antidepressant effects of N-methyl-D-aspartate receptor (NMDAR) antagonists, although the underlying mechanisms are still unclear. Death-associated protein kinase 1 (DAPK1) couples GluN2B subunits at extrasynaptic sites to regulate NMDAR channel conductance. In the present study, we found that chronic unpredictable stress (CUS) induced extracellular glutamate accumulation, accompanied by an increase in the DAPK1-NMDAR interaction, the high expression of DAPK1 and phosphorylated GluN2B at Ser1303, a decrease in phosphorylated DAPK1 at Ser308 and synaptic protein deficits in the rat medial prefrontal cortex (mPFC). CUS also enhanced GluN2B-mediated NMDA currents and extrasynaptic responses that were induced by bursts of high-frequency stimulation, which may be associated with the loss of astrocytes and low expression of glutamate transporter-1 (GLT-1). The blockade of GLT-1 in the mPFC was sufficient to induce depressive-like behavior and cause similar molecular changes. Selective GluN2B antagonist, DAPK1 knockdown by adeno-associated virus-mediated short-hairpin RNA or a pharmacological inhibitor, and the uncoupling of DAPK1 from the NMDAR GluN2B subunit produced rapid antidepressant-like effects and reversed CUS-induced alterations in the mPFC. The inhibition of DAPK1 and its interaction with GluN2B subunit in the mPFC also rescued CUS-induced depressive-like behavior 7 days after treatment. A selective GluN2B antagonist did not have rewarding effects in the conditioned place preference paradigm. Altogether, our findings suggest that the DAPK1 interaction with the NMDAR GluN2B subunit acts as a critical component in the pathophysiology of depression and is a potential target for new antidepressant treatments.

Characterization of the Effects of L-4-Chlorokynurenine on Nociception in Rodents

Upon systemic administration in rats, the prodrug L-4-chlorokynurenine (4-Cl-KYN; AV-101; VistaGen Therapeutics, Inc, South San Francisco, CA) is rapidly absorbed, actively transported across the blood-brain barrier, and converted in astrocytes to 7-chlorokynurenic acid (7-Cl-KYNA), a potent and specific antagonist of the glycine B coagonist site of the N-methyl-D-aspartate (NMDA) receptor. We examined the effects of 4-Cl-KYN in several rat models of hyperalgesia and allodynia and determined the concentrations of 4-Cl-KYN and newly produced 7-Cl-KYNA in serum, brain, and spinal cord. Adult male rats were given 4-Cl-KYN (56, 167, 500 mg/kg), the NMDA receptor antagonist MK-801 (.1, .3, 1.0 mg/kg), or gabapentin (33, 100, 300 mg/kg) intraperitoneally, and were then examined on rotarod, intraplantar formalin-evoked flinching, thermal escape in the normal and carrageenan-inflamed paw, and allodynia after sciatic nerve ligation. Our conclusions show that after systemic delivery, the highest 2 doses (167 and 500 mg/kg) of 4-Cl-KYN yielded brain concentrations of 7-Cl-KYNA exceeding its half maximal inhibitory concentration (IC₅₀) at the glycine B site and resulted in dose-dependent antihyperalgesia in the 4 models of facilitated processing associated with tissue inflammation and nerve injury. On the basis of the relative dose requirements for analgesic actions and side effect profiles from these experiments, 4-Cl-KYN is predicted to have antihyperalgesic efficacy and a therapeutic ratio equal to gabapentin and superior to MK-801.

PERSPECTIVE

These studies show that systemic administration of the prodrug 4-Cl-KYN produces high central nervous system levels of 7-Cl-KYNA, a potent and highly selective antagonist of the NMDA receptor. Compared with other drugs tested, 4-Cl-KYN has robust antinociceptive effects with a better side effect profile, highlighting its potential for treating hyperpathic pain states.

The chronic mild stress (CMS) model of depression: History, evaluation and usage

Now 30 years old, the chronic mild stress (CMS) model of depression has been used in >1300 published studies, with a year-on-year increase rising to >200 papers in 2015. Data from a survey of users show that while a variety of names are in use (chronic mild/unpredictable/varied stress), these describe essentially the same procedure. This paper provides an update on the validity and reliability of the CMS model, and reviews recent data on the neurobiological basis of CMS effects and the mechanisms of antidepressant action: the volume of this research may be unique in providing a comprehensive account of antidepressant action within a single model. Also discussed is the use of CMS in drug discovery, with particular reference to hippocampal and extra-hippocampal targets. The high translational potential of the CMS model means that the neurobiological mechanisms described may be of particular relevance to human depression and mechanisms of clinical antidepressant action.

AMPA Receptor Antagonist NBQX Decreased Seizures by Normalization of Perineuronal Nets

Epilepsy is a serious brain disorder with diverse seizure types and epileptic syndromes. AMPA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzoquinoxaline-2,3-dione (NBQX) attenuates spontaneous recurrent seizures in rats. However, the anti-epileptic effect of NBQX in chronic epilepsy model is poorly understood. Perineuronal nets (PNNs), specialized extracellular matrix structures, surround parvalbumin-positive inhibitory interneurons, and play a critical role in neuronal cell development and synaptic plasticity. Here, we focused on the potential involvement of PNNs in the treatment of epilepsy by NBQX. Rats were intraperitoneally (i.p.) injected with pentylenetetrazole (PTZ, 50 mg/kg) for 28 consecutive days to establish chronic epilepsy models. Subsequently, NBQX (20 mg/kg, i.p.) was injected for 3 days for the observation of behavioral measurements of epilepsy. The Wisteria floribundi agglutinin (WFA)-labeled PNNs were measured by immunohistochemical staining to evaluate the PNNs. The levels of three components of PNNs such as tenascin-R, aggrecan and neurocan were assayed by Western blot assay. The results showed that there are reduction of PNNs and decrease of tenascin-R, aggrecan and neurocan in the medial prefrontal cortex (mPFC) in the rats injected with PTZ. However, NBQX treatment normalized PNNs, tenascin-R, aggrecan and neurocan levels. NBQX was sufficient to decrease seizures through increasing the latency to seizures, decrease the duration of seizure onset, and reduce the scores for the severity of seizures. Furthermore, the degradation of mPFC PNNs by chondroitinase ABC (ChABC) exacerbated seizures in PTZ-treated rats. Finally, the anti-epileptic effect of NBQX was reversed by pretreatment with ChABC into mPFC. These findings revealed that PNNs degradation in mPFC is involved in the pathophysiology of epilepsy and enhancement of PNNs may be effective for the treatment of epilepsy.

BDNF-GSK-3β-β-Catenin Pathway in the mPFC Is Involved in Antidepressant-Like Effects of Morinda officinalis Oligosaccharides in Rats

BACKGROUND

Morinda officinalis oligosaccharides have been reported to exert neuroprotective and antidepressant-like effects in the forced swim test in mice. However, the mechanisms that underlie the antidepressant-like effects of Morinda officinalis oligosaccharides are unclear.

METHODS

Chronic unpredictable stress and forced swim test were used to explore the antidepressant-like effects of Morinda officinalis oligosaccharides and resilience to stress in rats. The phosphoinositide-3 kinase inhibitor LY294002 was microinjected in the medial prefrontal cortex to explore the role of glycogen synthase kinase-3β in the antidepressant-like effects of Morinda officinalis oligosaccharides. The expression of brain-derived neurotrophic factor, phosphorylated-Ser9-glycogen synthase kinase 3β, β-catenin, and synaptic proteins was determined in the medial prefrontal cortex and the orbitofrontal cortex by western blot.

RESULTS

We found that Morinda officinalis oligosaccharides effectively ameliorated chronic unpredictable stress-induced depression-like behaviors in the sucrose preference test and forced swim test. The Morinda officinalis oligosaccharides also significantly rescued chronic unpredictable stress-induced abnormalities in the brain-derived neurotrophic factor-glycogen synthase kinase-3β-β-catenin pathway and synaptic protein deficits in the medial prefrontal cortex but not orbitofrontal cortex. The activation of glycogen synthase kinase-3β by the phosphoinositide-3 kinase inhibitor LY294002 abolished the antidepressant-like effects of Morinda officinalis oligosaccharides in the forced swim test. Naïve rats that were treated with Morinda officinalis oligosaccharides exhibited resilience to chronic unpredictable stress, accompanied by increases in the expression of brain-derived neurotrophic factor, phosphorylated-Ser9-glycogen synthase kinase-3β, and β-catenin in the medial prefrontal cortex.

CONCLUSION

Our findings indicate that the brain-derived neurotrophic factor-glycogen synthase kinase-3β-β-catenin pathway in the medial prefrontal cortex may underlie the antidepressant-like effect of Morinda officinalis oligosaccharides and resilience to stress.

Ketamine-induced inhibition of glycogen synthase kinase-3 contributes to the augmentation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor signaling

OBJECTIVES

Sub-anesthetic doses of ketamine have been found to provide rapid antidepressant actions, indicating that the cellular signaling systems targeted by ketamine are potential sites for therapeutic intervention. Ketamine acts as an antagonist of N-methyl-D-aspartate (NMDA) receptors, and animal studies indicate that subsequent augmentation of signaling by α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors is critical for the antidepressant outcome.

METHODS

In this study, we tested if the inhibitory effect of ketamine on glycogen synthase kinase-3 (GSK3) affected hippocampal cell-surface AMPA receptors using immunoblotting of membrane and synaptosomal extracts from wild-type and GSK3 knockin mice.

RESULTS

Treatment with an antidepressant dose of ketamine increased the hippocampal membrane level of the AMPA glutamate receptor (GluA)1 subunit, but did not alter the localization of GluA2, GluA3, or GluA4. This effect of ketamine was abrogated in GSK3 knockin mice expressing mutant GSK3 that cannot be inhibited by ketamine, demonstrating that ketamine-induced inhibition of GSK3 is necessary for up-regulation of cell surface AMPA GluA1 subunits. AMPA receptor trafficking is regulated by post-synaptic density-95 (PSD-95), a substrate for GSK3. Ketamine treatment decreased the hippocampal membrane level of phosphorylated PSD-95 on Thr-19, the target of GSK3 that promotes AMPA receptor internalization.

CONCLUSIONS

These results demonstrate that ketamine-induced inhibition of GSK3 causes reduced phosphorylation of PSD-95, diminishing the internalization of AMPA GluA1 subunits to allow for augmented signaling through AMPA receptors following ketamine treatment.

EphB2 in the Medial Prefrontal Cortex Regulates Vulnerability to Stress

The ephrin B2 (EphB2) receptor is a tyrosine kinase receptor that is associated with synaptic development and maturation. It has recently been implicated in cognitive deficits and anxiety. However, still unknown is the involvement of EphB2 in the vulnerability to stress. In the present study, we observed decreases in EphB2 levels and their downstream molecules in the medial prefrontal cortex (mPFC) but not in the orbitofrontal cortex (OFC) in mice that were susceptible to chronic social defeat stress. The activation of EphB2 receptors with EphrinB1-Fc in the mPFC produced stress-resistant and antidepressant-like behavioral effects in susceptible mice that lasted for at least 10 days. EphB2 receptor knockdown by short-hairpin RNA in the mPFC increased the susceptibility to stress and induced depressive-like behaviors in a subthreshold chronic social defeat stress paradigm. These behavioral effects were associated with changes in the phosphorylation of cofilin and membrane α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) trafficking and the expression of some synaptic proteins in the mPFC. We also found that EphB2 regulated stress-induced spine remodeling in the mPFC. Altogether, these results indicate that EphB2 is a critical regulator of stress vulnerability and might be a potential target for the treatment of depression.

Betaine enhances antidepressant-like, but blocks psychotomimetic effects of ketamine in mice

Ketamine is emerging as a new hope against depression, but ketamine-associated psychotomimetic effects limit its clinical use. An adjunct therapy along with ketamine to alleviate its adverse effects and even potentiate the antidepressant effects might be an alternative strategy. Betaine, a methyl derivative of glycine and a dietary supplement, has been shown to have antidepressant-like effects and to act like a partial agonist at the glycine site of N-methyl-D-aspartate receptors (NMDARs). Accordingly, betaine might have potential to be an adjunct to ketamine treatment for depression. The antidepressant-like effects of ketamine and betaine were evaluated by forced swimming test and novelty suppressed feeding test in mice. Both betaine and ketamine produced antidepressant-like effects. Furthermore, we determined the effects of betaine on ketamine-induced antidepressant-like and psychotomimetic behaviors, motor incoordination, hyperlocomotor activity, and anesthesia. The antidepressant-like responses to betaine combined with ketamine were stronger than their individual effects. In contrast, ketamine-induced impairments in prepulse inhibition, novel object recognition test, social interaction, and rotarod test were remarkably attenuated, whereas ketamine-induced hyperlocomotion and loss of righting reflex were not affected by betaine. These findings revealed that betaine could enhance the antidepressant-like effects, yet block the psychotomimetic effects of ketamine, suggesting that betaine can be considered as an add-on therapy to ketamine for treatment-resistant depression and suitable for the treatment of depressive symptoms in patients with schizophrenia.

New perspectives on the involvement of mTOR in depression as well as in the action of antidepressant drugs

Despite the revolution in recent decades regarding monoamine involvement in the management of major depressive disorder (MDD), the biological mechanisms underlying this psychiatric disorder are still poorly understood. Currently available treatments require long time courses to establish antidepressant response and a significant percentage of people are refractory to single drug or combination drug treatment. These issues, and recent findings demonstrating the involvement of synaptic plasticity in the pathophysiological mechanisms of MDD, are encouraging researchers to explore the molecular mechanisms underlying psychiatric disease in more depth. The discovery of the rapid antidepressant effect exerted by glutamatergic and cholinergic agents highlights the mammalian target of rapamycin (mTOR) pathway as a critical pathway that contributes to the efficacy of these pharmacological agents in clinical and pre-clinical research. The mTOR pathway is a downstream intracellular signal that transmits information after the direct activation of α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) and neurotrophic factor receptors. Activation of these receptors is hypothesized to be one of the major axes involved in the synthesis of synaptogenic proteins underlying synaptic plasticity and critical to both the rapid and delayed effects exerted by classic antidepressants. This review focuses on the involvement of mTOR in the pathophysiology of depression and on molecular mechanisms involved in the activity of emerging and classic antidepressant agents.

Neuropeptide Trefoil Factor 3 Reverses Depressive-Like Behaviors by Activation of BDNF-ERK-CREB Signaling in Olfactory Bulbectomized Rats

The trefoil factors (TFFs) are a family of three polypeptides, among which TFF1 and TFF3 are widely distributed in the central nervous system. Our previous study indicated that TFF3 was a potential rapid-onset antidepressant as it reversed the depressive-like behaviors induced by acute or chronic mild stress. In order to further identify the antidepressant-like effect of TFF3, we applied an olfactory bulbectomy (OB), a classic animal model of depression, in the present study. To elucidate the mechanism underlying the antidepressant-like activity of TFF3, we tested the role of brain-derived neurotrophic factor (BDNF)-extracellular signal-related kinase (ERK)-cyclic adenosine monophosphate response element binding protein (CREB) signaling in the hippocampus in the process. Chronic systemic administration of TFF3 (0.1 mg/kg, i.p.) for seven days not only produced a significant antidepressant-like efficacy in the OB paradigm, but also restored the expression of BDNF, pERK, and pCREB in the hippocampal CA3. Inhibition of BDNF or extracellular signal-related kinase (ERK) signaling in CA3 blocked the antidepressant-like activity of TFF3 in OB rats. Our findings further confirmed the therapeutic effect of TFF3 against depression and suggested that the normalization of the BDNF-ERK-CREB pathway was involved in the behavioral response of TFF3 for the treatment of depression.

Fluoxetine regulates mTOR signalling in a region-dependent manner in depression-like mice

Previous studies have demonstrated that the mammalian target of rapamycin (mTOR) signaling pathway has an important role in ketamine-induced, rapid antidepressant effects despite the acute administration of fluoxetine not affecting mTOR phosphorylation in the brain. However, the effects of long-term fluoxetine treatment on mTOR modulation have not been assessed to date. In the present study, we examined whether fluoxetine, a type of commonly used antidepressant agent, alters mTOR signaling following chronic administration in different brain regions, including the frontal cortex, hippocampus, amygdala and hypothalamus. We also investigated whether fluoxetine enhanced synaptic protein levels in these regions via the activation of the mTOR signaling pathway and its downstream regulators, p70S6K and 4E-BP-1. The results indicated that chronic fluoxetine treatment attenuated the chronic, unpredictable, mild stress (CUMS)-induced mTOR phosphorylation reduction in the hippocampus and amygdala of mice but not in the frontal cortex or the hypothalamus. Moreover, the CUMS-decreased PSD-95 and synapsin I levels were reversed by fluoxetine, and these effects were blocked by rapamycin only in the hippocampus. In conclusion, our findings suggest that chronic treatment with fluoxetine can induce synaptic protein expression by activating the mTOR signaling pathway in a region-dependent manner and mainly in the hippocampus.

Involvement of normalized NMDA receptor and mTOR-related signaling in rapid antidepressant effects of Yueju and ketamine on chronically stressed mice

Yueju, a Traditional Chinese Medicine formula, exhibited fast-onset antidepressant responses similar to ketamine. This study focused on assessing the rapid and persistent antidepressant efficacy of Yueju and ketamine in chronically stressed mice and its association with alternations in prefrontal N-methyl-D-aspartate (NMDA) receptor and mammalian target of rapamycin (mTOR)-related activity. Chronic mild stress (CMS) led to deficits in sucrose preference test (SPT), forced swim test, tail suspension test, and novelty-suppressed feeding test, which were improved differently by acute Yueju or ketamine administration. The improvement in SPT started as soon as 2 hours post Yueju and ketamine but lasted for 6 days only by Yueju. Body weight was regained by Yueju more than ketamine at post-drug administration day (PAD) 6. CMS decreased phosphorylation of the mTOR effectors 4E-BP1 and p70S6K, their upstream regulators ERK and Akt, and downstream targets including synaptic protein GluR1. Yueju or ketamine reversed these changes at PAD 2, but only Yueju reversed phosphor-Akt at PAD 6. CMS selectively and lastingly increased NMDA receptor subunit NR1 expression, which was reversed by ketamine or Yueju at PAD 2 but only by Yueju at PAD 6. These findings suggest that NR1 and Akt/mTOR signaling are important therapeutic targets for depression.

The Prodrug 4-Chlorokynurenine Causes Ketamine-Like Antidepressant Effects, but Not Side Effects, by NMDA/GlycineB-Site Inhibition

Currently approved antidepressant drug treatment typically takes several weeks to be effective. The noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist ketamine has shown efficacy as a rapid-acting treatment of depression, but its use is associated with significant side effects. We assessed effects following blockade of the glycineB co-agonist site of the NMDA receptor, located on the GluN1 subunit, by the selective full antagonist 7-chloro-kynurenic acid (7-Cl-KYNA), delivered by systemic administration of its brain-penetrant prodrug 4-chlorokynurenine (4-Cl-KYN) in mice. Following administration of 4-Cl-KYN, 7-Cl-KYNA was promptly recovered extracellularly in hippocampal microdialysate of freely moving animals. The behavioral responses of the animals were assessed using measures of ketamine-sensitive antidepressant efficacy (including the 24-hour forced swim test, learned helplessness test, and novelty-suppressed feeding test). In these tests, distinct from fluoxetine, and similar to ketamine, 4-Cl-KYN administration resulted in rapid, dose-dependent and persistent antidepressant-like effects following a single treatment. The antidepressant effects of 4-Cl-KYN were prevented by pretreatment with glycine or the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX). 4-Cl-KYN administration was not associated with the rewarding and psychotomimetic effects of ketamine, and did not induce locomotor sensitization or stereotypic behaviors. Our results provide further support for antagonism of the glycineB site for the rapid treatment of treatment-resistant depression without the negative side effects seen with ketamine or other channel-blocking NMDA receptor antagonists.

Reduced cholesterol is associated with the depressive-like behavior in rats through modulation of the brain 5-HT1A receptor

Background

Low serum cholesterol levels are related to an increased risk of depression and its serious consequences. However, the effect of central cholesterol on depressive disorder and its potential regulatory mechanism is poorly understood. Therefore, brain cholesterol in patients with depression may not only decrease the risk for developing this disease but also increase the beneficial effects of treatment for depression.

Methods

In current study, rats were exposed to chronic mild stress (CMS) for consecutive 28 days, and the depressive-like behavior was tested by sucrose preference test, immobility in the forced swim test, locomotor activity in the open field test, decreased bodyweight and food intake. Additionally, the total cholesterol levels in the medial prefrontal cortex (mPFC) and the hippocampus of rats were measured by gas chromatograph mass spectrometer. Finally, 5-HT1A receptor antagonist WAY100635 was used to determine the potential role of serotonin system in the interaction between central cholesterol and depression.

Results

CMS significantly reduced total cholesterol levels in the mPFC but not in the hippocampus and resulted in depressive-like behavior. Chronic supplementation of cholesterol by food reversed the depressive-like behavior induced by CMS. Furthermore, pre-injection of 5-HT1A receptor antagonist WAY100635 into the mPFC blocked the treatment effects of cholesterol on the reversal of behavioral response.

Conclusion

This finding suggested that cholesterol in the mPFC may have an impact on the sensitivity of the 5-HT1A receptor in the development and treatment of depression. The treatment benefits of cholesterol could be through modulation of the brain 5-HT1A receptor.

7-Chlorokynurenic acid (7-CTKA) produces rapid antidepressant-like effects: through regulating hippocampal microRNA expressions involved in TrkB-ERK/Akt signaling pathways in mice exposed to chronic unpredictable mild stress

RATIONALE

7-Chlorokynurenic acid (7-CTKA), a NMDA receptor antagonist, has been reported as a potential rapid antidepressant with poor understanding about the molecular mechanism of its therapeutic action. MicroRNAs (miRNAs) are emerging as critical regulators of central nervous system plasticity and may play an important role in depression.

OBJECTIVE

The objective of this study was to investigate the molecular mechanism of antidepressant action of 7-CTKA in chronic unpredictable mild stress (CUMS) animal model.

METHODS

K252a (tropomyosin-related kinase receptor B (TrkB) antagonist), U0126 (extracellular signal-regulated kinase (ERK) phosphorylation inhibitor), LY294002 (serine-threonine kinase (Akt) phosphorylation inhibitor), or vehicle was given intracerebroventricularly to mice in each group 30 min before 7-CTKA or vehicle intraperitoneal injection. Behavioral changes were observed by sucrose preference test and miRNA microarray was performed to examine hippocampal miRNAs levels in mice. Quantitative RT-PCR was conducted to further confirm results in microarray study.

RESULTS

7-CTKA not only reversed the decrease in sucrose preference and multiple hippocampal miRNAs changes induced by CUMS but also mediated 15 common miRNAs via TrkB-ERK/Akt pathways. Among them, the expression levels of four miRNAs (miR-34a-5p, miR-200a-3p, miR-144-3p, miR-1894-5p) were validated by quantitative real-time PCR (qRT-PCR). The findings from qRT-PCR study support results from microarray analysis except for the non-significance of miR-1894-5p expression.

CONCLUSIONS

This demonstrated that the 15 miRNA targets shared by TrkB-ERK/Akt pathways might participate in rapid-acting molecular mechanism of antidepressant 7-CTKA.

The role of NMDA receptors in the pathophysiology and treatment of mood disorders

Mood disorders such as major depressive disorder and bipolar disorder are chronic and recurrent illnesses that cause significant disability and affect approximately 350 million people worldwide. Currently available biogenic amine treatments provide relief for many and yet fail to ameliorate symptoms for others, highlighting the need to diversify the search for new therapeutic strategies. Here we present recent evidence implicating the role of N-methyl-D-aspartate receptor (NMDAR) signaling in the pathophysiology of mood disorders. The possible role of NMDARs in mood disorders has been supported by evidence demonstrating that: (i) both BPD and MDD are characterized by altered levels of central excitatory neurotransmitters; (ii) NMDAR expression, distribution, and function are atypical in patients with mood disorders; (iii) NMDAR modulators show positive therapeutic effects in BPD and MDD patients; and (iv) conventional antidepressants/mood stabilizers can modulate NMDAR function. Taken together, this evidence suggests the NMDAR system holds considerable promise as a therapeutic target for developing next generation drugs that may provide more rapid onset relief of symptoms. Identifying the subcircuits involved in mood and elucidating the role of NMDARs subtypes in specific brain circuits would constitute an important step toward the development of more effective therapies with fewer side effects.

Progressive alterations of hippocampal CA3-CA1 synapses in an animal model of depression

Major depressive disorder is the most prevalent psychiatric condition, but the cellular and molecular mechanisms underlying this disorder are largely unknown, although multiple hypotheses have been proposed. The aim of this study was to characterize the progressive alteration of neuronal plasticity in the male rat hippocampus during depression induced by chronic unpredictable mild stress (CUMS), an established animal model of depression. The data in the hippocampus were collected on days 7, 14 and 21 after the onset of three-week CUMS. When analyzed on day 21, three-week CUMS induced typically depressive-like behaviors, impaired LTP induction, and decreased basal synaptic transmission at hippocampal CA3-CA1 synapses recorded in vivo, which was accompanied by decreased density of dendritic spines in CA1 and CA3 pyramidal neurons. The levels of both Kalirin-7 and brain-derived neurotrophic factor (BDNF) in the hippocampus were decreased at the same time. On day 14 (middle phase), some depressive-like behaviors were observed, which was accompanied by depressed basal synaptic transmission and enhanced LTP induction at the CA3-CA1 synapses. However, BDNF expression was decreased without alteration of Kalirin7 expression in comparison with no-stress control. Depressed basal synaptic transmission occurred in the middle phase of CUMS may contribute to decreased expression of BDNF. On day 7, depressive-like behaviors were not observed, and LTP induction, spine density, Kalirin-7 and BDNF expression were not altered by CUMS in comparison with no-stress control. These results showed that the functional changes at CA3-CA1synapses occurred earlier than the structural alteration during three-week CUMS as a strategy of neural adaptation, and rats required three weeks to develop depressive-like behaviors during CUMS. Our results suggest an important role of Kalirin-7 in CUMS-mediated alterations in spine density, synaptic function and overall depressive-like behaviors on day 21.

NMDA antagonists under investigation for the treatment of major depressive disorder

INTRODUCTION

Mood disorders, including depression, are becoming increasingly prevalent in the developed world. Furthermore, treatment of depression therapeutics, mainly influencing the serotonergic and adrenergic systems, is considered insufficient. The original NMDA-glutamate hypothesis mechanism of antidepressant action was first proposed ∼ 20 years ago. Since then, a number of preclinical and clinical studies have examined its rationale.

AREAS COVERED

This review highlights the recent clinical evidence for the use of functional NMDA receptor antagonists as antidepressants. Furthermore, the authors present the mechanism(s) of antidepressant action derived mostly from preclinical paradigms.

EXPERT OPINION

Currently, clinical studies mostly use ketamine (a noncompetitive high-potency NMDA antagonist) as an agent for rapid relief of depressive symptoms. However, due to the ketamine-induced psychotomimetic effects, new NMDA receptor antagonists (modulators) are continuously being introduced for rapid antidepressant action, especially for use in treatment-resistant patients. Recent clinical reports for the use of CP-101,606, MK-0657 (selective GluN2B subunit NMDA receptor antagonists), GLYX-13 and d-cycloserine (glycine site partial agonists) are optimistic but await further support.

Antidepressant Effects of Mallotus oppositifolius in Acute Murine Models

Objective. Hydroalcoholic extract of leaves of Mallotus oppositifolius (MOE), a plant used for CNS conditions in Ghana, was investigated for acute antidepressant effects in the forced swimming (FST) and tail suspension tests (TST). Results. In both FST and TST, MOE (10, 30, and 100 mg kg(-1)) significantly decreased immobility periods and frequencies. A 3-day pretreatment with 200 mg kg(-1), i.p., para-chlorophenylalanine (PCPA), a tryptophan hydroxylase inhibitor, reversed the decline in immobility and the increase of swimming score induced by MOE in the modified FST. Pretreatment with reserpine alone (1 mg kg(-1)), α -methyldopa alone (400 mg kg(-1), i.p.), or a combination of both drugs failed to reverse the decline in immobility or the increase in swimming score caused by the extract in the modified FST. The extract potentiated the frequency of head twitch responses induced by 5-hydroxytryptamine. Pretreatment with d-serine (600 mg kg(-1), i.p.), glycine/NMDA agonist, abolished the behavioural effects of MOE while d-cycloserine (2.5 mg kg(-1), i.p.), a glycine/NMDA partial agonist, potentiated it in both TST and modified FST. Conclusion. The extract exhibited antidepressant effects in mice which is mediated by enhancement of serotoninergic neurotransmission and inhibition of glycine/NMDA receptor activation.