The group II mGlu receptor antagonist LY341495 induces a rapid antidepressant-like effect and enhances the effect of ketamine in the chronic unpredictable mild stress model of depression in C57BL/6J mice

Subchronic administration of scopolamine reverses UCMS-induced behavior in mice via eEF2 protein dephosphorylation

BACKGROUND

The cholinergic system has been increasingly linked to the pathophysiology of mood disorders such as depression, with the potential involvement of nicotinic and/or muscarinic receptors. Conventional antidepressants usually require weeks of daily dosing to achieve a full antidepressant response. In contrast, clinical studies have shown that scopolamine, a nonselective muscarinic acetylcholine receptor antagonist, can induce potent and rapid antidepressant effects, requiring only a few days of treatment. This study aimed to examine the suitability of the unpredictable chronic mild stress (UCMS) model of depression to reproduce the above scopolamine antidepressant activity patterns.

METHODS

Rapid and sustained antidepressant-like effects were assessed by using the splash test, sucrose preference test (SPT), tail suspension test (TST), and forced swimming test (FST) in animals undergoing the UCMS procedure and stress-naïve C57BL/6J mice. Western Blotting was used to measure tropomyosin receptor kinase B (TrkB), mammalian target of rapamycin (mTOR), eukaryotic elongation factor (eEF2) and postsynaptic density protein 95 (PSD95) levels.

RESULTS

Scopolamine induced antidepressant-like effects in a dose-dependent manner only after subchronic, but not single, administration in the UCMS model of depression in C57BL/6J mice without affecting locomotor activity. Specifically, scopolamine administered at a dose of 0.3 mg/kg for four consecutive days significantly reversed the UCMS-induced depressive-like behavior, such as apathy, anhedonia, and behavioral despair, while scopolamine, given at the same dose but only once, did not relieve the above symptoms. Scopolamine treatment was accompanied by eEF2 protein dephosphorylation and its subsequent reactivation in the prefrontal cortex (PFC).

CONCLUSION

Subchronic administration of scopolamine is needed to ameliorate UCMS-induced depressive-like behavior. The suggested mechanism of scopolamine action covers eEF2 protein activity in the PFC.

Partial mGlu5 receptor NAM, M-5MPEP, induces rapid and sustained antidepressant-like effects in the BDNF-dependent mechanism and enhances (R)-ketamine action in mice

BACKGROUND

Partial negative allosteric modulators (NAM) of the metabotropic glutamate 5 (mGlu5) receptor are an excellent alternative to full antagonists and NAMs because they retain therapeutic effects and have a much broader therapeutic window. Here, we investigated whether partial mGlu5 NAM, 2-(2-(3-methoxyphenyl)ethynyl)-5-methylpyridine (M-5MPEP), induced a fast and sustained antidepressant-like effect, characteristic of rapid-acting antidepressant drugs (RAADs) like ketamine, in mice.

METHODS

A tail suspension test (TST) was used to investigate acute antidepressant-like effects. Sustained effects were studied 24 h after the four intraperitoneal (ip) administrations using the splash test, designed to measure apathy-like state, the sucrose preference test (SPT), reflecting anhedonia, and the TST. Western blot and ELISA techniques were used to measure brain-derived neurotrophic factor (BDNF) and selected protein levels.

METHODS

A tail suspension test (TST) was used to investigate acute antidepressant-like effects. Sustained effects were studied 24 h after the four intraperitoneal (ip) administrations using the splash test, designed to measure apathy-like state, the sucrose preference test (SPT), reflecting anhedonia, and the TST. Western blot and ELISA techniques were used to measure brain-derived neurotrophic factor (BDNF) and selected protein levels.

CONCLUSION

Partial mGlu5 receptor NAM, M-5MPEP, induced rapid and sustained antidepressant-like effects in the BDNF-dependent mechanism and enhanced (R)-ketamine action in mice, indicating both substances' convergent mechanisms of action and the possibility of their practical use in treating depression as RAAD.

Two polygenic mouse models of major depressive disorders identify TMEM161B as a potential biomarker of disease in humans

Treatments are only partially effective in major depressive disorders (MDD) but no biomarker exists to predict symptom improvement in patients. Animal models are essential tools in the development of antidepressant medications, but while recent genetic studies have demonstrated the polygenic contribution to MDD, current models are limited to either mimic the effect of a single gene or environmental factor. We developed in the past a model of depressive-like behaviors in mice (H/Rouen), using selective breeding based on behavioral reaction after an acute mild stress in the tail suspension test. Here, we propose a new mouse model of depression (H-TST) generated from a more complex genetic background and based on the same selection process. We first demonstrated that H/Rouen and H-TST mice had similar phenotypes and were more sensitive to glutamate-related antidepressant medications than selective serotonin reuptake inhibitors. We then conducted an exome sequencing on the two mouse models and showed that they had damaging variants in 174 identical genes, which have also been associated with MDD in humans. Among these genes, we showed a higher expression level of Tmem161b in brain and blood of our two mouse models. Changes in TMEM161B expression level was also observed in blood of MDD patients when compared with controls, and after 8-week treatment with duloxetine, mainly in good responders to treatment. Altogether, our results introduce H/Rouen and H-TST as the two first polygenic animal models of MDD and demonstrate their ability to identify biomarkers of the disease and to develop rapid and effective antidepressant medications.

The impact of stress on the behavior of C57BL/6 mice with liver injury: a comparative study

Introduction

Depressive-like behavior has been shown to be associated with liver damage. This study aimed to evaluate the impact of three different models of depression on the behavior of mice with liver injury.

Methods

During the 4 weeks of methionine/choline deficiency diet (MCD), adult C57BL/6 mice were randomly divided into four groups: MCD (no stress protocol, n = 6), chronic unpredictable mild stress (CUMS, n = 9), acute and repeated forced swim stress [aFSS (n = 9) and rFSS (n = 9)].

Results

All depression protocols induced increased anhedonia and anxiety-like behavior compared to baseline and had no impact on the severity of liver damage, according to ultrasonography. However, different protocols evoked different overall behavior patterns. After the depressive-like behavior induction protocols, animals subjected to aFSS did not exhibit anxiety-like behavior differences compared to MCD animals, while mice subjected to CUMS showed additional weight loss compared to FSS animals. All tested protocols for inducing depressive-like behavior decreased the short-term memory of mice with liver damage, as assessed by the novel object recognition test (NORT).

Discussion

Our results show that the use of all protocols seems to generate different levels of anxiety-like behavior, but only the depressive-like behavior induction procedures associate additional anhedonia and memory impairment in mice with liver injury.

The antidepressant-like and glioprotective effects of the Y2 receptor antagonist SF-11 in the astroglial degeneration model of depression in rats: Involvement of glutamatergic inhibition

In this study, we explored the potential antidepressant-like properties of the brain-penetrant Y2 receptor (Y2R) antagonist SF-11 [N-(4-ethoxyphenyl)- 4-(hydroxydiphenylmethyl)- 1-piperidinecarbothioamide] in the astroglial degeneration model of depression with an emphasis on checking the possible mechanisms implicated in this antidepressant-like effect. The model of depression relies on the loss of astrocytes in the medial prefrontal cortex (mPFC) in Sprague-Dawley rats after administering the gliotoxin L-alpha-aminoadipic acid (L-AAA). SF-11 was administered intraperitoneally (i.p.) once (10 mg/kg) or for three consecutive days (10 mg/kg/day), and the effects of L-AAA and SF-11 injected alone or in combination were investigated using the forced swim test (FST), sucrose intake test (SIT), Western blotting, immunohistochemical staining, and microdialysis. SF-11 produced an antidepressant-like effect after single or three-day administration in rats subjected to astrocyte impairment, as demonstrated by the FST and SIT, respectively. Immunoblotting and immunohistochemical analyses showed that SF-11 reversed the L-AAA-induced astrocyte cell death in the mPFC, suggesting it is glioprotective. Microdialysis studies showed that SF-11 decreased extracellular glutamate (Glu) levels compared to basal value when administered alone and compared to the basal value and control group in LAAA-treated rats. The results from immunoblotting analysis indicated the involvement of Y2Rs in the astrocyte ablation model of depression and the antidepressant-like effect of SF-11. In addition, we observed the participation of the caspase-3 apoptotic pathway in the mechanism of gliotoxin action induced by L-AAA. These findings demonstrate that SF-11, a Y2R antagonist, elicited a rapid antidepressant-like response, possibly linked to its ability to inhibit glutamatergic neurotransmission.

Interaction of hallucinogenic rapid-acting antidepressants with mGlu2/3 receptor ligands as a window for more effective therapies

The desire to find a gold-standard therapy for depression is still ongoing. Developing one universal and effective pharmacotherapy remains troublesome due to the high complexity and variety of symptoms. Over the last decades, the understanding of the mechanism of pathophysiology of depression and its key consequences for brain functioning have undergone significant changes, referring to the monoaminergic theory of the disease. After the breakthrough discovery of ketamine, research began to focus on the modulation of glutamatergic transmission as a new pharmacological target. Glutamate is a crucial player in mechanisms of a novel class of antidepressants, including hallucinogens such as ketamine. The role of glutamatergic transmission is also suggested in the antidepressant (AD) action of scopolamine and psilocybin. Despite fast, robust, and sustained AD action hallucinogens belonging to a group of rapid-acting antidepressants (RAA) exert significant undesired effects, which hamper their use in the clinic. Thus, the synergistic action of more than one substance in lower doses instead of monotherapy may alleviate the likelihood of adverse effects while improving therapeutic outcomes. In this review, we explore AD-like behavioral, synaptic, and molecular action of RAAs such as ketamine, scopolamine, and psilocybin, in combination with mGlu2/3 receptor antagonists.

mGlu2/3 receptor antagonists for depression: overview of underlying mechanisms and clinical development

Triggered by the ground-breaking finding that ketamine exerts robust and rapid-acting antidepressant effects in patients with treatment-resistant depression, glutamatergic systems have attracted attention as targets for the development of novel antidepressants. Among glutamatergic systems, group II metabotropic glutamate (mGlu) receptors, consisting of mGlu2 and mGlu3 receptors, are of interest because of their modulatory roles in glutamatergic transmission. Accumulating evidence has indicated that mGlu2/3 receptor antagonists have antidepressant-like effects in rodent models that mirror those of ketamine and that mGlu2/3 receptor antagonists also share underlying mechanisms with ketamine that are responsible for these antidepressant-like actions. Importantly, contrary to their antidepressant-like profile, preclinical studies have revealed that mGlu2/3 receptor antagonists are devoid of ketamine-like adverse effects, such as psychotomimetic-like behavior, abuse potential and neurotoxicity. Despite some discouraging results for an mGlu2/3 receptor antagonist decoglurant (classified as a negative allosteric modulator [NAM]) in patients with major depressive disorder, clinical trials of two mGlu2/3 receptor antagonists, a phase 2 trial of TS-161 (an orthosteric antagonist) and a phase 1 trial of DSP-3456 (a NAM), are presently on-going. mGlu2/3 receptors still hold promise for the development of safer and more efficacious antidepressants.

Anxiolytic-like effects of an mGluR 5 antagonist and a mGluR 2/3 agonist, and antidepressant-like effects of an mGluR 7 agonist in the chick social separation stress test, a dual-drug screening model of treatment-resistant depression

Modulation of glutamate receptors has demonstrated anxiolytic and/or antidepressant effects in rodent stress models. The chick social-separation stress paradigm exposes socially raised aves to an isolation stressor which elicits distress vocalizations (DVocs) in an attempt to re-establish contact. The model presents a state of panic during the first 5 min followed by a state of behavioral despair during the last 60 to 90 min. Making it useful as a dual anxiolytic/antidepressant screening assay. Further research has identified the Black Australorp strain as a stress-vulnerable, treatment-resistant, and ketamine-sensitive genetic line. Utilizing this genetic line, we sought to evaluate modulation of glutamatergic receptors for potential anxiolytic and/or antidepressant effects. Separate dose-response studies were conducted for the following drugs: the AMPA PAM LY392098, the mGluR 5 antagonist MPEP, the mGluR 2/3 agonist LY404039, the mGluR 2/3 antagonist LY341495, and the mGluR 7 agonist AMN082. The norepinephrine α² agonist clonidine and the NMDA antagonist ketamine were included as comparison for anxiolytic (anti-panic) and antidepressant effects, respectively. As in previous studies, clonidine reduced DVoc rates during the first 5 min (attenuation of panic) and ketamine elevated DVoc rates (attenuation of behavioral despair) during the last 60 min of isolation. The mGluR 2/3 agonist LY404039 and the mGluR 5 antagonist MPEP decreased DVoc rates during the first 5 min of isolation indicative of anxiolytic effects like that of clonidine while the mGluR 7 agonist AMN082 elevated DVoc rates in the later hour of isolation, representative of antidepressant effects like that of ketamine. Collectively, these findings suggest that certain glutamate targets may be clinically useful in treating panic disorder and/or treatment-resistant depression.

Impact of ketamine administration on chronic unpredictable stress-induced rat model of depression during extremely low-frequency electromagnetic field exposure: Behavioral, histological and molecular study

OBJECTIVES

In the study, we examined the effects of ketamine and extremely low-frequency electromagnetic fields (ELF-EMF) on depression-like behavior, learning and memory, expression of GFAP, caspase-3, p53, BDNF, and NMDA receptor in animals subjected to chronic unpredictable stress (CUS).

METHODS

After applying 21 days of chronic unpredictable stress, male rats received intraperitoneal (IP) of ketamine (5 mg/kg) and then were exposed to ELF-EMF (10-Hz, 10-mT exposure conditions) for 3 days (3 h per day) and behavioral assessments were performed 24 h after the treatments. Instantly after the last behavioral test, the brain was extracted for Nissl staining, immunohistochemistry, and real-time PCR analyses. Immunohistochemistry (IHC) was conducted to assess the effect of ketamine and ELF-EMF on the expression of astrocyte marker (glial fibrillary acidic protein, GFAP) in the CA1 area of the hippocampus and medial prefrontal cortex (mPFC). Also, real-time PCR analyses were used to investigate the impacts of the combination of ketamine and ELF-EMF on the expression of caspase3, p53, BDNF, and NMDA receptors in the hippocampus in rats submitted to the CUS procedure. Results were considered statistically significant when p < .05.

RESULTS

Our results revealed that the combination of ketamine and ELF-EMF increased depression-like behavior, increased degenerated neurons and decreased the number of GFAP (+) cells in the CA1 area and mPFC, incremented the expression of caspase-3, and reduced the expression of BDNF in the hippocampus but showed no effect on the expression of p53 and NMDA-R.

CONCLUSIONS

These results reveal that combining ketamine and ELF-EMF has adverse effects on animals under chronic unpredictable stress (CUS).

Ketamine and serotonergic psychedelics: An update on the mechanisms and biosignatures underlying rapid-acting antidepressant treatment

The discovery of ketamine as a rapid-acting antidepressant spurred significant research to understand its underlying mechanisms of action and to identify other novel compounds that may act similarly. Serotonergic psychedelics (SPs) have shown initial promise in treating depression, though the challenge of conducting randomized controlled trials with SPs and the necessity of long-term clinical observation are important limitations. This review summarizes the similarities and differences between the psychoactive effects associated with both ketamine and SPs and the mechanisms of action of these compounds, with a focus on the monoaminergic, glutamatergic, gamma-aminobutyric acid (GABA)-ergic, opioid, and inflammatory systems. Both molecular and neuroimaging aspects are considered. While their main mechanisms of action differ-SPs increase serotonergic signaling while ketamine is a glutamatergic modulator-evidence suggests that the downstream mechanisms of action of both ketamine and SPs include mechanistic target of rapamycin complex 1 (mTORC1) signaling and downstream GABAA receptor activity. The similarities in downstream mechanisms may explain why ketamine, and potentially SPs, exert rapid-acting antidepressant effects. However, research on SPs is still in its infancy compared to the ongoing research that has been conducted with ketamine. For both therapeutics, issues with regulation and proper controls should be addressed before more widespread implementation. This article is part of the Special Issue on "Ketamine and its Metabolites".

The Antidepressant-like Activity and Cognitive Enhancing Effects of the Combined Administration of (R)-Ketamine and LY341495 in the CUMS Model of Depression in Mice Are Related to the Modulation of Excitatory Synaptic Transmission and LTP in the PFC

(S)-Ketamine is the first rapid-acting antidepressant drug (RAAD) introduced for the treatment of depression. However, research is still being carried out on the search for further RAADs that will be not only effective but also safe to use. Recent data have indicated that the combined administration of (R)-ketamine and the mGlu2/3 receptor antagonist LY341495 (mixRL) induces rapid and sustained effects in the chronic unpredictable mild stress (CUMS) model of depression in mice, and the use of this drug combination is associated with a low risk of undesirable effects. Considering the possible influence of stress on cortical plasticity and, on the other hand, the role of this plasticity in the mechanism of action of ketamine, we decided to investigate whether mixed RL affects synaptic plasticity in the prefrontal cortex (PFC) in the CUMS model of depression using electrophysiological techniques and explore whether these effects are related to memory impairments. Using behavioral methods, we found that a single administration of mixRL reversed CUMS-induced PFC-dependent memory deficits and alleviated depression-like effects induced by CUMS. In turn, electrophysiological experiments indicated that the amplitude of field potentials as well as paired-pulse responses in CUMS mice were increased, and mixRL was found to reverse these effects. Additionally, the magnitude of long-term potentiation (LTP) was reduced in CUMS mice, and mixRL was shown to restore this parameter. In summary, mixRL appeared to exert its antidepressant effects and cognitive enhancing effects in a mouse model of depression, at least in part, by mechanisms involving modulation of glutamatergic transmission and LTP in the PFC.

The role of mGlu receptors in susceptibility to stress-induced anhedonia, fear, and anxiety-like behavior

Stress and trauma exposure contribute to the development of psychiatric disorders such as post-traumatic stress disorder (PTSD) and major depressive disorder (MDD) in a subset of people. A large body of preclinical work has found that the metabotropic glutamate (mGlu) family of G protein-coupled receptors regulate several behaviors that are part of the symptom clusters for both PTSD and MDD, including anhedonia, anxiety, and fear. Here, we review this literature, beginning with a summary of the wide variety of preclinical models used to assess these behaviors. We then summarize the involvement of Group I and II mGlu receptors in these behaviors. Bringing together this extensive literature reveals that mGlu5 signaling plays distinct roles in anhedonia, fear, and anxiety-like behavior. mGlu5 promotes susceptibility to stress-induced anhedonia and resilience to stress-induced anxiety-like behavior, while serving a fundamental role in the learning underlying fear conditioning. The medial prefrontal cortex, basolateral amygdala, nucleus accumbens, and ventral hippocampus are key regions where mGlu5, mGlu2, and mGlu3 regulate these behaviors. There is strong support that stress-induced anhedonia arises from decreased glutamate release and post-synaptic mGlu5 signaling. Conversely, decreasing mGlu5 signaling increases resilience to stress-induced anxiety-like behavior. Consistent with opposing roles for mGlu5 and mGlu2/3 in anhedonia, evidence suggests that increased glutamate transmission may be therapeutic for the extinction of fear learning. Thus, a large body of literature supports the targeting of pre- and post-synaptic glutamate signaling to ameliorate post-stress anhedonia, fear, and anxiety-like behavior.

Where do we go next in antidepressant drug discovery? A new generation of antidepressants: a pivotal role of AMPA receptor potentiation and mGlu2/3 receptor antagonism

INTRODUCTION

Major depressive disorder remains a prevalent world-wide health problem. Currently available antidepressant medications take weeks of dosing, do not produce antidepressant response in all patients, and have undesirable ancillary effects.

AREAS COVERED

The present opinion piece focuses on the major inroads to the creation of new antidepressants. These include N-methyl-D-aspartate (NMDA) receptor antagonists and related compounds like ketamine, psychedelic drugs like psilocybin, and muscarinic receptor antagonists like scopolamine. The preclinical and clinical pharmacological profile of these new-age antidepressant drugs is discussed.

EXPERT OPINION

Preclinical and clinical data have accumulated to predict a next generation of antidepressant medicines. In contrast to the current standard of care antidepressant drugs, these compounds differ in that they demonstrate rapid activity, often after a single dose, and effects that outlive their presence in brain. These compounds also can provide efficacy for treatment-resistant depressed patients. The mechanism of action of these compounds suggests a strong glutamatergic component that involves the facilitation of AMPA receptor function. Antagonism of mGlu2/3 receptors is also relevant to the antidepressant pharmacology of this new class of drugs. Based upon the ongoing efforts to develop these new-age antidepressants, new drug approvals are predicted in the near future.

The role of mGlu2/3 receptor antagonists in the enhancement of the antidepressant-like effect of ketamine

MGlu_2/3 receptor antagonists produce antidepressant-like effects in animal models of depression. A number of mechanisms responsible for these actions are convergent to the mechanism of the fast antidepressant-like effect of ketamine. Furthermore, the data indicate that ketamine effect is related to the action of mGlu₂ receptors and may be reduced by their agonists. The above facts became the basis for the hypothesis that the antidepressant effect of low doses of ketamine might be enhanced by coadministration of a mGlu₂ receptor antagonist. This strategy was aimed not only at enhancing the therapeutic effect of ketamine but also at reducing the risk of undesirable effects by lowering its therapeutic dose. It is known that ketamine, effective in relieving depressive symptoms in patients suffering from treatment-resistant depression (TRD), is burdened with a number of side effects, which may be particularly dangerous in psychiatric patients. Data have confirmed that subeffective doses of ketamine and its enantiomer, (R)-ketamine, coadministered with an mGlu_2/3 receptor antagonist, induce antidepressant-like effects in the screening tests and in the chronic-stress-induced model of depression. At the same time, these drug combinations did not cause undesirable effects characteristic of higher doses of ketamine and (S)-ketamine, including those related to psychostimulatory effects. Further research is required to prove whether this strategy will also be effective in depressive patients.

New investigational agents for the treatment of major depressive disorder

INTRODUCTION

Pharmacotherapy of depression is characterized by the delayed onset of action, chronic treatment requirements, and insufficient effectiveness. Ketamine, with its rapid action and long-lasting effects, represents a breakthrough in the modern pharmacotherapy of depression.

AREAS COVERED

: The current review summarizes the latest findings on the mechanism of the antidepressant action of ketamine and its enantiomers and metabolites. Furthermore, the antidepressant potential of psychedelics, non-hallucinogenic serotonergic modulators and metabotropic glutamate receptor ligands was discussed.

EXPERT OPINION

Recent data indicated that to achieve fast and long-acting antidepressant-like effects, compounds must induce durable effects on the architecture and density of dendritic spines in brain regions engaged in mood regulation. Such mechanisms underlie the actions of ketamine and psychedelics. These compounds trigger hallucinations; however, it is thought that these effects might be essential for their antidepressant action. Behavioral studies with serotonergic modulators affecting 5-HT1A (biased agonists), 5-HT4 (agonists), and 5-HT-7 (antagonists) receptors exert rapid antidepressant-like activity, but they seem to be devoid of this effects. Another way to avoid psychomimetic effects and achieve the desired rapid antidepressant-like effects is combined therapy. In this respect, ligands of metabotropic receptors show some potential.

Rewarding and Antidepressant Properties of Ketamine and Ethanol: Effects on the Brain-Derived Neurotrophic Factor and TrkB and p75NTR Receptors

There is a high level of comorbidity between depression and alcohol use disorder. Subanesthetic doses of ketamine induce short-acting and enduring antidepressant effects after a single or a few administrations. Considering such comorbidity, we assessed, in Swiss male mice, if ketamine-induced antidepressant-like effects would alter ethanol's rewarding effects; and, if ethanol pretreatment would alter the rewarding and antidepressant effects of ketamine. The role of the brain-derived neurotrophic factor (BDNF) and its high and low affinity receptors TrkB and p75NTR, respectively, in both reward and depression-related behaviors is well established. The present study assessed, in outbred Swiss male mice, the expression of these proteins in the prefrontal cortex and hippocampus. Ketamine did not alter the development of ethanol-induced conditioned place preference (CPP), yet ethanol inhibited the expression of CPP induced by 50 mg/kg ketamine. The antidepressant action of 50 mg/kg ketamine was attenuated after repeated treatment (i.e., developed tolerance), an effect blocked by ethanol preexposure; ethanol also inhibited the antidepressant effect of 30 mg/kg ketamine. Ketamine (50 mg/kg) and Ethanol-Ketamine (50 mg/kg) groups showed lower levels of 145 kDa TrkB in the hippocampus than Saline-treated group. Ethanol-Ketamine (50 mg/kg) decreased the hippocampal expression of p75NTR compared to Saline-Saline and Saline-Ethanol groups. Ketamine (50 mg/kg) induced hippocampal downregulation of 145 kDa TrkB may contribute to ketamine-induced antidepressant tolerance. Likewise, a relationship between low hippocampal levels of p75NTR in the Ethanol-Ketamine (50 mg/kg) and ketamine-induced CPP blockade may be considered. The findings underscore potential ethanol-ketamine interactions likely to undermine ketamine putative antidepressant effects.

Effects of Chronic LY341495 on Hippocampal mTORC1 Signaling in Mice with Chronic Unpredictable Stress-Induced Depression

In several rodent models, acute administration of the metabotropic glutamate 2/3 (mGlu2/3) receptor antagonist LY341495 induced antidepressant-like effects via a mechanism of action similar to that of ketamine. However, the effects of chronic mGlu2/3 antagonism have not yet been explored. Therefore, we investigated the effects of chronic LY341495 treatment on the mechanistic target of rapamycin complex 1 (mTORC1) signaling and the levels of synaptic proteins in mice subjected to chronic unpredictable stress (CUS). LY341495 (1 mg/kg) was administered daily for 4 weeks to mice with and without CUS exposure. After the final treatment, the forced swimming test (FST) was used to assess antidepressant-like effects. The hippocampal levels of mTORC1-related proteins were derived by Western blotting. Chronic LY341495 treatment reversed the CUS-induced behavioral effects of FST. CUS significantly reduced the phosphorylation of mTORC1 and downstream effectors [eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP-1) and small ribosomal protein 6 (S6)], as well as the expression of synaptic proteins postsynaptic density-95 (PSD-95) and AMPA receptor subunit GluR1 (GluA1) in the hippocampus. However, chronic LY341495 treatment rescued these deficits. Our results suggest that the activation of hippocampal mTORC1 signaling is related to the antidepressant effect of chronic LY341495 treatment in an animal model of CUS-induced depression.

The Potential Antidepressant Action of Duloxetine Co-Administered with the TAAR1 Receptor Agonist SEP-363856 in Mice

Here, we explored the possible interaction between duloxetine and SEP-363856 (SEP-856) in depression-related reactions. The results showed that oral administration of duloxetine showed powerful antidepressant-like effects in both the forced swimming test (FST) and the suspension tail test (TST). SEP-856 orally administered alone also exerted an antidepressant-like effect in FST and TST, especially at doses of 0.3, 1, and 10 mg/kg. In addition, duloxetine (15 mg/kg) and SEP-856 (15 mg/kg) both showed antidepressant-like effects in the sucrose preference test (SPT). Most importantly, in the above experiments, compared with duloxetine alone, the simultaneous use of duloxetine and SEP-856 caused a more significant antidepressant-like effect. It is worth noting that doses of drug combination in FST and TST did not change the motor activities of mice in the open-field test (OFT). Thus, duloxetine and SEP-856 seem to play a synergistic role in regulating depression-related behaviors and might be beneficial for refractory depression.

Rapid-acting antidepressants and the circadian clock

A growing number of epidemiological and experimental studies has established that circadian disruption is strongly associated with psychiatric disorders, including major depressive disorder (MDD). This association is becoming increasingly relevant considering that modern lifestyles, social zeitgebers (time cues) and genetic variants contribute to disrupting circadian rhythms that may lead to psychiatric disorders. Circadian abnormalities associated with MDD include dysregulated rhythms of sleep, temperature, hormonal secretions, and mood which are modulated by the molecular clock. Rapid-acting antidepressants such as subanesthetic ketamine and sleep deprivation therapy can improve symptoms within 24 h in a subset of depressed patients, in striking contrast to conventional treatments, which generally require weeks for a full clinical response. Importantly, animal data show that sleep deprivation and ketamine have overlapping effects on clock gene expression. Furthermore, emerging data implicate the circadian system as a critical component involved in rapid antidepressant responses via several intracellular signaling pathways such as GSK3β, mTOR, MAPK, and NOTCH to initiate synaptic plasticity. Future research on the relationship between depression and the circadian clock may contribute to the development of novel therapeutic strategies for depression-like symptoms. In this review we summarize recent evidence describing: (1) how the circadian clock is implicated in depression, (2) how clock genes may contribute to fast-acting antidepressants, and (3) the mechanistic links between the clock genes driving circadian rhythms and neuroplasticity.

Novel Pharmacological Approaches to the Treatment of Depression

Major depressive disorder is one of the most prevalent mental health disorders. Monoamine-based antidepressants were the first drugs developed to treat major depressive disorder. More recently, ketamine and other analogues were introduced as fast-acting antidepressants. Unfortunately, currently available therapeutics are inadequate; lack of efficacy, adverse effects, and risks leave patients with limited treatment options. Efforts are now focused on understanding the etiology of depression and identifying novel targets for pharmacological treatment. In this review, we discuss promising novel pharmacological targets for the treatment of major depressive disorder. Targeting receptors including N-methyl-D-aspartate receptors, peroxisome proliferator-activated receptors, G-protein-coupled receptor 39, metabotropic glutamate receptors, galanin and opioid receptors has potential antidepressant effects. Compounds targeting biological processes: inflammation, the hypothalamic-pituitary-adrenal axis, the cholesterol biosynthesis pathway, and gut microbiota have also shown therapeutic potential. Additionally, natural products including plants, herbs, and fatty acids improved depressive symptoms and behaviors. In this review, a brief history of clinically available antidepressants will be provided, with a primary focus on novel pharmaceutical approaches with promising antidepressant effects in preclinical and clinical studies.

Combined Administration of (R)-Ketamine and the mGlu2/3 Receptor Antagonist LY341495 Induces Rapid and Sustained Effects in the CUMS Model of Depression via a TrkB/BDNF-Dependent Mechanism

Ketamine is an effective, rapid-acting antidepressant drug (RAAD), but it induces side effects. To overcome these challenges, attempts have been made to use safer enantiomer ((R)-ketamine) or mGlu2/3 receptor antagonists, which induce ketamine-like effects and enhance its action. Here, we propose combining these two strategies to investigate the antidepressant-like effects of low doses of two ketamine enantiomers in combination with a low dose of the mGlu2/3 receptor antagonist LY341495. Rapid and sustained antidepressant-like effects were assessed in C57BL/6J mice using the tail suspension test (TST) and the chronic unpredictable mild stress (CUMS) model of depression in stress-naïve mice. ELISA was used to measure BDNF levels. In the TST, low doses of both (S)-ketamine and (R)-ketamine were potentiated by a subeffective dose of LY341495. However, in the CUMS model, only (R)-ketamine was able to induce long-lasting anti-apathetic and anti-anhedonic effects when coadministered with low-dose LY341495. The mechanism of this drug combination was dependent on BDNF and AMPA receptor activity. ELISA results suggest that the hippocampus might be the site of this action. MGlu2/3 receptor antagonists, in combination with (R)-ketamine, may serve as potential RAADs, with a high efficiency and low risk of side effects.

Antidepressant-like actions of the mGlu2/3 receptor antagonist TP0178894 in the chronic social defeat stress model: Comparison with escitalopram

The metabotropic glutamate 2/3 (mGlu2/3) receptor antagonists are reported to produce ketamine-like rapid-acting and sustained antidepressant-like effects in rodents. In this study, we compared the effects of single administration of the new mGlu2/3 receptor antagonist TP0178894 and the selective serotonin reuptake inhibitor (SSRI) escitalopram in the chronic social defeat stress (CSDS) model of depression, a model which has been shown to be resistant to treatment with a single dose of SSRI. In the tail suspension test and forced swimming test, high dose (3.0 mg/kg) of TP0178894 significantly attenuated the increased immobility time of these tests in CSDS susceptible mice, compared with vehicle-treated mice. In contrast, low doses (0.3 and 1.0 mg/kg) of TP0178894 and escitalopram (10 mg/kg) did not alter the increased immobility time of these two tests. In the sucrose preference test, TP0178894 (3.0 mg/kg) significantly improved the reduced sucrose preference of CSDS susceptible mice, three and seven days after a single dose. In addition, Western blot analyses showed that TP0178894 (3.0 mg/kg), but not low doses of TP0178894 and escitalopram, significantly attenuated the reduced expression of synaptic proteins [α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (GluA1) and postsynaptic density protein 95 (PSD-95)] in the prefrontal cortex from CSDS susceptible mice. This study suggests that TP0178894 shows rapid-acting and sustained antidepressant-like effects in CSDS model, as ketamine does.

Conditional Knockout of Pdha1 in Mouse Hippocampus Impairs Cognitive Function: The Possible Involvement of Lactate

Background and Purpose: Neurodegenerative diseases are associated with metabolic disturbances. Pyruvate dehydrogenase E1 component subunit alpha (PDHA1) is an essential component in the process of glucose metabolism, and its deficiency exists in various diseases such as Alzheimer’s disease (AD), epilepsy, Leigh’s syndrome, and diabetes-associated cognitive decline. However, the exact role of PDHA1 deficiency in neurodegenerative diseases remains to be elucidated. In this study, we explored the effect of PDHA1 deficiency on cognitive function and its molecular mechanism.

Methods: A hippocampus-specific Pdha1 knockout (Pdha1^–/–) mouse model was established, and behavioral tests were used to evaluate the cognitive function of mice. Transmission electron microscopy (TEM) was performed to observe the morphological changes of the hippocampus. The lactate level in the hippocampus was measured. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting were used to explore the possible mechanism of the effect of PDHA1 on cognition.

Results:Pdha1 knockout damaged the spatial memory of mice and led to the ultrastructural disorder of hippocampal neurons. Lactate accumulation and abnormal lactate transport occurred in Pdha1^–/– mice, and the cyclic AMP-protein kinase A-cAMP response element-binding protein (cAMP/PKA/CREB) pathway was inhibited.

Conclusion: Lactate accumulation caused by PDHA1 deficiency in the hippocampus may impair cognitive function by inhibiting the cAMP/PKA/CREB pathway.

The effectiveness of (R)-ketamine and its mechanism of action differ from those of (S)-ketamine in a chronic unpredictable mild stress model of depression in C57BL/6J mice

(S)-ketamine has been approved as a rapid-acting antidepressant drug (RAAD). Although ketamine has an advantage over classic antidepressants (ADs) due to its rapid action, it remains a controversial drug due to its undesirable effects. Behavioral studies indicate that another enantiomer of ketamine, namely, (R)-ketamine, has been proposed as a safer but still effective RAAD. However, these conclusions have not been confirmed in any model of depression based on chronic environmental stress, which effectively reflects the core symptoms of this disease. Thus, we decided to compare the effects of (R)- and (S)-ketamine on chronic unpredictable mild stress (CUMS) in mice. Behavioral studies showed that (R)-ketamine induced anti-anhedonic and anti-apathetic efficacy up to seven days after administration, while the (S)-ketamine effect persisted up to 24 h or 3 days after injection. The behavioral effects of (R)-ketamine depended on the activation of TrkB receptors, while the (S)-ketamine effects did not. Western blot analyses showed that (S)-ketamine action might be related to both mTOR and ERK pathway activation and to the increased expression of GluA1 protein in the prefrontal cortex (PFC). In contrast, (R)-ketamine did not change ERK phosphorylation in the PFC, while it increased mTOR expression. (S)-Ketamine produced behavioral effects indicative of possible side effects in the dose range studied, while (R)-ketamine did not. This indicates that (R)-ketamine may be more effective, have a longer-lasting effect, and be safer to use than (S)-ketamine.

Evaluation of the Safety, Tolerability, and Pharmacokinetic Profiles of TP0473292 (TS-161), A Prodrug of a Novel Orthosteric mGlu2/3 Receptor Antagonist TP0178894, in Healthy Subjects and Its Antidepressant-Like Effects in Rodents

BACKGROUND

TP0473292 (the active ingredient of TS-161) is a prodrug of a novel metabotropic glutamate (mGlu) 2/3 receptor antagonist being developed for the treatment of patients with depression. This study evaluated the safety, tolerability, and pharmacokinetics of orally administered TS-161 in healthy subjects.

METHODS

This was a first-in-human, phase 1, randomized, double-blind, placebo-controlled, single-ascending dose (15-400 mg TS-161) and 10-day multiple-ascending dose (50-150 mg TS-161) study in healthy subjects, conducted from June 2019 through February 2020. Plasma and urine concentrations of the prodrug and its metabolites, and cerebrospinal fluid (CSF) concentrations of the active metabolite TP0178894 were measured to evaluate the pharmacokinetic profiles after oral administration of TS-161.

RESULTS

Following single and multiple doses, TP0473292 was extensively converted into its active metabolite TP0178894. Plasma concentrations of TP0178894 reached peak (Cmax) within 5 hours post dose and declined with a t1/2 <13 hours. Plasma exposures of TP0178894 increased with increasing dose. TP0178894 penetrated into CSF and reached a Cmax of 9.892 ng/mL at a single dose of 100 mg, which was comparable with IC50 values of antagonist activity at mGlu2/3 receptors. The most frequently observed adverse events that showed exposure-related incidence during the study were nausea, vomiting, and dizziness.

CONCLUSIONS

The mGlu2/3 receptor antagonist prodrug TP0473292 is safe and well-tolerated, is orally bioavailable in humans with extensive conversion into the active metabolite TP0178894 with sufficient CSF penetration to exert the anticipated pharmacological effects, and is a promising candidate for further clinical development in treatment of patients with depression.

Models of Depression: Unpredictable Chronic Mild Stress in Mice

Major depression is a complex psychiatric disorder characterized by affective, cognitive, and physiological impairments that lead to maladaptive behavior. The high lifetime prevalence of this disabling condition, coupled with limitations of existing medications, make necessary the development of improved therapeutics. This requires animal models that allow investigation of key biological correlates of the disorder. Described in this article is the unpredictable chronic mild stress mouse model that can be used to screen for antidepressant drug candidates. Originally designed for rats, this model has been adapted for mice to capitalize on the advantages of this species as an experimental model, including inter-strain variability, which permits an exploration of the contribution of genetic background; the ability to create transgenic animals; and lower cost. Thus, because it combines genetic features and socio-environmental chronic stressful events, the unpredictable chronic mild stress model in mice is a relevant and valuable paradigm to gain insight into the etiological and developmental components of major depression, as well as to identify novel treatments for this condition. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Unpredictable Chronic Mild Stress (UCMS) Test in Mice Basic Protocol 2: Assessment Of Self-Directed Activity And Anhedonia in Mice.

Glutamic Acid Decarboxylase Concentration Changes in Response to Stress and Altered Availability of Glutamic Acid in Rabbit (Oryctolagus cuniculus) Brain Limbic Structures

Glutamic acid decarboxylase (GAD) is an enzyme that catalyses the formation of γ-aminobutyric acid (GABA), the most important inhibitory neurotransmitter, from glutamic acid (Glu), which is considered the most important excitatory transmitter in the central and peripheral nervous systems. GAD is a key enzyme that provides a balance between Glu and GABA concentration. Hence, it can be assumed that if the GAD executes the synthesis of GABA from Glu, it is important in the stress response, and thus also in triggering the emotional states of the body that accompany stress. The aim of the study was to investigate the concentration of the GAD in motivational structures in the brain of the rabbit (Oryctolagus cuniculus) under altered homeostatic conditions caused by stress and variable availability of Glu. Summarising, the experimental results clearly showed variable concentrations of GAD in the motivational structures of the rabbit brain. The highest concentration of GAD was found in the hypothalamus, which suggests a strong effect of Glu and GABA on the activity of this brain structure. The GAD concentrations in individual experimental groups depended to a greater extent on blocking the activity of glutamate receptors than on the effects of a single stress exposure. The results obtained clearly support the possibility that a rapid change in the concentration of GAD could shift bodily responses to quickly achieve homeostasis, especially in this species. Further studies are necessary to reveal the role of the Glu-GAD-GABA system in the modulation of stress situations as well as in body homeostasis.