Modulation Of Glutamate Receptors Research Articles

Motor behavior induced by bergamot essential oil in experimental tasks is differentially modulated by pretreatment with metabotropic glutamate receptor 2/3 or 5 antagonists.

Bergamot essential oil shows anxiolytic-relaxant effects devoid of sedative action and motor impairment typical of benzodiazepines. Considering the potential for clinical of these effects, it is important to understand the underlying mechanisms of the phytocomplex. Modulation of glutamate group I and II metabotropic receptors is involved in stress and anxiety disorders, in cognition and emotions and increases locomotor activity and wakefulness. Interestingly, early data indicate that bergamot essential oil modulates glutamatergic transmission in specific manifestations of the central nervous system. The aim of this work is to investigate if selective antagonists of metabotropic glutamate 2/3 and 5 receptors affect behavioral parameters modulated by the phytocomplex. Male Wistar rats were used to measure behavioral parameters to correlate anxiety and motor activity using elevated plus maze (EPM), open field (OF), and rotarod tasks. Bergamot essential oil increases in EPM the time spent in open/closed arms and reduces total number of entries. The essential oil also increases immobility in EPM and OF and not affect motor coordination in rotarod. Pretreatment with the metabotropic glutamate antagonists does not affect the time spent in open/close arms, however, differently affects motor behavior measured after administration of phytocomplex. Particularly, glutamate 2/3 antagonist reverts immobility and glutamate 5 antagonist potentiates this parameter induced by the phytocomplex. Our data show that modulation of both metabotropic glutamate receptors is likely involved in some of behavioral effects of bergamot essential oil.

Pharmacologic Management of Parkinsonism and Other Movement Disorders

Parkinsonism and other movement disorders constitute a diverse group of neurodegenerative conditions characterized by disturbances in motor control. This abstract provides an overview of the pharmacologic management strategies employed in the treatment of these disorders. Parkinson's disease, the most prevalent form of Parkinsonism, is primarily managed through dopaminergic therapies aimed at replenishing dopamine levels or enhancing its effects in the central nervous system. Levodopa, a precursor of dopamine, remains the gold standard, often combined with dopaminergic agonists or monoamine oxidase-B inhibitors for optimal efficacy.In addition to Parkinson's disease, other movement disorders such as essential tremor, dystonia, and chorea pose unique challenges. Beta-blockers and anticonvulsants, like primidone, are commonly prescribed for essential tremor, while dystonia may respond to anticholinergic agents or botulinum toxin injections. Huntington's disease, characterized by chorea, is managed through dopamine-depleting agents, tetrabenazine being a notable example.Recent advances in pharmacotherapy include the development of adenosine A2A receptor antagonists and glutamate receptor modulators, providing promising alternatives and adjuncts to traditional therapies. However, challenges such as medication-induced side effects, disease progression, and the need for personalized treatment plans persist.This abstract underscore the evolving landscape of pharmacologic interventions for managing Parkinsonism and other movement disorders. A comprehensive understanding of the underlying pathophysiology, coupled with ongoing research efforts, promises to enhance therapeutic options and improve the quality of life for individuals affected by these debilitating conditions.

Understanding nootropics and cognitive enhancement: mechanism of action and ethical considerations

Nootropics are substances that enhance cognition through various mechanisms. Nootropics include various substances, ranging from derivatives of neurotransmitters to naturally occurring plants. They are used therapeutically for certain psychological disorders including Alzheimer’s dementia and mild cognitive impairment. More recently, healthy individuals have been shown to consume nootropics to enhance mental processes above baseline levels. Nootropic modes of action vary, but the most supported mechanisms include increased acetylcholine levels in synapses, increased levels of monoamine oxidases, long-term potentiation through neural modulation of glutamate receptors, and decreased adenosine levels. However, numerous side effects can occur when taking nootropics, including insomnia, dependence, nausea, and anxiety. Nootropics also need to be considered when physicians prescribe them, as some individuals who request these drugs are perfectly healthy. In addition, the effects of nootropics are often misportrayed in popular media, leading individuals to think that these substances will give them a drastic increase in their cognitive ability.

2.52 New Potential Pharmacological Targets for Childhood Psychiatric Disorders Through Differential Modulation of Glutamate Receptors

2.52 New Potential Pharmacological Targets for Childhood Psychiatric Disorders Through Differential Modulation of Glutamate Receptors

The Lateral Metalation of Isoxazolo[3,4-d]pyridazinones towards Hit-to-Lead Development of Selective Positive Modulators of Metabotropic Glutamate Receptors.

Isoxazolo[3,4-d] pyridazinones ([3,4-d]s) were previously shown to have selective positive modulation at the metabotropic glutamate receptor (mGluR) Subtypes 2 and 4, with no functional cross-reactivity at mGluR1a, mGluR5, or mGluR8. Additional analogs were prepared to access more of the allosteric pocket and achieve higher binding affinity, as suggested by homology modeling. Two different sets of analogs were generated. One uses the fully formed [3,4-d] with an N6-aryl with and without halogens. These underwent successful selective lateral metalation and electrophilic quenching (LM&EQ) at the C3 of the isoxazole. In a second set of analogs, a phenyl group was introduced at the C4 position of the [3,4-d] ring via a condensation of 4-phenylacetyl-3-ethoxcarbonyl-5-methyl isoxazole with the corresponding hydrazine to generate the 3,4-ds 2b and 2j to 2n.

A Comparison between Single and Double-Dose Intravenous Ketamine Administration in Bipolar Mood Disorder: A Double-Blind Controlled Clinical Trial.

Objective: As glutamatergic system dysfunction is involved in bipolar depression pathophysiology, the glutamate receptor modulators such as Ketamine have been applied as complementary medication for mood stabilizers. While the treatment is currently just the intravenous injection of a single dose, and there is no robust conclusion on Ketamine effectiveness or its side effects in bipolar patients, this study aimed to consider single- and double-dose intravenous injections of Ketamine in bipolar patients compared to the placebo. Method : In a randomized, double-blind controlled clinical trial, 30 patients diagnosed with bipolar I and II disorders according to DSM-IV-TR (SCID-I) were randomly divided into three groups: the first group received an intravenous injection of Ketamine (0.5 mg/kg) and placebo with a three-day interval, the second group received two doses of Ketamine (0.5 mg/kg) in the same interval, and the third group received two placebo injections. Patients were assessed for depression, anxiety, and mania at various time points, including before the injection, 60 minutes after the injection, on the first, third, fifth, seventh, and 14th day, as well as at the end of the first month using the Hamilton Depression Rating Scale, Beck Anxiety Inventory, and Young Mania Scale, respectively. Data were analyzed using ANOVA and Repeated measure tests. Results: The mean age of patients was 36.8 ± 7.9 years, with 18 females (60%) and 12 (40%) males. Depression and anxiety showed significant differences in both the single- and double-dose Ketamine groups over time (P < 0.01). Moreover, mania displayed significant changes during the study time in the single- and double-dose Ketamine groups, as well as the in the control group. However, during the study time, there were no significant differences observed in depression, anxiety, and mania among the three groups (P = 0.198, P = 0.416, and P = 0.540, respectively). Patients did not indicate any side effects during the study. Conclusion: Intravenous Ketamine administration may relieve depressive manifestations in bipolar patients. The findings suggest that a double dose of Ketamine does not lead to greater improvement than a single dose.

Outside-in signaling through the major histocompatibility complex class-I cytoplasmic tail modulates glutamate receptor expression in neurons

The interplay between AMPA-type glutamate receptors (AMPARs) and major histocompatibility complex class I (MHC-I) proteins in regulating synaptic signaling is a crucial aspect of central nervous system (CNS) function. In this study, we investigate the significance of the cytoplasmic tail of MHC-I in synaptic signaling within the CNS and its impact on the modulation of synaptic glutamate receptor expression. Specifically, we focus on the Y321 to F substitution (Y321F) within the conserved cytoplasmic tyrosine YXXΦ motif, known for its dual role in endocytosis and cellular signaling of MHC-I. Our findings reveal that the Y321F substitution influences the expression of AMPAR subunits GluA2/3 and leads to alterations in the phosphorylation of key kinases, including Fyn, Lyn, p38, ERK1/2, JNK1/2/3, and p70 S6 kinase. These data illuminate the crucial role of MHC-I in AMPAR function and present a novel mechanism by which MHC-I integrates extracellular cues to modulate synaptic plasticity in neurons, which ultimately underpins learning and memory.

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.

Pharmacological evidence for glutamatergic pathway involvement in the antidepressant-like effects of 2-phenyl-3-(phenylselanyl)benzofuran in male Swiss mice.

Depression is a multifactorial and heterogeneous disease with several neurobiological mechanisms underlying its pathophysiology, including dysfunctional glutamatergic neurotransmission, which makes the exploration of the glutamate pathway an interesting strategy for developing novel rapid-acting antidepressant treatments. In the present study, we aimed to evaluate the possible glutamatergic pathway relation in the antidepressant-like action of 2-phenyl-3-(phenylselanyl)benzofuran (SeBZF1) in Swiss mice employing the tail suspension test (TST). Male Swiss mice received drugs targeting glutamate receptors before acute SeBZF1 administration at effective (50mg/kg) or subeffective (1mg/kg) dosesby intragastric route (ig). TST and the open-field test (OFT) were employed in all behavioral experiments. The pretreatment of mice with N-methyl-D-aspartate (NMDA) (0.1pmol/site, intracerebroventricular, icv, a selective agonist of the NMDA receptors), D-serine (30µg/site, icv, a co-agonist at the NMDA receptor), arcaine (1mg/kg, intraperitoneal, ip, an antagonist of the polyamine-binding site at the NMDA receptor), and 6,7-dinitroquinoxaline-2,3-dione (DNQX) (2,5µg/site, icv, an antagonist of the AMPA/kainate type of glutamate receptors) inhibited the antidepressant-like effects of SeBZF1 (50mg/kg, ig) in the TST. Coadministration of a subeffective dose of SeBZF1 with low doses of MK-801 (0.001mg/kg, ip, a non-competitive NMDA receptor antagonist) or ketamine (0.1mg/kg, ip, a non-selective antagonist of the NMDA receptors) produced significant antidepressant-like effects (synergistic action). These findings suggest the involvement of the glutamatergic system, probably through modulation of ionotropic glutamate receptors, in the antidepressant-like action of SeBZF1 in mice and contribute to a better understanding of the mechanisms underlying its pharmacological effects.

Antidepressant effects of repeated s-ketamine administration as NMDAR Antagonist: Involvement of CaMKIIα and mTOR signaling in the hippocampus of CUMS mice

With the approval of s-ketamine nasal spray as a novel antidepressant, its robust antidepressant effects have been intensively examined in clinical trials. However, the therapeutic efficacy and mechanisms of repeated intermittent drug administration remain unclear. In the present study, we applied a classic chronic unpredictable mild stress (CUMS) model to induce depressive-like behaviors of mice and evaluated the role of repeated s-ketamine administration (10 mg/kg, 7 consecutive days) in ameliorating depressive-like behaviors and modulating related molecular pathways. A battery of behavioral tests were performed to assess CUMS-induced depression. The protein expressions of GluN1, GluN2A, GluN2B, GluR1, CaMKIIα, phosphorylated CaMKIIα (p-CaMKIIα), BDNF, TrkB, phosphorylated TrkB (p-TrkB), mTOR, and phosphorylated mTOR (p-mTOR) as well as modification of synaptic ultrastructure was identified in hippocampal tissues. It turned out that s-ketamine manifested evident antidepressant effects with improved synaptic plasticity. Meanwhile, the results suggested that s-ketamine could differentially modulate glutamate receptors with upregulated GluN1 and GluR1 levels and downregulated GluN2B levels. CUMS-induced elevation of CaMKIIα phosphorylation and decline of BDNF, TrkB phosphorylation and mTOR could also be reversed through s-ketamine treatment. Together, our study provided evidence that selectively modulated glutamate receptors as well as CaMKIIα and mTOR signaling were involved in repeated s-ketamine administration.

Pharmacological Modulation of Excitotoxicity through the Combined Use of NMDA Receptor Inhibition and Group III mGlu Activation Reduces TMT-Induced Neurodegeneration in the Rat Hippocampus.

We studied the neuroprotective properties of the non-competitive NMDA receptor antagonist memantine, in combination with a positive allosteric modulator of metabotropic glutamate receptors of Group III, VU 0422288. The treatment was started 48 h after the injection of neurotoxic agent trimethyltin (TMT) at 7.5 mg/kg. Three weeks after TMT injection, functional and morphological changes in a rat hippocampus were evaluated, including the expression level of genes characterizing glutamate transmission and neuroinflammation, animal behavior, and hippocampal cell morphology. Significant neuronal cell death occurred in the CA3 and CA4 regions, and to a lesser extent, in the CA1 and CA2 regions. The death of neurons in the CA1 field was significantly reduced in animals with a combined use of memantine and VU 0422288. In the hippocampus of these animals, the level of expression of genes characterizing glutamatergic synaptic transmission (Grin2b, Gria1, EAAT2) did not differ from the level in control animals, as well as the expression of genes characterizing neuroinflammation (IL1b, TGF beta 1, Aif1, and GFAP). However, the expression of genes characterizing neuroinflammation was markedly increased in the hippocampus of animals treated with memantine or VU 0422288 alone after TMT. The results of immunohistochemical studies confirmed a significant activation of microglia in the hippocampus three weeks after TMT injection. In contrast to the hilus, microglia in the CA1 region had an increase in rod-like cells. Moreover, in the CA1 field of the hippocampus of the animals of the MEM + VU group, the amount of such microglia was close to the control. Thus, the short-term modulation of glutamatergic synaptic transmission by memantine and subsequent activation of Group III mGluR significantly affected the dynamics of neurodegeneration in the hippocampus.

Small-molecule screening in aged Drosophila identifies mGluR as a regulator of age-related sleep impairment.

As a normal physiological phenomenon, aging has a significant impact on sleep. Aging leads to sleep impairment, including sleep loss, fragmented sleep, and a lower arousal threshold, leading to various diseases. Because sleep regulates memory consolidation, age-dependent sleep impairment also affects memory. However, the mechanisms underlying age-related sleep dysregulation and its impact on memory remain unclear. Using male and female Drosophila as a model, which possesses sleep characteristics similar to those of mammals and exhibits age-dependent sleep impairment, we performed small-molecule screening to identify novel regulators of age-dependent decline in sleep. The screening identified 3,3'-difluorobenzaldazine (DFB), a positive allosteric modulator of the metabotropic glutamate receptor (mGluR) 5, as a novel sleep-promoting compound in aged flies. We found that mutant flies of mGluR, a single mGluR gene in Drosophila, and decreased mGluR expression had significant impairment in sleep and memory due to olfactory conditioning. The decreased sleep phenotype in the mGluR mutants was not promoted by DFB, suggesting that the effects of DFB on age-dependent sleep impairment are dependent on mGluR. Although aging decreases the expression of mGluR and the binding scaffold proteins Homer and Shank, the transient overexpression of mGluR in neurons improves sleep in both young and aged flies. Overall, these findings indicate that age-dependent decreased expression or function of mGluR impairs sleep and memory in flies, which could lead to age-related sleep and memory impairment.

The Effect of Clozapine and Novel Glutamate Modulator JNJ-46356479 on Nitrosative Stress in a Postnatal Murine Ketamine Model of Schizophrenia.

Schizophrenia (SZ) is a heterogeneous mental disorder, affecting ~1% of the worldwide population. One of the main pathophysiological theories of SZ is the imbalance of excitatory glutamatergic pyramidal neurons and inhibitory GABAergic interneurons, involving N-methyl-D-aspartate receptors (NMDAr). This may lead to local glutamate storms coupled with excessive dendritic pruning and subsequent cellular stress, including nitrosative stress, during a critical period of neurodevelopment, such as adolescence. Nitrosative stress is mediated by nitric oxide (NO), which is released by NO synthases (NOS) and has emerged as a key signaling molecule implicated in SZ. Regarding glutamatergic models of SZ, the administration of NMDAr antagonists has been found to increase NOS levels in the prefrontal cortex (PFC) and ventral hippocampus (HPC). We hypothesized that suboptimal NOS function in adolescence could be a target for early treatments, including clozapine (CLZ) and the novel metabotropic glutamate receptor modulator JNJ-46356479 (JNJ). We analyzed the protein levels of NOS isoforms in adult PFC and HPC of a postnatal ketamine induced murine model of SZ receiving CLZ or JNJ during adolescence by western blot. Endothelial NOS and neuronal NOS increased under ketamine administration in PFC and decreased in CLZ or JNJ treatments. The same trends were found in the HPC in neuronal NOS. In contrast, inducible NOS was increased under JNJ treatment with respect to ketamine induction in the HPC, and the same trends were found in the PFC. Taken together, our findings suggest a misbalance of the NOS system following NMDAr antagonist administration, which was then modulated under early CLZ and JNJ treatments.

An integrated cytokine and kynurenine network as the basis of neuroimmune communication.

Two of the molecular families closely associated with mediating communication between the brain and immune system are cytokines and the kynurenine metabolites of tryptophan. Both groups regulate neuron and glial activity in the central nervous system (CNS) and leukocyte function in the immune system, although neither group alone completely explains neuroimmune function, disease occurrence or severity. This essay suggests that the two families perform complementary functions generating an integrated network. The kynurenine pathway determines overall neuronal excitability and plasticity by modulating glutamate receptors and GPR35 activity across the CNS, and regulates general features of immune cell status, surveillance and tolerance which often involves the Aryl Hydrocarbon Receptor (AHR). Equally, cytokines and chemokines define and regulate specific populations of neurons, glia or immune system leukocytes, generating more specific responses within restricted CNS regions or leukocyte populations. In addition, as there is a much larger variety of these compounds, their homing properties enable the superimposition of dynamic variations of cell activity upon local, spatially limited, cell populations. This would in principle allow the targeting of potential treatments to restricted regions of the CNS. The proposed synergistic interface of 'tonic' kynurenine pathway affecting baseline activity and the superimposed 'phasic' cytokine system would constitute an integrated network explaining some features of neuroimmune communication. The concept would broaden the scope for the development of new treatments for disorders involving both the CNS and immune systems, with safer and more effective agents targeted to specific CNS regions.

Commentary on Cochrane review: "Ketamine and other glutamate receptor modulators for depression in adults with unipolar major depressive disorder".

Cochrane recently published a review of esketamine and other glutamate receptor modulators in depression. To address the limitations of the review, analyses of esketamine data were conducted to provide additional perspective to the reviewers' interpretation of their findings. Response rate, remission rate, and change from baseline in Montgomery-Åsberg Depression Rating Scale (MADRS) total score were determined using data from all esketamine phase 2/3 registration studies of treatment-resistant depression (TRD) and, separately, all esketamine phase 2/3 registration studies of major depressive disorder (MDD) and active suicidal ideation with intent. Outcomes were assessed at all timepoints (i.e., 24 h, 72 h (MDD with active suicidal intent only), and 1, 2, and 4 weeks). Enrollment criteria of the TRD studies were different than those of the studies of MDD and active suicidal ideation with intent, resulting in differences in patients' clinical characteristics and depression severity between the cohorts. Thus, we did not compare results between these cohorts (as was done in the Cochrane review). In the combined TRD studies, a statistically significant between-group difference favored esketamine plus antidepressant over antidepressant plus placebo at 24 h (based on response, remission, and change in MADRS score), 1 week (change in MADRS score), 2 weeks (response and change in MADRS score), and 4 weeks (response, remission, and change in MADRS score). In the combined studies of MDD and active suicidal ideation with intent, the between-group difference was statistically different, favoring esketamine plus standard-of-care over placebo plus standard-of-care, at 24 h (response, remission, and change in MADRS score), 72 h and 1 week (change in MADRS score), 2 weeks (response), and 4 weeks (response, remission, and change in MADRS score). For both study types, the between-group difference in outcomes was not statistically significant at the other timepoints. Esketamine improves response, remission, and depressive symptoms as early as 24 h post-first dose among patients with TRD and among patients with MDD and active suicidal ideation with intent.

A mechanistic overview of approaches for the treatment of psychostimulant dependence.

Psychostimulant use disorder is a major health issue around the world with enormous individual, family-related and societal consequences, yet there are no effective pharmacological treatments available. In this review, a target-based overview of pharmacological treatments toward psychostimulant addiction will be presented. We will go through therapeutic approaches targeting different aspects of psychostimulant addiction with focus on three major areas; 1) drugs targeting signalling, and metabolism of the dopamine system, 2) drugs targeting either AMPA receptors or metabotropic glutamate receptors of the glutamate system and 3) drugs targeting the severe side-effects of quitting long-term psychostimulant use. For each of these major modes of intervention, findings from pre-clinical studies in rodents to clinical trials in humans will be listed, and future perspectives of the different treatment strategies as well as their potential side-effects will be discussed. Pharmaceuticals modulating the dopamine system, such as antipsychotics, DAT-inhibitors, and disulfiram, have shown some promising results. Cognitive enhancers have been found to increase aspects of behavioural control, and drugs targeting the glutamate system such as modulators of metabotropic glutamate receptors and AMPA receptors have provided interesting changes in relapse behaviour. Furthermore, CRF-antagonists directed toward alleviating the symptoms of the withdrawal stage have been examined with interesting resulting changes in behaviour. There are promising results investigating therapeutics for psychostimulant addiction, but further preclinical work and additional human studies with a more stratified patient selection are needed to prove sufficient evidence of efficacy and tolerability.

Ketamine and Other Glutamate Receptor Modulating Agents for Treatment-Resistant Depression: A Systematic Review of Randomized Controlled Trials.

Objective: Available treatments of depression have limited efficacy and unsatisfactory remission rates. This study aims to review randomized controlled trials (RCTs) investigating effects of glutamate receptor modulators in treating patients with resistant depression. Method : The study protocol was registered in PROSPERO (CRD42021225516). Scopus, ISI Web of Science, Embase, Cochrane Library, Google Scholar, and three trial registries were searched up to September 2020 to find RCTs evaluating glutamate receptor modulators for resistant depression. The difference between intervention and control groups in changing depression scores from baseline to endpoint was considered the primary outcome. Version 2 of the Cochrane risk-of-bias tool for randomized trials was used to assess the quality of the RCTs. No funding was received. Results: Thirty-eight RCTs were included. Based on the included studies, compelling evidence was found for ketamine (with or without electroconvulsive therapy, intravenous or other forms), nitrous oxide, amantadine, and rislenemdaz (MK-0657); the results for MK-0657, amantadine, and nitrous oxide were only based on one study for each. Lithium, lanicemine, D-cycloserine, and decoglurant showed mixed results for efficacy, and, riluzole, and 7-chlorokynurenic acid were mostly comparable to placebo. A limited number of studies were available that addressed drugs other than ketamine. Conclusion: The study cannot determine the difference between statistical and clinical significance between the agents and placebo due to high heterogeneity among the RCTs. Nevertheless, ketamine could be used as an efficacious drug in TRD; still, additional studies are needed to delineate the optimum dosage, duration of efficacy, and intervals. Further studies are also recommended on the effectiveness of glutamatergic system modulators other than ketamine on treatment-resistant depression.

Allosteric Modulators of Metabotropic Glutamate Receptors as Novel Therapeutics for Neuropsychiatric Disease.

Metabotropic glutamate (mGlu) receptors, a family of G-protein-coupled receptors, have been identified as novel therapeutic targets based on extensive research supporting their diverse contributions to cell signaling and physiology throughout the nervous system and important roles in regulating complex behaviors, such as cognition, reward, and movement. Thus, targeting mGlu receptors may be a promising strategy for the treatment of several brain disorders. Ongoing advances in the discovery of subtype-selective allosteric modulators for mGlu receptors has provided an unprecedented opportunity for highly specific modulation of signaling by individual mGlu receptor subtypes in the brain by targeting sites distinct from orthosteric or endogenous ligand binding sites on mGlu receptors. These pharmacological agents provide the unparalleled opportunity to selectively regulate neuronal excitability, synaptic transmission, and subsequent behavioral output pertinent to many brain disorders. Here, we review preclinical and clinical evidence supporting the utility of mGlu receptor allosteric modulators as novel therapeutic approaches to treat neuropsychiatric diseases, such as schizophrenia, substance use disorders, and stress-related disorders.Significance StatementAllosteric modulation of metabotropic glutamate (mGlu) receptors represents a promising therapeutic strategy to normalize dysregulated cellular physiology associated with neuropsychiatric disease. This review summarizes preclinical and clinical studies using mGlu receptor allosteric modulators as experimental tools and potential therapeutic approaches for the treatment of neuropsychiatric diseases, including schizophrenia, stress, and substance use disorders.

VGLUT3 Ablation Differentially Modulates Glutamate Receptor Densities in Mouse Brain.

Type 3 vesicular glutamate transporter (VGLUT3) represents a unique modulator of glutamate release from both nonglutamatergic and glutamatergic varicosities within the brain. Despite its limited abundance, VGLUT3 is vital for the regulation of glutamate signaling and, therefore, modulates the activity of various brain microcircuits. However, little is known about how glutamate receptors are regulated by VGLUT3 across different brain regions. Here, we used VGLUT3 constitutive knock-out (VGLUT3–/–) mice and explored how VGLUT3 deletion influences total and cell surface expression of different ionotropic and metabotropic glutamate receptors. VGLUT3 deletion upregulated the overall expression of metabotropic glutamate receptors mGluR5 and mGluR2/3 in the cerebral cortex. In contrast, no change in the total expression of ionotropic NMDAR glutamate receptors were observed in the cerebral cortex of VGLUT3–/– mice. We noted significant reduction in cell surface levels of mGluR5, NMDAR2A, NMDAR2B, as well as reductions in dopaminergic D1 receptors and muscarinic M1 acetylcholine receptors in the hippocampus of VGLUT3–/– mice. Furthermore, mGluR2/3 total expression and mGluR5 cell surface levels were elevated in the striatum of VGLUT3–/– mice. Last, AMPAR subunit GluA1 was significantly upregulated throughout cortical, hippocampal, and striatal brain regions of VGLUT3–/– mice. Together, these findings complement and further support the evidence that VGLUT3 dynamically regulates glutamate receptor densities in several brain regions. These results suggest that VGLUT3 may play an intricate role in shaping glutamatergic signaling and plasticity in several brain areas.

Deficiency of autism-related Scn2a gene in mice disrupts sleep patterns and circadian rhythms

Autism spectrum disorder (ASD) affects ~2% of the population in the US, and monogenic forms of ASD often result in the most severe manifestation of the disorder. Recently, SCN2A has emerged as a leading gene associated with ASD, of which abnormal sleep pattern is a common comorbidity. SCN2A encodes the voltage-gated sodium channel NaV1.2. Predominantly expressed in the brain, NaV1.2 mediates the action potential firing of neurons. Clinical studies found that a large portion of children with SCN2A deficiency have sleep disorders, which severely impact the quality of life of affected individuals and their caregivers. The underlying mechanism of sleep disturbances related to NaV1.2 deficiency, however, is not known. Using a gene-trap Scn2a-deficient mouse model (Scn2atrap), we found that Scn2a deficiency results in increased wakefulness and reduced non-rapid-eye-movement (NREM) sleep. Brain region-specific Scn2a deficiency in the suprachiasmatic nucleus (SCN) containing region, which is involved in circadian rhythms, partially recapitulates the sleep disturbance phenotypes. At the cellular level, we found that Scn2a deficiency disrupted the firing pattern of spontaneously firing neurons in the SCN region. At the molecular level, RNA-sequencing analysis revealed differentially expressed genes in the circadian entrainment pathway including core clock genes Per1 and Per2. Performing a transcriptome-based compound discovery, we identified dexanabinol (HU-211), a putative glutamate receptor modulator, that can partially reverse the sleep disturbance in mice. Overall, our study reveals possible molecular and cellular mechanisms underlying Scn2a deficiency-related sleep disturbances, which may inform the development of potential pharmacogenetic interventions for the affected individuals.