Modulation Of Glutamate Receptors Research Articles

APOE and KIBRA Interactions on Brain Functional Connectivity in Healthy Young Adults.

Genetic variations of APOE and KIBRA have been associated with human memory and Alzheimer's disease. APOE and KIBRA can jointly modulate glutamate receptor to influence long-term potentiation; however, their interactions on brain functional connectivity remain unknown. Here, we investigated additive and epistatic interactions between APOE and KIBRA (rs17070145) on brain functional connectivity density (FCD) in 267 healthy young adults. A voxel-based FCD analysis was performed to identify brain regions with significant APOE-KIBRA interaction. Additive effects showed decreased FCD in the left parahippocampal gyrus and the right middle temporal gyrus and increased FCD in the bilateral middle occipital gyri, with the increase of the number of the risk-alleles of APOE and KIBRA. Epistatic effects showed APOE×KIBRA interaction in the FCD of the dorsolateral prefrontal cortex (DLPFC). The FCD of the DLPFC showed APOE risk-allele-dependent reduction (ε2>ε3>ε4) in KIBRA TT homozygotes, but APOE risk-allele-dependent increase (ε2<ε3<ε4) in KIBRA C-carriers. FCD differences were only significant between the 2 extreme subgroups in both additive and epistatic analyses. These findings suggest that APOE and KIBRA have region-dependent additive and epistatic interactions on brain connectivity in healthy young adults.

Niclosamide is a Negative Allosteric Modulator of Group I Metabotropic Glutamate Receptors: Implications for Neuropathic Pain.

Novel therapeutics are greatly needed that target specific pathological receptors and pathways involved in Neuropathic Pain (NP). Extending our previous work published in this Journal on Group I metabotropic glutamate receptor (mGluR) modulators, we now investigate the therapeutic potential of niclosamide in modulating aberrant glutamate transmission in NP. Calcium mobilization assays and cross-receptor selectivity experiments are conducted to characterize the pharmacological activity of niclosamide. A focused series of niclosamide analogues is then prepared to elucidate key structural determinants that emerged from computational molecular modeling analysis on drug-receptor interactions. Finally, niclosamide and a carbamate derivative are studied to assess their efficacy in an NP-evoked mechanical hyperalgesia model in rats. Niclosamide is a low-nanomolar allosteric antagonist of Group I mGluRs with high selectivity for Group I over homologous Group III mGluRs. The phenolic hydroxyl group of niclosamide forms a crucial hydrogen bond with mGluR1/5. Its bioactive coplanar conformation is further stabilized by the nitro substituent on the B ring and an intramolecular bond. Mechanical hyperalgesia in NP rats is reversed by niclosamide through three different dosing routes. To our knowledge, this is the first report of the salicylanilide class of compounds as potential treatments for NP.

Deeper Insights into the Allosteric Modulation of Ionotropic Glutamate Receptors

Two articles in this issue of Neuron (Yelshanskaya etal., 2016; Yi etal., 2016) explore the structural basis of allosteric inhibition in ionotropic glutamate receptors, providing key insights into how iGluRs function in the brain as well as how they might be pharmacologically modulated in neurological disorders and disease.

Development and Antiparkinsonian Activity of VU0418506, a Selective Positive Allosteric Modulator of Metabotropic Glutamate Receptor 4 Homomers without Activity at mGlu2/4 Heteromers.

Metabotropic glutamate receptor 4 (mGlu4) is emerging as a potential therapeutic target for numerous central nervous system indications, including Parkinson's disease (PD). As the glutamate binding sites among the eight mGlu receptors are highly conserved, modulation of receptor activity via allosteric sites within the receptor transmembrane domains using positive and negative allosteric modulators (PAMs and NAMs, respectively) has become a common strategy. We and others have used PAMs targeting mGlu4 to show that potentiation of receptor signaling induces antiparkinsonian activity in a variety of PD animal models, including haloperidol-induced catalepsy and 6-hydroxydopamine-induced lesion. Recently, mGlu4 has been reported to form heteromeric complexes with other mGlu receptor subtypes, such as mGlu2, and the resulting heteromer exhibits a distinct pharmacological profile in response to allosteric modulators. For example, some mGlu4 PAMs do not appear to potentiate glutamate activity when mGlu2 and mGlu4 are coexpressed, whereas other compounds potentiate mGlu4 responses regardless of mGlu2 coexpression. We report here the discovery and characterization of VU0418506, a novel mGlu4 PAM with activity in rodent PD models. Using pharmacological approaches and Complemented Donor-Acceptor resonance energy transfer (CODA-RET) technology, we find that VU0418506 does not potentiate agonist-induced activity when mGlu2 and mGlu4 are heterodimerized, suggesting that the antiparkinsonian action of mGlu4 PAMs can be induced by compounds without activity at mGlu2/4 heteromers.

Shedding Light on Metabotropic Glutamate Receptors

In this issue of Cell Chemical Biology, the elegant manuscript by Rovira etal. (2016) describes a negative allosteric modulator (NAM) of mGlu4 metabotropic glutamate receptors with invivo activity. This compound is rapidly and reversibly inactivated by light and represents a powerful pharmacological tool for the study of mGlu4 receptors in their native environment.

OptoGluNAM4.1, a Photoswitchable Allosteric Antagonist for Real-Time Control of mGlu4 Receptor Activity

OptoGluNAM4.1, a negative allosteric modulator (NAM) of metabotropic glutamate receptor 4 (mGlu4) contains a reactive group that covalently binds tothe receptor and a blue-light-activated, fast-relaxing azobenzene group that allows reversible receptor activity photocontrol invitro and invivo. OptoGluNAM4.1 induces light-dependent behavior in zebrafish and reverses the activity of the mGlu4 agonist LSP4-2022 in a mice model of chronic pain, defining a photopharmacological tool to better elucidate the physiological roles of the mGlu4 receptor in the nervous system.

Ketamine and other glutamate receptor modulators for depression in adults

Considering the ample evidence of involvement of the glutamate system in the pathophysiology of depression, pre-clinical and clinical studies have been conducted to assess the antidepressant efficacy of glutamate inhibition, and glutamate receptor modulators in particular. This review focuses on the use of glutamate receptor modulators in unipolar depression.

Ketamine and other glutamate receptor modulators for depression in bipolar disorder in adults

There is emerging evidence that glutamatergic system dysfunction might play an important role in the pathophysiology of bipolar depression. This review focuses on the use of glutamate receptor modulators for depression in bipolar disorder.

Is there a future for other glutamate receptor modulators in the pharmacotherapy of mood disorders?

There is increasing evidence that some glutamatergic drugs could have antidepressant effects. Ketamine as a promising prototype for novel glutamatergic antidepressants has a much faster onset of action and is...

ITI-007 in the treatment of schizophrenia: from novel pharmacology to clinical outcomes

ABSTRACTITI-007 is an investigational drug being developed for schizophrenia and other neuropsychiatric/neurodegenerative diseases. ITI-007 has a unique pharmacological profile, combining potent 5-HT2a receptor antagonism with cell-type-specific dopamine and glutamate receptor modulation, plus serotonin reuptake inhibition. At dopamine-D2 receptors, ITI-007 acts as a post-synaptic antagonist and pre-synaptic partial agonist. Additionally, ITI-007 stimulates phosphorylation of glutamatergic NMDA-NR2B receptors, downstream of dopamine-D1 receptor intracellular signaling. Based on a large, placebo and risperidone controlled, Phase-II trial, ITI-007 60 mg was shown to be effective in reducing symptoms in patients with acutely exacerbated schizophrenia. The antipsychotic efficacy of ITI-007 60 mg in this patient population was confirmed in a recently completed Phase III study. ITI-007 was associated with minimal safety risk compared to risperidone (Phase II study) or placebo (both studies) for neuromotor disturbances, prolactin changes, weight gain and metabolic abnormalities. A second 6-week, placebo and risperidone-controlled Phase-III trial in acutely exacerbated schizophrenia is ongoing.

Clinical aspects of urea cycle dysfunction and altered brain energy metabolism on modulation of glutamate receptors and transporters in acute and chronic hyperammonemia.

In living organisms, nitrogen arise primarily as ammonia (NH3) and ammonium (NH4(+)), which is a main component of the nucleic acid pool and proteins. Although nitrogen is essential for growth and maintenance in animals, but when the nitrogenous compounds exceeds the normal range which can quickly lead to toxicity and death. Urea cycle is the common pathway for the disposal of excess nitrogen through urea biosynthesis. Hyperammonemia is a consistent finding in many neurological disorders including congenital urea cycle disorders, reye's syndrome and acute liver failure leads to deleterious effects. Hyperammonemia and liver failure results in glutamatergic neurotransmission which contributes to the alteration in the function of the glutamate-nitric oxide-cGMP pathway, modulates the important cerebral process. Even though ammonia is essential for normal functioning of the central nervous system (CNS), in particular high concentrations of ammonia exposure to the brain leads to the alterations of glutamate transport by the transporters. Several glutamate transporters have been recognized in the central nervous system and each has a unique physiological property and distribution. The loss of glutamate transporter activity in brain during acute liver failure and hyperammonemia is allied with increased extracellular brain glutamate concentrations which may be conscientious for the cerebral edema and ultimately cell death.

Learning to cope with stress modulates anterior cingulate cortex stargazin expression in monkeys and mice

Intermittent mildly stressful situations provide opportunities to learn, practice, and improve coping with gains in subsequent emotion regulation. Here we investigate the effects of learning to cope with stress on anterior cingulate cortex gene expression in monkeys and mice. Anterior cingulate cortex is involved in learning, memory, cognitive control, and emotion regulation. Monkeys and mice were randomized to either stress coping or no-stress treatment conditions. Profiles of gene expression were acquired with HumanHT-12v4.0 Expression BeadChip arrays adapted for monkeys. Three genes identified in monkeys by arrays were then assessed in mice by quantitative real-time polymerase chain reaction. Expression of a key gene (PEMT) involved in acetylcholine biosynthesis was increased in monkeys by coping but this result was not verified in mice. Another gene (SPRY2) that encodes a negative regulator of neurotrophic factor signaling was decreased in monkeys by coping but this result was only partly verified in mice. The CACNG2 gene that encodes stargazin (also called TARP gamma-2) was increased by coping in monkeys as well as mice randomized to coping with or without subsequent behavioral tests of emotionality. As evidence of coping effects distinct from repeated stress exposures per se, increased stargazin expression induced by coping correlated with diminished emotionality in mice. Stargazin modulates glutamate receptor signaling and plays a role in synaptic plasticity. Molecular mechanisms of synaptic plasticity that mediate learning and memory in the context of coping with stress may provide novel targets for new treatments of disorders in human mental health.

P.1.007 Ketamine-induced plasticity in mouse-primary and human-iPSC-derived dopaminergic neurons involves D3R and mTOR pathway

Glutamatergic ionotropic and metabotropic receptor modulators have been shown to produce anticonvulsant activity in a number of animal seizure models, e.g. maximal electroshock (MES) and DBA/2 sensory-induced seizures. The 6 Hz model of partial seizures is an alternative low frequency, long duration stimulation paradigm resulting in a seizure characterized by jaw and forelimb clonus, immobility, and an elevated tail (Straub-tail). A unique aspect of this model is that it is the only acute electrically-induced seizure model in which levetiracetam has displayed anticonvulsant activity, suggesting that the 6 Hz seizure model may be useful in identifying compounds with unique anticonvulsant profiles. The purpose of the present study was to examine the role of glutamate receptors in the MES and 6 Hz seizure models using a number of NMDA, AMPA/KA, and mGlu receptor modulators. The pharmacological profile of the 6 Hz seizure model was compared to that of the MES model using eight ionotropic glutamate receptor antagonists and eight mGlu receptor modulators. The ionotropic receptor antagonists MK-801, LY235959, NBQX, LY293558, GYKI 52466, LY300168, and LY377770 produced complete protection from tonic extension in the MES model. Furthermore, the noncompetitive mGlu1 (LY456236) and mGlu5 (MPEP) metabotropic receptor antagonists and the mGlu8 metabotropic receptor agonist (PPG) were also effective in the MES model whereas the competitive mGlu1 (LY367385) receptor antagonist, the mGlu2/3 (LY379268 and LY389795) and Group III (l-AP4) metabotropic receptor agonists were ineffective. In contrast, all of the compounds tested, produced dose-dependent protection in the 6 Hz model with an increase in potency as compared to the MES model. The largest protective indices (P.I.=TD50/ED50) observed were associated with the iGlu5 antagonist LY382884 and the mGlu2/3 receptor agonists LY379268 and LY389795 (P.I.=>14, 14, and 4.9, respectively) in the 6 Hz model. The results from the present study support the continued search for glutamate receptor modulators as potential antiepileptic agents. Furthermore these results illustrate the importance of using several different animal seizure models in the search for novel AEDs and the potential utility of the 6 Hz seizure model in identifying novel AEDs.

Chronic Ampakine Treatments Stimulate Dendritic Growth and Promote Learning in Middle-Aged Rats.

Brain aging is characterized by a progressive loss of dendritic arbors and the emergence of impairments to learning-related synaptic plasticity. The present studies show that dendritic losses are evident by middle age despite housing in an enriched environment and can be mostly reversed by long-term, oral administration of a positive allosteric modulator of AMPA-type glutamate receptors. Dendritic recovery was accompanied by improvements to both synaptic plasticity and the encoding of long-term memory of a novel, complex environment. Because the short half-life compound had no evident negative effects, the results suggest a plausible strategy for treating age-related neuronal deterioration.

Modulation of Glutamate Receptors by Auxiliary Proteins a Structural Investigation

Ionotropic glutamate receptors (iGluRs) are the primary neurotransmitter receptors involved in excitatory synaptic transmission. iGluRs are tetrameric proteins comprised of extracellular amino terminal domains (ATD) and ligand binding domains (LBD), transmembrane domains (TM) and intercellular C-terminal domains. The LBD is a clamshell-like structure divided into segments termed S1 and S2 that form a cleft. Upon glutamate binding the LBD cleft closes and propagates its conformational change to the TM domains activating the cation-selective pore. Mutagenic disruptions in receptor structural organization clearly show distinct functional effects. Therefore, these structural changes serve as obvious targets for the modulation of receptor function. iGluR receptors are classified into subtypes according to their selective agonist; α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-D-aspartate (NMDA), and kainate receptors (KARs). AMPA and KARs have the most similar structural homology. Additionally they both have auxiliary subunit proteins shown to modulate receptor function, Gamma-2 and Neto2 respectively. Studies have confirmed the interaction and modulatory effect of the auxiliary proteins with their receptors; however, little is known concerning their structural influence and its translation to functional changes. In this study, we investigated the cleft closer and inter-subunit distances of AMPA (GluR2) and KAR (GluK2) with and without Gamma-2 and Neto2 using luminescence energy resonance transfer (LRET). The LRET data shows the auxiliary proteins alter the structure of kainate and AMPA receptor in similar ways. The addition of auxiliary protein moves GluK2 and GluR2 from a relaxed to a more constricted conformation. The auxiliary proteins act by supporting the receptor extracellular domains thereby cradling them into closer inter-domain proximity while keeping them more structurally organized.

Translational neurophysiological markers for activity of the metabotropic glutamate receptor (mGluR2) modulator JNJ-40411813: Sleep EEG correlates in rodents and healthy men

Alterations in rapid eye movement sleep (REM) have been suggested as valid translational efficacy markers: activation of the metabotropic glutamate receptor 2 (mGluR2) was shown to increase REM latency and to decrease REM duration.The present paper addresses the effects on vigilance states of the mGluR2 positive allosteric modulator (PAM) JNJ-40411813 at different circadian times in rats and after afternoon dosing in humans. Due to its dual mGluR2 PAM/serotonin 2A (5-HT2A) receptor antagonism in rodents, mGlu2R specificity of effects was studied in wild-type (WT) and mGluR2 (−/−) mice. 5-HT2A receptor occupancy was determined in humans using positron emission tomography (PET). Tolerance development was examined in rats after chronic dosing. EEG oscillations and network connectivity were assessed using multi-channel EEG.In rats, JNJ-40411813 increased deep sleep time and latency of REM onset but reduced REM time when administered 2 h after ‘lights on’ (CT2): this was sustained after chronic dosing. At CT5 similar effects were elicited, at CT10 only deep sleep was enhanced. Withdrawal resulted in baseline values, while re-administration reinstated drug effects. Parieto-occipital cortical slow theta and gamma oscillations were correlated with low locomotion. The specificity of functional response was confirmed in WT but not mGluR2 (−/−) mice. A double-blind, placebo-controlled polysomnographic study in healthy, elderly subjects showed that 500 mg of JNJ-40411813 consistently increased deep sleep time, but had no effect on REM parameters. This deep sleep effect was not explained by 5-HT2A receptor binding, as in the PET study even 700 mg only marginally displaced the tracer.JNJ-40411813 elicited comparable functional responses in rodents and men if circadian time of dosing was taken into account. These findings underscore the translational potential of sleep mechanisms in evaluating mGluR2 therapeutics when administered at the appropriate circadian time.

Neurobiological Insights from mGlu Receptor Allosteric Modulation.

Allosteric modulation of metabotropic glutamate (mGlu) receptors offers a promising pharmacological approach to normalize neural circuit dysfunction associated with various psychiatric and neurological disorders. As mGlu receptor allosteric modulators progress through discovery and clinical development, both technical advances and novel tool compounds are providing opportunities to better understand mGlu receptor pharmacology and neurobiology. Recent advances in structural biology are elucidating the structural determinants of mGlu receptor–negative allosteric modulation and supplying the means to resolve active, allosteric modulator-bound mGlu receptors. The discovery and characterization of allosteric modulators with novel pharmacological profiles is uncovering the biological significance of their intrinsic agonist activity, biased mGlu receptor modulation, and novel mGlu receptor heterodimers. The development and exploitation of optogenetic and optopharmacological tools is permitting a refined spatial and temporal understanding of both mGlu receptor functions and their allosteric modulation in intact brain circuits. Together, these lines of research promise to provide a more refined understanding of mGlu receptors and their allosteric modulation that will inform the development of mGlu receptor allosteric modulators as neurotherapeutics in the years to come.

Overview of Glutamatergic Dysregulation in Central Pathologies.

As the major excitatory neurotransmitter in the mammalian central nervous system, glutamate plays a key role in many central pathologies, including gliomas, psychiatric, neurodevelopmental, and neurodegenerative disorders. Post-mortem and serological studies have implicated glutamatergic dysregulation in these pathologies, and pharmacological modulation of glutamate receptors and transporters has provided further validation for the involvement of glutamate. Furthermore, efforts from genetic, in vitro, and animal studies are actively elucidating the specific glutamatergic mechanisms that contribute to the aetiology of central pathologies. However, details regarding specific mechanisms remain sparse and progress in effectively modulating glutamate to alleviate symptoms or inhibit disease states has been relatively slow. In this report, we review what is currently known about glutamate signalling in central pathologies. We also discuss glutamate’s mediating role in comorbidities, specifically cancer-induced bone pain and depression.

Ketamine and other glutamate receptor modulators for depression in bipolar disorder in adults.

There is emerging evidence that glutamatergic system dysfunction might play an important role in the pathophysiology of bipolar depression. This review focuses on the use of glutamate receptor modulators for depression in bipolar disorder. 1. To assess the effects of ketamine and other glutamate

Ketamine and other glutamate receptor modulators for depression in adults.

Considering the ample evidence of involvement of the glutamate system in the pathophysiology of depression, pre-clinical and clinical studies have been conducted to assess the antidepressant efficacy of glutamate inhibition, and glutamate receptor modulators in particular. This review focuses on the