On the hypes and falls in neuroprotection: targeting the NMDA receptor

Selective Reduction of Ca2+ Entry Through the Human NMDA Receptor: a Quantitative Study by Simultaneous Ca2+ and Na+ Imaging

Excessive Ca2+ influx through N-methyl-D-aspartate type glutamate receptors (NMDAR) is associated with excitotoxicity and neuronal death, but the inhibition of this receptor-channel causes severe adverse effects. Thus, a selective reduction of NMDA-mediated Ca2+ entry, leaving unaltered the Na+ current, could represent a valid neuroprotective strategy. We developed a new two-fluorophore approach to efficiently assess the Ca2+ permeability of ligand-gated ion channels, including NMDARs, in different conditions. This technique was able to discriminate differential Ca2+/Na+ permeation ratio through different receptor channels, and through the same channel in different conditions. With this method, we confirmed that EU1794-4, a negative allosteric modulator of NMDARs, decreased their Ca2+ permeability. Furthermore, we measured for the first time the fractional Ca2+ current (Pf, i.e. the percentage of the total current carried by Ca2+ ions) of human NMDARs in the presence of EU1794-4, exhibiting a 40% reduction in comparison to control conditions. EU1794-4 was also able to reduce NMDA-mediated Ca2+ entry in human neurons derived from induced pluripotent stem cells. This last effect was stronger in the absence of extracellular Mg2+, but still significant in its presence, supporting the hypothesis to use NMDA-selective allosteric modulators to lower Ca2+ influx in human neurons, to prevent Ca2+-dependent excitotoxicity and consequent neurodegeneration.

GluN2B subunit selective N-methyl-D-aspartate receptor ligands: Democratizing recent progress to assist the development of novel neurotherapeutics

N-methyl-D-aspartate receptors (NMDARs) play essential roles in vital aspects of brain functions. NMDARs mediate clinical features of neurological diseases and thus, represent a potential therapeutic target for their treatments. Many findings implicated the GluN2B subunit of NMDARs in various neurological disorders including epilepsy, ischemic brain damage, and neurodegenerative disorders such as Parkinson's disease, Alzheimer's disease, Huntington's chorea, and amyotrophic lateral sclerosis. Although a large amount of information is growing consistently on the importance of GluN2B subunit, however, limited recent data is available on how subunit-selective ligands impact NMDAR functions, which blunts the ability to render the diagnosis or craft novel treatments tailored to patients. To bridge this gap, we have focused on and summarized recently reported GluN2B selective ligands as emerging subunit-selective antagonists and modulators of NMDAR. Herein, we have also presented an overview of the structure-function relationship for potential GluN2B/NMDAR ligands with their binding sites and connection to CNS functionalities. Understanding of design rules and roles of GluN2B selective compounds will provide the link to medicinal chemists and neuroscientists to explore novel neurotherapeutic strategies against dysfunctions of glutamatergic neurotransmission.

Constituents of Stachys plants as potential dual inhibitors of AChE and NMDAR for the treatment of Alzheimer's disease: a molecular docking and dynamic simulation study

Alzheimer's disease (AD) is a chronic neurodegenerative condition characterized by progressive cognitive impairment. While the formation of β-amyloid plaques and neurofibrillary tangles are the hallmarks features of AD, the downstream consequence of these byproducts is the disruption of the cholinergic and glutamatergic neural systems. Growing evidence for the existence of interplay between AChE and NMDARs has opened up new venues for the discovery of novel ligands endowed with anticholinesterase and NMDAR-blocking activity. Plants belonging to the stachys genus have been extensively explored for having a broad range of therapeutic applications and have been used traditionally for millennia, to treat various CNS-related disorders, which makes them the ideal source of novel therapeutics. The present study was designed to identify natural dual-target inhibitors for AChE and NMDAR deriving from stachys genus for their potential use in AD. Using molecular docking, drug-likeness-profiling, MD simulation and MMGBSA calculations, an in-house database of biomolecules pertaining to the stachys genus was shortlisted based on their binding affinity, overall stability and critical ADMET parameters. Pre- and post-MD analysis revealed that Isoorientin effectively binds to AChE and NMDAR with various vital interactions, exhibits a stable behavior with minor fluctuations relative to two clinical drugs used as positive control, and displays strong and consistent interactions that lasted for the majority of the simulation. Findings from this study have elucidated the rationale behind the traditional use of Stachys plants for the treatment of AD and could provide new impetus for the development of novel dual-target therapeutics for AD treatment.Communicated by Ramaswamy H. Sarma.

Ischemia-reperfusion injury: molecular mechanisms and therapeutic targets

Ischemia-reperfusion (I/R) injury paradoxically occurs during reperfusion following ischemia, exacerbating the initial tissue damage. The limited understanding of the intricate mechanisms underlying I/R injury hinders the development of effective therapeutic interventions. The Wnt signaling pathway exhibits extensive crosstalk with various other pathways, forming a network system of signaling pathways involved in I/R injury. This review article elucidates the underlying mechanisms involved in Wnt signaling, as well as the complex interplay between Wnt and other pathways, including Notch, phosphatidylinositol 3-kinase/protein kinase B, transforming growth factor-β, nuclear factor kappa, bone morphogenetic protein, N-methyl-D-aspartic acid receptor-Ca2+-Activin A, Hippo-Yes-associated protein, toll-like receptor 4/toll-interleukine-1 receptor domain-containing adapter-inducing interferon-β, and hepatocyte growth factor/mesenchymal-epithelial transition factor. In particular, we delve into their respective contributions to key pathological processes, including apoptosis, the inflammatory response, oxidative stress, extracellular matrix remodeling, angiogenesis, cell hypertrophy, fibrosis, ferroptosis, neurogenesis, and blood-brain barrier damage during I/R injury. Our comprehensive analysis of the mechanisms involved in Wnt signaling during I/R reveals that activation of the canonical Wnt pathway promotes organ recovery, while activation of the non-canonical Wnt pathways exacerbates injury. Moreover, we explore novel therapeutic approaches based on these mechanistic findings, incorporating evidence from animal experiments, current standards, and clinical trials. The objective of this review is to provide deeper insights into the roles of Wnt and its crosstalk signaling pathways in I/R-mediated processes and organ dysfunction, to facilitate the development of innovative therapeutic agents for I/R injury.

Folic acid ameliorates synaptic impairment following cerebral ischemia/reperfusion injury via inhibiting excessive activation of NMDA receptors

Folic acid, a water-soluble B-vitamin, has been demonstrated to decrease the risk of first stroke and improve its poor prognosis. However, the molecular mechanisms responsible for the beneficial effect of folic acid on recovery from ischemic insult remain largely unknown. Excessive activation of the N-methyl-d-aspartate receptors (NMDARs) has been shown to trigger synaptic dysfunction and excitotoxic neuronal death in ischemic brains. Here, we hypothesized that the effects of folic acid on cognitive impairment may involve the changes in synapse loss and NMDAR expression and function following cerebral ischemia/reperfusion injury. The ischemic stroke models were established by middle cerebral artery occlusion/reperfusion (MCAO/R) and by oxygen-glucose deprivation and reperfusion (OGD/R)-treated primary neurons. The results showed that folic acid supplemented diets (8.0 mg/kg for 28 days) improved cognitive performances of rats after MCAO/R. Folic acid also caused a reduction in the number of neuronal death, an increase in the number of synapses and the expressions of synapse-related proteins including SNAP25, Syn, GAP-43 and PSD95, and a decrease in p-CAMKII expression in ischemic brains. Similar changes in synaptic functions were observed in folic acid (32 µM)-treated OGD/R neurons. Furthermore, NMDA treatment reduced folic acid-induced upregulations of synapse-associated proteins and Ca²⁺ influx, whereas downregulations of NMDARs by NR1 or both NR2A and NR2B siRNA further enhanced the expressions of synapse-related proteins raised by folic acid in OGD/R neurons. Our findings suggest that folic acid improves cognitive dysfunctions and ameliorates ischemic brain injury by strengthening synaptic functions via the NMDARs.

Calcitriol Pretreatment Attenuates Glutamate Neurotoxicity by Regulating NMDAR and CYP46A1 Gene Expression in Rats Subjected to Transient Middle Cerebral Artery Occlusion

Although the neuroprotective effects of calcitriol have been demonstrated in a variety of neurological diseases, such as stroke, the precise molecular mechanism has yet to be determined. This study aimed to investigate the possible role of calcitriol as a neuroprotective agent via CYP46A1 and glutamate receptors in a middle cerebral artery occlusion (MCAO) animal model. The MCAO technique was performed on adult male Wistar rats to induce focal cerebral ischemia for 1 hour followed by 23 hours of reperfusion. Calcitriol was given for 7 days prior to stroke induction. Sensorimotor functional tests were done 24 hours after ischemia/reperfusion, and infarct volume was estimated by tetrazolium chloride staining of brain sections. Gene expression of NR2A, NR2B, NR3B, and CYP46A1 was evaluated by RT-PCR followed by western blotting for NR3B protein. Our data revealed that calcitriol pretreatment reduced lesion volume and improved ischemic neurobehavioral parameters. Calcitriol therapy altered the expression of glutamate receptor and CYP46A1 genes. A possible molecular mechanism of calcitriol to reduce the severity and complications of ischemia may be through alterations of glutamate receptor and CYP46A1 gene expression.

Regulation of membrane NMDA receptors by dynamics and protein interactions

Understanding neurotransmitter system crosstalk in the brain is a major challenge in neurobiology. Several intracellular and genomic cascades have been identified in this crosstalk. However, the discovery that neurotransmitter receptors are highly diffusive in the plasma membrane of neurons, where they form heterocomplexes with other proteins, has profoundly changed our view of neurotransmitter signaling. Here, we review new insights into neurotransmitter crosstalk at the plasma membrane. We focus on the membrane organization and interactome of the ionotropic glutamate N-methyl-D-aspartate receptor (NMDAR) that plays a central role in excitatory synaptic and network physiology and is involved in the etiology of several major neuropsychiatric disorders. The nanoscale organization and dynamics of NMDAR is a key regulatory process for glutamate synapse transmission, plasticity, and crosstalk with other neurotransmitter systems, such as the monoaminergic ones. The plasma membrane appears to be a prime regulatory compartment for spatial and temporal crosstalk between neurotransmitter systems in the healthy and diseased brain. Understanding the molecular mechanisms regulating membrane neurotransmitter receptor crosstalk will likely open research avenues for innovative therapeutical strategies.

Brain NMDA Receptors in Schizophrenia and Depression

N-methyl-D-aspartate (NMDA) receptor antagonists such as phencyclidine (PCP), dizocilpine (MK-801) and ketamine have long been considered a model of schizophrenia, both in animals and humans. However, ketamine has been recently approved for treatment-resistant depression, although with severe restrictions. Interestingly, the dosage in both conditions is similar, and positive symptoms of schizophrenia appear before antidepressant effects emerge. Here, we describe the temporal mechanisms implicated in schizophrenia-like and antidepressant-like effects of NMDA blockade in rats, and postulate that such effects may indicate that NMDA receptor antagonists induce similar mechanistic effects, and only the basal pre-drug state of the organism delimitates the overall outcome. Hence, blockade of NMDA receptors in depressive-like status can lead to amelioration or remission of symptoms, whereas healthy individuals develop psychotic symptoms and schizophrenia patients show an exacerbation of these symptoms after the administration of NMDA receptor antagonists.

The dual-functional memantine nitrate MN-08 alleviates cerebral vasospasm and brain injury in experimental subarachnoid haemorrhage models

BACKGROUND AND PURPOSE

Cerebral vasospasm and neuronal apoptosis after subarachnoid haemorrhage (SAH) is the major cause of morbidity and mortality in SAH patients. So far, single-target agents have not prevented its occurrence. Memantine, a non-competitive NMDA re3ceptor antagonist, is known to alleviate brain injury and vasospasm in experimental models of SAH. Impairment of NO availability also contributes to vasospasm. Recently, we designed and synthesized a memantine nitrate MN-08, which has potent dual functions: neuroprotection and vasodilation. Here, we have tested the therapeutic effects of MN-08 in animal models of SAH.

EXPERIMENTAL APPROACH

Binding to NMDA receptors (expressed in HEK293 cells), NO release and vasodilator effects of MN-08 were assessed in vitro. Therapeutic effects of MN-08 were investigated in vivo, using rat and rabbit SAH models.

KEY RESULTS

MN-08 bound to the NMDA receptor, slowly releasing NO in vitro and in vivo. Consequently, MN-08 relaxed the pre-contracted middle cerebral artery ex vivo and increased blood flow velocity in small vessels of the mouse cerebral cortex. It did not, however, lower systemic blood pressure. In an endovascular perforation rat model of SAH, MN-08 improved the neurological scores and ameliorated cerebral vasospasm. Moreover, MN-08 also alleviated cerebral vasospasm in a cisterna magna single-injection model in rabbits. MN-08 attenuated neural cell apoptosis in both rat and rabbit models of SAH. Importantly, the therapeutic benefit of MN-08 was greater than that of memantine.

CONCLUSION AND IMPLICATIONS

MN-08 has neuroprotective potential and can ameliorate vasospasm in experimental SAH models.

Intranasal Erythropoietin Protects CA1 Hippocampal Cells, Modulated by Specific Time Pattern Molecular Changes After Ischemic Damage in Rats

Erythropoietin, a multitarget molecule exhibited neuroprotective properties, especially against cerebral ischemia. However, little effort has been made to determinate both the administration pathway and doses that diminishes neuronal damage. In this study, we investigate the effect on CA1 region of different intranasal doses of rHuEPO (500, 1000 and 2500 IU/kg) applied in distinct post-damage times (1, 6, and 24 h) against ischemic cellular damage. Furthermore, most effective dose and time were used to evaluate gen and protein expression changes in 3 key molecules (EPO, EPOR, and βcR). We established that CA1-region present histopathological damage in this ischemia model and that rHuEPO protects cells against damage, particularly at 1000 IU dose. Molecular data shows that EPO and EPOR gene expression are upregulated in a short term after damage treatment with rHuEPO (1 h); oppositely, BcR is upregulated in ischemic and Isc + EPO. Protein expression data displays no changes on EPO expression in evaluated times after treatment, but a tendency to increase 24 h after damage; in the opposite way, EPOR is upregulated significantly 6 h after treatment and this effect last until 24 h. So, our data suggest that a single intranasal dose of rHuEPO (1 h post-injury) provides histological neurorestoration in CA1 hippocampal region, even if we did not observe a dose-dependent dose effect, the medium dose evaluated (1000 UI/kg of b.w.) was more effective and sufficient for induces molecular changes that provides a platform for neuroprotection.

Extracellular mild acidosis decreases the Ca2+ permeability of the human NMDA receptors

NMDA receptors (NMDARs) are glutamate-gated ion channels involved in excitatory synaptic transmission and in others physiological processes such as synaptic plasticity and development. The overload of Ca²⁺ ions through NMDARs, caused by an excessive activation of receptors, leads to excitotoxic neuronal cell death. For this reason, the reduction of Ca²⁺ flux through NMDARs has been a central focus in finding therapeutic strategies to prevent neuronal cell damage. Extracellular H⁺ are allosteric modulators of NMDARs. Starting from previous studies showing that extracellular mild acidosis reduces NMDA-evoked whole cell currents, we analyzed the effects of this condition on the NMDARs Ca²⁺ permeability, measured as "fractional calcium current" (P_f, i.e. the percentage of the total current carried by Ca²⁺ ions), of human NMDARs NR1/NR2A and NR1/NR2B transiently transfected in HeLa cells. Extracellular mild acidosis significantly reduces P_f of both human NR1/NR2A and NR1/NR2B NMDARs, also decreasing single channel conductance in outside out patches for NR1/NR2A receptor. Reduction of Ca²⁺ flux through NMDARs was also confirmed in cortical neurons in culture. A comparative analysis of both NMDA evoked Ca²⁺ transients and whole cell currents showed that extracellular H⁺ differentially modulate the permeation of Na⁺ and Ca²⁺ through NMDARs. Our data highlight the synergy of two distinct neuroprotective mechanisms during acidosis: Ca²⁺ entry through NMDARs is lowered due to the modulation of both open probability and Ca²⁺ permeability. Furthermore, this study provides the proof of concept that it is possible to reduce Ca²⁺ overload in neurons modulating the NMDAR Ca²⁺ permeability.

The Role of NMDA Receptors in Alzheimer's Disease

In Alzheimer’s disease (AD), early synaptic dysfunction is associated with the increased oligomeric amyloid-beta peptide, which causes NMDAR-dependent synaptic depression and spine elimination. Memantine, low-affinity NMDAR channel blocker, has been used in the treatment of moderate to severe AD. However, clear evidence is still deficient in demonstrating the underlying mechanisms and a relationship between NMDARs dysfunction and AD. This review focuses on not only changes in expression of different NMDAR subunits, but also some unconventional modes of NMDAR action.

Glutamate-induced and NMDA receptor-mediated neurodegeneration entails P2Y1 receptor activation

Despite the characteristic etiologies and phenotypes, different brain disorders rely on common pathogenic events. Glutamate-induced neurotoxicity is a pathogenic event shared by different brain disorders. Another event occurring in different brain pathological conditions is the increase of the extracellular ATP levels, which is now recognized as a danger and harmful signal in the brain, as heralded by the ability of P2 receptors (P2Rs) to affect a wide range of brain disorders. Yet, how ATP and P2R contribute to neurodegeneration remains poorly defined. For that purpose, we now examined the contribution of extracellular ATP and P2Rs to glutamate-induced neurodegeneration. We found both in vitro and in vivo that ATP/ADP through the activation of P2Y1R contributes to glutamate-induced neuronal death in the rat hippocampus. We found in cultured rat hippocampal neurons that the exposure to glutamate (100 µM) for 30 min triggers a sustained increase of extracellular ATP levels, which contributes to NMDA receptor (NMDAR)-mediated hippocampal neuronal death through the activation of P2Y1R. We also determined that P2Y1R is involved in excitotoxicity in vivo as the blockade of P2Y1R significantly attenuated rat hippocampal neuronal death upon the systemic administration of kainic acid or upon the intrahippocampal injection of quinolinic acid. This contribution of P2Y1R fades with increasing intensity of excitotoxic conditions, which indicates that P2Y1R is not contributing directly to neurodegeneration, rather behaving as a catalyst decreasing the threshold from which glutamate becomes neurotoxic. Moreover, we unraveled that such excitotoxicity process began with an early synaptotoxicity that was also prevented/attenuated by the antagonism of P2Y1R, both in vitro and in vivo. This should rely on the observed glutamate-induced calpain-mediated axonal cytoskeleton damage, most likely favored by a P2Y1R-driven increase of NMDAR-mediated Ca²⁺ entry selectively in axons. This may constitute a degenerative mechanism shared by different brain diseases, particularly relevant at initial pathogenic stages.

Reducing excitoxicity with glutamate transporter-1 to treat stroke

The neurotransmitter glutamate is released following ischemic brain damage, and its excitotoxic effects contribute greatly to the development of stroke. Because this release of glutamate occurs within minutes, therapeutic drugs targeting the restriction of glutamate-induced excitotoxicity must be administered quickly following ischemic onset. Here, we evaluate an alternative research approach examining the overexpression of glutamate transporter 1 (GLT1) to reduce infarction and improve behavioral deficits induced by stroke in a rat model of stroke. Recent studies verify the role of glutamate overflow in the pathogenesis of stroke. The experimental approach evaluated glutamate clearance, following ischemia-induced overflow where the GLT had been genetically manipulated to be overexpressed in the ischemic region. A viral vector-mediated gene transfer approach activated the overexpression of GLT1 to successfully reduce ischemia-induced glutamate overflow, decrease cell death, and improve behavioral recovery among animal models. These findings further support the role of glutamate in the pathogenesis of stroke and the upregulation of endogenous GLT1 as a promising approach to protect against the effects of ischemic brain damage caused by glutamate excitotoxicity. This study is a review article. Referred literature in this paper has been listed in the references part. The datasets supporting the conclusions of this article are available online by searching the PubMed. Some original points in this article come from the laboratory practice in our research centers and our experiences.

Association of GRIN2B gene polymorphism and Obsessive Compulsive disorder and symptom dimensions: A pilot study

The etiology of OCD is largely unknown, but neuroimaging and pharmacological studies suggest that glutamatergic system plays a significant role on OCD development. We genotyped one polymorphism at GRIN2B (rs1019385) by real time Polymerase Chain Reaction in a sample of Brazilian Obsessive-Compulsive patients and healthy controls, and evaluated its influence on OCD. We found the T-allele and TT genotype to be significantly associated with OCD and ordering dimension. The T-allele was also significantly associated with checking. These preliminary results demonstrated that the GRIN2B gene may confer to some extent the susceptibility to OCD and its symptoms.

Review: Cav2.3 R-type Voltage-Gated Ca2+ Channels - Functional Implications in Convulsive and Non-convulsive Seizure Activity

Background:

Researchers have gained substantial insight into mechanisms of synaptic transmission, hyperexcitability, excitotoxicity and neurodegeneration within the last decades. Voltage-gated Ca²⁺ channels are of central relevance in these processes. In particular, they are key elements in the etiopathogenesis of numerous seizure types and epilepsies. Earlier studies predominantly targeted on Ca_v2.1 P/Q-type and Ca_v3.2 T-type Ca²⁺ channels relevant for absence epileptogenesis. Recent findings bring other channels entities more into focus such as the Ca_v2.3 R-type Ca²⁺ channel which exhibits an intriguing role in ictogenesis and seizure propagation. Ca_v2.3 R-type voltage gated Ca²⁺ channels (VGCC) emerged to be important factors in the pathogenesis of absence epilepsy, human juvenile myoclonic epilepsy (JME), and cellular epileptiform activity, e.g. in CA1 neurons. They also serve as potential target for various antiepileptic drugs, such as lamotrigine and topiramate.

Objective:

This review provides a summary of structure, function and pharmacology of VGCCs and their fundamental role in cellular Ca²⁺ homeostasis. We elaborate the unique modulatory properties of Ca_v2.3 R-type Ca²⁺ channels and point to recent findings in the proictogenic and proneuroapoptotic role of Ca_v2.3 R-type VGCCs in generalized convulsive tonic–clonic and complex-partial hippocampal seizures and its role in non-convulsive absence like seizure activity.

Conclusion:

Development of novel Ca_v2.3 specific modulators can be effective in the pharmacological treatment of epilepsies and other neurological disorders.

Mystixin-7 mini-peptide protects ionotropic glutamatergic mechanisms against oxygen-glucose deprivation in vitro

The aim of the present study was to explore the neuroprotective effects of the mystixin-7 mini-peptide (MTX, a synthetic corticotropin-releasing-factor-like, 7-amino-acid peptide) on an in vitro oxygen glucose deprivation model (OGD, 10min). The study used a technique of on-line monitoring of changes in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) and N-methyl-d-aspartic acid receptor (NMDAR)-mediated field excitatory postsynaptic potentials (fEPSPs) in the olfactory cortex slices in the OGD model. OGD resulted in an irreversible blockade of both AMPAR and NMDAR activity. Pretreatment of slices by MTX and their subsequent exposure to OGD resulted in decreased activity of these postsynaptic mechanisms (AMPARs, 71%; NMDARs, 68% as compared to baseline), but they were not blocked altogether. The degree protection of activity of both AMPARs and NMDARs had dose-dependent manner, with a maximal effect at 100mg/mL. These protective effects were retained after the removal of MTX from the bathing medium. To evaluate the protective efficacy of MTX on NMDARs, the slices were pretreated by MTX and exposed to OGD and then treated with l-glutamate (1mM). NMDARs' response to application of l-glutamate was minimal at higher concentrations of MTX and maximal at lower concentrations. These findings indicate that the molecules of MTX interact with a certain amount of NMDARs, and thereby protect them from the OGD. Pretreatment of slices with MTX contributed to the protection of network activity against OGD and promoted the development of the learning process in the form of long-term potentiation. To specify the protective effects of MTX, it was denatured by trypsin. The proteolytic cleavage of MTX resulted to a significant decrease in the activity of both AMPARs and NMDARs against OGD as compared with that of the native peptide. Together, these findings provide further insight into the protective potential of the MTX mini-peptide. We believe that the data presented can be the basis for the development of therapeutics MTX-based medications for the treatment of the ischemic stroke.

Leptin-mediated ion channel regulation: PI3K pathways, physiological role, and therapeutic potential

Leptin is produced by adipose tissue and identified as a "satiety signal," informing the brain when the body has consumed enough food. Specific areas of the hypothalamus express leptin receptors (LEPRs) and are the primary site of leptin action for body weight regulation. In response to leptin, appetite is suppressed and energy expenditure allowed. Beside this hypothalamic action, leptin targets other brain areas in addition to neuroendocrine cells. LEPRs are expressed also in the hippocampus, neocortex, cerebellum, substantia nigra, pancreatic β-cells, and chromaffin cells of the adrenal gland. It is intriguing how leptin is able to activate different ionic conductances, thus affecting excitability, synaptic plasticity and neurotransmitter release, depending on the target cell. Most of the intracellular pathways activated by leptin and directed to ion channels involve PI3K, which in turn phosphorylates different downstream substrates, although parallel pathways involve AMPK and MAPK. In this review we will describe the effects of leptin on BK, KATP, KV, CaV, TRPC, NMDAR and AMPAR channels and clarify the landscape of pathways involved. Given the ability of leptin to influence neuronal excitability and synaptic plasticity by modulating ion channels activity, we also provide a short overview of the growing potentiality of leptin as therapeutic agent for treating neurological disorders.

Olanzapine Prevents the PCP-induced Reduction in the Neurite Outgrowth of Prefrontal Cortical Neurons via NRG1

Accumulating evidence suggests that reducing neurite outgrowth and synaptic plasticity plays a critical role in the pathology of cognitive deficits in schizophrenia. The N-methyl-D-aspartate receptor antagonist phencyclidine (PCP) can induce symptoms of schizophrenia as well as reduce dendritic spine density and neurite growth. The antipsychotic drug olanzapine may improve these deficits. This study aimed to investigate: (1) if olanzapine prevents PCP-induced suppression of neurite outgrowth and synaptic protein expression; (2) if olanzapine affects the Akt-GSK3 signaling pathway; and (3) the role of neuregulin 1 (NRG1) in this process. Immunofluorescence revealed that PCP treatment for 24 hours reduces both neurite length (28.5%) and the number of neurite branches (35.6%) in primary prefrontal cortical neuron cultures. PCP reduced protein and mRNA expressions of synaptophysin (24.9% and 23.2%, respectively) and PSD95 (31.5% and 21.4%, respectively), and the protein expression of p-Akt (26.7%) and p-GSK3β (35.2%). Olanzapine co-treatment prevented these PCP-induced effects in normal neurons but not in neurons from NRG1-knockout mice. These results indicate that NRG1 mediates the preventive effects of olanzapine on the PCP-induced impairment of neurite outgrowth and synaptic protein expression. This study provides potential targets for interventions on improving the efficacy of olanzapine on preventing cognitive deficits in schizophrenia.

Influence of Genetic Variants of the N-Methyl-D-Aspartate Receptor on Emotion and Social Behavior in Adolescents

Considerable evidence has suggested that the epigenetic regulation of N-methyl-D-aspartate (NMDA) glutamate receptors plays a crucial role in neuropsychiatric disorders. Previous exploratory studies have been primarily based on evidence from patients and have rarely sampled the general population. This exploratory study examined the relationship of single-nucleotide polymorphism (SNP) variations in the genes encoding the NMDA receptor (i.e., GRIN1, GRIN2A, GRIN2B, GRIN2C, and GRIN2D) with emotion and social behavior in adolescents. For this study, 832 tenth-grade Taiwanese volunteers were recruited, and their scores from the Beck Youth Inventories were used to evaluate their emotional and social impairments. Based on these scores, GRIN1 (rs4880213) was significantly associated with depression and disruptive behavior. In addition, GRIN2B (rs7301328) was significantly associated with disruptive behavior. Because emotional and social impairment greatly influence learning ability, the findings of this study provide important information for clinical treatment and the development of promising prevention and treatment strategies, especially in the area of psychological adjustment.

Neuroprotective strategies against calpain-mediated neurodegeneration

Calpains are calcium-dependent proteolytic enzymes that have deleterious effects on neurons upon their pathological over-activation. According to the results of numerous studies to date, there is no doubt that abnormal calpain activation triggers activation and progression of apoptotic processes in neurodegeneration, leading to neuronal death. Thus, it is very crucial to unravel all the aspects of calpain-mediated neurodegeneration in order to protect neurons through eliminating or at least minimizing its lethal effects. Protecting neurons against calpain-activated apoptosis basically requires developing effective, reliable, and most importantly, therapeutically applicable approaches to succeed. From this aspect, the most significant studies focusing on preventing calpain-mediated neurodegeneration include blocking the N-methyl-d-aspartate (NMDA)-type glutamate receptor activities, which are closely related to calpain activation; directly inhibiting calpain itself via intrinsic or synthetic calpain inhibitors, or inhibiting its downstream processes; and utilizing the neuroprotectant steroid hormone estrogen and its receptors. In this review, the most remarkable neuroprotective strategies for calpain-mediated neurodegeneration are categorized and summarized with respect to their advantages and disadvantages over one another, in terms of their efficiency and applicability as a therapeutic regimen in the treatment of neurodegenerative diseases.

A novel treatment strategy for glioblastoma multiforme and glioma associated seizures: increasing glutamate uptake with PPARγ agonists

The established role of glutamate in the pathogenesis of glioma-associated seizures (GAS) led us to investigate a novel treatment method using an established drug class, peroxisome proliferator activated receptor (PPAR) gamma agonists. Previously, sulfasalazine has been shown to prevent release of glutamate from glioma cells and prevent GAS in rodent models. However, raising protein mediated glutamate transport via excitatory amino acid transporter 2 (EAAT2) has not been investigated previously to our knowledge. PPAR gamma agonists are known to upregulate functional EAAT2 expression in astrocytes and prevent excitotoxicity caused by glutamate excess. These agents are also known to have anti-neoplastic mechanisms. Herein we discuss and review the potential mechanisms of these drugs and highlight a novel potential treatment for GAS.

miR-137, a new target for post-stroke depression?

Expression of miR-137 is downregulated in brain tissue from patients with depression and suicidal behavior, and is also downregulated in peripheral blood from stroke patients. However, it is not yet known if miR-137 acts as a bridge between stroke and depression. To test this, we used middle cerebral artery occlusion and chronic mild stress to establish a post-stroke depression model in rats. Compared with controls, we found significantly lower miR-137 levels in the brain and peripheral blood from post-stroke depression rats. Injection of a miR-137 antagonist into the brain ventricles upregulated miR-137 levels, and improved behavioral changes in post-stroke depression rats. Luciferase assays showed miR-137 bound to the 3’UTR of Grin2A, regulating Grin2A expression in a neuronal cell line. Grin2A gene overexpression in the brain of post-stroke depression rats, noticeably suppressed the inhibitory effect of miR-137 on post-stroke depression. Overall, our results show that miR-137 suppresses Grin2A protein expression through binding to Grin2A mRNA, thereby exerting an inhibitory effect on post-stroke depression. Our results offer a new therapeutic direction for post-stroke depression.

The major cholesterol metabolite cholestane-3β,5α,6β-triol functions as an endogenous neuroprotectant

Overstimulation of NMDA-type glutamate receptors is believed to be responsible for neuronal death of the CNS in various disorders, including cerebral and spinal cord ischemia. However, the intrinsic and physiological mechanisms of modulation of these receptors are essentially unknown. Here we report that cholestane-3β,5α,6β-triol (triol), a major metabolite of cholesterol, is an endogenous neuroprotectant and protects against neuronal injury both in vitro and in vivo via negative modulation of NMDA receptors. Treatment of cultured neurons with triol protects against glutamate-induced neurotoxicity, and administration of triol significantly decreases neuronal injury after spinal cord ischemia in rabbits and transient focal cerebral ischemia in rats. An inducible elevation of triol is associated with ischemic preconditioning and subsequent neuroprotection in the spinal cord of rabbits. This neuroprotection is effectively abolished by preadministration of a specific inhibitor of triol synthesis. Physiological concentrations of triol attenuate [Ca(2+)]i induced by glutamate and decrease inward NMDA-mediated currents in cultured cortical neurons and HEK-293 cells transiently transfected with NR1/NR2B NMDA receptors. Saturable binding of [(3)H]triol to cerebellar granule neurons and displacement of [(3)H]MK-801 binding to NMDA receptors by triol suggest that direct blockade of NMDA receptors may underlie the neuroprotective properties. Our findings suggest that the naturally occurring oxysterol, the major cholesterol metabolite triol, functions as an endogenous neuroprotectant in vivo, which may provide novel insights into understanding and developing potential therapeutics for disorders in the CNS.

TrkB interacts with ErbB4 and regulates NRG1-induced NR2B phosphorylation in cortical neurons before synaptogenesis

Background

Neuregulin 1 (NRG1) and NMDARs play important roles in various neuronal functions including neural development. NMDARs also promote many cellular events such as proliferation and survival of neuroblasts before synapse formation. Although many recent studies have indicated that NRG1 regulates NMDAR function in cortical neurons, the effect of NRG1 on NMDAR activation before synapse formation is not well studied.

Results

NRG1 induces activation of NMDAR subunit NR2B, and tropomyosin-related kinase receptor B (TrkB), the receptor for BDNF via activation of phospholipase C-gamma (PLC-γ) in immature primary cortical neurons. Our data using TrkB inhibitor (K252a), TrkB siRNA and TrkB−/− neurons demonstrated that TrkB inhibition suppresses NRG1-induced NR2B activation in neurons. We found that NRG1 stimulation leads to GABA_A receptor-mediated TrkB activation. Co-immunoprecipitation and proximity ligase assay showed that TrkB interacts with ErbB4 (NRG1 receptor) and the TrkB-ErbB4 interaction was increased following NRG1 treatment. A significant reduction in TrkB-ErbB4 interaction was observed in the prefrontal cortex of schizophrenia subjects. We found significant increase in released BDNF levels following NRG1 treatment, which was inhibited by ErbB4 inhibitor, AG1478. In addition, pretreatment with BDNF neutralizing antibody, but not control IgG abolished NRG1-induced increases in phospho-TrkB and phospho-NR2B levels. Moreover, studies using TrkB mutants showed that intercellular domain of TrkB is necessary for TrkB-ErbB4 interaction and NR2B activation.

Conclusions

BDNF/TrkB signaling plays an important role in the NRG1-stimulated NR2B regulation. These findings could be of relevance to many neurodevelopmental disorders, as NRG1 and BDNF signaling pathways have been implicated in autism and schizophrenia.

Ion channels in cancer: future perspectives and clinical potential

Ion transport across the cell membrane mediated by channels and carriers participate in the regulation of tumour cell survival, death and motility. Moreover, the altered regulation of channels and carriers is part of neoplastic transformation. Experimental modification of channel and transporter activity impacts tumour cell survival, proliferation, malignant progression, invasive behaviour or therapy resistance of tumour cells. A wide variety of distinct Ca(2+) permeable channels, K(+) channels, Na(+) channels and anion channels have been implicated in tumour growth and metastasis. Further experimental information is, however, needed to define the specific role of individual channel isoforms critically important for malignancy. Compelling experimental evidence supports the assumption that the pharmacological inhibition of ion channels or their regulators may be attractive targets to counteract tumour growth, prevent metastasis and overcome therapy resistance of tumour cells. This short review discusses the role of Ca(2+) permeable channels, K(+) channels, Na(+) channels and anion channels in tumour growth and metastasis and the therapeutic potential of respective inhibitors.

Role of ion transport in control of apoptotic cell death

Cell shrinkage is a hallmark and contributes to signaling of apoptosis. Apoptotic cell shrinkage requires ion transport across the cell membrane involving K(+) channels, Cl(-) or anion channels, Na(+)/H(+) exchange, Na(+),K(+),Cl(-) cotransport, and Na(+)/K(+)ATPase. Activation of K(+) channels fosters K(+) exit with decrease of cytosolic K(+) concentration, activation of anion channels triggers exit of Cl(-), organic osmolytes, and HCO3(-). Cellular loss of K(+) and organic osmolytes as well as cytosolic acidification favor apoptosis. Ca(2+) entry through Ca(2+)-permeable cation channels may result in apoptosis by affecting mitochondrial integrity, stimulating proteinases, inducing cell shrinkage due to activation of Ca(2+)-sensitive K(+) channels, and triggering cell-membrane scrambling. Signaling involved in the modification of cell-volume regulatory ion transport during apoptosis include mitogen-activated kinases p38, JNK, ERK1/2, MEKK1, MKK4, the small G proteins Cdc42, and/or Rac and the transcription factor p53. Osmosensing involves integrin receptors, focal adhesion kinases, and tyrosine kinase receptors. Hyperosmotic shock leads to vesicular acidification followed by activation of acid sphingomyelinase, ceramide formation, release of reactive oxygen species, activation of the tyrosine kinase Yes with subsequent stimulation of CD95 trafficking to the cell membrane. Apoptosis is counteracted by mechanisms involved in regulatory volume increase (RVI), by organic osmolytes, by focal adhesion kinase, and by heat-shock proteins. Clearly, our knowledge on the interplay between cell-volume regulatory mechanisms and suicidal cell death is still far from complete and substantial additional experimental effort is needed to elucidate the role of cell-volume regulatory mechanisms in suicidal cell death.

Triheteromeric NMDA receptors at hippocampal synapses

NMDA receptors are composed of two GluN1 (N1) and two GluN2 (N2) subunits. Constituent N2 subunits control the pharmacological and kinetic characteristics of the receptor. NMDA receptors in hippocampal or cortical neurons are often thought of as diheteromeric, meaning that they contain only one type of N2 subunit. However, triheteromeric receptors with more than one type of N2 subunit also have been reported, and the relative contribution of diheteromeric and triheteromeric NMDA receptors at synapses has been difficult to assess. Because wild-type hippocampal principal neurons express N1, N2A, and N2B, we used cultured hippocampal principal neurons from N2A and N2B knock-out mice as templates for diheteromeric synaptic receptors. However, summation of N1/N2B and N1/N2A EPSCs could not account for the deactivation kinetics of wild-type EPSCs. To make a quantitative estimate of NMDA receptor subtypes at wild-type synapses, we used the deactivation kinetics and the effects of the competitive antagonist NVP-AAM077. Our results indicate that three types of NMDA receptors contribute to wild-type EPSCs, with at least two-thirds being triheteromeric receptors. Functional isolation of synaptic triheteromeric receptors revealed deactivation kinetics and pharmacology that were distinct from either diheteromeric receptor subtype. Because of differences in open probability, synaptic triheteromeric receptors outnumbered N1/N2A receptors by 5.8 to 1 and N1/N2B receptors by 3.2 to 1. Our results suggest that triheteromeric NMDA receptors must either be preferentially assembled or preferentially localized at synapses.

Sepsis-induced brain dysfunction

Systemic infection is often revealed by or associated with brain dysfunction, which is characterized by alteration of consciousness, ranging from delirium to coma, seizure or focal neurological signs. Its pathophysiology involves an ischemic process, secondary to impairment of cerebral perfusion and its determinants and a neuroinflammatory process that includes endothelial activation, alteration of the blood-brain barrier and passage of neurotoxic mediators. Microcirculatory dysfunction is common to these two processes. This brain dysfunction is associated with increased mortality, morbidity and long-term cognitive disability. Its diagnosis relies essentially on neurological examination that can lead to specific investigations, including electrophysiological testing or neuroimaging. In practice, cerebrospinal fluid analysis is indisputably required when meningitis is suspected. Hepatic, uremic or respiratory encephalopathy, metabolic disturbances, drug overdose, sedative or opioid withdrawal, alcohol withdrawal delirium or Wernicke's encephalopathy are the main differential diagnoses. Currently, treatment consists mainly of controlling sepsis. The effects of insulin therapy and steroids need to be assessed. Various drugs acting on sepsis-induced blood-brain barrier dysfunction, brain oxidative stress and inflammation have been tested in septic animals but not yet in patients.

Osthole attenuates spinal cord ischemia-reperfusion injury through mitochondrial biogenesis-independent inhibition of mitochondrial dysfunction in rats

BACKGROUND

Osthole, the main bioactive compounds isolated from the traditional Chinese medical herb broad Cnidium monnieri (L.) cusson, has been shown to exert spectrum of pharmacologic activities. The aim of this study was to investigate the potential neuroprotective effects of osthole against spinal cord ischemia-reperfusion injury in rats.

MATERIALS AND METHODS

Osthole was administrated at the concentration of 0.1, 1, 10, 50, or 200 mg/kg (intraperitoneally) 1 h before spinal cord ischemia. The effects on spinal cord injury were measured by spinal cord water content, infarct volume, hematoxylin and eosin staining, and neurologic assessment. Mitochondria were purified from injured spinal cord tissue to determine mitochondrial function.

RESULTS

We found that treatment with osthole (10 and 50 mg/kg) significantly decreased spinal cord water content and infarct volume, preserved normal motor neurons, and improved neurologic functions. These protective effects can be also observed even if the treatment was delayed to 4 h after reperfusion. Osthole treatment preserved mitochondrial membrane potential level, reduced reactive oxygen species production, increased adenosine triphosphate generation, and inhibited cytochrome c release in mitochondrial samples. Moreover, osthole increased mitochondria respiratory chain complex activities in spinal cord tissue, with no effect on mitochondrial DNA content and the expression of mitochondrial-specific transcription factors.

CONCLUSIONS

All these findings demonstrate the neuroprotective effect of osthole in spinal cord ischemia-reperfusion injury model and suggest that oshtole-induced neuroprotection was mediated by mitochondrial biogenesis-independent inhibition of mitochondrial dysfunction.

Involvement of the GluN2A and GluN2B subunits in synaptic and extrasynaptic N-methyl-D-aspartate receptor function and neuronal excitotoxicity

GluN2A and GluN2B are the major subunits of functional NMDA receptors (NMDAR). Previous studies have suggested that GluN2A and GluN2B may differentially mediate NMDAR function at synaptic and extrasynaptic locations and play opposing roles in excitotoxicity, such as neurodegeneration triggered by ischemic stroke and brain injury. By using pharmacological and molecular approaches to suppress or enhance the function of GluN2A and GluN2B in cultured cortical neurons, we examined NMDAR-mediated, bidirectional regulation of prosurvival signaling (i.e. the cAMP response element-binding protein (CREB)-Bdnf cascade) and cell death. Inhibition of GluN2A or GluN2B attenuated the up-regulation of prosurvival signaling triggered by the activation of either synaptic or extrasynaptic NMDAR. Inhibition of GluN2A or GluN2B also attenuated the down-regulation of prosurvival signaling triggered by the coactivation of synaptic and extrasynaptic receptors. The effects of GluN2B on CREB-Bdnf signaling were larger than those of GluN2A. Consistently, compared with suppression of GluN2A, suppression of GluN2B resulted in more reduction of NMDA- and oxygen glucose deprivation-induced excitotoxicity as well as NMDAR-mediated elevation of intracellular calcium. Moreover, excitotoxicity and down-regulation of CREB were exaggerated in neurons overexpressing GluN2A or GluN2B. Together, we found that GluN2A and GluN2B are involved in the function of both synaptic and extrasynaptic NMDAR, demonstrating that they play similar rather than opposing roles in NMDAR-mediated bidirectional regulation of prosurvival signaling and neuronal death.

NMDA receptor-mediated excitotoxicity depends on the coactivation of synaptic and extrasynaptic receptors

N-methyl-𝒟-aspartate receptors (NMDAR) overactivation is linked to neurodegeneration. The current prevailing theory suggests that synaptic and extrasynaptic NMDAR (syn- and ex-NMDAR) impose counteracting effects on cell fate, and neuronal cell death is mainly mediated by the activation of ex-NMDAR. However, several lines of evidence implicate the limitation of this theory. Here, we demonstrate that activation of NMDAR bi-directionally regulated cell fate through stimulating pro-survival or pro-death signaling. While low-dose NMDA preferentially activated syn-NMDAR and stimulated the extracellular signal-regulated kinase ½–cAMP responsive element-binding protein–brain-derived neurotrophic factor pro-survival signaling, higher doses progressively activated increasing amount of ex-NMDAR along with syn-NMDAR and triggered cell death program. Interestingly, the activation of syn- or ex-NMDAR alone did not cause measurable cell death. Consistently, activation of syn- or ex-NMDAR alone stimulated pro-survival but not pro-death signaling. Next, we found that memantine, which was previously identified as an ex-NMDAR blocker, inhibited intracellular signaling mediated by syn- or ex-NMDAR. Simultaneous blockade of syn- and ex-NMDAR by memantine dose-dependently attenuated NMDAR-mediated death. Moreover, long- but not short-term treatment with high-dose NMDA or oxygen–glucose deprivation triggered cell death and suppressed pro-survival signaling. These data implicate that activation of syn- or ex-NMDAR alone is not neurotoxic. The degree of excitotoxicity depends on the magnitude and duration of syn- and ex-NMDAR coactivation. Finally, genome-wide examination demonstrated that the activation of syn- and ex-NMDAR lead to significant overlapping rather than counteracting transcriptional responses.

Transcriptional expression patterns triggered by chemically distinct neuroprotective molecules

Glutamate-mediated excitotoxicity has been purported to underlie many neurodegenerative disorders. A subtype of glutamate receptors, namely N-methyl-d-aspartate (NMDA) receptors, has been recognized as potential targets for neuroprotection. To increase our understanding of the mechanisms that underlie this neuroprotection, we employed a mouse model of glutamate receptor-induced excitotoxic injury. Primary cortical neurons derived from postnatal day-0 CD-1 mice were cultured in the presence or absence of neuroprotective molecules and exposed to NMDA. Following a recovery period, whole genome expression was measured by microarray analysis. We used a combination of database and text mining, as well as systems modeling to identify signatures within the differentially expressed genes. While molecules differed in their mechanisms of action, we found significant overlap in the expression of a core group of genes and pathways. Many of these molecules have clear links to neuronal protection and survival, including ion channels, transporters, as well as signaling pathways including the mitogen-activated protein kinase (MAPK), the Toll-like receptor (TLR), and the hypoxic inducible factor (HIF). Within the TLR pathway, we also discovered a significant enrichment of interferon regulatory factor 7 (IRF7)-regulated genes. Knockdown of Irf7 by RNA interference resulted in reduced survival following NMDA treatment. Given the prominent role that IRF7 plays in the transduction of type-I interferons (IFNs), we also tested whether type-I IFNs alone functioned as neuroprotective agents and found that type-I IFNs were sufficient to promote neuronal survival. Our data suggest that the TLR/IRF7/IFN axis plays a significant role in recovery from glutamate-induced excitotoxicity.

Glycine receptor mutants of the mouse: what are possible routes of inhibitory compensation?

Defects in glycinergic inhibition result in a complex neuromotor disorder in humans known as hyperekplexia (OMIM 149400) with similar phenotypes in rodents characterized by an exaggerated startle reflex and hypertonia. Analogous to genetic defects in humans single point mutations, microdeletions, or insertions in the Glra1 gene but also in the Glrb gene underlie the pathology in mice. The mutations either localized in the α (spasmodic, oscillator, cincinnati, Nmf11) or the β (spastic) subunit of the glycine receptor (GlyR) are much less tolerated in mice than in humans, leaving the question for the existence of different regulatory elements of the pathomechanisms in humans and rodents. In addition to the spontaneous mutations, new insights into understanding of the regulatory pathways in hyperekplexia or glycine encephalopathy arose from the constantly increasing number of knock-out as well as knock-in mutants of GlyRs. Over the last five years, various efforts using in vivo whole cell recordings provided a detailed analysis of the kinetic parameters underlying glycinergic dysfunction. Presynaptic compensation as well as postsynaptic compensatory mechanisms in these mice by other GlyR subunits or GABA_A receptors, and the role of extra-synaptic GlyRs is still a matter of debate. A recent study on the mouse mutant oscillator displayed a novel aspect for compensation of functionality by complementation of receptor domains that fold independently. This review focuses on defects in glycinergic neurotransmission in mice discussed with the background of human hyperekplexia en route to strategies of compensation.

Association between the NMDA glutamate receptor GRIN2B gene and obsessive-compulsive disorder

BACKGROUND

Recent data from neuroimaging, genetic and clinical trials and animal models suggest a role for altered glutamatergic neuro transmission in the pathogenesis of obsessive-compulsive disorder (OCD). The aim of this study was to investigate whether variants in the GRIN2B gene, the gene encoding the NR2 subunit of the N-methyl-D-aspartate (NMDA) glutamate receptor, may contribute to genetic susceptibility to OCD or to different OCD subphenotypes.

METHODS

Between 2003 and 2008, we performed a case-control association study in which we genotyped 10 tag single-nucleotide polymorphisms (SNPs) in the 3' untranslated region (3' UTR) of GRIN2B. We performed SNP association and haplotype analysis considering the OCD diagnosis and different OCD subphenotypes: early-onset OCD, comorbid tic disorders and OCD clinical symptom dimensions.

RESULTS

We enrolled 225 patients with OCD and 279 controls recruited from the OCD Clinic at Bellvitge Hospital (Barcelona, Spain). No significant difference in the distribution of alleles or genotypes was detected between patients with OCD and controls. Nonetheless, on analyzing OCD subphenotypes, the rs1805476 SNP in male patients (95% confidence interval [CI] 1.37-4.22, p = 0.002) and a 4-SNP haplotype in the whole sample (rs1805476, rs1805501, rs1805502 and rs1805477; odds ratio 1.92, 95% CI 1.22-3.01; permutation p = 0.023) were significantly associated with the presence of contamination obsessions and cleaning compulsions.

LIMITATIONS

Study limitations included the risk of population stratification associated with the case-control design, use of psychiatrically unscreened blood donors as the control group, reduced sample size of participants with certain OCD subphenotypes and tested polymorphisms limited to 3' UTR and exon 13 of GRIN2B.

CONCLUSION

Our results converge with recent data suggesting a possible contribution of glutamatergic variants to the genetic vulnerability to OCD or at least to certain OCD manifestations. The dissection of OCD into more homogeneous subphenotypes may constitute a useful tool to disentangle the complex genetic basis of the disorder.

Maintenance of synaptic stability requires calcium-independent phospholipase A₂ activity

Phospholipases A₂ (PLA₂s) represent one of the largest groups of lipid-modifying enzymes. Over the years, significant advances have been made in understanding their potential physiological and pathological functions. Depending on their calcium requirement for activation, PLA₂s are classified into calcium dependent and independent. This paper mainly focuses on brain calcium-independent PLA₂ (iPLA₂) and on the mechanisms by which they influence neuronal function and regulate synaptic plasticity. Particular attention will be given to the iPLA₂γ isoform and its role in the regulation of synaptic glutamate receptors. In particular, the paper discusses the possibility that brain iPLA₂γ deficiencies could destabilise normal synaptic operation and might contribute to the aetiology of some brain disorders. In this line, the paper presents new data indicating that iPLA₂γ deficiencies accentuate AMPA receptor destabilization and tau phosphorylation, which suggests that this iPLA₂ isoform should be considered as a potential target for the treatment of Tau-related disorders.

Hypoxia associated NMDA receptor 2 subunit composition: developmental comparison between the hypoxia-tolerant subterranean mole-rat, Spalax, and the hypoxia-sensitive rat

Vertebrate brains are sensitive to oxygen depletion, which may lead to cell death. Hypoxia sensitivity originates from the high intrinsic rate of ATP consumption of brain tissue, accompanied by the release of glutamate, leading to the opening of ionotropic glutamate receptors, such as N-methyl-D-aspartate (NMDA) receptors (NMDARs). The relative expression levels of the four NMDAR-2 (NR2) subunits change during mammalian development with higher levels of units NR2B and NR2D observed during early development and correlated with hypoxic tolerance during embryonic and neonatal stages of development. Higher levels of NR2D are also abundant in brains of hypoxia tolerant species such as the crucian carp. The subterranean mole-rat, Spalax spends its life underground in sealed burrows and has developed a wide range of adaptations to this special niche including hypoxia-tolerance. In this study, we compared the in vivo mRNA expression of NR2 subunits in the brains of embryonic, neonatal and adult Spalax and rat. Our results demonstrate that under normoxic conditions, mRNA levels of NR2D are higher in Spalax than in rat at all developmental stages studied and are similar to levels in neonatal rat and in other hypoxia/anoxia tolerant species. Furthermore, under hypoxia Spalax NR2D mRNA levels increase while no response was observed in rat. Similarly, hypoxia induces an increase in mRNA levels of Spalax NR2A, claimed to promote neuronal survival. We suggest that indeed the proportional combinations of NMDAR-2 subunits contribute to the ability of the Spalax brain to cope with hypoxic environments.

Pharmacological modulation of NMDA receptor activity and the advent of negative and positive allosteric modulators

The NMDA receptor (NMDAR) family of l-glutamate receptors are well known to have diverse roles in CNS function as well as in various neuropathological and psychiatric conditions. Until recently, the types of agents available to pharmacologically regulate NMDAR function have been quite limited in terms of mechanism of action and subtype selectivity. This has changed significantly in the past two years. The purpose of this review is to summarize the many drug classes now available for modulating NMDAR activity. Previously, this included competitive antagonists at the l-glutamate and glycine binding sites, high and low affinity channel blockers, and GluN2B-selective N-terminal domain binding site antagonists. More recently, we and others have identified new classes of NMDAR agents that are either positive or negative allosteric modulators (PAMs and NAMs, respectively). These compounds include the pan potentiator UBP646, the GluN2A-selective potentiator/GluN2C and GluN2D inhibitor UBP512, the GluN2D-selective potentiator UBP551, the GluN2C/GluN2D-selective potentiator CIQ as well as the new NMDAR-NAMs such as the pan-inhibitor UBP618, the GluN2C/GluN2D-selective inhibitor QZN46 and the GluN2A inhibitors UBP608 and TCN201. These new agents do not bind within the l-glutamate or glycine binding sites, the ion channel pore or the N-terminal regulatory domain. Collectively, these new allosteric modulators appear to be acting at multiple novel sites on the NMDAR complex. Importantly, these agents display improved subtype-selectivity and as NMDAR PAMs and NAMs, they represent a new generation of potential NMDAR therapeutics.

Coumarin-3-carboxylic acid derivatives as potentiators and inhibitors of recombinant and native N-methyl-D-aspartate receptors

N-Methyl-d-aspartate receptors (NMDARs) are known to be involved in a range of neurological and neurodegenerative disorders and consequently the development of compounds that modulate the function of these receptors has been the subject of intense interest. We have recently reported that 6-bromocoumarin-3-carboxylic acid (UBP608) is a negative allosteric modulator with weak selectivity for GluN2A-containing NMDARs. In the present study, a series of commercially available and newly synthesized coumarin derivatives have been evaluated in a structure-activity relationship (SAR) study as modulators of recombinant NMDAR activity. The main conclusions from this SAR study were that substituents as large as iodo were accommodated at the 6-position and that 6,8-dibromo or 6,8-diiodo substitution of the coumarin ring enhanced the inhibitory activity at NMDARs. These coumarin derivatives are therefore excellent starting points for the development of more potent and GluN2 subunit selective inhibitors, which may have application in the treatment of a range of neurological disorders such as neuropathic pain, epilepsy and depression. Surprisingly, 4-methyl substitution of UBP608 to give UBP714, led to conversion of the inhibitory activity of UBP608 into potentiating activity at recombinant GluN1/GluN2 receptors. UBP714 also enhanced NMDAR mediated field EPSPs in the CA1 region of the hippocampus. UBP714 is therefore a novel template for the development of potent and subunit selective NMDAR potentiators that may have therapeutic applicability in the treatment of patients with cognitive deficits or schizophrenia.

Disruption of NMDAR-CRMP-2 signaling protects against focal cerebral ischemic damage in the rat middle cerebral artery occlusion model

Collapsin response mediator protein 2 (CRMP-2), traditionally viewed as an axon/dendrite specification and axonal growth protein, has emerged as nidus in regulation of both pre- and post-synaptic Ca ( 2+) channels. Building on our discovery of the interaction and regulation of Ca ( 2+) channels by CRMP-2, we recently identified a short sequence in CRMP-2 which, when appended to the transduction domain of HIV TAT protein, suppressed acute, inflammatory and neuropathic pain in vivo by functionally uncoupling CRMP-2 from the Ca ( 2+) channel. Remarkably, we also found that this region attenuated Ca ( 2+) influx via N-methylD-Aspartate receptors (NMDARs) and reduced neuronal death in a moderate controlled cortical impact model of traumatic brain injury (TBI). Here, we sought to extend these findings by examining additional neuroprotective effects of this peptide (TAT-CBD3) and exploring the biochemical mechanisms by which TAT-CBD3 targets NMDARs. We observed that an intraperitoneal injection of TAT-CBD3 peptide significantly reduced infarct volume in an animal model of focal cerebral ischemia. Neuroprotection was observed when TAT-CBD3 peptide was given either prior to or after occlusion but just prior to reperfusion. Surprisingly, a direct biochemical complex was not resolvable between the NMDAR subunit NR2B and CRMP-2. Intracellular application of TAT-CBD3 failed to inhibit NMDAR current. NR2B interactions with the post synaptic density protein 95 (PSD-95) remained intact and were not disrupted by TAT-CBD3. Peptide tiling of intracellular regions of NR2B revealed two 15-mer sequences, in the carboxyl-terminus of NR2B, that may confer binding between NR2B and CRMP-2 which supports CRMP-2's role in excitotoxicity and neuroprotection.

Structure-activity relationships for allosteric NMDA receptor inhibitors based on 2-naphthoic acid

Over-activation of N-methyl-d-aspartate (NMDA) receptors is critically involved in many neurological conditions, thus there has been considerable interest in developing NMDA receptor antagonists. We have recently identified a series of naphthoic and phenanthroic acid compounds that allosterically modulate NMDA receptors through a novel mechanism of action. In the present study, we have determined the structure-activity relationships of 18 naphthoic acid derivatives for the ability to inhibit the four GluN1/GluN2(A-D) NMDA receptor subtypes. 2-Naphthoic acid has low activity at GluN2A-containing receptors and yet lower activity at other NMDA receptors. 3-Amino addition, and especially 3-hydroxy addition, to 2-naphthoic acid increased inhibitory activity at GluN1/GluN2C and GluN1/GluN2D receptors. Further halogen and phenyl substitutions to 2-hydroxy-3-naphthoic acid leads to several relatively potent inhibitors, the most potent of which is UBP618 (1-bromo-2-hydroxy-6-phenylnaphthalene-3-carboxylic acid) with an IC(50) ∼ 2 μM at each of the NMDA receptor subtypes. While UBP618 is non-selective, elimination of the hydroxyl group in UBP618, as in UBP628 and UBP608, leads to an increase in GluN1/GluN2A selectivity. Of the compounds evaluated, specifically those with a 6-phenyl substitution were less able to fully inhibit GluN1/GluN2A, GluN1/GluN2B and GluN1/GluN2C responses (maximal % inhibition of 60-90%). Such antagonists may potentially have reduced adverse effects by not excessively blocking NMDA receptor signaling. Together, these studies reveal discrete structure-activity relationships for the allosteric antagonism of NMDA receptors that may facilitate the development of NMDA receptor modulator agents for a variety of neuropsychiatric and neurological conditions.