Differential roles of NMDA receptor subtypes in ischemic neuronal cell death and ischemic tolerance

Hypoxia tolerance determine differential gelsenicine-induced neurotoxicity between pig and mouse

BACKGROUND

Gelsemium elegans (G. elegans) is widely recognized as one of the most toxic plants globally, particularly harmful to humans. Some reports indicate that it is non-toxic to pigs and even has a growth-promoting effect; however, the underlying reasons for this paradox remain unclear.

METHODS

Gelsenicine is the main toxic component of G. elegans. This study characterized gelsenicine-induced toxicity using electrophysiological recordings, molecular dynamic simulations, c-Fos immunostaining, and multi-omics technologies. Additionally, we conducted a comprehensive analysis comparing the toxic effects of gelsenicine across various animal species through examinations of tissue distribution, blood gas analysis, metabonomics, and behavioral tests.

RESULTS

We demonstrated that gelsenicine-induced hypoxia leads to respiratory depression in mice by enhancing the effect of gamma-aminobutyric acid (GABA) on GABA receptors (GABARs). Glycine significantly ameliorated hypoxia and improved the survival of gelsenicine-poisoned mice. Under gelsenicine-induced hypoxic conditions, N-methyl-D-aspartate (NMDA) receptor function and mitochondrial energy metabolism processes were perturbed, resulting in neuronal excitotoxicity. Finally, we confirmed that pigs could tolerate hypoxia and were resistant to gelsenicine toxicity due to high concentrations of circulating glycine and low levels of NMDA receptors (NMDARs) in the hippocampus.

CONCLUSIONS

These findings suggest that hypoxic protection should be considered as a potential therapeutic strategy for gelsenicine poisoning. Our study contributes to preventing potential risks posed by G. elegans poisoning to human and animal health.

The diverse effects of ketamine, jack-of-all-trades: a narrative review

Ketamine, an N-methyl-D-aspartic acid receptor antagonist that was first discovered in 1962, has become established in anaesthesia providing dose-dependent anaesthetic, sedative, and analgesic effects. Ketamine, however, also acts on a wide range of other cellular targets, resulting in interesting and diverse effects on both physiological and pathological processes. Potential beneficial properties of ketamine include cardiovascular stability for patients undergoing sedation or anaesthesia, analgesia in both acute and chronic pain, bronchodilation in severe refractory asthma, anti-inflammatory properties particularly in sepsis, tumour inhibition, and antidepressant properties with marked ability to reverse suicidal ideation. The reluctance to adopt ketamine into routine practice is likely attributable in part to the stigma and negative reputation associated with its perceived side-effects and potential for abuse. This review explores the diverse properties and therapeutic potentials of ketamine being investigated across different fields whilst also identifying areas for ongoing and future research. Given the diverse range of potential benefits and promising early work, ketamine should be the focus of ongoing research in multiple different specialty areas. This includes areas relevant to anaesthesia and perioperative medicine, such as acute and chronic pain management, ICU sedation, and even tumour suppression in those undergoing surgical resection of malignancies.

Unveiling synergies: Integrating TCM herbal medicine and acupuncture with conventional approaches in stroke management

This review explores the mechanisms and treatment strategies of ischemic stroke, a leading cause of morbidity and mortality worldwide. Ischemic stroke results from the obstruction of blood flow to the brain, leading to significant neurological impairment. The paper categorizes ischemic stroke into subtypes based on etiology, including cardioembolism and large artery atherosclerosis, and discusses the challenges of current therapeutic approaches. Conventional treatments like tissue plasminogen activator (tPA) and surgical interventions are limited by narrow windows and potential complications. The review highlights the promise of acupuncture, which offers neuroprotective benefits by promoting cerebral ischemic tolerance and neural regeneration. Integrating acupuncture with conventional treatments may enhance patient outcomes. Emphasis is placed on understanding the pathophysiology to develop targeted therapies that mitigate neuronal damage and enhance recovery.

Piceatannol-3'-O-β-D-glucopyranoside inhibits neuroexcitotoxicity and ferroptosis through NMDAR/NRF2/BACH1/ACSL4 pathway in acute ischemic stroke

BACKGROUND

Neuronal protection is a well-established method of acute ischemic stroke (AIS) treatment. The pharmacodynamic effect of Piceatannol-3'-O-β-D-glucopyranoside (Chinese name: Hartigan, QZZG) on AIS has been reported, but the molecular mechanism of this effect remains unknown.

PURPOSE

The purpose of this study is to elucidate the pharmacodynamic effects and mechanisms of QZZG in the treatment of AIS.

METHODS

A combined network pharmacology and metabolomics approach was used to predict the key targets and pathways of QZZG in the treatment of AIS and to elucidate the mechanism of QZZG through experimental validation.

RESULTS

In this study, QZZG improved histopathologic features and reduced infarct volume and neurologic deficit scores. Integrated network pharmacology and metabolomics revealed that QZZG may protect neurons by regulating glutamate and its receptors, and that glutamate is closely related to NMDAR1, NRF2, and Caspase-3. Pathway analysis results suggested that NMDAR-mediated Ca2+ inward flow is one of the critical pathways. In terms of neuroexcitotoxicity QZZG inhibited glutamate content, reduced Ca2+ inward flow, protected mitochondrial function, and reduced ROS, as well as being able to effectively inhibit the expression of NMDAR1, Caspase-3, Bax, and promote the expression of Bcl-2, NMDAR2A. In terms of ferroptosis QZZG promoted NRF2, HO-1, GPX4 and nuclear-NRF2, inhibited the expression of BACH1 and ACSL4, and suppressed Fe2+ accumulation and lipid peroxidation. Silencing of BACH1 resulted in elevated expression of NRF2 and decreased expression of ACSL4, which inhibited the sensitivity of neurons to ferroptosis. QZZG was able to further increase NRF2 expression under conditions of silencing BACH1. QZZG induced NRF2 and inhibited BACH1, ACSL4 was inhibited by ML385, and inhibition of NRF2 induced the expression of BACH1 and ACSL4, QZZG protects neurons in an NRF2-dependent manner.

CONCLUSION

In summary, QZZG inhibited neuroexcitotoxicity and ferroptosis by regulating the NMDAR/NRF2/BACH1/ACSL4 pathway. The study provided a relatively novel perspective on the mechanism of traditional Chinese medicine (TCM) treatment of the disease.

The bile acid chenodeoxycholic acid associates with reduced stroke in humans and mice

Bile acids are liver-derived signaling molecules that can be found in the brain, but their role there remains largely unknown. We found increased brain chenodeoxycholic acid (CDCA) in mice with absent 12α-hydroxylase (Cyp8b1), a bile acid synthesis enzyme. In these Cyp8b1-/-, and in Wt mice administered CDCA, stroke infarct area was reduced. Elevated glutamate-induced excitotoxicity mediated by aberrant N-methyl-D-aspartate receptor (NMDAR) overactivation contributes to neuronal death in ischemic stroke. We found reduced glutamate-induced excitotoxicity in neurons from Cyp8b1-/- and CDCA-treated Wt mice. CDCA decreased NMDAR-mediated excitatory post-synaptic currents by reducing over-activation of NMDAR subunit GluN2B in Wt brains. Synaptic NMDAR activity was also decreased in Cyp8b1-/- brains. Expression and synaptic distribution of GluN2B were unaltered in Cyp8b1-/- mice, suggesting CDCA may directly antagonize GluN2B-containing NMDARs. Supporting our findings, in a case-control cohort of acute ischemic stroke patients, we found lower circulatory CDCA. Together, our data suggest that CDCA, acting in the liver-brain axis, decreases GluN2B-containing NMDAR overactivation, contributing to neuroprotection in stroke.

2-BFI protects against ischemic stroke by selectively acting on NR2B-containing NMDA receptors

BACKGROUND AND PURPOSE

The intricate roles of NMDA receptors, specifically those containing the NR2A or NR2B subunit, in ischemic stroke pathology necessitate targeted therapeutic investigations. Building on our prior discovery showcasing the neuroprotective potential of 2-(benzofuran-2-yl)-2-imidazoline (2-BFI), an imidazoline I2 receptor ligand, in inhibiting NMDA receptor currents during ischemic stroke, this study aims to elucidate the specific impact of 2-BFI on NR2A- and NR2B-containing NMDARs.

EXPERIMENTAL APPROACH

Through whole-cell patch-clamp techniques, we observed an inhibition by 2-BFI on NR2A-containing NMDAR currents (IC50 = 238.6 μM) and NR2B-containing NMDAR currents (IC50 = 18.47 μM). Experiments with HEK293 cells expressing exogenous receptor subunits revealed a significantly higher affinity of 2-BFI towards NR2B-containing NMDARs. In vivo studies involved the co-administration of 2-BFI and the NR2A subunit antagonist NVP-AAM077 in rats subjected to transient middle cerebral artery occlusion (tMCAO). Key results 2-BFI exhibited a pronounced preference for inhibiting NR2B-containing NMDAR currents, leading to a notable mitigation of cerebral ischemic injury when administered in conjunction with NVP-AAM077 in the tMCAO rat model. Furthermore, alterations in the expression of downstream proteins specific to NR2B-containing NMDA receptors were observed, suggesting targeted molecular effects. Conclusion and implications This study unveils the neuroprotective potential of 2-BFI in ischemic stroke by selectively inhibiting NR2B-containing NMDA receptors. These findings lay the foundation for precise therapeutic strategies, showcasing the differential roles of NR2A and NR2B subunits and paving the way for advancements in targeted interventions for ischemic stroke treatment.

Salidroside derivative SHPL-49 attenuates glutamate excitotoxicity in acute ischemic stroke via promoting NR2A-CAMKⅡα-Akt /CREB pathway

BACKGROUND

Ischemic stroke is a significant cause of death and disability with a limited treatment time window. The reduction of early glutamate excitotoxicity using neuroprotective agents targeting N-methyl-d-aspartic acid (NMDA) receptors have attracted recent research attention. SHPL-49, a structurally modified derivative of salidroside, was synthesized by our team. Previous studies have confirmed the neuroprotective efficacy of SHPL-49 in rats with ischemic stroke. However, the underlying mechanisms need to be clarified.

METHODS

We conducted in vivo experiments using the permanent middle cerebral artery occlusion rat model to investigate the role of SHPL-49 in glutamate release at different time points and treatment durations. Glutamate transporters and receptor proteins and neural survival proteins in the brain were also examined at the same time points. In vitro, primary neurons and the coculture system of primary neurons-astrocytes were subjected to oxygen-glucose deprivation and glutamate injury. Proteomics and parallel reaction monitoring analyses were performed to identify potential therapeutic targets of SHPL-49, which were further confirmed through in vitro experiments on the inhibition and mutation of the target.

RESULTS

SHPL-49 significantly reduced glutamate release caused by hypoxia-ischemia. One therapeutic pathway of SHPL-49 was promoting the expression of glutamate transporter-1 to increase glutamate reuptake and further reduce the occurrence of subsequent neurotoxicity. In addition, we explored the therapeutic targets of SHPL-49 and its regulatory effects on glutamate receptors for the first time. SHPL-49 enhanced neuroprotection by activating the NMDA subunit NR2A, which upregulated the cyclic-AMP response binding protein (CREB) neural survival pathway and Akt phosphorylation. Since calcium/calmodulin-dependent kinase IIα (CaMKIIα) is necessary for synaptic transmission of NMDA receptors, we explored the interaction between CaMKIIα and SHPL-49, which protected CaMKIIα from hypoxia-ischemia-induced autophosphorylation damage.

CONCLUSION

Overall, SHPL-49 enhanced neuronal survival and attenuated acute ischemic stroke by promoting the NR2A-CAMKⅡα-Akt/CREB pathway. Our study provides the first evidence demonstrating that the neuroprotective effect of SHPL-49 is achieved by promoting the NR2A subunit to extend the treatment time window, making it a promising drug for ischemic stroke.

GlyT1 inhibition promotes neuroprotection in the middle cerebral artery occlusion model through the activation of GluN2A-containing NMDAR

Glycine Transporter Type 1 (GlyT1) inhibition confers neuroprotection against different forms of cerebral damage. This effect occurs through the elevation of synaptic glycine concentrations, which enhances N-methyl-d-aspartate receptor (NMDAR) activation by glutamate. To investigate the neuroprotective mechanism of GlyT1 inhibition, we used the Middle Cerebral Artery Occlusion (MCAO) model in male C57BL/6 mice, aged 10-12 weeks. We administered N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl] sarcosine (NFPS), a GlyT1 inhibitor, 24 h prior to ischemia induction. NFPS pretreatment provided significant neuroprotection in the MCAO model, associated with modulation of pathways related to long-term potentiation. Specifically, GluN2A subunit expression was upregulated, while GluN2B subunit expression was downregulated in cortical areas, correlating with enhanced phosphorylation of CaMKIV and CREB proteins. Coadministration with the GluN2B antagonist Eliprodil or the CREB inhibitor C646 did not affect the neuroprotective effects of NFPS pretreatment, but TCN-201, a specific GluN2A antagonist, disrupted these effects. These findings suggest that GlyT1 inhibition mediates neuroprotection through activation of GluN2A-containing NMDARs and the GluN2A/CaMKIV/CREB signaling cascade, thereby modulating the balance between GluN2A and GluN2B subunits.

Kynurenic acid protects against ischemia/reperfusion injury by modulating apoptosis in cardiomyocytes

Acute myocardial infarction, often associated with ischemia/reperfusion injury (I/R), is a leading cause of death worldwide. Although the endogenous tryptophan metabolite kynurenic acid (KYNA) has been shown to exert protection against I/R injury, its mechanism of action at the cellular and molecular level is not well understood yet. Therefore, we examined the potential involvement of antiapoptotic mechanisms, as well as N-methyl-D-aspartate (NMDA) receptor modulation in the protective effect of KYNA in cardiac cells exposed to simulated I/R (SI/R). KYNA was shown to attenuate cell death induced by SI/R dose-dependently in H9c2 cells or primary rat cardiomyocytes. Analysis of morphological and molecular markers of apoptosis (i.e., membrane blebbing, apoptotic nuclear morphology, DNA double-strand breaks, activation of caspases) revealed considerably increased apoptotic activity in cardiac cells undergoing SI/R. The investigated apoptotic markers were substantially improved by treatment with the cytoprotective dose of KYNA. Although cardiac cells were shown to express NMDA receptors, another NMDA antagonist structurally different from KYNA was unable to protect against SI/R-induced cell death. Our findings provide evidence that the protective effect of KYNA against SI/R-induced cardiac cell injury involves antiapoptotic mechanisms, that seem to evoke independently of NMDA receptor signaling.

Neuroprotective effects of MK-801 against cerebral ischemia reperfusion

Introduction

& Objective: Cerebral ischemia/reperfusion (I/R) injury, the second cause of death globally, involves increased NMDA receptor activity leading to neuronal damage due to excessive sodium and calcium ion entry. Therefore, targeting NMDA receptor may potentially reduce cell death induced by brain injury. Our study aimed to investigate the role of NMDA receptors in hippocampal neuronal activity induced by I/R.

Methods

In this study, Wistar rats were divided into four groups: sham, I/R, I/R + MK801, and I/R + NMDA. Cerebral I/R injury was induced by temporarily occluding the common and vertebral carotid arteries, followed by reperfusion. MK801 or NMDA was administered to the rats after a specific reperfusion time. Neuronal density and cell morphology in the hippocampal CA1 region were assessed using Nissl and H&E staining. The expression of BDNF, p-CREB, and c-fos was evaluated through Western blot analysis. Additionally, neuronal activity in CA1 pyramidal neurons were examined using single unit recording technique.

Results

Our results showed that cerebral I/R injury caused significant damage to CA1 pyramidal neurons compared to the sham group. However, treatment with MK-801 improved hippocampal cell survival compared to the I/R group. Furthermore, MK-801 administration in I/R rats increased BDNF, c-fos, and p-CREB levels while decreasing cleaved caspase-3 activity compared to the I/R group. Additionally, electrophysiological data showed that MK-801 increased firing rates of CA1 pyramidal neurons during the reperfusion phase.

Conclusion

MK-801 shows promise as a therapeutic agent for cerebral I/R injury by enhancing cell survival, upregulating neuroplasticity factors, and increasing firing rates of CA1 pyramidal neurons. It exerts a specific protective effect against cerebral I/R injury.

THSG alleviates cerebral ischemia/reperfusion injury via the GluN2B-CaMKII-ERK1/2 pathway

BACKGROUND

The potential therapeutic targeting of PINK1-PARK2-mediated mitophagy against cerebral ischemia/reperfusion (CI/R) injury involves the pathophysiological processes of neurovascular unit (NVU) and is closely associated with N-methyl-D-aspartate receptors (NMDARs) commonly expressed in NVU. 2,3,5,4'-Tetrahydroxy-stilbene-2-O-β-D-glucoside (THSG), a compound derived from the traditional Chinese medicine Polygonum multiflorum Thunb., has demonstrated notable neuroprotective properties against CI/R injury. However, it remains unclear whether THSG exerts its protective effects through GluN2B related PINK1/ PARK2 pathway.

PURPOSE

This study aims to explore the pharmacological effects of THSG on alleviating CI/R injury via the GluN2B-CaMKII-ERK1/2 pathway.

METHODS

THSG neuroprotection against CI/R injury was studied in transient middle cerebral artery occlusion/reversion (tMCAO/R) model rats and in oxygen and glucose deprivation/ reoxygenation (OGD/R) induced neurons. PINK1-PARK2-mediated mitophagy involvement in the protective effect of THSG was investigated in tMCAO/R rats and OGD/R-induced neurons via THSG and 3-methyladenine (3-MA) treatment. Furthermore, the beneficial role of GluN2B in reperfusion and its contribution to the THSG effect via CaMKII-ERK1/2 and PINK1-PARK2-mediated mitophagy was explored using the GluN2B-selective antagonist Ro 25-6981 both in vivo and in vitro. Finally, the interaction between THSG and GluN2B was evaluated using molecular docking.

RESULTS

THSG significantly reduced infarct volume, neurological deficits, penumbral neuron structure, and functional damage, upregulated the inhibitory apoptotic marker Bcl-2, and suppressed the increase of pro-apoptotic proteins including cleaved caspase-3 and Bax in tMCAO/R rats. THSG (1 μM) markedly improved the neuronal survival under OGD/R conditions. Furthermore, THSG promoted PINK1 and PARK2 expression and increased mitophagosome numbers and LC3-II-LC3-I ratio both in vivo and in vitro. The effects of THSG were considerably abrogated by the mitophagy inhibitor 3-MA in OGD/R-induced neurons. Inhibiting GluN2B profoundly decreased mitophagosome numbers and OGD/R-induced neuronal viability. Specifically, inhibiting GluN2B abolished the protection of THSG against CI/R injury and reversed the upregulation of PINK1-PARK2-mediated mitophagy by THSG. Inhibiting GluN2B eliminated THSG upregulation of ERK1/2 and CaMKII phosphorylation. The molecular docking analysis results demonstrated that THSG bound to GluN2B (binding energy: -5.2 ± 0.11 kcal/mol).

CONCLUSIONS

This study validates the premise that THSG alleviates CI/R injury by promoting GluN2B expression, activating CaMKII and ERK1/2, and subsequently enhancing PINK1-PARK2-mediated mitophagy. This work enlightens the potential of THSG as a promising candidate for novel therapeutic strategies for treating ischemic stroke.

The underlying mechanism of calcium toxicity-induced autophagic cell death and lysosomal degradation in early stage of cerebral ischemia

Cerebral ischemia is the important cause of worldwide disability and mortality, that is one of the obstruction of blood vessels supplying to the brain. In early stage, glutamate excitotoxicity and high level of intracellular calcium (Ca2+) are the major processes which can promote many downstream signaling involving in neuronal death and brain tissue damaging. Moreover, autophagy, the reusing of damaged cell organelles, is affected in early ischemia. Under ischemic conditions, autophagy plays an important role to maintain energy of the brain and its function. In the other hand, over intracellular Ca2+ accumulation triggers excessive autophagic process and lysosomal degradation leading to autophagic process impairment which finally induce neuronal death. This article reviews the association between intracellular Ca2+ and autophagic process in acute stage of ischemic stroke.

Homocysteine-induced sustained GluN2A NMDA receptor stimulation leads to mitochondrial ROS generation and neurotoxicity

Homocysteine, a sulfur-containing amino acid derived from methionine metabolism, is a known agonist of N-methyl-D-aspartate receptor (NMDAR) and is involved in neurotoxicity. Our previous findings showed that neuronal exposure to elevated homocysteine levels leads to sustained low-level increase in intracellular Ca2+, which is dependent on GluN2A subunit-containing NMDAR (GluN2A-NMDAR) stimulation. These studies further showed a role of ERK MAPK in homocysteine-GluN2A-NMDAR-mediated neuronal death. However, the intracellular mechanisms associated with such sustained GluN2A-NMDAR stimulation and subsequent Ca2+ influx have remained unexplored. Using live-cell imaging with Fluo3-AM and biochemical approaches, we show that homocysteine-GluN2A NMDAR-induced initial Ca2+ influx triggers sequential phosphorylation and subsequent activation of the proline rich tyrosine kinase 2 (Pyk2) and Src family kinases, which in turn phosphorylates GluN2A-Tyr1325 residue of GluN2A-NMDARs to maintain channel activity. The continuity of this cycle of events leads to sustained Ca2+ influx through GluN2A-NMDAR. Our findings also show that lack of activation of the regulatory tyrosine phosphatase STEP, which can limit Pyk2 and Src family kinase activity further contributes to the maintenance of this cycle. Additional studies using live-cell imaging of neurons expressing a redox-sensitive GFP targeted to the mitochondrial matrix show that treatment with homocysteine leads to a progressive increase in mitochondrial reactive oxygen species generation, which is dependent on GluN2A-NMDAR-mediated sustained ERK MAPK activation. This later finding demonstrates a novel role of GluN2A-NMDAR in homocysteine-induced mitochondrial ROS generation and highlights the role of ERK MAPK as the intermediary signaling pathway between GluN2A-NMDAR stimulation and mitochondrial reactive oxygen species generation.

Discovery of novel positive allosteric modulators targeting GluN1/2A NMDARs as anti-stroke therapeutic agents

Excitotoxicity due to excessive activation of NMDARs is one of the main mechanisms of neuronal death during ischemic stroke. Previous studies have suggested that activation of either synaptic or extrasynaptic GluN2B-containing NMDARs results in neuronal damage, whereas activation of GluN2A-containing NMDARs promotes neuronal survival against ischemic insults. This study applied a systematic in silico, in vitro, and in vivo approach to the discovery of novel and potential GluN1/2A NMDAR positive allosteric modulators (PAMs). Ten compounds were obtained and identified as potential GluN1/2A PAMs by structure-based virtual screening and calcium imaging. The neuroprotective activity of the candidate compounds was demonstrated in vitro. Subsequently, compound 15 (aegeline) was tested further in the model of transient middle cerebral artery occlusion (tMCAO) in vivo, which significantly decreased cerebral infarction. The mechanism by which aegeline exerts its effect on allosteric modulation was revealed using molecular dynamics simulations. Finally, we found that the neuroprotective effect of aegeline was significantly correlated with the enhanced phosphorylation of cAMP response element-binding protein (CREB). Our study discovered the neuroprotective effect of aegeline as a novel PAM targeting GluN1/2A NMDAR, which provides a potential opportunity for the development of therapeutic agents for ischemic stroke.

GluN2B-containing NMDA receptor attenuated neuronal apoptosis in the mouse model of HIBD through inhibiting endoplasmic reticulum stress-activated PERK/eIF2α signaling pathway

Introduction

Neonatal hypoxic-ischemic brain damage (HIBD) refers to brain damage in newborns caused by hypoxia and reduced or even stopped cerebral blood flow during the perinatal period. Currently, there are no targeted treatments for neonatal ischemic hypoxic brain damage, primarily due to the incomplete understanding of its pathophysiological mechanisms. Especially, the role of NMDA receptors is less studied in HIBD. Therefore, this study explored the molecular mechanism of endogenous protection mediated by GluN2B-NMDAR in HIBD.

Method

Hypoxic ischemia was induced in mice aged 9-11 days. The brain damage was examined by Nissl staining and HE staining, while neuronal apoptosis was examined by Hoechst staining and TTC staining. And cognitive deficiency of mice was examined by various behavior tests including Barnes Maze, Three Chamber Social Interaction Test and Elevated Plus Maze. The activation of ER stress signaling pathways were evaluated by Western blot.

Results

We found that after HIBD induction, the activation of GluN2B-NMDAR attenuated neuronal apoptosis and brain damage. Meanwhile, the ER stress PERK/eIF2α signaling pathway was activated in a time-dependent manner after HIBE. Furthermore, after selective inhibiting GluN2B-NMDAR in HIBD mice with ifenprodil, the PERK/eIF2α signaling pathway remains continuously activated, leading to neuronal apoptosis, morphological brain damage. and aggravating deficits in spatial memory, cognition, and social abilities in adult mice.

Discussion

The results of this study indicate that, unlike its role in adult brain damage, GluN2B in early development plays a neuroprotective role in HIBD by inhibiting excessive activation of the PERK/eIF2α signaling pathway. This study provides theoretical support for the clinical development of targeted drugs or treatment methods for HIBD.

Pathophysiological changes of muscle after ischemic stroke: a secondary consequence of stroke injury

Sufficient clinical evidence suggests that the damage caused by ischemic stroke to the body occurs not only in the acute phase but also during the recovery period, and that the latter has a greater impact on the long-term prognosis of the patient. However, current stroke studies have typically focused only on lesions in the central nervous system, ignoring secondary damage caused by this disease. Such a phenomenon arises from the slow progress of pathophysiological studies examining the central nervous system. Further, the appropriate therapeutic time window and benefits of thrombolytic therapy are still controversial, leading scholars to explore more pragmatic intervention strategies. As treatment measures targeting limb symptoms can greatly improve a patient's quality of life, they have become a critical intervention strategy. As the most vital component of the limbs, skeletal muscles have become potential points of concern. Despite this, to the best of our knowledge, there are no comprehensive reviews of pathophysiological changes and potential treatments for post-stroke skeletal muscle. The current review seeks to fill a gap in the current understanding of the pathological processes and mechanisms of muscle wasting atrophy, inflammation, neuroregeneration, mitochondrial changes, and nutritional dysregulation in stroke survivors. In addition, the challenges, as well as the optional solutions for individualized rehabilitation programs for stroke patients based on motor function are discussed.

The GluN2B-Containing NMDA Receptor Alleviates Neuronal Apoptosis in Neonatal Hypoxic-Ischemic Encephalopathy by Activating PI3K-Akt-CREB Signaling Pathwa

Neonatal hypoxic-ischemic encephalopathy (HIE) is a disease caused by insufficient blood supply in the brain in newborns during the perinatal period. Severe HIE leads to patient death, and patients with mild HIE are at increased risk of cognitive deficits and behavioral abnormalities. The NMDA receptor is an important excitatory receptor in the central nervous system, and in adult hypoxic-ischemic injury both subtypes of the NMDA receptor play important but distinct roles. The GluN2A-containing NMDA receptor (GluN2A-NMDAR) could activate neuronal protective signaling pathway, while the GluN2B-NMDAR subtype is coupled to the apoptosis-inducing signaling pathway and leads to neuronal death. However, the expression level of GluN2B is higher in newborns than in adults, while the expression of GluN2A is lower. Therefore, it is not clear whether the roles of different NMDA receptor subtypes in HIE are consistent with those in adults. We investigated this issue in this study and found that in HIE, GluN2B plays a protective role by mediating the protective pathway through binding with PSD95, which is quite different to that in adults. The results of this study provided new theoretical support for the clinical treatment of neonatal hypoxic ischemia.

Short-term postsynaptic plasticity facilitates predictive tracking in continuous attractors

Introduction

The N-methyl-D-aspartate receptor (NMDAR) plays a critical role in synaptic transmission and is associated with various neurological and psychiatric disorders. Recently, a novel form of postsynaptic plasticity known as NMDAR-based short-term postsynaptic plasticity (STPP) has been identified. It has been suggested that long-lasting glutamate binding to NMDAR allows for the retention of input information in brain slices up to 500 ms, leading to response facilitation. However, the impact of STPP on the dynamics of neuronal populations remains unexplored.

Methods

In this study, we incorporated STPP into a continuous attractor neural network (CANN) model to investigate its effects on neural information encoding in populations of neurons. Unlike short-term facilitation, a form of presynaptic plasticity, the temporally enhanced synaptic efficacy resulting from STPP destabilizes the network state of the CANN by increasing its mobility.

Results

Our findings demonstrate that the inclusion of STPP in the CANN model enables the network state to predictively respond to a moving stimulus. This nontrivial dynamical effect facilitates the tracking of the anticipated stimulus, as the enhanced synaptic efficacy induced by STPP enhances the system's mobility.

Discussion

The discovered STPP-based mechanism for sensory prediction provides valuable insights into the potential development of brain-inspired computational algorithms for prediction. By elucidating the role of STPP in neural population dynamics, this study expands our understanding of the functional implications of NMDAR-related plasticity in information processing within the brain.

Conclusion

The incorporation of STPP into a CANN model highlights its influence on the mobility and predictive capabilities of neural networks. These findings contribute to our knowledge of STPP-based mechanisms and their potential applications in developing computational algorithms for sensory prediction.

Neuroprotective effects of oxytocin against ischemic stroke in rats by blocking glutamate release and CREB-mediated DNA hypermethylation

Glutamate plays a crucial role in cognitive impairments after ischemic stroke. There is a scarcity of information about how glutamate-induced activation of cAMP-response element binding (CREB) signaling pathway regulates both the negative and positive regulators of synaptic plasticity. Recent studies have demonstrated the involvement of prominent epigenetic repressors, such as MeCP2 and DNMTs, in stroke. Neuroprotective effects of oxytocin against ischemia have been previously reported, while the underlying mechanism is still elusive. In this research, the possible role of CREB-mediated DNA hypermethylation and the potential mechanism of oxytocin in a rat model of permanent middle cerebral artery occlusion (pMCAO) were assessed. Adult male Sprague-Dawley rats were pretreated with intraperitoneal injection of oxytocin at the onset of pMCAO. The effects of oxytocin on spines and the expression levels of synaptic genes were determined. The regulatory effects of oxytocin on glutamate level, N-methyl-D-aspartate receptors (NMDARs), its downstream CREB pathway, and global or gene-specific DNA methylation status were evaluated by immunofluorescence, co-immunoprecipitation, and chromatin immunoprecipitation, respectively. We found that CREB could act as a common transcription factor for MeCP2 and DNMT3B after ischemic stroke. Oxytocin dose-dependently deactivated NR2B-related CaM-CREB pathway and inhibited DNA hypermethylation at the CpG islands of Ngf gene in pMCAO-operated rats. Moreover, oxytocin prevented pMCAO-induced reduction in the number of spines and neural cells. DNA hypermethylation in Ngf gene contributed to the cognitive deficits post-stroke. The neuroprotective effects of oxytocin against ischemia could be attributed to inhibiting glutamate release, providing additional evidence on the mechanism of oxytocin against ischemic stroke.

Effect of caffeine on hippocampal memory and levels of gene expression in social isolation stress

BACKGROUND

Caffeine (Cf) antagonizes the adenosine receptors and has neuroprotective properties. The effect of Cf has been seen on stress-induced deficits of cognitive. In this study, we have investigated the effect of Cf on learning and memory functions induced by social isolation (SI) stress.

MATERIALS AND METHODS

In the present study, 21-day-old Wistar albino male rats (n = 28) were divided into four groups: the control (C), the SI, the Cf, and the social isolation + caffeine (SICf). Cf (0.3 g/L) was added to the drinking water of the experimental animals for 4 weeks. The learning and memory functions were assessed using the Morris Water Maze Test (MWMT). Following, was performed histopathological evaluation and determined hippocampal gene expression levels by RT-qPCR.

RESULTS

According to MWMT findings, the time spent in the quadrant where the platform removed was decreased in the SI group compared with the C (p < 0.05). Histological evaluation showed morphological changes in SI by irregular appearance, cellular edema, and dark pycnotic appearance of nuclei in some neurons. However, it was observed that the histological structure of most of the neurons in the SICf group was similar to the C and Cf groups. Hippocampal SNAP25 expression was decreased in the Cf and SICf groups than in the C group (p < 0.05). The GFAP expression was increased in the SICf group than in the C group (p < 0.05). NR2A increased in the SI and SICf groups compared with C and Cf groups (p < 0.05). NR2B expression decreased in the Cf group compared with C and SI groups (p < 0.05).

CONCLUSIONS

SI impaired spatial memory and causes morphological changes in adolescent rats, but this effect of isolation was not seen in Cf-treated animals. The effects of SI on NR2A, Cf on NR2B, and SNAP25 are remarkable. Here, we propose that the impaired effect of SI on spatial memory may be mediated by NR2A, but further studies are needed to explain this effect.

Blockade of adenosine A2A receptors reverses early spatial memory defects in the APP/PS1 mouse model of Alzheimer's disease by promoting synaptic plasticity of adult-born granule cells

BACKGROUND

The over-activation of adenosine A2A receptors (A2AR) is closely implicated in cognitive impairments of Alzheimer's disease (AD). Growing evidence shows that A2AR blockade possesses neuroprotective effects on AD. Spatial navigation impairment is an early manifestation of cognitive deficits in AD. However, whether A2AR blockade can prevent early impairments in spatial cognitive function and the underlying mechanism is still unclear.

METHODS

A transgenic APP/PS1 mouse model of AD amyloidosis was used in this study. Behavioral tests were conducted to observe the protective effects of A2AR blockade on early spatial memory deficits in 4-month old APP/PS1 mice. To investigate the underlying synaptic mechanism of the protective effects of A2AR blockade, we further examined long-term potentiation (LTP) and network excitation/inhibition balance of dentate gyrus (DG) region, which is relevant to unique synaptic functions of immature adult-born granule cells (abGCs). Subsequently, the protective effects of A2AR blockade on dendritic morphology and synaptic plasticity of 6-week-old abGCs was investigated using retrovirus infection and electrophysiological recordings. The molecular mechanisms underlying neuroprotective properties of A2AR blockade on the synaptic plasticity of abGCs were further explored using molecular biology methods.

RESULTS

APP/PS1 mice displayed DG-dependent spatial memory deficits at an early stage. Additionally, impaired LTP and an imbalance in network excitation/inhibition were observed in the DG region of APP/PS1 mice, indicating synaptic structural and functional abnormalities of abGCs. A2AR was found to be upregulated in the hippocampus of the APP/PS1 mouse model of AD. Treatment with the selective A2AR antagonist SCH58261 for three weeks significantly ameliorated spatial memory deficits in APP/PS1 mice and markedly restored LTP and network excitation/inhibition balance in the DG region. Moreover, SCH58261 treatment restored dendritic morphology complexity and enhanced synaptic plasticity of abGCs in APP/PS1 mice. Furthermore, SCH58261 treatment alleviated the impairment of synaptic plasticity in abGCs. It achieved this by remodeling the subunit composition of NMDA receptors and increasing the proportion of NR2B receptors in abGCs of APP/PS1 mice.

CONCLUSIONS

Blockade of A2AR improves early spatial memory deficits in APP/PS1 mice, possibly by reversing synaptic defects of abGCs. This finding suggests that A2AR blockade could be a potential therapy for AD.

Role of Neuronal TRPC6 Channels in Synapse Development, Memory Formation and Animal Behavior

The transient receptor potential cation channel, subfamily C, member 6 (TRPC6), has been believed to adjust the formation of an excitatory synapse. The positive regulation of TRPC6 engenders synapse enlargement and improved learning and memory in animal models. TRPC6 is involved in different synaptoprotective signaling pathways, including antagonism of N-methyl-D-aspartate receptor (NMDAR), activation of brain-derived neurotrophic factor (BDNF) and postsynaptic store-operated calcium entry. Positive regulation of TRPC6 channels has been repeatedly shown to be good for memory formation and storage. TRPC6 is mainly expressed in the hippocampus, particularly in the dentate granule cells, cornu Ammonis 3 (CA3) pyramidal cells and gamma-aminobutyric acid (GABA)ergic interneurons. It has been observed that TRPC6 agonists have a great influence on animal behavior including memory formation and storage The purpose of this review is to collect the available information on the role of TRPC6 in memory formation in various parts of the brain to understand how TRPC6-specific pharmaceutical agents will affect memory in distinct parts of the central nervous system (CNS).

GluN2B-containing NMDARs in the mammalian brain: pharmacology, physiology, and pathology

Glutamate N-methyl-D-aspartate receptor (NMDAR) is critical for promoting physiological synaptic plasticity and neuronal viability. As a major subpopulation of the NMDAR, the GluN2B subunit-containing NMDARs have distinct pharmacological properties, physiological functions, and pathological relevance to neurological diseases compared with other NMDAR subtypes. In mature neurons, GluN2B-containing NMDARs are likely expressed as both diheteromeric and triheteromeric receptors, though the functional importance of each subpopulation has yet to be disentangled. Moreover, the C-terminal region of the GluN2B subunit forms structural complexes with multiple intracellular signaling proteins. These protein complexes play critical roles in both activity-dependent synaptic plasticity and neuronal survival and death signaling, thus serving as the molecular substrates underlying multiple physiological functions. Accordingly, dysregulation of GluN2B-containing NMDARs and/or their downstream signaling pathways has been implicated in neurological diseases, and various strategies to reverse these deficits have been investigated. In this article, we provide an overview of GluN2B-containing NMDAR pharmacology and its key physiological functions, highlighting the importance of this receptor subtype during both health and disease states.

Design and synthesis of novel GluN2A NMDAR positive allosteric modulators via scaffold hopping strategy as anti-stroke therapeutic agents

NMDA receptor subunits have differential roles in mediating excitotoxic neuronal death both in vitro and in vivo . Activation of NR2A-containing NMDA receptors promotes neuronal survival and exerts a neuroprotective action, whereas over activating GluN2B-containing receptor results in excitotoxicity, increasing neuronal apoptosis. Our previous study has identified Npam 43 as a NMDAR positive allosteric modulators. However, the cis-trans isomerization impedes the development of Npam 43 as potential neuroprotective agents. To discover more potent and selective GluN2A NMDAR positive allosteric modulators, 38 derivatives were synthesized and evaluated their neuroprotective effect on glutamate-exposed PC-12 cells. The allosteric activities of compounds were evaluated using calcium imaging approaches. Among them, compound 5c exhibit GluN1/2A selectivity over GluN1/2B and show neuroprotective activity in vitro and in vivo. This study reported a series of GluN1/2A positive allosteric modulators as neuroprotective agents, and provided a potential opportunity to discover new drugs for stroke treatment.

The combination of Astragalus membranaceus and ligustrazine mitigates cerebral ischemia-reperfusion injury via regulating NR2B-ERK/CREB signaling

BACKGROUND AND PURPOSE

Cerebral ischemia-reperfusion (I/R) injury is a major factor underlying the high mortality and morbidity rates in stroke patients. Our previous study found that the combination of Astragalus membranaceus extract and ligustrazine (Ast+Lig) treatment could protect brain tissues against inflammation in rats with thrombolytic cerebral ischemia. Activation of N-methyl-D-aspartate receptors (NMDAR) is implicated in brain damage induced by cerebral I/R injury.

METHODS

We used in vivo and in vitro models of cerebral I/R injury for middle cerebral artery occlusion/reperfusion in mice and oxygen-glucose deprivation/reoxygenation in primary rat cerebral cortical neurons to evaluate the protective effects of Ast+Lig on cerebral I/R injury, and whether the protective mechanism was related to the regulation of NMDAR-ERK/CREB signaling.

RESULTS

Treatment with Ast+Lig, or MK-801 (an inhibitor of NMDAR) significantly ameliorated neurological deficits, decreased infarct volumes, suppressed neuronal damage and Ca²⁺ influx, and maintained the mitochondrial membrane potential in vivo and in vitro following cerebral I/R injury based on 2,3,5-triphenyl tetrazolium chloride staining, immunohistochemistry, and immunofluorescent staining. Furthermore, treatment with Ast+Lig evidently prevented the upregulation of NR2B, but not NR2A, in vivo and in vitro following cerebral I/R injury based on western blotting and reverse transcription-quantitative PCR analyses. Moreover, treatment with Ast+Lig significantly increased the phosphorylation of ERK and CREB, as well as increasing their mRNA expression levels in vivo and in vitro following cerebral I/R injury.

CONCLUSIONS

The overall results thus suggest that the Ast+Lig combination conferred neuroprotective properties against cerebral I/R injury via regulation of the NR2B-ERK/CREB signaling pathway.

The initiator of neuroexcitotoxicity and ferroptosis in ischemic stroke: Glutamate accumulation

Glutamate plays an important role in excitotoxicity and ferroptosis. Excitotoxicity occurs through over-stimulation of glutamate receptors, specifically NMDAR, while in the non-receptor-mediated pathway, high glutamate concentrations reduce cystine uptake by inhibiting the System Xc-, leading to intracellular glutathione depletion and resulting in ROS accumulation, which contributes to increased lipid peroxidation, mitochondrial damage, and ultimately ferroptosis. Oxidative stress appears to crosstalk between excitotoxicity and ferroptosis, and it is essential to maintain glutamate homeostasis and inhibit oxidative stress responses in vivo. As researchers work to develop natural compounds to further investigate the complex mechanisms and regulatory functions of ferroptosis and excitotoxicity, new avenues will be available for the effective treatment of ischaemic stroke. Therefore, this paper provides a review of the molecular mechanisms and treatment of glutamate-mediated excitotoxicity and ferroptosis.

Neonatal Arterial Ischaemic Stroke: Advances in Pathologic Neural Death, Diagnosis, Treatment, and Prognosis

Neonatal arterial ischaemic stroke (NAIS) is caused by focal arterial occlusion and often leads to severe neurological sequelae. Neural deaths after NAIS mainly include necrosis, apoptosis, necroptosis, autophagy, ferroptosis, and pyroptosis. These neural deaths are mainly caused by upstream stimulations, including excitotoxicity, oxidative stress, inflammation, and death receptor pathways. The current clinical approaches to managing NAIS mainly focus on supportive treatments, including seizure control and anticoagulation. In recent years, research on the pathology, early diagnosis, and potential therapeutic targets of NAIS has progressed. In this review, we summarise the latest progress of research on the pathology, diagnosis, treatment, and prognosis of NAIS and highlight newly potential diagnostic and treatment approaches.

Adaptive Responses to Hypoxia and/or Hyperoxia in Humans

Significance: Oxygen is indispensable for aerobic life, but its utilization exposes cells and tissues to oxidative stress; thus, tight regulation of cellular, tissue, and systemic oxygen concentrations is crucial. Here, we review the current understanding of how the human organism (mal-)adapts to low (hypoxia) and high (hyperoxia) oxygen levels and how these adaptations may be harnessed as therapeutic or performance enhancing strategies at the systemic level. Recent Advances: Hyperbaric oxygen therapy is already a cornerstone of modern medicine, and the application of mild hypoxia, that is, hypoxia conditioning (HC), to strengthen the resilience of organs or the whole body to severe hypoxic insults is an important preparation for high-altitude sojourns or to protect the cardiovascular system from hypoxic/ischemic damage. Many other applications of adaptations to hypo- and/or hyperoxia are only just emerging. HC-sometimes in combination with hyperoxic interventions-is gaining traction for the treatment of chronic diseases, including numerous neurological disorders, and for performance enhancement. Critical Issues: The dose- and intensity-dependent effects of varying oxygen concentrations render hypoxia- and/or hyperoxia-based interventions potentially highly beneficial, yet hazardous, although the risks versus benefits are as yet ill-defined. Future Directions: The field of low and high oxygen conditioning is expanding rapidly, and novel applications are increasingly recognized, for example, the modulation of aging processes, mood disorders, or metabolic diseases. To advance hypoxia/hyperoxia conditioning to clinical applications, more research on the effects of the intensity, duration, and frequency of altered oxygen concentrations, as well as on individual vulnerabilities to such interventions, is paramount. Antioxid. Redox Signal. 37, 887-912.

Transcriptional regulation of NRF1 on metabotropic glutamate receptors in a neonatal hypoxic‑ischemic encephalopathy rat model

BACKGROUND

Neonatal hypoxic-ischemic encephalopathy (HIE) is a kind of brain injury that causes severe neurological disorders in newborns. Metabotropic glutamate receptors (mGluRs) and ionotropic glutamate receptors (iGluRs) are significantly associated with HIE and are involved in ischemia-induced excitotoxicity. This study aimed to investigate the upstream mechanisms of mGluRs and the transcriptional regulation by nuclear respiratory factor 1 (NRF1).

METHODS

The rat model of neonatal HIE was created using unilateral carotid artery ligation and in vitro oxygen-glucose deprivation paradigm. We used western blot, immunofluorescence, Nissl staining, and Morris water maze to investigate the impact of NRF1 on brain damage and learning memory deficit by HIE. We performed ChIP and luciferase activities to identify the transcriptional regulation of NRF1 on mGluRs.

RESULTS

The neuronal NRF1 and some glutamatergic genes expression synchronously declined in infarcted tissues. The NRF1 overexpression effectively restored the expression of some glutamatergic genes and improved cognitive performance. NRF1 regulated some members of mGluRs and iGluRs in hypoxic-ischemic neurons. Finally, NRF1 is bound to the promoter regions of Grm1, Grm2, and Grm8 to activate their transcription.

CONCLUSIONS

NRF1 is involved in the pathology of the neonatal HIE rat model, suggesting a novel therapeutic approach to neonatal HIE.

IMPACT

NRF1 and some glutamatergic genes were synchronously downregulated in the infarcted brain of the neonatal HIE rat model. NRF1 overexpression could rescue cognitive impairment caused by the neonatal HIE rat model. NRF1 regulated the expressions of Grm1, Grm2, and Grm8, which activated their transcription by binding to the promoter regions.

NMDA Receptor C-Terminal Domain Signalling in Development, Maturity, and Disease

The NMDA receptor is a Ca²⁺-permeant glutamate receptor which plays key roles in health and disease. Canonical NMDARs contain two GluN2 subunits, of which 2A and 2B are predominant in the forebrain. Moreover, the relative contribution of 2A vs. 2B is controlled both developmentally and in an activity-dependent manner. The GluN2 subtype influences the biophysical properties of the receptor through difference in their N-terminal extracellular domain and transmembrane regions, but they also have large cytoplasmic Carboxyl (C)-terminal domains (CTDs) which have diverged substantially during evolution. While the CTD identity does not influence NMDAR subunit specific channel properties, it determines the nature of CTD-associated signalling molecules and has been implicated in mediating the control of subunit composition (2A vs. 2B) at the synapse. Historically, much of the research into the differential function of GluN2 CTDs has been conducted in vitro by over-expressing mutant subunits, but more recently, the generation of knock-in (KI) mouse models have allowed CTD function to be probed in vivo and in ex vivo systems without heterologous expression of GluN2 mutants. In some instances, findings involving KI mice have been in disagreement with models that were proposed based on earlier approaches. This review will examine the current research with the aim of addressing these controversies and how methodology may contribute to differences between studies. We will also discuss the outstanding questions regarding the role of GluN2 CTD sequences in regulating NMDAR subunit composition, as well as their relevance to neurodegenerative disease and neurodevelopmental disorders.

Targeting NMDA Receptors at the Neurovascular Unit: Past and Future Treatments for Central Nervous System Diseases

The excitatory neurotransmission of the central nervous system (CNS) mainly involves glutamate and its receptors, especially N-methyl-D-Aspartate receptors (NMDARs). These receptors have been extensively described on neurons and, more recently, also on other cell types. Nowadays, the study of their differential expression and function is taking a growing place in preclinical and clinical research. The diversity of NMDAR subtypes and their signaling pathways give rise to pleiotropic functions such as brain development, neuronal plasticity, maturation along with excitotoxicity, blood-brain barrier integrity, and inflammation. NMDARs have thus emerged as key targets for the treatment of neurological disorders. By their large extracellular regions and complex intracellular structures, NMDARs are modulated by a variety of endogenous and pharmacological compounds. Here, we will present an overview of NMDAR functions on neurons and other important cell types involved in the pathophysiology of neurodegenerative, neurovascular, mental, autoimmune, and neurodevelopmental diseases. We will then discuss past and future development of NMDAR targeting drugs, including innovative and promising new approaches.

Changes in NMDA Receptor Function in Rapid Ischemic Tolerance: A Potential Role for Tri-Heteromeric NMDA Receptors

In this study, we characterize biophysical changes in NMDA receptor function in response to brief non-injurious ischemic stress (ischemic preconditioning). Electrophysiological studies show NMDA receptor function is reduced following preconditioning in cultured rat cortical neurons. This functional change is not due to changes in the reversal potential of the receptor, but an increase in desensitization. We performed concentration-response analysis of NMDA-evoked currents, and demonstrate that preconditioned neurons show a reduced potency of NMDA to evoke currents, an increase in Mg2+ sensitivity, but no change in glycine sensitivity. Antagonists studies show a reduced inhibition of GluN2B antagonists that have an allosteric mode of action (ifenprodil and R-25-6981), but competitive antagonists at the GluR2A and 2B receptor (NVP-AMM077 and conantokin-G) appear to have similar potency to block currents. Biochemical studies show a reduction in membrane surface GluN2B subunits, and an increased co-immunoprecipitation of GluN2A with GluN2B subunits, suggestive of tri-heteromeric receptor formation. Finally, we show that blocking actin remodeling with jasplakinolide, a mechanism of rapid ischemic tolerance, prevents NMDA receptor functional changes and co-immunoprecipitation of GluN2A and 2B subunits. Together, this study shows that alterations in NMDA receptor function following preconditioning ischemia are associated with neuroprotection in rapid ischemic tolerance.

NMDA receptor antagonists reduce amyloid-β deposition by modulating calpain-1 signaling and autophagy, rescuing cognitive impairment in 5XFAD mice

Overstimulation of N-methyl-d-aspartate receptors (NMDARs) is the leading cause of brain excitotoxicity and often contributes to neurodegenerative diseases such as Alzheimer’s Disease (AD), the most common form of dementia. This study aimed to evaluate a new NMDA receptor antagonist (UB-ALT-EV) and memantine in 6-month-old female 5XFAD mice that were exposed orally to a chronic low-dose treatment. Behavioral and cognitive tests confirmed better cognitive performance in both treated groups. Calcium-dependent protein calpain-1 reduction was found after UB-ALT-EV treatment but not after memantine. Changes in spectrin breakdown products (SBDP) and the p25/p35 ratio confirmed diminished calpain-1 activity. Amyloid β (Aβ) production and deposition was evaluated in 5XFAD mice and demonstrated a robust effect of NMDAR antagonists on reducing Aβ deposition and the number and size of Thioflavin-S positive plaques. Furthermore, glycogen synthase kinase 3β (GSK3β) active form and phosphorylated tau (AT8) levels were diminished after UB-ALT-EV treatment, revealing tau pathology improvement. Because calpain-1 is involved in autophagy activation, autophagic proteins were studied. Strikingly, results showed changes in the protein levels of unc-51-like kinase (ULK-1), beclin-1, microtubule-associated protein 1A/1B-light chain 3(LC3B-II)/LC3B-I ratio, and lysosomal-associated membrane protein 1 (LAMP-1) after NMDAR antagonist treatments, suggesting an accumulation of autophagolysosomes in 5XFAD mice, reversed by UB-ALT-EV. Likewise, treatment with UB-ALT-EV recovered a WT mice profile in apoptosis markers Bcl-2, Bax, and caspase-3. In conclusion, our results revealed the potential neuroprotective effect of UB-ALT-EV by attenuating NMDA-mediated apoptosis and reducing Aβ deposition and deposition jointly with the autophagy rescue to finally reduce cognitive alterations in a mice model of familial AD.

Signaling pathways involved in ischemic stroke: molecular mechanisms and therapeutic interventions

Ischemic stroke is caused primarily by an interruption in cerebral blood flow, which induces severe neural injuries, and is one of the leading causes of death and disability worldwide. Thus, it is of great necessity to further detailly elucidate the mechanisms of ischemic stroke and find out new therapies against the disease. In recent years, efforts have been made to understand the pathophysiology of ischemic stroke, including cellular excitotoxicity, oxidative stress, cell death processes, and neuroinflammation. In the meantime, a plethora of signaling pathways, either detrimental or neuroprotective, are also highly involved in the forementioned pathophysiology. These pathways are closely intertwined and form a complex signaling network. Also, these signaling pathways reveal therapeutic potential, as targeting these signaling pathways could possibly serve as therapeutic approaches against ischemic stroke. In this review, we describe the signaling pathways involved in ischemic stroke and categorize them based on the pathophysiological processes they participate in. Therapeutic approaches targeting these signaling pathways, which are associated with the pathophysiology mentioned above, are also discussed. Meanwhile, clinical trials regarding ischemic stroke, which potentially target the pathophysiology and the signaling pathways involved, are summarized in details. Conclusively, this review elucidated potential molecular mechanisms and related signaling pathways underlying ischemic stroke, and summarize the therapeutic approaches targeted various pathophysiology, with particular reference to clinical trials and future prospects for treating ischemic stroke.

Retinal Glutamate Neurotransmission: From Physiology to Pathophysiological Mechanisms of Retinal Ganglion Cell Degeneration

Glutamate neurotransmission and metabolism are finely modulated by the retinal network, where the efficient processing of visual information is shaped by the differential distribution and composition of glutamate receptors and transporters. However, disturbances in glutamate homeostasis can result in glutamate excitotoxicity, a major initiating factor of common neurodegenerative diseases. Within the retina, glutamate excitotoxicity can impair visual transmission by initiating degeneration of neuronal populations, including retinal ganglion cells (RGCs). The vulnerability of RGCs is observed not just as a result of retinal diseases but has also been ascribed to other common neurodegenerative and peripheral diseases. In this review, we describe the vulnerability of RGCs to glutamate excitotoxicity and the contribution of different glutamate receptors and transporters to this. In particular, we focus on the N-methyl-d-aspartate (NMDA) receptor as the major effector of glutamate-induced mechanisms of neurodegeneration, including impairment of calcium homeostasis, changes in gene expression and signalling, and mitochondrial dysfunction, as well as the role of endoplasmic reticular stress. Due to recent developments in the search for modulators of NMDA receptor signalling, novel neuroprotective strategies may be on the horizon.

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.

Oxidative Stress in Ischemia/Reperfusion Injuries following Acute Ischemic Stroke

Recanalization therapy is increasingly used in the treatment of acute ischemic stroke. However, in about one third of these patients, recanalization is followed by ischemia/reperfusion injuries, and clinically to worsening of the neurological status. Much research has focused on unraveling the involved mechanisms in order to prevent or efficiently treat these injuries. What we know so far is that oxidative stress and mitochondrial dysfunction are significantly involved in the pathogenesis of ischemia/reperfusion injury. However, despite promising results obtained in experimental research, clinical studies trying to interfere with the oxidative pathways have mostly failed. The current article discusses the main mechanisms leading to ischemia/reperfusion injuries, such as mitochondrial dysfunction, excitotoxicity, and oxidative stress, and reviews the clinical trials with antioxidant molecules highlighting recent developments and future strategies.

Neuroprotective effect of pseudoginsenoside-F11 on permanent cerebral ischemia in rats by regulating calpain activity and NR2A submit-mediated AKT-CREB signaling pathways

BACKGROUND

N-methyl-d-aspartate receptors (NMDARs) have been demonstrated to play central roles in stroke pathology and recovery, including dual roles in promoting either neuronal survival or death with their different subtypes and locations.

PURPOSE

We have previously demonstrated that pseudoginsenoside-F11 (PF11) can provide long-term neuroprotective effects on transient and permanent ischemic stroke-induced neuronal damage. However, it is still needed to clarify whether NMDAR-2A (NR2A)-mediated pro-survival signaling pathway is involved in the beneficial effect of PF11 on permanent ischemic stroke.

MATERIAL AND METHODS

PF11 was administrated in permanent middle cerebral artery occlusion (pMCAO)-operated rats. The effect of PF11 on oxygen-glucose deprivation (OGD)-exposed primary cultured neurons were further evaluated. The regulatory effect of PF11 on NR2A expression and the activation of its downstream AKT-CREB pathway were detected by Western blotting and immunofluorescence in the presence or absence of a specific NR2A antagonist NVP-AAM077 (NVP) both in vivo and in vitro.

RESULTS

PF11 dose- and time-dependently decreased calpain1 (CAPN1) activity and its specific breakdown product α-Fodrin expression, while the expression of Ca²⁺/calmodulin-dependent protein kinase II alpha (CaMKII-α) was significantly upregulated in the cortex and striatum of rats at 24 h after the onset of pMCAO operation. Moreover, PF11 prevented the downregulation of NR2A, p-AKT/AKT, and p-CREB/CREB in both in vivo and in vitro stroke models. Finally, the results indicated treatment with NVP can abolish the effects of PF11 on alleviating the ischemic injury and activating NR2A-mediated AKT-CREB signaling pathway.

CONCLUSIONS

Our results demonstrate that PF11 can exert neuroprotective effects on ischemic stroke by inhibiting the activation of CAPN1 and subsequently enhancing the NR2A-medicated activation of AKT-CREB pathway, which provides a mechanistic link between the neuroprotective effect of PF11 against cerebral ischemia and NR2A-associated pro-survival signaling pathway.

Polygalasaponin F protects hippocampal neurons against glutamate-induced cytotoxicity

Excess extracellular glutamate leads to excitotoxicity, which induces neuronal death through the overactivation of N-methyl-D-aspartate receptors (NMDARs). Excitotoxicity is thought to be closely related to various acute and chronic neurological disorders, such as stroke and Alzheimer’s disease. Polygalasaponin F (PGSF) is a triterpenoid saponin monomer that can be isolated from Polygala japonica, and has been reported to protect cells against apoptosis. To investigate the mechanisms underlying the neuroprotective effects of PGSF against glutamate-induced cytotoxicity, PGSF-pretreated hippocampal neurons were exposed to glutamate for 24 hours. The results demonstrated that PGSF inhibited glutamate-induced hippocampal neuron death in a concentration-dependent manner and reduced glutamate-induced Ca²⁺ overload in the cultured neurons. In addition, PGSF partially blocked the excess activity of NMDARs, inhibited both the downregulation of NMDAR subunit NR2A expression and the upregulation of NMDAR subunit NR2B expression, and upregulated the expression of phosphorylated cyclic adenosine monophosphate-responsive element-binding protein and brain-derived neurotrophic factor. These findings suggest that PGSF protects cultured hippocampal neurons against glutamate-induced cytotoxicity by regulating NMDARs. The study was approved by the Institutional Animal Care Committee of Nanchang University (approval No. 2017-0006) on December 29, 2017.

Neuronal injuries in cerebral infarction and ischemic stroke: From mechanisms to treatment (Review)

Stroke is the leading cause of disabilities and cognitive deficits, accounting for 5.2% of all mortalities worldwide. Transient or permanent occlusion of cerebral vessels leads to ischemic strokes, which constitutes the majority of strokes. Ischemic strokes induce brain infarcts, along with cerebral tissue death and focal neuronal damage. The infarct size and neurological severity after ischemic stroke episodes depends on the time period since occurrence, the severity of ischemia, systemic blood pressure, vein systems and location of infarcts, amongst others. Ischemic stroke is a complex disease, and neuronal injuries after ischemic strokes have been the focus of current studies. The present review will provide a basic pathological background of ischemic stroke and cerebral infarcts. Moreover, the major mechanisms underlying ischemic stroke and neuronal injuries are summarized. This review will also briefly summarize some representative clinical trials and up-to-date treatments that have been applied to stroke and brain infarcts.

Distinct regulation of tonic GABAergic inhibition by NMDA receptor subtypes

Tonic inhibition mediated by extrasynaptic GABAARs regulates various brain functions. However, the mechanisms that regulate tonic inhibition remain largely unclear. Here, we report distinct actions of GluN2A- and GluN2B-NMDA receptors (NMDARs) on tonic inhibition in hippocampal neurons under basal and high activity conditions. Specifically, overexpression of GluN2B, but not GluN2A, reduces α5-GABAAR surface expression and tonic currents. Additionally, knockout of GluN2A and GluN2B decreases and increases tonic currents, respectively. Mechanistically, GluN2A-NMDARs inhibit and GluN2B-NMDARs promote α5-GABAAR internalization, resulting in increased and decreased surface α5-GABAAR expression, respectively. Furthermore, GluN2A-NMDARs, but not GluN2B-NMDARs, are required for homeostatic potentiation of tonic inhibition induced by prolonged increase of neuronal activity. Last, tonic inhibition decreases during acute seizures, whereas it increases 24 h later, involving GluN2-NMDAR-dependent signaling. Collectively, these data reveal an NMDAR subunit-specific regulation of tonic inhibition in physiological and pathological conditions and provide mechanistic insight into activity-dependent modulation of tonic inhibition.

Neuroprotective Effect of Moxibustion on Cerebral Ischemia/Reperfusion Injury in Rats by Downregulating NR2B Expression

Objective

Stroke is a common and frequently occurring disease of the central nervous system, which is characterized by high mortality and a high disability rate. Moxibustion is a common method for treating stroke in traditional Chinese medicine, but its neuroprotective mechanism is unknown. N-Methyl-D-Aspartate Receptor Subunit 2B (NR2B) plays an important role in neuronal apoptosis. The objective of this study was to explore the mechanisms underlying the neuroprotective effect of moxibustion on cerebral ischemia/reperfusion (I/R) injury based on NR2B.

Methods

Sprague-Dawley rats were randomly divided into 5 groups: the control group, I/R group, I/R + moxibustion group, I/R + Ro25-6981 (NR2B antagonist) group, and I/R + Ro25-6981 + moxibustion group. The cerebral ischemia/reperfusion model was induced by middle cerebral artery occlusion. Before the establishment of the model, the Ro25-6981 group received intraperitoneal injections of Ro25-6981, the moxibustion group received moxibustion, and the Ro25-6981 + moxibustion group received both interventions. The neurological dysfunction was evaluated by a neurological deficiency score (NDS). The infarct volume was examined by TTC (2,3,5-triphenyltetrazolium chloride) staining. The apoptosis rate of cerebral cells in the ischemic area was examined by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) staining, and the expression of Bcl-2, Bax, and caspase-3 was observed by western blot. NR2B and JNK were also observed by western blot.

Results

Compared with the I/R group, moxibustion significantly decreased the neurological deficiency score (P < 0.05) and the infarct rate (P < 0.01) in I/R rats which were similar to those in the Ro25-6981 group. After moxibustion treatment, there was a significant decrease in the apoptosis rate (P < 0.001) and the protein expression levels of Bax, caspase-3, and JNK (P < 0.001) and an increase in the expression of Bcl-2 (P < 0.01). Compared with the I/R group, moxibustion downregulated the expression of NR2B and decreased the activity of NR2B in the cerebral ischemia area (P < 0.001).

Conclusions

Moxibustion can improve neurological dysfunction and decrease infarction area and neuronal apoptosis caused by cerebral ischemia/reperfusion in rats. Its neuroprotective mechanism may be related to downregulating the expression of NR2B.

Methanol extract of Ficus platyphylla decreases cerebral ischemia induced injury in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Extracts of the stem bark of Ficus paltyphylla (FP) are used in the Nigerian traditional medicine to manage psychoses, depression, epilepsy, pain, and inflammation. Our previous studies revealed that the methanol extract of FP ameliorate body core temperature.

AIM OF THE STUDY

A number of pharmacological agents that utilize mechanisms that enhanced neuronal survival and/or neural regeneration have been developed for the treatment of stroke. Hypothermia protects the brain from damage caused by ischemia by attenuating destructive processes such as neuroinflammation, excitotoxicity, blood-brain barrier disruption, apoptosis, and free radical formation following cerebral ischemia. In the present study, we examined the neuroprotective potential of FP on permanent occlusion of the middle cerebral artery (MCAO)-induced ischemia in mice.

MATERIAL AND METHODS

C57Bl mice were subjected to MCAO. FP was administered 1 h prior to and immediately after surgery. The brains were collected 24 h later and infarct volumes were measured using immune-histochemical staining, DAPI, NeuN, synaptophysin, and NR2B were quantified.

RESULTS

Administration of FP prior to MCAO significantly reduced infarct volume, with no effect on infarct volume immediately after MCAO. Higher numbers of cells and neurons were observed in the peri-infarct area in both groups of mice. FP-induced hypothermia protected tissue in the peri-infarct region from synaptophysin reduction. NMDA receptor 2 (NR2B) immunoreactivity is enhanced by MCAO, with no difference observed in both sham-operated and FP-induced hypothermia groups of mice.

CONCLUSIONS

The data suggest that FP might be useful in the reduction of ischemia-induced infarct volume when administered prior to the initiation of ischemia with no effect observed after ischemia induction.

Regulation of Phosphorylated State of NMDA Receptor by STEP61 Phosphatase after Mild-Traumatic Brain Injury: Role of Oxidative Stress

Traumatic Brain Injury (TBI) mediates neuronal death through several events involving many molecular pathways, including the glutamate-mediated excitotoxicity for excessive stimulation of N-methyl-D-aspartate receptors (NMDARs), producing activation of death signaling pathways. However, the contribution of NMDARs (distribution and signaling-associated to the distribution) remains incompletely understood. We propose a critical role of STEP₆₁ (Striatal-Enriched protein tyrosine phosphatase) in TBI; this phosphatase regulates the dephosphorylated state of the GluN2B subunit through two pathways: by direct dephosphorylation of tyrosine-1472 and indirectly via dephosphorylation and inactivation of Fyn kinase. We previously demonstrated oxidative stress’s contribution to NMDAR signaling and distribution using SOD2^+/− mice such a model. We performed TBI protocol using a controlled frontal impact device using C57BL/6 mice and SOD2^+/− animals. After TBI, we found alterations in cognitive performance, NMDAR-dependent synaptic function (decreased synaptic form of NMDARs and decreased synaptic current NMDAR-dependent), and increased STEP₆₁ activity. These changes are reduced partially with the STEP₆₁-inhibitor TC-2153 treatment in mice subjected to TBI protocol. This study contributes with evidence about the role of STEP₆₁ in the neuropathological progression after TBI and also the alteration in their activity, such as an early biomarker of synaptic damage in traumatic lesions.

Blocking N-Methyl-D-aspartic Acid (NMDA) Receptor Inhibits Heat-Sensitization Response of Moxibustion in Stroke Rats

Our previous studies demonstrated that effects of moxibustion heavily relied on heat-sensitization response, a specific sensation induced by moxibustion in the ill body. On the sensation, long-term potentiation (LTP) of prelimbic cortex was attributed to heat-sensitization responses. The N-methyl-D-aspartic acid (NMDA) receptor plays a key role in LTP induction; however, little is known about the role of NMDA receptor in heat-sensitization response. The present study investigated the role of NMDA receptor in heat-sensitization response, specifically, NMDA receptor was inhibited by competitive glutamatergic antagonist, (±)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), observing the frequency of heat-sensitization response in moxibustion treatment and evaluating the conducive outcomes to cerebral infarct rats for rehabilitation. Heat-sensitization response in cerebral infarct rats was regularly measured for all the samples when exposed to moxibustion. Intraperitoneal injection of CPP was conducted, and soon afterwards, a significant drop of heat-sensitization response in all the samples was measured. Moreover, moxibustion efficiency on rehabilitation was unfavourably affected in cerebral infarct rats when compared to vehicle injection control. This indicated that NMDA receptor antagonist made a negative impact on induction of heat-sensitization response and consequently affected cerebral infarct rats to rehabilitate under moxibustion treatment. It also suggested that activating NMDA receptor played a positive part in ischemic stroke rehabilitation, and regulating its activity could be a feasible way to increase heat-sensitization response, improving the effect of moxibustion.

Role of Grina/Nmdara1 in the Central Nervous System Diseases

Glutamate receptor, ionotropic, N-methyl-D-aspartate associated protein 1 (GRINA) is a member of the NMDA receptors (NMDARs) and is involved in several neurological diseases, which governs the key processes of neuronal cell death or the release of neurotransmitters. Upregulation of GRINA has been reported in multiple diseases in human beings, such as major depressive disorder (MDD) and schizophrenia (SCZ), with which the underlying mechanisms remain elusive. In this review, we provide a general overview of the expression and physiological function of GRINA in the central nervous system (CNS) diseases, including stroke, depression, epilepsy, SCZ, and Alzheimer’s disease (AD).

Preconditioning-Activated AKT Controls Neuronal Tolerance to Ischemia through the MDM2-p53 Pathway

One of the most important mechanisms of preconditioning-mediated neuroprotection is the attenuation of cell apoptosis, inducing brain tolerance after a subsequent injurious ischemia. In this context, the antiapoptotic PI3K/AKT signaling pathway plays a key role by regulating cell differentiation and survival. Active AKT is known to increase the expression of murine double minute-2 (MDM2), an E3-ubiquitin ligase that destabilizes p53 to promote the survival of cancer cells. In neurons, we recently showed that the MDM2–p53 interaction is potentiated by pharmacological preconditioning, based on subtoxic stimulation of NMDA glutamate receptor, which prevents ischemia-induced neuronal apoptosis. However, whether this mechanism contributes to the neuronal tolerance during ischemic preconditioning (IPC) is unknown. Here, we show that IPC induced PI3K-mediated phosphorylation of AKT at Ser⁴⁷³, which in turn phosphorylated MDM2 at Ser¹⁶⁶. This phosphorylation triggered the nuclear stabilization of MDM2, leading to p53 destabilization, thus preventing neuronal apoptosis upon an ischemic insult. Inhibition of the PI3K/AKT pathway with wortmannin or by AKT silencing induced the accumulation of cytosolic MDM2, abrogating IPC-induced neuroprotection. Thus, IPC enhances the activation of PI3K/AKT signaling pathway and promotes neuronal tolerance by controlling the MDM2–p53 interaction. Our findings provide a new mechanistic pathway involved in IPC-induced neuroprotection via modulation of AKT signaling, suggesting that AKT is a potential therapeutic target against ischemic injury.

Regulation of the NMDA receptor by its cytoplasmic domains: (How) is the tail wagging the dog?

Excitatory neurotransmission mediated by N-methyl-d-aspartate receptors (NMDARs) is critical for synapse development, function, and plasticity in the brain. NMDARs are tetra-heteromeric cation-channels that mediate synaptic transmission and plasticity. Extensive human studies show the existence of genetic variants in NMDAR subunits genes (GRIN genes) that are associated with neurodevelopmental and neuropsychiatric disorders, including autism spectrum disorders (ASD), epilepsy (EP), intellectual disability (ID), attention deficit hyperactivity disorder (ADHD), and schizophrenia (SCZ). NMDAR subunits have a unique modular architecture with four semiautonomous domains. Here we focus on the carboxyl terminal domain (CTD), also known as the intracellular C-tail, which varies in length among the glutamate receptor subunits and is the most diverse domain in terms of amino acid sequence. The CTD shows no sequence homology to any known proteins but encodes short docking motifs for intracellular binding proteins and covalent modifications. Our review will discuss the many important functions of the CTD in regulating NMDA membrane and synaptic targeting, stabilization, degradation targeting, allosteric modulation and metabotropic signaling of the receptor. This article is part of the special issue on 'Glutamate Receptors - NMDA Receptors'.