Glycine Transporter 1 Inhibitors: Predictions on Their Possible Mechanisms in the Development of Opioid Analgesic Tolerance

The development of opioid tolerance in patients on long-term opioid analgesic treatment is an unsolved matter in clinical practice thus far. Dose escalation is required to restore analgesic efficacy, but at the price of side effects. Intensive research is ongoing to elucidate the underlying mechanisms of opioid analgesic tolerance in the hope of maintaining opioid analgesic efficacy. N-Methyl-D-aspartate receptor (NMDAR) antagonists have shown promising effects regarding opioid analgesic tolerance; however, their use is limited by side effects (memory dysfunction). Nevertheless, the GluN2B receptor remains a future target for the discovery of drugs to restore opioid efficacy. Mechanistically, the long-term activation of µ-opioid receptors (MORs) initiates receptor phosphorylation, which triggers β-arrestin-MAPKs and NOS-GC-PKG pathway activation, which ultimately ends with GluN2B receptor overactivation and glutamate release. The presence of glutamate and glycine as co-agonists is a prerequisite for GluN2B receptor activation. The extrasynaptic localization of the GluN2B receptor means it is influenced by the glycine level, which is regulated by astrocytic glycine transporter 1 (GlyT1). Enhanced astrocytic glycine release by reverse transporter mechanisms as a consequence of high glutamate levels or unconventional MOR activation on astrocytes could further activate the GluN2B receptor. GlyT1 inhibitors might inhibit this condition, thereby reducing opioid tolerance.

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.

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.

Carnosic Acid Attenuates AβOs-Induced Apoptosis and Synaptic Impairment via Regulating NMDAR2B and Its Downstream Cascades in SH-SY5Y Cells

Neuronal death and synaptic loss are principal pathological features of Alzheimer's disease (AD). Amyloid beta oligomers (AβOs) constitute the main neurotoxin underscoring AD pathology. AβOs interact with N-methyl-D-aspartate receptors (NMDARs), resulting in neurotoxic events, including activation of apoptosis and synaptic impairment. Carnosic acid (CA), extracted from Salvia rosmarinus, has been verified its neuroprotective effects in AD. However, the precise mechanisms by which CA induces synaptic protection remain unclear. In this study, we established an in vitro AD model using SH-SY5Y human neuroblastoma cells. We observed that CA improved neuronal survival by suppressing apoptosis. Moreover, CA restored synaptic impairments by increasing expression levels of brain-derived neurotrophic factor (BDNF), postsynaptic density protein-95 (PSD-95), and synaptophysin (Syn). Furthermore, we found these protective effects were dependent on inhibiting the phosphorylation of NMDAR subtype 2B (NMDAR2B), which further suppressed calcium overload and promoted activation of the extracellular signal-regulated kinase (ERK)-cAMP response element-binding protein (CREB) pathway. Administration of N-methyl-D-aspartic acid (NMDA), an agonist of NMDARs, abolished these effects of CA. Our findings demonstrate that CA exerts neuroprotective effects in an in vitro model of AD by regulating NMDAR2B and its downstream cascades, highlighting the therapeutic potential of CA as a NMDARs-targeted candidate in the treatment of AD.

Structural insights into assembly and function of GluN1-2C, GluN1-2A-2C, and GluN1-2D NMDARs

Neurotransmission mediated by diverse subtypes of N-methyl-D-aspartate receptors (NMDARs) is fundamental for basic brain functions and development as well as neuropsychiatric diseases and disorders. NMDARs are glycine- and glutamate-gated ion channels that exist as heterotetramers composed of obligatory GluN1 and GluN2(A-D) and/or GluN3(A-B). The GluN2C and GluN2D subunits form ion channels with distinct properties and spatio-temporal expression patterns. Here, we provide the structures of the agonist-bound human GluN1-2C NMDAR in the presence and absence of the GluN2C-selective positive allosteric potentiator (PAM), PYD-106, the agonist-bound GluN1-2A-2C tri-heteromeric NMDAR, and agonist-bound GluN1-2D NMDARs by single-particle electron cryomicroscopy. Our analysis shows unique inter-subunit and domain arrangements of the GluN2C NMDARs, which contribute to functional regulation and formation of the PAM binding pocket and is distinct from GluN2D NMDARs. Our findings here provide the fundamental blueprint to study GluN2C- and GluN2D-containing NMDARs, which are uniquely involved in neuropsychiatric disorders.

N-Methyl-D-Aspartate (NMDA)-Type Glutamate Receptors and Demyelinating Disorders: A Neuroimmune Perspective

N-methyl-D-aspartate receptors (NMDARs) are ionotropic glutamate receptors, highly important in regulating substantial physiologic processes in the brain and the nervous system, and disturbance in their function could contribute to different pathologies. Overstimulation and hyperactivity of NMDARs, termed as glutamate toxicity, could promote cell death and apoptosis. Meanwhile, their blockade could lead to dysfunction of the brain and nervous system as well. A growing body of evidence has demonstrated the prominent role of NMDARs in demyelinating disorders and anti-NMDAR encephalitis. Herein, we provide an overview of the role of NMDARs' dysfunction in the physiopathology of demyelinating disorders such as multiple sclerosis and neuromyelitis optica spectrum disorders.

Dietary zinc supplementation rescues fear-based learning and synaptic function in the Tbr1+/- mouse model of autism spectrum disorders

Background

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterised by a dyad of behavioural symptoms—social and communication deficits and repetitive behaviours. Multiple aetiological genetic and environmental factors have been identified as causing or increasing the likelihood of ASD, including serum zinc deficiency. Our previous studies revealed that dietary zinc supplementation can normalise impaired social behaviours, excessive grooming, and heightened anxiety in a Shank3 mouse model of ASD, as well as the amelioration of synapse dysfunction. Here, we have examined the efficacy and breadth of dietary zinc supplementation as an effective therapeutic strategy utilising a non-Shank-related mouse model of ASD—mice with Tbr1 haploinsufficiency.

Methods

We performed behavioural assays, amygdalar slice whole-cell patch-clamp electrophysiology, and immunohistochemistry to characterise the synaptic mechanisms underlying the ASD-associated behavioural deficits observed in Tbr1^+/− mice and the therapeutic potential of dietary zinc supplementation. Two-way analysis of variance (ANOVA) with Šídák's post hoc test and one-way ANOVA with Tukey’s post hoc multiple comparisons were performed for statistical analysis.

Results

Our data show that dietary zinc supplementation prevents impairments in auditory fear memory and social interaction, but not social novelty, in the Tbr1^+/− mice. Tbr1 haploinsufficiency did not induce excessive grooming nor elevate anxiety in mice. At the synaptic level, dietary zinc supplementation reversed α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) and N-methyl-d-aspartate receptor (NMDAR) hypofunction and normalised presynaptic function at thalamic-lateral amygdala (LA) synapses that are crucial for auditory fear memory. In addition, the zinc supplemented diet significantly restored the synaptic puncta density of the GluN1 subunit essential for functional NMDARs as well as SHANK3 expression in both the basal and lateral amygdala (BLA) of Tbr1^+/− mice.

Limitations

The therapeutic effect of dietary zinc supplementation observed in rodent models may not reproduce the same effects in human patients. The effect of dietary zinc supplementation on synaptic function in other brain structures affected by Tbr1 haploinsufficiency including olfactory bulb and anterior commissure will also need to be examined.

Conclusions

Our data further the understanding of the molecular mechanisms underlying the effect of dietary zinc supplementation and verify the efficacy and breadth of its application as a potential treatment strategy for ASD.

Astrocytic N-Methyl-D-Aspartate Receptors Protect the Hippocampal Neurons Against Amyloid-β142-Induced Synaptotoxicity by Regulating Nerve Growth Factor

BACKGROUND

Soluble oligomeric amyloid-β (Aβ)-induced synaptic dysfunction is an early event in Alzheimer's disease (AD) pathogenesis. Mounting evidence has suggested N-methyl-D-aspartate receptors (NMDARs) play an important role in Aβ-induced synaptotoxicity. Originally NMDARs were believed to be expressed exclusively in neurons; however, recent two decades studies have demonstrated functional NMDARs present on astrocytes. Neuronal NMDARs are modulators of neurodegeneration, while our previous initial study found that astrocytic NMDARs mediated synaptoprotection and identified nerve growth factor (NGF) secreted by astrocytes, as a likely mediator, but how astrocytic NMDARs protect neurons against Aβ-induced synaptotoxicity through regulating NGF remains unclear.

OBJECTIVE

To achieve further insight into the mechanism of astrocytic NMDARs oppose Aβ-induced synaptotoxicity through regulating NGF.

METHODS

With the primary hippocampal neuronal and astrocytic co-cultures, astrocytes were pretreated with agonist or antagonist of NMDARs before Aβ142 oligomers application to neuron-astrocyte co-cultures. Western blot, RT-PCR, etc., were used for the related proteins evaluation.

RESULTS

Activation of astrocytic NMDARs can significantly mitigate Aβ142-induced loss of PSD-95 and synaptophysin through increasing NGF release. Blockade of astrocytic NMDARs inhibited Aβ-induced compensatory protective NGF increase in protein and mRNA levels through modulating NF-κB of astrocytes. Astrocytic NMDARs activation can enhance Aβ-induced Furin increase, and blockade of astrocytic NMDARs inhibited Aβ-induced immunofluorescent intensity elevation of vesicle trafficking protein VAMP3 and NGF double-staining.

CONCLUSION

Astrocytic NMDARs oppose Aβ-induced synaptotoxicity through modulating the synthesis, maturation, and secretion of NGF in astrocytes. This new information may contribute to the quest for specific targeted strategy of intervention to delay the onset of AD.

GRIN2A Variants Associated With Idiopathic Generalized Epilepsies

Objective: The objective of this study is to explore the role of GRIN2A gene in idiopathic generalized epilepsies and the potential underlying mechanism for phenotypic variation.

Methods: Whole-exome sequencing was performed in a cohort of 88 patients with idiopathic generalized epilepsies. Electro-physiological alterations of the recombinant N-methyl-D-aspartate receptors (NMDARs) containing GluN2A mutants were examined using two-electrode voltage-clamp recordings. The alterations of protein expression were detected by immunofluorescence staining and biotinylation. Previous studies reported that epilepsy related GRIN2A missense mutations were reviewed. The correlation among phenotypes, functional alterations, and molecular locations was analyzed.

Results: Three novel heterozygous missense GRIN2A mutations (c.1770A > C/p.K590N, c.2636A > G/p.K879R, and c.3199C > T/p.R1067W) were identified in three unrelated cases. Electrophysiological analysis demonstrated R1067W significantly increased the current density of GluN1/GluN2A NMDARs. Immunofluorescence staining indicated GluN2A mutants had abundant distribution in the membrane and cytoplasm. Western blotting showed the ratios of surface and total expression of the three GluN2A-mutants were significantly increased comparing to the wild type. Further analysis on the reported missense mutations demonstrated that mutations with severe gain-of-function were associated with epileptic encephalopathy, while mutations with mild gain of function were associated with mild phenotypes, suggesting a quantitative correlation between gain-of-function and phenotypic severity. The mutations located around transmembrane domains were more frequently associated with severe phenotypes and absence seizure-related mutations were mostly located in carboxyl-terminal domain, suggesting molecular sub-regional effects.

Significance: This study revealed GRIN2A gene was potentially a candidate pathogenic gene of idiopathic generalized epilepsies. The functional quantitative correlation and the molecular sub-regional implication of mutations helped in explaining the relatively mild clinical phenotypes and incomplete penetrance associated with GRIN2A variants.

Reduced D-Serine Release May Contribute to Impairment of Long-Term Potentiation by Corticosterone in the Perforant Path-Dentate Gyrus

Long-term potentiation (LTP) is a neurobiological mechanism of cognitive function, and the N-methyl-D-aspartate (NMDA) receptors is fundamental for LTP. Previous studies showed that over activation of NMDA receptors may be a crucial cause of LTP and cognitive impairment induced by stress or corticosterone. However, other studies showed that the function of NMDA receptors is insufficient since the NMDA receptors co-agonist D-serine could improve stress-induced cognitive impairment. The purpose of this study is to clarify whether over activation of NMDA receptors or hypofunction of NMDA receptors is involved in hippocampal impairment of LTP by corticosterone and the underlying mechanisms. Results showed that hippocampal LTP and object location recognition memory were impaired in corticosterone-treated mice. Corticosterone increased the glutamate level in hippocampal tissues, neither NMDA receptors antagonist nor its subtype antagonists alleviated impairment of LTP, while enhancing the function of NMDA receptors by D-serine did alleviate impairment of LTP by corticosterone, suggesting that hypofunction of NMDA receptors might be one of the main reasons for impairment of LTP by corticosterone. Further results showed that the level of D-serine and its precursor L-serine did not change. D-serine release-related protein Na+-independent alanine-serine-cysteine transporter-1 (ASC-1) in the cell membrane was decreased and increasing D-serine release by the selective activator of ASC-1 antiporter activity alleviated impairment of LTP by corticosterone. Taken together, this study demonstrates that hypofunction of NMDA receptors may be involved in impairment of LTP by corticosterone and reduced D-serine release may be an important reason for its hypofunction, which is an important complement to existing mechanisms of corticosterone-induced LTP and cognitive impairment.

Chronic Ethanol Exposure Enhances Facial Stimulation-Evoked Mossy Fiber-Granule Cell Synaptic Transmission via GluN2A Receptors in the Mouse Cerebellar Cortex

Sensory information is transferred to the cerebellar cortex via the mossy fiber–granule cell (MF–GC) pathway, which participates in motor coordination and motor learning. We previously reported that chronic ethanol exposure from adolescence facilitated the sensory-evoked molecular layer interneuron–Purkinje cell synaptic transmission in adult mice in vivo. Herein, we investigated the effect of chronic ethanol exposure from adolescence on facial stimulation-evoked MF–GC synaptic transmission in the adult mouse cerebellar cortex using electrophysiological recording techniques and pharmacological methods. Chronic ethanol exposure from adolescence induced an enhancement of facial stimulation-evoked MF–GC synaptic transmission in the cerebellar cortex of adult mice. The application of an N-methyl-D-aspartate receptor (NMDAR) antagonist, D-APV (250 μM), induced stronger depression of facial stimulation-evoked MF–GC synaptic transmission in chronic ethanol-exposed mice compared with that in control mice. Chronic ethanol exposure-induced facilitation of facial stimulation evoked by MF–GC synaptic transmission was abolished by a selective GluN2A antagonist, PEAQX (10 μM), but was unaffected by the application of a selective GluN2B antagonist, TCN-237 (10 μM), or a type 1 metabotropic glutamate receptor blocker, JNJ16259685 (10 μM). These results indicate that chronic ethanol exposure from adolescence enhances facial stimulation-evoked MF–GC synaptic transmission via GluN2A, which suggests that chronic ethanol exposure from adolescence impairs the high-fidelity transmission capability of sensory information in the cerebellar cortex by enhancing the NMDAR-mediated components of MF–GC synaptic transmission in adult mice in vivo.

Effect of Lenalidomide on Pentylenetetrazole-Induced Clonic Seizure Threshold in Mice: A Role for N-Methyl-D-Aspartic Acid Receptor/Nitric Oxide Pathway

Background and Purpose

Accumulating evidence suggest that lenalidomide, a structural analog of thalidomide, has neuro-modulatory and neuroprotective properties. In the present study, we investigated effects of acute administration of lenalidomide on clonic seizure threshold in mice induced by pentylenetetrazole (PTZ) and possible role of N-methyl-D-aspartic acid receptor (NMDAR) and nitric oxide (NO) pathway.

Methods

We have utilized a clonic model of seizure in NMRI mice induced by PTZ to evaluate the potential effect of lenalidomide on seizure threshold. Different doses of lenalidomide (5, 10, 20, and 50 mg/kg, intraperitoneal [i.p.]) were administered 1 hour before PTZ. To evaluate probable role of NMDAR/NO signaling, the non-selective NO synthase inhibitor L-N^G-nitroarginine methyl ester (L-NAME; 10 mg/kg, i.p.), neuronal NOS (nNOS) inhibitor 7-nitroindazole (7-NI; 30 mg/kg, i.p.), selective inducible NOS inhibitor aminoguanidine (AG; 100 mg/kg, i.p.), selective NMDAR antagonist MK-801 (0.01 mg/kg, i.p.), and selective NMDAR agonist D-serine (30 mg/kg, i.p.) were injected 15 minutes before lenalidomide.

Results

Lenalidomide at 10 and 20 mg/kg significantly elevated the PTZ-induced seizure thresholds. Interestingly, L-NAME (10 mg/kg, i.p), 7-NI (30 mg/kg, i.p), and AG (100 mg/kg, i.p) reversed the anticonvulsive effect of lenalidomide (10 mg/kg). Moreover, treatment with the NMDAR agonist D-serine (30 mg/kg, i.p.) did not alter the anticonvulsive properties of lenalidomide (10 mg/kg, i.p). However, the NMDAR antagonist MK-801 (0.01 mg/kg, i.p) significantly reversed the anticonvulsive effects of lenalidomide (10 mg/kg).

Conclusions

Our study demonstrated a role for the NMDAR/NO pathway in the anticonvulsive effects of lenalidomide on the PTZ-induced clonic seizures in mice.

Chronically altered NMDAR signaling in epilepsy mediates comorbid depression

Depression is the most common psychiatric comorbidity of epilepsy. However, the molecular pathways underlying this association remain unclear. The NMDA receptor (NMDAR) may play a role in this association, as its downstream signaling has been shown to undergo long-term changes following excitotoxic neuronal damage. To study this pathway, we used an animal model of fluoxetine-resistant epilepsy-associated depression (EAD). We determined the molecular changes associated with the development of depressive symptoms and examined their response to various combinations of fluoxetine and a selective neuronal nitric oxide synthase inhibitor, 7-nitroindazole (NI). Depressive symptoms were determined using the forced swim test. Furthermore, expression and phosphorylation levels of markers in the ERK/CREB/ELK1/BDNF/cFOS pathway were measured to determine the molecular changes associated with these symptoms. Finally, oxidative stress markers were measured to more clearly determine the individual contributions of each treatment. While chronic fluoxetine (Flxc) and NI were ineffective alone, their combination had a statistically significant synergistic effect in reducing depressive symptoms. The development of depressive symptoms in epileptic rats was associated with the downregulation of ERK2 expression and ELK1 and CREB phosphorylation. These changes were exactly reversed upon Flxc + NI treatment, which led to increased BDNF and cFOS expression as well. Interestingly, ERK1 did not seem to play a role in these experiments. NI seemed to have augmented Flxc’s antidepressant activity by reducing oxidative stress. Our findings suggest NMDAR signaling alterations are a major contributor to EAD development and a potential target for treating conditions associated with underlying excitotoxic neuronal damage.

Ketamine infusion reduces narcotic requirements following gastric bypass surgery: a randomized controlled trial

BACKGROUND

As the obesity epidemic worsens, anesthesiologists should expect to see more obese patients presenting for surgical procedures. Opioids cause respiratory depression, which has caused complications in patients with obstructive sleep apnea. Opioids can also cause nausea, prolonging the time that patients spend in the postanesthesia care unit. Ketamine is a potential analgesic alternative that may have advantages to narcotics in the bariatric population.

OBJECTIVES

To determine whether an intraoperative ketamine infusion would reduce postoperative narcotic use in patients during the first 48 hours after laparoscopic gastric bypass.

SETTING

Major academic medical center.

METHODS

There were 54 participating patients. The intervention group (n = 27) was randomized to receive 100 μg of fentanyl with anesthesia induction, then a 20-mg bolus of ketamine, followed by a 5 μg/kg/min intraoperative ketamine infusion starting after anesthesia induction and ending after wound closure commenced. The control group (narcotic only, n = 27) also received 100 μg of fentanyl at anesthesia induction and intraoperative boluses of fentanyl at the discretion of the anesthesia team, with .3 mg of hydromorphone administered approximately 45 minutes before the completion of surgery.

RESULTS

At 24 hours, the mean morphine-equivalent units (MEUs) were 12.7 (standard deviation [SD], 9.9; 95% confidence interval [CI], 8.8-16.6) for the ketamine group (n = 28) and 16.5 (SD, 9.8; 95% CI, 12.6-20.4) for the control group (n = 28). At 48 hours, the MEUs were 16.7 (SD, 12.0; 95% CI, 11.9-21.4) for the ketamine group and 22.7 (SD, 14.9; 95% CI, 16.8-28.6) for the control group. Cumulative MEUs for 24 hours (P = .039) and 48 hours (P = .058) postoperatively were lower in the ketamine group compared with the narcotic-only (control) group, although the difference at 48 hours did not reach statistical significance. Compared with the narcotic-only group, the ketamine group used 26% fewer MEUs after 24 hours and 31% fewer MEUs after 48 hours. This difference can mostly be attributed to group differences during the first 6 hours after surgery.

CONCLUSIONS

Ketamine successfully reduced the amount of opioids required to control bariatric patients' pain at 24 hours postoperatively, but not over the 48-hour postoperative period.

Monoclonal antibody as an emerging therapy for acute ischemic stroke

Acute ischemic stroke (AIS) is the 5^th leading cause of death and the leading cause of neurological disability in the United States. The oxygen and glucose deprivation associated with AIS not only leads to neuronal cell death, but also increases the inflammatory response, therefore decreasing the functional outcome of the brain. The only pharmacological intervention approved by the US Federal Food and Drug Administration for treatment of AIS is tissue plasminogen activator (t-PA), however, such treatment can only be given within 4.5 hours of the onset of stroke-like symptoms. This narrow time-range limits its therapeutic application. Administrating t-PA outside of the therapeutic window may induce detrimental rather than beneficial effects to stroke patients. In order to reduce the infarct volume of an AIS while increasing the time period for treatment, new treatments are essential. Emerging monoclonal antibody (mAb) therapies reveal great potential by targeting signaling pathways activated after an AIS. With successful application of mAb in the treatment of cancer, other therapeutic uses for mAb are currently being evaluated. In this review, we will focus on recent advances on AIS therapy by using mAb that targets the signaling cascades and endogenous molecules such as inflammation, growth factors, acid-sensing ion channels, and N-methyl-D-aspartate receptors. Therefore, developing specific mAb to target the signaling pathways of ischemic brain injury will benefit patients being treated for an AIS.

Structural Basis of Functional Transitions in Mammalian NMDA Receptors

Excitatory neurotransmission meditated by glutamate receptors including N-methyl-D-aspartate receptors (NMDARs) is pivotal to brain development and function. NMDARs are heterotetramers composed of GluN1 and GluN2 subunits, which bind glycine and glutamate, respectively, to activate their ion channels. Despite importance in brain physiology, the precise mechanisms by which activation and inhibition occur via subunit-specific binding of agonists and antagonists remain largely unknown. Here, we show the detailed patterns of conformational changes and inter-subunit and -domain reorientation leading to agonist-gating and subunit-dependent competitive inhibition by providing multiple structures in distinct ligand states at 4 Å or better. The structures reveal that activation and competitive inhibition by both GluN1 and GluN2 antagonists occur by controlling the tension of the linker between the ligand-binding domain and the transmembrane ion channel of the GluN2 subunit. Our results provide detailed mechanistic insights into NMDAR pharmacology, activation, and inhibition, which are fundamental to the brain physiology.

Disrupting nNOS-PSD95 Interaction Improves Neurological and Cognitive Recoveries after Traumatic Brain Injury

Excessive activation of N-methyl-D-aspartate receptors (NMDARs) and the resulting neuronal nitric oxide synthase (nNOS) activation plays a crucial role in the pathogenesis of traumatic brain injury (TBI). However, directly inhibiting NMDARs or nNOS produces adverse side effects because they play key physiological roles in the normal brain. Since interaction of nNOS-PSD95 is a key step in NMDAR-mediated excitotoxicity, we investigated whether disrupting nNOS-PSD95 interaction with ZL006, an inhibitor of nNOS-PSD95 interaction, attenuates NMDAR-mediated excitotoxicity. In cortical neuronal cultures, ZL006 treatment significantly reduced glutamate-induced neuronal death. In a mouse model of controlled cortical impact (CCI), administration of ZL006 (10 mg/kg, i.p.) at 30 min postinjury significantly inhibited nNOS-PSD95 interaction, reduced TUNEL- and phospho-p38-positive neurons in the motor cortex. ZL006 treatment also significantly reduced CCI-induced cortical expression of apoptotic markers active caspase-3, PARP-1, ratio of Bcl-2/Bax, and phosphorylated p38 MAPK (p-p38). Functionally, ZL006 treatment significantly improved neuroscores and sensorimotor performance, reduced somatosensory and motor deficits, reversed CCI-induced memory deficits, and attenuated cognitive impairment. Histologically, ZL006 treatment significantly reduced the brain lesion volume. These findings collectively suggest that blocking nNOS-PSD95 interaction represents an attractive strategy for ameliorating consequences of TBI and that its action is mediated via inhibiting neuronal apoptosis and p38 MAPK signaling.

Red and near-infrared light induces intracellular Ca2+ flux via the activation of glutamate N-methyl-D-aspartate receptors

Red and near-infrared (NIR) light effect on Ca²⁺ ions flux through the influence on N-methyl-D-aspartate receptors (NMDARs) and their functioning in HeLa cells was studied in vitro. Cells were irradiated by 650 and 808 nm laser light at different power densities and doses and the obtained effect was compared with that caused by the pharmacological agents. The laser light was found to elevate Ca²⁺ influx into cell cytoplasm in a dose-dependent manner without changes of the NMDAR functioning. Furthermore, the light of both wavelengths demonstrated the ability to elevate Ca²⁺ influx under the pharmacological blockade of NMDARs and also might partially abolish the blockade enhancing Ca²⁺ influx after selective stimulation of the receptors with NMDA. Simultaneously, the light at moderate doses demonstrated a photobiostimulating effect on cells. Based on our experiments and data reported in the literature, we suggest that the low-power visible and NIR light can instigate a cell membrane depolarization via nonthermal activation, resulting in the fast induction of Ca²⁺ influx into cells. The obtained results also demonstrate that NIR light can be used for nonthermal and nonpharmacological stimulation of NMDARs in cancer cells.

Childhood Onset of Anti-N-Methyl-D-Aspartate Receptor Encephalitis Without Teratoma Masquerading as a Psychotic Disorder

Many neurologic disorders manifest as psychiatric symptoms. Anti-N-Methyl-D-Aspartate (NMDA) receptor encephalitis is an autoimmune disease of the brain characterized by numerous neurological and psychiatric features. Despite being rare, its prevalence is rapidly increasing and early management is critical in ensuring successful and sustainable recovery. Therefore, the illness should be considered as a differential diagnosis when clinically assessing patients. This report presents a case of a female child who was hospitalized for acute psychiatric manifestations, which was later confirmed as anti-NMDA receptor encephalitis. She recovered relatively successfully after combined neurological and psychiatric treatment. This report provides information on the clinical course of early onset anti-NMDA receptor encephalitis, including treatment strategy and prognosis.

Anti-NMDA receptor antibody positivity in acute psychotic states: An exploratory study

The glutamatergic theory of schizophrenia postulates N-methyl-D-aspartate receptor (NMDA-R) dysfunction. Anti-NMDA receptor antibodies may be present in some patients with psychosis. Fifteen patients presenting with acute psychotic states having one additional clinical feature suggestive of autoimmune etiology were recruited. Serum antibodies against NMDA-receptor were tested at baseline and at follow-up using Indirect Immunofluorescence Technique. None of the 15 patients had positive anti-NMDA antibody at baseline or at follow-up. The study failed to detect anti-NMDA antibodies in patients with acute psychotic states with clinical suspicion of autoimmunity. This does not rule out other mechanisms of NMDA receptor dysfunction in these patients. The glutamatergic theory of schizophrenia postulates N-methyl-D-aspartate receptor (NMDA-R) dysfunction. Anti-NMDA receptor antibodies may be present in some patients with psychosis. Fifteen patients presenting with acute psychotic states having one additional clinical feature suggestive of autoimmune etiology were recruited. Serum antibodies against NMDA-receptor were tested at baseline and at follow-up using Indirect Immunofluorescence Technique. None of the 15 patients had positive anti-NMDA antibody at baseline or at follow-up. The study failed to detect anti-NMDA antibodies in patients with acute psychotic states with clinical suspicion of autoimmunity. This does not rule out other mechanisms of NMDA receptor dysfunction in these patients.

Glutamatergic augmentation strategies in obsessive-compulsive disorder

Proven treatment strategies for obsessive-compulsive disorder (OCD) include pharmacotherapy with serotonin reuptake inhibitors and cognitive behavior therapy (CBT). A significant proportion of patients (25%-30%) fail to respond to these treatment options, necessitating the need for additional treatment options to improve treatment outcomes and quality of life in patients with OCD. Augmentation strategies using various glutamatergic agents have been explored, with diverse outcomes. The aim of this review is to give an overview of the glutamatergic system in the brain with a focus on glutamatergic abnormalities in OCD and to review the existing evidence for various glutamatergic agents used for augmentation.

NMDA Receptor Antagonist MK801 Protects Against 1-Bromopropane-Induced Cognitive Dysfunction

Occupational exposure to 1-bromopropane (1-BP) induces learning and memory deficits. However, no therapeutic strategies are currently available. Accumulating evidence has suggested that N-methyl-D-aspartate receptors (NMDARs) and neuroinflammation are involved in the cognitive impairments in neurodegenerative diseases. In this study we aimed to investigate whether the noncompetitive NMDAR antagonist MK801 protects against 1-BP-induced cognitive dysfunction. Male Wistar rats were administered with MK801 (0.1 mg/kg) prior to 1-BP intoxication (800 mg/kg). Their cognitive performance was evaluated by the Morris water maze test. The brains of rats were dissected for biochemical, neuropathological, and immunological analyses. We found that the spatial learning and memory were significantly impaired in the 1-BP group, and this was associated with neurodegeneration in both the hippocampus (especially CA1 and CA3) and cortex. Besides, the protein levels of phosphorylated NMDARs were increased after 1-BP exposure. MK801 ameliorated the 1-BP-induced cognitive impairments and degeneration of neurons in the hippocampus and cortex. Mechanistically, MK801 abrogated the 1-BP-induced disruption of excitatory and inhibitory amino-acid balance and NMDAR abnormalities. Subsequently, MK801 inhibited the microglial activation and release of pro-inflammatory cytokines in 1-BP-treated rats. Our findings, for the first time, revealed that MK801 protected against 1-BP-induced cognitive dysfunction by ameliorating NMDAR function and blocking microglial activation, which might provide a potential target for the treatment of 1-BP poisoning.

Astrocytic GluN2A and GluN2B Oppose the Synaptotoxic Effects of Amyloid-β1-40 in Hippocampal Cells

Early-stage Alzheimer's disease (AD) is characterized by synaptic dysfunction, a phenomenon in which soluble oligomers of amyloid-beta (Aβ) and N-methyl-D-aspartate receptor (NMDAR) are implicated. Here, we demonstrated that astrocytes express NMDARs and therefore have the potential to modulate the synaptotoxic actions of Aβ. We found that specific pharmacological antagonism of two of the major NMDAR subunits, GluN2A and GluN2B, exacerbates Aβ-induced synaptotoxicity suggesting, for the first time, that astrocytic GluN2A and GluN2B mediate synaptoprotection. From the perspective of the pathogenic mechanisms of Alzheimer's disease, in which Aβ and NMDAR play significant roles, these observations are striking since neuronal GluN2A and GluN2B are well known modulators of neurodegeneration. We did initial studies to understand the basis for the differential effects of astrocytic and neuronal GluN2A and GluN2B in the promotion of synapse survival, and identified a neurotrophin produced by astrocytes, nerve growth factor β (β-NGF), as a likely mediator of the synaptoprotective effects of astrocytic GluN2A and GluN2B activation. The results presented suggest that astrocytes may be suitable druggable targets for the prevention and/or delay of the synaptic loss that occurs during early stages of AD.

Sarcoma family kinase activity is required for cortical spreading depression

Objectives Sarcoma family kinase activity is associated with multiple diseases including ischemia and cancer; however, its role in the mechanism of migraine aura has been less well characterised. This study aims to investigate whether sarcoma family kinase is required for cortical spreading depression. Methods Cortical spreading depression was induced by topical application of K⁺ to the cerebral cortex and was monitored using electrophysiology in rats, and intrinsic optical signal in mouse brain slices. Drugs were perfused into the contralateral cerebral ventricle for pharmacological manipulations in rats. Western blot analysis was used for detecting the level of phosphorylated, and total, sarcoma family kinase in the ipsilateral cortex of rats. Key results The data demonstrate that a single cortical spreading depression in rats induced ipsilateral cortical sarcoma family kinase phosphorylation at the Y416 site. Deactivation of sarcoma family kinase by its inhibitor (3-(4-chlorophenyl) 1-(1,1-dimethylethyl)-1 H-pyrazolo[3,4- dpyrimidin-4-amine) suppressed the elevated enzyme activity and cortical susceptibility to cortical spreading depression. Interestingly, the inhibitory effect of the N-methyl-D-aspartate receptor antagonist NVP-AAM077 on cortical spreading depression was reversed by the sarcoma family kinase activator pYEEI (EPQY(PO₃H₂)EEEIPIYL), suggesting a link between this enzyme and N-methyl-D-aspartate receptors. Similarly, after deactivation of sarcoma family kinase, a reduction of sarcoma family kinase phosphorylation and cortical susceptibility to cortical spreading depression was observed with NVP-AAM077. Conclusions We conclude that activation of sarcoma family kinase is required for cortical spreading depression, and this process is regulated by recruiting N-methyl-D-aspartate receptors. This study provides novel insight for sarcoma family kinase function in the mechanism of migraine aura.

Molecular Basis for Subtype Specificity and High-Affinity Zinc Inhibition in the GluN1-GluN2A NMDA Receptor Amino-Terminal Domain

Zinc is vastly present in the mammalian brain and controls functions of various cell surface receptors to regulate neurotransmission. A distinctive characteristic of N-methyl-D-aspartate (NMDA) receptors containing a GluN2A subunit is that their ion channel activity is allosterically inhibited by a nano-molar concentration of zinc that binds to an extracellular domain called an amino-terminal domain (ATD). Despite physiological importance, the molecular mechanism underlying the high-affinity zinc inhibition has been incomplete because of the lack of a GluN2A ATD structure. Here we show the first crystal structures of the heterodimeric GluN1-GluN2A ATD, which provide the complete map of the high-affinity zinc-binding site and reveal distinctive features from the ATD of the GluN1-GluN2B subtype. Perturbation of hydrogen bond networks at the hinge of the GluN2A bi-lobe structure affects both zinc inhibition and open probability, supporting the general model in which the bi-lobe motion in ATD regulates the channel activity in NMDA receptors.

Application of the Co-culture Membrane System Pointed to a Protective Role of Catestatin on Hippocampal Plus Hypothalamic Neurons Exposed to Oxygen and Glucose Deprivation

Depletion of oxygen and glucose even for brief periods is sufficient to cause cerebral ischemia, which is a predominant worldwide cause of motor deficits with the reduction of life quality and subsequently death. Hence, more insights regarding protective measures against ischemic events are becoming a major research goal. Among the many neuronal factors, N-methyl-D-aspartate receptors (NMDAR), orexinergic neuroreceptors (ORXR), and sympatho-inhibitory neuropeptide catestatin (CST) are widely involved with ischemic episodes. In this study, it was possible to induce in vitro ischemic conditions of the hamster (Mesocricetus auratus) hippocampal and hypothalamic neuronal cultures, grown on a newly compartmentalized membrane system, via oxygen and glucose deprivation (OGD). These cultures displayed notably differentiated NMDARergic and ORXergic receptor expression activities along with evident brain-derived neurotrophic factor (BDNF) plus orexin A (ORX-A) secretion, especially under co-cultured conditions. Interestingly, addition of CST in OGD-insulted hippocampal cells accounted for upregulated GluN1 and ORX1R transcripts that in the case of the latter neuroreceptor was very strongly (p < 0.001) increased when co-cultured with hypothalamic cells. Similarly, hypothalamic neurons supplied very evident upregulations of GluN1, ORX1R, and above all of GluN2A transcripts along with increased BDNF and ORX-A secretion in the presence of hippocampal cells. Overall, the preferential CST effects on BDNF plus ORX-A production together with altered NMDAR and ORXR levels, especially in co-cultured hypothalamic cells pointed to ORX-containing neurons as major protective constituents against ischemic damages thus opening new scenarios on the cross-talking roles of CST during ischemic disorders.

Neurotoxicity of Ammonia

Abnormal liver function has dramatic effects on brain functions. Hyperammonemia interferes profoundly with brain metabolism, astrocyte volume regulation, and in particular mitochondrial functions. Gene expression in the brain and excitatory and inhibitory neurotransmission circuits are also affected. Experiments with a number of pertinent animal models have revealed several potential mechanisms which could underlie the pathological phenomena occurring in hepatic encephalopathy.

Neuroendothelial NMDA receptors as therapeutic targets in experimental autoimmune encephalomyelitis

Multiple sclerosis is among the most common causes of neurological disability in young adults. Here we provide the preclinical proof of concept of the benefit of a novel strategy of treatment for multiple sclerosis targeting neuroendothelial N-methyl-D-aspartate glutamate receptors. We designed a monoclonal antibody against N-methyl-D-aspartate receptors, which targets a regulatory site of the GluN1 subunit of N-methyl-D-aspartate receptor sensitive to the protease tissue plasminogen activator. This antibody reverted the effect of tissue plasminogen activator on N-methyl-D-aspartate receptor function without affecting basal N-methyl-D-aspartate receptor activity (n = 21, P < 0.01). This antibody bound N-methyl-D-aspartate receptors on the luminal surface of neurovascular endothelium in human tissues and in mouse, at the vicinity of tight junctions of the blood-spinal cord barrier. Noteworthy, it reduced human leucocyte transmigration in an in vitro model of the blood-brain barrier (n = 12, P < 0.05). When injected during the effector phase of MOG-induced experimental autoimmune encephalomyelitis (n = 24), it blocked the progression of neurological impairments, reducing cumulative clinical score (P < 0.001) and mean peak score (P < 0.001). This effect was observed in wild-type animals but not in tissue plasminogen activator knock-out animals (n = 10). This therapeutic effect was associated to a preservation of the blood-spinal cord barrier (n = 6, P < 0.001), leading to reduced leucocyte infiltration (n = 6, P < 0.001). Overall, this study unveils a critical function of endothelial N-methyl-D-aspartate receptor in multiple sclerosis, and highlights the therapeutic potential of strategies targeting the protease-regulated site of N-methyl-D-aspartate receptor.

Disruption of S2-M4 linker coupling reveals novel subunit-specific contributions to N-methyl-d-aspartate receptor function and ethanol sensitivity

The N-methyl-d-aspartate (NMDA) receptor is a glutamatergic ion channel and is a known site of ethanol action. Evidence suggests that ethanol inhibits NMDA receptor activity by reducing channel open probability and mean open time potentially via interaction with specific residues within the transmembrane (M) domains 3 and 4 of GluN subunits. Recent models of NMDAR function demonstrate that extracellular residues near the M domains are key regulators of gating, suggesting that they may contribute to ethanol sensitivity. To test this, we substituted cysteines at key positions in GluN1 and GluN2 M3-S2 and S2-M4 regions previously shown to affect channel open probability and mean open time similar to ethanol treatment. Although crosslinking of these domains was predicted to restrict linker domain movement and occlude ethanol inhibition, only intra-GluN1 M1:M4 linker-crosslinked receptors showed a decrease in ethanol sensitivity. For the converse experiment, we expressed NMDARs with glycine substitutions in the S2-M4 domain of GluN subunits to enhance M4 flexibility and recorded currents in response to ethanol. Glycine substitution in the GluN1 S2-M4 region significantly decreased glutamate potency of GluN1(A804G)/GluN2A receptors, while GluN1(A804G)/GluN2B receptors exhibited no change in glutamate sensitivity. In contrast, GluN1/GluN2B(S811G) receptors showed a 10-fold increase in glutamate potency while GluN1/GluN2A(S810G) receptors showed no change. Surprisingly, while S2-M4 glycine substitutions modulated ethanol sensitivity, this was observed only in receptors that did not display a change in agonist potency. Overall, these results suggest that S2-M4 linkers strongly influence receptor function and modestly impact ethanol efficacy in a subunit- and receptor subtype-dependent manner.

The Role of NMDA Receptors in the Development of Brain Resistance through Pre- and Postconditioning

Brain tolerance or resistance can be achieved by interventions before and after injury through potential toxic agents used in low stimulus or dose. For brain diseases, the neuroprotection paradigm desires an attenuation of the resulting motor, cognitive, emotional, or memory deficits following the insult. Preconditioning is a well-established experimental and clinical translational strategy with great beneficial effects, but limited applications. NMDA receptors have been reported as protagonists in the adjacent cellular mechanisms contributing to the development of brain tolerance. Postconditioning has recently emerged as a new neuroprotective strategy, which has shown interesting results when applied immediately, i.e. several hours to days, after a stroke event. Investigations using chemical postconditioning are still incipient, but nevertheless represent an interesting and promising clinical strategy. In the present review pre- and postconditioning are discussed as neuroprotective paradigms and the focus of our attention lies on the participation of NMDA receptors proteins in the processes related to neuroprotection.

Anti-N-methyl-D-aspartate receptor encephalitis: A case report and review of the literature

Anti-N-methyl-D-aspartate receptor encephalitis is a well characterized immune-mediated encephalitis. It is increasingly being recognized as one of the common causes of encephalitis, but is frequently misdiagnosed especially in resource-constrained settings. With a simple test available to diagnose the disorder and prospects of good recovery following early immunotherapy, the disorder should be kept as a differential diagnosis in patients presenting with unexplained behavioral/psychiatric symptoms and progressive encephalopathy with movement disorders.

Cloning and characterization of the N-methyl-D-aspartate receptor subunit NR1 gene from chum salmon, Oncorhynchus keta (Walbaum, 1792)

Here, we report the information about molecular and expression characterization of NR1 gene in chum salmon for the first time. The complete NR1 subunit showed a large open-reading frame of 2844 bp in the total length of 3193 bp, and this cDNA contained a coding region encoding 948 amino acids and a stop codon. The organization of the NR1 subunit of chum salmon were similar of most other fishes, except C’ terminal. The expression of NR1 subunit was to show higher in the natal river near to the hatchery than near to the coast. We expect that the information reported herein may facilitate further investigations on the relationship between memory factors of natal rivers and homing mechanisms in Salmonidae.

Antiallodynic effects of vitamin C and vitamin E in chronic post-ischemia pain rat model

Background

Recent research has shown that reactive oxygen species (ROS) play a significant role in the development and persistence of neuropathic pain through central sensitization via N-methyl-D-aspartate (NMDA) receptor activation. In the present study, we examined whether the intraperitoneal administration of vitamins C and E alone or together could alleviate mechanical allodynia in a chronic post-ischemia pain (CPIP) rat model.

Methods

Vitamins C and E were administered intraperitoneally to 48 male Sprague Dawley rats once per day for 3 days before hindpaw ischemia-reperfusion (I/R) injury was induced. On the third day, the CPIP rat model was produced by inducing ischemia in the left hindpaw by applying an O-ring for 3 h, followed by reperfusion. Three days after reperfusion, hindpaw mechanical allodynia was assessed by measuring the withdrawal response to von Frey filament stimulation. The rats were sacrificed immediately after behavioral testing to determine the phosphorylated NMDA receptor subunit 1 (pNR1) and extracellular-signal-regulated kinases (pERK) levels in the spinal cord.

Results

When the antioxidant vitamins C and E were administered intraperitoneally to CPIP rats, I/R injury-induced mechanical allodynia was attenuated, and pNR1 and pERK levels were decreased in the rat spinal cord. Additionally, the co-administration of both vitamins had an increased antiallodynic effect.

Conclusions

The reduced phosphorylated NR1 and ERK levels indicate that vitamins C and E inhibit the modulation of spinal cord neuropathic pain processing. Co-administration of vitamins C and E had a greater antiallodynic effect.

Phycocyanobilin promotes PC12 cell survival and modulates immune and inflammatory genes and oxidative stress markers in acute cerebral hypoperfusion in rats

Since the inflammatory response and oxidative stress are involved in the stroke cascade, we evaluated here the effects of Phycocyanobilin (PCB, the C-Phycocyanin linked tetrapyrrole) on PC12 cell survival, the gene expression and the oxidative status of hypoperfused rat brain. After the permanent bilateral common carotid arteries occlusion (BCCAo), the animals were treated with saline or PCB, taking samples 24h post-surgery. Global gene expression was analyzed with GeneChip Rat Gene ST 1.1 from Affymetrix; the expression of particular genes was assessed by the Fast SYBR Green RT-PCR Master Mix and Bioplex methods; and redox markers (MDA, PP, CAT, SOD) were evaluated spectrophotometrically. The PCB treatment prevented the H2O2 and glutamate induced PC12 cell injury assessed by the MTT assay, and modulated 190 genes (93 up- and 97 down-regulated) associated to several immunological and inflammatory processes in BCCAo rats. Furthermore, PCB positively modulated 19 genes mostly related to a detrimental pro-inflammatory environment and counteracted the oxidative imbalance in the treated BCCAo animals. Our results support the view of an effective influence of PCB on major inflammatory mediators in acute cerebral hypoperfusion. These results suggest that PCB has a potential to be a treatment for ischemic stroke for which further studies are needed.

Bis(7)-tacrine protects retinal ganglion cells against excitotoxicity via NMDA receptor inhibition

AIM

To investigate whether bis(7)-tacrine, a multifunctional drug, inhibits N-methyl-D-aspartate (NMDA) -activated current in retinal ganglion cells(RGC) and provides neuroprotection against retinal cell damage.

METHODS

Purified RGC cultures were obtained from retinas of 1-3 days old Sprague-Dawley(SD) rats, following a two-step immunopanning procedure. After 7 days of cultivation, the inhibition of NMDA-activated current by bis(7)-tacrine was measured by using patch-clamp recording techniques. In animal experiments, RGCs were damaged after intravitreal injection of NMDA (5µL, 40nmol) in adult rats. Bis(7)-tacrine(0.05, 0.1, 0.2mg/kg) or memantine(20mg/kg) was intraperitoneal administered to the rats fifteen minutes before intravitreally injection of NMDA. RGC damage was analyzed by histologic techniques, TUNEL and retrograde labeling techniques.

RESULTS

Whole-cell patch-clamp recordings demonstrated that NMDA (30µmol/L) resulted in approximately -50 pA inward currents that were blocked by bis(7)-tacrine(1µmol/L). Histological examination and retrograde labeling analysis revealed that bis(7)-tacrine induced a significant neuroprotective effect against NMDA-induced cell damage 7 days after NMDA injection. TUNEL staining showed that pretreatment with bis(7)-tacrine was effective in ameliorating NMDA-induced apoptotic cell loss in the retinal ganglion cell layer 18 hours after injection.

CONCLUSION

Bis(7)-tacrine possesses remarkable neuroprotective activities against retinal excitotoxicity through inhibition of NMDA receptors.