NMDA Receptors In Rats Research Articles

Synthesis of New Conjugates of Edaravone and 1-Aminoadamantanes and Their Interaction with NMDA Receptors in Rats

Synthesis of New Conjugates of Edaravone and 1-Aminoadamantanes and Their Interaction with NMDA Receptors in Rats

Sympathoexcitation and pressor responses induced by acetate, an ethanol metabolite in the hypothalamic paraventricular nucleus involves activation of NMDA receptors in rats

Alcohol abuse plays a crucial role in the prevalence of cardiovascular and neuronal degenerated diseases. However, the central mechanism that mediates these effects are not fully understood. It has been well know that autonomic hypothalamic paraventricular nucleus (PVN) play an important role in regulating sympathetic outflow and arterial blood pressure (ABP). Moreover, it has been demonstrated that the increased glutamatergic activity among PVN neurons contributed to the sympathoexcitation and development of hypertension. Furthermore, we have reported that ethanol and acetate increase sympathetic outflow and arterial pressure, which may involve the activation of NMDA receptors in autonomic central nucleus of amygdala. Combing with the fact that autonomic PVN neurons are abundantly expressed NMDA receptors, we hypothesize that acetate, the metabolic products from alcohol, activates the PVN neurons through the increase in glutamatergic activity and contributes to the sympathoexcitation and development of chronic diseases, such as hypertension. In anesthetized rats, the effect of acetate microinjected in the PVN on the renal sympathetic nerve activity (RSNA) and arterial blood pressure (ABP) was determined. The PVN acetate microinjection increased sympathoexcitatiory and pressor response in a dose dependent dose-dependent (1.5mm, 0.5mm, 2.0mm, 7.5mm) manner, and 2mm of acetate showed a minimum dose evoked a maximal response. To determine the role of acetate-stimulated glutamatergic receptor activation in driving sympathoexcitatory and pressor responses, either 2mm acetate or pre-treatment of Kynurenic acid (KYN, 7.2mm) ionotropic excitatory amino acid receptor blocker, or D-2-amino-5-phosphopentanoate (AP5, 3.0mm), a N-methyl-D-aspartate (NMDA) receptor antagonist, followed by 2mm acetate were microinjected into the PVN of male Sprague Dawley rats (300-500g, n= 6-9/ group). RSNA and ABP responses were compared among vehicle (saline) and 2mm acetate, pre-treatment of KYN and 2mm acetate, or pre-treatment AP5 and 2mm acetate protocols. 2mm acetate significantly increased RSNA (60-70% baseline, p < 0.001) and mean arterial pressure (MAP, 10-12mmHg, p < 0.05). Non-selective glutamatergic receptor antagonist, KYN significantly blocked the sympathoexcitatory (RSNA, p < 0.05) and pressor response (MAP, p < 0.05) evoked by 2mm acetate in the PVN. Furthermore, selective NMDA receptor antagonist, AP5 significantly attenuates the sympathoexcitatory response induced by PVN 2mm acetate (RSNA, P < 0.05 and MAP, p < 0.01). These data indicate acetate can increase glutamatergic activity and excitability of pre-sympathetic PVN neurons via activation of local NMDA receptors. The metabolism of ethanol to acetate following by alcohol consumption may contribute, in part, to the development of neurogenic hypertension and/or other cardiovascular diseases associated with increased sympathetic outflow. R15HL145655, R15HL150703 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

NMDA Receptors Contribute to Postnatal Developmental Downregulation of Connexin Expressions in the Rat Locus Coeruleus

It has been shown that during postnatal development, gap junctions decrease. This phenomenon overlaps with the major period of chemical synapse formation and increased synaptic activity during postnatal weeks 1–3. In current study, the expression of connexin 36 (Cx36), Cx32, and Cx43 proteins in locus coeruleus (LC) was examined using Western blot analysis in (postnatal day) PND14 and PND28 following blockade of NMDA receptors in rats to evaluate the role of these receptors in the expression of Cxs. MK801, as an NMDA receptor antagonist, was injected subcutaneously from the first day of birth until 14 or 28 days depending on the experimental groups. The control group received a saline injection in the same volume. Expression of Cxs declined in PND28 compared to PND14 in LC neurons. Also, we found that the expression of Cx36, Cx32, and Cx43 augmented in the rats’ LC in PND14 and PND28 following the blockade of NMDA receptors. The present results suggest that the activity of NMDA receptors may contribute to the downregulation of Cx36, Cx32, and Cx43 in LC during postnatal development.

Effect of Mucuna pruriens on brain NMDA receptor and tau protein gene expression in cerebral ischemic rats.

Present study aimed to assess effect of pre-treatment with Mucuna pruriens seed extract and its bioactive molecule(s) on NMDAR and Tau protein gene expression in cerebral ischemic rodent model. Methanol extract of M. pruriens seeds was characterized by HPLC, and β-sitosterol was isolated by flash chromatography. In vivo studies to observe the effect of pre-treatment (28 days) with methanol extract of M. pruriens seed and β-sitosterol on the unilateral cerebral ischemic rat model. Cerebral ischemia induced by left common carotid artery occlusion (LCCAO) for 75min (on day 29) followed by reperfusion for 12h. Rats (n = 48) divided into four groups. GroupI (control,Untreated + LCCAO)-No pre-treatment + cerebral ischemia; GroupII(β-sitosterol + Sham)-pre-treatment with β-sitosterol, 10mg/kg/day + sham-operated; GroupIII(β-sitosterol + LCCAO)-pre-treatment with β-sitosterol, 10mg/kg/day + cerebral ischemia; GroupIV(methanol extract + LCCAO)-pre-treatment with methanol extract of M. pruriens seeds, 50mg/kg/day + cerebral ischemia. Neurological deficit score was assessed just before sacrifice. Experimental animals were sacrificed after 12h reperfusion. Brain histopathology was performed. Gene expression of NMDAR and Tau protein of left cerebral hemisphere (occluded side) was performed by RT-PCR. Results revealed that the neurological deficit score was lower in groups III and IV compared to group I. NMDAR and tau protein mRNA expression in left cerebral hemisphere were upregulated in Group I, downregulated in groups III and IV. Histopathology of left cerebral hemisphere (occluded side) in Group I showed features of ischemic brain damage. Groups III and IV, left cerebral hemisphere showed less ischemic damage compared GroupI. Right cerebral hemisphere showed no areas of ischemia-induced brain changes. Pre-treatment with β-sitosterol and methanol extract of M. pruriens seeds may reduce ischemic brain injury following unilateral common carotid artery occlusion in rats.

Stimulation On Central NR2B NMDA Receptor in Neonatal and Juvenile Rats

Objective: To observe the excitability of neonatal and juvenile rats (P35~P38) stirred by a strong electrical stimulation, that is registered by the hippocampus and anterior cortex. Methods: The spinal dorsal horn was examined before and after electrical stimulation. The hippocampal CA1 region, the anterior of cerebral cortex and the spinal dorsal horn were subjected to formaldehyde treatment. Immunohistochemistry and western blot were used to analyze the number of FOS protein positive cells in the spinal dorsal horn the hippocampal CA1 region and the anterior cortex of the brain. Results: The sciatic nerve performance of neonatal and juvenile rats was compared with that of adult rats under the same noxious stimulating condition (by strong electrical stimulation). Immunohistochemistry and western blot analysis revealed that LTP and FOS protein were more prominent, but after the application of ifenprodil, these proteins were significantly inhibited. Conclusions: Reducing the stress response induced by peripheral nociceptive stimulation in neonatal and juvenile rats also inhibits the NR2B subunit in NMDA receptors.

Physiopathological Relevance of D-Serine in the Mammalian Cochlea

NMDA receptors (NMDARs) populate the complex between inner hair cell (IHC) and spiral ganglion neurons (SGNs) in the developing and mature cochlea. However, in the mature cochlea, activation of NMDARs is thought to mainly occur under pathological conditions such as excitotoxicity. Ototoxic drugs such as aspirin enable cochlear arachidonic-acid-sensitive NMDAR responses, and induced chronic tinnitus was blocked by local application of NMDAR antagonists into the cochlear fluids. We largely ignore if other modulators are also engaged. In the brain, D-serine is the primary physiological co-agonist of synaptic NMDARs. Whether D-serine plays a role in the cochlea had remained unexplored. We now reveal the presence of D-serine and its metabolic enzymes prior to, and at hearing onset, in the sensory and non-neuronal cells of the cochlea of several vertebrate species. In vivo intracochlear perfusion of D-serine in guinea pigs reduces sound-evoked activity of auditory nerve fibers without affecting the receptor potentials, suggesting that D-serine acts specifically on the postsynaptic auditory neurons without altering the functional state of IHC or of the stria vascularis. Indeed, we demonstrate in vitro that agonist-induced activation of NMDARs produces robust calcium responses in rat SGN somata only in the presence of D-serine, but not of glycine. Surprisingly, genetic deletion in mice of serine racemase (SR), the enzyme that catalyzes D-serine, does not affect hearing function, but offers protection against noise-induced permanent hearing loss as measured 3 months after exposure. However, the mechanisms of activation of NMDA receptors in newborn rats may be different from those in adult guinea pigs. Taken together, these results demonstrate for the first time that the neuro-messenger D-serine has a pivotal role in the cochlea by promoting the activation of silent cochlear NMDAR in pathological situations. Thus, D-serine and its signaling pathway may represent a new druggable target for treating sensorineural hearing disorders (i.e., hearing loss, tinnitus).

GABAA and NMDA receptor density alterations and their behavioral correlates in the gestational methylazoxymethanol acetate model for schizophrenia

Hippocampal hyperactivity driven by GABAergic interneuron deficits and NMDA receptor hypofunction is associated with the hyperdopaminergic state often observed in schizophrenia. Furthermore, previous research in the methylazoxymethanol acetate (MAM) rat model has demonstrated that repeated peripubertal diazepam administration can prevent the emergence of adult hippocampal hyperactivity, dopamine-system hyperactivity, and associated psychosis-relevant behaviors. Here, we sought to characterize hippocampal GABAA and NMDA receptors in MAM-treated rats and to elucidate the receptor mechanisms underlying the promising effects of peripubertal diazepam exposure. Quantitative receptor autoradiography was used to measure receptor density in the dorsal hippocampus CA1, ventral hippocampus CA1, and ventral subiculum. Specifically, [3H]-Ro15-4513 was used to quantify the density of α5GABAA receptors (α5GABAAR), [3H]-flumazenil to quantify α1-3;5GABAAR, and [3H]-MK801 to quantify NMDA receptors. MAM rats exhibited anxiety and schizophrenia-relevant behaviors as measured by elevated plus maze and amphetamine-induced hyperlocomotion (AIH), although diazepam only partially rescued these behaviors. α5GABAAR density was reduced in MAM-treated rats in all hippocampal sub-regions, and negatively correlated with AIH. Ventral hippocampus CA1 α5GABAAR density was positively correlated with anxiety-like behavior. Dorsal hippocampus CA1 NMDA receptor density was increased in MAM-treated rats, and positively correlated with AIH. [3H]-flumazenil revealed no significant effects. Finally, we found no significant effect of diazepam treatment on receptor densities, potentially related to the only partial rescue of schizophrenia-relevant phenotypes. Overall, our findings provide first evidence of α5GABAAR and NMDA receptor abnormalities in the MAM model, suggesting that more selective pharmacological agents may become a novel therapeutic mechanism in schizophrenia.

Interaction between orexin and N-Methyl-D-Aspartate (NMDA) receptors in hypertensive and normotensive rats: an insight into predictive biomarkers for hypertension

High Blood Pressure also known as hypertension (HTN) is one of the most common lifestyles based chronic diseases. HTN is a high-risk contributing factor towards stroke or any other cerebrovascular disorder (CVD). Many endogenous chemicals are involved in HTN such as orexin (also known as hypocretin), which is a neuropeptide produced by the neurons located mainly in the hypothalamus. Other areas of the brain such as Locus coeruleus (LC) and Rostral ventrolateral medulla (RVLM) and endogenous chemicals such as neurotransmitters, hormones and enzymes are also directly or indirectly involved in the regulation of HTN. We are essentially focusing on the orexin neurons that are activated by a type of glutamate receptor known as N-Methyl-D-Aspartate (NMDA). This review will discuss the role of molecules such as m-calpain and Jacob, produced because of the interaction between orexin and NMDA receptors in spontaneous hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats.

Rapamycin Improves Spatial Learning Deficits, Vulnerability to Alcohol Addiction and Altered Expression of the GluN2B Subunit of the NMDA Receptor in Adult Rats Exposed to Ethanol during the Neonatal Period.

Ethanol exposure during pregnancy alters the mammalian target of rapamycin (mTOR) signaling pathway in the fetal brain. Hence, in adult rats exposed to ethanol during the neonatal period, we investigated the influence of rapamycin, an mTOR Complex 1 (mTORC1) inhibitor, on deficits in spatial memory and reversal learning in the Barnes maze task, as well as the ethanol-induced rewarding effects (1.0 or 1.5 g/kg) using the conditioning place preference (CPP) paradigm. Rapamycin (3 and 10 mg/kg) was given before intragastric ethanol (5 g/kg/day) administration at postnatal day (PND)4–9 (an equivalent to the third trimester of human pregnancy). Spatial memory/reversal learning and rewarding ethanol effect were evaluated in adult (PND60–70) rats. Additionally, the impact of rapamycin pre-treatment on the expression of the GluN2B subunit of NMDA receptor in the brain was assessed in adult rats. Our results show that neonatal ethanol exposure induced deficits in spatial memory and reversal learning in adulthood, but the reversal learning outcome may have been due to spatial learning impairments rather than cognitive flexibility impairments. Furthermore, in adulthood the ethanol treated rats were also more sensitive to the rewarding effect of ethanol than the control group. Rapamycin prevented the neonatal effect of ethanol and normalized the GluN2B down-regulation in the hippocampus and the prefrontal cortex, as well as normalized this subunit’s up-regulation in the striatum of adult rats. Our results suggest that rapamycin and related drugs may hold promise as a preventive therapy for fetal alcohol spectrum disorders.

Early and Delayed Impact of Nanosilver on the Glutamatergic NMDA Receptor Complex in Immature Rat Brain.

Silver nanoparticles (AgNPs) are the one of the most extensively used nanomaterials. The strong antimicrobial properties of AgNPs have led to their use in a wide range of medical and consumer products. Although the neurotoxicity of AgNPs has been confirmed, the molecular mechanisms have not been extensively studied, particularly in immature organisms. Based on information gained from previous in vitro studies, in the present work, we examine whether ionotropic NMDA glutamate receptors contribute to AgNP-induced neurotoxicity in an animal model of exposure. In brains of immature rats subjected to a low dose of AgNPs, we identified ultrastructural and molecular alterations in the postsynaptic region of synapses where NMDA receptors are localized as a multiprotein complex. We revealed decreased expression of several NMDA receptor complex-related proteins, such as GluN1 and GluN2B subunits, scaffolding proteins PSD95 and SynGAP, as well as neuronal nitric oxide synthase (nNOS). Elucidating the changes in NMDA receptor-mediated molecular mechanisms induced by AgNPs, we also identified downregulation of the GluN2B-PSD95-nNOS-cGMP signaling pathway which maintains LTP/LTD processes underlying learning and memory formation during development. This observation is accompanied by decreased density of NMDA receptors, as assessed by a radioligand binding assay. The observed effects are reversible over the post-exposure time. This investigation reveals that NMDA receptors in immature rats are a target of AgNPs, thereby indicating the potential health hazard for children and infants resulting from the extensive use of products containing AgNPs.

Stimulation On Central NR2B NMDA Receptor in Neonatal and Juvenile Rats

Objective: To observe the excitability of neonatal and juvenile rats (P35~P38) stirred by a strong electrical stimulation, that is registered by the hippocampus and anterior cortex. Methods: The spinal dorsal horn was examined before and after electrical stimulation. The hippocampal CA1 region, the anterior of cerebral cortex and the spinal dorsal horn were subjected to formaldehyde treatment. Immunohistochemistry and western blot were used to analyze the number of FOS protein positive cells in the spinal dorsal horn the hippocampal CA1 region and the anterior cortex of the brain. Results: The sciatic nerve performance of neonatal and juvenile rats was compared with that of adult rats under the same noxious stimulating condition (by strong electrical stimulation). Immunohistochemistry and western blot analysis revealed that LTP and FOS protein were more prominent, but after the application of ifenprodil, these proteins were significantly inhibited. Conclusions: Reducing the stress response induced by peripheral nociceptive stimulation in neonatal and juvenile rats also inhibits the NR2B subunit in NMDA receptors.

Exposure to bacterial lipopolysaccharide in early life affects the expression of ionotropic glutamate receptor genes and is accompanied by disturbances in long-term potentiation and cognitive functions in young rats

Infections in childhood play an essential role in the pathogenesis of cognitive and psycho-emotional disorders. One of the possible mechanisms of these impairments is changes in the functional properties of NMDA and AMPA glutamate receptors in the brain. We suggest that bacterial infections during the early life period, which is critical for excitatory synapse maturation, can affect the subunit composition of NMDA and AMPA receptors. In the present study, we investigated the effect of repetitive lipopolysaccharide (LPS) intraperitoneal (i.p.) administration (25 μg/kg/day on P14, 16, and 18), mimicking an infectious disease, on the expression of subunits of NMDA and AMPA receptors in young rats. We revealed a substantial decrease of GluN2B subunit expression in the hippocampus at P23 using Western blot analysis and real-time polymerase chain reaction assay. Moderate changes were also found in GluN1, GluN2A, and GluA1 mRNA expression. The LPS-treated rats exhibited decreased exploratory and locomotor activity in the open field test and the impairment of spatial learning in the Morris water maze. Behavioral impairments were accompanied by a significant reduction in long-term hippocampal synaptic potentiation. Our data indicate that LPS-treatment in the critical period for excitatory synapse maturation alters ionotropic glutamate receptor gene expression, disturbs synaptic plasticity, and alters behavior.

Comment on " In Vivo [18F]GE-179 Brain Signal Does Not Show NMDA-Specific Modulation with Drug Challenges in Rodents and Nonhuman Primates".

Schoenberger and colleagues ( Schoenberger et al. ( 2018 ) ACS Chem. Neurosci. 9 , 298 - 305 ) recently reported attempts to demonstrate specific binding of the positron emission tomography (PET) radiotracer, [18F]GE-179, to NMDA receptors in both rats and Rhesus macaques. GE-179 did not work as expected in animal models; however, we disagree with the authors' conclusion that "the [18F]GE-179 signal seems to be largely nonspecific". It is extremely challenging to demonstrate specific binding for the use-dependent NMDA receptor intrachannel ligands such as [18F]GE-179 in animals via traditional blocking, due to its low availability of target sites ( Bmax'). Schoenberger and colleagues anesthetized rats and Rhesus monkeys using isoflurane, which has an inhibitory effect on NMDA receptor function and thus would be expected to further reduce the Bmax'. The extent of glutamate release achieved in the provocation experiments is uncertain, as is whether a significant increase in NMDA receptor channel opening can be expected under anesthesia. Prior data suggest that the uptake of disubstituted arylguanidine-based ligands such as GE-179 can be reduced by phencyclidine binding site antagonists, if injection is performed in the absence of ketamine and isoflurane anesthesia, e.g., with GE-179's antecedent, CNS 5161 ( Biegon et al. ( 2007 ) Synapse 61 , 577 - 586 ), and with GMOM ( van der Doef et al. ( 2016 ) J. Cereb. Blood Flow Metab. 36 , 1111 - 1121 ). However, the extent of nonspecific uptake remains uncertain.

Comparing the Effects of Prenatal Stress on Corticosterone Levels in Blood and Brain Excitatory Receptors

Introduction: The mother's stress during pregnancy can be a potential factor in the development of some neurological diseases in offspring. Biochemical pathway in response to stress is the secretion of corticotrophin releasing factor CRF from the paraventricular nucleus, which stimulates the secretion of ACTH and ultimately increases plasma glucocorticoids content. Increasing of CBL in rat offsprings is indicative of the induction of prenatal stress and can prone next generation to diseases such as epilepsy and learning disorders. In this study we tried to understand the effects of two types of stress (restraint and predatory) on CBL and brains NMDA receptors in rats. Materials & methods: 96 female rats (Wistar) were selected and after mating, pregnant rats were exposed to two kinds of prenatal stress (restraint and predator stress) during the last week of gestation. After parturition, CBL and NMDA receptors in the brains of newborns were studied. Findings: CBL especially in the male pups were higher. In second day after birth, male pups in stress groups had more NMDA receptors than control group. All pups in restraint stress group had more NMDA receptors than control group in sixth day after birth. In 15th day after birth all pups in Predator stress group express had more NMDA receptors than restraint group which in turn had more of these receptors than control group. Discussion & conclusions: stress is an effective impact on the next generation which is capable to lead to neurological diseases in the future

In silico analysis of binding interaction of conantokins with NMDA receptors for potential therapeutic use in Alzheimer\u2019s disease

BackgroundThe N-methyl-D-aspartate (NMDA) receptors are glutamate receptors that play vital roles in central nervous system development and are involved in synaptic plasticity, which is an essential process for learning and memory. The subunit N-methyl D-aspartate receptor subtype 2B (NR2B) is the chief excitatory neurotransmitter receptor in the mammalian brain. Disturbances in the neurotransmission mediated by the NMDA receptor are caused by its overexposure to glutamate neurotransmitter and can be treated by its binding to an antagonist. Among several antagonists, conantokins from cone snails are reported to bind to NMDA receptors.MethodsThis study was designed to analyze the binding mode of conantokins with NMDA receptors in both humans and rats. To study interactions, dockings were performed using AutoDock 4.2 and their results were further analyzed using various computational tools.ResultsDetailed analyses revealed that these ligands can bind to active site residues of both receptors as reported in previous studies.ConclusionsIn light of the present results, we suggest that these conantokins can act as antagonists of those receptors and play an important role in understanding the importance of inhibition of NMDA receptors for treatment of Alzheimer’s disease.

Memory consolidation within the central amygdala is not necessary for modulation of cerebellar learning.

Amygdala lesions impair, but do not prevent, acquisition of cerebellum-dependent eyeblink conditioning suggesting that the amygdala modulates cerebellar learning. Two-factor theories of eyeblink conditioning posit that a fast-developing memory within the amygdala facilitates slower-developing memory within the cerebellum. The current study tested this hypothesis by impairing memory consolidation within the amygdala with inhibition of protein synthesis, transcription, and NMDA receptors in rats. Rats given infusions of anisomycin or DRB into the central amygdala (CeA) immediately after each eyeblink conditioning session were severely impaired in contextual and cued fear conditioning, but were completely unimpaired in eyeblink conditioning. Rats given the NMDA antagonist ifenprodil into the CeA before each eyeblink conditioning session also showed impaired fear conditioning, but no deficit in eyeblink conditioning. The results indicate that memory formation within the CeA is not necessary for its modulation of cerebellar learning mechanisms. The CeA may modulate cerebellar learning and retention through an attentional mechanism that develops within the training sessions.

Expression of NMDA receptor and microRNA-219 in rats submitted to cerebral ischemia associated with alcoholism.

To evaluate the microRNA-219 and NMDA expression in brain tissue and blood of animals subjected to cerebral ischemia associated with alcoholism. Fifty Wistar rats were divided into groups: control, sham, ischemic, alcoholic, and ischemic plus alcoholic. The expression of microRNA-219 and NMDA were analyzed by real-time PCR. When compared to the control group, the microRNA-219 in brain tissue was less expressed in the ischemic, alcoholic, and ischemic plus alcoholic groups. In the blood, this microRNA had lower expression in alcoholic and ischemic plus alcoholic groups. In the brain tissue the NMDA gene expression was greater in the ischemic, alcoholic, and ischemic plus alcoholic groups. A possible modulation of NMDA by microRNA-219 was observed with an inverse correlation between them.

Activation of NMDA receptors and the mechanism of inhibition by ifenprodil.

SUMMARYThe physiology of N-Methyl-D-aspartate (NMDA) receptors in mammals is fundamental to brain development and function. NMDA receptors are ionotropic glutamate receptors that function as heterotetramers composed mainly of GluN1 and GluN2 subunits. Activation of NMDA receptors requires binding of neurotransmitter agonists to a ligand-binding domain (LBD) and structural rearrangement of an amino terminal domain (ATD). Recent crystal structures of GluN1/GluN2B NMDA receptors in the presence of agonists and an allosteric inhibitor, ifenprodil, represent the allosterically inhibited state. However, how the ATD and LBD move to activate the NMDA receptor ion channel remains unclear. Here, we combine x-ray crystallography, single-particle electron cryomicroscopy, and electrophysiology to show that, in the absence of ifenprodil, the bi-lobed structure of GluN2 ATD adopts an open-conformation accompanied by rearrangement of the GluN1-GluN2 ATD heterodimeric interface, altering subunit orientation in the ATD and LBD and forming an active receptor conformation that gates the ion channel.

Neuropathic pain depends upon d-serine co-activation of spinal NMDA receptors in rats

Activation of N-methyl-d-aspartate (NMDA) receptors is critical for hypersensitivity in chronic neuropathic pain. Since astroglia can regulate NMDA receptor activation by releasing the NMDA receptor co-agonist d-serine, we investigated the role of NMDA receptor and d-serine in neuropathic chronic pain. Male Wistar rats underwent right L5–L6 spinal nerve ligation or sham surgery and were tested for mechanical allodynia and hyperalgesia after 14 days. Acute intrathecal administration of the NMDA receptor antagonist d-AP5 as well as chronic administration of the glia metabolism inhibitor fluoroacetate significantly reduced mechanical allodynia in neuropathic rats. The effect of fluoroacetate was reversed by acutely administered intrathecal d-serine. Degrading d-serine using acute intrathecal administration of d-aminoacid oxidase also reduced pain symptoms. Immunocytochemistry showed that about 70% of serine racemase, the synthesizing enzyme of d-serine, was expressed in astrocyte processes in the superficial laminae of L5 dorsal horn. Serine racemase expression was upregulated in astrocyte processes in neuropathic rats compared to sham rats. These results show that neuropathic pain depends upon glial d-serine that co-activates spinal NMDA receptors.

Sympathoexcitation and pressor responses induced by ethanol in the central nucleus of amygdala involves activation of NMDA receptors in rats.

The central nervous system plays an important role in regulating sympathetic outflow and arterial pressure in response to ethanol exposure. However, the underlying neural mechanisms have not been fully understood. In the present study, we tested the hypothesis that injection of ethanol in the central nucleus of the amygdala (CeA) increases sympathetic outflow, which may require the activation of local ionotropic excitatory amino acid receptors. In anesthetized rats, CeA injection of ethanol (0, 0.17, and 1.7 μmol) increased splanchnic sympathetic nerve activity (SSNA), lumbar sympathetic nerve activity (LSNA), and mean arterial pressure (MAP) in a dose-dependent manner. A cocktail containing ethanol (1.7 μmol) and kynurenate (KYN), an ionotropic excitatory amino acid receptor blocker, showed significantly blunted sympathoexcitatory and pressor responses compared with those elicited by CeA-injected ethanol alone (P < 0.01). A cocktail containing ethanol and d-2-amino-5-phosphonovalerate, an N-methyl-d-aspartate (NMDA) receptor antagonist, elicited attenuated sympathoexcitatory and pressor responses that were significantly less than ethanol alone (P < 0.01). In addition, CeA injection of acetate (0.20 μmol, n = 7), an ethanol metabolite, consistently elicited sympathoexcitatory and pressor responses, which were effectively blocked by d-2-amino-5-phosphonovalerate (n = 9, P < 0.05). Inhibition of neuronal activity of the rostral ventrolateral medulla (RVLM) with KYN significantly (P < 0.01) attenuated sympathoexcitatory responses elicited by CeA-injected ethanol. Double labeling of immune fluorescence showed NMDA NR1 receptor expression in CeA neurons projecting to the RVLM. We conclude that ethanol and acetate increase sympathetic outflow and arterial pressure, which may involve the activation of NMDA receptors in CeA neurons projecting to the RVLM.