NMDA Receptor Density Research Articles

Efficacy and safety of ketamine for neonatal refractory status epilepticus: case report and systematic review.

Evidence-based data on treatment of neonatal status epilepticus (SE) are scarce. We aimed to collect data on the efficacy and safety of ketamine for the treatment of neonatal SE and to assess its possible role in the treatment of neonatal SE. We described a novel case and conducted a systematic literature review on neonatal SE treated with ketamine. The search was carried out in Pubmed, Cochrane, Clinical Trial Gov, Scopus and Web of Science. Seven published cases of neonatal SE treated with ketamine were identified and analyzed together with our novel case. Seizures typically presented during the first 24 h of life (6/8). Seizures were resistant to a mean of five antiseizure medications. Ketamine, a NMDA receptor antagonist, appeared to be safe and effective in all neonates treated. Neurologic sequelae including hypotonia and spasticity were reported for 4/5 of the surviving children (5/8). 3/5 of them were seizure free at 1-17 months of life. Neonatal brain is more susceptible to seizures due to a shift towards increased excitation because of a paradoxical excitatory effect of GABA, a greater density of NMDA receptors and higher extracellular concentrations of glutamate. Status epilepticus and neonatal encephalopathy could further enhance these mechanisms, providing a rationale for the use of ketamine in this setting. Ketamine in the treatment of neonatal SE showed a promising efficacy and safety profile. However, further in-depth studies and clinical trials on larger populations are needed.

The Effect of Piracetam and Noopept on NMDA and 5-HT<sub>2A</sub> Receptors in the Brain of Mice with Congenital β-Arrestin Deficiency

Based on the special role of the signal protein β-arrestin in the processes of neuronal plasticity and receptor activation, the effects of the nootropic drugs Piracetam (2-oxo-1-pyrrodinyl-acetamide, UCB 6215, 200 mg/kg, I.P.) and Noopept (ethyl ether N-phenyl-acetyl-L-prolyl-glycine, GVS-111, 0.5 mg/kg, I.P.) in mice with congenital deficiency of β-arrestin-2 (BARR2-KO mice) and in mice of the C57Bl/6 line (wild type for the BARR2-KO, WT line). Serotonin (5-HT2A) and NMDA-receptors of the brain, which play an important role in cognitive processes, but differ in the type of structure and activation mechanism, were chosen as the object of the study. Using radioligand analysis, it was found that the BARR2-KO mouse line differs from the C57Bl/6 mice by a significantly higher density (Bmax) of both NMDA-receptors in the hippocampus (by 85%) and 5-HT2A -receptors in the cerebral cortex (by 54%). Interestingly, both drugs after chronic administration increased the number of NMDA-receptors in the hippocampus both in the BARR2-KO strain (Piracetam – by 76%, Noopept – by 78%) and in the C57Bl/6 strain (Piracetam – by 112%, Noopept – by 49%). At the same time, the effect of both drugs on the density of serotonin 5-HT2A-receptors in BARR2-KO and C57Bl/6 mice was not the same. In particular, Piracetam caused an increase in the density of 5-HT2A-receptors in the cerebral cortex of BARR2-KO mice by 31%, whereas on the comparison line C57Bl/6 neither Piracetam nor Noopept had any effect. Thus, the absence of the β-arrestin signaling protein in BARR2-KO mice is accompanied by an increase in the density of NMDA- and 5-HT2A-receptors in the brain. At the same time, the different effects of Piracetam and Noopept on NMDA receptors both in the line with congenital β‑arrestin deficiency and in the line with normal expression may indicate that this type of receptor is a common primary target for the action of nootropics of various structures.

Participation of Brain Receptors in the Mechanism of Anticonvulsant Action of a New 4-Benzoylpyridine Oxime Derivative GIZH-298

The aim of the work was to study the involvement of glutamate, dopamine and serotonin receptors in the mechanism of the anticonvulsant action of the 4-benzoylpyridine oxime derivative (GIZh-298). After a single exposure to the cornea with maximum electric shock (MES) and subsequent tonic-clonic seizures, an increase in the density (Bmax) of NMDA receptors in the hippocampus by 27% and a decrease in the number of mGluII receptors (mGluR2/3) by 25% in the prefrontal cortex of the brain of rats are noted. At the same time, the number of 5-HT2A receptors in the prefrontal cortex did not change. GIZh-298 (60 mg/kg) with a single application inhibits convulsive reactions, but does not affect the quantitative changes induced by MES in glutamate receptors and does not affect them under normal conditions, without MES. In tests on mice, subchronic (5 days) corneal exposure to MES reduced the density (Bmax) of D2 receptors in the striatum by 17% and did not change this parameter in the prefrontal cortex. GIZh-298 (60 mg/kg/5 days) eliminates clonic-tonic convulsions in mice and prevents a decrease in the number of D2 receptors from striatal membranes, and also increases their number by 13% in mice without MES in the same structure. The data obtained indicate significant changes in the functional activity of NMDA, mGluII and D2 receptors in the brains of animals that suffered seizures. The anticonvulsant effects of GIZH-298 are accompanied by the restoration of the number of D2 receptors in the striatum..

Mu Opioid Receptor Activation Mediates (S)-ketamine Reinforcement in Rats: Implications for Abuse Liability

Background(S)-ketamine is an NMDA receptor antagonist, but it also binds to and activates mu opioid receptors (MORs) and kappa opioid receptors in vitro. However, the extent to which these receptors contribute to (S)-ketamine’s in vivo pharmacology is unknown. MethodsWe investigated the extent to which (S)-ketamine interacts with opioid receptors in rats by combining in vitro and in vivo pharmacological approaches, in vivo molecular and functional imaging, and behavioral procedures relevant to human abuse liability. ResultsWe found that the preferential opioid receptor antagonist naltrexone decreased (S)-ketamine self-administration and (S)-ketamine–induced activation of the nucleus accumbens, a key brain reward region. A single reinforcing dose of (S)-ketamine occupied brain MORs in vivo, and repeated doses decreased MOR density and activity and decreased heroin reinforcement without producing changes in NMDA receptor or kappa opioid receptor density. ConclusionsThese results suggest that (S)-ketamine’s abuse liability in humans is mediated in part by brain MORs.

Regional binding of [3H]‐MK801 to NMDA receptors in young and aged rat brain membranes

Norepinephrine (NE) and dopamine (DA) are essential neuromodulators in the central nervous system. They regulate several crucial physiological processes, including arousal/attention, focus, neuroendocrine functions, and the sleep‐wake cycle; they also play complex roles in regulating cognition and affect; therefore, dysfunctions in catecholaminergic neurotransmission are associated with various neurological consequences. Previously, we confirmed that in brain slices from aged Fischer 344 rats, there is an age‐related decrease in glutamate‐stimulated NE release in the cerebral cortex and hippocampus (Gonzales et al., 1991 & Dezfuli et al., 2019) and a regionally specific decline in glutamate‐stimulated DA release, with a deficit in the striatum but not in the olfactory tubercle (Aljohani et al., 2021a). Importantly, our studies demonstrated that NMDA receptors mediate glutamate‐stimulated NE and DA release. We also have shown that the alpha‐2 adrenergic receptors agonist clonidine decreases this glutamate‐stimulated NE release in a concentration‐dependent manner; while in contrast, blockade of these receptors with phentolamine, an alpha‐1 and alpha‐2 adrenergic receptor blocker, or with idazoxan, a selective alpha‐2 receptor blocker, markedly potentiates glutamate‐stimulated NE release in cortical brain slices (Aljohani et al., 2021b). Since aging has heterogeneous effects on NMDA receptors in different brain areas, we have now begun to examine [3H]‐MK801 binding to NMDA receptors to compare changes in receptor density and responsiveness during aging in the cortex, hippocampus, striatum, and olfactory tubercle, as a possible mechanistic explanation for the changes in NE and DA release. The data from cortical membrane preparations suggest that young and old rats have similar NMDA receptor densities but may differ in their response to stimulation with glutamate/glycine.

Amyloid \u03b2 / PKC-dependent alterations in NMDA receptor composition are detected in early stages of Alzheimer\xb4s disease

Amyloid beta (Aβ)-mediated synapse dysfunction is an early event in Alzheimer’s disease (AD) pathogenesis and previous studies suggest that NMDA receptor (NMDAR) dysregulation may contribute to these pathological effects. Although Aβ peptides impair NMDAR expression and activity, the mechanisms mediating these alterations in the early stages of AD are unclear. Here, we observed that NMDAR subunit NR2B and PSD-95 levels were aberrantly upregulated and correlated with Aβ42 load in human postsynaptic fractions of the prefrontal cortex in early stages of AD patients, as well as in the hippocampus of 3xTg-AD mice. Importantly, NR2B and PSD95 dysregulation was revealed by an increased expression of both proteins in Aβ-injected mouse hippocampi. In cultured neurons, Aβ oligomers increased the NR2B-containing NMDAR density in neuronal membranes and the NMDA-induced intracellular Ca2+ increase, in addition to colocalization in dendrites of NR2B subunit and PSD95. Mechanistically, Aβ oligomers required integrin β1 to promote synaptic location and function of NR2B-containing NMDARs and PSD95 by phosphorylation through classic PKCs. These results provide evidence that Aβ oligomers modify the contribution of NR2B to NMDAR composition and function in the early stages of AD through an integrin β1 and PKC-dependent pathway. These data reveal a novel role of Aβ oligomers in synaptic dysfunction that may be relevant to early-stage AD pathogenesis.

Spatial mapping of subcellular disease pathways and cytoarchitecture to anatomical brain regions for multi‐scale brain simulation with The Virtual Brain

AbstractBackgroundComprehensive knowledge bases as NeuroMMSig, a knowledge base of multimodal mechanistic signatures, catalog knowledge about Alzheimer's Disease (AD) and its underlying candidate mechanisms. Besides, digital atlases provide information about cytoarchitectonics and receptor densities, e.g. JuBrain at the EBRAINS platform of the Human Brain Project. However, a gap exists presently with respect to the integration of the various knowledge sources. The Virtual Brain (TVB) is a full brain simulation platform that integrates multimodal imaging data with mathematical brain networks. We present a methodology to map semantic information about AD to 3D brain atlases and to use it for simulations with TVB – increasing the biological plausibility of whole‐brain simulations and disease specificity.MethodOur framework allows topological assignment of brain‐related data from different sources to the Multimodal surface‐based cortical parcellation (MMP) of the Human Connectome Project. Our tool allows mapping of stochastic information from the literature database SCAIView to brain regions. The relevance score for a specific query is calculated for anatomy‐related words from the anatomic ontology Uberon, which we transfer by a unique matrix to MMP parcels. Re‐sampling by the fsaverage brain space of freesurfer allows interoperability with other atlases. In addition, atlas‐annotated data from EBRAINS and neuroimaging data are co‐registered with MMP, enabling knowledge integration into a standardized 3D brain space.ResultOur methodologic pipeline can be used as a software to map semantic information to the brain, which we demonstrate with NeuroMMSig pathways. We further demonstrate how the resulting maps constrain TVB simulations. Face validity is provided through reproducing group‐level (AD versus controls) results of simulations integrating subject‐specific positron emission tomography when semantic information about AD stages is integrated into TVB. We elucidate how brain maps derived from different semantic queries can change simulated brain dynamics fundamentally. Literature‐derived NMDA receptor densities show significant differences between AD and healthy controls. When used to constrain TVB models, this leads to an in silico disruption of functional subnetworks in AD.ConclusionWe developed a tool for mapping semantic knowledge to anatomical brain regions. This enables multi‐scale brain simulations with increases biological plausibility and disease‐specificity for translational research.

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.

Protective effects of Da-cheng-qi decoction in rats with intracerebral hemorrhage

BackgroundIntracerebral hemorrhage (ICH), the most fatal subtype of stroke, has no disease-modifying treatment. Da-cheng-qi decoction (DCQ), composed of rhubarb, is one of the most commonly used Chinese traditional decoctions in ICH treatment. But the mechanism is not clear. Emodin is an active compound found in rhubarb. PurposeTo study the protective effects of DCQ on ICH and its possible mechanisms of action. MethodsThe ICH model was reproduced by injecting collagenase-VII into the left caudate putamen (CPu) of rats. DCQ and emodin were used to treat the ICH rats for 7 days. Behavior tests, proteomic analysis, morphological studies, and western blotting were performed. ResultsThe neurological deficits in the ICH rats recovered with DCQ and emodin on the 14th day after ICH. The proteomics data revealed that DCQ significantly corrected the pathological signals in the CPu and hippocampus after ICH. The numbers of amoebic microglia in the CPu and M2 microglia in both CPu and hippocampus were significantly increased after DCQ and emodin treatment. The increase in GluN2B-containing NMDA receptor (NR2B) and postsynaptic density protein-95, activation of mitogen-activated protein kinase (MAPK) signals in the CPu, and secondary neurodegeneration (SND) in the hippocampus were significantly recovered in DCQ-treated rats. Inhibition of MAPK p38 (p38) in the hippocampus was observed after DCQ and emodin treatment. ConclusionThe protective effects of DCQ on ICH were confirmed in this study, and its mechanism may be related to the inhibition of MAPK and activation of M2 microglia. These results are beneficial to the development of ICH therapeutic targets.

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.

A Mechanistic Model of NMDA and AMPA Receptor-Mediated Synaptic Transmission in Individual Hippocampal CA3-CA1 Synapses: A Computational Multiscale Approach.

Inside hippocampal circuits, neuroplasticity events that individual cells may undergo during synaptic transmissions occur in the form of Long-Term Potentiation (LTP) and Long-Term Depression (LTD). The high density of NMDA receptors expressed on the surface of the dendritic CA1 spines confers to hippocampal CA3-CA1 synapses the ability to easily undergo NMDA-mediated LTP and LTD, which is essential for some forms of explicit learning in mammals. Providing a comprehensive kinetic model that can be used for running computer simulations of the synaptic transmission process is currently a major challenge. Here, we propose a compartmentalized kinetic model for CA3-CA1 synaptic transmission. Our major goal was to tune our model in order to predict the functional impact caused by disease associated variants of NMDA receptors related to severe cognitive impairment. Indeed, for variants Glu413Gly and Cys461Phe, our model predicts negative shifts in the glutamate affinity and changes in the kinetic behavior, consistent with experimental data. These results point to the predictive power of this multiscale viewpoint, which aims to integrate the quantitative kinetic description of large interaction networks typical of system biology approaches with a focus on the quality of a few, key, molecular interactions typical of structural biology ones.

Predominance of Nootropic or Anxiolytic Effects of Selank, Semax, and Noopept Peptides Depending on the Route of Administration to BALB/c and С57BL/6 Mice

Abstract—The pharmacological effects of intraperitoneal (i.p.) and intranasal (i.n.) administration of the peptides selank (300 µg/kg/day), noopept (1 mg/kg/day), and semax (0.6 mg/kg/day), which are known to possess anxiolytic and nootropic properties, were compared by studying the elevated-plus-maze (EPM) behavior of inbred BALB/c and C57BL/6 mice, and studying their effects on NMDA- and mGluII- receptors in the brain. Semax, noopept, and selank administered via both routes improved exploratory activity and reduced anxiety in BALB/c mice, but the anxiolytic efficiency was higher after intraperitoneal injection and the nootropic efficiency was higher after intranasal administration. In C57BL/6 mice, semax, noopept, and selank did not affect the efficiency of exploratory behavior or anxiety after administration via either route, except for i.p. injection of semax, which showed a greater anxiogenic effect compared to intranasal administration. In BALB/c mice, i.p. administration of noopept and i.n. administration of selank increased the density of NMDA-receptors in the hippocampus and i.n. administration of noopept and semax reduced their density, with no effect on mGluII-receptors. In C57BL/6 mice, i.p. semax and i.n. noopept reduced the number of NMDA-receptor binding sites, and i.p. noopept and semax administered via either route reduced the density of mGluII-receptors in the cerebral cortex.

The Involvement of the Serotonin, Glutamate, and GABA Receptors in the Manifestation of the Antidepressant-Like Effect of Cycloprolylglycine

Abstract—We studied the effect of a 2-week administration of cycloprolylglycine peptide (CPG) (1 and 2 mg/kg/day, i.p.) on the binding characteristics of serotonin 5-HT2A-, NMDA-, metabotropic glutamate mGluII-, GABAA- and GABAB-receptors in the brain of inbred BALB/c mice in vitro and ex vivo. It was found that CPG at doses of 1 and 2 mg/kg/day reduces the density of 5-HT2A receptors in the striatum of mice by 24 and 28%, respectively. A decrease in the density of NMDA receptors in the hippocampus was observed only at a dose of 2 mg/kg/day; it was 22%. At the same time, there was an increase in the density of GABAA receptors in the frontal cortex at a dose of 1 mg/kg/day by 36% compared with the control. The 2-week administration of CPG at both doses did not affect Bmax of mGluII- and GABAB receptors, as well as Kd in all groups. In the in vitro radioligand assay, the CPG did not affect the specific binding of the labeled ligands of the studied receptors. These data indicate the functional involvement of 5-HT2A, NMDA, and GABAA receptors in the formation of the antidepressant-like effect of cycloprolylglycine in BALB/c mice for the first time.

Variability in the Drug Response of M4 Muscarinic Receptor Knockout Mice During Day and Night Time.

Mice are nocturnal animals. Surprisingly, the majority of physiological/pharmacological studies are performed in the morning, i.e., in the non-active phase of their diurnal cycle. We have shown recently that female (not male) mice lacking the M4 muscarinic receptors (MR, M4KO) did not differ substantially in locomotor activity from their wild-type counterparts (C57Bl/6Tac) during the inactive period. Increased locomotion has been shown in the active phase of their diurnal cycle. We compared the effects of scopolamine, oxotremorine, and cocaine on locomotor response, hypothermia and spontaneous behavior in the open field arena in the morning (9:00 AM) and in the evening (9:00 PM) in WT and in C57Bl/6NTac mice lacking the M4 MR. Furthermore, we also studied morning vs. evening densities of muscarinic, GABAA, D1-like, D2-like, NMDA and kainate receptors using autoradiography in the motor, somatosensory and visual cortex and in the striatum, thalamus, hippocampus, pons, and medulla oblongata. At 9:00 AM, scopolamine induced an increase in motor activity in WT and in M4KO, yet no significant increase was observed at 9:00 PM. Oxotremorine induced hypothermic effects in both WT and M4KO. Hypothermic effects were more evident in WT than in M4KO. Hypothermia in both cases was more pronounced at 9:00 AM than at 9:00 PM. Cocaine increased motor activity when compared to saline. There was no difference in behavior in the open field between WT and M4KO when tested at 9:00 AM; however, at 9:00 PM, activity of M4KO was doubled in comparison to that of WT. Both WT and KO animals spent less time climbing in their active phase. Autoradiography revealed no significant morning vs. evening difference. Altogether, our results indicate the necessity of comparing morning vs. evening drug effects

PIP3-Phldb2 is crucial for LTP regulating synaptic NMDA and AMPA receptor density and PSD95 turnover

The essential involvement of phosphoinositides in synaptic plasticity is well-established, but incomplete knowledge of the downstream molecular entities prevents us from understanding their signalling cascades completely. Here, we determined that Phldb2, of which pleckstrin-homology domain is highly sensitive to PIP3, functions as a phosphoinositide-signalling mediator for synaptic plasticity. BDNF application caused Phldb2 recruitment toward postsynaptic membrane in dendritic spines, whereas PI3K inhibition resulted in its reduced accumulation. Phldb2 bound to postsynaptic scaffolding molecule PSD-95 and was crucial for localization and turnover of PSD-95 in the spine. Phldb2 also bound to GluA1 and GluA2. Phldb2 was indispensable for the interaction between NMDA receptors and CaMKII, and the synaptic density of AMPA receptors. Therefore, PIP3-responsive Phldb2 is pivotal for induction and maintenance of LTP. Memory formation was impaired in our Phldb2−/− mice.

Effects of Low Doses of Ketamine on Pyramidal Neurons in Rat Prefrontal Cortex

Indirect evidence suggests that low doses of ketamine disinhibit (excite) pyramidal neurons in the prefrontal cortex (PFC). In this study, we directly examined the effect of ketamine on PFC pyramidal neurons using simultaneous single-cell and local-field-potential (LFP) recording in chloral hydrate-anesthetized rats. In all animals studied, PFC LFPs showed oscillations (0.3–1.5 Hz) between the active UP state and the relatively quiescent DOWN state, and pyramidal neurons fired preferentially during the UP state. Ketamine (1.25–20 mg/kg, i.v.) inhibited 80% of cells tested and consistently shifted PFC LFPs toward the DOWN state. The inhibitory effect of ketamine was mimicked by MK801, but not by the NR2B-selective NMDA receptor antagonist Ro25-6981. It was not blocked by the dopamine receptor antagonist fluphenazine, the GABAA receptor antagonist picrotoxinin, or the GABAB receptor antagonist CGP46381. These results are consistent with the high density of NMDA receptors expressed on PFC pyramidal neurons and our previous studies showing that blockade of NMDA receptors by ketamine inhibits dendritic NMDA receptor-mediated bursting in PFC pyramidal neurons. Thus, in addition to the previously proposed disinhibitory effect mediated through PFC interneurons, our data suggest that ketamine has an inhibitory effect on PFC pyramidal neurons. Our evidence further suggests that the effect is mediated through non-NR2B-containing NMDA receptors, independent of ketamine’s effect on dopamine and GABA transmission. Further understanding of the two opposing effects of ketamine on PFC pyramidal neurons may provide important new insights into its mechanism of action.

Selective enhancement of NMDA receptor-mediated locomotor hyperactivity by male sex hormones in mice.

Altered glutamate NMDA receptor function is implicated in schizophrenia, and gender differences have been demonstrated in this illness. This study aimed to investigate the interaction of gonadal hormones with NMDA receptor-mediated locomotor hyperactivity and PPI disruption in mice. The effect of 0.25mg/kg of MK-801 on locomotor activity was greater in male mice than in female mice. Gonadectomy (by surgical castration) significantly reduced MK-801-induced hyperlocomotion in male mice, but no effect of gonadectomy was seen in female mice or on amphetamine-induced locomotor hyperactivity. The effect of MK-801 on prepulse inhibition of startle (PPI) was similar in intact and castrated male mice and in ovariectomized (OVX) female mice. In contrast, there was no effect of MK-801 on PPI in intact female mice. Forebrain NMDA receptor density, as measured with [3H]MK-801 autoradiography, was significantly higher in male than in female mice but was not significantly altered by either castration or OVX. These results suggest that male sex hormones enhance the effect of NMDA receptor blockade on psychosis-like behaviour. This interaction was not seen in female mice and was independent of NMDA receptor density in the forebrain. Male sex hormones may be involved in psychosis by an interaction with NMDA receptor hypofunction.

Evidence that remodeling of insular cortex neurovascular unit contributes to hypertension-related sympathoexcitation.

The intermediate region of the posterior insular cortex (intermediate IC) mediates sympathoexcitatory responses to the heart and kidneys. Previous studies support hypertension‐evoked changes to the structure and function of neurons, blood vessels, astrocytes and microglia, disrupting the organization of the neurovascular unit (NVU). In this study, we evaluated the functional and anatomical integrity of the NVU at the intermediate IC in the spontaneously hypertensive rat (SHR) and its control the Wistar‐Kyoto (WKY). Under urethane anesthesia, NMDA microinjection (0.2 mmol/L/100 nL) was performed at the intermediate IC with simultaneous recording of renal sympathetic nerve activity (RSNA), heart rate (HR) and mean arterial pressure (MAP). Alterations in NVU structure were investigated by immunofluorescence for NMDA receptors (NR1), blood vessels (70 kDa FITC‐dextran), astrocytes (GFAP), and microglia (Iba1). Injections of NMDA into intermediate IC of SHR evoked higher amplitude responses of RSNA, MAP, and HR. On the other hand, NMDA receptor blockade decreased baseline RSNA, MAP and HR in SHR, with no changes in WKY. Immunofluorescence data from SHR intermediate IC showed increased NMDA receptor density, contributing to the SHR enhanced sympathetic responses, and increased in vascular density (increased number of branches and endpoints, reduced average branch length), suggesting angiogenesis. Additionally, IC from SHR presented increased GFAP immunoreactivity and contact between astrocyte processes and blood vessels. In SHR, IC microglia skeleton analysis supports their activation (reduced number of branches, junctions, endpoints and process length), suggesting an inflammatory process in this region. These findings indicate that neurogenic hypertension in SHR is accompanied by marked alterations to the NVU within the IC and enhanced NMDA‐mediated sympathoexcitatory responses likely contributors of the maintenance of hypertension.

Parafascicular thalamic nucleus deep brain stimulation decreases NMDA receptor GluN1 subunit gene expression in the prefrontal cortex

The rodent parafascicular nucleus (PFn) or the centromedian-parafascicular complex of primates is a posterior intralaminar nucleus of the thalamus related to cortical activation and maintenance of states of consciousness underlying attention, learning and memory. Deep brain stimulation (DBS) of the PFn has been proved to restore arousal and consciousness in humans and to enhance performance in learning and memory tasks in rats. The primary expected effect of PFn DBS is to induce plastic changes in target neurons of brain areas associated with cognitive function. In this study, Wistar rats were stimulated for 20mins in the PFn following a DBS protocol that had previously facilitated memory in rats. NMDA and GABAB receptor binding, and gene expression of the GluN1subunit of the NMDA receptor (NMDAR) were assessed in regions related to cognitive functions, such as the prefrontal cortex and hippocampus. The results showed that PFn DBS induced a decrease in NMDAR GluN1 subunit gene expression in the cingulate and prelimbic cortices, but no significant statistical differences were found in the density of NMDA or GABAB receptors in any of the analyzed regions. Taken together, our findings suggest a possible role for the NMDAR GluN1 subunit in the prefrontal cortex in the procognitive actions of the PFn DBS.

Temporal Dynamics of Antidepressant Ketamine Effects on Glutamine Cycling Follow Regional Fingerprints of AMPA and NMDA Receptor Densities.

The anterior cingulate cortex (ACC) has shown decreased glutamate levels in patients with major depressive disorder. Subanesthetic doses of ketamine were repeatedly shown to improve depressive symptoms within 24 h after infusion and this antidepressant effect was attributed to increased α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) throughput. To elucidate ketamine's mechanism of action, we tested whether the clinical time course of the improvement is mirrored by the change of glutamine/glutamate ratio and if such effects show a regional and temporal specificity in two distinct subdivisions of ACC with different AMPA/N-methyl-D-aspartate receptor profiles. In a double-blind, placebo-controlled intravenous infusion study of ketamine, we measured glutamate and glutamine in the pregenual ACC (pgACC) and the anterior midcingulate cortex at 1 and 24 h post infusion with magnetic resonance spectroscopy at 7 T. A significant interaction of time, region, and treatment was found for the glutamine/glutamate ratios (placebo, n=14; ketamine, n=12). Post-hoc analyses revealed that the glutamine/glutamate ratio increased significantly in the ketamine group, compared with placebo, specifically in the pgACC after 24 h. The glutamine/glutamate increase in the pgACC caused by ketamine at 24 h post infusion was reproduced in an enlarged sample (placebo, n=24; ketamine, n=20). Our results support a significant temporal and regional response in glutamine/glutamate ratios to a single subanesthetic dose of ketamine, which mirrors the time course of the antidepressant response and reversal of the molecular deficits in patients and which may be associated with the histoarchitectonical receptor fingerprints of the ACC subregions.