A novel Na+‐Independent alanine‐serine‐cysteine transporter 1 inhibitor inhibits both influx and efflux of D‐Serine

NMDA receptor dysfunctions are hypothesized to underlie the pathophysiology of schizophrenia, and treatment with D‐serine (D‐Ser), an NMDA receptor coagonist, may improve the clinical symptoms of schizophrenia. Thus, upregulating the synaptic D‐Ser level is a novel strategy for schizophrenia treatment. Na⁺‐independent alanine‐serine‐cysteine transporter 1 (asc‐1) is a transporter responsible for regulating the extracellular D‐Ser levels in the brain. In this study, we discovered a novel asc‐1 inhibitor, (+)‐amino(1‐(3,5‐dichlorophenyl)‐3,5‐dimethyl‐1H‐pyrazol‐4‐yl)acetic acid (ACPP), and assessed its pharmacological profile. ACPP inhibited the D‐[³H]Ser uptake in human asc‐1‐expressing CHO cells and rat primary neurons with IC₅₀ values of 0.72 ± 0.13 and 0.89 ± 0.30 μM, respectively. In accordance with the lower asc‐1 expression levels in astrocytes, ACPP did not inhibit D‐Ser uptake in rat primary astrocytes. In a microdialysis study, ACPP dose dependently decreased the extracellular D‐Ser levels in the rat hippocampus under the same conditions in which the asc‐1 inhibitor S‐methyl‐L‐cysteine (SMLC) increased it. To obtain insights into this difference, we conducted a D‐[³H]Ser efflux assay using asc‐1‐expressing CHO cells. ACPP inhibited D‐[³H]Ser efflux, whereas SMLC increased it. These results suggest that ACPP is a novel inhibitor of asc‐1. © 2016 Wiley Periodicals, Inc.     

D‐serine is distributed in neurons in the brain of the sea lamprey

The amino acid D‐serine is an endogenous coagonist of N‐methyl‐D‐aspartate (NMDA) receptors in mammals that has been shown to play an important role in synaptic function, behavior, learning, and memory. The distribution and cellular location of D‐serine in the brain of the sea lamprey was investigated by using immunofluorescence methods. One major finding of our study, unlike early studies of mammals, was the localization of D‐serine immunoreactivity in perikarya and dendrites of neurons, whereas D‐serine immunoreactivity was not generally observed in the lamprey glia. D‐serine‐immunoreactive neurons were observed in different brain regions, including the olfactory bulb, medial pallium, thalamus, torus semicircularis, isthmus, and reticular formation. The colocalization of D‐serine with γ‐aminobutyric acid (GABA) was also studied with a double‐immunofluorescence technique. The relationship between D‐serine and glycine immunoreactivities was studied in alternate parallel series of sections stained for either D‐serine/GABA or glycine/GABA. Colocalization with GABA was observed in various D‐serine‐immunoreactive populations, and codistribution and possible colocalization with glycine was also observed in some populations, mainly in the dorsal isthmic gray, medial octavolateral nucleus, dorsal column nucleus, interpeduncular nucleus, and reticular formation. Although numerous fibers were strongly GABA‐ and glycine‐immunoreactive, D‐serine immunoreactivity was observed mostly in cell perikarya and dendrites. The present results indicate that the D‐serine immunoreactive cells are small to medium‐sized neurons, some exhibiting classical inhibitory neurotransmitters, in which D‐serine might be acting as a modulator. The neuronal distribution of D‐serine and its frequent colocalization and/or codistribution with the two main inhibitory neurotransmitters appeared early in vertebrates. J. Comp. Neurol. 518:1688–1710, 2010. © 2009 Wiley‐Liss, Inc.     

Potential roles of D‐serine and serine racemase in experimental temporal lobe epilepsy

To confirm the roles of D‐serinergic gliotransmission in epilepsy, we investigated the relationship between spatiotemporally specific glial responses and the D‐serine/serine racemase system in mesial temporal structures following status epilepticus (SE). In control animals, D‐serine and serine racemase immunoreactivities were detected mainly in astrocytes. After SE, D‐serine and serine racemase immunoreactivities were increased in astrocytes. Double‐immunofluorescence study revealed that up‐regulation of serine racemase immunoreactivity was relevant not to D‐serine immunoreactivity but to nestin or vimentin immunoreactivity. Neither D‐serine nor serine racemase was found in naïve or reactive microglia. In addition, phosphorylated N‐methyl‐D‐aspartate (NMDA) receptor subunit 1 (pNR1‐Ser896) immunoreactivity in the hippocampus was increased compared with controls. Increased D‐serine immunoreactivity showed direct correlation with the phosphorylation of Ser896 of NR1. Given the findings of our previous study, these findings suggest that D ‐serine and serine racemase in astrocytes may play roles in neuronal hyperexcitability via a cooperative activation of NMDA receptors. Furthermore, serine racemase may be involved in migration and differentiation of immature astrocytes, which is relevant to reactive astrogliosis. © 2010 Wiley‐Liss, Inc.     

Mutant disrupted‐in‐schizophrenia 1 in astrocytes: Focus on glutamate metabolism

Disrupted‐in‐schizophrenia 1 (DISC1) is a genetic risk factor that has been implicated in major mental disorders. DISC1 binds to and stabilizes serine racemase to regulate production of D‐serine by astrocytes, contributing to glutamate (GLU) neurotransmission. However, the possible involvement of astrocytic DISC1 in synthesis, metabolism, reuptake, or secretion of GLU remains unexplored. Therefore, we studied the effects of dominant‐negative mutant DISC1 on various aspects of GLU metabolism by using primary astrocyte cultures and hippocampal tissue from transgenic mice with astrocyte‐restricted expression of mutant DISC1. Although mutant DISC1 had no significant effects on astrocyte proliferation, GLU reuptake, glutaminase, or glutamate carboxypeptidase II activity, expression of mutant DISC1 was associated with increased levels of alanine‐serine‐cysteine transporter 2, vesicular glutamate transporters 1 and 3 in primary astrocytes and in the hippocampus, and elevated expression of the NR1 subunit and diminished expression of the NR2A subunit of N‐methyl‐D‐aspartate (NMDA) receptors in the hippocampus, at postnatal day 21. Our findings indicate that decreased D‐serine production by astrocytic mutant DISC1 might lead to compensatory changes in levels of the amino acid transporters and NMDA receptors in the context of tripartite synapse. © 2014 Wiley Periodicals, Inc.     

Increased burst‐firing of ventral tegmental area dopaminergic neurons in d‐amino acid oxidase knockout mice in vivo

d ‐Amino acid oxidase (DAO) degrades the N‐methyl‐d ‐aspartate (NMDA) receptor co‐agonist d ‐serine, and is implicated in schizophrenia as a risk gene and therapeutic target. In schizophrenia, the critical neurochemical abnormality affects dopamine, but to date there is little evidence that DAO impacts on the dopamine system. To address this issue, we measured the electrophysiological properties of dopaminergic (DA) and non‐DA neurons in the ventral tegmental area (VTA) of anaesthetised DAO knockout (DAO^?/?) and DAO heterozygote (DAO^+/?) mice as compared with their wild‐type (DAO^+/+) littermates. Genotype was confirmed at the protein level by western blotting and immunohistochemistry. One hundred and thirty‐nine VTA neurons were recorded in total, and juxtacellular labelling of a subset revealed that neurons immunopositive for tyrosine hydroxylase had DA‐like electrophysiological properties that were distinct from those of neurons that were tyrosine hydroxylase‐immunonegative. In DAO^?/? mice, approximately twice as many DA‐like neurons fired in a bursting pattern than in DAO^+/? or DAO^+/+ mice, but other electrophysiological properties did not differ between genotypes. In contrast, non‐DA‐like neurons had a lower firing rate in DAO^?/? mice than in DAO^+/? or DAO^+/+ mice. These data provide the first direct evidence that DAO modulates VTA DA neuron activity, which is of interest for understanding both the glutamatergic regulation of dopamine function and the therapeutic potential of DAO inhibitors. The increased DA neuron burst‐firing probably reflects increased availability of d ‐serine at VTA NMDA receptors, but the site, mechanism and mediation of the effect requires further investigation, and may include both direct and indirect processes.     

Effects of endogenous agonists,glycine and D-serine,on in vivo specific binding of [11C]L-703,717, a PET radioligand for the glycine-binding site of NMDA receptors

A positron-emitter (carbon-11) labeled antagonist for the glycine-binding site of NMDA receptors, [(11)C]L-703,717, has a unique in vivo binding characteristic, in which it preferentially binds to cerebellar-specific NMDA receptors consisting of a GluRepsilon3 subunit and eventually accumulates in rodent cerebellum under in vivo conditions, but not under in vitro conditions. In order to understand the in vivo-specific site and subunit localization of this radioligand, we examined the effect of the endogenous glycine site agonists, glycine and D-serine, on in vivo [(11)C]L-703,717 binding. An increase in extracellular glycine concentration by treatment with a glycine transporter 1 (GlyT1)-selective inhibitor, NFPS ethyl ester, significantly decreased the cerebellar localization of [(11)C]L-703,717 in rats. D-serine is known to be concentrated in mammalian forebrain regions. The lack of D-serine detection in the cerebellum may be due to the fact that it has the highest enzymatic activity of D-amino acid oxidase (DAO). It was found that the cerebellar localization of [(11)C]L-703,717 is greatly diminished in mutant mice lacking DAO, in which D-serine content in the cerebellum is drastically increased from a nondetectable level in normal mice. These studies indicate that [(11)C]L-703,717 is susceptible to inhibition by glycine site agonists in its in vivo binding, and suggest that regional differences in inhibitions by endogenous agonists may be a crucial factor in the site- and subunit-specific binding of this glycine-site antagonist.     

Subsaturation of the N‐methyl‐D‐aspartate receptor glycine site allows the regulation of bursting activity in juvenile rat nigral dopamine neurons

The activation of N‐methyl‐D‐aspartate receptors (NMDARs) in substantia nigra pars compacta (SNc) dopamine (DA) cells is central to generate the bursting activity, a phasic signal linked to DA‐related behaviours via the change in postsynaptic DA release. NMDARs are recruited during excitatory synaptic transmission by glutamate release, but the glycine site level of occupancy of these receptors during basal action potential‐dependent activity is not known for SNc DA neurons. We explored NMDAR‐dependent signals during exogenous applications of co‐agonists in midbrain slices from juvenile rats. We found that both glycine and D‐serine strengthened the NMDAR‐dependent component of excitatory postsynaptic currents (EPSCs) in a concentration‐dependent manner. EPSCs were also increased by endogenous glycine via the blockade of the glycine transport. The glycine site of NMDARs contributing to synaptic transmission is therefore subsaturated. The behaviourally relevant burst firing was more sensitive to exogenous D‐serine and endogenous glycine than to exogenous glycine. The mechanisms regulating the availability of the co‐agonists exert consequently a critical influence on the excitability of DA neurons via NMDARs. The modulation of the phasic firing in DA neurons by ambient NMDAR co‐agonists may be important for nigral information processing and downstream motor‐related behaviour.     

AR-R15896AR blocks the early NMDA-induced loss of MAP2 in primary cortical cultures

Abstract

The low-affinity use-dependent N-methyl-D-aspartate (NMDA) receptor antagonist AR-R15896AR is neuroprotective in primary rat cortical cultures exposed to toxic concentrations of NMDA and reduces the magnitude of NMDA-triggered increases in [Ca²⁺],. Here we show using fluorescence staining and measurements of microtubule-associated protein-2 (MAP2) levels, that AR-R15896AR inhibits the NMDA- induced loss of MAP2 that occurs within 2 min following NMDA exposure. Understanding the multiple, Ca²⁺-triggered intracellular events that occur following NMDA receptor stimulation is important to the development of safe and effective neuroprotective agents. [Neurol Res 1999; 21: 524–528]     

Role of P2Y1 receptor in astroglia‐to‐neuron signaling at dorsal spinal cord

Several studies have shown that astrocytes release neurotransmitters into the extracellular space that may then activate receptors on nearby neurons. In the present study, the actions of adenosine 5′‐O‐(2‐thiodiphosphate) (ADPbetaS)‐activated astrocyte conditioned medium (ADPbetaS‐ACM) on cultured dorsal spinal cord neurons were evaluated by using confocal laser scanning microscopy and whole‐cell patch‐clamp recording. ADPbetaS caused astrocytic glutamate efflux (43 μM), which in turn induced inward currents in dorsal horn neurons with short time in culture. The inward currents were abolished by 2‐amino‐5‐phosphonlanoicacid (AP‐5; NMDAR antagonist) plus 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX; non‐NMDAR antagonist) but were unaffected by MRS2179 (selective P2Y₁ receptor antagonist). Furthermore, N6‐methyl‐2′‐deoxyadenosine‐3′,5′‐bisphosphate (MRS2179) was used to block glutamate release from astrocytes. As a result, ADPbetaS‐ ACM‐induced inward currents in neurons were significantly blocked. On the other hand, both NMDAR and non‐NMDAR were involved in ADPbetaS‐ACM (concentration was diluted to one‐tenth)‐evoked small [Ca²⁺]_i transients in neurons. Under this condition, the values of glutamate concentrations in the medium are close to values for extracellular glutamate concentrations under physiological conditions. For this reason, it is possible that astrocyte‐derived glutamate is important for distant neuron under physiological conditions at dorsal spinal cord. These observations indicate that astrocytic P2Y₁ receptor activation triggered glutamate efflux, which acts on distant neurons to elevate calcium levels or acts on nearby neurons to evoke inward current. Finally, our results support the conclusion that the astrocytic P2Y₁ receptor plays an important role in bidirectional communication between astrocytes and neurons. © 2009 Wiley‐Liss, Inc.     

Simultaneous efflux of endogenous D‐ser and L‐glu from single acute hippocampus slices during oxygen glucose deprivation

D‐serine and L‐glutamate play crucial roles in excitotoxicity through N‐methyl‐D‐aspartate receptor coactivation, but little is known about the temporal profile of efflux during cerebral ischemia. We utilized a newly designed brain slice microperfusion device coupled offline to capillary electrophoresis laser‐induced fluorescence to monitor dynamic efflux of endogenous D‐ser and L‐glu in response to oxygen glucose deprivation (OGD) in single acute hippocampus slices. Efflux profiles with 2‐min temporal resolution in response to 24‐min OGD show that efflux of D‐ser slightly precedes efflux of L‐glu by one 2‐min sampling interval. Thus both coagonists are available to activate NMDA receptors by the time when glu is released. The magnitude of D‐ser efflux relative to baseline values is, however, less than that for L‐glu. Peak efflux during OGD, expressed as pre‐OGD baseline values, was as follows: D‐ser 254% ± 24%, L‐glu 1,675% ± 259%, L‐asp 519% ± 128%, and L‐thr 313% ± 33%. L‐glutamine efflux was shown to decrease significantly in response to OGD. The microperfusion/CE‐LIF approach shows several promising attributes for studying endogenous chemical efflux from single, acute brain slices. © 2009 Wiley‐Liss, Inc.     

Cytomegalovirus infection inhibits the expression of N-methyl-d-aspartate receptors in the developing mouse hippocampus and primary neuronal cultures

Cytomegalovirus (CMV) is the most significant infectious cause of developmental brain disorders in humans. The infection occasionally persists and causes neurological disorders. The N-methyl-d-aspartate (NMDA) subtype of glutamate receptors is essential for the development and plasticity of synapses, but also is involved in neuronal excitotoxicity during viral infection. Here we investigated the effects of murine CMV (MCMV) infection on the expression of NMDA receptors in the hippocampal neurons of neonatal mice and primary neuronal cultures. Viral antigen was mostly found in hippocampal pyramidal neurons from the CA1 to CA3. Image analysis of immunohistochemistry demonstrated that the expression of NMDA receptor subunit 1 (NMDA-R1) protein in CA1 neurons of MCMV-infected brain was reduced to 40% of that in uninfected brain. The signal of in situ hybridization for NMDA-R1 mRNA was also decreased in CA1 neurons of MCMV-infected brain. In primary neuronal cultures, reduction of NMDA-R1 expression in MCMV-infected neurons was also detected by immunocytochemistry and Western blotting. These results suggest that reduction of NMDA receptor expression by MCMV infection may cause a decrease in the susceptibility of the neurons to excitotoxic cell death, and may be related to the establishment of viral persistence and functional disturbances in MCMV-infected neurons.     

D‐Serine metabolism in C6 glioma cells: Involvement of alanine‐serine‐cysteine transporter (ASCT2) and serine racemase (SRR) but not D‐amino acid oxidase (DAO)

D‐serine is an endogenous N‐methyl‐D‐aspartate (NMDA) receptor coagonist. It is synthesized from L‐serine by serine racemase (SRR), but many aspects of its metabolism remain unclear, especially in the forebrain, which lacks active D‐amino acid oxidase (DAO), the major D‐serine degradative enzyme. Candidate mechanisms include SRR operating in α,β‐eliminase mode (converting D‐serine to pyruvate) and regulation by serine transport, in which the alanine‐serine‐cysteine transporter ASCT2 is implicated. Here we report studies in C6 glioma cells, which “simulate” the forebrain, in that the cells express SRR and ASCT2 but lack DAO activity. We measured D‐serine, ASCT2, SRR, and DAO expression and DAO activity in two situations: after incubation of cells for 48 hr with serine isomers and after increased or decreased SRR expression by transfection and RNA interference, respectively. Incubation with serine enantiomers decreased [³H]D‐serine uptake and ASCT2 mRNA and increased SRR immunoreactivity but did not alter DAO immunoreactivity, and DAO activity remained undetectable. SRR overexpression increased D‐serine and pyruvate and decreased [³H]D‐serine uptake and ASCT2 mRNA but did not affect DAO. SRR knockdown did not alter any of the parameters. Our data suggest that D‐serine transport mediated by ASCT2 contributes prominently to D‐serine homeostasis when DAO activity is absent. The factors regulating D‐serine are important for understanding normal NMDA receptor function and because D‐serine, along with DAO and SRR, is implicated in the pathogenesis and treatment of schizophrenia. © 2010 Wiley‐Liss, Inc.     

Effects of asenapine on prefrontal N‐methyl‐D‐aspartate receptor‐mediated transmission: Involvement of dopamine D1 receptors

Asenapine is a novel psychopharmacologic agent being developed for schizophrenia and bipolar disorder. Like clozapine, asenapine facilitates cortical dopaminergic and N‐methyl‐D ‐aspartate (NMDA) receptor‐mediated transmission in rats. The facilitation of NMDA‐induced currents in cortical pyramidal cells by clozapine is dependent on dopamine and D₁ receptor activation. Moreover, previous results show that clozapine prevents and reverses the blockade of NMDA‐induced currents and firing activity in the pyramidal cells by the noncompetitive NMDA receptor antagonist phencyclidine (PCP). Here, we investigated the effects of asenapine in these regards using intracellular electrophysiological recording in vitro. Asenapine (5 nM) significantly facilitated NMDA‐induced currents (162 ± 15% of control) in pyramidal cells of the medial prefrontal cortex (mPFC). The asenapine‐induced facilitation was blocked by the D₁ receptor antagonist SCH23390 (1 μM). Furthermore, the PCP‐induced blockade of cortical NMDA‐induced currents was effectively reversed by 5 nM asenapine. Our results demonstrate a clozapine‐like facilitation of cortical NMDA‐induced currents by asenapine that involves prefrontal dopamine and activation of D₁ receptors. Asenapine and clozapine also share the ability to reverse functional PCP‐induced hypoactivity of cortical NMDA receptors. The ability of asenapine to increase both cortical dopaminergic and NMDA receptor‐mediated glutamatergic transmission suggests that this drug may have an advantageous effect not only on positive symptoms in patients with schizophrenia, but also on negative and cognitive symptoms. Synapse 64:870–874, 2010. © 2010 Wiley‐Liss, Inc.     

The glycine transporter GlyT1 controls N‐methyl‐D‐aspartic acid receptor coagonist occupancy in the mouse retina

We examined the role of GlyT1, the high‐affinity glycine transporter, in the mouse retina with an emphasis on the role of glycine as a coagonist of N‐methyl‐D‐aspartic acid (NMDA) receptors. We pursued this objective by studying heterozygote mice deficient in the GlyT1 transporter (GlyT1^?/+) and compared those results with wild‐type (WT) littermate controls (GlyT1^+/+). Capillary electrophoresis was used to separate and quantitatively measure glycine release from isolated retina preparations; pharmacologically blocking GlyT1 with N‐[3‐([1,1‐biphenyl]‐4‐yloxy)‐3‐(4‐fluorophenyl)propyl]‐N‐methylglycine in the WT retina generated a significantly larger accumulation of glycine into the bathing environment when compared with the GlyT1^?/+ retinas. The relative occupancy state of the NMDA receptor coagonist sites was tested using whole‐cell recordings from ganglion cells while bath applying D‐serine or D‐serine + NMDA. The interpretation of these studies was simplified by blocking post‐synaptic inhibition with picrotoxinin and strychnine. NMDA receptor coagonist sites were more saturated and less enhanced by D‐serine in the GlyT1^?/+ mice compared with the WT controls. Immunoblots of NMDA receptor subunits (NR1, NR2A and NR2B) in WT and GlyT1^?/+ animals showed that the NR1 subunits were identical. These observations are discussed in view of contemporary issues about NMDA receptor coagonist function in the vertebrate retina and the role of glycine vs. D‐serine as the endogenous coagonist.     

N‐methyl‐D‐aspartate receptor antibodies in post–herpes simplex virus encephalitis neurological relapse

Herpes simplex virus encephalitis (HSVE) is a devastating condition that relapses, often with a chorea in children, despite adequate antiviral treatment. At relapse, evidence of viral replication is frequently absent, suggesting that the relapse may be immune‐mediated. Seven children who had a neurological relapse following their initial encephalitis, identified from 20 cases of pediatric HSVE, were studied. Serum and/or cerebrospinal fluid (CSF) were tested for N‐methyl‐D‐aspartate receptor (NMDAR) and other antibodies previously reported in central nervous system autoimmunity. Five of the 7 relapsing children had choreoathetosis; 2 of these were NMDAR antibody–positive, 2 were negative (1 with HSV‐positive CSF), and 1 was not available for testing. An additional patient, who relapsed with cognitive regression but with no movement disorder, was also NMDAR antibody–positive. In 2 of the NMDAR antibody–positive patients who were treated at relapse and in 1 who was treated only after 10 years of having a relapsing encephalopathy, a beneficial response was observed. Neurological relapses after HSVE may frequently be immune‐mediated, particularly in children with chorea. NMDAR antibodies are common, and immunotherapy may be beneficial. © 2013 International Parkinson and Movement Disorder Society     

Inhibition of glutamate uptake induces progressive accumulation of extracellular glutamate and neuronal damage in rat cortical cultures

It is known that neurons exposed to high concentrations of glutamate degenerate and die. The clearance of this amino acid from the extracellular space depends on their active transport by Na⁺-dependent high-affinity carriers. In the present study we tested whether inhibition of glutamate transport in mixed glial/neuronal cortical cultures induces accumulation of extracellular glutamate and whether such increase results in cell damage. Three inhibitors of glutamate transport were used: L-trans-pyrrolidine-2,4-dicarboxylate (PDC), DL-threo-β-hydroxyaspartate (THA), and dihydrokainate (DHK). Cell damage was assessed by light microscopy observations, reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, and leakage of lactate dehydrogenase. PDC induced a significant concentration- and time-dependent neuronal damage, whereas pure glial cultures were not affected. A good correlation was found between this damage and elevations of glutamate concentration in the medium. These effects of PDC were similar in glutamine-free medium and in medium supplemented with glutamine. THA induced identical cell damage and elevations of extracellular glutamate to those produced by PDC, while DHK did not affect at all any of these parameters. PDC- and THA-induced toxicity was protected by the N-methyl-D-aspartate receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo-(a,d)cyclohepten-5,10-imine maleate but not by the non-N-methyl-D-aspartate receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline. © 1996 Wiley-Liss, Inc.     

Neonatal mouse cortical but not isogenic human astrocyte feeder layers enhance the functional maturation of induced pluripotent stem cell‐derived neurons in culture

Human induced pluripotent stem (iPS) cell‐derived neurons and astrocytes are attractive cellular tools for nervous system disease modeling and drug screening. Optimal utilization of these tools requires differentiation protocols that efficiently generate functional cell phenotypes in vitro. As nervous system function is dependent on networked neuronal activity involving both neuronal and astrocytic synaptic functions, we examined astrocyte effects on the functional maturation of neurons from human iPS cell‐derived neural stem cells (NSCs). We first demonstrate human iPS cell‐derived NSCs can be rapidly differentiated in culture to either neurons or astrocytes with characteristic cellular, molecular and physiological features. Although differentiated neurons were capable of firing multiple action potentials (APs), few cells developed spontaneous electrical activity in culture. We show spontaneous electrical activity was significantly increased by neuronal differentiation of human NSCs on feeder layers of neonatal mouse cortical astrocytes. In contrast, co‐culture on feeder layers of isogenic human iPS cell‐derived astrocytes had no positive effect on spontaneous neuronal activity. Spontaneous electrical activity was dependent on glutamate receptor‐channel function and occurred without changes in I_Na, I_K, V_m, and AP properties of iPS cell‐derived neurons. These data demonstrate co‐culture with neonatal mouse cortical astrocytes but not human isogenic iPS cell‐derived astrocytes stimulates glutamatergic synaptic transmission between iPS cell‐derived neurons in culture. We present RNA‐sequencing data for an immature, fetal‐like status of our human iPS cell‐derived astrocytes as one possible explanation for their failure to enhance synaptic activity in our co‐culture system.     

Measurement of glycine binding site of N-methyl-D-asparate receptors in living human brain using 4-acetoxy derivative of L-703,717, 4-acetoxy-7-chloro-3-[3-(4-[11c] methoxybenzyl) phenyl]-2(1H)-quinolone (AcL703) with positron emission tomography

N-methyl-D-aspartate (NMDA) receptors are of major interest in brain functions and neuropsychiatric disorders. However, at present there are few suitable radioligands for in vivo imaging of NMDA receptors. 7-choloro-4-hydroxy-3-[3-(4-methoxybenzyl) phenyl]-2(1H)-quinolone (L-703,717) is one of the potent ligands for the glycine-binding site of NMDA receptors. 4-Acetoxy derivative of L-703,717 (AcL703) is a candidate, as a positron emission tomography (PET) ligand for NMDA receptors, because of its better permeability at the blood-brain barrier compared with L-703,717. After intravenous injection of 624-851 MBq of [11C]AcL703, dynamic PET scan was performed on six healthy males for 90 min. Regions-of-interest were located on the cerebral cortices, cerebellar cortex, and cerebral white matter. The binding potential (BP) was calculated from the ratio of the area under the curve (AUC) of radioactivities from 40 to 90 min in the target region to that in white matter. Regional radioactivities reached close to equilibrium in all regions after about 40 min postinjection. Regional brain uptake of [11C]AcL703 at 40 min after injection was 0.00028-0.00065% of the injected dose/milliliter. Radioactivity concentration of [11C]AcL703 was highest in the cerebellar cortex and lowest in white matter. AUC in the cerebellar cortex was higher than those of cerebral cortices, thalamus, striatum, and white matter. BP in the cerebellar cortex was twofold higher than in the cerebral cortices (cerebellar cortex: BP=2.20+/-0.72; cerebral cortices: BP=1.05+/-0.45). Despite the low brain uptake of [11C]AcL703, regional distributions were in good agreement with our previous studies of rodents. This indicates the possibility of in vivo evaluation of NMDA receptors using PET with [11C]AcL703 in living human brain.     

Roles of AEG‐1 in CNS neurons and astrocytes during noncancerous processes

Since its initial identification, Astrocyte Elevated Gene‐1 (AEG‐1 ) has been recognized as a “star” gene detected in most of the analyzed cancers; AEG‐1 can interact with signaling transduction molecules, such as PI3K/Akt and MAPK, to affect the function and viability of cells. Furthermore, its multiple other functions are also gradually being recognized. AEG‐1 participates in several biological processes, including embryonic development, glutamate excitotoxicity, inflammation, and endoplasmic reticulum stress. Most of the noncancerous roles of the AEG‐1 were identified in studies of the neurological disorders of the CNS. As an oncogene that promotes aberrant cellular processes within the CNS, AEG‐1 may also represent an important therapeutic target for the treatment of neurological disease. However, the exact role of the AEG‐1 in CNS under normal conditions is still unknown. This review will focus on the literature describing the role of this molecule in CNS neurons and astrocytes during noncancerous processes. © 2017 Wiley Periodicals, Inc.