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Summary: Regeneration of diesel particulate filter (DPF) is a complicated process due to its high operating temperature and associated oxidation of soot on the filter substrate. Several oxidation mechanisms of diesel soot have been proposed based on reaction kinetics, but more information about the oxidation phenomena is needed in a practical system, that is, soot oxidation on a DPF substrate. In this work, the DPF regeneration process was, for the first time, visualized at the particle scale ex‐situ, in time‐lapse series, using field emission scanning electron microscopy (FE‐SEM). Time‐lapse transformation of soot cake layer on a real DPF was followed from initiation through the complete regeneration process. In parallel, transformation of the soot primary particle diameter was directly measured using high‐resolution transmission electron microscopy. FE‐SEM visualization clearly showed shrinkage of the soot cake layer on the DPF wall as oxidation progressed. Furthermore, diameter distribution analysis revealed a trend of shrinkage of the nanoscale soot primary particles during oxidation, supporting the FE‐SEM observations of the micron‐scale shrinkage of the agglomerated soot cake layer. Fragmentation of the shrunken soot cake layer was also observed and is suspected to be a result of locally higher gas flow that depends on surface pore morphology of the filter substrate. Lay Description: In this work, the DPF regeneration process was, for the first time, visualized at the particle scale ex‐situ, in time‐lapse series, using field emission scanning electron microscopy (FE‐SEM). Time‐lapse transformation of soot cake layer on a real DPF was followed from initiation through the complete regeneration process. In parallel, transformation of the soot primary particle diameter was directly measured using high resolution transmission electron microscopy. FE‐SEM visualization clearly showed shrinkage of the soot cake layer on the DPF wall as oxidation progressed. Furthermore, diameter distribution analysis revealed a trend of shrinkage of the nano‐scaled soot primary particles during oxidation, supporting the FE‐SEM observations of the shrinkage of the micron‐scale agglomerated soot cake layer. Fragmentation of the shrunken soot cake layer was also observed and is suspected to be a result of locally higher gas flow that depends on surface pore morphology of the filter substrate. Further detail mechanism about transformations of the soot cake layer was additionally discussed based on electrostatic attraction. [ABSTRACT FROM AUTHOR]

Particulate matter trapping and regeneration processes in wall-flow diesel particulate filters (DPFs) without catalysts were investigated through micro- and macroscopic visualization experiment. The vertical walls of a small DPF were polished using a lapping process to create a mirror-like surface on each ceramic particle grain. Using an all-in-focus optical microscope, micro-scale flow pores inside the DPF wall could be clearly observed from the polished surface to a depth of 100 mm. Furthermore, a real-time video with a speed of 30 frames per second could be sharply recorded. Through the microscopic cross-sectional view, transition from depth filtration to surface filtration could be observed clearly. Only surface pores opened on the wall surface were related to the filtration depth, i.e. the penetration depth. During regeneration of the DPF without catalyst, after a particulate (soot) cake was burnt out, the particulates trapped inside the surface pores were oxidized. On the other hand, using a half- cylindrical-shaped, wall-flow DPF, the overall trapping phenomena and regeneration process were clarified through a long-distance focusing lens camera. Diesel particulates were trapped almost uniformly over the entire surface of an inflow channel of the DPF in the direction of the channel flow, while the trapped particulates were not necessarily oxidized uniformly since there was a large temperature difference between the inlet and the outlet of the flow channel. The regeneration patterns were strongly dependent on the initial particulate mass and the inlet temperature of the working gas, including the microscopic phenomena in each location. Consequently, microscopic surface pores played a significant role in the regeneration process as well as in the beginning of trapping. Furthermore, at a macroscopic level, a uniform temperature and wall-flow distributions were found to be significant for quick regeneration. [ABSTRACT FROM AUTHOR]

Distribution of oxygen isotope 18O concentration which was labeled in lanthanum strontium manganese (LSM) – yttria-stabilized zirconia (YSZ) cathode of a solid oxide fuel cell (SOFC) is predicted through numerical simulations using a three-dimensional microstructure which was reconstructed by a focused ion beam-scanning electron microscopy (FIB-SEM). The electrochemical reaction under the SOFC operation is first numerically simulated, then the unsteady 18O transport is simulated by coupling self-diffusion by concentration gradient, migration by the electrochemical potential field, and electrochemical reaction at the triple phase boundaries. Predicted results were compared with the measured 18O concentration by a secondary ion mass spectrometry taken at the intermediate plane of the reconstructed 3D microstructure, which showed qualitative consistency between them. Thus, from the direct correlation of the electrochemical reaction and 18O concentration in an actual electrode microstructure, influence of electrochemical reaction was discussed. The present approach provides useful information for the interpretation of the oxygen labeling experiment results, which can cultivate better understanding of the electrochemical reaction mechanism in the SOFC electrodes. • Three-dimensional 18O distribution in LSM-YSZ under operation is simulated. • The simulated 18O distributions are compared to the local experimental data. • Inhomogeneous 18O concentration is induced by local electrochemical reactions. • The incorporation of 18O into LSM under polarization is reproduced. [ABSTRACT FROM AUTHOR]

Global positioning system (GPS) data loggers are commonly used to track the movements and distribution of both wild and domestic animals. However, the expense often poses a challenge for researchers. Recently, there has been a rise in the utilization of affordable and user-friendly GPS data loggers for tracking animal movements, albeit with compromised accuracy. We aimed to identify factors influencing the accuracy of a low-cost GPS data logger (I-gotU GT-600) and to enhance its location accuracy. Initial investigations revealed that recording intervals impacted the location error of the GPS data logger. To elucidate the relationship between recording intervals and location accuracy, we conducted stationary and motion tests. Our findings indicated that recording intervals of less than 15 sec substantially enhances the location accuracy of the low-cost GPS data logger. Our results highlight the relationship between the fix schedule and location accuracy for these GPS data loggers. Our study provides information that enhances the quality of data for researchers using low-cost GPS data loggers for short-term studies in various settings, such as zoos and livestock facilities.

Nedd4-2 is an E3 ubiquitin ligase in which missense mutation is related to familial epilepsy, indicating its critical role in regulating neuronal network activity. However, Nedd4-2 substrates involved in neuronal network function have yet to be identified. Using mouse lines lacking Nedd4-1 and Nedd4-2, we identified astrocytic channel proteins inwardly rectifying K+ channel 4.1 (Kir4.1) and Connexin43 as Nedd4-2 substrates. We found that the expression of Kir4.1 and Connexin43 is increased upon conditional deletion of Nedd4-2 in astrocytes, leading to an elevation of astrocytic membrane ion permeability and gap junction activity, with a consequent reduction of γ-oscillatory neuronal network activity. Interestingly, our biochemical data demonstrate that missense mutations found in familial epileptic patients produce gain-of-function of the Nedd4-2 gene product. Our data reveal a process of coordinated astrocytic ion channel proteostasis that controls astrocyte function and astrocyte-dependent neuronal network activity and elucidate a potential mechanism by which aberrant Nedd4-2 function leads to epilepsy., (© 2023 Altas et al.)

Methotrexate (MTX) is an anti-metabolite that has been used for the treatment of patients of acute lymphocytic leukemia or non-Hodgikin lymphoma for decades. In some cases, MTX-treated patients suffer from neurological side effects, including seizures and cognitive dysfunctions. While most patients are at developmental stages, information of the mechanisms of the side effects of MTX treatment on the developing neurons has been limited. Neurons develop in five steps in the human brain: neurogenesis, polarity formation, dendrite and axon development, synapse formation, and neuronal death. Except for neurogenesis, these processes can be recapitulated in the primary culture system of cortical neurons. Using primary cultured cortical neurons, we studied the impact of MTX treatment on dendrite development, synapse formation, and neuronal death in the present report. MTX treatment impaired neuronal survival, dendrite development, and synapse formation. Interestingly, half maximal effective concentrations (EC 50 s) of MTX for all three processes are at the similar range and lower than the MTX concentration in the cerebrospinal fluid in treated patients. Our results provide possible mechanisms of neurological side effects in treated patients., (© 2023 Molecular Biology Society of Japan and John Wiley & Sons Australia, Ltd.)

A granular substrate used as a support for a three-way catalyzed (TWC) solid-particle membrane filter was investigated through numerical simulation. The proposed support could reduce the amount of required catalyst material by 39% and lower the pressure drop by 33%, compared to a conventional filter, while achieving almost 100% soot-filtration. Moreover, TWC porous particles, which are designed to introduce a fluid flow into their interconnected pore network, further decrease the pressure drop. However, a trade-off exists between the amount of the introduced fluid flow and the specific surface area.

Kaufman oculocerebrofacial syndrome (KOS) is an autosomal recessive developmental disorder. Inactivating mutations in UBE3B, an E3 ubiquitin ligase gene are causative for KOS. We have reported that towards postnatal week three, its murine ortholog, Ube3b, acts as a negative regulator of the number of dendritic spines. In this study, we investigated the role of Ube3b at the synapse in the young adult mice. With an improved estimation method, images from the hippocampal CA1 and CA2 regions acquired with 3D Stimulated Emission Depletion (3D-STED) microscopy were used to quantify the excitatory synapse numbers. In the young adult mice, the excitatory synapse density was decreased in brain-specific Ube3b conditional knockout mice as compared to the control. Our results indicate the novel role of Ube3b in the maintenance of synapse numbers in the young adult period., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Morphologically dynamic dendritic spines are the major sites of neuronal plasticity in the brain; however, the molecular mechanisms underlying their morphological dynamics have not been fully elucidated. Phldb2 is a protein that contains two predicted coiled-coil domains and the pleckstrin homology domain, whose binding is highly sensitive to PIP 3 . We have previously demonstrated that Phldb2 regulates synaptic plasticity, glutamate receptor trafficking, and PSD-95 turnover. Drebrin is one of the most abundant neuron-specific F-actin-binding proteins that are pivotal for synaptic morphology and plasticity. We observed that Phldb2 bound to drebrin A (adult-type drebrin), but not to drebrin E (embryonic-type drebrin). In the absence of Phldb2, the subcellular localization of drebrin A in the hippocampal spines and its distribution in the hippocampus were altered. Immature spines, such as the filopodium type, increased relatively in the CA1 regions of the hippocampus, whereas mushroom spines, a typical mature type, decreased in Phldb2 -/- mice. Phldb2 suppressed the formation of an abnormal filopodium structure induced by drebrin A overexpression. Taken together, these findings demonstrate that Phldb2 is pivotal for dendritic spine morphology and possibly for synaptic plasticity in mature animals by regulating drebrin A localization., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could influence the work reported in this study., (Copyright © 2022 Japan Neuroscience Society and Elsevier Ltd. All rights reserved.)

The chemical synapse is one type of cell-adhesion system that transmits information from a neuron to another neuron in the complex neuronal network in the brain. Synaptic transmission is the rate-limiting step during the information processing in the neuronal network and its plasticity is involved in cognitive functions. Thus, morphological and electrophysiological analyses of synapses are of particular importance in neuroscience research. In the current study, we applied super-resolved three-dimensional stimulated emission depletion (3D-STED) microscopy for the morphological analyses of synapses. This approach allowed us to estimate the precise number of excitatory and inhibitory synapses in the mouse hippocampal tissue. We discovered a region-specific increase in excitatory synapses in a model mouse of autism spectrum disorder, Neuroligin-3 KO, with this method. This type of analysis will open a new field in developmental neuroscience in the future., (Copyright © 2021 Elsevier Inc. All rights reserved.)

With new and advanced technology, human exploration has reached outside of the Earth's boundaries. There are plans for reaching Mars and the satellites of Jupiter and Saturn, and even to build a permanent base on the Moon. However, human beings have evolved on Earth with levels of gravity and radiation that are very different from those that we have to face in space. These issues seem to pose a significant limitation on exploration. Although there are plausible solutions for problems related to the lack of gravity, it is still unclear how to address the radiation problem. Several solutions have been proposed, such as passive or active shielding or the use of specific drugs that could reduce the effects of radiation. Recently, a method that reproduces a mechanism similar to hibernation or torpor, known as synthetic torpor, has started to become possible. Several studies show that hibernators are resistant to acute high-dose-rate radiation exposure. However, the underlying mechanism of how this occurs remains unclear, and further investigation is needed. Whether synthetic hibernation will also protect from the deleterious effects of chronic low-dose-rate radiation exposure is currently unknown. Hibernators can modulate their neuronal firing, adjust their cardiovascular function, regulate their body temperature, preserve their muscles during prolonged inactivity, regulate their immune system, and most importantly, increase their radioresistance during the inactive period. According to recent studies, synthetic hibernation, just like natural hibernation, could mitigate radiation-induced toxicity. In this review, we see what artificial hibernation is and how it could help the next generation of astronauts in future interplanetary missions.

Physical characteristics and quantitative elemental composition of PM and residual ash produced from sugarcane leaves (SCL) combustion were investigated using TEM-EDS compared with forest leaves (FRL). SEM-EDS was used to analyze the microstructure and chemical composition of biomass raw leaves and PM. XRD analysis was also performed to investigate the characterization of the crystalline nanostructure, structure of PM, and residual ash compared to the TEM image processing method. The oxidation kinetics of biomass raw materials, PM, and residual ash were investigated by TGA. The morphology of fine and ultrafine agglomerate structure of SCL soot and residual ash are not significantly different from the FRL soot and residual ash. The average diameter sizes of single primary nanoparticles of SCL and FRL soot are approximately 37 nm and 35 nm, while the sizes of residual ash are about 18 nm and 22 nm, respectively. The single primary nanoparticles of soot are mainly composed of curve line crystallites of carbon fringes, while residual ash is composed of straight-line lattice fringes. The average fringe lengths of SCL and FRL soot are about 1.25 nm and 1.04 nm from the outer shell and 0.89 nm and 0.74 nm from the inner core. The interlayer spacing of curve line carbon fringes of SCL and FRL soot is approximately 0.359 nm and 0.362 nm by the TEM image analysis and it was matched with XRD analysis. The biomass PMs are mainly composed of soot, Si, Ca, and K compounds: SiO 2 , CaCO 3 , and KCl., (Copyright © 2020. Published by Elsevier B.V.)

Spectral absorptance of a metal-semiconductor-metal (MSM) thin-multilayer structured thermo-photovoltaic cell was experimentally investigated. A MSM consists of a thin GaSb-semiconductor sandwiched between a top fishnet-type electrode and a flat backside electrode made of gold. A thin GaSb layer was grown on a substrate made of InAs using molecular beam epitaxy, and then all of the InAs substrate was removed using wet etching. The GaSb film was bonded on a surface of gold, which was sputtered on a Si substrate, using a van der Waals bonding method. The top fishnet-type electrode was made using electron beam lithography and a lift-off process. In the case of a 115 nm thick GaSb layer and a square fishnet aperture of a 300 nm × 310 nm size, the spectral absorptance of MSM reached a local peak (95%) at a wavelength of 1.66 µm, which is similar to spectra predicted by numerical simulation. Moreover, the equivalent resonance cavity model and LC circuit model functioned well to indicate the wavelength of several distinct peaks of absorptance.

Abnormal metabotropic glutamate receptor (mGluR) activity could cause brain disorders; however, its regulation has not yet been fully understood. Here, we report that protein kinase N1 (PKN1), a protein kinase expressed predominantly in neurons in the brain, normalizes group 1 mGluR function by upregulating a neuronal glutamate transporter, excitatory amino acid transporter 3 (EAAT3), and supports silent synapse activation. Knocking out PKN1a, the dominant PKN1 subtype in the brain, unmasked abnormal input-nonspecific mGluR-dependent long-term depression (mGluR-LTD) and AMPA receptor (AMPAR) silencing in the developing hippocampus. mGluR-LTD was mimicked by inhibiting glutamate transporters in wild-type mice. Knocking out PKN1a decreased hippocampal EAAT3 expression and PKN1 inhibition reduced glutamate uptake through EAAT3. Also, synaptic transmission was immature; there were more silent synapses and fewer spines with shorter postsynaptic densities in PKN1a knockout mice than in wild-type mice. Thus, PKN1 plays a critical role in regulation of synaptic maturation by upregulating EAAT3 expression.

Soybean isoflavones, such as genistein, daidzein, and its metabolite, S-equol, are widely known as phytoestrogens. Their biological actions are thought to be exerted via the estrogen signal transduction pathway. Estrogens, such as 17β-estradiol (E2), play a crucial role in the development and functional maintenance of the central nervous system. E2 bind to the nuclear estrogen receptor (ER) and regulates morphogenesis, migration, functional maturation, and intracellular metabolism of neurons and glial cells. In addition to binding to nuclear ER, E2 also binds to the G-protein-coupled estrogen receptor (GPER) and activates the nongenomic estrogen signaling pathway. Soybean isoflavones also bind to the ER and GPER. However, the effect of soybean isoflavone on brain development, particularly glial cell function, remains unclear. We examined the effects of soybean isoflavones using an astrocyte-enriched culture and astrocyte-derived C6 clonal cells. Isoflavones increased glial cell migration. This augmentation was suppressed by co-exposure with G15, a selective GPER antagonist, or knockdown of GPER expression using RNA interference. Isoflavones also activated actin cytoskeleton arrangement via increased actin polymerization and cortical actin, resulting in an increased number and length of filopodia. Isoflavones exposure increased the phosphorylation levels of FAK (Tyr397 and Tyr576/577), ERK1/2 (Thr202/Tyr204), Akt (Ser473), and Rac1/cdc42 (Ser71), and the expression levels of cortactin, paxillin and ERα. These effects were suppressed by knockdown of the GPER. Co-exposure of isoflavones to the selective RhoA inhibitor, rhosin, selective Cdc42 inhibitor, casin, or Rac1/Cdc42 inhibitor, ML-141, decreased the effects of isoflavones on cell migration. These findings indicate that soybean isoflavones exert their action via the GPER to activate the PI3K/FAK/Akt/RhoA/Rac1/Cdc42 signaling pathway, resulting in increased glial cell migration. Furthermore, in silico molecular docking studies to examine the binding mode of isoflavones to the GPER revealed the possibility that isoflavones bind directly to the GPER at the same position as E2, further confirming that the effects of the isoflavones are at least in part exerted via the GPER signal transduction pathway. The findings of the present study indicate that isoflavones may be an effective supplement to promote astrocyte migration in developing and/or injured adult brains., (Copyright © 2020 Ariyani, Miyazaki, Amano, Hanamura, Shirao and Koibuchi.)

Objective: Drebrins are crucial for synaptic function and dendritic spine development, remodeling, and maintenance. In temporal lobe epilepsy (TLE) patients, a significant hippocampal synaptic reorganization occurs, and synaptic reorganization has been associated with hippocampal hyperexcitability. This study aimed to evaluate, in TLE patients, the hippocampal expression of drebrin using immunohistochemistry with DAS2 or M2F6 antibodies that recognize adult (drebrin A) or adult and embryonic (pan-drebrin) isoforms, respectively., Methods: Hippocampal sections from drug-resistant TLE patients with hippocampal sclerosis (HS; TLE, n = 33), of whom 31 presented with type 1 HS and two with type 2 HS, and autopsy control cases (n = 20) were assayed by immunohistochemistry and evaluated for neuron density, and drebrin A and pan-drebrin expression. Double-labeling immunofluorescences were performed to localize drebrin A-positive spines in dendrites (MAP2), and to evaluate whether drebrin colocalizes with inhibitory (GAD65) and excitatory (VGlut1) presynaptic markers., Results: Compared to controls, TLE patients had increased pan-drebrin in all hippocampal subfields and increased drebrin A-immunopositive area in all hippocampal subfields but CA1. Drebrin-positive spine density followed the same pattern as total drebrin quantification. Confocal microscopy indicated juxtaposition of drebrin-positive spines with VGlut1-positive puncta, but not with GAD65-positive puncta. Drebrin expression in the dentate gyrus of TLE cases was associated negatively with seizure frequency and positively with verbal memory. TLE patients with lower drebrin-immunopositive area in inner molecular layer (IML) than in outer molecular layer (OML) had a lower seizure frequency than those with higher or comparable drebrin-immunopositive area in IML compared with OML., Significance: Our results suggest that changes in drebrin-positive spines and drebrin expression in the dentate gyrus of TLE patients are associated with lower seizure frequency, more preserved verbal memory, and a better postsurgical outcome., (© 2020 International League Against Epilepsy.)

Introduction: Detection of drug effects on neuronal synapses is important for predicting their adverse effects. We have used drebrin as a marker to detect the synaptic changes in cultured neurons. High concentration of glutamate decreases the amount of drebrin in synapses. To increase the availability of this method for high throughput analysis, we applied the drebrin-based evaluation of synapses to high-content imaging analysis using microplates., Methods: Three weeks old cultured neurons were fixed and processed for immunocytochemistry to visualize drebrin clusters, dendrites and neuronal cell bodies. After automated image acquisition, total number of drebrin clusters per fields, linear density of drebrin cluster along dendrites, dendrite length and neuron number were automatically measured by a custom-designed protocol., Results: Automated image acquisition and analysis showed that dendrite length and drebrin cluster density along dendrites are measured consistently and reproducibly. In addition, application of 10-100 μM glutamate for 10 min or 0.5-50 μM latrunculin A for 5 min significantly decreased drebrin cluster density without affecting neuron number. These results were consistent with our previous results using manual image acquisition and analysis with regular fluorescence microscope and image analysis software. Furthermore, 0.3 or 1.0 μM staurosporine for 24 h significantly decreased neuron number., Discussion: The present study demonstrates that this high-throughput imaging analysis of drebrin cluster density along dendrites for detecting the effects of substances on synapses is sensitive enough to detect the effects of glutamate receptor activation and latrunculin A treatment, and indicates that this analysis will be useful for safety pharmacology study., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Introduction: In recent years, new psychoactive substances (NPS) have been widely distributed for abuse purposes. Effective measures to counter the spread of NPS are to promptly legislate them through the risk assessment. Phencyclidine analogues having inhibitory effects toward NMDA receptor (NMDAR) have recently emerged in Japan. Therefore, it is important to establish a high-throughput system for efficiently detecting NPS that can inhibit NMDAR activity., Methods: Hippocampal neurons prepared from embryonic rats were incubated in 96-well microplates. After 3 weeks in vitro, cultured neurons were preincubated with phencyclidine (PCP) or PCP-analogues, including 3-methoxyphencyclidine (3-MeO-PCP) and 4-[1-(3-methoxyphenyl)cyclohexyl]morpholine (3-MeO-PCMo), and then treated with 100 μM glutamate for 10 min. After fixation, cultured neurons were immunostained with anti-drebrin and anti-MAP2 antibodies. The linear cluster density of drebrin along the dendrites was automatically quantified using a protocol that was originally developed by us., Results: The high-throughput immunocytochemical assay, measuring drebrin cluster density of cultured neurons, demonstrated that glutamate-induced reduction of drebrin cluster density in 96-well plates is competitively inhibited by NMDAR antagonist, APV. The reduction was also antagonized by PCP, 3-MeO-PCP and 3-MeO-PCMo. The inhibitory activity of 3-MeO-PCMo was lower than that of PCP or 3-MeO-PCP, with IC 50 values of 26.67 μM (3-MeO-PCMo), 2.02 μM (PCP) and 1.51 μM (3-MeO-PCP)., Discussion: The relative efficacy among PCP, 3-MeO-PCP and 3-MeO-PCMo calculated from IC 50 are similar to those from Ki values. This suggests that the high-throughput imaging analysis is useful to speculate the Ki values of new PCP analogues without performing the kinetic studies., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Drebrin is an actin-binding protein that is preferentially expressed in the brain. It is highly localized in dendritic spines and regulates spine shapes. The embryonic-type (drebrin E) is expressed in the embryonic and early postnatal brain and is replaced by the adult-type (drebrin A) during development. In parallel, NMDA receptor (NMDAR)-dependent long-term depression (LTD) of synaptic transmission, induced by low-frequency stimulation (LFS), is dominant in the immature brain and decreases during development. Here, we report that drebrin regulates NMDAR-dependent and group 1 metabotropic glutamate receptor (mGluR)-dependent LTD induction in the hippocampus. While LFS induced NMDAR-dependent LTD in the developing hippocampus in wild-type (WT) mice, it did not induce LTD in developing drebrin E and A double knockout (DXKO) mice, indicating that drebrin is required for NMDAR-dependent LTD. On the other hand, LFS induced robust LTD dependent on mGluR5, one of group 1 mGluRs, in both developing and adult brains of drebrin A knockout (DAKO) mice, in which drebrin E is expressed throughout development and adulthood. Agonist-induced mGluR-dependent LTD was normal in WT and DXKO mice; however, it was enhanced in DAKO mice. Also, mGluR1, another group 1 mGluR, was involved in agonist-induced mGluR-dependent LTD in DAKO mice. These data suggest that abnormal drebrin E expression in adults promotes group 1 mGluR-dependent LTD induction. Therefore, while drebrin expression is critical for NMDAR-dependent LTD induction, developmental conversion from drebrin E to drebrin A prevents robust group 1 mGluR-dependent LTD.

Dendritic spines have stable filamentous actin (F-actin) and dynamic F-actin. The formation of stable F-actin plays a pivotal role in spine formation. Drebrin binds to and stabilizes F-actin in dendritic spines. Interestingly, the conversion of the drebrin E isoform to drebrin A occurs in parallel with synapse formation, suggesting that this conversion promotes synapse formation via F-actin accumulation. In this study, we measured the dynamics of GFP-tagged drebrin E (GFP-DE) and drebrin A (GFP-DA) in cultured hippocampal neurons by fluorescence recovery after photobleaching analysis. We found that GFP-DA has a larger stable fraction than GFP-DE. The stable drebrin fraction reflects its accumulation in dendritic spines, therefore the isoform conversion may increase the amount of stable F-actin in dendritic spines. The stable fraction was dependent on the drebrin A-specific sequence "Ins2", located in the middle of the drebrin protein. In addition, F-actin depolymerization with latrunculin A significantly reduced the stable GFP-DA fraction. These findings indicate that preferential binding of drebrin A to F-actin than drebrin E causes higher stable fraction of drebrin A in dendritic spines, although the F-actin-binding ability of purified drebrin E and drebrin A are comparable. Therefore, we suggest that a drebrin isoform conversion from drebrin E to drebrin A in dendritic spines results in the accumulation of drebrin-bound stable F-actin, which plays a pivotal role in synapse formation., (Copyright © 2018. Published by Elsevier Ltd.)

Dendritic filopodia select synaptic partner axons by interviewing the cell surface of potential targets, but how filopodia decipher the complex pattern of adhesive and repulsive molecular cues to find appropriate contacts is unknown. Here, we demonstrate in cortical neurons that a single cue is sufficient for dendritic filopodia to reject or select specific axonal contacts for elaboration as synaptic sites. Super-resolution and live-cell imaging reveals that EphB2 is located in the tips of filopodia and at nascent synaptic sites. Surprisingly, a genetically encoded indicator of EphB kinase activity, unbiased classification, and a photoactivatable EphB2 reveal that simple differences in the kinetics of EphB kinase signaling at the tips of filopodia mediate the choice between retraction and synaptogenesis. This may enable individual filopodia to choose targets based on differences in the activation rate of a single tyrosine kinase, greatly simplifying the process of partner selection and suggesting a general principle., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Dendritic spines form typical excitatory synapses in the brain and their shapes vary depending on synaptic inputs. It has been suggested that the morphological changes of dendritic spines play an important role in synaptic plasticity. Dendritic spines contain a high concentration of actin, which has a central role in supporting cell motility, and polymerization of actin filaments (F-actin) is most likely involved in spine shape changes. Drebrin is an actin-binding protein that forms stable F-actin and is highly accumulated within dendritic spines. Drebrin has two isoforms, embryonic-type drebrin E and adult-type drebrin A, that change during development from E to A. Inhibition of drebrin A expression results in a delay of synapse formation and inhibition of postsynaptic protein accumulation, suggesting that drebrin A has an important role in spine maturation. In mature synapses, glutamate stimulation induces rapid spine-head enlargement during long-term potentiation (LTP) formation. LTP stimulation induces Ca 2+ entry through N-methyl-d-aspartate (NMDA) receptors, which causes drebrin exodus from dendritic spines. Once drebrin exits from dendritic spine heads, the dynamic actin pool increases in spine heads to facilitate F-actin polymerization. To maintain enlarged spine heads, drebrin-decorated F-actin is thought to reform within the spine heads. Thus, drebrin plays a pivotal role in spine plasticity through regulation of F-actin., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

Extracellular phosphorylation of proteins was suggested in the late 1800s when it was demonstrated that casein contains phosphate. More recently, extracellular kinases that phosphorylate extracellular serine, threonine, and tyrosine residues of numerous proteins have been identified. However, the functional significance of extracellular phosphorylation of specific residues in the nervous system is poorly understood. Here we show that synaptic accumulation of GluN2B-containing N-methyl-D-aspartate receptors (NMDARs) and pathological pain are controlled by ephrin-B-induced extracellular phosphorylation of a single tyrosine (p*Y504) in a highly conserved region of the fibronectin type III (FN3) domain of the receptor tyrosine kinase EphB2. Ligand-dependent Y504 phosphorylation modulates the EphB-NMDAR interaction in cortical and spinal cord neurons. Furthermore, Y504 phosphorylation enhances NMDAR localization and injury-induced pain behavior. By mediating inducible extracellular interactions that are capable of modulating animal behavior, extracellular tyrosine phosphorylation of EphBs may represent a previously unknown class of mechanism mediating protein interaction and function.

Drebrin is an actin-binding protein that changes the helical pitch of actin filaments (F-actin), and drebrin-decorated F-actin shows slow treadmilling and decreased rate of depolymerization. Moreover, the characteristic morphology of drebrin-decorated F-actin enables it to respond differently to the same signals from other actin cytoskeletons. Drebrin consists of two major isoforms, drebrin E and drebrin A. In the developing brain, drebrin E appears in migrating neurons and accumulates in the growth cones of axons and dendrites. Drebrin E-decorated F-actin links lamellipodium F-actin to microtubules in the growth cones. Then drebrin A appears at nascent synapses and drebrin A-decorated F-actin facilitates postsynaptic molecular assembly. In the adult brain, drebrin A-decorated F-actin is concentrated in the central region of dendritic spines. During long-term potentiation initiation, NMDA receptor-mediated Ca 2+ influx induces the transient exodus of drebrin A-decorated F-actin via myosin II ATPase activation. Because of the unique physical characteristics of drebrin A-decorated F-actin, this exodus likely contributes to the facilitation of F-actin polymerization and spine enlargement. Additionally, drebrin reaccumulation in dendritic spines is observed after the exodus. In our drebrin exodus model of structure-based synaptic plasticity, reestablishment of drebrin A-decorated F-actin is necessary to keep the enlarged spine size during long-term potentiation maintenance. In this review, we introduce the genetic and biochemical properties of drebrin and the roles of drebrin in early stage of brain development, synaptic formation and synaptic plasticity. Further, we discuss the pathological relevance of drebrin loss in Alzheimer's disease. This article is part of the mini review series "60th Anniversary of the Japanese Society for Neurochemistry"., (© 2017 International Society for Neurochemistry.)

Developmental changes in the expression and localization of drebrin has been mainly analyzed in chick embryo and young rat by various anti-drebrin polyclonal and monoclonal antibodies. Immunoblot analysis demonstrated that the adult drebrin isoform (drebrin A) is restricted to neural tissues, while the embryonic drebrin isoforms (drebrin E1 and E2 in chicken and drebrin E in mammals) are found in a wide variety of tissues. In the developing brain, drebrin E (including chicken drebrin E2) is expressed in newly generated neurons. During neuronal migration, drebrin E is distributed ubiquitously within the neurons. Once drebrin A is expressed in the developing neuron, drebrin E is no longer present within the cell soma and accumulates in the growth cone of growing processes, resulting in the cessation of neuronal migration. The limited subcellular localization of drebrin A, which is possibly regulated by a drebrin A-specific mechanism, is likely to affect the localization of drebrin E. In the adult brain, drebrin is mainly localized in dendritic spines, but in some nuclei, drebrin can be detected in neuronal somata as well as dendritic spines. The fact that the developmental changes in drebrin expression highly correlate in time with the sensitive period of visual cortical plasticity in kittens suggests that synaptic plasticity depends on drebrin.