Damping and Interfacial Dzyaloshinskii-Moriya Interaction in Thulium Iron Garnet/Bismuth-Substituted Yttrium Iron Garnet Bilayers.

Thin films of ferrimagnetic iron garnets can exhibit useful magnetic properties, including perpendicular magnetic anisotropy (PMA) and high domain wall velocities. In particular, bismuth-substituted yttrium iron garnet (BiYIG) films grown on garnet substrates have a low Gilbert damping but zero Dzyaloshinskii-Moriya interaction (DMI), whereas thulium iron garnet (TmIG) films have higher damping but a nonzero DMI. We report the damping and DMI of thulium-substituted BiYIG (BiYTmIG) and TmIG|BiYIG bilayer thin films deposited on (111) substituted gadolinium gallium garnet and neodymium gallium garnet (NGG) substrates. The films are epitaxial and exhibit PMA. BiYIG|TmIG bilayers have a damping value that is an order of magnitude lower than that of TmIG, and BiYIG|TmIG|NGG have DMI of 0.0145 ± 0.0011 mJ/m2, similar to that of TmIG|NGG. The bilayer therefore provides a combination of DMI and moderate damping, useful for the development of high-speed spin orbit torque-driven devices.

Dendritic voltage imaging maps the biophysical basis of plateau potentials in the hippocampus.

Dendrites on neurons integrate synaptic inputs to determine spike timing. Dendrites also convey back-propagating action potentials (bAPs) which interact with synaptic inputs to produce plateau potentials and to mediate synaptic plasticity. The biophysical rules which govern the timing, spatial structures, and ionic character of dendritic excitations are not well understood. We developed molecular, optical, and computational tools to map sub-millisecond voltage dynamics throughout the dendritic trees of CA1 pyramidal neurons under diverse optogenetic and synaptic stimulus patterns, in acute brain slices. We observed history-dependent bAP propagation in distal dendrites, driven by locally generated Na + spikes (dSpikes). Dendritic depolarization creates a transient window for dSpike propagation, opened by A-type K V channel inactivation, and closed by slow Na V inactivation. Collisions of dSpikes with synaptic inputs triggered calcium channel and N-methyl-D-aspartate receptor (NMDAR)-dependent plateau potentials, with accompanying complex spikes at the soma. This hierarchical ion channel network acts as a spike-rate accelerometer, providing an intuitive picture of how dendritic excitations shape associative plasticity rules.

Cortical astrocytes modulate dominance behavior in male mice by regulating synaptic excitatory and inhibitory balance.

Social hierarchy is established as an outcome of individual social behaviors, such as dominance behavior during long-term interactions with others. Astrocytes are implicated in optimizing the balance between excitatory and inhibitory (E/I) neuronal activity, which may influence social behavior. However, the contribution of astrocytes in the prefrontal cortex to dominance behavior is unclear. Here we show that dorsomedial prefrontal cortical (dmPFC) astrocytes modulate E/I balance and dominance behavior in adult male mice using in vivo fiber photometry and two-photon microscopy. Optogenetic and chemogenetic activation or inhibition of dmPFC astrocytes show that astrocytes bidirectionally control male mouse dominance behavior, affecting social rank. Dominant and subordinate male mice present distinct prefrontal synaptic E/I balance, regulated by astrocyte activity. Mechanistically, we show that dmPFC astrocytes control cortical E/I balance by simultaneously enhancing presynaptic-excitatory and reducing postsynaptic-inhibitory transmission via astrocyte-derived glutamate and ATP release, respectively. Our findings show how dmPFC astrocyte-neuron communication can be involved in the establishment of social hierarchy in adult male mice.

Erratum: Large Anomalous Frequency Shift in Perpendicular Standing Spin Wave Modes in BiYIG Films Induced by Thin Metallic Overlayers [Phys. Rev. Lett. 130, 126703 (2023)].

This corrects the article DOI: 10.1103/PhysRevLett.130.126703.

Large Anomalous Frequency Shift in Perpendicular Standing Spin Wave Modes in BiYIG Films Induced by Thin Metallic Overlayers.

Interface-driven effects on magnon dynamics are studied in magnetic insulator-metal bilayers using Brillouin light scattering. It is found that the Damon-Eshbach modes exhibit a significant frequency shift due to interfacial anisotropy generated by thin metallic overlayers. In addition, an unexpectedly large shift in the perpendicular standing spin wave mode frequencies is also observed, which cannot be explained by anisotropy-induced mode stiffening or surface pinning. Rather, it is suggested that additional confinement may result from spin pumping at the insulator-metal interface, which results in a locally overdamped interface region. These results uncover previously unidentified interface-driven changes in magnetization dynamics that may be exploited to locally control and modulate magnonic properties in thin-film heterostructures.

Hippocampal engram networks for fear memory recruit new synapses and modify pre-existing synapses in vivo.

As basic units of neural networks, ensembles of synapses underlie cognitive functions such as learning and memory. These synaptic engrams show elevated synaptic density among engram cells following contextual fear memory formation. Subsequent analysis of the CA3-CA1 engram synapse revealed larger spine sizes, as the synaptic connectivity correlated with the memory strength. Here, we elucidate the synapse dynamics between CA3 and CA1 by tracking identical synapses at multiple time points by adapting two-photon microscopy and dual-eGRASP technique in vivo. After memory formation, synaptic connections between engram populations are enhanced in conjunction with synaptogenesis within the hippocampal network. However, extinction learning specifically correlated with the disappearance of CA3 engram to CA1 engram (E-E) synapses. We observed "newly formed" synapses near pre-existing synapses, which clustered CA3-CA1 engram synapses after fear memory formation. Overall, we conclude that dynamics at CA3 to CA1 E-E synapses are key sites for modification during fear memory states.

Hippocampal astrocytes modulate anxiety-like behavior.

Astrocytes can affect animal behavior by regulating tripartite synaptic transmission, yet their influence on affective behavior remains largely unclear. Here we showed that hippocampal astrocyte calcium activity reflects mouse affective state during virtual elevated plus maze test using two-photon calcium imaging in vivo. Furthermore, optogenetic hippocampal astrocyte activation elevating intracellular calcium induced anxiolytic behaviors in astrocyte-specific channelrhodopsin 2 (ChR2) transgenic mice (hGFAP-ChR2 mice). As underlying mechanisms, we found ATP released from the activated hippocampal astrocytes increased excitatory synaptic transmission in dentate gyrus (DG) granule cells, which exerted anxiolytic effects. Our data uncover a role of hippocampal astrocytes in modulating mice anxiety-like behaviors by regulating ATP-mediated synaptic homeostasis in hippocampal DG granule cells. Thus, manipulating hippocampal astrocytes activity can be a therapeutic strategy to treat anxiety.

Dynamics of axonal ß-actin mRNA in live hippocampal neurons.

Localization of mRNA facilitates spatiotemporally controlled protein expression in neurons. In axons, mRNA transport followed by local protein synthesis plays a critical role in axonal growth and guidance. However, it is not yet clearly understood how mRNA is transported to axonal subcellular sites and what regulates axonal mRNA localization. Using a transgenic mouse model in which endogenous ß-actin mRNA is fluorescently labeled, we investigated ß-actin mRNA movement in axons of hippocampal neurons. We cultured neurons in microfluidic devices to separate axons from dendrites and performed single-particle tracking of axonal ß-actin mRNA. Compared with dendritic ß-actin mRNA, axonal ß-actin mRNA showed less directed motion and exhibited mostly subdiffusive motion, especially near filopodia and boutons in mature dissociated hippocampal neurons. We found that axonal ß-actin mRNA was likely to colocalize with actin patches (APs), regions that have a high density of filamentous actin (F-actin) and are known to have a role in branch initiation. Moreover, simultaneous imaging of F-actin and axonal ß-actin mRNA in live neurons revealed that moving ß-actin mRNA tended to be docked in the APs. Our findings reveal that axonal ß-actin mRNA localization is facilitated by actin networks and suggest that localized ß-actin mRNA plays a potential role in axon branch formation.

Real-time visualization of mRNA synthesis during memory formation in live mice.

Memories are thought to be encoded in populations of neurons called memory trace or engram cells. However, little is known about the dynamics of these cells because of the difficulty in real-time monitoring of them over long periods of time in vivo. To overcome this limitation, we present a genetically encoded RNA indicator (GERI) mouse for intravital chronic imaging of endogenous Arc messenger RNA (mRNA)-a popular marker for memory trace cells. We used our GERI to identify Arc-positive neurons in real time without the delay associated with reporter protein expression in conventional approaches. We found that the Arc-positive neuronal populations rapidly turned over within 2 d in the hippocampal CA1 region, whereas ∼4% of neurons in the retrosplenial cortex consistently expressed Arc following contextual fear conditioning and repeated memory retrievals. Dual imaging of GERI and a calcium indicator in CA1 of mice navigating a virtual reality environment revealed that only the population of neurons expressing Arc during both encoding and retrieval exhibited relatively high calcium activity in a context-specific manner. This in vivo RNA-imaging approach opens the possibility of unraveling the dynamics of the neuronal population underlying various learning and memory processes.

De novo generation of a bright blue fluorophore from 2-oxoglutarate in biological samples.

We discovered the generation of a new bright blue fluorophore from a particular type of amine and 2-oxoglutarate (2-OG) under mild conditions without any chemical additives. Two ß-aminoethylamine molecules and three 2-OG molecules form an unprecedented 2-pyridone structure with a fused γ-lactam ring (DTPP) via complex reactions including double decarboxylation and quintuple dehydration. The DTPP fluorophore shows a high quantum yield (80%) and photostability. The great potential of the present DTPP generation in the quantitative analysis of 2-OG in biosamples is demonstrated.

Relativistic kinematics of a magnetic soliton.

A tenet of special relativity is that no particle can exceed the speed of light. In certain magnetic materials, the maximum magnon group velocity serves as an analogous relativistic limit for the speed of magnetic solitons. Here, we drive domain walls to this limit in a low-dissipation magnetic insulator using pure spin currents from the spin Hall effect. We achieve record current-driven velocities in excess of 4300 meters per second-within ~10% of the relativistic limit-and we observe key signatures of relativistic motion associated with Lorentz contraction, which leads to velocity saturation. The experimental results are well explained through analytical and atomistic modeling. These observations provide critical insight into the fundamental limits of the dynamics of magnetic solitons and establish a readily accessible experimental framework to study relativistic solitonic physics.

Visualization of Single mRNAs in Live Neurons.

Transcription and post-transcriptional regulations are critical in gene expression. To study the spatiotemporal regulation of RNA inside a cell, techniques for high-resolution imaging of RNA have been developed. In this chapter, we describe RNA fluorescent labeling methods using MS2 and PP7 systems to detect single RNA molecules in live neurons. We use hippocampal neurons cultured from knock-in mouse models in which ß-actin or Arc mRNAs are tagged with MS2 or PP7 stem-loops. Adeno-associated virus (AAV) or lentiviral vectors are used to express MS2 or PP7 capsid proteins fused with GFP in those neurons. Then, GFP-labeled RNAs in live neurons can be detected by epifluorescence microscopy, and their moving pathways can be analyzed using single-particle tracking software. For these processes, we introduce protocols for neuron culture, transfection, imaging, and particle tracking methods.

HybTrack: A hybrid single particle tracking software using manual and automatic detection of dim signals.

Single particle tracking is a compelling technique for investigating the dynamics of nanoparticles and biological molecules in a broad range of research fields. In particular, recent advances in fluorescence microscopy have made single molecule tracking a prevalent method for studying biomolecules with a high spatial and temporal precision. Particle tracking algorithms have matured over the past three decades into more easily accessible platforms. However, there is an inherent difficulty in tracing particles that have a low signal-to-noise ratio and/or heterogeneous subpopulations. Here, we present a new MATLAB based tracking program which combines the benefits of manual and automatic tracking methods. The program prompts the user to manually locate a particle when an ambiguous situation occurs during automatic tracking. We demonstrate the utility of this program by tracking the movement of ß-actin mRNA in the dendrites of cultured hippocampal neurons. We show that the diffusion coefficient of ß-actin mRNA decreases upon neuronal stimulation by bicuculline treatment. This tracking method enables an efficient dissection of the dynamic regulation of biological molecules in highly complex intracellular environments.

Distributed Coordination for Optimal Energy Generation and Distribution in Cyber-Physical Energy Networks.

This paper proposes three coordination laws for optimal energy generation and distribution in energy network, which is composed of physical flow layer and cyber communication layer. The physical energy flows through the physical layer; but all the energies are coordinated to generate and flow by distributed coordination algorithms on the basis of communication information. First, distributed energy generation and energy distribution laws are proposed in a decoupled manner without considering the interactive characteristics between the energy generation and energy distribution. Second, a joint coordination law to treat the energy generation and energy distribution in a coupled manner taking account of the interactive characteristics is designed. Third, to handle over- or less-energy generation cases, an energy distribution law for networks with batteries is designed. The coordination laws proposed in this paper are fully distributed in the sense that they are decided optimally only using relative information among neighboring nodes. Through numerical simulations, the validity of the proposed distributed coordination laws is illustrated.

The Clinical Significance of Lumbosacral Transitional Vertebrae on the Surgical Outcomes of Lumbar Discectomy: A Retrospective Cohort Study of Young Adults.

OBJECTIVE: To evaluate whether the presence of lumbosacral transitional vertebrae (LSTV) affects the clinical outcomes of microdiscectomy (MD) in young adults with lumbar disc herniation. METHODS: We retrospectively included 398 patients who were followed-up for at least 2 years after MD for lumbar disc herniation at L4/5 (disc above the LSTV). The patients were divided into 2 groups. Group A was made up of 31 patients in whom LSTV was detected. Group B, in contrast, was made up of 35 patients in whom LSTV was not detected. The LSTV were classified using plain radiographs and three-dimensional computed tomography by Castellvi et al. The primary outcome measure was pain intensity at each follow-up visit assessed with visual analog scale for back and leg. Secondary outcome measures included the Oswestry Disability Index, a 12-item short-form health survey for quality of life, complications, and recurrence rate. RESULTS: After surgery, the visual analog scale scores for the back and leg decreased significantly in both groups. However, the back pain intensity in group A worsened at 12 and 24 months postoperatively. The Oswestry Disability Index scores and 12-item short-form health survey (both mental and physical) worsened at 12 and 24 months postoperatively in group A. Two cases of reherniation (6.5 %) were observed in group A, who required reoperation. CONCLUSIONS: LSTV can limit a patient's clinical improvement after MD with regard to pain intensity and recurrence. Caution must be taken when a patient is scheduled to undergo surgery.

Imaging Single-mRNA Localization and Translation in Live Neurons.

Local protein synthesis mediates precise spatio-temporal regulation of gene expression for neuronal functions such as long-term plasticity, axon guidance and regeneration. To reveal the underlying mechanisms of local translation, it is crucial to understand mRNA transport, localization and translation in live neurons. Among various techniques for mRNA analysis, fluorescence microscopy has been widely used as the most direct method to study localization of mRNA. Live-cell imaging of single RNA molecules is particularly advantageous to dissect the highly heterogeneous and dynamic nature of messenger ribonucleoprotein (mRNP) complexes in neurons. Here, we review recent advances in the study of mRNA localization and translation in live neurons using novel techniques for single-RNA imaging.

Radiologic Findings and Risk Factors of Adjacent Segment Degeneration after Anterior Cervical Discectomy and Fusion : A Retrospective Matched Cohort Study with 3-Year Follow-Up Using MRI.

OBJECTIVE: The purpose of this study was to figure out the radiologic findings and risk factors related to adjacent segment degeneration (ASD) after anterior cervical discectomy and fusion (ACDF) using 3-year follow-up radiography, computed tomography (CT), and magnetic resonance image (MRI). METHODS: A retrospective matched comparative study was performed for 64 patients who underwent single-level ACDF with a cage and plate. Radiologic parameters, including upper segment range of motion (USROM), lower segment range of motion (LSROM), upper segment disc height (UDH), and lower segment disc height (LDH), clinical outcomes assessed with neck and arm visual analogue scale (VAS), and risk factors were analyzed. RESULTS: Patients were categorized into the ASD (32 patients) and non-ASD (32 patients) group. The decrease of UDH was significantly greater in the ASD group at each follow-up visit. At 36 months postoperatively, the difference for USROM value from the preoperative one significantly increased in the ASD group than non-ASD group. Preoperative other segment degeneration was significantly associated with the increased incidence of ASD at 36 months. However, pain intensity for the neck and arm was not significantly different between groups at any post-operative follow-up visit. CONCLUSION: The main factor affecting ASD is preoperative other segment degeneration out of the adjacent segment. In addition, patients over the age of 50 are at higher risk of developing ASD. Although there was definite radiologic degeneration in the ASD group, no significant difference was observed between the ASD and non-ASD groups in terms of the incidence of symptomatic disease.

Comparison of Outcomes of Percutaneous Endoscopic Lumbar Discectomy and Open Lumbar Microdiscectomy for Young Adults: A Retrospective Matched Cohort Study.

OBJECTIVE: There have been only a few studies on surgical treatment of lumbar disc herniation (LDH) in young adults. In addition, previous studies do not provide detailed information on the surgical outcomes for young adults with LDH. The purpose of this study was to compare the outcome of transforaminal percutaneous endoscopic lumbar discectomy (PELD) and open lumbar microdiscectomy for active, young adults (age 20-25 years). METHODS: We performed retrospective chart and radiography. The patients were divided into 2 groups according to the surgical methods. Group A included the patients who underwent transforaminal PELD, and Group B included the patients who underwent open lumbar microdiscectomy for LDH at L4/5. After we matched for several factors, 32 young patients in group A and 34 young patients in group B were analyzed. We compared the outcomes between the 2 groups in terms of clinical, radiologic, perioperative outcomes, and surgery-related complications. RESULTS: The clinical results for leg pain and radiologic results for decompression were the same in both groups. Most of complications in the PELD group occurred in the early phase. The recurrence rate and operation failure rate was no difference between the groups. The PELD brought significant advantages in the following areas: back pain, operation time, blood loss, hospital stay, and return-to-work. CONCLUSIONS: Although a learning curve is needed in order to become familiar with PELD, PELD seemed to be a good choice for disc herniation in the lumbar spine for active, young adults.

Evaluation of muscle damage using ultrasound imaging.

[Purpose] This study aimed to quantitatively analyze characteristics of and changes in internal muscle structure according to the time of delayed onset muscle soreness (DOMS) using ultrasound imaging, thereby presenting clinical evidential data for evaluation of muscle damage. [Subjects] We recruited 38 male subjects. [Methods] Ultrasound images of the medial gastrocnemius muscle prior to induction of DOMS and immediately after, 24 hours after, 48 hours after, and 72 hours after induction of DOMS were obtained, and the thickness and pennation angle of the muscle were measured. [Results] The muscle thickness gradually increased until 48 hours after induction of DOMS and decreased after 72 hours. The pennation angle also gradually increased until 48 hours after induction of DOMS and decreased after 72 hours. [Conclusion] Ultrasound imaging is considered useful for assessment of structural characteristics of muscles when muscle damage like DOMS takes place.