Freezing Shrinkage Dynamics and Surface Dendritic Growth of Floating Refractory Alloy Droplets in Outer Space

The freezing shrinkage and dendritic growth are of great importance for various alloys solidified from high-temperature liquids to solids since they dominate microstructure patterns and follow-up processing. However, the microgravity freezing shrinkage dynamics is scarcely explored on the ground as it is hard to suppress the strong natural convection inside liquid alloys. Here, a series of in-orbit solidification experiments is conducted aboard the China Space Station with a long-term stable 10-5 g0 microgravity condition. The highest temperature up to 2265 K together with substantial liquid undercoolings far from a thermodynamically stable state are attained for both Nb82.7Si17.3 and Zr64V36 refractory alloys. Furthermore, the solidification under microgravity of a droplet is simulated to reveal the liquid-solid interface migration, temperature gradient, and flow field. The microgravity solidification process leads to freezing shrinkage cavities and distinctive surface dendritic microstructure patterns. The combined effects of shrinkage dynamics and liquid surface flow in outer space result in the dendrites growing not only along the tangential direction but also along the normal direction to the droplet surface. These space experimental results contribute to a further understanding of the solidification behavior of liquid alloys under a weaker convection condition, which is often masked by gravity on the ground.

Deterministic Formation and Growth of Dendritic Crystals of Attractive Colloids

Dendrites are ubiquitous crystals produced in supersaturated solutions and supercooled melts, but considerably less is known about their formation and growth kinetics. Here, the key factors are explored that dictate dendrite formation and growth, utilizing experimental colloidal models in which the particles act as molecules with Mie potential. Depletion attraction is employed to colloids and manipulate their strength to control supersaturation. Dendrites are predominantly produced under conditions of low supersaturation, where the separation between crystals is large due to slow nucleation. The dendrites do not emerge directly from nuclei. Instead, isotropic grains, initially produced from nuclei, morph into polygons. Arms then sprout from the vertices of these polygons, eventually giving rise to dendrites. Triggering this polygon-to-dendrite transformation requires a high diffusional flux. This necessitates a prolonged diffusion time to maintain a steep concentration gradient in the surrounding environment even after the transformation from circular grains to polygons.

Low-Temperature and High-Performance Vanadium-Based Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries have attracted attention due to their low cost and high safety. Unfortunately, dendrite growth, hydrogen evolution reactions, cathodic dissolution, and other problems are more serious; not only that, but also the cathodic and anodic materials' lattices contract when the temperature drops, and charge transfer and solid phase diffusion become slow, seriously aggravating dendrite growth. At present, there are few studies on the low-temperature system, and studies on retaining high specific capacity are even more rare. Herein, ethylene glycol (EG) and manganese sulfate (MSO) are selected as additives, and the manganese vanadate (MVO) cathode is used to find a high-performance solution at low temperature. MVO can provide higher specific capacity and better structural stability than MnO2 to adapt to a low-temperature environment. At the same time, Mn2+ in MSO can produce a cationic shield covering the initial zinc tip at an appropriate concentration to avoid the tip effect and inhibit the dissolution of MVO. EG can not only reduce the freezing point of the electrolyte but also promote the desolvation of [Zn(H2O)6]2+. The synergistic effect of the three elements prevents the dissolution equilibrium of Mn2+ in MVO from fluctuating greatly due to the change of temperature. Therefore, when we use EG@0.2 M MnSO4 + 2 M ZnSO4 (EG + 0.2Mn/2ZSO) electrolyte at -30 °C, the Zn||Zn batteries which used this type of electrolyte can remain 350 h at 1 mA cm-2 without failure. The Zn||Cu batteries can retain 100% Coulombic efficiency after more than 2000 cycles at 0.2 mA cm-2. The Zn||MVO battery can reach 231.13 mA h g-1 at its first cycle, and the capacity retention rate is still above 85% after 1000 cycles, which is higher than that of the existing low-temperature research system.

Gintonin stimulates dendritic growth in striatal neurons by activating Akt and CREB

Gintonin, a glycolipid protein conjugated with lysophosphatidic acid (LPA), is a newly identified compound extracted from Korean ginseng. LPA receptor isotypes exhibit high affinity for gintonin and mediate intracellular calcium signaling in various animal cell models. In this study, we found that gintonin induced the activation of Akt and cAMP-response element binding protein (CREB) in mouse striatal neurons, and chronic treatment with gintonin potently induced dendritic growth and filopodia formation. Gintonin-induced Akt/CREB activation and dendritic development were significantly impaired by LPA receptor (LPAR1/3) inhibition with Ki16425. Intriguingly, prolonged treatment with gintonin ameliorated the reduction in dendritic formation caused by Shank3 and Slitrk5 deficiency in the striatal neurons. In addition, gintonin and brain-derived neurotrophic factor (BDNF) had a synergistic effect on AKT/CREB activation and dendritic growth at suboptimal concentrations. These findings imply that gintonin-stimulated LPA receptors play a role in dendritic growth in striatal neurons and that they may act synergistically with BDNF, which is known to play a role in dendritogenesis.

Analysis of the boundary integral equation for the growth of a parabolic/paraboloidal dendrite with convection

The growth of a parabolic/paraboloidal dendrite streamlined by viscous and potential flows in an undercooled one-component melt is analyzed using the boundary integral equation. The total melt undercooling is found as a function of the Péclet, Reynolds, and Prandtl numbers in two- and three-dimensional cases. The solution obtained coincides with the modified Ivantsov solution known from previous theories of crystal growth. Varying Péclet and Reynolds numbers we show that the melt undercooling practically coincides in cases of viscous and potential flows for a small Prandtl number, which is typical for metals. In cases of water solutions and non-metallic alloys, the Prandtl number is not small enough and the melt undercooling is substantially different for viscous and potential flows. In other words, a simpler potential flow hydrodynamic model can be used instead of a more complicated viscous flow model when studying the solidification of undercooled metals with convection.

Capicua Regulates Dendritic Morphogenesis Through Ets in Hippocampal Neurons in vitro

Capicua (Cic), a transcriptional repressor frequently mutated in brain cancer oligodendroglioma, is highly expressed in adult neurons. However, its function in the dendritic growth of neurons in the hippocampus remains poorly understood. Here, we confirmed that Cic was expressed in hippocampal neurons during the main period of dendritogenesis, suggesting that Cic has a function in dendrite growth. Loss-of-function and gain-of function assays indicated that Cic plays a central role in the inhibition of dendritic morphogenesis and dendritic spines in vitro. Further studies showed that overexpression of Cic reduced the expression of Ets in HT22 cells, while in vitro knockdown of Cic in hippocampal neurons significantly elevated the expression of Ets. These results suggest that Cic may negatively control dendrite growth through Ets, which was confirmed by ShRNA knockdown of either Etv4 or Etv5 abolishing the phenotype of Cic knockdown in cultured neurons. Taken together, our results suggest that Cic inhibits dendritic morphogenesis and the growth of dendritic spines through Ets.

Dendritic growth of ice crystals: a test of theory with experiments

Motivated by an important application of dendritic crystals in the form of an elliptical paraboloid, which widely spread in nature (ice crystals), we develop here the selection theory of their stable growth mode. This theory enables us to separately define the tip velocity of dendrites and their tip diameter as functions of the melt undercooling. This, in turn, makes it possible to judge the microstructure of the material obtained as a result of the crystallization process. So, in the first instance, the steady-state analytical solution that describes the growth of such dendrites in undercooled one-component liquids is found. Then a system of equations consisting of the selection criterion and the undercooling balance that describes a stable growth mode of elliptical dendrites is formulated and analyzed. Three parametric solutions of this system are deduced in an explicit form. Our calculations based on these solutions demonstrate that the theoretical predictions are in good agreement with experimental data for ice dendrites growing at small undercoolings in pure water.

Disabling VEGF-Response of Purkinje Cells by Downregulation of KDR via miRNA-204-5p

The vascular endothelial growth factor (VEGF) is well known for its wide-ranging functions, not only in the vascular system, but also in the central (CNS) and peripheral nervous system (PNS). To study the role of VEGF in neuronal protection, growth and maturation processes have recently attracted much interest. These effects are mainly mediated by VEGF receptor 2 (VEGFR-2). Current studies have shown the age-dependent expression of VEGFR-2 in Purkinje cells (PC), promoting dendritogenesis in neonatal, but not in mature stages. We hypothesize that microRNAs (miRNA/miR) might be involved in the regulation of VEGFR-2 expression during the development of PC. In preliminary studies, we performed a miRNA profiling and identified miR204-5p as a potential regulator of VEGFR-2 expression. In the recent study, organotypic slice cultures of rat cerebella (postnatal day (p) 1 and 9) were cultivated and VEGFR-2 expression in PC was verified via immunohistochemistry. Additionally, PC at age p9 and p30 were isolated from cryosections by laser microdissection (LMD) to analyse VEGFR-2 expression by quantitative RT-PCR. To investigate the influence of miR204-5p on VEGFR-2 levels in PC, synthetic constructs including short hairpin (sh)-miR204-5p cassettes (miRNA-mimics), were microinjected into PC. The effects were analysed by confocal laser scanning microscopy (CLSM) and morphometric analysis. For the first time, we could show that miR204-5p has a negative effect on VEGF sensitivity in juvenile PC, resulting in a significant decrease of dendritic growth compared to untreated juvenile PC. In mature PC, the overexpression of miR204-5p leads to a shrinkage of dendrites despite VEGF treatment. The results of this study illustrate, for the first time, which miR204-5p expression has the potential to play a key role in cerebellar development by inhibiting VEGFR-2 expression in PC.

Phosphorylation of Collapsin Response Mediator Protein 1 (CRMP1) at Tyrosine 504 residue regulates Semaphorin 3A-induced cortical dendritic growth

Collapsin response mediator proteins (CRMPs) have been identified as mediating proteins of repulsive axon guidance cue Semaphorin-3A (Sema3A). Phosphorylation of CRMPs plays a crucial role in the Sema3A signaling cascade. It has been shown that Fyn phosphorylates CRMP1 at Tyrosine 504 residue (Tyr504); however, the physiological role of this phosphorylation has not been examined. We found that CRMP1 was the most strongly phosphorylated by Fyn among the five members of CRMPs. We confirmed Tyr504 phosphorylation of CRMP1 by Fyn. Immunocytochemistry of mouse dorsal root ganglion (DRG) neurons showed that phosphotyrosine signal in the growth cones was transiently increased in the growth cones upon Sema3A stimulation. Tyr504-phosphorylated CRMP1 also tended to increase after Sema3A simulation. Ectopic expression of a single amino acid mutant of CRMP1 replacing Tyr504 with phenylalanine (CRMP1-Tyr504Phe) suppressed Sema3A-induced growth cone collapse response in chick DRG neurons. CRMP1-Tyr504Phe expression in mouse hippocampal neurons also suppressed Sema3A but not Sema3F-induced growth cone collapse response. Immunohistochemistry showed that Tyr504-phosphorylated CRMP1 was present in the cell bodies and in the dendritic processes of mouse cortical neurons. CRMP1-Tyr504Phe suppressed Sema3A-induced dendritic growth of primary cultured mouse cortical neurons as well as the dendritic development of cortical pyramidal neurons in vivo. Fyn^± ; Crmp1^± double heterozygous mutant mice exhibited poor development of cortical layer V basal dendrites, which was the similar phenotype observed in Sema3a^-/- , Fyn^-/- , and Crmp1^-/- mice. These findings demonstrate that Tyr504 phosphorylation of CRMP1 by Fyn is an essential step of Sema3A-regulated dendritic development of cortical pyramidal neurons. (247 words).

Early Dendritic Morphogenesis of Adult-Born Dentate Granule Cells Is Regulated by FHL2

Dentate granule cells (DGCs), the progeny of neural stem cells (NSCs) in the sub-granular zone of the dentate gyrus (DG), must develop and functionally integrate with the mature cohort of neurons in order to maintain critical hippocampal functions throughout adulthood. Dysregulation in the continuum of DGC development can result in aberrant morphology and disrupted functional maturation, impairing neuroplasticity of the network. Yet, the molecular underpinnings of the signaling involved in adult-born DGC maturation including dendritic growth, which correlates with functional integration, remains incompletely understood. Given the high metabolic activity in the dentate gyrus (DG) required to achieve continuous neurogenesis, we investigated the potential regulatory role of a cellular metabolism-linked gene recently implicated in NSC cycling and neuroblast migration, called Four and a half LIM domain 2 (FHL2). The FHL2 protein modulates numerous pathways related to proliferation, migration, survival and cytoskeletal rearrangement in peripheral tissues, interacting with the machinery of the sphingosine-1-phosphate pathway, also known to be highly active especially in the hippocampus. Yet, the potential relevance of FHL2 to adult-born DGC development remains unknown. To elucidate the role of FHL2 in DGC development in the adult brain, we first confirmed the endogenous expression of FHL2 in NSCs and new granule cells within the DG, then engineered viral vectors for genetic manipulation experiments, investigating morphological changes in early stages of DGC development. Overexpression of FHL2 during early DGC development resulted in marked sprouting and branching of dendrites, while silencing of FHL2 increased dendritic length. Together, these findings suggest a novel role of FHL2 in adult-born DGC morphological maturation, which may open up a new line of investigation regarding the relevance of this gene in physiology and pathologies of the hippocampus such as mesial temporal lobe epilepsy (MTLE).

Primary Crystal Orientation of the Thin-Walled Area of Single-Crystalline Turbine Blade Airfoils

The thin-walled airfoil areas of as-cast single-crystalline turbine blades made of CMSX-4 superalloy were studied. The blades were produced by the industrial Bridgman technique at withdrawal rates of 2, 3 and 4 mm/min. The angle between the [001] crystallographic direction and blade axis, related to the primary orientation, was defined by the Ω-scan X-ray diffraction method at points on the camber line located near the tip of an airfoil and at points of a line located in parallel and near the trailing edge. Additionally, primary crystal orientation was determined by Laue diffraction at the selected points of an airfoil. The influence of mould wall inclination on the primary crystal orientation of the thin-walled areas is discussed. The effect of change in the [001] crystallographic direction, named as "force directing", was considered with regard to the arrangement of primary dendrite arms in relation to the trailing edge and the camber line. It was stated that when the distance between the mould walls is less than the critical value of about 1.5 mm the "force directing" increases as the distance between the walls of the mould decreases. The effect may be controlled by selecting an appropriate secondary orientation using a seed crystal in the blade production process. The model of dendrite interaction with the mould walls, including bending and "deflection", was proposed.

Thermo-solutal and kinetic modes of stable dendritic growth with different symmetries of crystalline anisotropy in the presence of convection

Motivated by important applications in materials science and geophysics, we consider the steady-state growth of anisotropic needle-like dendrites in undercooled binary mixtures with a forced convective flow. We analyse the stable mode of dendritic evolution in the case of small anisotropies of growth kinetics and surface energy for arbitrary Péclet numbers and n-fold symmetry of dendritic crystals. On the basis of solvability and stability theories, we formulate a selection criterion giving a stable combination between dendrite tip diameter and tip velocity. A set of nonlinear equations consisting of the solvability criterion and undercooling balance is solved analytically for the tip velocity V and tip diameter ρ of dendrites with n-fold symmetry in the absence of convective flow. The case of convective heat and mass transfer mechanisms in a binary mixture occurring as a result of intensive flows in the liquid phase is detailed. A selection criterion that describes such solidification conditions is derived. The theory under consideration comprises previously considered theoretical approaches and results as limiting cases. This article is part of the theme issue 'From atomistic interfaces to dendritic patterns'.This article is part of the theme issue 'From atomistic interfaces to dendritic patterns'.

Highly Efficient Br-/NO3- Dual-Anion Electrolyte for Suppressing Charging Instabilities of Li-O2 Batteries

The main issues with Li-O₂ batteries are the high overpotential at the cathode and the dendrite formation at the anode during charging. Various types of redox mediators (RMs) have been proposed to reduce the charging voltage. However, the RMs tend to lose their activity during cycling owing to not only decomposition reactions but also undesirable discharge (shuttle effect) at the Li metal anode. Moreover, the dendrite growth of the Li metal anode is not resolved by merely adding RMs to the electrolytes. Here we report a simple yet highly effective method to reduce the charge overpotential while protecting the Li metal anode by incorporating LiBr and LiNO₃ in a tetraglyme solvent as the electrolyte for Li-O₂ cells. The Br^-/Br₃^- couple acts as an RM to oxidize the discharge product Li₂O₂ at the cathode, whereas the NO₃^- anion oxidizes the Li metal surface to prevent the shuttle reaction. In this work, we found that both anions work synergistically in the mixed Br^-/NO₃^- electrolyte to dramatically suppress both parasitic reactions and dendrite formation by generating a solid Li₂O thin film on the Li metal anode. As a result, the charge voltage was reduced to below 3.6 V over 40 cycles. The O₂ evolution during charging was more than 80% of the theoretical value, and CO₂ emission during charging was negligible. After cycling, the Li metal anode showed smooth surfaces with no indication of dendrite formation. These observations clearly demonstrate that the Br^-/NO₃^- dual-anion electrolyte can solve the problems associated with both the overpotential at the cathode and the dendrite formation at the anode.

Detection of 3,3'-Dichlorobiphenyl in Human Maternal Plasma and Its Effects on Axonal and Dendritic Growth in Primary Rat Neurons

3,3'-Dichlorobiphenyl (PCB 11), a byproduct of pigment production, is increasingly detected in environmental samples. While more highly chlorinated PCB congeners are known developmental neurotoxicants, nothing is known about the potential developmental neurotoxicity of PCB 11. To address this critical data gap, we measured PCB 11 levels in human maternal plasma and quantified the effects of PCB 11 and its major metabolites on morphometric parameters of neuronal connectivity in cultured primary neurons. Mass spectrometry analyses of plasma from 241 pregnant women enrolled in the MARBLES study (University of California, Davis) detected PCB 11 in all samples at concentrations ranging from 0.005 to 1.717 ng/ml. Morphometric analyses of primary neuron-glia co-cultures dissociated from the neocortices or hippocampi of neonatal Sprague Dawley rats exposed to vehicle or concentrations ranging from 1 attamolar (aM) to 1 micromolar (µM) of PCB 11, OH-PCB 11, or PCB 11 sulfate indicated that PCB 11 and both metabolites significantly increased axonal and dendritic growth in cortical and hippocampal pyramidal neurons. PCB 11 significantly altered neuronal morphogenesis at concentrations as low as 1 femtomolar (fM), which is ∼0.22 ng/ml. These data suggest the potential for the developing human brain to be exposed to PCB 11, and demonstrate that environmentally relevant levels of PCB 11 alter axonal and dendritic growth in neuronal cell types critically involved in cognitive and higher-order behaviors. These findings identify PCB 11 as a potential environmental risk factor for adverse neurodevelopmental outcomes in humans.

Protein Tyrosine Phosphatase δ Mediates the Sema3A-Induced Cortical Basal Dendritic Arborization through the Activation of Fyn Tyrosine Kinase

Leukocyte common antigen-related (LAR) class protein tyrosine phosphatases (PTPs) are critical for axonal guidance; however, their relation to specific guidance cues is poorly defined. We here show that PTP-3, a LAR homolog in Caenorhabditis elegans, is involved in axon guidance regulated by Semaphorin-2A-signaling. PTPδ, one of the vertebrate LAR class PTPs, participates in the Semaphorin-3A (Sema3A)-induced growth cone collapse response of primary cultured dorsal root ganglion neurons from Mus musculus embryos. In vivo, however, the contribution of PTPδ in Sema3A-regualted axon guidance was minimal. Instead, PTPδ played a major role in Sema3A-dependent cortical dendritic growth. Ptpδ^-/- and Sema3a^-/- mutant mice exhibited poor arborization of basal dendrites of cortical layer V neurons. This phenotype was observed in both male and female mutants. The double-heterozygous mutants, Ptpδ^+/-; Sema3a^+/-, also showed a similar phenotype, indicating the genetic interaction. In Ptpδ^-/- brains, Fyn and Src kinases were hyperphosphorylated at their C-terminal Tyr527 residues. Sema3A-stimulation induced dephosphorylation of Tyr527 in the dendrites of wild-type cortical neurons but not of Ptpδ^-/- Arborization of cortical basal dendrites was reduced in Fyn^-/- as well as in Ptpδ^+/-; Fyn^+/- double-heterozygous mutants. Collectively, PTPδ mediates Sema3A-signaling through the activation of Fyn by C-terminal dephosphorylation.SIGNIFICANCE STATEMENT The relation of leukocyte common antigen-related (LAR) class protein tyrosine phosphatases (PTPs) and specific axon guidance cues is poorly defined. We show that PTP-3, a LAR homolog in Caenorhabditis elegans, participates in Sema2A-regulated axon guidance. PTPδ, a member of vertebrate LAR class PTPs, is involved in Sema3A-regulated cortical dendritic growth. In Sema3A signaling, PTPδ activates Fyn and Src kinases by dephosphorylating their C-terminal Tyr residues. This is the first evidence showing that LAR class PTPs participate in Semaphorin signaling in vivo.

TLR3 downregulates expression of schizophrenia gene Disc1 via MYD88 to control neuronal morphology

Viral infection during fetal or neonatal stages increases the risk of developing neuropsychiatric disorders such as schizophrenia and autism spectrum disorders. Although neurons express several key regulators of innate immunity, the role of neuronal innate immunity in psychiatric disorders is still unclear. Using cultured neurons and in vivo mouse brain studies, we show here that Toll‐like receptor 3 (TLR3) acts through myeloid differentiation primary response gene 88 (MYD88) to negatively control Disrupted in schizophrenia 1 (Disc1) expression, resulting in impairment of neuronal development. Cytokines are not involved in TLR3‐mediated inhibition of dendrite outgrowth. Instead, TLR3 signaling suppresses expression of several psychiatric disorder‐related genes, including Disc1. The impaired dendritic arborization caused by TLR3 activation is rescued by MYD88 deficiency or DISC1 overexpression. In addition, TLR3 activation at the neonatal stage increases dendritic spine density, but narrows spine heads at postnatal day 21 (P21), suggesting a long‐lasting effect of TLR3 activation on spinogenesis. Our study reveals a novel mechanism of TLR3 in regulation of dendritic morphology and provides an explanation for how environmental factors influence mental health.

Cellular and molecular mechanisms regulating neuronal growth by brain-derived neurotrophic factor

Brain-derived neurotrophic factor (BDNF) and its receptors TrkB and p75 regulate dendritic and axonal growth during development and maintenance of the mature nervous system; however, the cellular and molecular mechanisms underlying this process are not fully understood. In recent years, several advances have shed new light on the processes behind the regulation of BDNF-mediated structural plasticity including control of neuronal transcription, local translation of proteins, and regulation of cytoskeleton and membrane dynamics. In this review, we summarize recent advances in the field of BDNF signaling in neurons to induce neuronal growth. © 2016 Wiley Periodicals, Inc.

Neuroligin-1 knockdown reduces survival of adult-generated newborn hippocampal neurons

Survival of adult-born hippocampal granule cells is modulated by neural activity, and thought to be enhanced by excitatory synaptic signaling. Here, we report that a reduction in the synaptogenic protein neuroligin-1 in adult-born neurons in vivo decreased their survival, but surprisingly, this effect was independent of changes in excitatory synaptic function. Instead, the decreased survival was associated with unexpected changes in dendrite and spine morphology during granule cell maturation, suggesting a link between cell growth and survival.

PCB 136 atropselectively alters morphometric and functional parameters of neuronal connectivity in cultured rat hippocampal neurons via ryanodine receptor-dependent mechanisms

We recently demonstrated that polychlorinated biphenyl (PCB) congeners with multiple ortho chlorine substitutions sensitize ryanodine receptors (RyRs), and this activity promotes Ca²⁺-dependent dendritic growth in cultured neurons. Many ortho-substituted congeners display axial chirality, and we previously reported that the chiral congener PCB 136 (2,2',3,3',6,6'-hexachlorobiphenyl) atropselectively sensitizes RyRs. Here, we test the hypothesis that PCB 136 atropisomers differentially alter dendritic growth and other parameters of neuronal connectivity influenced by RyR activity. (-)-PCB 136, which potently sensitizes RyRs, enhances dendritic growth in primary cultures of rat hippocampal neurons, whereas (+)-PCB 136, which lacks RyR activity, has no effect on dendritic growth. The dendrite-promoting activity of (-)-PCB 136 is observed at concentrations ranging from 0.1 to 100 nM and is blocked by pharmacologic RyR antagonism. Neither atropisomer alters axonal growth or cell viability. Quantification of PCB 136 atropisomers in hippocampal cultures indicates that atropselective effects on dendritic growth are not due to differential partitioning of atropisomers into cultured cells. Imaging of hippocampal neurons loaded with Ca²⁺-sensitive dye demonstrates that (-)-PCB 136 but not (+)-PCB 136 increases the frequency of spontaneous Ca²⁺ oscillations. Similarly, (-)-PCB 136 but not (+)-PCB 136 increases the activity of hippocampal neurons plated on microelectrode arrays. These data support the hypothesis that atropselective effects on RyR activity translate into atropselective effects of PCB 136 atropisomers on neuronal connectivity, and suggest that the variable atropisomeric enrichment of chiral PCBs observed in the human population may be a significant determinant of individual susceptibility for adverse neurodevelopmental outcomes following PCB exposure.

Association of VSNL1 with schizophrenia, frontal cortical function, and biological significance for its gene product as a modulator of cAMP levels and neuronal morphology

We report an association of single-nucleotide polymorphisms (SNPs) for the VSNL1 gene (visinin-like 1) with schizophrenia and frontal cortical function in a sample of patients with Diagnostic and Statistical Manual of Mental Disorder-IV (DSM-IV) diagnoses of schizophrenia, compared with healthy controls. Moreover, VSNL1 SNPs were associated with performance in the Wisconsin Card Sorting Test, a measure for the assessment of frontal cortical function. The VSNL1 gene product, Visinin-like-protein-1 (VILIP-1), is a member of the neuronal EF-hand Ca(2+)-sensor protein family. Previously, VILIP-1 mRNA and protein expression were shown to be altered in animal models and in schizophrenia patients. VILIP-1 influences cytosolic cyclic adenosine mono phosphate (cAMP) levels, cell migration, exocytotic processes and differentiation in the periphery. This raises the question, whether, similar to other potential schizophrenia susceptibility genes such as Disc1, PDE4B and Akt, VSNL1 may affect cAMP signaling and neurite outgrowth in neurons. In dissociated rat hippocampal neurons, VILIP-1 small interfering RNA knockdown decreased cAMP levels and reduced dendrite branching, compared with control-transfected cells. In contrast, VILIP-1 overexpression had the opposite effect. Similar results have been obtained in the human dopaminergic neuronal cell line SH-SY5Y, where the effect on neurite branching and length was attenuated by the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine and the protein kinase A inhibitor KT5720. These results show that the association of VSNL1 SNPs with the disease and cognitive impairments, together with previously observed pathological changes in VILIP-1 protein expression, possibly occurring during brain development, may contribute to the morphological and functional deficits observed in schizophrenia.

Biosynthesis, mode of action, and functional significance of neurosteroids in the purkinje cell

The brain has traditionally been considered to be a target site of peripheral steroid hormones. In addition to this classical concept, we now know that the brain has the capacity to synthesize steroids de novo from cholesterol, the so-called "neurosteroids." In the middle 1990s, the Purkinje cell, an important cerebellar neuron, was identified as a major site for neurosteroid formation in the brain of mammals and other vertebrates. This discovery has provided the opportunity to understand neuronal neurosteroidogenesis in the brain. In addition, biological actions of neurosteroids are becoming clear by the studies using the Purkinje cell, an excellent cellular model, which is known to play an important role in memory and learning processes. Based on the studies on mammals over the past decade, it is considered that the Purkinje cell actively synthesizes progesterone and estradiol from cholesterol during neonatal life, when cerebellar neuronal circuit formation occurs. Both progesterone and estradiol promote dendritic growth, spinogenesis, and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell. Such neurosteroid actions mediated by neurotrophic factors may contribute to the formation of cerebellar neuronal circuit during neonatal life. 3α,5α-Tetrahydroprogesterone (allopregnanolone), a progesterone metabolite, is also synthesized in the cerebellum and considered to act as a survival factor of Purkinje cells in the neonate. This review summarizes the current knowledge regarding the biosynthesis, mode of action, and functional significance of neurosteroids in the Purkinje cell during development in terms of synaptic formation of cerebellar neuronal networks.

Inhibitory but not excitatory cortical neurons require presynaptic brain-derived neurotrophic factor for dendritic development, as revealed by chimera cell culture

To address questions of whether endogenous BDNF acts differentially on inhibitory and excitatory neurons, and through what routes, we used chimera culture of cerebral cortical neurons derived from BDNF-/- mice and another type of transgenic mice that express green fluorescence protein and BDNF. Presynaptic BDNF transferred to both types of neurons, GABA-synthesizing enzyme-positive and -negative neurons. The latter neurons were confirmed to be glutamatergic with immunocytochemistry. Dendritic development of the former inhibitory neurons was promoted by endogenous BDNF transferred from presynaptic, excitatory neurons. In contrast, dendritic development of excitatory neurons was not related to the presence or absence of presynaptic BDNF, suggesting that BDNF acts on inhibitory neurons through an anterograde, transsynaptic route so as to promote dendritic development, whereas this is not the case in excitatory neurons.

Unilateral sensorimotor cortex lesions in adult rats facilitate motor skill learning with the "unaffected" forelimb and training-induced dendritic structural plasticity in the motor cortex

In humans and other animals, sufficient unilateral damage to the sensorimotor cortex can cause impairments in the opposite forelimb and the development of a hyper-reliance on the nonimpaired limb. This hyper-reliance is adaptive to the extent that it contributes to functional compensation for lesion-induced impairments. We have found that unilateral lesions of the forelimb region of the sensorimotor cortex (FLsmc) in rats, or callosal transections, cause neurons of the opposite motor cortex to become exceptionally responsive to changes in forelimb behavior. This enhanced responsiveness might facilitate learning of compensatory strategies with the nonimpaired forelimb after unilateral FLsmc lesions. The possibility that these lesions facilitate learning with the nonimpaired forelimb was addressed in this study. Rats were required to learn a skilled forelimb reaching task after either unilateral FLsmc lesions or sham operations. The trained limb in animals with lesions was the nonimpaired limb. Compared with shams, rats with unilateral lesions had a greater rate of acquisition and asymptotic performance level on the task, which was especially evident on more difficult trials. Quantitative measures of microtubule associated protein-2 (MAP2) immunostained dendrites indicated an enhancement of training-induced dendritic cytoskeletal changes in the motor cortex opposite lesions. Thus, unilateral FLsmc lesions facilitate learning of at least some types of motor skills using the nonimpaired forelimb as well as some of the neuronal changes associated with this learning. This facilitation could be a substrate underlying behavioral compensation for unilateral FLsmc damage and may contribute to the phenomenon of learned nonuse of the impaired limb.

Dynamic regulation of cpg15 during activity-dependent synaptic development in the mammalian visual system

During visual system development, neural activity regulates structural changes in connectivity including axonal branching and dendritic growth. Here we have examined a role for the candidate plasticity gene 15 (cpg15), which encodes an activity-regulated molecule that can promote dendritic growth, in this process. We report that cpg15 is expressed in the cat visual system at relatively high levels in the lateral geniculate nucleus (LGN) but at very low levels in its synaptic target, layer 4 of the visual cortex. Prenatally, when cpg15 mRNA in the LGN is most abundant, expression is insensitive to action potential blockade by tetrodotoxin. Postnatally, activity regulation of cpg15 emerges in the LGN coincident with development of ocular dominance columns in the visual cortex. cpg15 can be detected in layers 2/3 and 5/6 of visual cortex postnatally, and expression in layers 2/3 is activity-regulated during known periods of activity-dependent plasticity for these layers. Localization and regulation of cpg15 expression in the visual system are consistent with a presynaptic role for CPG15 in shaping dendritic arbors of target neurons during activity-dependent synaptic rearrangements, both in development and adulthood.