Numerous candidate plasticity-related genes revealed by differential cDNA cloning

Neuronal activity modifies the chromatin accessibility landscape in the adult brain

Neuronal activity-induced gene expression modulates the function and plasticity of the nervous system. It is unknown whether and to what extent neuronal activity may trigger changes in chromatin accessibility, a major mode of epigenetic regulation of gene expression. Here we compared chromatin accessibility landscapes of adult mouse dentate granule neurons in vivo before and after synchronous neuronal activation using ATAC-seq. We found widespread, genome-wide changes one hour after activation, with enrichment of gained-open sites at active enhancer regions and at binding sites for AP1 complex components, including cFos. Some changes remain stable for at least twenty-four hours. Functional analysis further implicates a critical role of cFos in initiating, but not maintaining, neuronal activity-induced chromatin opening. Our results reveal dynamic changes of chromatin accessibility in the adult mammalian brain and suggest an epigenetic mechanism by which transient neuronal activation leads to dynamic changes in gene expression via modifying chromatin accessibility.

Soluble cpg15 from Astrocytes Ameliorates Neurite Outgrowth Recovery of Hippocampal Neurons after Mouse Cerebral Ischemia

The present study focuses on the function of cpg15, a neurotrophic factor, in ischemic neuronal recovery using transient global cerebral ischemic (TGI) mouse model and oxygen-glucose deprivation (OGD)-treated primary cultured cells. The results showed that expression of cpg15 proteins in astrocytes, predominantly the soluble form, was significantly increased in mouse hippocampus after TGI and in the cultured astrocytes after OGD. Addition of the medium from the cpg15-overexpressed astrocytic culture into the OGD-treated hippocampal neuronal cultures reduces the neuronal injury, whereas the recovery of neurite outgrowths of OGD-injured neurons was prevented when cpg15 in the OGD-treated astrocytes was knocked down, or the OGD-treated-astrocytic medium was immunoadsorbed by cpg15 antibody. Furthermore, lentivirus-delivered knockdown of cpg15 expression in mouse hippocampal astrocytes diminishes the dendritic branches and exacerbates injury of neurons in CA1 region after TGI. In addition, treatment with inhibitors of MEK1/2, PI3K, and TrkA decreases, whereas overexpression of p-CREB, but not dp-CREB, increases the expression of cpg15 in U118 or primary cultured astrocytes. Also, it is observed that the Flag-tagged soluble cpg15 from the astrocytes transfected with Flag-tagged cpg15-expressing plasmids adheres to the surface of neuronal bodies and the neurites. In conclusion, our results suggest that the soluble cpg15 from astrocytes induced by ischemia could ameliorate the recovery of the ischemic-injured hippocampal neurons via adhering to the surface of neurons. The upregulated expression of cpg15 in astrocytes may be activated via MAPK and PI3K signal pathways, and regulation of CREB phosphorylation.SIGNIFICANCE STATEMENT Neuronal plasticity plays a crucial role in the amelioration of neurological recovery of ischemic injured brain, which remains a challenge for clinic treatment of cerebral ischemia. cpg15 as a synaptic plasticity-related factor may participate in promoting the recovery process; however, the underlying mechanisms are still largely unknown. The objective of this study is to reveal the function and mechanism of neuronal-specific cpg15 expressed in astrocytes after ischemia induction, in promoting the recovery of injured neurons. Our findings provided new mechanistic insight into the neurological recovery, which might help develop novel therapeutic options for cerebral ischemia via astrocytic-targeting interference of gene expression.

Recombinant hNeuritin Promotes Structural and Functional Recovery of Sciatic Nerve Injury in Rats

Neuritin is a new neurotropic factor implicated in nervous system development and plasticity. Studies have shown that Neuritin is upregulated in injured nerves, suggesting that it is involved in nerve repair. To test this hypothesis, we investigated whether recombinant human Neuritin could restore nerve structure and function in a rat model of sciatic nerve injury. Neuritin treatment had a dose-dependent effect on functional recovery 4 weeks after injury, as determined by the walking-track test. Similar trends were observed for gastrocnemius muscular strength and nerve conduction velocity. Additionally, sciatic nerve fiber density and organization as well as degree of remyelination were increased, while growth-associated protein 43 and neurofilament 200 expression was upregulated upon treatment with Neuritin. These findings demonstrate that Neuritin stimulates nerve regeneration and functional recovery and thus promotes the repair of injured sciatic nerves.

Involvement of NRN1 gene in schizophrenia-spectrum and bipolar disorders and its impact on age at onset and cognitive functioning

OBJECTIVES

Neuritin 1 gene (NRN1) is involved in neurodevelopment processes and synaptic plasticity and its expression is regulated by brain-derived neurotrophic factor (BDNF). We aimed to investigate the association of NRN1 with schizophrenia-spectrum disorders (SSD) and bipolar disorders (BPD), to explore its role in age at onset and cognitive functioning, and to test the epistasis between NRN1 and BDNF.

METHODS

The study was developed in a sample of 954 SSD/BPD patients and 668 healthy subjects. Genotyping analyses included 11 SNPs in NRN1 and one functional SNP in BDNF.

RESULTS

The frequency of the haplotype C-C (rs645649-rs582262) was significantly increased in patients compared to controls (P = 0.0043), while the haplotype T-C-C-T-C-A (rs3763180-rs10484320-rs4960155-rs9379002-rs9405890-rs1475157) was more frequent in controls (P = 3.1 × 10(-5)). The variability at NRN1 was nominally related to changes in age at onset and to differences in intelligence quotient, in SSD patients. Epistasis between NRN1 and BDNF was significantly associated with the risk for SSD/BPD (P = 0.005).

CONCLUSIONS

Results suggest that: (i) NRN1 variability is a shared risk factor for both SSD and BPD, (ii) NRN1 may have a selective impact on age at onset and intelligence in SSD, and (iii) the role of NRN1 seems to be not independent of BDNF.

An Evolutionarily Conserved Mechanism for Activity-Dependent Visual Circuit Development

Neural circuit development is an activity-dependent process. This activity can be spontaneous, such as the retinal waves that course across the mammalian embryonic retina, or it can be sensory-driven, such as the activation of retinal ganglion cells (RGCs) by visual stimuli. Whichever the source, neural activity provides essential instruction to the developing circuit. Indeed, experimentally altering activity has been shown to impact circuit development and function in many different ways and in many different model systems. In this review, we contemplate the idea that retinal waves in amniotes, the animals that develop either in ovo or utero (namely reptiles, birds and mammals) could be an evolutionary adaptation to life on land, and that the anamniotes, animals whose development is entirely external (namely the aquatic amphibians and fish), do not display retinal waves, most likely because they simply don’t need them. We then review what is known about the function of both retinal waves and visual stimuli on their respective downstream targets, and predict that the experience-dependent development of the tadpole visual system is a blueprint of what will be found in future studies of the effects of spontaneous retinal waves on instructing development of retinorecipient targets such as the superior colliculus (SC) and the lateral geniculate nucleus.

Neuritin Mediates Activity-Dependent Axonal Branch Formation in Part via FGF Signaling

Aberrant branch formation of granule cell axons (mossy fiber sprouting) is observed in the dentate gyrus of many patients with temporal lobe epilepsy and in animal models of epilepsy. However, the mechanisms underlying mossy fiber sprouting remain elusive. Based on the hypothesis that seizure-mediated gene expression induces abnormal mossy fiber growth, we screened activity-regulated genes in the hippocampus and found that neuritin, an extracellular protein anchored to the cell surface, was rapidly upregulated after electroconvulsive seizures. Overexpression of neuritin in the cultured rat granule cells promoted their axonal branching. Also, kainic acid-dependent axonal branching was abolished in the cultured granule cells fromneuritinknock-out mice, suggesting that neuritin may be involved in activity-dependent axonal branching. Moreover,neuritinknock-out mice showed less-severe seizures in chemical kindling probably by reduced mossy fiber sprouting and/or increased seizure resistance. We found that inhibition of the fibroblast growth factor (FGF) receptor attenuated the neuritin-dependent axonal branching. FGF administration also increased branching in granule neurons, whereasneuritinknock-out mice did not show FGF-dependent axonal branching. In addition, FGF and neuritin treatment enhanced the recruitment of FGF receptors to the cell surface. These findings suggest that neuritin and FGF cooperate in inducing mossy fiber sprouting through FGF signaling. Together, these results suggest that FGF and neuritin-mediated axonal branch induction are involved in the aggravation of epilepsy.

SIGNIFICANCE STATEMENT

This study reveals the molecular mechanism underlying mossy fiber sprouting. Mossy fiber sprouting is the aberrant axonal branching of granule neurons in the hippocampus, which is observed in patients with epilepsy. Excess amounts of neuritin, a protein upregulated by neural activity, promoted axonal branching in granule neurons. A deficiency of neuritin suppressed mossy fiber sprouting and resulted in mitigation of seizure severity. Neuritin and fibroblast growth factor (FGF) cooperated in stimulating FGF signaling and enhancing axonal branching. Neuritin is necessary for FGF-mediated recruitment of FGF receptors to the cell surface. The recruitment of FGF receptors would promote axonal branching. The discovery of this new mechanism should contribute to the development of novel antiepileptic drugs to inhibit axonal branching via neuritin-FGF signaling.

Development of TIMP1 magnetic nanoformulation for regulation of synaptic plasticity in HIV-1 infection

Although the introduction of antiretroviral therapy has reduced the prevalence of severe forms of neurocognitive disorders, human immunodeficiency virus (HIV)-1-associated neurocognitive disorders were observed in 50% of HIV-infected patients globally. The blood–brain barrier is known to be impermeable to most of antiretroviral drugs. Successful delivery of antiretroviral drugs into the brain may induce an inflammatory response, which may further induce neurotoxicity. Therefore, alternate options to antiretroviral drugs for decreasing the HIV infection and neurotoxicity may help in reducing neurocognitive impairments observed in HIV-infected patients. In this study, we explored the role of magnetic nanoparticle (MNP)-bound tissue inhibitor of metalloproteinase-1 (TIMP1) protein in reducing HIV infection levels, oxidative stress, and recovering spine density in HIV-infected SK-N-MC neuroblastoma cells. We did not observe any neuronal cytotoxicity with either the free TIMP1 or MNP-bound TIMP1 used in our study. We observed significantly reduced HIV infection in both solution phase and in MNP-bound TIMP1-exposed neuronal cells. Furthermore, we also observed significantly reduced reactive oxygen species production in both the test groups compared to the neuronal cells infected with HIV alone. To observe the effect of both soluble-phase TIMP1 and MNP-bound TIMP1 on spine density in HIV-infected neuronal cells, confocal microscopy was used. We observed significant recovery of spine density in both the test groups when compared to the cells infected with HIV alone, indicting the neuroprotective effect of TIMP1. Therefore, our results suggest that the MNP-bound TIMP1 delivery method across the blood–brain barrier can be used for reducing HIV infectivity in brain tissue and neuronal toxicity in HIV-infected patients.

Upregulation of μ3A Drives Homeostatic Plasticity by Rerouting AMPAR into the Recycling Endosomal Pathway

Synaptic scaling is a form of homeostatic plasticity driven by transcription-dependent changes in AMPA-type glutamate receptor (AMPAR) trafficking. To uncover the pathways involved, we performed a cell-type-specific screen for transcripts persistently altered during scaling, which identified the μ subunit (μ3A) of the adaptor protein complex AP-3A. Synaptic scaling increased μ3A (but not other AP-3 subunits) in pyramidal neurons and redistributed dendritic μ3A and AMPAR to recycling endosomes (REs). Knockdown of μ3A prevented synaptic scaling and this redistribution, while overexpression (OE) of full-length μ3A or a truncated μ3A that cannot interact with the AP-3A complex was sufficient to drive AMPAR to REs. Finally, OE of μ3A acted synergistically with GRIP1 to recruit AMPAR to the dendritic membrane. These data suggest that excess μ3A acts independently of the AP-3A complex to reroute AMPAR to RE, generating a reservoir of receptors essential for the regulated recruitment to the synaptic membrane during scaling up.

REVIEW ■ : Jun, Fos, and CREB/ATF Transcription Factors in the Brain: Control of Gene Expression under Normal and Pathophysiological Conditions

The expression and activation of transcription factors and the control of gene transcription in the nervous system is a recent and rapidly expanding field in neurosciences. This research area may provide insights concerning the information transfer that arises from postsynaptic potentials or ligand-coupling of membrane receptors and terminates in gene expression. Visualization of both de novo synthesis of inducible transcription factors (ITFs) and phosphorylation of preexisting transcription factors have been used to mark neurons, pathways, and networks excited by various stimuli. This article summarizes basics of the transcription process and the complex functions of Jun, Fos, and CREB/ATF proteins, as well as the use of ITFs as experimental instruments in neurophysiology and neurobiology. The major focus is on the alterations in ITF expression following acute or chronic pathophysiological stimuli as mirrors of alterations in neuronal programs underlying adaptation, dysfunctions, or the development of diseases affecting the nervous system. NEUROSCIENTIST 2:153-161, 1996

Multiplexed Intact-Tissue Transcriptional Analysis at Cellular Resolution

In recently developed approaches for high-resolution imaging within intact tissue, molecular characterization over large volumes has been largely restricted to labeling of proteins. But volumetric nucleic acid labeling may represent a far greater scientific and clinical opportunity, enabling detection of not only diverse coding RNA variants but also non-coding RNAs. Moreover, scaling immunohistochemical detection to large tissue volumes has limitations due to high cost, limited renewability/availability, and restricted multiplexing capability of antibody labels. With the goal of versatile, high-content, and scalable molecular phenotyping of intact tissues, we developed a method using carbodiimide-based chemistry to stably retain RNAs in clarified tissue, coupled with amplification tools for multiplexed detection. The resulting technology enables robust measurement of activity-dependent transcriptional signatures, cell-identity markers, and diverse non-coding RNAs in rodent and human tissue volumes. The growing set of validated probes is deposited in an online resource for nucleating related developments from across the scientific community.

Gene Expression in Hippocampal Long-Term Potentiation

Recent work on hippocampal LTP has focused on gene expression induced with high-frequency stimulation, as well as the signal transduction cascades responsible for the induction of these genes. Many scenarios for LTP lasting for greater than 5 hours include some or all of the following processes: 1) tagging of potentiated synapses, possibly by phosphorylation; 2) signaling to the nucleus; 3) kinase cascades and transcription factors in the nucleus;, 4) expression of immediate-early genes and/or synaptic proteins; and, finally, 5) targeting of newly synthesized proteins (or RNAs) to the potentiated synapses (and not to the unpotentiated synapses). Unfortunately, most scenarios proposed for the late-phase expression of LTP are still highly speculative at this time. A critical review of the literature relating to the role of gene expression in hippocampal LTP and a discussion of recent work on the subject will be presented.

Transient ECM protease activity promotes synaptic plasticity

Activity-dependent proteolysis at a synapse has been recognized as a pivotal factor in controlling dynamic changes in dendritic spine shape and function; however, excessive proteolytic activity is detrimental to the cells. The exact mechanism of control of these seemingly contradictory outcomes of protease activity remains unknown. Here, we reveal that dendritic spine maturation is strictly controlled by the proteolytic activity, and its inhibition by the endogenous inhibitor (Tissue inhibitor of matrix metalloproteinases-1 – TIMP-1). Excessive proteolytic activity impairs long-term potentiation of the synaptic efficacy (LTP), and this impairment could be rescued by inhibition of protease activity. Moreover LTP is altered persistently when the ability of TIMP-1 to inhibit protease activity is abrogated, further demonstrating the role of such inhibition in the promotion of synaptic plasticity under well-defined conditions. We also show that dendritic spine maturation involves an intermediate formation of elongated spines, followed by their conversion into mushroom shape. The formation of mushroom-shaped spines is accompanied by increase in AMPA/NMDA ratio of glutamate receptors. Altogether, our results identify inhibition of protease activity as a critical regulatory mechanism for dendritic spines maturation.

Adult Deletion of SRF Increases Epileptogenesis and Decreases Activity-Induced Gene Expression

Although the transcription factor serum response factor (SRF) has been suggested to play a role in activity-dependent gene expression and mediate plasticity-associated structural changes in the hippocampus, no unequivocal evidence has been provided for its role in brain pathology, such as epilepsy. A genome-wide program of activity-induced genes that are regulated by SRF also remains unknown. In the present study, we show that the inducible and conditional deletion of SRF in the adult mouse hippocampus increases the epileptic phenotype in the kainic acid model of epilepsy, reflected by more severe and frequent seizures. Moreover, we observe a robust decrease in activity-induced gene transcription in SRF knockout mice. We characterize the genetic program controlled by SRF in neurons and using functional annotation, we find that SRF target genes are associated with synaptic plasticity and epilepsy. Several of these SRF targets function as regulators of inhibitory or excitatory balance and the structural plasticity of neurons. Interestingly, mutations in those SRF targets have found to be associated with such human neuropsychiatric disorders, as autism and intellectual disability. We also identify novel direct SRF targets in hippocampus: Npas4, Gadd45g, and Zfp36. Altogether, our data indicate that proteins that are highly upregulated by neuronal stimulation, identified in the present study as SRF targets, may function as endogenous protectors against overactivation. Thus, the lack of these effector proteins in SRF knockout animals may lead to uncontrolled excitation and eventually epilepsy.

Exploring Memory Representations with Activity-Based Genetics

The brain is thought to represent specific memories through the activity of sparse and distributed neural ensembles. In this review, we examine the use of immediate early genes (IEGs), genes that are induced by neural activity, to specifically identify and genetically modify neurons activated naturally by environmental experience. Recent studies using this approach have identified cellular and molecular changes specific to neurons activated during learning relative to their inactive neighbors. By using opto- and chemogenetic regulators of neural activity, the neurons naturally recruited during learning can be artificially reactivated to directly test their role in coding external information. In contextual fear conditioning, artificial reactivation of learning-induced neural ensembles in the hippocampus or neocortex can substitute for the context itself. That is, artificial stimulation of these neurons can apparently cause the animals to "think" they are in the context. This represents a powerful approach to testing the principles by which the brain codes for the external world and how these circuits are modified with learning.

Genomic mapping and cellular expression of human CPG2 transcripts in the SYNE1 gene

Bipolar disorder (BD) is a prevalent and severe mood disorder characterized by recurrent episodes of mania and depression. Both genetic and environmental factors have been implicated in BD etiology, but the biological underpinnings remain elusive. Recent genome-wide association studies (GWAS) for identifying genes conferring risk for schizophrenia, BD, and major depression, identified an association between single-nucleotide polymorphisms (SNPs) in the SYNE1 gene and increased risk of BD. SYNE1 has also been identified as a risk locus for multiple other neurological or neuromuscular genetic disorders. The BD associated SNPs map within the gene region homologous to part of rat Syne1 encompassing the brain specific transcripts encoding CPG2, a postsynaptic neuronal protein localized to excitatory synapses and an important regulator of glutamate receptor internalization. Here, we use RNA-seq, ChIP-seq and RACE to map the human SYNE1 transcriptome, focusing on the CPG2 locus. We validate several CPG2 transcripts, including ones not previously annotated in public databases, and identify and clone a full-length CPG2 cDNA expressed in human neocortex, hippocampus and striatum. Using lenti-viral gene knock down/replacement and surface receptor internalization assays, we demonstrate that human CPG2 protein localizes to dendritic spines in rat hippocampal neurons and is functionally equivalent to rat CPG2 in regulating glutamate receptor internalization. This study provides a valuable gene-mapping framework for relating multiple genetic disease loci in SYNE1 with their transcripts, and for evaluating the effects of missense SNPs identified by patient genome sequencing on neuronal function.

Overexpression of neuritin in gastric cancer

The aim of the present study was to investigate the expression of neuritin in gastric cancer tissues, in order to explore the association between the expression of neuritin and the occurrence and development of gastric cancer. Tissue specimens were collected from 58 patients with gastric cancer. Immunohistochemistry, western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) were used to determine the expression of neuritin in the gastric cancer and corresponding adjacent normal gastric tissues. The expression rate of neuritin in gastric cancer tissues was 96.55% (56/58), demonstrating no statistically significant difference from the expression rate in the adjacent normal tissues (94.83%) (P>0.05). However, the rate of strong neuritin expression in gastric cancer tissues (82.76%) was significantly increased compared with the rate in the adjacent normal tissues (15.52%) (P<0.05). Neuritin expression exhibited no correlation with the gender or age of patients, tumor-node-metastasis staging, tumor depth, presence of lymph node metastasis, histological or pathological type of the tumor or presence of distant metastasis (P>0.05). As determined by RT-PCR and western blot analysis, the mRNA expression of neuritin in gastric cancer tissues was markedly increased compared with the expression in the adjacent normal tissues. In conclusion, neuritin is highly expressed in gastric cancer tissues, suggesting that neuritin may act as a novel potential target for the treatment of gastric cancer.

Effects of a Neonatal Experience Involving Reward Through Maternal Contact on the Noradrenergic System of the Rat Prefrontal Cortex

The noradrenergic system plays an important role in prefrontal cortex (PFC) function. Since early life experiences play a crucial role in programming brain function, we investigated the effects of a neonatal experience involving reward through maternal contact on the noradrenergic system of the rat PFC. Rat pups were exposed during Postnatal days (PNDs) 10-13, to a T-maze in which contact with the mother was used as a reward (RER). RER males had higher norepinephrine levels in the PFC both on PND 13 and in adulthood. The RER experience resulted in adulthood in increased levels of the active demethylase GADD45b, hypomethylation of the β1 adrenergic receptor (ADRB1) gene promoter, and consequent enhanced expression of its mRNA in the PFC. In addition, protein and binding levels of the ADRB1, as well as those of its downstream effector phosphorylated cAMP response element-binding protein were elevated in RER males. The higher activity of the PFC noradrenergic system of the RER males was reflected in their superior performance in the olfactory discrimination and the contextual fear extinction, 2 PFC noradrenergic system-dependent behavioral tasks.

Neuritin 1 promotes retinal ganglion cell survival and axonal regeneration following optic nerve crush

Neuritin 1 (Nrn1) is an extracellular glycophosphatidylinositol-linked protein that stimulates axonal plasticity, dendritic arborization and synapse maturation in the central nervous system (CNS). The purpose of this study was to evaluate the neuroprotective and axogenic properties of Nrn1 on axotomized retinal ganglion cells (RGCs) in vitro and on the in vivo optic nerve crush (ONC) mouse model. Axotomized cultured RGCs treated with recombinant hNRN1 significantly increased survival of RGCs by 21% (n=6–7, P<0.01) and neurite outgrowth in RGCs by 141% compared to controls (n=15, P<0.05). RGC transduction with AAV2-CAG–hNRN1 prior to ONC promoted RGC survival (450%, n=3–7, P<0.05) and significantly preserved RGC function by 70% until 28 days post crush (dpc) (n=6, P<0.05) compared with the control AAV2-CAG–green fluorescent protein transduction group. Significantly elevated levels of RGC marker, RNA binding protein with multiple splicing (Rbpms; 73%, n=5–8, P<0.001) and growth cone marker, growth-associated protein 43 (Gap43; 36%, n=3, P<0.01) were observed 28 dpc in the retinas of the treatment group compared with the control group. Significant increase in Gap43 (100%, n=5–6, P<0.05) expression was observed within the optic nerves of the AAV2–hNRN1 group compared to controls. In conclusion, Nrn1 exhibited neuroprotective, regenerative effects and preserved RGC function on axotomized RGCs in vitro and after axonal injury in vivo. Nrn1 is a potential therapeutic target for CNS neurodegenerative diseases.

Neuritin can normalize neural deficits of Alzheimer's disease

Reductions in hippocampal neurite complexity and synaptic plasticity are believed to contribute to the progressive impairment in episodic memory and the mild cognitive decline that occur particularly in the early stages of Alzheimer's disease (AD). Despite the functional and therapeutic importance for patients with AD, intervention to rescue or normalize dendritic elaboration and synaptic plasticity is scarcely provided. Here we show that overexpression of neuritin, an activity-dependent protein, promoted neurite outgrowth and maturation of synapses in parallel with enhanced basal synaptic transmission in cultured hippocampal neurons. Importantly, exogenous application of recombinant neuritin fully restored dendritic complexity as well as spine density in hippocampal neurons prepared from Tg2576 mice, whereas it did not affect neurite branching of neurons from their wild-type littermates. We also showed that soluble recombinant neuritin, when chronically infused into the brains of Tg2576 mice, normalized synaptic plasticity in acute hippocampal slices, leading to intact long-term potentiation. By revealing the protective actions of soluble neuritin against AD-related neural defects, we provide a potential therapeutic approach for patients with AD.

Extracellular matrix control of dendritic spine and synapse structure and plasticity in adulthood

Dendritic spines are the receptive contacts at most excitatory synapses in the central nervous system. Spines are dynamic in the developing brain, changing shape as they mature as well as appearing and disappearing as they make and break connections. Spines become much more stable in adulthood, and spine structure must be actively maintained to support established circuit function. At the same time, adult spines must retain some plasticity so their structure can be modified by activity and experience. As such, the regulation of spine stability and remodeling in the adult animal is critical for normal function, and disruption of these processes is associated with a variety of late onset diseases including schizophrenia and Alzheimer's disease. The extracellular matrix (ECM), composed of a meshwork of proteins and proteoglycans, is a critical regulator of spine and synapse stability and plasticity. While the role of ECM receptors in spine regulation has been extensively studied, considerably less research has focused directly on the role of specific ECM ligands. Here, we review the evidence for a role of several brain ECM ligands and remodeling proteases in the regulation of dendritic spine and synapse formation, plasticity, and stability in adults.

Human neural stem cell transplantation provides long-term restoration of neuronal plasticity in the irradiated hippocampus

For the majority of CNS malignancies, radiotherapy provides the best option for forestalling tumor growth, but is frequently associated with debilitating and progressive cognitive dysfunction. Despite the recognition of this serious side effect, satisfactory long-term solutions are not currently available and have prompted our efforts to explore the potential therapeutic efficacy of cranial stem cell transplants. We have demonstrated that intrahippocampal transplantation of human neural stem cells (hNSCs) can provide long-lasting cognitive benefits using an athymic rat model subjected to cranial irradiation. To explore the possible mechanisms underlying the capability of engrafted cells to ameliorate radiation-induced cognitive dysfunction we analyzed the expression patterns of the behaviorally induced activity-regulated cytoskeleton-associated protein (Arc) in the hippocampus at 1 and 8 months postgrafting. While immunohistochemical analyses revealed a small fraction (4.5%) of surviving hNSCs in the irradiated brain that did not express neuronal or astroglial makers, hNSC transplantation impacted the irradiated microenvironment of the host brain by promoting the expression of Arc at both time points. Arc is known to play key roles in the neuronal mechanisms underlying long-term synaptic plasticity and memory and provides a reliable marker for detecting neurons that are actively engaged in spatial and contextual information processing associated with memory consolidation. Cranial irradiation significantly reduced the number of pyramidal (CA1) and granule neurons (DG) expressing behaviorally induced Arc at 1 and 8 months postirradiation. Transplantation of hNSCs restored the expression of plasticity-related Arc in the host brain to control levels. These findings suggest that hNSC transplantation promotes the long-term recovery of host hippocampal neurons and indicates that one mechanism promoting the preservation of cognition after irradiation involves trophic support from engrafted cells.

Neuritin attenuates cognitive function impairments in tg2576 mouse model of Alzheimer's disease

Neuritin, also known as CPG15, is a neurotrophic factor that was initially discovered in a screen to identify genes involved in activity-dependent synaptic plasticity. Neuritin plays multiple roles in the process of neural development and synaptic plasticity, although its binding receptor(s) and downstream signaling effectors remain unclear. In this study, we found that the cortical and hippocampal expression of neuritin is reduced in the brains of Alzheimer's disease (AD) patients and demonstrated that viral-mediated expression of neuritin in the dentate gyrus of 13-month-old Tg2576 mice, an AD animal model, attenuated a deficit in learning and memory as assessed by a Morris water maze test. We also found that neuritin restored the reduction in dendritic spine density and the maturity of individual spines in primary hippocampal neuron cultures prepared from Tg2576 mice. It was also shown that viral-mediated expression of neuritin in the dentate gyrus of 7-week-old Sprague-Dawley rats increased neurogenesis in the hippocampus. Taken together, our results demonstrate that neuritin restores the reduction in dendritic spine density and the maturity of individual spines in primary hippocampal neurons from Tg2576 neurons, and also attenuates cognitive function deficits in Tg2576 mouse model of AD, suggesting that neuritin possesses a therapeutic potential for AD.

Combined neuroimaging and gene expression analysis of the genetic basis of brain plasticity indicates across species homology

Brain plasticity and memory formation depend on the expression of a large number of genes. This relationship had been studied using several experimental approaches and researchers have identified genes regulating plasticity through a variety of mechanisms. Despite this effort, a great deal remains unknown regarding the role of different genes in brain plasticity. Previous studies usually focused on specific brain structures and many of the genes influencing plasticity have yet to be identified. In this work, we integrate results of in vivo neuroimaging studies of plasticity with whole-brain gene expression data for the study of neuroplasticity. Brain regions, found in the imaging study to be involved in plasticity, are first spatially mapped to the anatomical framework of the genetic database. Feature ranking methods are then applied to identify genes that are differentially expressed in these regions. We find that many of our highly ranked genes are involved in synaptic transmission and that some of these genes have been previously associated with learning and memory. We show these results to be consistent when applying our method to gene expression data from four human subjects. Finally, by performing similar experiments in mice, we reveal significant cross species correlation in the ranking of genes. In addition to the identification of plasticity related candidate genes, our results also demonstrate the potential of data integration approaches as a tool to link high level phenomena such as learning and memory to underlying molecular mechanisms.

Matrix metalloproteinase-9 involvement in the structural plasticity of dendritic spines

Dendritic spines are the locus for excitatory synaptic transmission in the brain and thus play a major role in neuronal plasticity. The ability to alter synaptic connections includes volumetric changes in dendritic spines that are driven by scaffolds created by the extracellular matrix (ECM). Here, we review the effects of the proteolytic activity of ECM proteases in physiological and pathological structural plasticity. We use matrix metalloproteinase-9 (MMP-9) as an example of an ECM modifier that has recently emerged as a key molecule in regulating the morphology and dysmorphology of dendritic spines that underlie synaptic plasticity and neurological disorders, respectively. We summarize the influence of MMP-9 on the dynamic remodeling of the ECM via the cleavage of extracellular substrates. We discuss its role in the formation, modification, and maintenance of dendritic spines in learning and memory. Finally, we review research that implicates MMP-9 in aberrant synaptic plasticity and spine dysmorphology in neurological disorders, with a focus on morphological abnormalities of dendritic protrusions that are associated with epilepsy.

Molecular mechanisms of activity-dependent changes in dendritic morphology: role of RGK proteins

The nervous system has the amazing capacity to transform sensory experience from the environment into changes in neuronal activity that, in turn, cause long-lasting alterations in neuronal morphology. Recent findings indicate that, surprisingly, sensory experience concurrently activates molecular signaling pathways that both promote and inhibit dendritic complexity. Historically, a number of positive regulators of activity-dependent dendritic complexity have been described, whereas the list of identified negative regulators of this process is much shorter. In recent years, there has been an emerging appreciation of the importance of the Rad/Rem/Rem2/Gem/Kir (RGK) GTPases as mediators of activity-dependent structural plasticity. In the following review, we discuss the traditional view of RGK proteins, as well as our evolving understanding of the role of these proteins in instructing structural plasticity.

The neuronal activity-driven transcriptome

Activity-driven transcription is a key event associated with long-lasting forms of neuronal plasticity. Despite the efforts to investigate the regulatory mechanisms that control this complex process and the important advances in the knowledge of the function of many activity-induced genes in neurons, as well as the specific contribution of activity-regulated transcription factors, our understanding of how activity-driven transcription operates at the systems biology level is still very limited. This review focuses on the research of neuronal activity-driven transcription from an "omics" perspective. We will discuss the different high-throughput approaches undertaken to characterize the gene programs downstream of specific activity-regulated transcription factors, including CREB, SRF, MeCP2, Fos, Npas4, and others, and the interplay between epigenetic and transcriptional mechanisms underlying neuronal plasticity changes. Although basic questions remain unanswered and important challenges still lie ahead, the refinement of genome-wide techniques for investigating the neuronal transcriptome and epigenome promises great advances.

Aberrant development and plasticity of excitatory visual cortical networks in the absence of cpg15

During development, experience plays a crucial role in sculpting neuronal connections. Patterned neural activity guides formation of functional neural circuits through the selective stabilization of some synapses and the pruning of others. Activity-regulated factors are fundamental to this process, but their roles in synapse stabilization and maturation is still poorly understood. CPG15, encoded by the activity-regulated gene candidate plasticity gene 15, is a small, glycosylphosphatidylinositol (GPI)-linked, extracellular protein that promotes synapse stabilization. Here we show that global knock-out of cpg15 results in abnormal postnatal development of the excitatory network in visual cortex and an associated disruption in development of visual receptive field properties. In addition, whereas repeated stimulation induced potentiation and depression in wild-type mice, the depression was slower in cpg15 knock-out mice, suggesting impairment in short-term depression-like mechanisms. These findings establish the requirement for cpg15 in activity-dependent development of the visual system and demonstrate the importance of timely excitatory network development for normal visual function.

Adipose tissue insulin receptor knockdown via a new primate-derived hybrid recombinant AAV serotype

Adipose tissue plays an essential role in metabolic homeostasis and holds promise as an alternative depot organ in gene therapy. However, efficient methods of gene transfer into adipose tissue in vivo have yet to be established. Here, we assessed the transduction efficiency to fat depots by a family of novel engineered hybrid capsid serotypes (Rec1~4) recombinant adeno-associated viral (AAV) vectors in comparison with natural serotypes AAV1, AAV8, and AAV9. Rec2 serotype led to widespread transduction in both brown fat and white fat with the highest efficiency among the seven serotypes tested. As a proof-of-efficacy, Rec2 serotype was used to deliver Cre recombinase to adipose tissues of insulin receptor floxed animals. Insulin receptor knockdown led to decreased fat pad mass and morphological and molecular changes in the targeted depot. These novel hybrid AAV vectors can serve as powerful tools to genetically manipulate adipose tissue and provide valuable vehicles to gene therapy targeting adipose tissue.

Neural ECM proteases in learning and synaptic plasticity

Recent studies implicate extracellular proteases in synaptic plasticity, learning, and memory. The data are especially strong for such serine proteases as thrombin, tissue plasminogen activator, neurotrypsin, and neuropsin as well as matrix metalloproteinases, MMP-9 in particular. The role of those enzymes in the aforementioned phenomena is supported by the experimental results on the expression patterns (at the gene expression and protein and enzymatic activity levels) and functional studies, including knockout mice, specific inhibitors, etc. Counterintuitively, the studies have shown that the extracellular proteolysis is not responsible mainly for an overall degradation of the extracellular matrix (ECM) and loosening perisynaptic structures, but rather allows for releasing signaling molecules from the ECM, transsynaptic proteins, and latent form of growth factors. Notably, there are also indications implying those enzymes in the major neuropsychiatric disorders, probably by contributing to synaptic aberrations underlying such diseases as schizophrenia, bipolar, autism spectrum disorders, and drug addiction.

Regulation of glutamate receptor internalization by the spine cytoskeleton is mediated by its PKA-dependent association with CPG2

A key neuronal mechanism for adjusting excitatory synaptic strength is clathrin-mediated endocytosis of postsynaptic glutamate receptors (GluRs). The actin cytoskeleton is critical for clathrin-mediated endocytosis, yet we lack a mechanistic understanding of its interaction with the endocytic process and how it may be regulated. Here we show that F-actin in dendritic spines physically binds the synaptic nuclear envelope 1 gene product candidate plasticity gene 2 (CPG2) in a PKA-dependent manner, and that this association is required for synaptic GluR internalization. Mutating two PKA sites on CPG2 disrupts its cytoskeletal association, attenuating GluR endocytosis and affecting the efficacy of synaptic transmission in vivo. These results identify CPG2 as an F-actin binding partner that functionally mediates interaction of the spine cytoskeleton with postsynaptic endocytosis. Further, the regulation of CPG2/F-actin association by PKA provides a gateway for cellular control of synaptic receptor internalization through second messenger signaling pathways. Recent identification of human synaptic nuclear envelope 1 as a risk locus for bipolar disorder suggests that CPG2 could play a role in synaptic dysfunction underlying neuropsychiatric disease.

The secretogranin II gene is a signal integrator of glutamate and dopamine inputs

Cooperative gene regulation by different neurotransmitters likely underlies the long-term forms of associative learning and memory, but this mechanism largely remains to be elucidated. Following cDNA microarray analysis for genes regulated by Ca(2+) or cAMP, we found that the secretogranin II gene (Scg2) was cooperatively activated by glutamate and dopamine in primary cultured mouse hippocampal neurons. The Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM) and the mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor PD98059 prevented Scg2 activation by glutamate or dopamine; thus, the Ca(2+) /MEK pathway is predicted to include a convergence point(s) of glutamatergic and dopaminergic signaling. Unexpectedly, the protein kinase A inhibitor KT5720 enhanced Scg2 activation by dopamine. The protein-synthesis inhibitor cycloheximide also enhanced Scg2 activation, and the proteasome inhibitor ZLLLH diminished the KT5720-mediated augmentation of Scg2 activation. These results are concordant with the notion that dopaminergic input leads to accumulation of a KT5720-sensitive transcriptional repressor, which is short-lived because of rapid degradation by proteasomes. This repression pathway may effectively limit the time window permissive to Scg2 activation by in-phase glutamate and dopamine inputs via the Ca(2+) /MEK pathway. We propose that the regulatory system of Scg2 expression is equipped with machinery that is refined for the signal integration of in-phase synaptic inputs. We proposed hypothetical mechanism for the regulation of the secretogranin II gene as a signal integrator of glutamate and dopamine inputs. Glutamate or dopamine activates the Ca(2+) /MEK/ERK pathway, which thus contributes to the signal integration. Concurrently, activation of the PKA inhibitor KT5720-sensitive pathway by dopamine leads to accumulation of the repressor protein X that is otherwise susceptible to proteasome degradation. This repression system may determine the time window permissive to the cooperative activation by in-phase glutamate and dopamine inputs.

Genome-wide profiling of the activity-dependent hippocampal transcriptome

Activity-dependent gene expression is central for sculpting neuronal connectivity in the brain. Despite the importance for synaptic plasticity, a comprehensive analysis of the temporal changes in the transcriptomic response to neuronal activity is lacking. In a genome wide survey we identified genes that were induced at 1, 4, 8, or 24 hours following neuronal activity in the hippocampus. According to their distinct expression kinetics we assigned these genes to five clusters, each containing approximately 200 genes. Using in situ hybridizations the regulated expression of 24 genes was validated. Apart from known activity-dependent genes our study reveals a large number of unknown induced genes with distinct expression kinetics. Among these we identified several genes with complex temporal expression patterns. Furthermore, our study provides examples for activity-induced exon switching in the coding region of genes and activity-induced alternative splicing of the 3'-UTR. One example is Zwint. In contrast to the constitutively expressed variant, the induced Zwint transcript harbors multiple regulatory elements in the 3'-UTR. Taken together, our study provides a comprehensive analysis of the transcriptomic response to neuronal activity and sheds new light on expression kinetics and alternative splicing events.

Splitting hares and tortoises: a classification of neuronal immediate early gene transcription based on poised RNA polymerase II

Immediate early transcription is an integral part of the neuronal response to environmental stimulation and serves many brain processes including development, learning, triggers of programmed cell death, and reaction to injury and drugs. Following a stimulus, neurons express a select few genes within a short period of time without undergoing de novo protein translation. Referred to as the 'gateway to genetic response', these immediate early genes (IEGs) are either expressed within a few minutes of stimulation or later within the hour. In neuronal IEGs that are expressed rapidly, productive elongation in response to neuronal activity is jump-started by constitutive transcription initiation together with RNA polymerase II stalling in the vicinity of the promoter. IEGs expressed later in the hour do not depend on this mechanism. On the basis of this Polymerase II poising, we propose that the immediate early genes can be grouped in two distinct classes: the rapid and the delayed IEGs. The possible biological relevance of these classes in neurons is discussed.

Roles of matrix metalloproteinases and their targets in epileptogenesis and seizures

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) remodel the pericellular environment by regulating the cleavage of extracellular matrix proteins, cell surface components, neurotransmitter receptors, and growth factors, which together regulate cell adhesion, synaptogenesis, synaptic plasticity, and long-term potentiation. Increased MMP activity and dysregulation of the balance between MMPs and TIMPs have also been implicated in various pathological conditions. Recent studies have suggested that prolonged seizures are associated with high MMP levels in serum and neural tissues, and certain extracellular macromolecule targets may influence the pathogenesis of epilepsy and seizure. In this review, we discuss the roles of MMP activation in animal models of epilepsy.

Activity-dependent NPAS4 expression and the regulation of gene programs underlying plasticity in the central nervous system

The capability of the brain to change functionally in response to sensory experience is most active during early stages of development but it decreases later in life when major alterations of neuronal network structures no longer take place in response to experience. This view has been recently challenged by experimental strategies based on the enhancement of environmental stimulation levels, genetic manipulations, and pharmacological treatments, which all have demonstrated that the adult brain retains a degree of plasticity that allows for a rewiring of neuronal circuitries over the entire life course. A hot spot in the field of neuronal plasticity centres on gene programs that underlie plastic phenomena in adulthood. Here, I discuss the role of the recently discovered neuronal-specific and activity-dependent transcription factor NPAS4 as a critical mediator of plasticity in the nervous system. A better understanding of how modifications in the connectivity of neuronal networks occur may shed light on the treatment of pathological conditions such as brain damage or disease in adult life, some of which were once considered untreatable.

Active DNA demethylation in post-mitotic neurons: a reason for optimism

Over the last several years proteins involved in base excision repair (BER) have been implicated in active DNA demethylation. We review the literature supporting BER as a means of active DNA demethylation, and explain how the various components function and cooperate to remove the potentially most enduring means of epigenetic gene regulation. Recent evidence indicates that the same pathways implicated during periods of widespread DNA demethylation, such as the erasure of methyl marks in the paternal pronucleus soon after fertilization, are operational in post-mitotic neurons. Neuronal functional identities, defined here as the result of a combination of neuronal subtype, location, and synaptic connections are largely maintained through DNA methylation. Chronic mental illnesses, such as schizophrenia, may be the result of both altered neurotransmitter levels and neurons that have assumed dysfunctional neuronal identities. A limitation of most current psychopharmacological agents is their focus on the former, while not addressing the more profound latter pathophysiological process. Previously, it was believed that active DNA demethylation in post-mitotic neurons was rare if not impossible. If this were the case, then reversing the factors that maintain neuronal identity, would be highly unlikely. The emergence of an active DNA demethylation pathway in the brain is a reason for great optimism in psychiatry as it provides a means by which previously pathological neurons may be reprogrammed to serve a more favorable role. Agents targeting epigenetic processes have shown much promise in this regard, and may lead to substantial gains over traditional pharmacological approaches.

Genome-wide profiling identifies a subset of methamphetamine (METH)-induced genes associated with METH-induced increased H4K5Ac binding in the rat striatum

BACKGROUND

METH is an illicit drug of abuse that influences gene expression in the rat striatum. Histone modifications regulate gene transcription.

METHODS

We therefore used microarray analysis and genome-scale approaches to examine potential relationships between the effects of METH on gene expression and on DNA binding of histone H4 acetylated at lysine 4 (H4K5Ac) in the rat dorsal striatum of METH-naïve and METH-pretreated rats.

RESULTS

Acute and chronic METH administration caused differential changes in striatal gene expression. METH also increased H4K5Ac binding around the transcriptional start sites (TSSs) of genes in the rat striatum. In order to relate gene expression to histone acetylation, we binned genes of similar expression into groups of 100 genes and proceeded to relate gene expression to H4K5Ac binding. We found a positive correlation between gene expression and H4K5Ac binding in the striatum of control rats. Similar correlations were observed in METH-treated rats. Genes that showed acute METH-induced increased expression in saline-pretreated rats also showed METH-induced increased H4K5Ac binding. The acute METH injection caused similar increases in H4K5Ac binding in METH-pretreated rats, without affecting gene expression to the same degree. Finally, genes that showed METH-induced decreased expression exhibited either decreases or no changes in H4K5Ac binding.

CONCLUSION

Acute METH injections caused increased gene expression of genes that showed increased H4K5Ac binding near their transcription start sites.

Nesprins: from the nuclear envelope and beyond

Nuclear envelope spectrin-repeat proteins (Nesprins), are a novel family of nuclear and cytoskeletal proteins with rapidly expanding roles as intracellular scaffolds and linkers. Originally described as proteins that localise to the nuclear envelope (NE) and establish nuclear-cytoskeletal connections, nesprins have now been found to comprise a diverse spectrum of tissue specific isoforms that localise to multiple sub-cellular compartments. Here, we describe how nesprins are necessary in maintaining cellular architecture by acting as essential scaffolds and linkers at both the NE and other sub-cellular domains. More importantly, we speculate how nesprin mutations may disrupt tissue specific nesprin scaffolds and explain the tissue specific nature of many nesprin-associated diseases, including laminopathies.

Cation-chloride cotransporters NKCC1 and KCC2 as potential targets for novel antiepileptic and antiepileptogenic treatments

In cortical and hippocampal neurons, cation-chloride cotransporters (CCCs) control the reversal potential (EGABA) of GABAA receptor-mediated current and voltage responses and, consequently, they modulate the efficacy of GABAergic inhibition. Two members of the CCC family, KCC2 (the major neuron-specific K-Cl cotransporter; KCC isoform 2) and NKCC1 (the Na-K-2Cl cotransporter isoform 1 which is expressed in both neurons and glial cells) have attracted much interest in studies on GABAergic signaling under both normal and pathophysiological conditions, such as epilepsy. There is tentative evidence that loop diuretic compounds such as furosemide and bumetanide may have clinically relevant antiepileptic actions, especially when administered in combination with conventional GABA-mimetic drugs such as phenobarbital. Furosemide is a non-selective inhibitor of CCCs while at low concentrations bumetanide is selective for NKCCs. Search for novel antiepileptic drugs (AEDs) is highly motivated especially for the treatment of neonatal seizures which are often resistant to, or even aggravated by conventional AEDs. This review shows that the antiepileptic effects of loop diuretics described in the pertinent literature are based on widely heterogeneous mechanisms ranging from actions on both neuronal NKCC1 and KCC2 to modulation of the brain extracellular volume fraction. A promising strategy for the development of novel CCC-blocking AEDs is based on prodrugs that are activated following their passage across the blood-brain barrier. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.

NKAIN1-SERINC2 is a functional, replicable and genome-wide significant risk gene region specific for alcohol dependence in subjects of European descent

OBJECTIVE

We aimed to identify novel, functional, replicable and genome-wide significant risk regions specific for alcohol dependence using genome-wide association studies (GWASs).

METHODS

A discovery sample (1409 European-American cases with alcohol dependence and 1518 European-American controls) and a replication sample (6438 European-Australian family subjects with 1645 alcohol dependent probands) underwent association analysis. Nineteen other cohorts with 11 different neuropsychiatric disorders served as contrast groups. Additional eight samples underwent expression quantitative locus (eQTL) analysis.

RESULTS

A genome-wide significant risk gene region (NKAIN1-SERINC2) was identified in a meta-analysis of the discovery and replication samples. This region was enriched with 74 risk SNPs (unimputed); half of them had significant cis-acting regulatory effects. The distributions of -log(p) values for the SNP-disease associations or SNP-expression associations in this region were consistent throughout eight independent samples. Furthermore, imputing across the NKAIN1-SERINC2 region, we found that among all 795 SNPs in the discovery sample, 471 SNPs were nominally associated with alcohol dependence (1.7×10(-7)≤p≤0.047); 53 survived region- and cohort-wide correction for multiple testing; 92 SNPs were replicated in the replication sample (0.002≤p≤0.050). This region was neither significantly associated with alcohol dependence in African-Americans, nor with other non-alcoholism diseases. Finally, transcript expression of genes in NKAIN1-SERINC2 was significantly (p<3.4×10(-7)) associated with expression of numerous genes in the neurotransmitter systems or metabolic pathways previously associated with alcohol dependence.

CONCLUSION

NKAIN1-SERINC2 may harbor a causal variant(s) for alcohol dependence. It may contribute to the disease risk by way of neurotransmitter systems or metabolic pathways.

[Progress in activity-dependent structural plasticity of neural circuits in cortex]

Neural circuits of mammalian cerebral cortex have exhibited amazing abilities of structural and functional plasticity in development, learning and memory, neurological and psychiatric diseases. With the new imaging techniques and the application of molecular biology methods, observation neural circuits' structural dynamics within the cortex in vivo at the cellular and synaptic level was possible, so there were many great progresses in the field of the activity-dependent structural plasticity over the past decade. This paper reviewed some of the aspects of the experimental results, focused on the characteristics of dendritic structural plasticity in individual growth and development, rich environment, sensory deprivation, and pathological conditions, as well as learning and memory, especially the dynamics of dendritic spines on morphology and quantity; after that, we introduced axonal structural plasticity, the molecular and cellular mechanisms of structural plasticity, and proposed some future problems to be solved at last.

Thalamus-derived molecules promote survival and dendritic growth of developing cortical neurons

The mammalian neocortex is composed of various types of neurons that reflect its laminar and area structures. It has been suggested that not only intrinsic but also afferent-derived extrinsic factors are involved in neuronal differentiation during development. However, the role and molecular mechanism of such extrinsic factors are almost unknown. Here, we attempted to identify molecules that are expressed in the thalamus and affect cortical cell development. First, thalamus-specific molecules were sought by comparing gene expression profiles of the developing rat thalamus and cortex using microarrays, and by constructing a thalamus-enriched subtraction cDNA library. A systematic screening by in situ hybridization showed that several genes encoding extracellular molecules were strongly expressed in sensory thalamic nuclei. Exogenous and endogenous protein localization further demonstrated that two extracellular molecules, Neuritin-1 (NRN1) and VGF, were transported to thalamic axon terminals. Application of NRN1 and VGF to dissociated cell culture promoted the dendritic growth. An organotypic slice culture experiment further showed that the number of primary dendrites in multipolar stellate neurons increased in response to NRN1 and VGF, whereas dendritic growth of pyramidal neurons was not promoted. These molecules also increased neuronal survival of multipolar neurons. Taken together, these results suggest that the thalamus-specific molecules NRN1 and VGF play an important role in the dendritic growth and survival of cortical neurons in a cell type-specific manner.

Matrix metalloproteinase-9 (MMP-9) in human intractable epilepsy caused by focal cortical dysplasia

Focal cortical dysplasia (FCD) is a developmental brain disorder characterized by localized abnormalities of cortical layering and neuronal morphology. It is associated with pharmacologically intractable forms of epilepsy in both children and adults. The mechanisms that underlie FCD-associated seizures and lead to the progression of the disease are unclear. Matrix metalloproteinases (MMPs) are enzymes that are able to influence neuronal function through extracellular proteolysis in various normal and pathological conditions. The results of experiments that have used rodent models showed that extracellular MMP-9 can play an important role in epileptogenesis. However, no studies have shown that MMP-9 is involved in the pathogenesis of human epilepsy. The aim of the present study was to determine whether MMP-9 plays a role in intractable epilepsy. Using an unbiased antibody microarray approach, we found that up regulation of MMP-9 is prominent and consistent in FCD tissue derived from epilepsy surgery, regardless of the patient's age. Additionally, an up regulation of MMP-1, -2, -8, -10, and -13 was found but was either less pronounced or limited only to adult cases. In the dysplastic cortex, immunohistochemistry revealed that the highest MMP-9 immuno reactivity occurred in the cytoplasm of abnormal neurons and balloon cells. The neuronal over expression of MMP-9 also occurred in sclerotic hippocampi that were excised together with the dysplastic cortex, but sclerotic hippocampi were free of dysplastic features. In both locations, MMP-9 was also found in reactive astrocytes, albeit to a lesser extent. At the subcellular level, increased MMP-9 immunoreactivity was prominently upregulated at synapses. Thus, although upregulation of the enzyme in FCD is not causally linked to the developmental malformation, it may be a result of ongoing abnormal synaptic plasticity. The present findings support the hypothesis of the pathogenic role of MMP-9 in human epilepsy and may stimulate discussions about whether MMPs could be novel therapeutic targets for intractable epilepsy.