Neuronal Synaptic Function Research Articles

Towards understanding the genetics of Autism

Autism spectrum disorder (ASD) includes a group of neurodevelopmental disorders that affect communication skills, social interaction and intellectual ability. Despite evidence suggesting a strong genetic link with ASD, the genetic determinant remains unclear. Early studies focusing on candidate genes have shown that several genes associated with neuronal synaptic function are involved in development of ASD. Linkage studies have identified several single nucleotide polymorphisms (SNPs) associated with ASD, and genome-wide association studies have implicated several loci, but failed to recognize a single specific locus with strong significance, indicating heterogeneity in ASD genetic determinants. Detection of de novo copy number variations and single nucleotide variants in several ASD probands has confirmed the genetic heterogeneity of the disease. More interestingly, next generation sequencing approaches have recently identified novel candidate genes and several point mutations in sporadic ASDs, thus increasing our knowledge of ASD etiology. The current review summarizes the findings of recent studies using genetic and genomic approaches to understand the underlying molecular mechanisms of ASD.

Effects of Chronic Dopamine D2R Agonist Treatment and Polysialic Acid Depletion on Dendritic Spine Density and Excitatory Neurotransmission in the mPFC of Adult Rats.

Dopamine D2 receptors (D2R) in the medial prefrontal cortex (mPFC) are key players in the etiology and therapeutics of schizophrenia. The overactivation of these receptors contributes to mPFC dysfunction. Chronic treatment with D2R agonists modifies the expression of molecules implicated in neuronal structural plasticity, synaptic function, and inhibitory neurotransmission, which are also altered in schizophrenia. These changes are dependent on the expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a plasticity-related molecule, but nothing is known about the effects of D2R and PSA-NCAM on excitatory neurotransmission and the structure of mPFC pyramidal neurons, two additional features affected in schizophrenia. To evaluate these parameters, we have chronically treated adult rats with PPHT (a D2R agonist) after enzymatic removal of PSA with Endo-N. Both treatments decreased spine density in apical dendrites of pyramidal neurons without affecting their inhibitory innervation. Endo-N also reduced the expression of vesicular glutamate transporter-1. These results indicate that D2R and PSA-NCAM are important players in the regulation of the structural plasticity of mPFC excitatory neurons. This is relevant to our understanding of the neurobiological basis of schizophrenia, in which structural alterations of pyramidal neurons and altered expression of D2R and PSA-NCAM have been found.

Proteomic analysis of cortical brain tissue from the BTBR mouse model of autism: Evidence for changes in STOP and myelin-related proteins

Autism is a neurodevelopmental disorder characterized by abnormal reciprocal social interactions, communication deficits, and repetitive behaviors with restricted interests. However, the widely accepted biomarkers for autism are still lacking. In this study, we carried out a quantitative proteomic profiling study of cortical brain tissue from BTBR T+Itpr3tf (BTBR) mice, a mouse model that displays an autism-like phenotype. Using isobaric tag for relative and absolute quantification (iTRAQ) coupled with LC–MS/MS, a total of 3611 proteins were quantitated in mouse cortices. As compared to C57BL/6J (B6) mice, 126 differentially expressed proteins were found in the brain from BTBR mice. The functional annotation and categories of differentially expressed proteins were analyzed. Especially, the stable tubule only polypeptide (STOP) protein and myelin-related proteins down-regulated significantly in BTBR mice were confirmed by Western blotting. Furthermore, the BTBR mice displayed reduced levels of staining with ferric alum in comparison to B6 controls, indicative of myelin disruption. Finally, we propose that reduced STOP expression in the brain could be involved in the mediation of autism-like behaviors through impairments of myelination in oligodendrocytes and synaptic function in neurons. Manipulation of STOP protein could be a promising avenue for therapeutic interventions to autism.

The cell- and tissue-specific transcription mechanism of the TATA-less syntaxin 1A gene.

Syntaxin 1A (Stx1a) plays an important role in regulation of neuronal synaptic function. To clarify the mechanism of basic transcriptional regulation and neuron-specific transcription of Stx1a we cloned the Stx1a gene from rat, in which knowledge of the expression profile was accumulated, and elucidated that Stx1a consisting of 10 exons, possesses multiple transcription initiation sites and a 204-bp core promoter region (CPR) essential for transcription in PC12 cells. The TATA-less, conserved, GC-rich CPR has 2 specific protein (SP) sites that bind SP1 and are responsible for 65% of promoter activity. The endogenous CPR, including 23 CpG sites, is not methylated in PC12 cells, which express Stx1a and fetal rat skin keratinocyte (FRSK) cells, which do not, although an exogenous methylated CPR suppresses reporter activity in both lines. Trichostatin A (TSA) and class I histone deacetylase (HDAC) inhibitors, but not 5-azacytidine, induce Stx1a in FRSK cells. Acetylated histone H3 only associates to the CPR in FRSK cells after TSA addition, whereas the high acetylated histone H3-CPR association in PC12 cells was unchanged following treatment. HDAC inhibitor induction of Stx1a was negated by mithramycin A and deletion/mutation of 2 SP sites. HDAC1, HDAC2, and HDAC8 detach from the CPR when treated with TSA in FRSK cells and are associated with the CPR in lungs, and acetylated histone H3 associates to this region in the brain. In the first study characterizing a syntaxin promoter, we show that association of SP1 and acetylated histone H3 to CPR is important for Stx1a transcription and that HDAC1, HDAC2, and HDAC8 decide cell/tissue specificity in a suppressive manner.

Dysregulation and restoration of translational homeostasis in fragile X syndrome

Fragile X syndrome (FXS), the most-frequently inherited form of intellectual disability and the most-prevalent single-gene cause of autism, results from a lack of fragile X mental retardation protein (FMRP), an RNA-binding protein that acts, in most cases, to repress translation. Multiple pharmacological and genetic manipulations that target receptors, scaffolding proteins, kinases and translational control proteins can rescue neuronal morphology, synaptic function and behavioural phenotypes in FXS model mice, presumably by reducing excessive neuronal translation to normal levels. Such rescue strategies might also be explored in the future to identify the mRNAs that are critical for FXS pathophysiology.

Abnormal neuronal morphology and neurochemistry in the auditory brainstem of Fmr1 knockout rats

Fragile X syndrome (FXS) is an inherited neurodevelopmental disorder affecting nearly one in 5000 newborn males and is a leading genetic cause of autism spectrum disorder. In addition to developmental delays and intellectual impairment, FXS is characterized by seizures, attention deficit, and hypersensitivity to visual, tactile and auditory stimuli. The Fmr1 gene encodes Fragile X mental retardation protein (FMRP), which is abundant in neurons, binds select mRNAs and functions as a negative regulator of mRNA translation. A deficiency in FMRP, as in FXS and Fmr1 knockout (KO) animals, results in neuronal dysmorphology and altered synaptic function. Additionally, there is evidence for disruption of GABAergic circuits in subjects lacking FMRP. Our previous studies demonstrated widespread expression of FMRP in human auditory brainstem neurons. Given this observation, we hypothesized that FMRP is highly expressed in rat auditory brainstem neurons and that the auditory hypersensitivity characteristic of FXS results from dysfunction of brainstem networks secondary to decreased expression of FMRP. In our investigation of postnatal day 50 (P50) control rats, we found that FMRP was widely expressed in neurons of the superior olivary complex (SOC). In P50 Fmr1 KO rats, many SOC neurons had a smaller soma when compared to controls, indicative of abnormal neuronal morphology. Additionally, neurons in the medial superior olive (MSO) were more round in Fmr1 KO rats. There was also reduced expression of glutamic acid decarboxylase (GAD67) in neurons of the superior paraolivary nucleus (SPON) and a reduction in the number of calretinin-immunoreactive terminals associated with neurons of the medial nucleus of the trapezoid body (MNTB). Together, these findings support the conclusion that the auditory dysfunction characteristic of FXS arises, at least in part, from defective brainstem networks.

Miro's N-Terminal GTPase Domain Is Required for Transport of Mitochondria into Axons and Dendrites

Mitochondria are dynamically transported in and out of neuronal processes to maintain neuronal excitability and synaptic function. In higher eukaryotes, the mitochondrial GTPase Miro binds Milton/TRAK adaptor proteins linking microtubule motors to mitochondria. Here we show that Drosophila Miro (dMiro), which has previously been shown to be required for kinesin-driven axonal transport, is also critically required for the dynein-driven distribution of mitochondria into dendrites. In addition, we used the loss-of-function mutations dMiroT25N and dMiroT460N to determine the significance of dMiro's N-terminal and C-terminal GTPase domains, respectively. Expression of dMiroT25N in the absence of endogenous dMiro caused premature lethality and arrested development at a pupal stage. dMiroT25N accumulated mitochondria in the soma of larval motor and sensory neurons, and prevented their kinesin-dependent and dynein-dependent distribution into axons and dendrites, respectively. dMiroT25N mutant mitochondria also were severely fragmented and exhibited reduced kinesin and dynein motility in axons. In contrast, dMiroT460N did not impair viability, mitochondrial size, or the distribution of mitochondria. However, dMiroT460N reduced dynein motility during retrograde mitochondrial transport in axons. Finally, we show that substitutions analogous to the constitutively active Ras-G12V mutation in dMiro's N-terminal and C-terminal GTPase domains cause neomorphic phenotypic effects that are likely unrelated to the normal function of each GTPase domain. Overall, our analysis indicates that dMiro's N-terminal GTPase domain is critically required for viability, mitochondrial size, and the distribution of mitochondria out of the neuronal soma regardless of the employed motor, likely by promoting the transition from a stationary to a motile state.

Protein Arginine Methylation of Tubulin Beta Decreases Binding of Taxol in Neuro2a Cells

Tubulin α and β heterodimers are the building blocks of microtubules, which are part of the cytoskeleton in eukaryotic cells. Microtubules play critical roles in both development and synaptic function in neurons and are the target of various anti‐cancer drugs. Tubulins undergo multiple post‐translational modifications which influence microtubule stability, motor protein guidance and contribute to the “microtubule code” that selectively and specifically regulates the functions of microtubules. Here we report that tubulin β is methylated on two novel arginine (R) residues. Using mass spectrometry, R62 and R282 were identified to be methylated in Neuro2a cells. The location of these methylated residues suggests a role in microtubule stability. Furthermore, R282 is involved in binding to microtubule stabilizing drugs such as taxol and epothilone derivatives and mutants of R282 are associated with anti‐cancer drug resistance. Computer modelling using protein‐docking simulations on taxol binding to tubulin β with and without methylation of R282, suggested that methylation on R282 reduces taxol binding. This prediction was supported experimentally by cell cycle analysis of Neuro2a cells using flow cytometry. Inhibition of methylation by AdOx caused an increased effect of taxol with more cells being arrested in the G2 phase. Hence our findings add a new player to the multitude of post‐translational modifications of the “microtubule code” and have potentially important implications for anti‐cancer drug design, brain development and synaptic function.

Lurasidone exerts antidepressant properties in the chronic mild stress model through the regulation of synaptic and neuroplastic mechanisms in the rat prefrontal cortex.

Background:Major depression is associated with several alterations, including reduced neuronal plasticity and impaired synaptic function, which represent an important target of pharmacological intervention.Methods:In the present study, we have investigated the ability of the antipsychotic drug lurasidone to modulate behavioral and neuroplastic alterations in the chronic mild stress model of depression.Results:Rats that show reduced sucrose consumption after 2 weeks of chronic mild stress have reduced expression of the pool of Bdnf transcripts with the long 3′ untranslated region (3′-UTR) that may be targeted to the synaptic compartment, suggesting the contribution of the neurotrophin to the behavioral dysfunction produced by chronic mild stress. The downregulation of Bdnf expression persisted also after 7 weeks of chronic mild stress, whereas chronic lurasidone treatment improved anhedonia in chronic mild stress rats and restored Bdnf mRNA levels in the prefrontal cortex. Moreover, chronic lurasidone treatment was able to normalize chronic mild stress-induced defects of Psd95 and Gfap as well as changes in molecular regulators of protein translation at the synapse, including mTOR and eEF2.Conclusions:These results demonstrate that lurasidone shows antidepressant properties in the chronic mild stress model through the modulation of synaptic and neuroplastic proteins. Such changes may contribute to the amelioration of functional capacities, which are deteriorated in patients with major depression and stress-related disorders.

MicroRNA-Seq Data Analysis Pipeline to Identify Blood Biomarkers for Alzheimer's Disease from Public Data.

BACKGROUNDAlzheimer’s disease (AD) is the most common cause of dementia with no curative therapy currently available. Establishment of sensitive and non-invasive biomarkers that promote an early diagnosis of AD is crucial for the effective administration of disease-modifying drugs. MicroRNAs (miRNAs) mediate posttranscriptional repression of numerous target genes. Aberrant regulation of miRNA expression is implicated in AD pathogenesis, and circulating miRNAs serve as potential biomarkers for AD. However, data analysis of numerous AD-specific miRNAs derived from small RNA-sequencing (RNA-Seq) is most often laborious.METHODSTo identify circulating miRNA biomarkers for AD, we reanalyzed a publicly available small RNA-Seq dataset, composed of blood samples derived from 48 AD patients and 22 normal control (NC) subjects, by a simple web-based miRNA data analysis pipeline that combines omiRas and DIANA miRPath.RESULTSBy using omiRas, we identified 27 miRNAs expressed differentially between both groups, including upregulation in AD of miR-26b-3p, miR-28–3p, miR-30c-5p, miR-30d-5p, miR-148b-5p, miR-151a-3p, miR-186–5p, miR-425–5p, miR-550a-5p, miR-1468, miR-4781–3p, miR-5001–3p, and miR-6513–3p and downregulation in AD of let-7a-5p, let-7e-5p, let-7f-5p, let-7g-5p, miR-15a-5p, miR-17–3p, miR-29b-3p, miR-98–5p, miR-144–5p, miR-148a-3p, miR-502–3p, miR-660–5p, miR-1294, and miR-3200–3p. DIANA miRPath indicated that miRNA-regulated pathways potentially downregulated in AD are linked with neuronal synaptic functions, while those upregulated in AD are implicated in cell survival and cellular communication.CONCLUSIONSThe simple web-based miRNA data analysis pipeline helps us to effortlessly identify candidates for miRNA biomarkers and pathways of AD from the complex small RNA-Seq data.

α-synuclein and synapsin III cooperatively regulate synaptic function in dopamine neurons.

The main neuropathological features of Parkinson's disease are dopaminergic nigrostriatal neuron degeneration, and intraneuronal and intraneuritic proteinaceous inclusions named Lewy bodies and Lewy neurites, respectively, which mainly contain α-synuclein (α-syn, also known as SNCA). The neuronal phosphoprotein synapsin III (also known as SYN3), is a pivotal regulator of dopamine neuron synaptic function. Here, we show that α-syn interacts with and modulates synapsin III. The absence of α-syn causes a selective increase and redistribution of synapsin III, and changes the organization of synaptic vesicle pools in dopamine neurons. In α-syn-null mice, the alterations of synapsin III induce an increased locomotor response to the stimulation of synapsin-dependent dopamine overflow, despite this, these mice show decreased basal and depolarization-dependent striatal dopamine release. Of note, synapsin III seems to be involved in α-syn aggregation, which also coaxes its increase and redistribution. Furthermore, synapsin III accumulates in the caudate and putamen of individuals with Parkinson's disease. These findings support a reciprocal modulatory interaction of α-syn and synapsin III in the regulation of dopamine neuron synaptic function.

Non-microtubular localizations of microtubule-associated protein 6 (MAP6).

MAP6 proteins (MAP6s), which include MAP6-N (also called Stable Tubule Only Polypeptide, or STOP) and MAP6d1 (MAP6 domain-containing protein 1, also called STOP-Like protein 21 kD, or SL21), bind to and stabilize microtubules. MAP6 deletion in mice severely alters integrated brain functions and is associated with synaptic defects, suggesting that MAP6s may also have alternative cellular roles. MAP6s reportedly associate with the Golgi apparatus through palmitoylation of their N-terminal domain, and specific isoforms have been shown to bind actin. Here, we use heterologous systems to investigate several biochemical properties of MAP6 proteins. We demonstrate that the three N-terminal cysteines of MAP6d1 are palmitoylated by a subset of DHHC-type palmitoylating enzymes. Analysis of the subcellular localization of palmitoylated MAP6d1, including electron microscopic analysis, reveals possible localization to the Golgi and the plasma membrane but no association with the endoplasmic reticulum. Moreover, we observed localization of MAP6d1 to mitochondria, which requires the N-terminus of the protein but does not require palmitoylation. We show that endogenous MAP6d1 localized at mitochondria in mature mice neurons as well as at the outer membrane and in the intermembrane space of purified mouse mitochondria. Last, we found that MAP6d1 can multimerize via a microtubule-binding module. Interestingly, most of these properties of MAP6d1 are shared by MAP6-N. Together, these results describe several properties of MAP6 proteins, including their intercellular localization and multimerization activity, which may be relevant to neuronal differentiation and synaptic functions.

Complementary roles of the neuron-enriched endosomal proteins NEEP21 and calcyon in neuronal vesicle trafficking.

Understanding mechanisms governing the trafficking of transmembrane (TM) cargoes to synapses and other specialized membranes in neurons represents a long-standing challenge in cell biology. Investigation of the neuron-enriched endosomal protein of 21kDa (NEEP21, or NSG1or P21) and Calcyon (Caly, or NSG3) indicates that the emergence of the NEEP21/Caly/P19 gene family could play a vital role in the success of these mechanisms in vertebrates. The upshot of a sizeable body of work is that the NEEP21 and Caly perform distinct endocytic and recycling functions, which impact (i) α amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptor trafficking at excitatory synapses; (ii) transport to/in neuronal axons; as well as (iii) proteolytic processing of amyloid precursor protein and neuregulin 1, suggesting roles in neuron development, synaptic function, and neurodegeneration. We argue that their distinct effects on cargo endocytosis and recycling depend on interactions with vesicle trafficking and synaptic scaffolding proteins. As they play complementary, but opposing roles in cargo endocytosis, recycling, and degradation, balancing NEEP21 and Caly expression levels or activity could be important for homeostasis in a variety of signaling pathways, and also lead to a novel therapeutic strategy for disorders like Alzheimer's disease and schizophrenia. This review focuses on two closely related, neuron-enriched endosomal proteins: NEEP21 and Calcyon which perform distinct roles in regulating receptor endocytosis, recycling, and degradation. Based on an in-depth examination of the literature, we argue that these two proteins carry out complementary yet sometimes opposing vesicle trafficking functions that impact excitatory transmission, transcytosis, axonal transport, and also proteolytic processing by beta-secretase I (BACE1). Finally, we propose that balancing NEEP21 and Calcyon expression and/or activity could be important for homeostasis in a variety of signaling pathways, and also lead to a novel therapeutic strategy for disorders like Alzheimer's disease and schizophrenia. AMPA=α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor; NMDA=N-Methyl-D-aspartate.

Astrocyte regulation of synaptic behavior.

Astrocytes regulate multiple aspects of neuronal and synaptic function from development through to adulthood. Instead of addressing each function independently, this review provides a comprehensive overview of the different ways astrocytes modulate neuronal synaptic function throughout life, with a particular focus on recent findings in each area. It includes the emerging functions of astrocytes, such as a role in synapse formation, as well as more established roles, including the uptake and recycling of neurotransmitters. This broad approach covers the many ways astrocytes and neurons constantly interact to maintain the correct functioning of the brain. It is important to consider all of these diverse functions of astrocytes when investigating how astrocyte-neuron interactions regulate synaptic behavior to appreciate the complexity of these ongoing interactions.

α-Synuclein Multimers Cluster Synaptic Vesicles and Attenuate Recycling

The normal functions and pathologic facets of the small presynaptic protein α-synuclein (α-syn) are of exceptional interest. In previous studies, we found that α-syn attenuates synaptic exo/endocytosis; however, underlying mechanisms remain unknown. More recent evidence suggests that α-syn exists as metastable multimers and not solely as a natively unfolded monomer. However, conformations of α-syn at synapses--its physiologic locale--are unclear, and potential implications of such higher-order conformations to synaptic function are unknown. Exploring α-syn conformations and synaptic function in neurons, we found that α-syn promptly organizes into physiological multimers at synapses. Furthermore, our experiments indicate that α-syn multimers cluster synaptic vesicles and restrict their motility, suggesting a novel role for these higher-order structures. Supporting this, α-syn mutations that disrupt multimerization also fail to restrict synaptic vesicle motility or attenuate exo/endocytosis. We propose a model in which α-syn multimers cluster synaptic vesicles, restricting their trafficking and recycling, and consequently attenuate neurotransmitter release.

Research round-up

An advance in understanding of the genetic origins of schizophrenia has been made by the Schizophrenia Working Group of the Psychiatric Genomics Consortium. In a genome-wide association study, the researchers identified previously unreported schizophrenia-associated loci. The study included 36 989 patients with schizophrenia, and 113 075 controls. 128 independent associations were identified across 108 loci. Genes identified within the implicated loci included DRD2 (dopamine receptor) and GRM3 (metabotropic glutamate receptor)—both of which could be of therapeutic importance in schizophrenia—and other genes involved in glutamatergic neurotransmission, neuronal calcium signalling, synaptic function and plasticity, and neurodevelopment. According to researchers, results from a clinical trial suggest that gamma ventral capsulotomy could have a role in the treatment of patients with intractable obsessive-compulsive disorder. In the study, 16 patients were randomly assigned to gamma ventral capsulotomy or sham intervention. At 12 months, mean symptom score (measured with the Yale-Brown Obsessive-Compulsive Scale) was 20·9 (SD 11·0) in the intervention group compared with 31·9 (4·1) in the sham group (p=0·046). Three of eight patients (38%) in the intervention arm responded at 12 months (absolute risk reduction 0·375, 95% CI 0·04–0·71); during open-label follow-up, the number of responders increased to 63% (5/8) at 54 months. Although most adverse events were short-lived, one patient in the intervention arm developed radiation-induced perilesional oedema 8 months after radiosurgery; at month 54, the patient developed a brain cyst. A report from a long-term follow-up of a trial of psychotherapy in social anxiety disorder shows promising results. In their original trial, researchers assessed the effect of cognitive-behavioural therapy (CBT) and psychodynamic therapy on rates of remission and response. Subsequently, patients were followed up for up to 24 months after therapy. By the end of the follow-up period there were no significant differences between the two treatment modalities with respect to response and remission rates or secondary outcome measures. In intention-to-treat analysis with multiple imputation for missing data, 24 months after treatment the response rate was 69% in both the CBT group (n=209) and psychodynamic therapy group (n=207), and remission rates were 39% and 38%, respectively. Researchers of a small multifaceted study propose that screening for suicidal behaviour in at-risk populations with a biomarker could be possible in the future. The authors carried out genome-wide DNA methylation screening using post-mortem brain samples. They identified genetic and epigenetic variation within the SKA2 gene as being associated with suicide cases; results were replicated in two independent cohorts. Further investigation showed that there was significantly (p<0·001) lower gene expression of SKA2 in the post-mortem brain samples from the suicide cases (n=23) than in samples from the comparison group (n=35), and that expression was negatively associated with DNA methylation status. A link between SKA2 variation and suicidal ideation was confirmed with blood samples from three living cohorts. “Future studies should be carried out to further evaluate the prospective efficacy of this finding in additional populations”, concluded the authors. Some insight into the molecular basis of fear memory consolidation has been provided by researchers who showed in a study in adult mice that shortly after auditory fear conditioning, miR-34a was significantly upregulated in the amygdala compared with controls (p<0·05). Analysis suggested that miR-34a targeted the Notch pathway, and that Notch pathway mRNA and protein levels were decreased in the amygdala of mice after auditory fear conditioning. Increased downstream Notch signalling in the amygdala was associated with a lower freeze response to an auditory cue after auditory fear conditioning than in control mice (p=0·043)—ie, decreased fear memory consolidation. The authors concluded, “We would do well to co-opt relevant therapeutic agents that regulate Notch signalling and use them in the treatment or prevention of disorders [with] a substantial memory component.” Data from a cohort study provide further insight into the links between electronic gaming and psychosocial adjustment. Using a subsample from a UK longitudinal study, a cohort of young people aged 10–15 years (2436 boys and 2463 girls) were studied. Compared with non-players, young people engaging in game play of less than 1 h per day had higher prosocial behaviour and life satisfaction (p<0·001). There was no difference in the results of psychosocial assessments between young people partaking in game play of 1–3 h per day and non-players. However, game play of more than 3 h per day was associated with lower levels of prosocial behaviour and life satisfaction, and more internalising and externalising problems, than in non–players (p<0·001).

The Neuroplastin adhesion molecules: key regulators of neuronal plasticity and synaptic function.

The Neuroplastins Np65 and Np55 are neuronal and synapse-enriched immunoglobulin superfamily molecules that play important roles in a number of key neuronal and synaptic functions including, for Np65, cell adhesion. In this review we focus on the physiological roles of the Neuroplastins in promoting neurite outgrowth, regulating the structure and function of both inhibitory and excitatory synapses in brain, and in neuronal and synaptic plasticity. We discuss the underlying molecular and cellular mechanisms by which the Neuroplastins exert their physiological effects and how these are dependent upon the structural features of Np65 and Np55, which enable them to bind to a diverse range of protein partners. In turn this enables the Neuroplastins to interact with a number of key neuronal signalling cascades. These include: binding to and activation of the fibroblast growth factor receptor; Np65 trans-homophilic binding leading to activation of p38 MAPK and internalization of glutamate (GluR1) receptor subunits; acting as accessory proteins for monocarboxylate transporters, thus affecting neuronal energy supply, and binding to GABAA α1, 2 and 5 subunits, thus regulating the composition and localization of GABAA receptors. An emerging theme is the role of the Neuroplastins in regulating the trafficking and subcellular localization of specific binding partners. We also discuss the involvement of Neuroplastins in a number of pathophysiological conditions, including ischaemia, schizophrenia and breast cancer and the role of a single nucleotide polymorphism in the human Neuroplastin (NPTN) gene locus in impairment of cortical development and cognitive functions. Neuroplastins are neuronal cell adhesion molecules, which induce neurite outgrowth and play important roles in synaptic maturation and plasticity. This review summarizes the functional implications of Neuroplastins for correct synaptic membrane protein localization, neuronal energy supply, expression of LTP and LTD, animal and human behaviour, and pathophysiology and disease. It focuses particularly on Neuroplastin binding partners and signalling mechanisms, and proposes perspectives for future research on these important immunoglobulin superfamily members.

Mitochondrial trafficking and anchoring in neurons: New insight and implications

Mitochondria are essential organelles for neuronal growth, survival, and function. Neurons use specialized mechanisms to drive mitochondria transport and to anchor them in axons and at synapses. Stationary mitochondria buffer intracellular Ca2+ and serve as a local energy source by supplying ATP. The balance between motile and stationary mitochondria responds quickly to changes in axonal and synaptic physiology. Defects in mitochondrial transport are implicated in the pathogenesis of several major neurological disorders. Recent work has provided new insight in the regulation of microtubule-based mitochondrial trafficking and anchoring, and on how mitochondrial motility influences neuron growth, synaptic function, and mitophagy.

Transcriptomic Analyses of Neurotoxic Effects in Mouse Brain After Intermittent Neonatal Administration of Thimerosal

Thimerosal is a vaccine antimicrobial preservative which has long been suspected an iatrogenic factor possibly contributing to neurodevelopmental disorders including autism. The association between infant vaccine thimerosal exposure and autism remains an open question. Although thimerosal has been removed from mandatory childhood vaccines in the United States, thimerosal-preserved vaccines are still widely used outside of the United States especially in developing countries. Notably, thimerosal-containing vaccines are being given to the newborns within the first 12-24 h after birth in some countries. To examine the possible neurotoxic effects of early neonatal exposure to a higher level of thimerosal, FVB mice were subcutaneously injected with thimerosal-mercury at a dose which is 20× higher than that used for regular Chinese infant immunization during the first 4 months of life. Thimerosal-treated mice exhibited neural development delay, social interaction deficiency, and inclination of depression. Apparent neuropathological changes were also observed in adult mice neonatally treated with thimerosal. High-throughput RNA sequencing of autistic-behaved mice brains revealed the alternation of a number of canonical pathways involving neuronal development, neuronal synaptic function, and the dysregulation of endocrine system. Intriguingly, the elevation of anterior pituitary secreting hormones occurred exclusively in male but not in female thimerosal-treated mice, demonstrating for the first time the gender bias of thimerosal-mercury toxicity with regard to endocrine system. Our results indicate that higher dose of neonatal thimerosal-mercury (20× higher than that used in human) is capable of inducing long-lasting substantial dysregulation of neurodevelopment, synaptic function, and endocrine system, which could be the causal involvements of autistic-like behavior in mice.

Choline‐mediated modulation of hippocampal sharp wave–ripple complexes in vitro

The cholinergic system is critically involved in the modulation of cognitive functions, including learning and memory. Acetylcholine acts through muscarinic (mAChRs) and nicotinic receptors (nAChRs), which are both abundantly expressed in the hippocampus. Previous evidence indicates that choline, the precursor and degradation product of Acetylcholine, can itself activate nAChRs and thereby affects intrinsic and synaptic neuronal functions. Here, we asked whether the cellular actions of choline directly affect hippocampal network activity. Using mouse hippocampal slices we found that choline efficiently suppresses spontaneously occurring sharp wave-ripple complexes (SPW-R) and can induce gamma oscillations. In addition, choline reduces synaptic transmission between hippocampal subfields CA3 and CA1. Surprisingly, these effects are mediated by activation of both mAChRs and α7-containing nAChRs. Most nicotinic effects became only apparent after local, fast application of choline, indicating rapid desensitization kinetics of nAChRs. Effects were still present following block of choline uptake and are, therefore, likely because of direct actions of choline at the respective receptors. Together, choline turns out to be a potent regulator of patterned network activity within the hippocampus. These actions may be of importance for understanding state transitions in normal and pathologically altered neuronal networks. In this study we asked whether choline, the precursor and degradation product of acetylcholine, directly affects hippocampal network activity. Using mouse hippocampal slices we found that choline efficiently suppresses spontaneously occurring sharp wave-ripple complexes (SPW-R). In addition, choline reduces synaptic transmission between hippocampal subfields. These effects are mediated by direct activation of muscarinic as well as nicotinic cholinergic pathways. Together, choline turns out to be a potent regulator of patterned activity within hippocampal networks.