1,720,967 research outputs found
Interaction of betaine with the γ-aminobutyric acid (GABA) transporters
Full text linkBetaine, N-trimethyl glycine, is a natural, stable, and non-toxic osmolyte, whose supplementation is reported to ameliorate symptoms in neurological and neurodegenerative diseases. Evidence of positive action is reported in Alzheimer’s, Parkinson’s disease, and schizophrenia, despite that there is uncertainty around its transport and action mechanism in the brain. Although there are betaine transporters present in the brain i.e., betaine/γ-aminobutyric acid (GABA) transporter 1 (SLC6A12) and the sodium-coupled neutral amino acid transporter 2 (SLC38A2), their low expression propose that the positive effect of betaine should be related to interaction with proteins of the GABAergic pathways.
By two-electrode voltage clamp experiments in Xenopus laevis oocytes heterologously expressing rGAT1, we demonstrate that betaine induces dose-, voltage-, and Na+ dependent inward transport currents, that are blocked by GAT1 specific inhibitors. The affinity of betaine for GAT1 (K0.5,betaine≈11mM at -60mV) is greatly lower than for GABA, though coherent with its physiological concentration in neuronal tissue. The transport of betaine by GAT1 has also been confirmed using the radiolabelled release assay in HEK293 cells, LCMS-MS technique, and supported by molecular docking.
A peculiar behaviour of GAT1 was revealed by investigating GABA and betaine relationship. Betaine plays a dual role in GAT1 transport: at μM concentration it blocks the GABA transport, given the extracellular GABA is lower than its K0.5,GABA (≈16 μM at -60mV), at mM concentration it behaves like a secondary substrate. Analysing the cytoplasmic presence of GABA and betaine by LCMS-MS in oocytes expressing rGAT1 incubated in different GABA and betaine concentration, confirmed the electrophysiological findings. Our results show that betaine, by preventing the uptake of GABA, can increase the strength of the inhibitory pathway when GABA extracellular levels are low. This modulatory behaviour supports a possible role in maintaining excitatory/inhibitory balance in the central nervous system and the positive effect on neurological conditions.Betaine, N-trimethyl glycine, is a natural, stable, and non-toxic osmolyte, whose supplementation is reported to ameliorate symptoms in neurological and neurodegenerative diseases. Evidence of positive action is reported in Alzheimer’s, Parkinson’s disease, and schizophrenia, despite that there is uncertainty around its transport and action mechanism in the brain. Although there are betaine transporters present in the brain i.e., betaine/γ-aminobutyric acid (GABA) transporter 1 (SLC6A12) and the sodium-coupled neutral amino acid transporter 2 (SLC38A2), their low expression propose that the positive effect of betaine should be related to interaction with proteins of the GABAergic pathways.
By two-electrode voltage clamp experiments in Xenopus laevis oocytes heterologously expressing rGAT1, we demonstrate that betaine induces dose-, voltage-, and Na+ dependent inward transport currents, that are blocked by GAT1 specific inhibitors. The affinity of betaine for GAT1 (K0.5,betaine≈11mM at -60mV) is greatly lower than for GABA, though coherent with its physiological concentration in neuronal tissue. The transport of betaine by GAT1 has also been confirmed using the radiolabelled release assay in HEK293 cells, LCMS-MS technique, and supported by molecular docking.
A peculiar behaviour of GAT1 was revealed by investigating GABA and betaine relationship. Betaine plays a dual role in GAT1 transport: at μM concentration it blocks the GABA transport, given the extracellular GABA is lower than its K0.5,GABA (≈16 μM at -60mV), at mM concentration it behaves like a secondary substrate. Analysing the cytoplasmic presence of GABA and betaine by LCMS-MS in oocytes expressing rGAT1 incubated in different GABA and betaine concentration, confirmed the electrophysiological findings. Our results show that betaine, by preventing the uptake of GABA, can increase the strength of the inhibitory pathway when GABA extracellular levels are low. This modulatory behaviour supports a possible role in maintaining excitatory/inhibitory balance in the central nervous system and the positive effect on neurological conditions
Bile acid interactions with neurotransmitter transporters
Full text linkSynthesized in the liver from cholesterol, the bile acids (BAs) primary role is emulsifying fats to facilitate their absorption. BAs can cross the blood-brain barrier (BBB) and be synthesized in the brain. Recent evidence suggests a role for BAs in the gut-brain signaling by modulating the activity of various neuronal receptors and transporters, including the dopamine transporter (DAT). In this study, we investigated the effects of BAs and their relationship with substrates in three transporters of the solute carrier 6 family. The exposure to obeticholic acid (OCA), a semi-synthetic BA, elicits an inward current (I-BA) in the DAT, the GABA transporter 1 (GAT1), and the glycine transporter 1 (GlyT1b); this current is proportional to the current generated by the substrate, respective to the transporter. Interestingly, a second consecutive OCA application to the transporter fails to elicit a response. The full displacement of BAs from the transporter occurs only after exposure to a saturating concentration of a substrate. In DAT, perfusion of secondary substrates norepinephrine (NE) and serotonin (5-HT) results in a second OCA current, decreased in amplitude and proportional to their affinity. Moreover, co-application of 5-HT or NE with OCA in DAT, and GABA with OCA in GAT1, did not alter the apparent affinity or the I-max, similar to what was previously reported in DAT in the presence of DA and OCA. The findings support the previous molecular model that suggested the ability of BAs to lock the transporter in an occluded conformation. The physiological significance is that it could possibly avoid the accumulation of small depolarizations in the cells expressing the neurotransmitter transporter. This achieves better transport efficiency in the presence of a saturating concentration of the neurotransmitter and enhances the action of the neurotransmitter on their receptors when they are present at reduced concentrations due to decreased availability of transporters
The kinase LRRK2 is required for the physiological function and expression of the glial glutamate transporter EAAT2 (SLC1A2)
Full text linkNeurotransmitter transporters (NTTs) control synaptic responses by modulating the concentration of neurotransmitters at the synaptic cleft. Glutamate is the most abundant excitatory neurotransmitter in the brain and needs to be finely tuned in time and space to maintain a healthy brain and precise neurotransmission. The glutamate transporter EAAT2 (SLC1A2) is primarily responsible for glutamate clearance. EAAT2 impairment has been associated with Alzheimer's disease (AD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and Parkinson's disease (PD). Mutations in leucine-rich repeat kinase 2 (LRRK2) contribute to both monogenic and sporadic forms of PD, of which the common substitution Gly2019Ser is associated with a significant deficit in EAAT2 expression. The role of pathological mutants of the LRRK2 is intensively studied and reviewed. Here we have focused the attention on the physiological role of LRRK2 on EAAT2, comparing the activity of NTTs with or without the LRRK2 kinase. By heterologous expression in Xenopus laevis oocytes and two-electrode voltage clamp, the current amplitudes of the selected NTTs and kinetic parameters have been collected in the presence and absence of LRRK2. The results show that EAAT2 expression and function are impaired in the absence of the kinase and also under its pharmacological inhibition via MLi-2 treatment. LRRK2 stabilizes EAAT2 expression increasing the amount of transporter at the plasma membrane. Interestingly, the LRRK2 action is EAAT2-specific, as we observed no significant changes in the transport current amplitude and kinetic parameters obtained for the other excitatory and inhibitory NTTs studied. This study, for the first time, demonstrates the physiological importance of LRRK2 in EAAT2 function, highlighting the specificity of LRRK2-mediated modulation of EAAT2 and suggesting a potential role for the kinase as a checkpoint for preserving neurons from excitotoxicity. In brain conditions associated with impaired glutamate clearance, targeting LRRK2 for EAAT2 regulation may offer novel therapeutic opportunities
Betaine-The dark knight of the brain
Full text linkThe role of betaine in the liver and kidney has been well documented, even from the cellular and molecular point of view. Despite literature reporting positive effects of betaine supplementation in Alzheimer's, Parkinson's and schizophrenia, the role and function of betaine in the brain are little studied and reviewed. Beneficial effects of betaine in neurodegeneration, excitatory and inhibitory imbalance and against oxidative stress in the central nervous system (CNS) have been collected and analysed to understand the main role of betaine in the brain. There are many 'dark' aspects needed to complete the picture. The understanding of how this osmolyte is transported across neuron and glial cells is also controversial, as the expression levels and functioning of the known protein capable to transport betaine expressed in the brain, betaine-GABA transporter 1 (BGT-1), is itself not well clarified. The reported actions of betaine beyond BGT-1 related to neuronal degeneration and memory impairment are the focus of this work. With this review, we underline the scarcity of detailed molecular and cellular information about betaine action. Consequently, the requirement of detailed focus on and study of the interaction of this molecule with CNS components to sustain the therapeutic use of betaine
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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