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Aurelio Galli - One of the best experts on this subject based on the ideXlab platform.
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Hypoinsulinemia Regulates Amphetamine- Induced Reverse Transport of Dopamine
2016Co-Authors: Jason M. Williams, Gregory H. Turner, Christine Saunders, Randy D. Blakely, Anthony W. Owens, Aurelio GalliAbstract:The behavioral effects of psychomotor stimulants such as amphetamine (AMPH) arise from their ability to elicit increases in extracellular dopamine (DA). These AMPH-induced increases are achieved by DA Transporter (DAT)-mediated transmitter efflux. Recently, we have shown that AMPH self-administration is reduced in rats that have been depleted of insulin with the diabetogenic agent streptozotocin (STZ). In vitro studies suggest that hypoinsulinemia may regulate the actions of AMPH by inhibiting the insulin downstream effectors phosphotidylinositol 3-kinase (PI3K) and protein kinase B (PKB, or Akt), which we have previously shown are able to fine-tune DAT cell-surface expression. Here, we demonstrate that striatal Akt function, as well as DAT cell-surface expression, are significantly reduced by STZ. In addition, our data show that the release of DA, determined by high-speed chronoamperometry (HSCA) in the striatum, in response to AMPH, is severely impaired in these insulin-deficient rats. Importantly, selective inhibition o
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flotillin 1 is essential for pkc triggered endocytosis and membrane microdomain localization of dat
Nature Neuroscience, 2011Co-Authors: Laura M Cremona, Nicole Speed, Brandon J Lute, Monique Anderson, Sabrina D Robertson, Roxanne A Vaughan, Erica Bowton, James E Rothman, Heinrich J G Matthies, Aurelio GalliAbstract:The authors report that the protein Flotillin-1/Reggie-2 (Flot1) is required for PKC-regulated internalization of the dopamine Transporter (DAT) and the glial glutamate Transporter EAAT2. Flot1 was required to localize DAT within plasma membrane microdomains in stable cell lines, and for amphetamine-induced Reverse Transport of dopamine in neurons.
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Hypoinsulinemia regulates amphetamine-induced Reverse Transport of dopamine.
PLoS biology, 2007Co-Authors: Jason M. Williams, W. Anthony Owens, Gregory H. Turner, Christine Saunders, Concetta Dipace, Randy D. Blakely, John C. Gore, Lynette C. Daws, Malcolm J. Avison, Aurelio GalliAbstract:The behavioral effects of psychomotor stimulants such as amphetamine (AMPH) arise from their ability to elicit increases in extracellular dopamine (DA). These AMPH-induced increases are achieved by DA Transporter (DAT)-mediated transmitter efflux. Recently, we have shown that AMPH self-administration is reduced in rats that have been depleted of insulin with the diabetogenic agent streptozotocin (STZ). In vitro studies suggest that hypoinsulinemia may regulate the actions of AMPH by inhibiting the insulin downstream effectors phosphotidylinositol 3-kinase (PI3K) and protein kinase B (PKB, or Akt), which we have previously shown are able to fine-tune DAT cell-surface expression. Here, we demonstrate that striatal Akt function, as well as DAT cell-surface expression, are significantly reduced by STZ. In addition, our data show that the release of DA, determined by high-speed chronoamperometry (HSCA) in the striatum, in response to AMPH, is severely impaired in these insulin-deficient rats. Importantly, selective inhibition of PI3K with LY294002 within the striatum results in a profound reduction in the subsequent potential for AMPH to evoke DA efflux. Consistent with our biochemical and in vivo electrochemical data, findings from functional magnetic resonance imaging experiments reveal that the ability of AMPH to elicit positive blood oxygen level-dependent signal changes in the striatum is significantly blunted in STZ-treated rats. Finally, local infusion of insulin into the striatum of STZ-treated animals significantly recovers the ability of AMPH to stimulate DA release as measured by high-speed chronoamperometry. The present studies establish that PI3K signaling regulates the neurochemical actions of AMPH-like psychomotor stimulants. These data suggest that insulin signaling pathways may represent a novel mechanism for regulating DA transmission, one which may be targeted for the treatment of AMPH abuse and potentially other dopaminergic disorders.
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mechanisms of neurotransmitter release by amphetamines a review
Progress in Neurobiology, 2005Co-Authors: David Sulzer, Mark S Sonders, Nathan W Poulsen, Aurelio GalliAbstract:Amphetamine and substituted amphetamines, including methamphetamine, methylphenidate (Ritalin), methylenedioxymethamphetamine (ecstasy), and the herbs khat and ephedra, encompass the only widely administered class of drugs that predominantly release neurotransmitter, in this case principally catecholamines, by a non-exocytic mechanism. These drugs play important medicinal and social roles in many cultures, exert profound effects on mental function and behavior, and can produce neurodegeneration and addiction. Numerous questions remain regarding the unusual molecular mechanisms by which these compounds induce catecholamine release. We review current issues on the two apparent primary mechanisms — the redistribution of catecholamines from synaptic vesicles to the cytosol, and induction of Reverse Transport of transmitter through plasma membrane uptake carriers — and on additional drug effects that affect extracellular catecholamine levels, including uptake inhibition, effects on exocytosis, neurotransmitter synthesis, and metabolism. # 2005 Elsevier Ltd. All rights reserved.
David Sulzer - One of the best experts on this subject based on the ideXlab platform.
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how addictive drugs disrupt presynaptic dopamine neurotransmission
Neuron, 2011Co-Authors: David SulzerAbstract:The fundamental principle that unites addictive drugs appears to be that each enhances synaptic dopamine by means that dissociate it from normal behavioral control, so that they act to reinforce their own acquisition. This occurs via the modulation of synaptic mechanisms that can be involved in learning, including enhanced excitation or disinhibition of dopamine neuron activity, blockade of dopamine reuptake, and altering the state of the presynaptic terminal to enhance evoked over basal transmission. Amphetamines offer an exception to such modulation in that they combine multiple effects to produce nonexocytic stimulation-independent release of neurotransmitter via Reverse Transport independent from normal presynaptic function. Questions about the molecular actions of addictive drugs, prominently including the actions of alcohol and solvents, remain unresolved, but their ability to co-opt normal presynaptic functions helps to explain why treatment for addiction has been challenging.
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mechanisms of neurotransmitter release by amphetamines a review
Progress in Neurobiology, 2005Co-Authors: David Sulzer, Mark S Sonders, Nathan W Poulsen, Aurelio GalliAbstract:Amphetamine and substituted amphetamines, including methamphetamine, methylphenidate (Ritalin), methylenedioxymethamphetamine (ecstasy), and the herbs khat and ephedra, encompass the only widely administered class of drugs that predominantly release neurotransmitter, in this case principally catecholamines, by a non-exocytic mechanism. These drugs play important medicinal and social roles in many cultures, exert profound effects on mental function and behavior, and can produce neurodegeneration and addiction. Numerous questions remain regarding the unusual molecular mechanisms by which these compounds induce catecholamine release. We review current issues on the two apparent primary mechanisms — the redistribution of catecholamines from synaptic vesicles to the cytosol, and induction of Reverse Transport of transmitter through plasma membrane uptake carriers — and on additional drug effects that affect extracellular catecholamine levels, including uptake inhibition, effects on exocytosis, neurotransmitter synthesis, and metabolism. # 2005 Elsevier Ltd. All rights reserved.
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l 3 4 dihydroxyphenylalanine increases the quantal size of exocytotic dopamine release in vitro
Journal of Neurochemistry, 2002Co-Authors: Emmanuel N Pothos, Mark Desmond, David SulzerAbstract:The catecholamine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) is used to augment striatal dopamine (DA), although its mechanism of altering neurotransmission is not well understood. We observed the effects of L-DOPA on catecholamine release in ventral midbrain neuron and PC12 pheochromocytoma cell line cultures. In ventral midbrain neuron cultures exposed to 40 mM potassium-containing media, L-DOPA (100 microM for 1 h) increased DA release by > 10-fold. The elevated extracellular DA levels were not significantly blocked by the DA/norepinephrine Transport inhibitor nomifensine, demonstrating that Reverse Transport through catecholamine-uptake carriers plays little role in this release. In PC12 cells, where DA release from individual secretory vesicles can be observed, L-DOPA (50 microM for 1 h) elevated DA release in high-potassium media by 370%. Amperometric measurements demonstrated that L-DOPA (50 microM for 40-70 min) did not raise the frequency of vesicular exocytosis but increased the average size of quantal release to at least 250% of control levels. Together, these findings suggest that L-DOPA can increase stimulation-dependent transmitter release from DA cells by augmenting cytosolic neurotransmitter, leading to increased quantal size.
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electrochemical detection of Reverse Transport from planorbis giant dopamine neuron
Methods in Enzymology, 1998Co-Authors: Brian B Anderson, Andrew G Ewing, David SulzerAbstract:Publisher Summary This chapter highlights how studies of the giant dopamine neuron (GDN) located in the left pedal ganglion of the pond snail Planorbis corneus have provided direct demonstration of Reverse Transport from a neuron in real time. The GDN is advantageous for these studies because it has nomifensine-sensitive plasma membrane dopamine (DA) uptake, reserpine-sensitive vesicular DA uptake, it metabolizes DA to dihydroxyphenylacetic acid, and lacks ascorbic acid, facilitating the unambiguous amperometric detection of DA. Exocytic quantal release events can easily be distinguished from release by Reverse Transport using carbon fiber electrodes. The large size of the neuron allows the estimation of cytosolic levels of DA with intracellular carbon electrodes. The large size of the cell, the presence of the DA uptake system, and presence of many synaptic vesicles provides an enormous transmitter pool, proving the means to detect Reverse Transport from a single cell.
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amphetamine redistributes dopamine from synaptic vesicles to the cytosol and promotes Reverse Transport
The Journal of Neuroscience, 1995Co-Authors: David Sulzer, Stephen Rayport, Takung Chen, H Kristensen, Andrew G EwingAbstract:Whether amphetamine acts principally at the plasma membrane or at synaptic vesicles is controversial. We find that d-amphetamine injection into the Planorbis giant dopamine neuron causes robust dopamine release, demonstrating that specific amphetamine uptake is not required. Arguing for action at vesicles, whole-cell capillary electrophoresis of single Planorbis dopamine neurons shows that amphetamine reduces vesicular dopamine, while amphetamine reduces quantal dopamine release from PC12 cells by > 50% per vesicle. Intracellular injection of dopamine into the Planorbis dopamine neuron produces rapid nomifensine-sensitive release, showing that an increased substrate concentration gradient is sufficient to induce release. These experiments indicate that amphetamine acts at the vesicular level where it redistributes dopamine to the cytosol, promoting Reverse Transport, and dopamine release.
Daniel J. Rader - One of the best experts on this subject based on the ideXlab platform.
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molecular regulation of macrophage Reverse cholesterol Transport
Current Opinion in Cardiology, 2007Co-Authors: Xun Wang, Daniel J. RaderAbstract:Purpose of reviewMacrophage Reverse cholesterol Transport is one of the key mechanisms mediating the protective effects of high-density lipoproteins on atherosclerosis. This review focuses on the recent developments in our understanding of molecular mechanisms of macrophage Reverse Transport and reg
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overexpression of apolipoprotein a i promotes Reverse Transport of cholesterol from macrophages to feces in vivo
Circulation, 2003Co-Authors: Yuzhen Zhang, George H Rothblat, Ilaria Zanotti, Muredach P Reilly, Jane M Glick, Daniel J. RaderAbstract:Background— Abundant data indicate that overexpression of apolipoprotein A-I (apoA-I) in mice inhibits atherosclerosis. One mechanism is believed to be promotion of Reverse cholesterol Transport, but no direct proof of this concept exists. We developed a novel approach to trace Reverse Transport of labeled cholesterol specifically from macrophages to the liver and feces in vivo and have applied this approach to investigate the ability of apoA-I overexpression to promote macrophage-specific Reverse cholesterol Transport. Method and Results— J774 macrophages were loaded with cholesterol by incubation with acetylated LDL, labeled with 3H-cholesterol, and then injected intraperitoneally into mice. Plasma and feces were collected at 24 hours and 48 hours, when mice were exsanguinated, tissues were harvested, and all were analyzed for tracer counts. 3H-cholesterol was found in the plasma, liver, and feces. For apoA-I overexpression, mice were injected intravenously with apoA-I adenovirus (1011 particles per ani...
Wagner Ferreira Dos Santos - One of the best experts on this subject based on the ideXlab platform.
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enhancing glutamate Transport mechanism of action of parawixin1 a neuroprotective compound from parawixia bistriata spider venom
Molecular Pharmacology, 2007Co-Authors: Andreia Cristina Karklin Fontana, Rene Oliveira Beleboni, Joaquim Coutinhonetto, Wagner Ferreira Dos Santos, Marcin W Wojewodzic, Nina Julie Grutle, Spencer D Watts, Niels C Danbolt, Susan G AmaraAbstract:Previous studies have shown that a compound purified from the spider Parawixia bistriata venom stimulates the activity of glial glutamate Transporters and can protect retinal tissue from ischemic damage. To understand the mechanism by which this compound enhances Transport, we examined its effects on the functional properties of glutamate Transporters after solubilization and reconstitution in liposomes and in transfected COS-7 cells. Here, we demonstrate in both systems that Parawixin1 promotes a direct and selective enhancement of glutamate influx by the EAAT2 Transporter subtype through a mechanism that does not alter the apparent affinities for the cosubstrates glutamate or sodium. In liposomes, we observed maximal enhancement by Parawixin1 when extracellular sodium and intracellular potassium concentrations are within physiological ranges. Moreover, the compound does not enhance the Reverse Transport of glutamate under ionic conditions that favor efflux, when extracellular potassium is elevated and the sodium gradient is reduced, nor does it alter the exchange of glutamate in the absence of internal potassium. These observations suggest that Parawixin1 facilitates the reorientation of the potassium-bound Transporter, the rate-limiting step in the Transport cycle, a conclusion further supported by experiments showing that Parawixin1 does not stimulate uptake by an EAAT2 Transport mutant (E405D) defective in the potassium-dependent reorientation step. Thus, Parawixin1 enhances Transport through a novel mechanism targeting a step in the Transport cycle distinct from substrate influx or efflux and provides a basis for the design of new drugs that act allosterically on Transporters to increase glutamate clearance.
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neurochemical characterization of a neuroprotective compound from parawixia bistriata spider venom that inhibits synaptosomal uptake of gaba and glycine
Molecular Pharmacology, 2006Co-Authors: Rene Oliveira Beleboni, Leonardo Gobboneto, Norberto Peporine Lopes, Joaquim Coutinhonetto, Renato Guizzo, Andreia Cristina Karklin Fontana, Andrea Baldocchi Pizzo, Ruither O G Carolino, Wagner Ferreira Dos SantosAbstract:The major contribution of this work is the isolation of a neuroprotective compound referred to as 2-amino-5-ureidopentanamide (FrPbAII) (M(r) = 174) from Parawixia bistriata spider venom and an investigation of its mode of action. FrPbAII inhibits synaptosomal GABA uptake in a dose-dependent manner and probably does not act on Na(+), K(+), and Ca(2+) channels, GABA(B) receptors, or gamma-aminobutyrate:alpha-ketoglutarate aminotransferase enzyme; therefore, it is not directly dependent on these structures for its action. Direct increase of GABA release and Reverse Transport are also ruled out as mechanisms of FrPbAII activities as well as unspecific actions on pore membrane formation. Moreover, FrPbAII is selective for GABA and glycine Transporters, having slight or no effect on monoamines or glutamate Transporters. According to our experimental glaucoma data in rat retina, FrPbAII is able to cross the blood-retina barrier and promote effective protection of retinal layers submitted to ischemic conditions. These studies are of relevance by providing a better understanding of neurochemical mechanisms involved in brain function and for possible development of new neuropharmacological and therapeutic tools.
Susan G Amara - One of the best experts on this subject based on the ideXlab platform.
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cysteine Transport through excitatory amino acid Transporter 3 eaat3
PLOS ONE, 2014Co-Authors: Spencer D Watts, Delany Torressalazar, Christopher B Divito, Susan G AmaraAbstract:Excitatory amino acid Transporters (EAATs) limit glutamatergic signaling and maintain extracellular glutamate concentrations below neurotoxic levels. Of the five known EAAT isoforms (EAATs 1-5), only the neuronal isoform, EAAT3 (EAAC1), can efficiently Transport the uncharged amino acid L-cysteine. EAAT3-mediated cysteine Transport has been proposed to be a primary mechanism used by neurons to obtain cysteine for the synthesis of glutathione, a key molecule in preventing oxidative stress and neuronal toxicity. The molecular mechanisms underlying the selective Transport of cysteine by EAAT3 have not been elucidated. Here we propose that the Transport of cysteine through EAAT3 requires formation of the thiolate form of cysteine in the binding site. Using Xenopus oocytes and HEK293 cells expressing EAAT2 and EAAT3, we assessed the Transport kinetics of different substrates and measured Transporter-associated currents electrophysiologically. Our results show that L-selenocysteine, a cysteine analog that forms a negatively-charged selenolate ion at physiological pH, is efficiently Transported by EAATs 1-3 and has a much higher apparent affinity for Transport when compared to cysteine. Using a membrane tethered GFP variant to monitor intracellular pH changes associated with Transport activity, we observed that Transport of either L-glutamate or L-selenocysteine by EAAT3 decreased intracellular pH, whereas Transport of cysteine resulted in cytoplasmic alkalinization. No change in pH was observed when cysteine was applied to cells expressing EAAT2, which displays negligible Transport of cysteine. Under conditions that favor release of intracellular substrates through EAAT3 we observed release of labeled intracellular glutamate but did not detect cysteine release. Our results support a model whereby cysteine Transport through EAAT3 is facilitated through cysteine de-protonation and that once inside, the thiolate is rapidly re-protonated. Moreover, these findings suggest that cysteine Transport is predominantly unidirectional and that Reverse Transport does not contribute to depletion of intracellular cysteine pools.
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enhancing glutamate Transport mechanism of action of parawixin1 a neuroprotective compound from parawixia bistriata spider venom
Molecular Pharmacology, 2007Co-Authors: Andreia Cristina Karklin Fontana, Rene Oliveira Beleboni, Joaquim Coutinhonetto, Wagner Ferreira Dos Santos, Marcin W Wojewodzic, Nina Julie Grutle, Spencer D Watts, Niels C Danbolt, Susan G AmaraAbstract:Previous studies have shown that a compound purified from the spider Parawixia bistriata venom stimulates the activity of glial glutamate Transporters and can protect retinal tissue from ischemic damage. To understand the mechanism by which this compound enhances Transport, we examined its effects on the functional properties of glutamate Transporters after solubilization and reconstitution in liposomes and in transfected COS-7 cells. Here, we demonstrate in both systems that Parawixin1 promotes a direct and selective enhancement of glutamate influx by the EAAT2 Transporter subtype through a mechanism that does not alter the apparent affinities for the cosubstrates glutamate or sodium. In liposomes, we observed maximal enhancement by Parawixin1 when extracellular sodium and intracellular potassium concentrations are within physiological ranges. Moreover, the compound does not enhance the Reverse Transport of glutamate under ionic conditions that favor efflux, when extracellular potassium is elevated and the sodium gradient is reduced, nor does it alter the exchange of glutamate in the absence of internal potassium. These observations suggest that Parawixin1 facilitates the reorientation of the potassium-bound Transporter, the rate-limiting step in the Transport cycle, a conclusion further supported by experiments showing that Parawixin1 does not stimulate uptake by an EAAT2 Transport mutant (E405D) defective in the potassium-dependent reorientation step. Thus, Parawixin1 enhances Transport through a novel mechanism targeting a step in the Transport cycle distinct from substrate influx or efflux and provides a basis for the design of new drugs that act allosterically on Transporters to increase glutamate clearance.