bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glutamate‐dependent transcriptional regulation of GLAST: role of PKC
Authors: López‐Bayghen Esther , Ortega Arturo 
Published: March 2006

AbstractThe Na+‐dependent glutamate/aspartate transporter GLAST plays a major role in the removal of glutamate from the synaptic cleft. Short‐term, as well as long‐term changes in transporter activity are triggered by glutamate. An important locus of regulation is the density of transporter molecules present at the plasma membrane. A substrate‐dependent change in the translocation rate of the transporter molecules accounts for the short‐term effect, whereas the long‐term modulation apparently involves transcriptional regulation. Using cultured chick cerebellar Bergmann glial cells, we report here that glutamate receptors activation mediate a substantial reduction in the transcriptional activity of the chglast promoter through the Ca2+/diacylglicerol‐dependent protein kinase (PKC) signaling cascade. Overexpression of constitutive active PKC isoforms of mimic the glutamate effect. Accordingly, increased levels of c‐Jun or c‐Fos, but not Jun‐B, Jun‐D or Fos‐B, lower the chglast promoter activity. Serial deletions and electrophorectic mobility shift assays were used to define a specific region within the 5′ proximal region of the chglast promoter, associated with transcriptional repression. A putative glutamate response element could be defined in the proximal promoter stretch more likely between nts – 40 and − 78. These results demonstrate that GLAST is under glutamate‐dependent transcriptional control through PKC, and support the notion of a pivotal role of this neurotransmitter in the regulation of its own removal from the synaptic cleft, thereby modulating, mainly in the long term, glutamatergic transmission.
Voltammetric study of the control of striatal dopamine release by glutamate
Authors: Borland Laura M. , Michael Adrian C. 
Published: March 2006

AbstractThe central dopamine systems are involved in several aspects of normal brain function and are implicated in a number of human disorders. Hence, it is important to understand the mechanisms that control dopamine release in the brain. The striatum of the rat receives both dopaminergic and glutamatergic projections that synaptically target striatal neurons but not each other. Nevertheless, these afferents do form frequent appositional contacts, which has engendered interest in the question of whether they communicate with each other despite the absence of a direct synaptic connection. In this study, we used voltammetry in conjunction with carbon fiber microelectrodes in anesthetized rats to further examine the effect of the ionotropic glutamate antagonist, kynurenate, on extracellular dopamine levels in the striatum. Intrastriatal infusions of kynurenate decreased extracellular dopamine levels, suggesting that glutamate acts locally within the striatum via ionotropic receptors to regulate the basal extracellular dopamine concentration. Infusion of tetrodotoxin into the medial forebrain bundle or the striatum did not alter the voltammetric response to the intrastriatal kynurenate infusions, suggesting that glutamate receptors control a non‐vesicular release process that contributes to the basal extracellular dopamine level. However, systemic administration of the dopamine uptake inhibitor, nomifensine (20 mg/kg i.p.), markedly decreased the amplitude of the response to kynurenate infusions, suggesting that the dopamine transporter mediates non‐vesicular dopamine release. Collectively, these findings are consistent with the idea that endogenous glutamate acts locally within the striatum via ionotropic receptors to control a tonic, impulse‐independent, transporter‐mediated mode of dopamine release. Although numerous prior in vitro studies had suggested that such a process might exist, it has not previously been clearly demonstrated in an in vivo experiment.
Insulin exerts neuroprotection by counteracting the decrease in cell‐surface GABAA receptors following oxygen–glucose deprivation in cultured cortical neurons
Authors: Mielke John G. , Wang Yu Tian 
Published: March 2006

AbstractA loss of balance between excitatory and inhibitory signaling leads to excitoxicity, and contributes to ischemic cell death. Reduced synaptic inhibition as a result of dysfunction of the ionotropic GABAA receptor has been suggested as one of the major causes for this imbalance, although the underlying mechanisms remain poorly understood. In the present study, we investigated whether oxygen–glucose deprivation (OGD), an ischemia‐like challenge, alters cell‐surface expression of GABAA receptors in cultured hippocampal neurons, and thereby leads to excitotoxic cell death. Using cell culture ELISA as a cell surface receptor assay, we found that OGD produced a marked decrease in cell surface GABAA receptors, without altering the total amount of receptors. Furthermore, the reduction could be prevented by inhibition of receptor endocytosis with hypertonic sucrose treatment. Notably, insulin significantly limited OGD‐induced changes in cell‐surface GABAA receptors. In parallel, insulin protected cultured neurons against both glutamate toxicity and OGD, as assayed by mitochondrial reduction of Alamar Blue. Importantly, insulin‐mediated neuroprotection was eliminated when bicuculline, a GABAA receptor antagonist, was co‐applied with insulin during OGD. Together, our results strongly suggest that ischemia‐like insults decrease cell surface GABAA receptors in neurons via accelerated internalization, and that insulin provides neuroprotection by counteracting this reduction.
Evidence on extracellular dopamine level in rat striatum: implications for the validity of quantitative microdialysis
Authors: Chen Kevin C. 
Published: March 2006

AbstractMicrodialysis zero‐net‐flux (ZNF) method is commonly used to monitor drug‐induced changes in neurotransmitter baseline and release/uptake processes. Recent studies in this field suggest that microdialysis ZNF method seriously underestimates the resting concentration of extracellular dopamine in the rat neostriatum because probe implantation preferentially damages nearby dopamine release sites and that dopamine uptake inhibition increases the relative recovery of dopamine by microdialysis. This study assessed the validity of these claims by examining current data on extracellular dopamine levels at rest and after drug application obtained by voltammetry, a technique thought to induce less tissue disruption than microdialysis. To obtain the extracellular baseline value for dopamine from the evoked overflow data, we modified the existing dopamine kinetic model to suit both the resting and stimulated circumstances. It was found that dopamine uptake inhibition did in fact decrease the microdialysis relative recovery of dopamine, implying that the average basal extracellular dopamine level is within the range of 7–20 nmin rat striatum. This study concludes that the microdialysis ZNF method indeed underestimates the extracellular dopamine concentration, although not by as much as had been thought. Chronic microdialysis damages both neurotransmitter release and uptake, but it does so in a somewhat relative and proportional way for both processes. Thus the validity of the microdialysis ZNF method is not seriously undermined.
Increased mitochondrial respiration maintains the mitochondrial membrane potential and promotes survival of cerebellar neurons in an endogenous model of glutamate receptor activation
Authors: García Octavio , Almeida Angeles , Massieu Lourdes , Bolaños Juan P. 
Published: March 2006

AbstractIt is thought that the combination of extracellular glutamate accumulation and mitochondrial damage is involved in neuronal death associated with brain ischemia and hypoglycemia, and some neurodegenerative diseases such as Huntington's disease. However, the mechanism whereby those two factors interact together to trigger neurodegeneration in this and other neurodegenerative disorders is still elusive. Here, we have addressed this issue using a model of mild and sustained accumulation of extracellular glutamate in cerebellar cultured neurons, which are mostly glutamatergic and commonly used to study glutamate neurotoxicity. The resulting stimulation of glutamate receptors triggered a ∼ 50% persistent increase in mitochondrial respiration that was associated with free radicals formation, and which was found to be necessary to prevent the collapse of the mitochondial membrane potential (Δψm) and apoptotic cell death. In fact, hampering the glutamate‐mediated increase in mitochondrial respiration with an inhibitor of the mitochondrial respiratory chain stopped neurons from producing free radicals, but led them to undergo rapid and profound Δψm collapse and apoptotic cell death. Thus, we suggest that the formation of reactive oxygen species by glutamate receptor activation is the unavoidable consequence of an increase in the mitochondrial respiration aimed to prevent Δψm collapse and neurodegeneration. These results may be relevant to understand the pathophysiology of those neurodegenerative diseases associated with both mitochondrial respiratory chain and glutamate transporter defects.
Biochemical fingerprints of prion diseases: scrapie prion protein in human prion diseases that share prion genotype and type
Authors: Pan Tao , Li Ruliang , Kang Shin‐Chung , Pastore Manuela , Wong Boon‐Seng , Ironside James , Gambetti Pierluigi , Sy Man‐Sun 
Published: March 2006

AbstractThe phenotype of human prion diseases is influenced by the prion protein (PrP) genotype as determined by the methionine (M)/valine (V) polymorphism at codon 129, the scrapie PrP (PrPSc) type and the etiology. To gain further insight into the mechanisms of phenotype determination, we compared two‐dimensional immunoblot profiles of detergent insoluble and proteinase K‐resistant PrP species in a type of sporadic Creutzfeldt‐Jakob disease (sCJDMM2), variant CJD (vCJD) and sporadic fatal insomnia (sFI). Full‐length and truncated PrP forms present in the insoluble fractions were also separately analyzed. These three diseases were selected because they have the same M/M PrP genotype at codon 129 and the same type 2 PrPSc, but different etiologies, also sCJDMM2 and sFI are sporadic, whereas vCJD is acquired by infection. We observed minor differences in the PrP detergent‐insoluble fractions between sCJDMM2 and vCJD, although both differ in the corresponding fractions from sFI. We detected more substantial heterogeneity between sCJDMM2 and vCJD in the two‐dimensional blots of the proteinase K‐resistant PrP fraction suggesting that different PrP species are selected for conversion to proteinase K‐resistant PrP in sCJDMM2 and vCJD. These differences are mostly, but not exclusively, due to variations in the type of the N‐linked glycans. We also show that the over‐representation of the highly glycosylated forms distinctive of the proteinase K‐resistant PrPSc of vCJD in one‐dimensional blots is due to differences in both the amount and the natures of the glycans. Overall, these findings underline the complexity of phenotypic determination in human prion diseases.
Molecular cloning, localization and circadian expression of chicken melanopsin (Opn4): differential regulation of expression in pineal and retinal cell types
Authors: Chaurasia S. S. , Rollag M. D. , Jiang G. , Hayes W. P. , Haque R. , Natesan A. , Zatz M. , Tosini G. , Liu C. , Korf H. W. , Iuvone P. M. , Provencio I. 
Published: March 2006

AbstractThe avian retina and pineal gland contain autonomous circadian oscillators and photo‐entrainment pathways, but the photopigment(s) that mediate entrainment have not been definitively identified. Melanopsin (Opn4) is a novel opsin involved in entrainment of circadian rhythms in mammals. Here, we report the cDNA cloning of chicken melanopsin and show its expression in retina, brain and pineal gland. Like the melanopsins identified in amphibians and mammals, chicken melanopsin is more similar to the invertebrate retinaldehyde‐based photopigments than the retinaldehyde‐based photopigments typically found in vertebrates. In retina, melanopsin mRNA is expressed in cells of all retinal layers. In pineal gland, expression was strong throughout the parenchyma of the gland. In brain, expression was observed in a few discrete nuclei, including the lateral septal area and medial preoptic nucleus. The retina and pineal gland showed distinct diurnal expression patterns. In pineal gland, melanopsin mRNA levels were highest at night at Zeitgeber time (ZT) 16. In contrast, transcript levels in the whole retina reached their highest levels in the early morning (ZT 0–4). Further analysis of melanopsin mRNA expression in retinal layers isolated by laser capture microdissection revealed different patterns in different layers. There was diurnal expression in all retinal layers except the ganglion cell layer, where heavy expression was localized to a small number of cells. Expression of melanopsin mRNA peaked during the daytime in the retinal pigment epithelium and inner nuclear layer but, like in the pineal, at night in the photoreceptors. Localization and regulation of melanopsin mRNA in the retina and pineal gland is consistent with the hypothesis that this novel photopigment plays a role in photic regulation of circadian function in these tissues.
Matrix metalloproteinase‐7 disrupts dendritic spines in hippocampal neurons through NMDA receptor activation
Authors: Bilousova Tina V. , Rusakov Dmitri A. , Ethell Douglas W. , Ethell Iryna M. 
Published: March 2006

AbstractDendritic spines are protrusions from the dendritic shaft that host most excitatory synapses in the brain. Although they first emerge during neuronal maturation, dendritic spines remain plastic through adulthood, and recent advances in the molecular mechanisms governing spine morphology have shown them to be exquisitely sensitive to changes in the micro‐environment. Among the many factors affecting spine morphology are components and regulators of the extracellular matrix (ECM). Modification of the ECM is critical to the repair of injuries throughout the body, including the CNS. Matrix metalloproteinase (MMP)‐7/matrilysin is a key regulator of the ECM during pathogen infection, after nerve crush and in encephalitogenic disorders. We have investigated the effects of MMP‐7 on dendritic spines in hippocampal neuron cultures and found that it induces the transformation of mature, short mushroom‐shaped spines into long, thin filopodia reminiscent of immature spines. These changes were accompanied by a dramatic redistribution of F‐actin from spine heads into thick, rope‐like structures in the dendritic shaft. Strikingly, MMP‐7 effects on dendritic spines were similar to those of NMDA treatment, and both could be blocked by channel‐specific antagonists. These findings are the first direct evidence that MMPs can influence the morphology of mature dendritic spines, and hence synaptic stability.
Mnk is a negative regulator of cap‐dependent translation in Aplysia neurons
Authors: Ross Gabriel , Dyer John R. , Castellucci Vincent F. , Sossin Wayne S. 
Published: March 2006

AbstractTo investigate the mechanisms underlying regulation of eukaryotic initiation factor 4E (eIF4E) phosphorylation in Aplysia neurons, we have cloned the Aplysia homolog of the vertebrate eIF4E kinases, Mnk1 and ‐2. Aplysia Mnk shares many conserved regions with vertebrate Mnk, including putative eukaryotic initiation factor 4G binding regions, activation loop phosphorylation sites, and a carboxy‐terminal anchoring site for MAP kinases. As expected, purified Aplysia Mnk phosphorylated Aplysia eIF4E at a conserved carboxy‐terminal serine and over‐expression of Aplysia Mnk in sensory neurons led to increased phosphorylation of endogenous eIF4E. Over‐expression of Aplysia Mnk led to strong decreases in cap‐dependent translation, while generally sparing internal ribosomal entry site (IRES)‐dependent translation. However, decreases in cap‐dependent translation seen after expression of Aplysia Mnk could only be partly explained by increases in eIF4E phosphorylation. In Aplysia sensory neurons, phosphorylation of eIF4E is reduced during intermediate memory formation. However, we found that this physiological regulation of eIF4E phosphorylation was independent of changes in Aplysia Mnk phosphorylation. We propose that changes in eIF4E phosphorylation in Aplysia neurons are a consequence of changes in cap‐dependent translation that are independent of regulation of Aplysia Mnk.
Visualization of APP dimerization and APP‐Notch2 heterodimerization in living cells using bimolecular fluorescence complementation
Authors: Chen Ci‐Di , Oh Sun‐Young , Hinman Jason D. , Abraham Carmela R. 
Published: March 2006

AbstractWe previously demonstrated that the amyloid precursor protein (APP) interacts with Notch receptors. Here, we confirmed the APP/Notch1 endogenous interaction in embryonic day 17 rat brain tissue, suggesting the interaction was not as a result of over‐expression artifacts. To investigate potential homodimeric and heterodimeric interactions of APP and Notch2 (N2), we have visualized the subcellular localization of the APP/N2 complexes formed in living cells using bimolecular fluorescence complementation (BiFC) analysis. BiFC was accomplished by fusing the N‐terminal fragment or the C‐terminal fragment of yellow fluorescent protein (YFP) to APP, N2, and a C‐terminally truncated form of N2. When expressed in COS‐7 cells, these tagged proteins alone did not produce a fluorescent signal. The tagged APP homodimer produced a weak fluorescent signal, while neither full‐length N2, nor a truncated N2 alone, produced a visible signal, suggesting that N2 receptors do not form homodimers. The strongest fluorescent signal was obtained with co‐expression of the C‐terminal fragment of YFP fused to APP and the N‐terminal fragment of YFP fused to the truncated form of N2. This heterodimer localized to plasma membrane, endoplasmic reticulum (ER), Golgi and other compartments. The results were confirmed and quantified by flow cytometry. The BiFC method of specifically visualizing APP/Notch interactions can be applied to study APP and Notch signaling during development, aging and neurodegeneration.
Modulation of bradykinin signaling by EP24.15 and EP24.16 in cultured trigeminal ganglia
Authors: Jeske Nathaniel A. , Berg Kelly A. , Cousins Joanne C. , Ferro Emer S. , Clarke William P. , Glucksman Marc J. , Roberts James L. 
Published: March 2006

AbstractMetalloendopeptidases expressed in neural tissue are characterized in terms of their neuropeptide substrates. One such neuropeptide, bradykinin (BK), is an important inflammatory mediator that activates the type‐2 BK receptor (B2R) on the terminal endings of specialized pain‐sensing neurons known as nociceptors. Among several metalloendopeptidases that metabolize and inactivate BK, EP24.15 and EP24.16 are known to associate with the plasma membrane in several immortalized cell lines. Potentially, the colocalization of EP24.15/16 and B2R at plasma membrane microdomains known as lipid rafts in a physiologically relevant nociceptive system would allow for discrete, peptidase regulation of BK signaling. Western blot analysis of crude subcellular fractions and lipid raft preparations of cultured rat trigeminal ganglia demonstrate similar expression profiles between EP24.15/16 and B2R on a subcellular level. Furthermore, the treatment of primary cultures of trigeminal ganglia with inhibitors of EP24.15/16 led to the potentiation of several bradykinin‐induced events that occur downstream of B2R activation. EP24.15/16 inhibition byN‐[1(R,S)‐carboxy‐3‐phenylpropyl]‐Ala‐AlalTyr‐p‐aminobenzoate (cFP) resulted in a 1000‐fold increase in B2R sensitivity to BK as measured by inositol phosphate accumulation. In addition, cFP treatment resulted in a 31.1 ± 5.0% potentiation of the ability of BK to inhibit protein kinase B (Akt) activity. Taken together, these data demonstrate that EP24.15/16 modulate intracellular, peptidergic signaling cascades through B2R in a physiologically relevant nociceptive system.
Ion interaction at the pore of Lc‐type Ca2+ channel is sufficient to mediate depolarization‐induced exocytosis
Authors: Lerner Immanuel , Trus Michael , Cohen Roy , Yizhar Ofer , Nussinovitch Itzhak , Atlas Daphne 
Published: March 2006

AbstractThe coupling of voltage‐gated Ca2+ channel (VGCC) to exocytotic proteins suggests a regulatory function for the channel in depolarization‐evoked exocytosis. To explore this possibility we have examined catecholamine secretion in PC12 and chromaffin cells. We found that replacing Ca2+ with La3+ or other lanthanide ions supported exocytosis in divalent ion‐free solution. Cd2+, nifedipine, or verapamil inhibited depolarization‐evoked secretion in La3+, indicating specific binding of La3+ at the pore of L‐type VGCC, probably at the poly‐glutamate (EEEE) locus. Lanthanide efficacy was stringently dependent on ionic radius with La3+ > Ce3+ > Pr3+, consistent with a size‐selective binding interface of trivalent cations at the channel pore. La3+ inward currents were not detected and the highly sensitive La3+/fura‐2 imaging assay (∼1 pm) detected no La3+ entry, cytosolic La3+ build‐up, or alterations in cytosolic Ca2. These results provide strong evidence that occupancy of the pore of the channel by an impermeable cation leads to a conformational change that is transmitted to the exocytotic machinery upstream of intracellular cation build‐up (intracellular Ca2+ concentration). Our model allows for a tight temporal and spatial coupling between the excitatory stimulation event and vesicle fusion. It challenges the conventional view that intracellular Ca2+ ion build‐up via VGCC permeation is required to trigger secretion and establishes the VGCC as a plausible Ca2+ sensor protein in the process of neuroendocrine secretion.
The dopamine transporter proteome
Authors: Torres Gonzalo E. 
Published: March 2006

AbstractDopamine (DA) uptake through the neuronal plasma membrane DA transporter (DAT) is essential for the maintenance of normal DA homeostasis in the brain. The DAT‐mediated re‐uptake system limits not only the intensity but also the duration of DA actions at presynaptic and postsynaptic receptors. This protein is the primary target for cocaine and amphetamine, both highly addictive and major substances of abuse worldwide. DAT is also the molecular target for therapeutic agents used in the treatment of mental disorders, such as attention deficit hyperactivity disorder and depression. Given the role played by the DAT in regulation of DA neurotransmission and its contribution to the abuse potential of psychostimulants, it becomes not only important but also necessary to understand the functional regulation of this protein. To investigate the cellular and molecular mechanisms associated with DAT function and regulation, our laboratory and others have embarked on a systematic search for DAT protein–protein interactions. Recently, a growing number of proteins have been shown to interact with DAT. These novel interactions might be important in the assembly, targeting, trafficking and/or regulation of transporter function. In this review, I summarize the main findings obtained from the characterization of DAT‐interacting proteins and discuss the functional implications of these novel interactions. Based on these new data, I propose to use the term DAT proteome to explain how interacting proteins regulate DAT function. These novel interactions might help define new mechanisms associated with the function of the transporter.