bluuebunny/crossref_metadata_2025_split huggingface dataset:
Agonist‐independent internalization of metabotropic glutamate receptor 1a is arrestin‐ and clathrin‐dependent and is suppressed by receptor inverse agonists
Authors: Pula Giordano , Mundell Stuart J. , Roberts Peter J. , Kelly Eamonn 
Published: March 2006

AbstractThree group I mGluR antagonists CPCCOEt, LY367385 and BAY36‐7620, were analyzed for their effect on cell surface expression of metabotropic glutamate receptor 1a and 1b. All three antagonists inhibited glutamate‐induced internalization of mGluR1a and mGluR1b. However, when added alone, either LY367385 or BAY36‐7620 increased the cell surface expression of mGluR1a but not mGluR1b. Both LY367385 and BAY36‐7620 displayed inverse agonist activity as judged by their ability to inhibit basal inositol phosphate accumulation in cells expressing the constitutively active mGluR1a. Interestingly, mGluR1a but not mGluR1b was constitutively internalized in HEK293 cells and both LY367385 and BAY36‐7620 inhibited the constitutive internalization of this splice variant. Furthermore, coexpression of dominant negative mutant constructs of arrestin‐2 [arrestin‐2‐(319–418)] or Eps15 [Eps15(EΔ95‐295)] increased cell surface expression of mGluR1a and blocked constitutive receptor internalization. In the presence of these dominant negative mutants, incubation of cells with LY367385 and BAY36‐7620 produced no further increase in cell surface expression of mGluR1a. Taken together, these results suggest that the constitutive activity of mGluR1a triggers the internalization of the receptor through an arrestin‐ and clathrin‐dependent pathway, and that inverse agonists increase the cell surface expression of mGluR1a by promoting an inactive form of mGluR1a, which does not undergo constitutive internalization.
Stress induces activation of stress‐activated kinases in the mouse brain
Authors: Liu Ya Fang , Bertram Kurt , Perides George , McEwen Bruce S. , Wang Dechun 
Published: March 2006

AbstractStress is a part of daily life. However, molecular mechanisms underlying the activation of limbic‐hypothalamic‐pituitary‐adrenal (LHPA) axis remains unknown. In this study, we explored whether activation of the mitogen‐activated kinase kinase 4 (MKK4)‐c‐Jun‐N‐terminal kinase (JNK) signaling pathway may play a role in the activation of the LHPA axis. We found that forced‐swim stress induced elevation of activated MKK4 in the hippocampal formation, amygdala, and hypothalamus. Unlike MKK4, a high basal level of JNK activity is present in many brain areas of unstressed mice. Forced‐swim stress significantly elevated JNK activity in the hypothalamus and amygdala and, to a lesser extent, in the cortex, CA1 and CA3 regions, and the dentate gyrus. To further investigate the role of MKK4 and JNK in induction of stress responses, we investigated whether a different stress, namely, restraint stress, induced activation of MKK4 or JNK in the brain. We found that restraint stress also induced elevation of activated MKK4 and JNK in the hippocampal formation, amygdala, and hypothalamus. Because MKK4 and JNK were activated within 5 min following stress, we propose that the MKK4‐JNK signaling may be an early neural event in the initiation of neuroendocrine, autonomic and behavioral stress responses.
Nitric oxide‐induced cell death of cerebrocortical murine astrocytes is mediated through p53‐ and Bax‐dependent pathways
Authors: Yung Hong Wa , Bal‐Price Anna K. , Brown Guy C. , Tolkovsky Aviva M. 
Published: March 2006

AbstractWe have investigated the mechanism by which nitric oxide (NO) induces the death of mouse astrocytes. We show that NO (from donor diethylenetriamine‐NO adduct) induces death with several features of apoptosis, including chromatin condensation, phosphatidylserine exposure on the outer leaflet of the plasma membrane, Bax translocation to the mitochondria and cytochromecrelease, but no caspase activation or nuclear fragmentation is observed. Nitric oxide also elevates p53 expression, causing a concomitant increase in p53 serine 18 phosphorylation and p53 translocation from the cytoplasm to the nucleus. Activation of Bax and p53 is important for NO‐induced apoptosis‐like cell death because Bax‐ or p53‐deficient astrocytes are much more resistant than wild‐type cells to the same NO treatment. We further demonstrate that LY294002‐sensitive kinases are responsible for controlling serine 18 phosphorylation of p53, thereby regulating the pro‐apoptotic activity of p53 in astrocytes. While apoptosis is suppressed in the presence of LY294002, however, death by necrosis is increased, suggesting that LY294002‐sensitive kinases additionally suppress a latent necrotic response to NO. We conclude that NO‐induced death in astrocytes is mediated by p53‐ and Bax‐dependent mechanisms, although full manifestation of apoptosis is aborted by concomitant inhibition of caspase activation. More generally, our data suggest that apoptotic mediators should be evaluated as the cause of cell death even in cases where a full apoptotic phenotype is lacking.
Genetic ablation of tumor necrosis factor‐alpha (TNF‐α) and pharmacological inhibition of TNF‐synthesis attenuates MPTP toxicity in mouse striatum
Authors: Ferger Boris , Leng Andreas , Mura Anna , Hengerer Bastian , Feldon Joram 
Published: March 2006

AbstractThe impact of pro‐inflammatory cytokines such as tumor necrosis factor‐α (TNF‐α) in the pathology of Parkinson's disease (PD) and in MPTP neurotoxicity remains unclear. Here, male TNF‐α (–/–) deficient mice and C57bL/6 mice were treated with MPTP (4 × 15mg/kg, 24 h intervals) and in one series, thalidomide was administered to inhibit TNF‐α synthesis. Real‐time RT‐PCR revealed that the striatal mRNA levels of TNF‐α, of the astrocytic marker glial fibrillary acidic protein (GFAP) and of the marker for activated microglia, macrophage antigen complex‐1 (MAC‐1), were significantly enhanced after MPTP administration. Thalidomide (50 mg/kg, p.o.) partly protected against the MPTP‐induced dopamine (DA) depletion, and TNF‐α (–/–) mice showed a significant attenuation of striatal DA and DA metabolite loss as well as striatal tyrosine hydroxylase (TH) fiber density, but no difference in nigral TH and DA transporter immunoreactivity. TNF‐α deficient mice suffered a lower mortality (10%) compared to the high mortality (75%) seen in wild‐type mice after acute MPTP treatment (4 × 20mg/kg, 2 h interval). HPLC measurement of MPP+ levels revealed no differences in TNF‐α (–/–), wild‐type and thalidomide treated mice. This study demonstrates that TNF‐α is involved in MPTP toxicity and that inhibition of TNF‐α response may be a promising target for extending beyond symptomatic treatment and developing anti‐parkinsonian drugs for the treatment of the inflammatory processes in PD.
Motor activity and gene expression in rats with neonatal 6‐hydroxydopamine lesions
Authors: Masuo Yoshinori , Ishido Masami , Morita Masatoshi , Oka Syuichi , Niki Etsuo 
Published: March 2006

AbstractA rat model of a hyperkinetic disorder was used to investigate the mechanisms underlying motor hyperactivity. Rats received an intracisternal injection of 6‐hydroxydopamine on post‐natal day 5. At 4 weeks of age, the animals showed significant motor hyperactivity during the dark phase, which was attenuated by methamphetamine injection. Gene expression profiling was carried out in the striatum and midbrain using a DNA macroarray. In the striatum at 4 weeks, there was increased gene expression of the NMDA receptor 1 and tachykinins, and decreased expression of a GABA transporter. At 8 weeks, expression of the NMDA receptor 1 in the striatum was attenuated, with enhanced expression of the glial glutamate/aspartate transporter. In the midbrain, a number of genes, including the GABA transporter gene, showed decreased expression at 4 weeks. At 8 weeks, gene expression was augmented for the dopamine transporter, D4 receptor, and several genes encoding peptides, such as tachykinins and their receptors. These results suggest that in the striatum the neurotransmitters glutamate, GABA and tachykinin may play crucial roles in motor hyperactivity during the juvenile period. Several classes of neurotransmitters, including dopamine and peptides, may be involved in compensatory mechanisms during early adulthood. These data may prompt further neurochemical investigations in hyperkinetic disorders.
Kainate seizures increase nociceptin/orphanin FQ release in the rat hippocampus and thalamus: a microdialysis study
Authors: Aparicio Liliana Carmona , Candeletti Sanzio , Binaschi Anna , Mazzuferi Manuela , Mantovani Simona , Di Benedetto Manuela , Landuzzi Daniela , Lopetuso Giuseppe , Romualdi Patrizia , Simonato Michele 
Published: March 2006

AbstractThe neuropeptide nociceptin/orphanin FQ (N/OFQ) has been suggested to play a facilitatory role in kainate seizure expression. Furthermore, mRNA levels for the N/OFQ precursor are increased following kainate seizures, while its receptor (NOP) density is decreased. These data suggest increased N/OFQ release. To obtain direct evidence that this is the case, we have developed a microdialysis technique, coupled with a sensitive radioimmunoassay, that allows measurement of N/OFQ release from the hippocampus and thalamus of awake, freely moving animals. In both these brain areas, the spontaneous N/OFQ efflux decreased by approximately 50% and 65% when Ca2+ was omitted and when tetrodotoxin was added to the perfusion medium, respectively. Perfusion of the dialysis probe with high K+increased N/OFQ release (approximately threefold) in a Ca2+‐dependent and tetrodotoxin‐sensitive manner. Kainate seizures caused a twofold increase in N/OFQ release followed, within 3 h, by a return to baseline levels. Approximately 5 h after kainate, a late increase in N/OFQ release was observed. On the following day, when animals were having only low grade seizures, N/OFQ release was not significantly different from normal. These phenomena were observed with similar patterns in the hippocampus and in the thalamus. The present data indicate that acute limbic seizures are associated with increased N/OFQ release, which may prime the molecular changes described above, i.e. cause down‐regulation of NOP receptors and activation of N/OFQ biosynthesis.
Induction of glial glutamate transporters in adult mesenchymal stem cells
Authors: De Hemptinne Isabelle , Vermeiren Céline , Maloteaux Jean‐Marie , Hermans Emmanuel 
Published: March 2006

AbstractAdult bone marrow mesenchymal stem cells are multipotent cells that can differentiate into a variety of mesodermal tissues. Recent studies have reported on their ability to also evolve into non‐mesodermal cells, especially neural cells. While most of these studies revealed that manipulating these cells triggers the expression of typical neurone markers, less is known about the induction of neuronal‐ or glial‐related physiological properties. The present study focused on the characterisation of glutamate transporters expression and activity in rat mesenchymal stem cells grown in culture conditions favouring their differentiation into astroglial cells. Ten days exposure of the cells to the culture supplement G5 was found to increase the expression of nestin (neuro‐epithelial stem cell intermediate filament), an intermediate filament protein expressed by neural stem cells. Simultaneously, a robust induction of the high‐affinity glutamate transporter GLT‐1 (and GLAST) expression was detected by RT‐PCR and immunocytochemistry. This expression was correlated with a highly significant increase in the Na+‐dependent [3H]d‐aspartate uptake. Finally, while glial fibrillary acidic protein immunoreactivity could not be detected, the induced expression of the astrocytic enzyme glutamine synthetase was demonstrated. These results indicate that in vitro differentiation of adult mesenchymal stem cells in neural precursors coincides with the induction of functional glutamate transport systems. Although the astrocytic nature of these cells remains to be confirmed, this observation gives support to the study of mesenchymal stem cells as a promising tool for the treatment of neurological diseases involving glutamate excitoxicity.
Nicastrin expression in mouse peripheral tissues is not co‐ordinated with presenilin and is high in muscle
Authors: Ilaya Nancy T. , Evin Geneviève , Masters Colin L. , Culvenor Janetta G. 
Published: March 2006

AbstractNicastrin was the first binding partner of presenilin (PS) shown to be a critical component of the presenilin/γ‐secretase complex essential in development and differentiation, and in generation of Alzheimer's disease Aβ amyloid peptide. To investigate the function of this glycoprotein, we compared nicastrin and presenilin protein expression in various mouse tissues. Western blot analysis of PS1, PS2 and nicastrin indicates their expression levels are not coordinated. In adult mouse, nicastrin is highly expressed in muscle membranes, whereas presenilin levels are very low. By Blue Native electrophoresis, a PS1 complex of 400 kDa was detected in lung, brain, thymus and heart; nicastrin was also detected as a 400‐kDa complex in brain but in muscle it was detected with a complex mobility of 240 and 290 kDa, suggesting association with alternate protein complexes. Immunocytochemistry confirms strong intracellular expression of nicastrin in skeletal muscle and blood vessel smooth muscle. These findings suggest a function for nicastrin in muscle other than participation in the γ‐secretase complex.
The mood stabilizer valproic acid stimulates GABA neurogenesis from rat forebrain stem cells
Authors: Laeng Pascal , Pitts Richard L. , Lemire Andrew L. , Drabik Christopher E. , Weiner Arin , Tang Haiping , Thyagarajan Rathi , Mallon Barbara S. , Altar C. Anthony 
Published: March 2006

AbstractValproate, an anticonvulsant drug used to treat bipolar disorder, was studied for its ability to promote neurogenesis from embryonic rat cortical or striatal primordial stem cells. Six days of valproate exposure increased by up to fivefold the number and percentage of tubulin β III‐immunopositive neurons, increased neurite outgrowth, and decreased by fivefold the number of astrocytes without changing the number of cells. Valproate also promoted neuronal differentiation in human fetal forebrain stem cell cultures. The neurogenic effects of valproate on rat stem cells exceeded those obtained with the neurotrophins brain‐derived growth factor (BDNF) or NT‐3, and slightly exceeded the effects obtained with another mood stabilizer, lithium. No effect was observed with carbamazepine. Most of the newly formed neurons were GABAergic, as shown by 10‐fold increases in neurons that immunostained for GABA and the GABA‐synthesizing enzyme GAD65/67. Double immunostaining for bromodeoxyuridine and tubulin β III showed that valproate increased by four‐ to fivefold the proliferation of neuronal progenitors derived from rat stem cells and increased cyclin D2 expression. Valproate also regulated the expression of survival genes, Bad and Bcl‐2, at different times of treatment. The expression of prostaglandin E synthase, analyzed by quantitative RT‐PCR, was increased by ninefold as early as 6 h into treatment by valproate. The enhancement of GABAergic neuron numbers, neurite outgrowth, and phenotypic expression via increases in the neuronal differentiation of neural stem cell may contribute to the therapeutic effects of valproate in the treatment of bipolar disorder.
Enhanced activation of Akt and extracellular‐regulated kinase pathways by simultaneous occupancy of Gq‐coupled 5‐HT2Areceptors and Gs‐coupled 5‐HT7Areceptors in PC12 cells
Authors: Johnson‐Farley Nadine N. , Kertesy Sylvia B. , Dubyak George R. , Cowen Daniel S. 
Published: March 2006

AbstractThe most commonly prescribed antidepressants, the serotonin (5‐HT) selective reuptake inhibitors, increase 5‐HT without targeting specific receptors. Yet, little is known about the interaction of multiple receptor subtypes expressed by individual neurons. Specifically, the effect of increases in cAMP induced by Gs‐coupled 5‐HT receptor subtypes on the signaling pathways modulated by other receptor subtypes has not been studied. We have, therefore, examined the activation of the extracellular‐regulated kinase (ERK) and Akt pathways by Gs‐coupled 5‐HT7Areceptors and Gq‐coupled 5‐HT2Areceptors, which are co‐expressed in discrete brain regions. Agonists for both receptors were found to activate ERK and Akt in transfected PC12 cells. 5‐HT2Areceptor‐mediated activation of the two pathways was found to be Ca2+‐dependent. In contrast, 5‐HT7Areceptor‐mediated activation of Akt required increases in both [cAMP] and intracellular [Ca2+], while activation of ERK was inhibited by Ca2+. The activation of ERK and Akt stimulated by simultaneous treatment of cells with 5‐HT2Aand 5‐HT7Areceptor agonists was found to be at least additive. Cell‐permeable cAMP analogs mimicked 5‐HT7Areceptor agonists in enhancing 5‐HT2Areceptor‐mediated activation of ERK and Akt. A role was identified for the cAMP–guanine exchange factor, Epac, in this augmentation of ERK, but not Akt, activation. Our finding of enhanced activation of neuroprotective Akt and ERK pathways by simultaneous occupancy of 5‐HT2Aand 5‐HT7Areceptors may also be relevant to the interaction of other neuronally expressed Gq‐ and Gs‐coupled receptors.
RNAi knockdown of Par‐4 inhibits neurosynaptic degeneration in ALS‐linked mice
Authors: Xie Jun , Awad Keytam S. , Guo Qing 
Published: March 2006

AbstractEvidence from human amyotrophic lateral sclerosis (ALS) patients and ALS‐linked Cu/Zn superoxide dismutase (Cu/Zn‐SOD) transgenic mice bearing the mutation of glycine to alanine at position 93 (G93A) suggests that the pro‐apoptotic protein prostate apoptosis response‐4 (Par‐4) might be a critical link in the chain of events leading to motor neuron degeneration. We now report that Par‐4 is enriched in synaptosomes and post‐synaptic density from the ventral horn of the spinal cord. Levels of Par‐4 in synaptic compartments increased significantly during rapid and slow declining stages of muscle strength in hSOD1 G93A mutant mice. In the pre‐muscle weakness stage, hSOD1 G93A mutation sensitized synaptosomes from the ventral horn of the spinal cord to increased levels of Par‐4 expression following excitotoxic and apoptotic insults. In ventral spinal synaptosomes, Par‐4‐mediated production of pro‐apoptotic cytosolic factor(s) was significantly enhanced by the hSOD1 G93A mutation. RNA interference (RNAi) knockdown of Par‐4 inhibited mitochondrial dysfunction and caspase‐3 activation induced by G93A mutation in synaptosomes from the ventral horn of the spinal cord, and protected spinal motor neurons from apoptosis. These results identify the synapse as a crucial cellular site for the cell death promoting actions of Par‐4 in motor neurons, and suggest that targeted inhibition of Par‐4 by RNAi may prove to be a neuroprotective strategy for motor neuron degeneration.
Activation of NADPH oxidase and extracellular superoxide production in seizure‐induced hippocampal damage
Authors: Patel Manisha , Li Qing‐You , Chang Ling‐Yi , Crapo James , Liang Li‐Ping 
Published: March 2006

AbstractWe sought to determine whether the extracellular compartment contributed to seizure‐induced superoxide (O2.−) production and to determine the role of the NADPH oxidase complex as a source of this O2.− production. The translocation of NADPH oxidase subunits (p47phox, p67phox and rac1) was assessed by immunoblot analysis and NADPH‐driven O2.− production was measured using 2‐(4‐hydroxybenzyl)‐6‐(4‐hydroxyphenyl)‐8‐benzyl‐3,7‐dihydroimidazo [1,2‐α] pyrazin‐3‐one‐enhanced chemiluminescence. Kainate‐induced status epilepticus resulted in a time‐dependent translocation of NADPH oxidase subunits (p47phox, p67phox and rac‐1) from hippocampal cytosol to membrane fractions. Hippocampal membrane fractions from kainate‐injected rats showed increased NADPH‐driven and diphenylene iodonium‐sensitive O2.− production in comparison to vehicle‐treated rats. The time‐course of kainate‐induced NADPH oxidase activation coincided with microglial activation in the rat hippocampus. Finally, kainate‐induced neuronal damage and membrane oxygen consumption were inhibited in mice overexpressing extracellular superoxide dismutase. These results suggest that seizure activity activates the membrane NADPH oxidase complex resulting in increased formation of O2.−.
Chronic exposure to ammonia induces isoform‐selective alterations in the intracellular distribution and NMDA receptor‐mediated translocation of protein kinase C in cerebellar neurons in culture
Authors: Giordano Gennaro , Sanchez‐Perez Ana M. , Burgal Maria , Montoliu Carmina , Costa Lucio G , Felipo Vicente 
Published: March 2006

AbstractHyperammonemia is responsible for most neurological alterations in patients with hepatic encephalopathy by mechanisms that remain unclear. Hyperammonemia alters phosphorylation of neuronal protein kinase C (PKC) substrates and impairs NMDA receptor‐associated signal transduction. The aim of this work was to analyse the effects of hyperammonemia on the amount and intracellular distribution of PKC isoforms and on translocation of each isoform induced by NMDA receptor activation in cerebellar neurons. Chronic hyperammonemia alters differentially the intracellular distribution of PKC isoforms. The amount of all isoforms (except PKC ζ) was reduced (17–50%) in the particulate fraction. The contents of α, β1, and ε isoforms decreased similarly in cytosol (65–78%) and membranes (66–83%), whereas γ, δ, and θ isoforms increased in cytosol but decreased in membranes, and ζ isoform increased in membranes and decreased in cytosol. Chronic hyperammonemia also affects differentially NMDA‐induced translocation of PKC isoforms. NMDA‐induced translocation of PKC α and β is prevented by ammonia, whereas PKC γ, δ, ε, or θ translocation is not affected. Inhibition of phospholipase C did not affect PKC α translocation but reduced significantly PKC γ translocation, indicating that NMDA‐induced translocation of PKC α is mediated by Ca2+, whereas PKC γ translocation is mediated by diacylglycerol. Chronic hyperammonemia reduces Ca+2‐mediated but not diacylglycerol‐mediated translocation of PKC isoforms induced by NMDA.
Pathogenic mutations inactivate parkin by distinct mechanisms
Authors: Henn Iris H. , Gostner Johanna M. , Lackner Peter , Tatzelt Jörg , Winklhofer Konstanze F. 
Published: March 2006

AbstractLoss of parkin function is the major cause of autosomal recessive Parkinson's disease (ARPD). A wide variety of parkin mutations have been identified in patients; however, the pathophysiological mechanisms leading to the inactivation of mutant parkin are poorly understood. In this study we characterized pathogenic C‐ and N‐terminal parkin mutants and found distinct pathways of parkin inactivation. Deletion of the C terminus abrogated the association of parkin with cellular membranes and induced rapid misfolding and aggregation. Four N‐terminal missense mutations, located within the ubiquitin‐like domain (UBL), decrease the stability of parkin; as a consequence, these mutants are rapidly degraded by the proteasome. Furthermore, we present evidence that a smaller parkin species of 42 kDa, which is present in extracts prepared from human brain and cultured cells, originates from an internal start site and lacks the N‐terminal UBL domain.