bluuebunny/crossref_metadata_2025_split huggingface dataset:
AMPA receptor‐mediated toxicity in oligodendrocyte progenitors involves free radical generation and activation of JNK, calpain and caspase 3
Authors: Liu Hsueh‐Ning , Giasson Benoit I. , Mushynski Walter E. , Almazan Guillermina 
Published: March 2003

AbstractThe molecular mechanisms underlying AMPA (α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate) receptor‐mediated excitotoxicity were characterized in rat oligodendrocyte progenitor cultures. Activation of AMPA receptors, in the presence of cyclothiazide to selectively block desensitization, produced a massive Ca2+ influx and cytotoxicity which were blocked by the antagonists CNQX and GYKI 52466. A role for free radical generation in oligodendrocyte progenitor cell death was deduced from three observations: (i) treatment with AMPA agonists decreased intracellular glutathione; (ii) depletion of intracellular glutathione with buthionine sulfoximine potentiated cell death; and (iii) the antioxidant N‐acetylcysteine replenished intracellular glutathione and protected cultures from AMPA receptor‐mediated toxicity. Cell death displayed some characteristics of apoptosis, including DNA fragmentation, chromatin condensation and activation of caspase‐3 and c‐Jun N‐terminal kinase (JNK). A substrate of calpain and caspase‐3, α‐spectrin, was cleaved into characteristic products following treatment with AMPA agonists. In contrast, inhibition of either caspase‐3 by DEVD‐CHO or calpain by PD 150606 protected cells from excitotoxicity. Our results indicate that overactivation of AMPA receptors causes apoptosis in oligodendrocyte progenitors through mechanisms involving Ca2+ influx, depletion of glutathione, and activation of JNK, calpain, and caspase‐3.
Altered processing of the neurotensin/neuromedin N precursor in PC2 knock down mice: a biochemical and immunohistochemical study
Authors: Villeneuve Pierre , Feliciangeli Sylvain , Croissandeau Gilles , Seidah Nabil G. , Mbikay Majambu , Kitabgi Patrick , Beaudet Alain 
Published: March 2003

AbstractNeurotensin (NT) and neuromedin N (NN) are generated by endoproteolytic cleavage of a common precursor molecule, pro‐NT/NN. To gain insight into the role of prohormone convertases PC1, PC2, and PC7 in this process, we investigated the maturation of pro‐NT/NN in the brain of PC7 (PC7−/–), PC2 (PC2–/–), and/or PC1 (PC1+/– and PC2–/–; PC1+/–) knock down mice. Inactivation of the PC7 gene was without effect, suggesting that this convertase is not involved in the processing of pro‐NT/NN. By contrast, there was a 15% decrease in NT and a 50% decrease in NN levels, as measured by radioimmunoassay, in whole brain extracts from PC2 null as compared with wild type mice. Using immunohistochemistry, we found that this decrease in pro‐NT/NN maturation products was uneven and that it was most pronounced in the medial preoptic area, lateral hypothalamus, and paraventricular hypothalamic nuclei. These results suggest that PC2 plays a critical role in the processing of pro‐NT/NN in mouse brain and that its deficiency may be compensated to a regionally variable extent by other convertases. Previous data have suggested that PC1 might be subserving this role. However, there was no change in the maturation of pro‐NT/NN in the brain of mice in which the PC1 gene had been partially inactivated, implying that complete PC1 knock down may be required for loss of function.
Alternative splicing of the 5′‐sequences of the mouse EAAT2 glutamate transporter and expression in a transgenic model for amyotrophic lateral sclerosis
Authors: Münch C. , Ebstein M. , Seefried U. , Zhu B. , Stamm S. , Landwehrmeyer G. B. , Ludolph A. C. , Schwalenstöcker B. , Meyer T. 
Published: March 2003

AbstractGlutamate‐mediated neurotoxicity and a reduced expression of the excitatory amino acid transporter 2 (EAAT2) have been described in the pathogenesis of several acute and chronic neurological conditions. EAAT2 is the major carrier of glutamate in the mammalian brain. However, the principles of EAAT2 expression regulation are not fully understood. For the human brain, extensive alternative splicing of the EAAT2 RNA has been shown. To delineate the complex RNA regulation of EAAT2 we investigated whether the murine species is a suitable model for the study of EAAT2 splicing events. We identified five splice variants (mEAAT2/5UT1–5) encoding different 5′‐untranslated sequences and two distinct N‐termini of the putative EAAT2 polypeptide. In the murine CNS we found a region‐specific expression pattern of the novel 5′‐variants of EAAT2 as shown by in situ hybridization, dot blotting and competitive reverse transcription polymerase chain reaction. Furthermore, we performed an expression analysis of the EAAT2 splice variants in the spinal cord of a transgenic model (SOD1G93A) of amyotrophic lateral sclerosis, a motor neurone disease for which altered splicing of EAAT2 has been discussed. We found an increased expression of mEAAT2/5UT4 and a reduction of mEAAT2/5UT5 in the early course of the disease. We conclude that alternative splicing of 5′‐sequences may contribute to the regional expression of the EAAT2 RNA and was altered in the pre‐symptomatic stage of the SOD1G93A‐mouse model for amyotrophic lateral sclerosis.
N‐Methyl‐d‐aspartate receptor subtype‐selectivity of homoquinolinate: an electrophysiological and radioligand binding study using both native and recombinant receptors
Authors: Grimwood, Sarah , Wafford Keith A. , Macaulay Alison , Hutson Pete H. 
Published: March 2003

AbstractHomoquinolinate, a derivative of the endogenous NMDA agonist, quinolinate, has been shown to display higher affinity for Xenopus oocytes expressing NR2A‐ and NR2B‐containing receptors, compared to NR2C‐ and NR2D‐containing receptors, whilst autoradiographical experiments subsequently showed that [3H]homoquinolinate labelled a subpopulation of NMDA receptors in rat brain sections, with a similar distribution to NR2B‐containing receptors. In this study, we have shown that NMDA‐specific [3H]homoquinolinate binding to rat brain membranes comprised 44% of total binding with a Bmax value of 5.73 pmol/mg protein, which was inhibited by NMDA with Ki=0.867 µm. However, NMDA‐specific [3H]homoquinolinate binding was not observed for a number of human recombinant NMDA receptors investigated, suggesting that there are subtle differences between the binding sites of recombinant and native receptors. Electrophysiological experiments revealed that homoquinolinate activated human recombinant NR1a/NR2A, NR1a/NR2B and NR1a/NR2A/NR2B receptors with EC50 values of 25.2, 13.8 and 9.04 µm, respectively, with intrinsic activities of 148, 93.3 and 125%, respectively, compared to glutamate (=100%). In contrast to an autoradiographical study, these radioligand binding and electrophysiological experiments suggest that homoquinolinate is not highly selective for NR2B‐containing receptors.
Developmental alteration of nerve injury induced glial cell line‐derived neurotrophic factor (GDNF) receptor expression is crucial for the determination of injured motoneuron fate
Authors: Honma Masaru , Namikawa, Kazuhiko , Mansur, Khalil , Iwata, Tatsuya , Mori, Nozomu , Iizuka Hajime , Kiyama Hiroshi 
Published: March 2003

AbstractAxotomy‐induced neuronal death occurs in neonatal motoneurons, but not in adult rat. Here we demonstrated that during the course of postnatal development, nerve injury induced down‐regulation of the glial cell line‐derived neurotrophic factor (GDNF) receptor GFRα1 in axotomized hypoglossal motoneurons of rat are gradually converted to the adult up‐regulation pattern of response. The compensatory expression of GFRα1 specifically in the injured motoneurons of neonates by adenovirus succeeded in rescuing the injured neurons without an application of growth factors. To the contrary, the nuclear antisense RNA for GFRα1 expression accelerates the axotomy‐induced neuronal death in pups. These findings suggest that the receptor expression response after nerve injury is critical for the determination of injured motoneuron fate.
Glial cell line‐derived neurotrophic factor up‐regulates GTP‐cyclohydrolase I activity and tetrahydrobiopterin levels in primary dopaminergic neurones
Authors: Bauer M. , Suppmann S. , Meyer M. , Hesslinger C. , Gasser T. , Widmer H. R. , Ueffing M. 
Published: March 2003

AbstractGlial cell line‐derived neurotrophic factor (GDNF) protects dopaminergic neurones against toxic and physical damage. In addition, GDNF promotes differentiation and structural integrity of dopaminergic neurones. Here we show that GDNF can support the function of primary dopaminergic neurones by triggering activation of GTP‐cyclohydrolase I (GTPCH I), a key enzyme in catecholamine biosynthesis. GDNF stimulation of primary dopaminergic neurones expressing both tyrosine 3‐monooxygenase and GTPCH I resulted in a dose‐dependent doubling of GTPCH I activity, and a concomitant increase in tetrahydrobiopterin levels whereas tyrosine 3‐monooxygenase activity was not altered. Actinomycin D, asan inhibitor of de novo biosynthesis, abolished any GDNF‐mediated up‐regulation of GTPCH I activity. However, GTPCH I mRNA levels in primary dopaminergic neurones were not altered by GDNF treatment, suggesting that the mode of action for that up‐regulation is not directly connected to the regulation of GTPCH I transcription. We conclude that GDNF, in addition to its action in structural differentiation, also promotes differentiation regarding expression and enzymatic activity of a crucial component in the dopaminergic biosynthetic pathway.
Expression of mRNAs of multidrug resistance proteins (Mrps) in cultured rat astrocytes, oligodendrocytes, microglial cells and neurones
Authors: Hirrlinger Johannes , König Jörg , Dringen Ralf 
Published: March 2003

AbstractMultidrug resistance proteins (Mrps) are ATP‐driven export pumps that mediate the export of organic anions from cells. So far only little information is available on expression and physiological functions of Mrps in brain. The expression of mRNAs of six Mrp paralogs in rat brain, as well as in rat cultures enriched for neurones, astrocytes, oligodendrocytes and microglial cells, was studied by qualitative and semiquantitative RT‐PCR analysis. In adult rat brain as well as in neural cell cultures the mRNAs coding for Mrp1, Mrp3, Mrp4 and Mrp5 were detected. Semiquantitative analysis revealed that the mRNAs coding for Mrp1 and Mrp5 were more abundant in the four cell culture types than mRNAs of the other Mrps. mRNAs coding for Mrp3 and Mrp4 were found at significant levels in cultured astrocytes and microglial cells, whereas cultures of neurones and oligodendrocytes contained only marginal quantities of these mRNAs. Putative physiological functions of Mrps in brain cells are discussed.
The production of hydrogen sulfide is regulated by testosterone and S‐adenosyl‐l‐methionine in mouse brain
Authors: Eto Ko , Kimura Hideo 
Published: March 2003

AbstractHydrogen sulfide (H2S) is endogenously produced in the brain from l‐cysteine by the enzyme cystathionine β‐synthase (CBS) and functions as a neuromodulator in the brain. H2S selectively enhances NMDA receptor‐mediated responses and alters hippocampal long‐term potentiation (LTP). The production of H2S is regulated by Ca2+/calmodulin‐mediated pathways and is enhanced in response to neuronal excitation. In addition to this fast regulation, we describe here a slower form of the regulation of H2S production by testosterone and S‐adenosyl‐l‐methionine (SAM), a CBS activator. Endogenous H2S in the mouse brain increases after birth, reaches a maximum level at 8 weeks and then decreases. Female brain contains less H2S than male brain at each age. A single administration of testosterone to female mice increases the endogenous H2S and SAM, which reach levels similar to those of male mice. In contrast, castration of male mice decreases the levels of testosterone, SAM and H2S in the brain. Administration of SAM once a day for 3 days increases the brain H2S without significantly changing the testosterone level. These observations suggest that testosterone can regulate the brain H2S level via changing the level of SAM.
Specific diadenosine pentaphosphate receptor coupled to extracellular regulated kinases in cerebellar astrocytes
Authors: Jiménez Ana I. , Castro Enrique , Delicado Esmerilda G. , Miras‐Portugal M. Teresa 
Published: March 2003

AbstractIn this study, we show specific intracellular responses evoked by the stimulation of astrocytes with the P1,P5‐di(adenosine‐5′)pentaphosphate, Ap5A. The stimulation of astrocytes with micromolar concentrations of the dinucleotide elicited rapid increases in intracellular calcium concentration ([Ca2+]i), showing an EC50 value of 15.27 ± 0.61 µm. Moreover, the stimulation of cells with nanomolar concentrations of Ap5A, unable to induce calcium responses, increased the phosphorylated forms of extracellular‐signal regulated kinase 1/2 (ERK) with an EC50 value of 9.8 ± 2.4 nm. The maximal activation was observed at 100 nm Ap5A, which was similar to that produced by epidermal growth factor (EGF) under the same experimental conditions. The present data reported here indicate that Ap5A mediated these effects by interacting with a specific receptor, not yet identified, which was different from the P2Y1 and P2Y2/P2Y4 receptors present in all individual astrocytes.
Bovine serum albumin enhances nicotinic acetylcholine receptor function in mouse thalamic synaptosomes
Authors: Butt Christopher M. , Hutton Scott R. , Marks Michael J. , Collins Allan C. 
Published: March 2003

AbstractBovine serum albumin (BSA) enhances nicotinic agonist‐induced 86Rb+ efflux from synaptosomal fractions of the mouse thalamus, but how it does so is not understood. The experiments reported here indicated that BSA enhancement of nicotinic acetylcholine receptor function was rapid, reversible, depended on BSA concentration, and occurred at all points of the nicotinic agonist concentration‐response curve. We hypothesized that BSA‐extractable compounds, such as long‐chain fatty acids, were responsible for inhibiting nicotinic responses in the absence of BSA. The hypothesis was tested by applying arachidonic, linolenic, or oleic acids in the absence of BSA after an initial prewash with BSA. All three fatty acids exhibited a rapid, concentration‐dependent inhibition of nicotinic‐agonist stimulated ion flux. Concentration‐response curves produced after 30 s of pre‐treatment with arachidonic acid were similar to those seen when BSA was completely absent. The effects of pre‐treatment were reversed immediately by the introduction of BSA. Furthermore, no effects of fatty acids were observed when preparations were continuously exposed to BSA or when BSA was continuously absent. These results suggest that the removal of endogenous, inhibitory compounds is largely responsible for the rapid, potentiating action of BSA at nicotinic acetylcholine receptors expressed in the mouse thalamus.
Brevican isoforms associate with neural membranes
Authors: Seidenbecher Constanze I. , Smalla Karl‐Heinz , Fischer Nora , Gundelfinger Eckart D. , Kreutz Michael R. 
Published: March 2003

AbstractBrevican is a neural‐specific proteoglycan of the brain extracellular matrix, which is particularly abundant in the terminally differentiated CNS. It is expressed by neuronal and glial cells, and as a component of the perineuronal nets it decorates the surface of large neuronal somata and primary dendrites. One brevican isoform harbors a glycosylphosphatidylinositol anchor attachment site and, as shown by ethanolamine incorporation studies, is indeed glypiated in stably transfected HEK293 cells as well as in oligodendrocyte precursor Oli‐neu cells. The major isoform is secreted into the extracellular space, although a significant amount appears to be tightly attached to the cell membrane, as it floats up in sucrose gradients. Flotation is sensitive to detergent treatment. Brevican is most prominent in the microsomal, light membrane and synaptosomal fractions of rat brain membrane preparations. The association with the particulate fraction is in part sensitive to chondroitinase ABC and phosphatidylinositol‐specific phospholipase C treatment. Furthermore, brevican staining on the surface of hippocampal neurons in culture is diminished after hyaluronidase or chondroitinase ABC treatment. Taken together, this could provide a mechanism by which perineuronal nets are anchored on neuronal surfaces.
Increased synthesis but decreased processing of neuronal proCCK in prohormone convertase 2 and 7B2 knockout animals
Authors: Rehfeld Jens F. , Lindberg Iris , Friis‐Hansen Lennart 
Published: March 2003

AbstractIn addition to its role as a gut hormone, cholecystokinin (CCK) is a widespread and potent neurotransmitter. Its biosynthesis requires endoproteolytic cleavage of proCCK at several mono‐ and dibasic sites by subtilisin‐like prohormone convertases (PCs). Of these, PC1 and PC2 are specific for neuroendocrine cells. We have now examined the role of PC2 and its binding protein, 7B2, in the neuronal processing of proCCK by measurement of precursor, processing‐intermediates and bioactive end‐products in brain extracts from PC2‐ and 7B2‐null mice and from corresponding controls. PC2‐null mice displayed a nine‐fold increase of cerebral proCCK concentrations, and a two‐fold increase in the concentrations of the processing‐intermediate, glycine‐extended CCK, whereas the concentrations of transmitter‐active (i.e. α‐amidated andO‐sulfated) CCK peptides were reduced (61%). Chromatography showed thatO‐sulfated CCK‐8 still is the predominant transmitter‐active CCK in PC2‐null brains, but that the fraction of intermediate‐sized CCK‐peptides (CCK‐58, ‐33 and ‐22) was eight‐fold increased. 7B2‐null brains displayed a similar pattern but with less pronounced precursor accumulation. In contrast with the cerebral changes, PC2 deficiency was without effect on proCCK synthesis and processing in intestinal endocrine cells, whereas 7B2 deficiency halved the concentration of bioactive CCK in the intestine. The results show that PC2 plays a major neuron‐specific role in the processing of proCCK.
Modulation of somatostatin receptors, somatostatin content and Gi proteins by substance P in the rat frontoparietal cortex and hippocampus
Authors: Puebla Lilian , Arilla‐Ferreiro Eduardo 
Published: March 2003

AbstractSubstance P (SP) and somatostatin (SRIF) are widely spread throughout the CNS where they play a role as neurotransmitters and/or neuromodulators. A colocalization of both neuropeptides has been demonstrated in several rat brain areas and SP receptors have been detected in rat cortical and hippocampal somatostatinergic cells. The present study was thus undertaken to determine whether SP could modulate SRIF signaling pathways in the rat frontoparietal cortex and hippocampus. A single intraperitoneal injection of SP (50, 250 or 500 µg/kg) induced an increase in the density of SRIF receptors in membranes from the rat frontoparietal cortex at 24 h of its administration, with no change in the hippocampus. The functionality of the SRIF receptors was next investigated. Western blot analysis of Gi proteins demonstrated a significant decrease in Giα1 levels in frontoparietal cortical membranes from rats treated acutely (24 h) with 250 µg/kg of SP, which correlated with a decrease in functional Gi activity, as assessed by use of the non‐hydrolyzable GTP analog 5′‐guanylylimidodiphosphate. SRIF‐mediated inhibition of basal or forskolin‐stimulated adenylyl cyclase activity was also significantly lower in the frontoparietal cortex of the SP‐treated group, with no alterations in the catalytic subunit of the enzyme. SRIF‐like immunoreactivity content was increased in the frontoparietal cortex after acute (24 h) SP administration (250 or 500 µg/kg) as well as in the hippocampus in response to 7 days of SP (250 µg/kg) administration. All these SP‐mediated effects were prevented by pretreatment with the NK1 receptor antagonist RP‐67580. Although the physiologic significance of these results are unknown, the increase in SRIF receptor density together with the desensitization of the SRIF inhibitory signaling pathway might be a mechanism to potentiate the stimulatory pathway of SRIF, inducing a preferential coupling of the receptors to PLC.
Palmitic and stearic fatty acids induce caspase‐dependent and ‐independent cell death in nerve growth factor differentiated PC12 cells
Authors: Ulloth Joel E. , Casiano Carlos A. , De Leon Marino 
Published: March 2003

AbstractApoptotic cell death has been proposed to play a role in the neuronal loss observed following traumatic injury in the CNS and PNS. The present study uses an in vitro tissue culture model to investigate whether free fatty acids (FFAs), at concentrations comparable to those found following traumatic brain injury, trigger cell death. Nerve growth factor (NGF)‐differentiated PC12 cells exposed to oleic and arachidonic acids (2 : 1 ratio FFA/BSA) showed normal cell survival. However, when cells were exposed to stearic and palmitic acids, there was a dramatic loss of cell viability after 24 h of treatment. The cell death induced by stearic acid and palmitic acid was apoptotic as assessed by morphological analysis, and activation of caspase‐8 and caspase‐3‐like activities. Western blotting showed that differentiated PC12 cells exposed to stearic and palmitic acids exhibited the signature apoptotic cleavage fragment of poly (ADP‐ribose) polymerase (PARP). Interestingly, blockade of caspase activities with the pan‐caspase inhibitor z‐VAD‐fmk failed to prevent the cell death observed induced by palmitic or stearic acid. RT‐PCR and RNA blot experiments showed an up‐regulation of the Fas receptor and ligand mRNA. These findings are consistent with our hypothesis that FFAs may play a role in the cell death associated with trauma in the CNS and PNS.
Glutamate levels and transport in cat (Felis catus) area 17 during cortical reorganization following binocular retinal lesions
Authors: Massie Ann , Cnops Lieselotte , Jacobs Sandy , Van Damme Katrien , Vandenbussche Erik , Eysel Ulf T. , Vandesande Frans , Arckens Lutgarde 
Published: March 2003

AbstractGlutamate is known to play a crucial role in the topographic reorganization of visual cortex after the induction of binocular central retinal lesions. In this study we investigated the possible involvement of the glial high‐affinity Na+/K+‐dependent glutamate transporters in cortical plasticity using western blotting and intracortical microdialysis. Basal extracellular glutamate levels and the re‐uptake activity for glutamate have been determined by comparing the extracellular glutamate concentration before and during the blockage of glutamate removal from the synaptic cleft with the potent transporter inhibitor l‐trans‐pyrrolidine‐3,4‐dicarboxylic acid. In cats with central retinal lesions we observed increased basal extracellular glutamate concentrations together with a decreased re‐uptake activity in non‐deprived, peripheral area 17, compared with the sensory‐deprived, central cortex of the same animal as well as the topographically matching regions of area 17 in normal subjects. Western blotting experiments revealed a parallel decrease in the expression level of the glial glutamate transporter proteins GLT‐1 and GLAST in non‐deprived cortex compared with sensory‐deprived cortex of lesion cats and the corresponding regions of area 17 of normal subjects. This study shows that partial sensory deprivation of the visual cortex affects the removal of glutamate from the synaptic cleft and implicates a role for glial–neuronal interactions in adult brain plasticity.