bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of the brain serotonergic system with labeled α‐methyl‐l‐tryptophan
Authors: Diksic Mirko , Young Simon N. 
Published: March 2003

α‐Methyl‐l‐tryptophan (α‐MTrp) is an artificial amino acid and an analog of tryptophan (Trp), the precursor of the neurotransmitter serotonin (5‐HT). In this article we have summarized available data, which suggest that the measurement of the unidirectional uptake of α‐MTrp and its conversion to 5‐HT synthesis rates is a valid approach for the determination of brain 5‐HT synthesis rates. The main feature on which the model is based is the trapping of labeled α‐MTrp in brain tissue. An overview of opposing opinions, which suggest that there is a need for a metabolic conversion of tracer, is also presented and discussed critically. As with all biological modeling there is likely to be room for improvements of the proposed biological model. In addition, there are a limited number of clearly defined circumstances in which the method is confounded by the metabolism of labeled α‐MTrp via the kynurenine pathway. Nonetheless, a significant body of evidence suggests that labeled α‐MTrp is a useful tracer to study brain 5‐HT synthesis in most circumstances. Calculation of 5‐HT synthesis rates depends on the plasma‐free tryptophan concentration, which, according to the balance of arguments in the literature, is a more appropriate parameter than the total‐plasma tryptophan. The method, as proposed by us, can be used in conjunction with autoradiographic measurements in laboratory animals, and with positron emission tomography in large animals and humans. We review studies in animals looking at the normal control of 5‐HT synthesis and the way in which it is altered by drugs, as well as initial studies investigating healthy humans and patients with neuropsychiatric disorders.
Efflux of a suppressive neurotransmitter, GABA, across the blood–brain barrier
Authors: Kakee Atsuyuki , Takanaga Hitomi , Terasaki Tetsuya , Naito Mikihiko , Tsuruo Takashi , Sugiyama Yuichi 
Published: March 2003

In this study, GABA efflux transport from brain to blood was estimated by using the brain efflux index (BEI) method. [3H]GABA microinjected into partietal cortex area 2 (Par2) of the rat brain was eliminated from the brain with an apparent elimination half‐life of 16.9 min. The blood–brain barrier (BBB) efflux clearance of [3H]GABA was at least 0.153 mL/min/g brain, which was calculated from the elimination rate constant (7.14 × 10−2 min−1) and the distribution volume in the brain (2.14 mL/g brain). Direct comparison of the apparent BBB influx clearance [3H]GABA (9.29 µL/min/g brain) and the apparent efflux clearance (153 µL/min/g brain) indicated that the efflux clearance was at least 16‐fold greater than the influx clearance. In order to reduce the effect of metabolism in the neuronal cells following intracerebral microinjection, we determined the apparent efflux of [3H]GABA in the presence of nipecotic acid, a GABA transport inhibitor in parenchymal cells, using the BEI method. Under such conditions, the elimination of [3H]GABA across the BBB showed saturation and inhibition by probenecid in the presence of nipecotic acid. Furthermore, the uptake of [3H]GABA by MBEC4 cells was inhibited by GABA, taurine, β‐alanine and nipecotic acid in a concentration‐dependent manner. It is likely that GABA inhibits the first step in the abluminal membrane uptake by brain endothelial cells, and that probenecid selectively inhibits the luminal membrane efflux transport process from the brain capillary endothelial cells based on the in vivo and in vitro evidence. The BBB acts as the efflux pump for GABA to reduce the brain interstitial fluid concentration.
Two caspase‐2 transcripts are expressed in rat hippocampus after global cerebral ischemia
Authors: Jin Kunlin , Nagayama Tetsuya , Mao Xiaoou , Kawaguchi Kenji , Hickey Robert W. , Greenberg David A. , Simon Roger P. , H. Graham Steven 
Published: March 2003

AbstractCaspase family genes play a critical role in the initiation and execution of programmed cell death. Programmed cell death is an important contributor to neuronal loss following cerebral ischemia. We have performed a series of experiments to investigate the role of a specific caspase, caspase‐2, in the development of delayed neuronal death following transient global ischemia in the rat. A rat ischemic brain cDNA library was screened, and two splice‐variants of caspase‐2 mRNA were identified, caspase‐2S and caspase‐2L, which were highly homologous with the sequences of human and mouse caspase‐2S and caspase‐2L genes, respectively. RT‐PCR demonstrated an increase in expression of both caspase‐2S and caspase‐2L mRNA at 8, 24 and 72 h of reperfusion after global ischemia. The ratio of the two PCR fragments did not change significantly throughout the time course of reperfusion. Western blot with monoclonal antibody specific to the pro‐apoptotic caspase‐2L splice variant revealed an increase in procaspase‐2 (51 kDa) protein from 4 to 72 h following ischemia compared with sham‐operated controls. Furthermore, an approximately 30‐kDa cleavage product appeared at 8 h and increased with increasing duration of reperfusion. Thus, caspase‐2L is both translated and activated following transient global ischemia. Finally, intraventricular administration of the caspase‐2‐like inhibitor (VDVAD‐FMK) 30 min before induction of ischemia decreased the number of CA1 neurons staining positively for DNA damage (Klenow‐labeling assay) and increased the number of healthy‐appearing CA1 neurons (cresyl violet) compared with vehicle‐treated controls. Taken together, the data suggest that caspase‐2 induction and activation are important mediators of delayed neuronal death following transient global ischemia.
Selective zif268 mRNA induction in the perirhinal cortex of macaque monkeys during formation of visual pair‐association memory
Authors: Tokuyama Wataru , Okuno Hiroyuki , Hashimoto Takanori , Li Yue Xin , Miyashita Yasushi 
Published: March 2003

AbstractTo elucidate the molecular basis of cognitive memory formation in the primate, transcriptional activation during learning of a visual pair‐association (PA) task was evaluated systematically along the occipito‐temporo‐hippocampal pathway in the macaque monkey brain. Split‐brain monkeys were used for intra‐animal comparison, which enables elimination of animal‐to‐animal variation in gene expression. We found that the expression of the mRNA of an immediate‐early gene (IEG), zif268, was up‐regulated selectively in the perirhinal cortex (area 36) during the formation of PA memory compared to that during learning of a visual control task. The mRNA expression levels of another IEG, c‐jun, were not up‐regulated during the PA learning in any cortical areas examined. We also showed that cells strongly expressing zif 268 mRNA accumulated in patches in area 36 during learning of the PA task. As the zif 268 gene encodes a transcription factor, these results suggest that the activation of zif 268 mRNA in area 36 may function as a trigger of the cascade of gene activation that leads to cellular events underlying neuronal reorganization for visual long‐term memory formation.
A non‐amyloidogenic function of BACE‐2 in the secretory pathway
Authors: Fluhrer Regina , Capell Anja , Westmeyer Gil , Willem Michael , Hartung Bianka , Condron Margaret M. , Teplow David B. , Haass Christian , Walter Jochen 
Published: March 2003

Abstractβ‐Site amyloid precursor protein cleavage enzyme (BACE)‐1 and BACE‐2 are members of a novel family of membrane‐bound aspartyl proteases. While BACE‐1 is known to cleave β‐amyloid precursor protein (βAPP) at the β‐secretase site and to be required for the generation of amyloid β‐peptide (Aβ), the role of its homologue BACE‐2 in amyloidogenesis is less clear. We now demonstrate that BACE‐1 and BACE‐2 have distinct specificities in cleavage of βAPP in cultured cells. Radiosequencing of the membrane‐bound C‐terminal cleavage product revealed that BACE‐2 cleaves βAPP in the middle of the Aβ domain between phenylalanines 19 and 20, resulting in increased secretion of APPs‐α‐ and p3‐like products and reduced production of Aβ species. This cleavage can occur in the Golgi and later secretory compartments. We also demonstrate that BACE‐1‐mediated cleavage of βAPP at Asp1 of the Aβ domain can occur as early as in the endoplasmic reticulum, while cleavage at Glu11 occurs in later compartments. These data indicate that the distinct specificities of BACE‐1 and BACE‐2 in their cleavage of βAPP differentially affect the generation of Aβ.
Shp‐2 positively regulates brain‐derived neurotrophic factor‐promoted survival of cultured ventral mesencephalic dopaminergic neurons through a brain immunoglobulin‐like molecule with tyrosine‐based activation motifs/Shp substrate‐1
Authors: Takai Satomi , Yamada Masashi , Araki Toshiyuki , Koshimizu Hisatsugu , Nawa Hiroyuki , Hatanaka Hiroshi 
Published: March 2003

AbstractTo examine the roles of Shp‐2, a cytoplasmic tyrosine phosphatase, in neuronal survival, we generated and used recombinant adenoviruses expressing wild type and phosphatase‐inactive (C/S), phosphatase domain‐deficient (delta P) and constitutively active (D61A and E76A) mutants of Shp‐2. We found that wild‐type Shp‐2 enhanced brain‐derived neurotrophic factor (BDNF)‐promoted survival of cultured ventral mesencephalic dopaminergic neurons. In contrast, the C/S and delta P mutants of Shp‐2 did not affect survival. In addition, the constitutively active D61A and E76A mutants mimicked BDNF and promoted survival. Furthermore, to examine the effects of BIT/SHPS‐1, a substrate of Shp‐2, on the BDNF‐promoted survival, we generated adenovirus vectors expressing wild‐type BIT/SHPS‐1 and its 4F mutant in which all tyrosine residues in the cytoplasmic domain of BIT/SHPS‐1 were replaced with phenylalanine. We found that BDNF‐promoted survival of cultured mesencephalic dopaminergic neurons was enhanced by expression of the 4F mutant but not of wild‐type BIT/SHPS‐1. In addition, we found that co‐expression of wild‐type BIT/SHPS‐1 with Shp‐2 significantly enhanced the survival‐promoting effect of BDNF on cultured mesencephalic dopaminergic neurons. These results indicated that Shp‐2 positively regulates the survival‐promoting effect of BDNF on cultured ventral mesencephalic dopaminergic neurons. Dephosphorylation of BIT/SHPS‐1 by Shp‐2 may participate in BDNF‐stimulated survival signaling.
p‐Methylthioamphetamine and 1‐(m‐chlorophenyl)piperazine, two non‐neurotoxic 5‐HT releasers in vivo, differ from neurotoxic amphetamine derivatives in their mode of action at 5‐HT nerve endings in vitro
Authors: Gobbi M. , Moia M. , Pirona L. , Ceglia I. , Reyes‐Parada M. , Scorza C. , Mennini T. 
Published: March 2003

AbstractThe mechanism underlying the serotoninergic neurotoxicity of some amphetamine derivatives, such as p‐chloroamphetamine (pCA) and 3,4‐methylenedioxymethamphetamine (MDMA), is still debated. Their main acute effect, serotonin (5‐HT) release from nerve endings, involves their interaction with 5‐HT transporters (SERTs), as substrates. Although this interaction is required for the neurotoxic effects, 5‐HT release alone may not be sufficient to induce long‐term 5‐HT deficits. Some non‐neurotoxic compounds, including p‐methylthioamphetamine (MTA) and 1‐(m‐chlorophenyl)piperazine (mCPP), have 5‐HT releasing properties in vivo and in brain slices comparable to that of neurotoxic amphetamine derivatives. We measured 5‐HT release in superfused rat brain synaptosomes preloaded with [3H]5‐HT, a model that distinguishes a releasing effect from reuptake inhibition. MTA and mCPP induced much lower release than pCA and MDMA. The striking difference between our findings in synaptosomes and those obtained in vivo or in brain slices is probably related to a different compartmentalisation of 5‐HT in the different experimental models. Studies in synaptosomes, where the vesicular storage of 5‐HT is predominant, could therefore bring to light differences between neurotoxic and non‐neurotoxic 5‐HT releasing agents which cannot be appreciated in other experimental models and might be useful to identify the mechanisms responsible for the neurotoxicity induced by amphetamine derivatives.
Neuronal‐induced and glutamate‐dependent activation of glial glutamate transporter function
Authors: Poitry‐Yamate Carol L. , Vutskits Laszlo , Rauen Thomas 
Published: March 2003

AbstractThe activity of high‐affinity glutamate transporters is essential for the normal function of the mammalian central nervous system. Using a combined pharmacological, confocal immunocytochemical, enzyme‐based microsensor and fluorescence imaging approach, we examined glutamate uptake and transporter protein localization in single astrocytes of neuron‐containing and neuron‐free microislands prior to pre‐synaptic transmitter secretion and during functional neuronal activity. Here, we report that the presence or absence of neurons strikingly affects the uptake capacity of the astroglial glutamate transporters GLT1 and GLAST1. Induction of transporter function is activated by neurons and this effect is mimicked by pre‐incubation of astrocytes with micromolar concentrations of glutamate. Moreover, increased glutamate transporter activation is reproduced by endogenous release of glutamate via activation of neuronal nicotinic receptors. The increase in transport activity is dependent on neuronal release of glutamate, is associated with the local redistribution (clustering) of GLT1 and GLAST1 but is independent of transporter synthesis and of glutamate receptor activation. Together, these results suggest an activity‐dependent neuronal feedback system for rapid astroglial glutamate transporter regulation where neuron‐derived glutamate is the physiological signal that triggers transporter function.
Trax is a component of the Translin‐containing RNA binding complex
Authors: Finkenstadt Patricia M. , Jeon Mihee , Baraban Jay M. 
Published: March 2003

AbstractTranslin is a nucleic acid binding protein that has been implicated in regulating the targeting and translation of dendritic RNA. In previous studies, we found that Translin and its partner protein, Trax, are components of a gel‐shift complex that is highly enriched in brain extracts. In those studies, we employed a DNA oligonucleotide, GS1, as a probe to label the complex. Translin has also been identified as a component of a gel‐shift complex detected using an RNA oligonucleotide probe, derived from the 3′ UTR of protamine‐2 mRNA. Although we had assumed that these probes labeled the same complex, recent studies indicate that association of Trax with Translin suppresses its RNA binding activity. As these findings challenge this assumption and suggest that the native RNA binding complex does not contain Trax, we have re‐examined this issue. We have found that the gel‐shift complexes labeled with either GS1 or protamine‐2 probes are ‘supershifted’ by addition of Trax antibodies, indicating that both are heteromeric Translin/Trax complexes. In addition, cross‐competition studies provide additional evidence that these probes label the same complex. Furthermore, analysis of recombinant Translin/Trax complexes generated by co‐transfection of Trax with Translin in hEK293T demonstrates that they are labeled with either probe. Although recombinant Translin forms a homomeric nucleic acid binding complex in vitro, our findings indicate that both Trax and Translin are components of the native gel‐shift complex labeled with either GS1 or protamine‐2 probes.
Striatal dopamine–NMDA receptor interactions in the modulation of glutamate release in the substantia nigra pars reticulata in vivo: opposite role for D1 and D2 receptors
Authors: Marti Matteo , Mela Flora , Bianchi Clementina , Beani Lorenzo , Morari Michele 
Published: March 2003

AbstractDual probe microdialysis was employed in conscious rats to investigate whether endogenous dopamine is involved in the stimulation of glutamate release in the substantia nigra pars reticulata following striatal NMDA receptor activation. Intrastriatal perfusion with NMDA (1 and 10 µm) facilitated nigral glutamate release (dizocilpine‐ and tetrodotoxin‐sensitive). The D2 dopamine receptor antagonist raclopride increased spontaneous nigral glutamate release and caused a leftward shift in the NMDA sensitivity, lowering NMDA effective concentrations to submicromolar levels. Conversely, the D1 antagonist SCH23390 prevented the effect of NMDA (1 µm) and caused a rightward shift in the NMDA sensitivity. It was tested whether the antagonist effects were due to dopamine receptor blockade or increased tone on D1/D2 receptors. SCH23390 prevented the raclopride‐induced enhancement of spontaneous but not NMDA‐evoked glutamate release while raclopride left unchanged the SCH23390‐induced inhibition. The physiopathological relevance of the dopaminergic modulation was strengthened by perfusing NMDA in the dopamine‐depleted striatum of hemiparkinsonian rats. Nigral glutamate responsiveness to NMDA was enhanced as with raclopride. We conclude that endogenous striatal dopamine regulates both spontaneous and NMDA‐induced nigral glutamate release via an opposite control mediated by D1 facilitatory and D2 inhibitory receptors. Alterations of this control may subserve the motor symptoms of Parkinson's disease.
The neuroprotective agents chlomethiazole and SB203580 inhibit IL‐1β signalling but not its biosynthesis in rat cortical glial cells
Authors: Simi Anastasia , Porsmyr‐Palmertz Margareta , Hjertén Anna , Ingelman‐Sundberg Magnus , Tindberg Niclas 
Published: March 2003

AbstractChlomethiazole and pyridinyl imidazole compounds, exemplified by SB203580, are structurally distinct p38 mitogen‐activated protein kinase inhibitors with neuroprotective properties in models of cerebral ischaemia. We have examined their effects in interleukin‐1β (IL‐1β) synthesis, release and signalling in rat cortical glial cells, given the important role of IL‐1β in cerebral ischaemia. We analysed (i) IL‐1β mRNA expression by northern blot, (ii) IL‐1β protein precursor levels within the cells by western blot, and (iii) the levels of the mature IL‐1β protein secreted into the medium by enzyme‐linked immunosorbent assay (ELISA) after treatment of rat cortical glial cells with lipopolysaccharide. While the induction of IL‐1β expression by lipopolysaccharide or by IL‐1β itself was very sensitive to nuclear factor kappa B (NF‐κB) inhibitors, chlomethiazole or SB203580 were nearly without effect, indicating a differential regulation as compared to peripheral cells, e.g. monocytes. In contrast, chlomethiazole and SB203580 potently inhibited the IL‐1β‐induced expression of c‐fos and inducible nitric oxide synthase, as monitored by northern blot and quantitative RT–PCR, respectively. Because IL‐1β‐induced expression of c‐fos and inducible nitric oxide synthase is believed to directly contribute to the pathology of cerebral ischaemic injury, the results suggest a direct mechanism for the neuroprotective effects of chlomethiazole and SB203580, and further establish the anti‐inflammatory properties of chlomethiazole.
Intercommunications between brain capillary endothelial cells and glial cells increase the transcellular permeability of the blood–brain barrier during ischaemia
Authors: Brillault Julien , Berezowski Vincent , Cecchelli Roméo , Dehouck Marie‐Pierre 
Published: March 2003

AbstractIncreased cerebrovascular permeability is an important factor in the development of cerebral oedema after stroke, implicating the blood–brain barrier (BBB). To investigate the effect of hypoxia on the permeability changes, we used a cell culture model of the BBB consisting of a co‐culture of brain capillary endothelial cells and glial cells. When endothelial cells from this co‐culture model were submitted alone to hypoxic conditions, long exposures (48 h) were necessary to result in an increase in endothelial cell monolayer permeability to [3H]inulin. When endothelial cells were incubated in presence of glial cells, a huge increase in permeability occurred after 9 h of hypoxic conditions. Oxygen glucose deprivation (OGD) resulted in a much shorter time (i.e. 2 h) required for an increase in permeability. We have demonstrated that this OGD‐induced permeability increase involves a transcellular rather than a paracellular pathway. Conditioned medium experiments showed that glial cells secrete soluble permeability factors during OGD. However, endothelial cells have to be made sensitive by OGD in order to respond to these glial soluble factors. This work shows that an early cross‐talk between glial and endothelial cells occurs during ischaemic stroke and alters BBB transcellular transport by means of glial factor secretions.
Study of the nematode putative GABA type‐A receptor subunits: evidence for modulation by ivermectin
Authors: Feng Xiao‐Peng , Hayashi Jon , Beech Robin N. , Prichard Roger K. 
Published: March 2003

AbstractTwo alleles of the HG1 gene, which encodes a putative GABA receptor α/γ subunit, were isolated from Haemonchus contortus. These two alleles were shown previously to be associated with ivermectin susceptibility (HG1A) and resistance (HG1E), respectively. Sequence analysis indicates that they differ in four amino acids. To explore the functional properties of the two alleles, a full‐length cDNA encoding the β subunit, a key functional component of the GABA receptor, was isolated from Caenorhabditis elegans (gab‐1, corresponding to the GenBank locus ZC482.1) and coexpressed in Xenopus oocytes with the HG1 alleles. When gab‐1 was coexpressed with either the HG1A allele or the HG1E allele in Xenopus oocytes, γ‐aminobutyric acid (GABA)‐responsive channels with different sensitivity to the agonist were formed. The effects of ivermectin on the hetero‐oligomeric receptors were determined. Application of ivermectin alone had no effect on the receptors. However, when coapplied with 10 µm GABA, ivermectin potentiated the GABA‐evoked current of the GAB‐1/HG1A receptor, but attenuated the GABA response of the GAB‐1/HG1E receptor. We demonstrated that the coexpressed HG1 and GAB‐1 receptors are GABA‐responsive, and provide evidence for the possible involvement of GABA receptors in the mechanism of ivermectin resistance.
Extracellular ATP and nerve growth factor intensify hypoglycemia‐induced cell death in primary neurons: role of P2 and NGFRp75 receptors
Authors: Cavaliere Fabio , Sancesario Giuseppe , Bernardi Giorgio , Volonté Cinzia 
Published: March 2003

AbstractIn this study, we monitored the direct expression of P2 receptors for extracellular ATP in cerebellar granule neurons undergoing metabolism impairment. Glucose deprivation for 30–60 min inhibited P2Y1 receptor protein, only weakly modulated P2X1, P2X2 and P2X3, and up‐regulated by about two‐fold P2X4, P2X7 and P2Y4. The P2X/Y antagonist basilen blue, protecting cerebellar neurons from hypoglycemic cell death, maintained within basal levels only the expression of P2X7 and P2Y4 proteins, but not P2X4 or P2Y1. Glucose starvation transiently increased (up to three‐fold) the expression of NGFRp75 receptor protein and strongly stimulated the extracellular release of nerve growth factor (NGF; about 10‐fold). Exogenously added NGF then augmented hypoglycemic neuronal death by about 60%, increasing the percentage of Höechst‐positive nuclei (from approximately 62 to 95%), reducing lactate dehydrogenase (LDH) release (from about 50 to 14%) and significantly overstimulating the hypoglycemia‐induced expression of P2X7 and P2Y4. Conversely, extracellular ATP augmented hypoglycemic neuronal death by about 80%, reducing the number of Höechst‐positive nuclei (from approximately 62% to 14%), augmenting LDH outflow (by about 30%) and further increasing the hypoglycemia‐induced expression of NGFRp75. Our results indicate that P2 and NGFRp75 receptors are modulated during glucose starvation and that extracellular ATP and NGF drive features of, respectively, necrotic and apoptotic hypoglycemic cell death, aggravating the consequences of metabolism impairment in cerebellar primary neurons.