bluuebunny/crossref_metadata_2025_split huggingface dataset:
Presynaptic NMDA autoreceptors facilitate axon excitability: a new molecular target for the anticonvulsant gabapentin
Authors: Suárez Luz M. , Suárez Francisco , Del Olmo Nuria , Ruiz Manuel , González‐Escalada José R. , Solís José M. 
Published: January 2005

AbstractGabapentin is a drug with anticonvulsant and analgesic properties causing the reduction of neurotransmitter release. We show that one of the mechanisms implicated in this effect of gabapentin is the reduction of the axon excitability measured as an amplitude change of the presynaptic fibre volley (FV) in the CA1 area of rat hippocampal slices. Interestingly, we found that gabapentin‐induced depression of FV is mimicked and occluded by NMDA receptor (NMDA‐R) antagonists, indicating that these receptors are located presynaptically and are activated by ambient levels of glutamate. Conversely, NMDA application (20 µm, 10 min) elicits a reversible FV potentiation which is reduced by gabapentin. Both NMDA‐ and gabapentin‐induced FV changes are partially explained by modifications in the firing threshold of individual fibres. Increasing [K+]o does not mimic or occlude (at a concentration of 6.5 mm) the effect of NMDA on FV amplitude, which makes it unlikely that a rise in [K+]o induced by NMDA receptor activation could indirectly participate in the potentiation of the FV. The NMDA‐induced FV potentiation is independent of extracellular calcium presence but is completely inhibited in a low‐Na+ solution (50% reduction) or under NMDA channel block (high Mg2+ or MK 801). These findings suggest that sodium entry through presynaptic NMDA‐R channels facilitates axon excitability. The interaction of gabapentin with this newly described mechanism might contribute to its therapeutic benefits.
A rat model of slow Wallerian degeneration (WldS) with improved preservation of neuromuscular synapses
Authors: Adalbert Robert , Gillingwater Thomas H. , Haley Jane E. , Bridge Katherine , Beirowski Bogdan , Berek Livia , Wagner Diana , Grumme Daniela , Thomson Derek , Celik Arzu , Addicks Klaus , Ribchester Richard R. , Coleman Michael P. 
Published: January 2005

AbstractThe slow Wallerian degeneration phenotype, WldS, which delays Wallerian degeneration and axon pathology for several weeks, has so far been studied only in mice. A rat model would have several advantages. First, rats model some human disorders better than mice. Second, the larger body size of rats facilitates more complex surgical manipulations. Third, rats provide a greater yield of tissue for primary culture and biochemical investigations. We generated transgenic WldS rats expressing the Ube4b/Nmnat1 chimeric gene in the central and peripheral nervous system. As in WldS mice, their axons survive up to 3 weeks after transection and remain functional for at least 1 week. Protection of axotomized nerve terminals is stronger than in mice, particularly in one line, where 95–100% of neuromuscular junctions remained intact and functional after 5 days. Furthermore, the loss of synaptic phenotype with age was much less in rats than in mice. Thus, the slow Wallerian degeneration phenotype can be transferred to another mammalian species and synapses may be more effectively preserved after axotomy in species with longer axons.
The astrocytic barrier to axonal regeneration at the dorsal root entry zone is induced by rhizotomy
Authors: McPhail Lowell T. , Plunet Ward T. , Das Partha , Ramer Matt S. 
Published: January 2005

AbstractAfter dorsal rhizotomy, sensory axons fail to regenerate beyond the astrocytic glia limitans at the dorsal root entry zone (DREZ) but this inhibition can be overcome with the delivery of exogenous neurotrophin‐3. We investigated whether axonal inhibition at the DREZ is constitutive or induced after dorsal rhizotomy. Primary afferent neurones from enhanced green fluorescent protein‐expressing mice were transplanted into adult rat dorsal root ganglia in the presence or absence of dorsal rhizotomy. In the absence of dorsal rhizotomy mouse axons freely extended into the rat central nervous system. After host dorsal rhizotomy, mouse axons were unable to cross the DREZ. However, in rats that received a dorsal rhizotomy concomitant with intrathecal neurotrophin‐3, the mouse axons were able to cross the DREZ. These results indicate that, under normal circumstances, the adult DREZ is permissive to the regeneration of adult sensory axons and that it only becomes inhibitory once dorsal root axons have been injured and astrocytes at the DREZ have become reactive.
Deafferentation and neurotrophin‐mediated intraspinal sprouting: a central role for the p75 neurotrophin receptor
Authors: Scott Angela L. M. , Borisoff Jaimie F. , Ramer Matt S. 
Published: January 2005

AbstractAxonal plasticity in the adult spinal cord is governed by intrinsic neuronal growth potential and by extracellular cues. The p75 receptor (p75NTR) binds growth‐promoting neurotrophins (NTs) as well as the common receptor for growth‐inhibiting myelin‐derived proteins (the Nogo receptor) and so is well situated to gauge the balance of positive and negative influences on axonal plasticity. Using transgenic mice lacking the extracellular NT‐binding domain of p75NTR (p75–/– mice), we have examined the influence of p75NTR on changes in the density of primary afferent (calcitonin gene‐related peptide‐expressing) and descending monoaminergic (serotonin‐ and tyrosine hydroxylase‐expressing) projections to the dorsal horn after dorsal rhizotomy, with and without concomitant application of exogenous nerve growth factor and NT‐3. We found that, in intact p75–/– mice, the axon density of all populations was equal to or less than that in wild‐type mice but that rhizotomy‐induced intraspinal sprouting was significantly augmented. Monoaminergic axon sprouting was enhanced in both nerve growth factor‐ and NT‐3‐treated p75–/– mice compared with similarly treated wild‐type mice. Primary afferent sprouting was particularly robust in NT‐3‐treated p75–/– mice. These in vivo results illustrate the interactions of p75NTR with NTs, with their respective tropomyosin‐related kinase receptors and with inhibitory myelin‐derived molecules. Our findings illustrate the pivotal role of p75NTR in spinal axonal plasticity and identify it as a potential therapeutic target for spinal cord injury.
Dopaminergic control of local interneuron activity in the thalamus
Authors: Munsch Thomas , Yanagawa Yuchio , Obata Kunihiko , Pape Hans‐Christian 
Published: January 2005

AbstractThe dorsal lateral geniculate nucleus (dLGN), the major thalamic station of the visual pathway, contains a fairly large number of dopaminergic terminals, and dopamine was found to reduce spontaneous and visually evoked activity in the dLGN in vivo. The cellular basis of this influence remained unknown. Here we have used whole cell patch‐clamp techniques to analyse the effects of dopamine (DA) on GABAergic transmission in dLGN slices of juvenile postnatal day (P) 12–P24 Long–Evans rats or juvenile (P12–P22) GAD67‐GFP (Δneo) mice. Spontaneous inhibitory postsynaptic currents (sIPSCs) were increased in frequency by the D2‐like agonist quinpirole (QUIN) in rat (n = 6), as well as in mouse (n = 5) thalamic slices. This effect was blocked in the presence of the D2‐like antagonist sulpiride (SULP, n = 5) and was absent in the ventrobasal complex (VB) of rat (n = 7) and mouse (n = 4) thalamus, which is devoid of GABAergic interneurons. Direct recordings from labelled GABAergic neurons in the dLGN of GAD67‐GFP mice revealed a QUIN‐mediated membrane depolarization (n = 12), which was attenuated by SULP (n = 6). These data demonstrate that DA through activation of D2‐like receptors in GABAergic interneurons induces an increase in inhibitory interactions most likely at F2 dendrodendritic terminals, thereby providing a cellular correlate of the observation made in vivo that DA predominantly acts through inhibition of relay cell activity in the dLGN.
GABAergic transmission in the rat paraventricular nucleus of the hypothalamus is suppressed by corticosterone and stress
Authors: Verkuyl J. Martin , Karst Henk , Joëls Marian 
Published: January 2005

AbstractParvocellular neurons in the hypothalamic paraventricular nucleus receive hormonal inputs mediated by corticosterone as well as neuronal inputs, prominent among which is a GABAergic inhibitory projection. In the present study we examined the functional properties of this GABAergic innervation when corticosteroid levels fluctuate. Frequency, amplitude and kinetic properties of miniature inhibitory postsynaptic potentials (mIPSCs), mediated by γ amino butyric acid (GABA) were studied with whole cell recording in parvocellular neurons. Injection of a high dose of corticosterone in vivo suppressed the frequency but did not change the amplitude and kinetic properties of mIPSCs recorded 1–5 h later in vitro. Similar effects were observed after restraint stress. The corticosteroid actions do not require involvement of extrahypothalamic brain regions, because in vitro administration of 100 nm corticosterone (20 min) directly to a hypothalamic slice also suppressed the frequency of mIPSCs recorded several hours later. Corticosterone administration to hypothalamic slices from restraint rats did not result in stronger reduction of mIPSC frequency than either treatment alone, pointing to a common underlying mechanism. Paired pulse response inhibition was reduced by corticosterone, suggesting that the hormone decreases the release probability of GABA‐containing vesicles. Unlike neurosteroids, corticosterone induced no rapid effects on mIPSC properties. These results indicate that increases in glucocorticoid level due to stress can slowly but persistently inhibit the GABAergic tone on parvocellular hypothalamic neurons via a hitherto unknown local mechanism independent of limbic projections.
Excitotoxic death induced by released glutamate in depolarized primary cultures of mouse cerebellar granule cells is dependent on GABAA receptors and niflumic acid‐sensitive chloride channels
Authors: Babot Zoila , Cristòfol Rosa , Suñol Cristina 
Published: January 2005

AbstractExcitotoxic neuronal death has been linked to neurological and neurodegenerative diseases. Several studies have sought to clarify the involvement of Cl– channels in neuronal excitotoxicity using either N‐methyl‐d‐aspartic acid (NMDA) or α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate/kainic acid agonists. In this work we induced excitotoxic death in primary cultures of cerebellar granule cells by means of endogenously released glutamate. Excitotoxicity was provoked by exposure to high extracellular K+ concentrations ([K+]o) for 5 min. Under these conditions, a Ca2+‐dependent release of glutamate was evoked. When extracellular glutamate concentration rose to between 2 and 4 µm, cell viability was significantly reduced by 30–40%. The NMDA receptor antagonists (MK‐801 and d‐2‐amino‐5‐phosphonopentanoic acid) prevented cell death. Exposure to high [K+]o produced a 36Cl– influx which was significantly reduced by picrotoxinin. In addition, the GABAA receptor antagonists (bicuculline, picrotoxinin and SR 95531) protected cells from high [K+]o‐triggered excitotoxicity and reduced extracellular glutamate concentration. The Cl– channel blockers niflumic acid and 5‐nitro‐2‐(3‐phenylpropylamino)benzoic acid also exerted a neuroprotective effect and reduced extracellular glutamate concentration, even though they did not reduce high [K+]o‐induced 36Cl– influx. Primary cultures of cerebellar granule cells also contain a population of GABAergic neurons that released GABA in response to high [K+]o. Chronic treatment of primary cultures with kainic acid abolished GABA release and rendered granule cells insensitive to high [K+]o exposure, even though NMDA receptors were functional. Altogether, these results demonstrate that, under conditions of membrane depolarization, low micromolar concentrations of extracellular glutamate might induce an excitotoxic process through both NMDA and GABAA receptors and niflumic acid‐sensitive Cl– channels.
Inflammation alters somatostatin mRNA expression in sensory neurons in the rat
Authors: El‐Aleem Seham A. Abd , Morales‐Aza Begonia M. , McQueen Daniel S. , Donaldson Lucy F. 
Published: January 2005

AbstractProinflammatory neuropeptides, such as substance P and calcitonin gene‐related peptide, are up‐regulated in primary afferent neurons in acute and chronic inflammation. While these neuropeptides have been intensively studied, potentially anti‐inflammatory and/or anti‐nociceptive neuropeptides such as somatostatin (SS) have been less widely investigated. Endogenous somatostatin is thought to exert a tonic antinociceptive effect. Exogenous SS is anti‐inflammatory and antinociceptive and is thought to exert these actions through inhibition of proinflammatory neuropeptide release. In this study we have compared the expression of somatostatin in two inflammatory models: arthritis, a condition associated with increased nociception, and periodontitis, in which there is little evidence of altered nociceptive thresholds. In acute arthritis (< 24 h) SS mRNA was down‐regulated in ipsilateral dorsal root ganglia (DRG; 52 ± 7% of control, P < 0.05), and up‐regulated in contralateral DRG (134 ± 10% of control; P < 0.05). In chronic arthritis (14 days) this pattern of mRNA regulation was reversed, with SS being up‐regulated ipsilaterally and down‐regulated contralaterally. In chronic mandibular periodontitis (7–10 days), SS mRNA was up‐regulated in only the mandibular division of the ipsilateral trigeminal ganglion (TG) (day 7, 219 ± 9% and day 10, 217 ± 12% of control; P < 0.02) but showed no change in other divisions of the trigeminal ganglion or in the mesencephalic nucleus. These data show that antinociceptive and anti‐inflammatory neuropeptides are also regulated in inflammation. It is possible that the degree of inflammation and nociception seen may depend on the balance of pro‐ and anti‐inflammatory and nociceptive peptide expression in a particular condition.
Metabolic engineering of the mevalonate and non‐mevalonate isopentenyl diphosphate‐forming pathways for the production of health‐promoting isoprenoids in tomato
Authors: Enfissi Eugenia M. A. , Fraser Paul D. , Lois Luisa‐Maria , Boronat Albert , Schuch Wolfgang , Bramley Peter M. 
Published: January 2005

SummaryThe genetic manipulation of both the mevalonic acid (MVA) and methylerythritol‐4‐phosphate (MEP) pathways, leading to the formation of isopentenyl diphosphate (IPP), has been achieved in tomato using 3‐hydroxymethylglutaryl CoA (hmgr‐1) and 1‐deoxy‐d‐xylulose‐5‐phosphate synthase (dxs) genes, respectively. Transgenic plants containing an additional hmgr‐1 from Arabidopsis thaliana, under the control of the cauliflower mosaic virus (CaMV) 35S constitutive promoter, contained elevated phytosterols (up to 2.4‐fold), but IPP‐derived isoprenoids in the plastid were unaltered. Transgenic lines containing a bacterial dxs targeted to the plastid with the tomato dxs transit sequence resulted in an increased carotenoid content (1.6‐fold), which was inherited in the next generation. Phytoene and β‐carotene exhibited the greatest increases (2.4‐ and 2.2‐fold, respectively). Extra‐plastidic isoprenoids were unaffected in these lines. These data are discussed with respect to the regulation, compartmentalization and manipulation of isoprenoid biosynthetic pathways and their relevance to plant biotechnology.
Initial evaluation of sugarcane as a production platform for p‐hydroxybenzoic acid
Authors: McQualter Richard B. , Chong Barrie Fong , Meyer Knut , Van Dyk Drew E. , O'Shea Michael G. , Walton Nicholas J. , Viitanen Paul V. , Brumbley Stevens M. 
Published: January 2005

SummarySugarcane (Saccharum hybrids) was evaluated as a production platform for p‐hydroxybenzoic acid using two different bacterial proteins (a chloroplast‐targeted version of Escherichia coli chorismate pyruvate‐lyase and 4‐hydroxycinnamoyl‐CoA hydratase/lyase from Pseudomonas fluorescens) that both provide a one‐enzyme pathway from a naturally occurring plant intermediate. The substrates for these enzymes are chorismate (a shikimate pathway intermediate that is synthesized in plastids) and 4‐hydroxycinnamoyl‐CoA (a cytosolic phenylpropanoid intermediate). Although both proteins have previously been shown to elevate p‐hydroxybenzoic acid levels in plants, they have never been evaluated concurrently in the same laboratory. Nor are there any reports on their efficacy in stem tissue. After surveying two large populations of transgenic plants, it was concluded that the hydratase/lyase is the superior catalyst for leaf and stem tissue, and further studies focused on this pathway. p‐Hydroxybenzoic acid was quantitatively converted to glucose conjugates by endogenous uridine diphosphate (UDP)‐glucosyltransferases and presumably stored in the vacuole. The largest amounts detected in leaf and stem tissue were 7.3% and 1.5% dry weight (DW), respectively, yet there were no discernible phenotypic abnormalities. However, as a result of diverting carbon away from the phenylpropanoid pathway, there was a severe reduction in leaf chlorogenic acid, subtle changes in lignin composition, as revealed by phloroglucinol staining, and an apparent compensatory up‐regulation of phenylalanine ammonia‐lyase. Although product accumulation in the leaves at the highest level of gene expression obtained in the present study was clearly substrate‐limited, additional experiments are necessary before this conclusion can be extended to the stalk.
High‐level production of yeast (Schwanniomyces occidentalis) phytase in transgenic rice plants by a combination of signal sequence and codon modification of the phytase gene
Authors: Hamada Akira , Yamaguchi Ken‐ichi , Ohnishi Naoto , Harada Michiko , Nikumaru Seiya , Honda Hideo 
Published: January 2005

SummaryThis study was designed to produce yeast (Schwanniomyces occidentalis) phytase in rice with a view to future applications in the animal feed industry. To achieve high‐level production, chimeric genes with the secretory signal sequence of the rice chitinase‐3 gene were constructed using either the original full‐length or N‐truncated yeast phytase gene, or a modified gene whose codon usage was changed to be more similar to that of rice, and then introduced into rice (Oryza sativa L.). When the original phytase genes were used, the phytase activity in the leaves of transgenic rice was of the same level as in wild‐type plants, whose mean value was 0.039 U/g fresh weight (g‐FW) (1 U of activity was defined as 1 µmol P released per min at 37 °C). In contrast, the enzyme activity was increased markedly when codon‐modified phytase genes were introduced: up to 4.6 U/g‐FW of leaves for full‐length codon‐modified phytase, and 10.6 U/g‐FW for truncated codon‐modified phytase. A decrease in the optimum temperature and thermal stability was observed in the truncated heterologous enzyme, suggesting that the N‐terminal region plays an important role in enzymatic properties. In contrast, the optimum temperature and pH of full‐length heterologous phytase were indistinguishable from those of the benchmark yeast phytase, although the heterologous enzyme was less glycosylated. Full‐length heterologous phytase in leaf extract showed extreme stability. These results indicate that codon modification, combined with the use of a secretory signal sequence, can be used to produce substantial amounts of yeast phytase, and possibly any phytases from various organisms, in an active and stable form.
Enhanced levels of methionine and cysteine in transgenic alfalfa (Medicago sativaL.) plants over‐expressing theArabidopsiscystathionine γ‐synthase gene
Authors: Avraham Tal , Badani Hanna , Galili Shmuel , Amir Rachel 
Published: January 2005

SummaryWith the aim of increasing the methionine level in alfalfa (Medicago sativaL.) and thus improving its nutritional quality, we produced transgenic alfalfa plants that expressed theArabidopsiscystathionine γ‐synthase (AtCGS), the enzyme that controls the synthesis of the first intermediate metabolite in the methionine pathway. The AtCGScDNA was driven by theArabidopsisrubisco small subunit promoter to obtain expression in leaves. Thirty transgenic plants were examined for the transgene protein expression, and four lines with a high expression level were selected for further work. In these lines, the contents of methionine,S‐methylmethionine (SMM), and methionine incorporated into the water‐soluble protein fraction increased up to 32‐fold, 19‐fold, and 2.2‐fold, respectively, compared with that in wild‐type plants. Notably, in these four transgenic lines, the levels of free cysteine (the sulphur donor for methionine synthesis), glutathione (the cysteine storage and transport form), and protein‐bound cysteine increased up to 2.6‐fold, 5.5‐fold, and 2.3‐fold, respectively, relative to that in wild‐type plants. As the transgenic alfalfa plants over‐expressing AtCGS had significantly higher levels of both soluble and protein‐bound methionine and cysteine, they may represent a model and target system for improving the nutritional quality of forage crops.
Expression of a fungal phytase gene in Nicotiana tabacum improves phosphorus nutrition of plants grown in amended soils
Authors: George Timothy S. , Simpson Richard J. , Hadobas Paul A. , Richardson Alan E. 
Published: January 2005

SummaryTransgenic Nicotiana tabacum plants expressing a chimeric phytase gene (ex::phyA) from the soil fungus Aspergillus niger were generated. Three independently transformed lines showed increased extracellular phytase activity compared with a vector control and wild‐type plants, both of which had no detectable extracellular phytase. Transgenic N. tabacum plants grown in sterile agar supplied with phosphorus (P) as phytate accumulated 3.7‐fold more P than vector control plants. Despite this, the expression of ex::phyA in plants did not lead to an improved accumulation of P from two unamended P‐deficient soils. However, when soils were amended with either phytate or phosphate and lime, transgenic plants accumulated up to 52% more P than controls. Positive responses by transgenic plants were, in some instances, coincident with a putative increase in soil phytate. We conclude that the development of plants that exude phytase to the soil may not ensure improved plant P nutrition, as the availability of phytate in the soil also appears to be critical. Nevertheless, if plants that express ex::phyA are combined with soil amendments that promote the availability of phytate, there is the potential to enhance the P nutrition of crop plants and to improve the efficiency of P fertilizer use in agricultural systems.