bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cells defective in sphingolipids biosynthesis express low amounts of muscle nicotinic acetylcholine receptor
Authors: Roccamo A. M. , Pediconi M. F. , Aztiria E. , Zanello L. , Wolstenholme A. , Barrantes F. J. 
Published: March 2003

AbstractThe properties of the nicotinic acetylcholine receptor (AChR) are modulated by its lipid microenvironment. Studies of such modulation are hampered by the cell's homeostatic mechanisms that impede sustained modification of membrane lipid composition. We have devised a novel strategy to circumvent this problem and study the effect of changes in plasma membrane lipid composition on the functional properties of AChR. This approach is based on the stable transfection of AChR subunit cDNAs into cells defective in a specific lipid metabolic pathway. In the present work we illustrate this new strategy with the successful transfection of a temperature‐sensitive Chinese hamster ovary (CHO) cell line, SPB‐1, with the genes corresponding to the four adult mouse AChR subunits. The new clone, SPB‐1/SPH, carries a mutation of the gene coding for serine palmitoyl transferase, the enzyme that catalyses the first step in sphingomyelin (Sph) biosynthesis. This defect causes a decrease of Sph de novo synthesis at non‐permissive temperatures. The IC50 for inhibition of α‐BTX binding with the agonist carbamoylcholine exhibited values of 3.6 and 2.7 μm in the wild‐type and Sph‐deficient cell lines, respectively. The corresponding IC50 values for the competitive antagonist d‐tubocurarine (d‐TC) were 2.8 and 3.4 μm, respectively. No differences in single‐channel properties were observed between wild‐type and mutant cell lines grown at the non‐permissive, lipid defect‐expressing temperature using the patch‐clamp technique. Both cells exhibited two open times with mean values of 0.35 ± 0.05 and 1.78 ± 0.2 ms at 12 °C. Taken together, these results suggest that the AChR is expressed as the complete heteroligomer. However, only 10–20% of the total AChR synthesized reached the surface membrane in the mutant cell line and exhibited a higher metabolic turnover, with a half‐life about 50% shorter than the wild‐type cells. When control CHO‐K1/A5 cells were treated with fumonisin B1, an inhibitor of sphingosine (sphinganine) N‐acetyltransferase (ceramide synthase), a 45.5% decrease in cell surface AChR expression was observed. The results suggest that sphingomyelin deficiency conditions AChR targeting to the plasma membrane.
Anatomical and functional demonstration of a multisynaptic suprachiasmatic nucleus adrenal (cortex) pathway
Authors: Buijs Ruud M. , Wortel Joke , Van Heerikhuize Joop J. , Feenstra Matthijs G. P. , Ter Horst Gert J. , Romijn Herms J. , Kalsbeek Andries 
Published: March 2003

AbstractIn view of mounting evidence that the suprachiasmatic nucleus (SCN) is directly involved in the setting of sensitivity of the adrenal cortex to ACTH, the present study investigated possible anatomical and functional connections between SCN and adrenal. Transneuronal virus tracing from the adrenal revealed first order labelling in neurons in the intermedio‐lateral column of the spinal cord that were shown to receive an input from oxytocin fibres and subsequently second‐order labelling in neurons of the autonomic division of the paraventricular nucleus. The latter neurons were shown to receive an input from vasopressin or vasoactive intestinal peptide (VIP) containing SCN efferents. The true character of this SCN input to second‐order neurons was also demonstrated by the fact that third‐order labelling was present within the SCN, vasopressin or VIP neurons. The functional presence of the SCN–adrenal connection was demonstrated by a light‐induced fast decrease in plasma corticosterone that could not be attributed to a decrease in ACTH. Using intact and SCN‐lesioned animals, the immediate decrease in plasma corticosterone was only observed in intact animals and only at the beginning of the dark period. This fast decrease of corticosterone was accompanied by constant basal levels of blood adrenaline and noradrenaline, and is proposed to be due to a direct inhibition of the neuronal output to the adrenal cortex by light‐mediated activation of SCN neurons. As a consequence, it is proposed that the SCN utilizes neuronal pathways to spread its time of the day message, not only to the pineal, but also to other organs, including the adrenal, utilizing the autonomic nervous system.
Alterations in the morphology of dendrites and dendritic spines in the nucleus accumbens and prefrontal cortex following repeated treatment with amphetamine or cocaine
Authors: Robinson Terry E. , Kolb Bryan 
Published: March 2003

AbstractRepeated treatment with psychostimulant drugs produces changes in brain and behaviour that far outlast their initial neuropharmacological actions. The nature of persistent drug‐induced neurobehavioural adaptations is of interest because they are thought to contribute to the development of dependence and addiction, and other forms of psychopathology, e.g. amphetamine psychosis. There are many reports that psychostimulants produce biochemical adaptations in brain monoamine systems, especially dopamine systems. The purpose of the present study was to determine if they might also alter the morphology of neurons in brain regions that receive monoaminergic innervation. Rats were given repeated injections of either amphetamine or cocaine, or, to control for general motor activity, allowed access to a running wheel. They were then left undisturbed for 24–25 days before their brains were processed for Golgi–Cox staining. Treatment with either amphetamine or cocaine (but not wheel running experience) increased the number of dendritic branches and the density of dendritic spines on medium spiny neurons in the shell of the nucleus accumbens, and on apical dendrites of layer V pyramidal cells in the prefrontal cortex. Cocaine also increased dendritic branching and spine density on the basilar dendrites of pyramidal cells. In addition, both drugs doubled the incidence of branched spines on medium spiny neurons. It is suggested that some of the persistent neurobehavioural consequences of repeated exposure to psychostimulant drugs may be due to their ability to reorganize patterns of synaptic connectivity in the nucleus accumbens and prefrontal cortex.
Apoptotic cell death of proliferating neuroepithelial cells in the embryonic retina is prevented by insulin
Authors: Díaz Begoña , Pimentel Belén , De Pablo Flora , De La Rosa Enrique J. 
Published: March 2003

AbstractThe role of programmed cell death is well established for connecting neurons. Conversely, much less is known about apoptosis affecting proliferating neuroepithelial cells. Chick retina from day 4 to day 6 of embryonic development (E), essentially proliferative, presented a defined distribution of apoptotic cells during normal in vivo development, as visualized by TdT‐mediated dUTP nick end labelling (TUNEL). Insulin, expressed in the early chick embryonic retina as proinsulin, attenuated apoptosis in growth factor‐deprived organotypic culture of E5 retina. This effect was demonstrated both by TUNEL and by staining of pyknotic nuclei, as well as by release of nucleosomes. Application of a 1 h [methyl‐3H]thymidine pulse in ovo at E5, followed by organotypic culture in the presence or absence of insulin, showed that this factor alone decreased the degradation of labelled DNA to nucleosomes by 40%, as well as the proportion of labelled pyknotic nuclei. Both features are a consequence of apoptosis affecting neuroepithelial cells, which were in S‐phase or shortly after. In addition, when the E5 embryos were maintained in ovo after the application of [methyl‐3H]thymidine, 70% of the apoptotic retinal cells were labelled, indicating the in vivo prevalence of cell death among actively proliferating neuroepithelial cells. Apoptotic cell death is thus temporally and spatially regulated during proliferative stages of retinal neurogenesis, and embryonic proinsulin is presumably an endogenous protective factor.
Calcium‐dependent mechanisms involved in presynaptic long‐term depression at the hippocampal mossy fibre–CA3 synapse
Authors: Kobayashi Katsunori , Manabe Toshiya , Takahashi Tomoyuki 
Published: March 2003

AbstractLong‐term potentiation (LTP) and long‐term depression (LTD) are induced presynaptically at the hippocampal mossy fibre–CA3 synapse. Activation of presynaptic metabotropic glutamate receptors (mGluRs) is necessary, but not sufficient for the LTD induction. Using mouse hippocampal slices, we attempted to identify additional presynaptic factors involved in the induction of mossy fibre LTD. Suppression of a rise in the presynaptic intracellular Ca2+ concentration ([Ca2+]i) with a membrane‐permeable Ca2+ chelator, 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetic acid tetraacetoxymethyl ester (BAPTA‐AM), reduced the magnitude of LTD, whereas an increase in Ca2+ influx induced LTD, suggesting that an elevation of presynaptic [Ca2+]i is crucial for the LTD induction. A broad‐spectrum protein kinase inhibitor, H‐7, blocked LTD without affecting a presynaptic inhibition induced by an mGluR agonist. Furthermore, LTD was reduced by an inhibitor of calmodulin or Ca2+/calmodulin‐dependent protein kinases. Thus, we conclude that mossy fibre LTD requires an increase in presynaptic [Ca2+]i and subsequent activation of Ca2+/calmodulin‐dependent protein kinases. Because mossy fibre LTP may also require a rise in presynaptic [Ca2+]i, bidirectional long‐term plasticity at the mossy fibre synapse is likely to be regulated by presynaptic Ca2+‐dependent processes.
Adrenalectomy increases neurogenesis but not PSA‐NCAM expression in aged dentate gyrus
Authors: Montaron M. F. , Petry K. G. , Rodriguez J. J. , Marinelli M. , Aurousseau C. , Rougon G. , Le Moal M. , Abrous D. N. 
Published: March 2003

AbstractAgeing is accompanied by a decline in neurogenesis and in polysialylated isoforms of neural cell adhesion molecule (PSA‐NCAM) expression within the hippocampus and by elevated basal levels of circulating corticosterone. In a companion study, we demonstrated that suppression of corticosterone by adrenalectomy increased neurogenesis and PSA‐NCAM expression in the dentate gyrus of adult rats. Here we show that adrenalectomy increased neurogenesis in this structure in old rats, as measured by the incorporation of 5‐bromo‐2′‐deoxyuridine in neuronal progenitors. This effect was prevented by corticosterone replacement. In contrast, PSA‐NCAM expression remained unchanged in comparison with controls. Thus, in the aged brain, stem cells are still present and able to enter the cell cycle. This may point to ways of protecting or treating age‐related cognitive impairments.
BDNF stimulates expression, activity and release of tissue‐type plasminogen activator in mouse cortical neurons
Authors: Fiumelli Hubert , Jabaudon Denis , Magistretti Pierre J. , Martin Jean‐Luc 
Published: March 2003

AbstractBrain‐derived neurotrophic factor (BDNF) is a neurotrophic factor involved in neuronal development and synaptic plasticity. Although the physiological effects of BDNF have been examined in detail, target proteins which mediate its actions remain largely unknown. Here, we report that BDNF stimulates the expression of tissue‐type plasminogen activator (tPA) in primary cultures of cortical neurons in a time‐ and concentration‐dependent manner. Among the other members of the neurotrophin family, neurotrophin‐4 (NT‐4) and to a lesser extent neurotrophin‐3 (NT‐3) also increased tPA mRNA expression, while nerve growth factor (NGF) was devoid of any effect. Induction of tPA expression by BDNF is accompanied by an increase in the proteolytic activity of tPA associated with cortical neurons and a release of tPA into the extracellular space. Release of tPA induced by BDNF depends on extracellular Ca2+ since it is markedly reduced in the presence of ethylene glycol‐bis(β‐aminoethylether)‐N,N,N′,N′‐tetraacetic acid (EGTA). Up‐regulation of tPA expression by BDNF is followed by the induction of plasminogen activator inhibitor 2 (PAI‐2), an inhibitor of tPA. Together these results suggest that activation of tPA by BDNF may contribute to structural changes associated with neuronal development or synaptic plasticity.
Alterations in the expression of GABAA receptor subunits in cerebellar granule cells after the disruption of the α6 subunit gene
Authors: Nusser Zoltan , Ahmad Zahida , Tretter Verena , Fuchs Karoline , Wisden William , Sieghart Werner , Somogyi Peter 
Published: March 2003

AbstractAny given subunit of the heteromultimeric type‐A γ‐aminobutyric acid (GABA) GABAA receptor may be present in several receptor subtypes expressed by individual neurons. Changes in the expression of a subunit may result in differential changes in the expression of other subunits depending on the subunit composition of the receptor subtype, leading to alterations in neuronal responsiveness to GABA. We used the targeted disruption of the α6 subunit gene to test for changes in the expression of other GABAA receptor subunits. Immunoprecipitation and ligand binding experiments indicated that GABAA receptors were reduced by ≈ 50% in the cerebellum of α6 –/– mice. Western blot experiments indicated that the α6 subunit protein completely disappeared from the cerebellum of α6 –/– mice, which resulted in the disappearance of the δ subunit from the plasma membrane of granule cells. The amount of β2, β3 and γ2 subunits was reduced by ≈ 50%, 20% and 40%, respectively, in the cerebella of α6 –/– mice. A comparison of the reduction in the level of α1, β2, β3, γ2, or δ‐subunit‐containing receptors in α6 –/– cerebellum with those observed after removal of α6‐subunit‐containing receptors from the cerebella of α6 +/+ mice by immuno‐affinity chromatography demonstrated the presence of a significantly higher than expected proportion of receptors containing β3 subunits in α6 –/– mice. The receptors containing α1, β2, β3 and γ2 subunits were present in the plasma membrane of granule cells of α6 –/– mice at both synaptic and extrasynaptic sites, as shown by electron microscopic immunocytochemistry. Despite the changes, the α1 subunit content of Golgi‐cell‐to‐granule‐cell synapses in α6 –/– animals remained unaltered, as did the frequency of α1 immunopositive synapses in the glomeruli. Furthermore, no change was apparent in the expression of the α1, β2 and γ2 subunits in Purkinje cells and interneurons of the molecular layer.These results demonstrate that in α6 –/– mice, the cerebellum expresses only half of the number of GABAA receptors present in wild‐type animals. Since these animals have no gross motor deficits, synaptic integration in granule cells is apparently maintained by α1‐subunit‐containing receptors with an altered overall subunit composition, and/or by changes in the expression of other ligand and voltage gated channels.
BDNF and NT‐4 differentiate two pathways in the modulation of neuropeptide protein levels in postnatal hippocampal interneurons
Authors: Marty Serge , Onténiente Brigitte 
Published: March 2003

AbstractNeuropeptide protein levels in hippocampal interneurons exhibit a considerable maturation in postnatal animals. This study characterizes the role of neuronal activity in determining neuropeptide protein levels in postnatal hippocampal interneurons, and the involvement of neurotrophins. In hippocampal slices from 7‐day‐old rats cultured for 2 weeks, treatment with the γ‐aminobutyric acidA (GABAA) receptor antagonist bicuculline increased the staining intensity and the number of neurons immunoreactive for neuropeptide Y (NPY). An opposite effect was observed when non‐N‐methyl‐d‐aspartate (non‐NMDA) excitatory transmission was blocked. The effects of either treatment were reversed after return to control medium. These findings were similar to those previously obtained on the effects of activity on somatostatin immunostaining. Blockade of endogenous tyrosine kinase neurotrophin receptors using K252a prevented the effects of bicuculline on NPY‐ and somatostatin‐immunoreactive neurons. Application of exogenous neurotrophin‐3 (NT‐3) increased NPY and somatostatin protein levels in long‐term but not short‐term cultures, while nerve growth factor (NGF) had no effect. In contrast, brain‐derived neurotrophic factor (BDNF) or neurotrophin‐4 (NT‐4) did not affect equally NPY and somatostatin immunoreactivity: they mimicked the effects of bicuculline treatment on NPY‐immunoreactive neurons, but exerted no conspicuous effect on somatostatin immunostaining. These results indicate that although neuronal activity plays a major role in determining neuropeptide protein levels in postnatal hippocampal interneurons, its effects on different neuropeptides might be exerted through different mechanisms, with or without the mediation of BDNF or NT‐4.
The effect of microglia on embryonic dopaminergic neuronal survival in vitro: diffusible signals from neurons and glia change microglia from neurotoxic to neuroprotective
Authors: Zietlow R. , Dunnett S. B. , Fawcett J. W. 
Published: March 2003

AbstractWhen embryonic dopaminergic neurons are transplanted into the adult brain, ≈ 95% die within a few days. To assess whether microglia activated during transplantation might be responsible for this rapid death, we examined the effect of microglia on rat embryonic dopaminergic neurons in vitro. Conditioned medium from 7‐day‐old microglia was found to decrease the number of dopamine neurons surviving in primary culture, but activation of the microglia with N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP) or Zymosan A did not increase the toxicity of the conditioned medium. We next tested the effect of coculturing microglia and dopaminergic neurons by placing microglia in semipermeable well inserts over the neuronal cultures. The presence of microglia now increased dopaminergic neuronal survival, microglial activation again having no effect. To increase yet further the possible interactions between microglia and neurons, the mesencephalic cells and microglia were mixed together and placed as a tissue in three‐dimensional culture, and here again the presence of microglia increased dopaminergic neuronal survival with no effect of activation. Contact of microglia with the mesencephalic cells therefore converted them from being toxic to dopaminergic neurons to promoting their survival. The change in microglial effect from toxic to protective was caused by soluble molecules secreted by cells in the neuronal cultures, as conditioned medium derived from microglia–neuronal cocultures also had a dopaminergic neuron survival effect, indicating that microglia in cocultures behave differently from microglia removed from neuronal and glial influence. Microglia cocultured with either neurons or astrocytes downregulated inducible nitric oxide synthase (iNOS), indicating a decrease in the production of nitric oxide and possibly other toxic molecules. These findings indicate that in their natural environment, microglia are likely to be beneficial for the survival of embryonic dopaminergic grafts.
Cytoskeleton mediates inhibition of the fast Na+ current in respiratory brainstem neurons during hypoxia
Authors: Mironov S. L. , Richter D. W. 
Published: March 2003

AbstractWhole‐cell Na+ currents (INa) were recorded in inspiratory neurons in a medullary slice preparation from neonatal mouse that contains the functional respiratory network. Hypoxia and metabolic poisoning with KCN rapidly inhibited INa by reducing the number of Na+ channels available for opening during depolarization. Application of agents specific for G‐proteins, protein kinase C and A, intracellular Ca2+ and pH did not prevent the hypoxic inhibition of INa. The effects of hypo‐osmolarity and hypoxia were additive, whereas hyperosmolarity partially prevented a subsequent hypoxic inhibition of INa. Cytochalasin B and colchicine decreased, and taxol or phalloidin increased INa and reduced its hypoxic inhibition. We conclude that cytoskeleton rearrangements during hypoxia are responsible for suppression of a fast INa in brainstem respiratory neurons, which could be mediated by the uncoupling of channel inactivation gates from cytoskeletal elements.
The role of p75NTR in modulating neurotrophin survival effects in developing motoneurons
Authors: Wiese Stefan , Metzger Friedrich , Holtmann Bettina , Sendtner Michael 
Published: March 2003

AbstractNeurotrophins exert their biological functions on neuronal cells through two types of receptors, the trk tyrosine kinases and the low‐affinity neurotrophin receptor (p75NTR), which can bind all neurotrophins with similar affinity. The p75NTR is highly expressed in developing motoneurons and in adult motoneurons after axotomy, suggestive of a physiological role in mediating neurotrophin responses under such conditions. In order to characterize this specific function of p75NTR, we have tested the effects of nerve growth factor (NGF) on embryonic motoneurons from control and p75NTR‐deficient mice. NGF antagonizes brain‐derived neurotrophic factor (BDNF)‐ and neurotrophin‐3 (NT‐3)‐mediated survival in control but not p75NTR‐deficient motoneurons. Survival of cultured motoneurons in the presence of 0.5 ng/mL of either ciliary neurotrophic factor (CNTF) or glial‐derived neurotrophic factor (GDNF) was not reduced by 20 ng/mL NGF. Dose–response investigations revealed that five times higher concentrations of BDNF are required for half‐maximal survival of p75NTR‐deficient motoneurons in comparison to motoneurons from wild‐type controls. After facial nerve lesion in newborn wild‐type mice, local administration of NGF reduced survival of corresponding motoneurons to less than 2% compared to the unlesioned control side. In p75NTR‐deficient mice, the same treatment did not enhance facial motoneuron death on the lesioned side. In the facial nucleus of 1‐week‐old p75NTR–/– mice, a significant reduction of motoneurons was observed at the unlesioned side in comparison to p75NTR +/+ mice. The observation that motoneuron cell numbers are reduced in the facial nucleus of newborn p75NTR‐deficient mice suggests that p75NTR might not function as a physiological cell death receptor in developing motoneurons.
Thalamic projections of the fusiform gyrus in man
Authors: Clarke Stephanie , Riahi‐Arya Sahba , Tardif Eric , Eskenasy Anne‐Claude Cottier , Probst Alphonse 
Published: March 2003

AbstractPrevious retrograde degeneration studies have shown that human extrastriate visual cortex receives projections from the pulvinar, but their precise topographical organization remained unknown. We report on the distribution of thalamic projections originating in the fusiform gyrus, as studied with the Nauta method for anterogradely degenerating axons, in a case of right fusiform gyrus infarction. Ipsilaterally to the lesion, high density of afferents was found in the inferior pulvinar nucleus and a low density in the medial pulvinar nucleus as well as in the postero‐inferior part of the reticular nucleus; no degenerating fibres were found in the lateral geniculate body. Degenerating axons were completely absent in the contralateral thalamus. Thus, there is a precise topographic relationship between parts of the extrastriate cortex and the pulvinar, suggesting segregated thalamocortical pathways for different parts of the extrastriate cortex. As in nonhuman primates, the human inferior temporal cortex has no direct output to the lateral geniculate body.