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S Pons

Publications and source records attributed to S Pons.

At least 19 recordsLinked to original sources
PubMed2006

Coexistence of one- and two-dimensional supramolecular assemblies of terephthalic acid on Pd(111) due to self-limiting deprotonation.

The adsorption of terephthalic acid [C(6)H(4)(COOH)(2), TPA] on a Pd(111) surface has been investigated by means of scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy, and near-edge x-ray absorption fine structure spectroscopy under ultrahigh vacuum conditions at room temperature. We find the coexistence of one- (1D) and two-dimensional (2D) molecular ordering. Our analysis indicates that the 1D phase consists of intact TPA chains stabilized by a dimerization of the self-complementary carboxyl groups, whereas in the 2D phase, consisting of deprotonated entities, the molecules form lateral ionic hydrogen bonds. The supramolecular growth dynamics and the resulting structures are explained by a self-limiting deprotonation process mediated by the catalytic activity of the Pd surface. Our models for the molecular ordering are supported by molecular mechanics calculations and a simulation of high resolution STM images.

Journal Article↗
PubMed2006

Targeted in vivo expression of nicotinic acetylcholine receptors in mouse brain using lentiviral expression vectors.

Nicotinic acetylcholine receptors (nAChRs) in the brain exhibit diverse functional properties and ubiquitous distribution. Yet, except for providing a receptor for the exogenously applied nicotine of tobacco products, their role in the normal functioning of the brain has remained elusive. We have used a lentiviral expression vector to re-express the beta2 subunit specifically in the ventral tegmental area (VTA) of beta2-/- mice. The viral vector efficiently expresses beta2- subunit protein leading to new nAChR-binding sites. VTA neurons transduced by the lentiviral vector are responsive to intravenous nicotine when analyzed using in vivo electrophysiology. Nicotine-induced dopamine release from the nucleus accumbens (NuAcc) was also restored in re-expressing beta2-/- mice. Intra-VTA injection of nicotine was found to be reinforcing in both wild-type and beta2-subunit re-expressing beta2-/- mice, but not in beta2-/- mice. Furthermore, in the absence of applied nicotine, the spontaneous slow exploratory behavior of the mice was restored, whereas fast navigation did not change. This latter behavioral analysis suggests a role for beta2* nAChR, specifically expressed in the VTA, in mammalian cognitive function.

Animals↗
PubMed2005

Nicotine reinforcement and cognition restored by targeted expression of nicotinic receptors.

Worldwide, 100 million people are expected to die this century from the consequences of nicotine addiction, but nicotine is also known to enhance cognitive performance. Identifying the molecular mechanisms involved in nicotine reinforcement and cognition is a priority and requires the development of new in vivo experimental paradigms. The ventral tegmental area (VTA) of the midbrain is thought to mediate the reinforcement properties of many drugs of abuse. Here we specifically re-expressed the beta2-subunit of the nicotinic acetylcholine receptor (nAChR) by stereotaxically injecting a lentiviral vector into the VTA of mice carrying beta2-subunit deletions. We demonstrate the efficient re-expression of electrophysiologically responsive, ligand-binding nicotinic acetylcholine receptors in dopamine-containing neurons of the VTA, together with the recovery of nicotine-elicited dopamine release and nicotine self-administration. We also quantified exploratory behaviours of the mice, and showed that beta2-subunit re-expression restored slow exploratory behaviour (a measure of cognitive function) to wild-type levels, but did not affect fast navigation behaviour. We thus demonstrate the sufficient role of the VTA in both nicotine reinforcement and endogenous cholinergic regulation of cognitive functions.

Animals↗
PubMed2005

[Mechanisms of protein expression in the rat optic nerve. Modifications by alcohol exposure].

PURPOSE: Previous work from our group demonstrated that regular high consumption of ethanol during pregnancy induces a delay in growth and structural changes in the developing eye and vision (Pinazo-Duran et al., Teratology '93; Eur J Ophthalmol '97; Stromland and Pinazo-Duran, Teratology '94; Alcohol Alcoholism '02). Our main goal is to study at a cellular and molecular level, whether or not the prenatal alcohol exposure may change the development of the glial cells and inducing the optic nerve dysmorphogenesis. We have used key protein markers to analyse the expression in the rat optic nerve throughout the pre- and postnatal periods. METHODS: To better understanding the actions of ethanol on optic nerve development in alcohol-induced and control dams, these were fed a liquid diet during gestation and lactation, containing either ethanol (5% w/, 35% of the daily food intake) or isocaloric carobydrates (35% of the daily food intake). Eyes were enucleated and processed to immunocytochemical and morphological tecnhiques and western blot approaches, using antibodies against the glial fibrillary acidid protein (GFAP), neurofilament protein (NFP) and myelin basic protein (MBP). RESULTS: Three main observations were made in the ethanol-exposed and control groups: 1) the optic nerve size was significantly lower in the ethanol group than in the control group, 2) there were statistically significant changes in optic nerve astrocytes and oligodendrocytes, optic axons and myelin sheaths and 3) a delay and altered expression of developmental proteins. CONCLUSIONS: All data support our earlier studies confirming the deleterious effects of ethanol on the developing visual system. We suggest that ethanol may alter the expression of precise genes involved in eye development and posterior remodelling. These results can be extrapolated to clinical advances in fetal alcohol syndrome and toxic optic neuropathies.

Animals↗
PubMed2004

Critical role of the C-terminal segment in the maturation and export to the cell surface of the homopentameric alpha 7-5HT3A receptor.

Many neurological pathologies are related to misfolded proteins. During folding and assembly in the endoplasmic reticulum, the nicotinic acetylcholine receptor (nAChR) subunits undergo several conformational changes to acquire the ability to bind ligands. After folding and maturation, by mechanisms largely unknown, receptors are exported to the cell surface. We investigated the maturational role of the extracellular C-terminal segment located at the boundary between the extracellular and the transmembrane domains. In the functional chimeric alpha7-5HT3A receptor used as a model system, amino acids from the C-terminal segment were successively deleted or mutated. Upon progressive shortening of the peptide we observed less and less alpha-bungarotoxin binding sites until no sites could be detected when the entire peptide had been deleted (chimera Del 5). Protein synthesis and pentameric assembly were not altered. In Del 5 transfected cells, pentameric receptors present in the endoplasmic reticulum were not detected on the cell surface where Del 5 proteins appeared as patches. With the Del 5 chimera, export of proteins to the cell surface diminished to about half that of wild-type. We propose that the C-terminal segment plays a double role: (i) through an interaction between the penultimate tyrosine residue of the C-terminal segment and the Cys loop of the N-terminal domain, it locks the receptor in a mature alpha-bungarotoxin binding conformation; (ii) this mature conformation, in turn, masks a retention signal present in the first transmembrane segment allowing properly assembled and matured receptors to escape to the cell surface.

Amino Acid Sequence↗
PubMed2004

[Hypokalemic metabolic alkalosis: apropos of a case of Gitelman's syndrome].

We present a case of Gitelman's Syndrome in a 20 year-old woman who came to our service with weakness, asthenia, leg cramps and tetany. Laboratory studies revealed metabolic alkalosis with hypokalemia, hypomagnesemia and low calcium in a 24-hour urine test. The diagnosis of this syndrome is made in some cases during adult life because this syndrome is asymptomatic over several years. Gitelman's Syndrome is autosomal recessive as is Bartter's Syndrome. The gene is located in chromosome 16q, which encodes the cotransporter Na/Cl sensitive to thiazide in the distal convoluted tubule. The defect of cotransporter produces an alteration of sodium reabsorption that causes electrolytic disorders typical of this Syndrome and different from Bartter's Syndrome. The typical electrolytic alterations are hypocalciuria and hypomagnesemia secondary to high urinary magnesium excretion. The prognosis of this syndrome is excellent and treatment consists in correction of serum electrolytes with oral administration of magnesium and potassium. In spite of this treatment, in some cases it is very difficult to reach normal serum levels of magnesium because of the high doses of oral magnesium, which produce common crises of diarrhea that increase magnesium gastrointestinal losses.

Alkalosis↗
PubMed2003

Glutamate excitotoxicity attenuates insulin-like growth factor-I prosurvival signaling.

Recent evidence suggests that impaired insulin/insulin-like growth factor I (IGF-I) input may be associated to neurodegeneration. Several major neurodegenerative diseases involve excitotoxic cell injury whereby excess glutamate signaling leads to neuronal death. Recently it was shown that glutamate inactivates Akt, a serine-kinase crucially involved in the prosurvival actions of IGF-I. We now report that excitotoxic doses of glutamate antagonize Akt activation by IGF-I and inhibit the neuroprotective effects of this growth factor on cultured neurons. Glutamate induces loss of sensitivity to IGF-I by phosphorylating the IGF-I receptor docking protein insulin-receptor-substrate (IRS)-1 in Ser(307) through a pathway involving activation of PKA and PKC in a hierarchical fashion. Administration of Ro320432, a selective PKC inhibitor, abrogates the inhibitory effects of glutamate on IGF-I-induced Akt activation in vitro and in vivo and is sufficient to block the neurotoxic action of glutamate on cultured neurons. Notably, administration of Ro320432 after ischemic insult, a major form of excitotoxic injury in vivo, results in a marked decrease ( approximately 50%) in infarct size. Therefore, uncoupling of IGF-I signaling by glutamate may constitute an additional route contributing to excitotoxic neuronal injury. Further work should determine the potential use of PKC inhibitors as a novel therapeutic strategy in ischemia and other excitotoxic insults.

Animals↗
PubMed2003

An in vitro study of the sub-cellular distribution of nicotinic receptors.

Nicotinic and serotoninergic 5HT3 receptors share important sequence identities except for their cytoplasmic loop. Both ends of this loop display conserved 3D helical structures with distinct primary sequences. We decided to check whether these two helices named F and G play a role in the sub-cellular distribution of different nicotinic receptors. We systematically exchanged each helix with the equivalent sequence of neuronal nicotinic and alpha4, beta2 and alpha7 subunits in the functional chimeric alpha7-5HT3 receptor used as a model system. The new chimeras were expressed in vitro in polarized epithelial cells from pig kidney. We quantified synthesis and export of the receptors to the cell surface by measuring alpha-bungarotoxin binding sites. Immunogold labelling was used, at the electron microscope level, to determine the amount of each chimera present at either domain, apical and/or basolateral, of these cells. We noticed that in epithelial cells the majority of alpha-bungarotoxin binding sites remained sequestered in the cytoplasm as already observed in neurons in vivo. The majority of the pentamers present at the cell surface were located at the apical domain. Our results suggest that helix F and G differently regulate assembly and export to the cell surface of alpha-bungarotoxin binding receptors.

Amino Acid Sequence↗
PubMed2001

[Transdermal nitroglycerin versus corticosteroid infiltration for rotator cuff tendinitis].

AIMS: To compare transdermal nitroglycerin (NTG) and corticosteroid infiltration in patients with rotator cuff tendinitis (RCT). DESIGN: Experimental, randomized controlled study. SETTING: Semirural basic health area in the Garraf region of Barcelona province, Spain, with a population of public health service users of 12000. PATIENTS AND METHODS: Patients diagnosed as having RCT of less than 6 weeks' evolution who had not responded to treatment with oral nonsteroid antiinflammatory drugs. The patients were distributed randomly into two groups: a) group A, local infiltration via a posterior approach with a depot corticosteroid and local anesthesia, and b) group B, treated for 3 days with a 5-mg NTC patch. MAIN MEASURES: Age, sex, pain (measured with an analog visual scale) and adverse events. In patients who showed a partial response, treatment was repeated up to 3 times at 15-day intervals. Pain was tested after 7-10 days of treatment. Complete improvement was considered a reduction in pain of more than 5 points on the analog visual scale; partial improvement was considered a reduction of 3-5 points, and treatment failure was recorded when there was no improvement in pain or when there was a decrease of less than 3 points. RESULTS: A total of 48 patients were included; 33 (69%) were women and 15 (31%) were men. Mean age was 61 years. In group A, complete improvement was seen in 19 patients and partial improvement in 3; treatment failed in 2 patients. In group B complete improvement was seen in 5 patients, partial improvement in 5, and failure of treatment in 14. The difference between groups was statistically significant. Adverse events were mild pain at the injection site in 4 patients from group A, and headache in 15 patients from group B, 8 of whom abandoned treatment for this reason. CONCLUSION: Treatment with NTG is not a clear alternative to infiltration of corticosteroids in patients with RCT, because of its lack of effectiveness and because of the greater number of patients who had adverse events that lead them to abandon treatment.

Analgesics↗
PubMed2001

Insulin-like growth factor I potentiates kainate receptors through a phosphatidylinositol 3-kinase dependent pathway.

Neurotrophic factors modulate synaptic plasticity through mechanisms that include regulation of membrane ion channels and neurotransmitter receptors. Recently, it was shown that insulin-like growth factor I (IGF-I) induces depression of AMPA-mediated currents without affecting NMDA-receptor function in neurons. We now report that IGF-I markedly potentiates the kainate-preferring ionotropic glutamate receptor in young cerebellar granule neurons expressing functional kainate-, but not AMPA-mediated currents. Potentiation of kainate responses by IGF-I is blocked by wortmannin, a phosphatidylinositol 3-kinase (P13K) inhibitor, indicating a role for this kinase in the effect of IGF-I. These results reinforce the notion that modulation of ionotropic glutamate receptors are involved in the regulatory actions of IGF-I on neuronal plasticity.

Androstadienes↗
PubMed2001

Phosphatidylinositol-3-OH kinase regulatory subunits are differentially expressed during development of the rat cerebellum.

Recent evidence implicates a central role for PI3K signalling in mediating cell survival during the process of neuronal differentiation. Although PI3K activity is stimulated by a wide range of growth factors and cytokines in different cell lines and tissues, activation of this pathway by insulin-like growth factor I (IGF-I) most likely represents the main survival signal during neuronal differentiation. IGF-I is highly expressed during development of the central nervous system, and thus is a critical factor for the development and maturation of the cerebellum. Upon ligand binding, the IGF-I receptor phosphorylates tyrosine residues in SHC and insulin receptor substrates (IRSs) initiating two main signalling cascades, the MAP kinase and the phosphatidylinositol 3-kinase (PI3K) pathways. Activated PI3K is composed of a catalytic subunit (p110alpha or beta) associated with one of a large family of regulatory subunits (p85alpha, p85beta, p55gamma, p55alpha, and p50alpha). To evaluate the contributions of these various regulatory subunits to neuronal differentiation, we have used antibodies specific for each of the PI3K subunits. Using these antisera, we now demonstrate that PI3K subunits are differentially regulated in cerebellar development, and that the expression level of the p55gamma regulatory subunit reaches a maximum during postnatal development, decreasing thereafter to low levels in the adult cerebellum. Furthermore, our studies reveal that the distribution of the various PI3K regulatory subunits varies during development of the cerebellum. Interestingly, p55gamma is expressed in both glial and neuronal cells; moreover, in Purkinje neurones, this subunit colocalises with the IGF-IR.

Animals↗
PubMed2001

Association of insulin receptor substrate 1 (IRS-1) y895 with Grb-2 mediates the insulin signaling involved in IRS-1-deficient brown adipocyte mitogenesis.

We have recently generated immortalized fetal brown adipocyte cell lines from insulin receptor substrate 1 (IRS-1) knockout mice and demonstrated an impairment in insulin-induced lipid synthesis as compared to wild-type cell lines. In this study, we investigated the consequences of IRS-1 deficiency on mitogenesis in response to insulin. The lack of IRS-1 resulted in the inability of insulin-stimulated IRS-1-deficient brown adipocytes to increase DNA synthesis and enter into S/G2/M phases of the cell cycle. These cells showed a severe impairment in activating mitogen-activated protein kinase kinase (MEK1/2) and p42-p44 mitogen-activated protein kinase (MAPK) upon insulin stimulation. IRS-1-deficient cells also lacked tyrosine phosphorylation of SHC and showed no SHC-Grb-2 association in response to insulin. The mitogenic response to insulin could be partially restored by enhancing IRS-2 tyrosine phosphorylation and its association with Grb-2 by inhibition of phosphatidylinositol 3-kinase activity through a feedback mechanism. Reconstitution of IRS-1-deficient brown adipocytes with wild-type IRS-1 restored insulin-induced IRS-1 and SHC tyrosine phosphorylation and IRS-1-Grb-2, IRS-1-SHC, and SHC-Grb-2 associations, leading to the activation of MAPK and enhancement of DNA synthesis. Reconstitution of IRS-1-deficient brown adipocytes with the IRS-1 mutant Tyr895Phe, which lacks IRS-1-Grb-2 binding, restored SHC-IRS-1 association and SHC-Grb-2 association. However, the lack of IRS-1-Grb-2 association impaired MAPK activation and DNA synthesis in insulin-stimulated mutant cells. These data provide strong evidence for an essential role of IRS-1 and its direct association with Grb-2 in the insulin signaling pathway leading to MAPK activation and mitogenesis in brown adipocytes.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Vitronectin regulates Sonic hedgehog activity during cerebellum development through CREB phosphorylation.

During development of the cerebellum, Sonic hedgehog (SHH) is expressed in migrating and settled Purkinje neurons and is directly responsible for proliferation of granule cell precursors in the external germinal layer. We have previously demonstrated that SHH interacts with vitronectin in the differentiation of spinal motor neurons. Here, we analysed whether similar interactions between SHH and extracellular matrix glycoproteins regulate subsequent steps of granule cell development. Laminins and their integrin receptor subunit alpha6 accumulate in the outer most external germinal layer where proliferation of granule cell precursors is maximal. Consistent with this expression pattern, laminin significantly increases SHH-induced proliferation in primary cultures of cerebellar granule cells. Vitronectin and its integrin receptor subunits alpha(v) are expressed in the inner part of the external germinal layer where granule cell precursors exit the cell cycle and commence differentiation. In cultures, vitronectin is able to overcome SHH-induced proliferation, thus allowing granule cell differentiation. Our studies indicate that the pathway in granule cell precursors responsible for the conversion of a proliferative SHH-mediated response to a differentiation signal depends on CREB. Vitronectin stimulates phosphorylation of cyclic-AMP responsive element-binding protein (CREB), and over-expression of CREB is sufficient to induce granule cell differentiation in the presence of SHH. Taken together, these data suggest that granule neuron differentiation is regulated by the vitronectin-induced phosphorylation of CREB, a critical event that terminates SHH-mediated proliferation and permits the differentiation program to proceed in these cells.

Animals↗
PubMed2000

Insulin-like growth factor-I stimulates dephosphorylation of ikappa B through the serine phosphatase calcineurin (protein phosphatase 2B).

Astrocytes represent the most abundant cell type of the adult nervous system. Under normal conditions, astrocytes participate in neuronal feeding and detoxification. However, following brain injury, local increases in inflammatory cytokines trigger a reactive phenotype in astrocytes during which these cells produce their own inflammatory cytokines and neurotoxic free radicals. Indeed, progression of this inflammatory reaction is responsible for most neurological damage associated with brain trauma. Insulin-like growth factor-I (IGF-I) protects neurons against a variety of brain pathologies associated with glial overproduction of proinflammatory cytokines. Here, we demonstrate that in astrocyte cultures IGF-I regulates NFkappaB, a transcription factor known to play a key role in the inflammatory reaction. IGF-I induces a site-specific dephosphorylation of IkappaBalpha (phospho-Ser(32)) in astrocytes. Moreover, IGF-I-mediated dephosphorylation of IkappaBalpha protects this molecule from tumor necrosis factor alpha (TNFalpha)-stimulated degradation; therefore, IGF-I also inhibits the nuclear translocation of NFkappaB (p65) induced by TNFalpha exposure. Finally, we show that dephosphorylation of IkappaBalpha by IGF-I pathways requires activation of calcineurin. Activation of this phosphatase is independent of phosphatidylinositol 3-kinase and mitogen-activated protein kinase. Thus, these data suggest that the therapeutic benefits associated with IGF-I treatment of brain injury are derived from both its positive effects on neuronal survival and inhibition of the glial inflammatory reaction.

Animals↗
PubMed2000

Ring chromosome 7 and sacral agenesis.

A ring chromosome 7 was found in a 19-month-old girl with microcephaly, growth and developmental delay, multiple angiomas, and partial sacral agenesis. Absent sacrum is a frequent finding in patients with 7q terminal deletions; in fact, genes involved in the sacral agenesis are localized in 7q36. However, this anomaly was not described previously in patients with a ring chromosome 7. High resolution G-banding chromosome and fluorescence in situ hybridization (FISH) demonstrated that our patient lost this region during ring formation.

Chromosome Aberrations↗
PubMed2000

Abnormal lipid peroxidation in patients with sleep apnoea.

The prevalence of cardiovascular diseases is increased in patients with the obstructive sleep apnoea syndrome (OSAS). The fall and rise of arterial oxygenation that follows each apnoea may increase lipid peroxidation and contributes to explaining this association. In the present study, the authors determined lipid peroxidation in patients with OSAS and the effect of treatment with continuous positive airway pressure (CPAP). Fourteen male patients with severe OSAS (59+/-5 apnoea x h(-1)) (+/-SEM) and 13 healthy nonsmoking, male volunteers of similar age were studied. Patients were studied at diagnosis and after treatment with CPAP for more than 1 yr (>4 h x night(-1)). A venous blood sample was obtained early in the morning after fasting all night. In patients with OSAS, a sample before and during sleep was also obtained. Low density lipoprotein (LDL) particles were isolated by sequential ultracentrifugation. Their level of oxidation was determined by the thiobarbituric acid assay (TBARs), and their susceptibility to oxidation by the lag phase measurement. Patients with OSAS showed higher TBARs (28.1+/-2.8 versus 20.0+/-1.8 nmol x malondialdehyde x mgLDL protein(-1), p=0.02) and shorter lag phase values (83.8+/-3.4 versus 99.7+/-3.4 min, p=0.005) than controls. These differences were not due to the smoking status of the patient. Likewise, these values did not change significantly throughout the night yet, the lag phase value was significantly improved by treatment with CPAP (124.9+/-8.5 min; p<0.001). These results indicate that obstructive sleep apnoea syndrome is associated with abnormal lipid peroxidation and that this is improved by chronic use of Continuous positive airway pressure. These results can contribute towards explaining the high prevalence of cardiovascular diseases seen in Obstructive sleep apnoea syndrome.

Adult↗
PubMed2000

Sonic hedgehog synergizes with the extracellular matrix protein vitronectin to induce spinal motor neuron differentiation.

Patterning of the vertebrate neural tube depends on intercellular signals emanating from sources such as the notochord and the floor plate. The secreted protein Sonic hedgehog and the extracellular matrix protein Vitronectin are both expressed in these signalling centres and have both been implicated in the generation of ventral neurons. The proteolytic processing of Sonic hedgehog is fundamental for its signalling properties. This processing generates two secreted peptides with all the inducing activity of Shh residing in the highly conserved 19 kDa amino-terminal peptide (N-Shh). Here we show that Vitronectin is also proteolitically processed in the embryonic chick notochord, floor plate and ventral neural tube and that this processing is spatiotemporally correlated with the generation of motor neurons. The processing of Vitronectin produces two fragments of 54 kDa and 45 kDa, as previously described for Vitronectin isolated from chick yolk. The 45 kDa fragment lacks the heparin-binding domain and the integrin-binding domain, RGD, present in the non-processed Vitronectin glycoprotein. Here we show that N-Shh binds to the three forms of Vitronectin (70, 54 and 45 kDa) isolated from embryonic tissue, although is preferentially associated with the 45 kDa form. Furthermore, in cultures of dissociated neuroepithelial cells, the combined addition of N-Shh and Vitronectin significantly increases the extent of motor neuron differentiation, as compared to the low or absent inducing capabilities of either N-Shh or Vitronectin alone. Thus, we conclude that the differentiation of motor neurons is enhanced by the synergistic action of N-Shh and Vitronectin, and that Vitronectin may be necessary for the proper presentation of the morphogen N-Shh to one of its target cells, the differentiating motor neurons.

Animals↗