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Biomedical subjects

M Tessari

Publications and source records attributed to M Tessari.

At least 19 recordsLinked to original sources
PubMed2005

Selective down-regulation of [(125)I]Y0-alpha-conotoxin MII binding in rat mesostriatal dopamine pathway following continuous infusion of nicotine.

Prolonged exposure to nicotine, as occurs in smokers, results in up-regulation of all the neuronal nicotinic acetylcholine receptor subtypes studied so far, the only differences residing in the extent and time course of the up-regulation. alpha6beta2*-Nicotinic acetylcholine receptors are selectively enriched in the mesostriatal dopaminergic system and may play a crucial role in nicotine dependence. Here we show that chronic nicotine treatment (3mg/kg/day for two weeks, via s.c. osmotic minipumps) caused a significant decrease (36% on average) in the binding of [(125)I]Y(0)-alpha-conotoxin MII (a selective ligand for alpha6beta2*-nicotinic acetylcholine receptors in this system) to all the five regions of the rat dopaminergic pathway analyzed in this study. After one week of withdrawal, binding was still lower than control in striatal terminal regions (namely the caudate putamen and the accumbens shell and core). In somatodendritic regions (the ventral tegmental area and the substantia nigra) the decrease was significant at the end of the treatment and recovered within one day of withdrawal. This effect was not due to displacement of [(125)I]Y(0)-alpha-conotoxin MII binding by residual nicotine. In fact the binding was not changed by 565 ng/g nicotine (obtained with a single injection of nicotine), a concentration much higher than that found in the brain of rats chronically treated with nicotine (240 ng/g). In addition, consistent with previous studies reporting an up-regulation of other subtypes of nicotinic acetylcholine receptors, we found that nicotine exposure significantly increased (40% on average) the binding of [(125)I]epibatidine (a non-selective agonist at most neuronal heteromeric nicotinic acetylcholine receptors) in three up to five regions containing only alpha-conotoxin MII-insensitive [(125)I]epibatidine binding sites, namely the primary motor, somatosensory and auditory cortices. In conclusion, this work is the first to demonstrate that alpha6beta2*-nicotinic acetylcholine receptors, unique within the nicotinic acetylcholine receptor family, are down-regulated following chronic nicotine treatment in rat dopaminergic mesostriatal pathway, a finding that may shed new light in the complex mechanisms of nicotine dependence.

Animals↗
PubMed2001

Nicotine self-administration and withdrawal: modulation of anxiety in the social interaction test in rats.

RATIONALE: Most smokers report smoking has an anxiolytic effect, which may contribute to nicotine dependence. OBJECTIVE: To examine effects in the social interaction test (SI) of anxiety after 4 weeks' self-administered nicotine (15 infusions of 0.03 mg/kg, totalling 0.45 mg/kg per day), and after 24 and 72 h of withdrawal. The effect of exposure to the operant chamber on withdrawal responses was also examined. METHODS: Animals were trained to self-administer saline or nicotine and after 4 weeks they were tested in SI after their daily self-administration session. Animals were retested after 24 and 72 h withdrawal, when they were either taken directly from the home cage or were tested 5 min after a 30-min exposure to the operant chamber. RESULTS: Compared with the saline control group, the animals that had been self-administering nicotine for 4 weeks showed decreased social interaction with no decrease in locomotor activity, indicating a significant anxiogenic effect of the nicotine infusions. There was no change in social interaction after 24 and 72 h withdrawal from chronic nicotine, regardless of whether or not the rats were exposed to the operant chamber just prior to being tested. CONCLUSIONS: Nicotine self-administration is not maintained because of its anxiolytic effect, but despite, or because of, its anxiogenic effect. There was no evidence of an anxiogenic response after either 24 or 72 h of withdrawal and thus increased anxiety on withdrawal from nicotine does not seem to contribute to nicotine self-administration.

Animals↗
PubMed2000

A novel experiment for the quantitative measurement of CSA(1H(N))/CSA(15N) cross-correlated relaxation in 15N-labeled proteins.

An experiment is presented which allows for the quantitative measurement of the relaxation interference between the 1H(N) CSA and 15N CSA interactions in 15N labeled proteins. A constant-time buildup scheme is used to measure the differential relaxation rate, eta, between double-quantum (DQ) and zero-quantum (ZQ) 1H(N)-15N coherences. The CSA/CSA experiment was recorded at three different Bo field strengths. The CSA(1H(N))/CSA(15N) cross-correlation rate was obtained from the linear fit of the measured rate, eta, versus Bo2 for 77 residues of the EH2 domain from mouse Eps15.

Adaptor Proteins, Signal Transducing↗
PubMed2000

The Mad1-Sin3B interaction involves a novel helical fold.

Sin3A or Sin3B are components of a corepressor complex that mediates repression by transcription factors such as the helix-loop-helix proteins Mad and Mxi. Members of the Mad/Mxi family of repressors play important roles in the transition between proliferation and differentiation by down-regulating the expression of genes that are activated by the proto-oncogene product Myc. Here, we report the solution structure of the second paired amphipathic helix (PAH) domain (PAH2) of Sin3B in complex with a peptide comprising the N-terminal region of Mad1. This complex exhibits a novel interaction fold for which we propose the name 'wedged helical bundle'. Four alpha-helices of PAH2 form a hydrophobic cleft that accommodates an amphipathic Mad1 alpha-helix. Our data further show that, upon binding Mad1, secondary structure elements of PAH2 are stabilized. The PAH2-Mad1 structure provides the basis for determining the principles of protein interaction and selectivity involving PAH domains.

Amino Acid Sequence↗
PubMed1999

The EH1 domain of Eps15 is structurally classified as a member of the S100 subclass of EF-hand-containing proteins.

The Eps15 homology (EH) domain is a protein-protein interaction module that binds to proteins containing the asparagine-proline-phenylalanine (NPF) or tryptophan/phenylalanine-tryptophan (W/FW) motif. EH domain-containing proteins serve important roles in signaling and processes connected to transport, protein sorting, and organization of subcellular structure. Here, we report the solution structure of the apo form of the EH1 domain of mouse Eps15, as determined by high-resolution multidimensional heteronuclear NMR spectroscopy. The polypeptide folds into six alpha-helices and a short antiparallel beta-sheet. Additionally, it contains a long, structured, topologically unique C-terminal loop. Helices 2-5 form two EF-hand motifs. Structural similarity and Ca(2+) binding properties lead to classification of the EH1 domain as a member of the S100 subclass of EF-hand-containing proteins, albeit with a unique set of interhelical angles. Binding studies using an eight-residue NPF-containing peptide derived from RAB, the cellular cofactor of the HIV Rev protein, show a hydrophobic peptide-binding pocket formed by conserved tryptophan and leucine residues.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Heteronuclear NMR studies of the combined Src homology domains 2 and 3 of pp60 c-Src: effects of phosphopeptide binding.

The results of heteronuclear NMR studies on the combined Src homology domains 2 and 3 (SH3-SH2) of pp60 c-Src are presented. Resonance assignments were obtained using heteronuclear triple-resonance experiments in conjunction with 15N-separated nuclear Overhauser effect spectroscopy (NOESY) data. A modified three-dimensional 13CO-15N-1H spectral correlation experiment [(HACA)CO(CA)-NH] with improved sensitivity is presented that provided additional sequential information and resolved several ambiguities. Chemical shifts and sequential- and medium-range NOE cross peaks indicate that the structures of both the SH3 and SH2 portions of the polypeptide are very similar to those of the isolated SH3 and SH2 domains. Binding of a high-affinity phosphopeptide, EPQpYEEIPIYL, induces large chemical shift changes at several locations in the SH2 domain. Comparison with known results for peptide binding to SH2 domains shows that the residues displaying the largest effects are all involved in peptide binding or undergo significant conformational changes upon binding. However, subtle changes of both 1H and 15N chemical shifts are observed for residues within the SH3 domain and the connecting linker region, indicating possible cross-domain communication.

Amino Acid Sequence↗
PubMed1997

Common neural substrates for the addictive properties of nicotine and cocaine.

Regional brain activation was assessed by mapping of Fos-related protein expression in rats trained to self-administration of intravenous nicotine and cocaine. Both drugs produced specific overlapping patterns of activation in the shell and the core of the nucleus accumbens, medial prefrontal cortex, and medial caudate areas, but not in the amygdala. Thus, the reinforcing properties of cocaine and nicotine map on selected structures of the terminal fields of the mesocorticolimbic dopamine system, supporting the idea that common substrates for these addictive drugs exist.

Amygdala↗
PubMed1996

Developmental and plasticity-related differential expression of two SNAP-25 isoforms in the rat brain.

In this article we study the relationship between the expression pattern of two recently identified isoforms of the 25-kD synaptosomal-associated protein (SNAP-25a and SNAP-25b) and the morphological changes inherent to neuronal plasticity during development and kainic acid treatment. SNAP-25 has been involved in vescicle fusion in the nerve terminal, and most likely participates in different membrane fusion-related processes, such as those involved in neurotransmitter release and axonal growth. In the adult brain, SNAP-25b expression exceeded SNAP-25a in distribution and intensity, being present in most brain structures . Moderate or high levels of SNAP-25a hybridization signal were found in neurons of the olfactory bulb, the layer Va of the frontal and parietal cortices, the piriform cortex, the subiculum and the hippocampal CA4 field, the substantia nigra/pars compacta, and the pineal gland, partially overlapping SNAP-25b mRNA distribution. In restricted regions of cerebral cortex, thalamus, mammillary bodies, substantia nigra, and pineal glands the two isoforms were distributed in reciprocal fashion. During development SNAP-25a mRNA was the predominant isoform, whereas SNAP-25b expression increased postnatally. The early expression of SNAP-25a in the embryo and the decrease after P21 is suggestive of a potential involvement of this isoform in axonal growth and/or synaptogenesis. This conclusion is indirectly supported by the observation that SNAP-25a mRNA, but not SNAP-25b mRNA, was upregulated in the granule cells of the adult dentate gyrus 48 hours after kainate-induced neurotoxic damage of the hippocampal CA3-CA4 regions. Increase of SNAP-25 immunoreactivity was observed as early as 4 days after kainate injection within the mossy fiber terminals of the CA3 region, and in the newly formed mossy fiber aberrant terminals of the supragranular layer. These data suggest an isoform-specific role of SNAP-25 in neural plasticity.

Animals↗
PubMed1996

Nicotine reinstatement of nicotine self-administration after long-term extinction.

The effect of non-contingent priming injections of nicotine on the reinstatement of drug-seeking behaviour was studied in rats following the long-term extinction of nicotine self-administration. Male rats were trained to lever press for 0.03 mg/kg per infusion of intravenous nicotine. Nicotine maintained a robust self-administration behaviour (11.5 +/- 1.2; mean+/-SEM infusions/1-h session). When nicotine availability was discontinued, and only a non-contingent saline infusion was presented to the experimental subjects at the beginning of each daily session, responding for the drug-paired lever decreased to low values. After 4-13 sessions, responding extinguished. During this "extinction" period, non-contingent priming infusions of nicotine 0.001, 0.003, 0.01 or 0.03 mg/kg per infusion induced reinstatement of responding for the drug-paired lever. The increased responding, compared with the corresponding previous day on saline, was observed at all four nicotine doses but was not statistically significant for the higher priming dose (0.03 mg/kg per infusion). These preliminary results indicate that nicotine priming is able to induce reinstatement of drug-seeking behaviour in rats similarly to other reinforcing drugs. The present findings show analogies with similar phenomena described in ex-smokers and support the addictive role of nicotine in tobacco smoking.

Animals↗
PubMed1996

The reinforcing properties of nicotine are associated with a specific patterning of c-fos expression in the rat brain.

Rats were trained for nicotine intravenous infusions in a self-administration paradigm. The effect of nicotine self-administration on regional brain activity was studied by mapping changes of c-fos expression. Specific nicotine effects were determine by comparing the patterning of Fos-like immunoreactivity (Fos-Ll) in nicotine self-administering rats with that in three different control groups. Controls included rats exposed to the same manipulation as nicotine self-administering rats who received intravenous saline instead of nicotine. In addition, two groups of untrained sham-operated rats exposed daily to the same operant boxes were included: one group had the same food restriction used in the operant training, the other was fed ad libitum. Nicotine self-administration, exposure to saline and food restriction increased Fos-Ll in 43, 33 and three brain regions, respectively, when compared with the control group fed ad libitum. Computer-assisted image analysis of Fos-Ll profiles performed on 16 relevant limbic and sensory structures showed that in saline-treated rats a significant (P < 0.01) increase of Fos-Ll profiles was observed in medial prefrontal cortex, lateral septum, core and ventral shell of nucleus accumbens, claustrum, amygdaloid nuclei, paraventricular thalamic nucleus and lateral geniculate nucleus. A significant (P < 0.01) further increase produced by nicotine was found in medial prefrontal cortex and ventral shell of nucleus accumbens. Interestingly, cingulate and piriform cortex, superior colliculus and medial terminal nucleus of the accessory optic tract were specifically activated by nicotine but not saline. These results show that nicotine self-administration activates sensory structures, as well as limbic structures involved in natural rewarding pathways. The results suggest the involvement of restricted terminal regions of the mesocorticolimbic dopaminergic system in the maintenance of nicotine self-administration.

Analysis of Variance↗
PubMed1995

Solution structure of porcine pancreatic phospholipase A2.

The lipolytic enzyme phospholipase A2 (PLA2) is involved in the degradation of high-molecular weight phospholipid aggregates in vivo. The enzyme has very high catalytic activities on aggregated substrates compared with monomeric substrates, a phenomenon called interfacial activation. Crystal structures of PLA2s in the absence and presence of inhibitors are identical, from which it has been concluded that enzymatic conformational changes do not play a role in the mechanism of interfacial activation. The high-resolution NMR structure of porcine pancreatic PLA2 free in solution was determined with heteronuclear multidimensional NMR methodology using doubly labeled 13C, 15N-labeled protein. The solution structure of PLA2 shows important deviations from the crystal structure. In the NMR structure the Ala1 alpha-amino group is disordered and the hydrogen bonding network involving the N-terminus and the active site is incomplete. The disorder observed for the N-terminal region of PLA2 in the solution structure could be related to the low activity of the enzyme towards monomeric substrates. The NMR structure of PLA2 suggests, in contrast to the crystallographic work, that conformational changes do play a role in the interfacial activation of this enzyme.

Animals↗
PubMed1995

Solution structure of porcine pancreatic phospholipase A2 complexed with micelles and a competitive inhibitor.

The three-dimensional structure of porcine pancreatic PLA2 (PLA2), present in a 40 kDa ternary complex with micelles and a competitive inhibitor, has been determined using multidimensional heteronuclear NMR spectroscopy. The structure of the protein (124 residues) is based on 1854 constraints, comprising 1792 distance and 62 phi torsion angle constraints. A total of 18 structures was calculated using a combined approach of distance geometry and restrained molecular dynamics. The atomic rms distribution about the mean coordinate positions for residues 1-62 and 72-124 is 0.75 +/- 0.09 A for the backbone atoms and 1.14 +/- 0.10 A for all atoms. The rms difference between the averaged minimized NMR structures of the free PLA2 and PLA2 in the ternary complex is 3.5 A for the backbone atoms and 4.0 A for all atoms. Large differences occur for the calcium-binding loop and the surface loop from residues 62 through 72. The most important difference is found for the first three residues of the N-terminal alpha-helix. Whereas free in solution Ala1, Leu2 and Trp3 are disordered, with the alpha-helical conformation with the alpha-amino group buried inside the protein. As a consequence, the important conserved hydrogen bonding network which is also seen in the crystal structures is present only in the ternary complex, but not in free PLA2. Thus, the NMR structure of the N-terminal region (as well as the calcium-binding loop and the surface loop) of PLA2 in the ternary complex resembles that of the crystal structure. Comparison of the NMR structures of the free enzyme and the enzyme in the ternary complex indicates that conformational changes play a role in the interfacial activation of PLA2.

Animals↗
PubMed1995

Nicotine reinforcement in rats with histories of cocaine self-administration.

Few reports have described conditions under which nicotine self-administration occurs in rats. In this study, rats which initially lever pressed for cocaine infusion (0.05 mg/kg) during 1 h experimental sessions continued to obtain similar infusion numbers when nicotine (0.03 mg/kg) was available. When saline was substituted for nicotine, infusions decreased from 11.8 +/- 4.5/h to 5.4 +/- 1.1/h but returned to pre-saline levels when it was reintroduced (12.0 +/- 5.4/h). These results indicate that nicotine can serve as a positive reinforcer for rats under the historical and schedule conditions described.

Animals↗
PubMed1995

NMR structures of phospholipase A2 reveal conformational changes during interfacial activation.

It has long been proposed that the higher activity of phospholipase A2 (PLA2) for substrates presented as multimolecular aggregates compared to dispersed molecules (interfacial activation) arises due to a conformational change in the enzyme. X-ray studies have, however, failed to identify any such change. Here we report the solution structures of porcine pancreatic PLA2 both free and as a ternary complex with micelles and a competitive inhibitor. Important differences between these structures indicate that conformational changes may play an important role in the mechanism of interfacial activation in PLA2s.

Amino Acid Sequence↗
PubMed1993

Conformation and interactions of uteroglobin fragments 4-14 and 49-65 in aqueous solution containing surfactant micelles.

The conformation of two fragments of rabbit uteroglobin is described. The peptides are PRFAHVIENLL and PQTTRENIMKLTEKIVK, corresponding to helices I and IV in the crystal structure. CD shows that both peptides interact with sodium dodecyl sulfate (SDS) micelles and change their conformation to an alpha-helix. The helical content estimated from the CD band at 222 nm is about 40% in each peptide. Surface tension measurements show that both peptides lower the critical micellar concentration (cmc) of SDS, with a more dramatic effect in the case of helix I. This peptide by itself acts as a surfactant, and is able to interact with SDS even below the observed cmc, forming beta aggregates. Proton magnetic resonance (1H-nmr) suggests that flexible helices are present. The longest helical stretches compatible with 1H-nmr data extend from Phe6 to Leu14 for helix I and from Arg53 to Ile63 for helix IV.

Amino Acid Sequence↗