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A Ambrosini

Publications and source records attributed to A Ambrosini.

At least 55 records · Page 3Linked to original sources
PubMed1997

Topography of spatially enhanced human short-latency somatosensory evoked potentials.

In the present study modern high resolution electroencephalography (EEG) was used to spatially enhance human median nerve short-latency somatosensory evoked potentials (SEPs). It was shown that the spatially enhanced N30 consisted of two frontal subcomponents, one located in the frontal-lateral area of the scalp, the other located in the frontal-mesial area. Both of these subcomponents were most reduced in amplitude (or disappeared) during concomitant hand movement ipsilateral to the stimulus, but were differentially influenced by executed contralateral movement and imagined ipsilateral movement. These results support the hypothesis of an involvement of the frontal-mesial cortex (including the supplementary motor area) in the generation of the frontal N30.

Brain↗
PubMed1996

Pupillometric evaluation and analysis of light reflex in healthy subjects as a tool to study autonomic nervous system changes with aging.

To assess the relationships between aging and autonomic control of pupillary functions, TV-pupillometry and light reflex evaluation were performed in 52 healthy volunteers in the age range 15-75 years, grouped into four age classes (group 1: 15-29 years, Group 2: 30-44 years, Group 3: 45-59 years, Group 4: 60-75 years). Baseline light pupil diameter was found to be age-dependent, together with light reflex contraction velocity, which presented a linear correlation with age. Light reflex amplitude and half-redilatation velocity were reduced in older subjects, but presented only a weak linear correlation with age, while latency, contraction time and half-redilatation time percent of secondary dilatation and redilatation at 5 seconds did not show significant changes with age. These results confirm that there are important age-dependent changes in the mechanisms involved in pupillary autonomic functions, regarding both sympathetic and parasympathetic components. These changes appear to be easily detectable by making use of a sensitive and non-invasive technique such as TV-pupillometry.

Adolescent↗
PubMed1996

Cyclic GMP inhibition of metabotropic glutamate receptor-induced phosphoinositide hydrolysis in mesencephalic neurons.

The effect of cGMP on metabotropic glutamate receptor-induced stimulation of phosphoinositide hydrolysis in mesencephalic neuronal cultures was evaluated by cell incubation with the stable analogue dibutyryl-cGMP (10 microM). A complete blockade of (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid- or quisqualate-induced inositol phosphate formation was observed. Ionotropic glutamate receptors in mesencephalic neurons activate cGMP formation and, through this intracellular messenger, they might control mGluR activity.

Animals↗
PubMed1996

A unitary non-NMDA receptor short subunit from Xenopus: DNA cloning and expression.

A high-affinity homomeric, non-NMDA glutamate receptor was previously purified from the amphibian Xenopus laevis. We have obtained nine peptide sequences from its subunit, applied in cDNA cloning. The cDNA encodes a subunit (XenU1) containing all nine sequences. The 51,600-dalton mature subunit has four hydrophobic domains homologous to the four in the C-terminal half of mammalian non-NMDA receptor subunits. Transient expression in COS cells showed 1:1 binding (at Bmax) of [3H] kainate (KD = 9.1 nM) and of [3H] AMPA (alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid; KD = 62 nM). The competitive binding series domoate > kainate > AMPA > NBQX > glutamate was established (where NBQX is 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo (f) quinoxaline). Each agonist shows the same KI value against [3H] kainate and [3H] AMPA binding, suggesting a common agonist site, but two conformations thereof are distinguishable by their different affinities for the antagonist NBQX and by the allosteric effect of thiocyanate anion (greatly potentiating AMPA binding, inert with kainate). XenU1 is exceptional among non-NMDA receptor subunits because it lacks most of the large N-terminal domain found in those of mammals and it has high affinity for both kainate and AMPA. It differs from the similarly-short "kainate-binding proteins" (KBPs), in binding AMPA and in forming glutamate receptor channels when the native protein is reconstituted. Moreover, whereas a full-length kainate receptor of mammals, GluR6, is shown here (from a partial cDNA sequence) to exist also in Xenopus, with approximately 97% sequence identity to rat GluR6, XenU1 is much less homologous to any rat kainate or AMPA receptor and also to the KBPs, even from another amphibian, Rana. Another difference is that a potential concensus sequence ("EF hand") for Ca2+ binding is present in the N-terminal domain of XenU1, but not in the chicken (glial) KBP. XenU1 is deduced to be in a new family of non-NMDA receptors.

Amino Acid Sequence↗
PubMed1995

Metabotropic glutamate receptors negatively coupled to adenylate cyclase inhibit N-methyl-D-aspartate receptor activity and prevent neurotoxicity in mesencephalic neurons in vitro.

The functional effects of G protein-linked glutamate receptor activation have been studied in mouse mesencephalic neurons in vitro. We have been able to identify two receptor classes, one linked to phosphoinositide hydrolysis and another that inhibits adenylate cyclase. The agonist (1S,3R)-aminocyclopentane-1,3-dicarboxylate (ACPD) affected the two responses with similar potency (EC50 = 2 and 7 microM, respectively). In contrast, (2S,3S,4S)-alpha-(carboxycyclopropyl)glycine selectively decreased adenylate cyclase activity (EC50 = 150 nM), without interfering with the phosphoinositide pathway. Activation of ion channel-linked glutamate receptors in mesencephalic neurons leads to cGMP formation. In this study, we demonstrate that cell pretreatment with ACPD or (2S,3S,4S)-alpha-(carboxycyclopropyl)glycine prevented, in a dose-dependent fashion, N-methyl-D-aspartate (NMDA)-induced cGMP formation but not the kainate-stimulated response. The pharmacological profile suggests that receptors that are negatively coupled to adenylate cyclase are responsible for this effect. Coexposure of neurons to ACPD and Ba2+, a K+ channel blocker, counteracted the ACPD-induced blockade of NMDA receptors, suggesting that activation of K+ conductances could be involved in the post-transduction events triggered by metabotropic receptors in the mesencephalon. Neuronal treatment with NMDA for 10 min caused a reduction in mitochondrial activity. Direct inhibition of nitric oxide synthase with the inhibitor NG-nitro-L-arginine or removal of extracellular nitric oxide with reduced hemoglobin did not prevent this metabolic impairment, thus excluding a role for nitric oxide in this test for excitotoxicity. On the contrary, the mitochondrial function was maintained when neurons exposed to NMDA were preincubated with metabotropic receptor agonists. To summarize, our results suggest that metabotropic receptors that are negatively coupled to adenylate cyclase exert modulatory control specifically on NMDA receptor activity. This event could also contribute to the reduction of neurotoxic effects due to NMDA receptor hyperactivity.

Adenylyl Cyclase Inhibitors↗
PubMed1994

The effect of N-acyl ethanolamines on phosphatidylethanolamine phase transitions studied by laurdan generalised polarisation.

The effect of N-lauroylethanolamine (N-LEA) and N-oleoylethanolamine (N-OEA) on the thermal behaviour of fully hydrated egg phosphatidylethanolamine (TPE) was investigated by the steady-state fluorescence of 2-dimethylamino-(6-lauroyl)-naphtalene (laurdan) and 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). The parameter generalised polarisation (GP), calculated by exciting laurdan at 340 and 410 nm, revealed the gel to liquid crystalline lamellar (L alpha) as well as the L alpha to inverse hexagonal (HII) phase transitions of TPE. The L alpha to HII phase transition was not detected in TPE/N-OEA system, probably because of the formation of an intermediate Q224 cubic phase. The formation of Q224 phase in TPE/N-OEA and TPE/N-LEA systems was previously demonstrated by X-ray diffraction, but neither laurdan generalised polarisation nor TMA-DPH steady-state fluorescence anisotropy measurements revealed the presence of this phase. It is suggested that the lack of detection of the cubic phase is probably due to the similarity in dynamic characteristics and hydration levels of phospholipid headgroups in the bilayer and cubic phases.

2-Naphthylamine↗
PubMed1993

Glutamate receptor-induced cyclic GMP formation in primary cultures of mesencephalic neurons.

The link between excitatory amino acid (EAA) receptor activation and the nitric oxide/cyclic GMP intracellular pathway was investigated in primary cultures of mouse mesencephalic neurons. L-glutamate, N-methyl-D-aspartate (NMDA), kainate (KA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate were able to induce cyclic GMP formation. NMDA and KA were the most effective and their action could be blocked, besides the specific antagonists 2-amino-5-phosphonopentanoate and 6-cyano-7-nitroquinoxaline-2,3-dione, by NG-nitro-L-arginine, a nitric oxide synthase inhibitor. This finding demonstrates that nitric oxide generation is necessary for EAA-induced cyclic GMP formation and provides indirect evidence for nitric oxide synthase activity in mesencephalic neurons. GMP increase induced by NMDA or KA was potentiated by carbachol or by exogenous activation of protein kinase C with phorbol esters. A clarification of the early intracellular events that follow EAA receptor activation may be important for understanding the physiological and excitotoxic events linked to these receptors in the mesencephalon.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1993

N-acylethanolamines as membrane topological stress compromising agents.

The effect of different N-acylethanolamines on the phase behaviour of fully hydrated egg phosphatidylethanolamines is reported. In particular, in the presence of N-acylethanolamines, the transition from the liquid-crystalline lamellar (L alpha) to the inverse hexagonal (HII) phase is observed at higher temperature with respect to the temperature transition of pure phosphatidylethanolamine. Moreover, in correspondence of this transition, an intermediate Q224 (space group Pn3m) cubic phase has been detected. Since the structure of this cubic phase presents unique topological analogies with the lipid bilayer organization, these data suggest the possible role of N-acylethanolamines in stabilizing the biological membranes by avoiding a sudden change to a non-bilayer phase in those tissues which undergo stress conditions.

Calorimetry, Differential Scanning↗
PubMed1993

Effect of N-acylethanolamines with different acyl-chains on DPPC multilamellar liposomes.

The influence of N-acylethanolamines with different acyl-chains on the physico-chemical state of neutral phospholipids was investigated using dipalmitoyl phosphatidylcholine (DPPC) multilamellar liposomes. The thermal dependence of steady state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) and its charged derivative 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) was recorded. The N-acylethanolamines modified the DPPC phase transition temperature and broadened the transition temperature range in different ways depending on the N-acylethanolamines acyl chain characteristics. Our data suggest that the N-acylethanolamine acyl chain length and unsaturation play an important role in the interaction of these compounds with model membranes. The results show that long-chain-N-acylethanolamines interact largely with DPPC model membranes while a similar effect is not observed for the short ones.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1992

Purified unitary kainate/alpha-amino-3-hydroxy-5-methylisooxazole-propionate (AMPA) and kainate/AMPA/N-methyl-D-aspartate receptors with interchangeable subunits.

We have purified and characterized two vertebrate excitatory amino acid ionotropic receptors from the Xenopus central nervous system. Each is a unitary receptor (i.e., having more than one class of excitatory amino acid agonist specificity within one protein oligomer). The first is a unitary non-N-methyl-D-aspartate (non-NMDA) receptor and the second is a unitary NMDA/non-NMDA receptor. The specific agonist-activated channel activity and pharmacology of each type were recognized by patch-clamping lipid bilayers in which the isolated protein was reconstituted. In the second case, the NMDA and the non-NMDA sites could not be physically separated and exhibited functional interaction. Parallel evidence for this was obtained when poly(A) RNA from Xenopus brain was translated in oocytes: a noncompetitive inhibition of the response to L-kainate is produced by NMDA to a maximum depression of 30% at 1 mM NMDA. Each isolated oligomer contains 42-kDa subunits of the non-NMDA ligand binding type, but the second type has an additional NMDA-receptor-specific 100-kDa subunit. Thus, a subunit-exchange hypothesis can account for the known multiplicity of excitatory amino acid receptor types.

Animals↗
PubMed1992

[Role of endoscopy in the diagnosis and follow-up of bleeding lesions of the colon].

Considering the results of the centre of colonoscopy we can draw some considerations about the irreplaceable role of endoscopy in the diagnosis of bleeding colonic lesions and about its greater security in comparison with the traditional radiologic exam, about its possibilities to be sometimes resolutive even for the therapy and about its great importance in the follow-up of patients treated for lesions of this kind.

Angiodysplasia↗
PubMed1991

AMPA and kainate-operated channels reconstituted in artificial bilayers.

Cationic channels which can be activated by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) and kainate play a key role in the generation of excitatory postsynaptic potentials in the brain of all vertebrates. On a protein carrying binding sites for both these ligands, affinity-purified from the Xenopus nervous system, electrical measurements have been performed to investigate its functional properties after the pure complex had been incorporated into planar lipid bilayers. Domoate, AMPA or kainate added to the reconstituted protein activated cationic channels, which were blocked by typical antagonists for this neurotransmitter system. These data suggest that the reconstituted protein is an ionotropic receptor of the unitary non-NMDA subtype.

Animals↗
PubMed1991

Effect of the fungicides tributyltin acetate and tributyltin chloride on multilamellar liposomes: fluorescence studies.

The influence of tri-n-butyltin acetate (TBTA) and tri-n-butyltin chloride (TBTC) on the physico-chemical state of charged and neutral phospholipids was investigated using multilamellar liposomes. The thermal dependence of steady state fluorescence polarization of DPH and its charged derivative TMA-DPH was recorded. The two fungicides lowered DPPC phase transition temperature and broadened the temperature range of the transition in different ways. The effects were concentration-dependent. The results show that TBTC interacts more effectively with DPPC model membranes rather than TBTA. Moreover, TBTC broadens and shifts the main phase transition (Tm) more effectively in DPPC rather than in DMPC liposomes. Below Tm, TBTC decreases fluorescence polarization (P) in all phospholipids used. Above Tm P is almost constant in phospholipids with saturated acyl chains, except for DMPG. In fact, an increase of P is detectable in this lipid as in PLs with unsaturated acyl chains. It is suggested that the effects of TBT on liposomal membranes are dependent on the anion moiety and phospholipids characteristics.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

Differential scanning calorimetry characterization of oxidized egg phosphatidylcholine liposomes.

Differential scanning calorimetry has been used to characterize liposomes made from mixtures of unoxidized and singlet oxygen oxidized egg phosphatidylcholine. Cooling scans reveal that trapped water decreases when the oxidized phosphatidylcholine content is increased in the liposomes. Liposomes made from mixtures containing more than 50% by weight of oxidized phosphatidylcholine do not show trapped water.

Calorimetry↗
PubMed1990

Interaction of the herbicide atrazine with model membranes. I: Physico-chemical studies on dipalmitoyl phosphatidylcholine liposomes.

Atrazine (2-chloro-4 ethylamino-6-(isopropylamino)-s-triazine) is one of the most widely used herbicides. Fourier transform infrared spectroscopy, differential scanning calorimetry and fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and of its derivative 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) were used to study the interaction of atrazine with dipalmitoyl phosphatidylcholine liposomes used as a model for biological membranes. The results show that atrazine does not perturb the hydrophobic core of the lipid bilayer and suggest that the herbicide localizes near the glycerol backbone of the lipid.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

Interaction of the herbicide atrazine with model membranes. II: Effect of atrazine on fusion of phospholipid vesicles.

The effect of atrazine on Ca2+ induced fusion of cardiolipin(CL) and phosphatidylserine (PS) vesicles is studied by Tb3+/dipicolinic acid fluorescence and turbidity measurements. The interaction of herbicide with CL and PS membranes is studied by DPH fluorescence polarization. At low concentrations the pesticide partially inhibits fusion, especially in CL vesicles. Higher concentrations of atrazine decrease inhibition of fusion in CL, while fusion is slightly increased in PS. The Ca2(+)-induced increase of turbidity is not affected by atrazine in both PS and CL aggregation experiments. DPH polarization measurements show a perturbation only of the membrane hydrophobic core of PS, in presence of Ca2+. It is hypothesized that this biphasic effect shown by low and high atrazine concentrations on Ca2(+)-induced fusion of vesicles is due to a different localization of the pesticide in the membrane.

Atrazine↗