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Biomedical subjects

P Gambardella

Publications and source records attributed to P Gambardella.

At least 19 recordsLinked to original sources
PubMed2004

Oscillatory magnetic anisotropy in one-dimensional atomic wires.

One-dimensional Co atomic wires grown on Pt(997) have been investigated by x-ray magnetic circular dichroism. Strong changes of the magnetic properties are observed as the system evolves from 1D- to 2D-like. The easy axis of magnetization, the magnetic anisotropy energy, and the coercive field oscillate as a function of the transverse width of the wires, in agreement with theoretical predictions for 1D metal systems.

Journal Article↗
PubMed2003

Giant magnetic anisotropy of single cobalt atoms and nanoparticles.

The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface. Single cobalt atoms deposited onto platinum (111) are found to have a magnetic anisotropy energy of 9 millielectron volts per atom arising from the combination of unquenched orbital moments (1.1 Bohr magnetons) and strong spin-orbit coupling induced by the platinum substrate. By assembling cobalt nanoparticles containing up to 40 atoms, the magnetic anisotropy energy is further shown to be dependent on single-atom coordination changes. These results confirm theoretical predictions and are of fundamental value to understanding how magnetic anisotropy develops in finite-sized magnetic particles.

Journal Article↗
PubMed2002

Ferromagnetism in one-dimensional monatomic metal chains.

Two-dimensional systems, such as ultrathin epitaxial films and superlattices, display magnetic properties distinct from bulk materials. A challenging aim of current research in magnetism is to explore structures of still lower dimensionality. As the dimensionality of a physical system is reduced, magnetic ordering tends to decrease as fluctuations become relatively more important. Spin lattice models predict that an infinite one-dimensional linear chain with short-range magnetic interactions spontaneously breaks up into segments with different orientation of the magnetization, thereby prohibiting long-range ferromagnetic order at a finite temperature. These models, however, do not take into account kinetic barriers to reaching equilibrium or interactions with the substrates that support the one-dimensional nanostructures. Here we demonstrate the existence of both short- and long-range ferromagnetic order for one-dimensional monatomic chains of Co constructed on a Pt substrate. We find evidence that the monatomic chains consist of thermally fluctuating segments of ferromagnetically coupled atoms which, below a threshold temperature, evolve into a ferromagnetic long-range-ordered state owing to the presence of anisotropy barriers. The Co chains are characterized by large localized orbital moments and correspondingly large magnetic anisotropy energies compared to two-dimensional films and bulk Co.

Journal Article↗
PubMed2002

Localized magnetic states of Fe, Co, and Ni impurities on alkali metal films.

X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) have been used to study transition metal impurities on K and Na films. The multiplet structure of the XAS spectra indicates that Fe, Co, and Ni have localized atomic ground states with predominantly d7, d8, and d9 character, respectively. XMCD shows that the localized impurity states possess large, atomiclike, magnetic orbital moments that are progressively quenched as clusters are formed. Ni impurities on Na films are found to be nonmagnetic, with a strongly increased d10 character of the impurity state. The results show that the high magnetic moments of transition metals in alkali hosts originate from electron localization.

Journal Article↗
PubMed2001

Oxygen dissociation at Pt steps.

Using scanning tunneling microscopy, thermal energy atom scattering, and density functional theory we have characterized O (2) dissociation on Pt(111) stepped surfaces at the atomic scale. The most reactive site is at the top of the Pt steps. In both the molecular precursor state (MPS) and the transition state (TS), the O (2) has its axis aligned parallel to the step edge. Controlled step decoration with Ag monatomic chains was used to locally tune the reactivity of Pt step sites. The enhanced reactivity at the Pt step sites is not caused by a decrease of the local dissociation barriers from the MPS but is related to a stabilization of both the MPS and TS.

Journal Article↗
PubMed2000

Early death in two sisters with Hennekam syndrome.

We report on two sisters with facial anomalies, protein-losing enteropathy, and intestinal lymphangiectasia consistent with the diagnosis of Hennekam syndrome. Both patients had a number of other anomalies not previously described in this autosomal recessive disorder, i.e., primary hypothyroidism, hypertrophic pyloric stenosis, and an early fatal outcome. These cases support the autosomal recessive transmission and the expansion of the phenotype of the Hennekam syndrome.

Abnormalities, Multiple↗
PubMed1995

Circadian rhythms of lipid and apolipoprotein pattern in adult fasted rats.

Data on circadian rhythms of serum lipids and apolipoproteins in animals and in human subjects are scarce. The goal of this study was to investigate the existence of circadian rhythms in the lipids and apolipoproteins of fasted rats. We showed that in fasted rats well-defined circadian rhythms were present in total serum triglycerides and in cholesterol and triglycerides of very low density lipoprotein (VLDL), intermediate density lipoprotein-low density lipoprotein (IDL-LDL) and high density lipoprotein (HDL). Moreover, our data clearly show that the circadian rhythm of lipoproteins is accompanied by a well defined circadian rhythm of B apoprotein, in all lipoprotein classes examined.

Animals↗
PubMed1994

Individual housing modulates daily rhythms of hypothalamic catecholaminergic system and circulating hormones in adult male rats.

Circadian rhythms of hypothalamic catecholamines and their metabolites and of prolactin and corticosterone circulating hormones were determined over 24 h in group-housed (six per cage; control) and individually housed, 90-day-old male albino rats adapted to a 12:12 light/dark cycle. After 5 weeks of adaptation, in individually housed rats, norepinephrine (NE) turnover increased, since lower NE (p < 0.01) and higher MOPEG metabolite (p < 0.01) levels were measured. As concerns the dopaminergic system, individually housed rats increased both dopamine (DA) synthesis and turnover as revealed by higher DOPAC (p < 0.01) and HVA (p < 0.05) metabolites without modification of DA levels. Moreover, in individually housed rats, corticosterone (p < 0.01) and prolactin (p < 0.05) mean levels were higher than in the control group.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1992

Circadian rhythms of hypothalamic norepinephrine and of some circulating substances in individually housed adult rats.

The circadian rhythms of hypothalamic norepinephrine (NE) and of circulating norepinephrine, epinephrine (E), corticosterone, aldosterone, and serotonin (5HT) were determined in group-housed and in individually housed male adult rats, adapted to a 12/12 light/dark cycle. After 5 weeks of individual housing, compared to group-housed animals, hypothalamic NE mesor decreased, while circulating NE, E, and corticosterone mesor increased. The circadian rhythms of aldosterone and 5HT were unaffected by individual housing.

Adrenocorticotropic Hormone↗
PubMed1992

Effects of a new calf thymus protein on 3-hydroxy-3-methylglutaryl-CoA reductase activity in rat (Rattus bubalus) hepatocyte cells (BRL-3A).

1. In a previous paper we described the purification steps of a new calf thymus protein able to activate the LDL receptor catabolism. 2. In this paper we examine the modulatory effect of this new calf thymus protein on 3HMG-CoA reductase activity in rat hepatocyte cells to better clarify the role of this protein on cholesterol metabolism. 3. The results obtained show that the calf thymus protein inhibits the HMG-CoA reductase, and support the hypothesis that the activation of LDL receptor catabolism is mediated by a decreased amount of cellular cholesterol following HMG-CoA reductase inhibition.

Animals↗
PubMed1990

Blood cellular and biochemical changes after extracorporeal shock wave lithotripsy.

The present study deals with blood cell behaviour and related hematochemical changes occurring in man after exposure to extracorporeal shock wave lithotripsy (ESWL). The following parameters have been investigated, before and after treatment, in a longitudinal study carried out on 58 patients of our Center: RBC count, Ht, Blood Hb, Plasma Hb, autohemolysis after 72 hours, bilirubinemia, WBC count, platelet count, in vitro platelet aggregation, beta-TG, sideremia and urinary post-exposure transferrin concentration. After exposure to ESWL, with pulse numbers ranging from 350 to 3,000, 18-20 KV, direct and indirect evidences of hemolysis have been found when number of SW exceeded 1,000. The hemolysis rate in different models of in vitro exposure to ESWL of blood samples was also investigated. Increase of WBC count, and changes of the platelet in vitro aggregation patterns were also observed. Changes in sideremia values have been related to urinary loss of transferrin.

Blood Cell Count↗
PubMed1990

Chronic administration of imipramine antagonizes deranged circadian rhythm phases in individually housed rats.

The circadian rhythms of hypothalamic serotonin (5HT), tryptophan (TP) and 5-hydroxy-indoleacetic acid (5HIAA), and serum corticosterone were determined in male Wistar rats. The animals underwent a five-week 12:12-hr light/dark cycle conditioning period and were divided into three groups: rats housed four to a cage (group C, control), rats housed individually (group I), and rats housed individually and treated for two weeks with 10 mg/kg/day of imipramine continuously administered by osmotic pumps implanted under the skin (group T). Significant differences were found in the acrophases of 5HT, TP and 5HIAA between group I and group C, and corticosterone mesor was higher in group I than in group C. On the contrary, no differences were observed between group T (individually housed, but given imipramine) and group C. Therefore, chronically administered imipramine antagonizes the circadian changes induced by individual housing.

Animals↗
PubMed1990

Circadian rhythm variations in the adult rat induced by low and high protein diets administered at various stages of development.

Hypothalamic tryptophan (TP), serotonin (5HT) and 5-hydroxy-indoleacetic acid (5HIAA), serum tryptophan (free and total), and circulating corticosterone and aldosterone were measured over 24 hr in 60-day-old male rats fed high (60%) and low (6%) protein diets. The diets were administered during specific stages of rat growth: fetal phase and suckling (when the process of mitosis is most rapid), post-lactation, and from the fetal phase through to the adult stage. In all groups, there was a direct correlation between protein intake and hypothalamic and serum TP levels. Remarkable decreases in the amplitude and mesor of the aldosterone rhythm were observed when the hyperprotein diet was administered in the fetal and suckling phases, or from the fetal phase until the adult stages. The rhythm of the serotonin system was significantly altered by a low protein diet: decreased 5-HT amplitude (low protein diet in the fetal stage and suckling), decreased 5-HT amplitude and deranged 5-HIAA rhythm (low protein in the post-lactation period), deranged 5-HIAA rhythm (low protein diet throughout the experiment). Lastly, there was a remarkable increase in the corticosterone mesor in rats administered a low protein diet after weaning and in rats constantly given this diet. Growth was greatly inhibited in these two groups of animals, therefore, it cannot be excluded that the high levels of circulating hormone resulted from their debilitated condition.

Aldosterone↗
PubMed1989

Effects of individual housing on circadian rhythms of adult rats.

Circadian rhythms of hypothalamic serotonin (5HT), its precursor tryptophan (TP) and its metabolite 5-hydroxy-indoleacetic acid (5HIAA), and of prolactin and corticosterone circulating hormones were determined in group-housed and in individually-housed male rats, adapted to a 12:12 light/dark cycle. After 5 weeks of individual housing, 5HT peaked later, TP and 5HIAA peaked earlier, and the mesor level of TP and 5HIAA decreased with respect to group-housed animals. Individual housing caused an increase in the corticosterone mesor level, but did not affect amplitude or acrophase. The circadian rhythm of prolactin was unchanged by individual housing.

Animals↗
PubMed1988

Tricyclic imipramine modification of the circadian rhythms of hypothalamic serotonin, its precursors and acid catabolite in individually housed rats.

Circadian rhythms of serotonin (5HT), its precursors tryptophan (TP) and 5-hydroxy-tryptophan (5HTP) and its acid catabolite 5-hydroxy-indoleacetic acid (5HIAA), were determined in the hypothalamus of control rats and rats which had been treated continuously with subcutaneous imipramine (10 mg/kg/day) for 2 weeks. Rats were individually housed and entrained to LD 12:12. Controls showed the 5HT and TP peaks in the light and dark periods respectively, as reported in the literature, but no inverted correlation (antiphase) between 5HT and 5HIAA rhythms. Imipramine significantly modified circadian rhythm characteristics: the 5HT acrophase was advanced, that of TP and 5HIAA was delayed. Imipramine also significantly increased hypothalamic 5HT and TP concentrations.

5-Hydroxytryptophan↗