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Biomedical subjects

M Manghi

Publications and source records attributed to M Manghi.

At least 19 recordsLinked to original sources
PubMed2006

Fluctuation-induced interactions between domains in membranes.

We study a model lipid bilayer composed of a mixture of two incompatible lipid types which have a natural tendency to segregate in the absence of membrane fluctuations. The membrane is mechanically characterized by a local bending rigidity kappa(phi) which varies with the average local lipid composition phi. We show, in the case where kappa varies weakly with phi, that the effective interaction between lipids of the same type either can be everywhere attractive or can have a repulsive component at intermediate distances greater than the typical lipid size. When this interaction has a repulsive component, it can prevent macrophase separation and lead to separation in mesophases with a finite domain size. This effect could be relevant to certain experimental and numerical observations of mesoscopic domains in such systems.

Computer Simulation↗
PubMed2004

Short commentary: Theoretical considerations on concentrated polymer interfaces: an attempt to explain dewetting of ultra-thin films.

We discuss the dewetting of ultra-thin molten polymer films within the framework of the Cahn-Hilliard theory for liquid interfaces. We argue that a) we need a pair of descriptors to characterize the bulk liquid of polymer chains (rather than the monomer density alone), b) the so-called loop density S, first introduced to describe polymer layers, may be a good scalar candidate for the configurational descriptor, c) the results found for the variation of S with distance might suggest an explanation for dewetting of ultra-thin polymer films.

Journal Article↗
PubMed2004

Variational theory for a single polyelectrolyte chain revisited.

We reconsider the electrostatic contribution to the persistence length, le, of a single, infinitely long-charged polymer in the presence of screening. A Gaussian variational method is employed, taking le as the only variational parameter. For weakly charged and flexible chains, crumpling occurs at small length scales because conformational fluctuations overcome electrostatic repulsion. The electrostatic persistence length depends on the square of the screening length, le approximately kappa(-2), as first argued by Khokhlov and Khachaturian by applying the Odijk-Skolnick-Fixman (OSF) theory to a string of crumpled blobs. We compare our approach to previous theoretical works (including variational formulations) and show that the result le approximately kappa(-2), found by several authors comes from the improper use of a cutoff at small length scales. For highly charged and stiff chains, crumpling does not occur; here we recover the OSF result and validate the perturbative calculation for slightly bent rods.

Journal Article↗
PubMed2003

Mobile polymer connectors.

We study the junction between two solid objects, formed by polymer connectors which are supposed to freely explore the two grafting surfaces. We focus on the sphere-plane and sphere-sphere geometries. Because the chains are mobile, they are able to adapt both the local grafting density and their conformation to the position of the surfaces. Using a scaling approach, we show that, in chemical equilibrium, local grafting density is non-monotonic, and the junction can be divided into two different regions: the center, where connectors are compressed and exert a repulsive force between the objects (high excluded-volume interactions) and an external corona, where chains are stretched and attract the two objects. The relative importance of these regions varies for different separations and depends on surface geometries. When an external force is applied, this spatially inhomogeneous constraint exerted by the junction leads to specific force-distance profiles, which differ from profiles in the case of fixed connectors. An effective interaction potential and the adhesion energy are computed, showing a strong dependence on the geometry of surfaces.

Biophysical Phenomena↗
PubMed2001

Social stress, myocardial damage and arrhythmias in rats with cardiac hypertrophy.

In rat models of cardiac hypertrophy (moderate aortic coarctation: ACm, n=18; severe aortic coarctation: ACs, n=27; aging: OLD, n=25; spontaneous chronic hypertension: SHR, n=18) and properly matched control animals (C(ACm), n=17; C(ACs), n=19; C(OLD), n=24; C(SHR), n=22), we investigated the relative contribution of intense autonomic activity and cardiac structural damage to ventricular arrhythmogenesis. We used an "in vivo" to tissue level approach, by correlating in the same animal: (i) social stress-induced ventricular arrhythmias, telemetrically recorded, and (ii) left ventricular weights (LVW) and amount and geometrical properties of myocardial fibrosis (MF). Arterial blood pressure was significantly higher in ACm (+11%), ACs (+28%) and SHR (+34%) than in controls. LVW were approximately 20% greater in ACm, ACs and OLD and 50% greater in SHR. MF was about twice as great and characterized by more frequent occurrence of microscopic scarring in ACm and ACs, and eight times greater and associated with both a higher number and a larger size of fibrotic foci in OLD and SHR compared to controls. Social stress increased ventricular arrhythmia vulnerability in all models of cardiac hypertrophy, as well as in controls. The arrhythmogenic action of stress was facilitated in ACs, OLD and SHR. A correlation between structural cardiac remodeling and ventricular arrhythmias was found only in SHR and OLD, which exhibited the greatest increase in LVW and/or MF. Social stress proved to be a valuable tool for analyzing the combined effects of autonomic stimulation and altered myocardial substrate on the genesis of potentially life-threatening arrhythmias in social animals.

Aging↗
PubMed2001

Cardiac autonomic responses to intermittent social conflict in rats.

Intermittent exposure to the same stressor can lead to a gradual decline in physiological, neuroendocrine and behavioral stress responses (habituation). We investigated possible habituation of cardiac autonomic responsiveness and susceptibility to cardiac arrhythmias in male rats exposed to either intermittent social victory (VIC) or defeat (DEF) stress (10 exposures in each case). Electrocardiograms were recorded via radiotelemetry and the sympathovagal balance at the level of the heart was evaluated via time-domain measurements of heart rate variability, namely average R--R interval (average time interval between two consecutive heart beats, RR), the standard deviation of RR (SD(RR)) and the root-mean-square of successive R--R interval differences (r-MSSD). Values of these parameters were significantly lower in DEF as compared to VIC rats in the second part of the test period (from Minute 6 to Minute 15), suggesting a more pronounced sympathetic dominance in the former group of animals. Accordingly, the occurrence of the most frequent cardiac arrhythmias (ventricular and supraventricular premature beats) was higher in DEF rats. Habituation of cardiac autonomic responsivity was observed across repeated exposure to victory, both in terms of sympathovagal balance and susceptibility to cardiac tachyarrhythmias, whereas no habituation was found in repeatedly defeated animals. A possible explanation to this discrepancy could be the different degree of controllability characterizing the two social challenging situations.

Animals↗
PubMed2001

[The mechanism of impulse initiation: high-resolution epicardial pace-mapping in rat heart].

UNLABELLED: Simulations of cardiac tissue bidomain model indicate that point cathodal stimulation gives rise to a dog-bone depolarized region (virtual cathode) extending across fibers, limited by two symmetric hyperpolarized regions (virtual anode) extending along fibers. These predictions were experimentally confirmed by optical mapping studies of transmembrane potentials while no direct validation is reported at the extracellular level. The present study aims at defining the influence of the virtual cathode on extracellular potentials by means of high-density epicardial mapping. METHODS: Epicardial potentials were measured in seven exposed rat hearts by means of a 11 x 11 electrode array with 360 x 540 microns resolution. Cathodal current pulses, 100-200 microA intensity and 1 ms duration, to avoid superposition of stimulus and activation potentials, were delivered from one of the electrode array and unipolar potentials were measured from all other electrodes. RESULTS AND DISCUSSION: a) During stimulus, negative equipotential lines were elliptic along fibers, as expected, but for a 2 mm circular region at the pacing site. b) During 1-2 ms interval between stimulus offset and start of activation, equipotential lines became elliptic across fibers in the presence of the region directly excited by the stimulus field. Start of activation was either symmetric with isochrones initially circular around the pacing site and then elliptic along fibers, or asymmetric initiating at only one side of the pacing site across fibers with isochrones elliptic along fibers. In the latter case, the wave front was blocked through the refractory region directly excited by the stimulus field, subdivided into two wings which collided and merged at the opposite side, giving rise to a plane wave front propagating across fibers away from the pacing site. CONCLUSIONS: High spatial resolution epicardial potential mapping reveals the existence of the virtual cathode and its influence on impulse initiation and conduction. The unexpected existence of a region of conduction block at the pacing site, due to spatial asymmetry of normal cardiac tissue which enhances activation threshold at one of the two sides of the virtual cathode, is intriguing since it is one of the requirements for reentry of conduction in the presence of a circuit with decreased conduction velocity and short duration of refractory period.

Animals↗
PubMed2000

Interfacial properties of polymeric liquids

We show that the variations of the surface tension of polymeric solutions gamma with the molecular weight of the sample M(n), the temperature T, and the volume fraction of monomers straight phi(b) are explained by the self-organization of the long flexible chains that are present in the immediate vicinity of the interface. Within a scaling functional theory we find a simple law gamma(straight phi(b),M(n),T) which accounts quantitatively for the experimental data available in the literature with a very high accuracy.

Journal Article↗
PubMed2000

Time patterns of sperm whale codas recorded in the Mediterranean Sea 1985-1996.

A distinctive vocalization of the sperm whale, Physeter macrocephalus (=P. catodon), is the coda: a short click sequence with a distinctive stereotyped time pattern [Watkins and Schevill, J. Acoust. Soc. Am. 62, 1485-1490 (1977)]. Coda repertoires have been found to vary both geographically and with group affiliation [Weilgart and Whitehead, Behav. Ecol. Sociobiol. 40, 277-285 (1997)]. In this work, the click timings and repetition patterns of sperm whale codas recorded in the Mediterranean Sea are characterized statistically, and the context in which the codas occurred are also taken into consideration. A total of 138 codas were recorded in the central Mediterranean in the years 1985-1996 by several research groups using a number of different detection instruments, including stationary and towed hydrophones, sonobuoys and passive sonars. Nearly all (134) of the recorded codas share the same "3+1" (/// /) click pattern. Coda durations ranged from 456 to 1280 ms, with an average duration of 908 ms and a standard deviation of 176 ms. Most of the codas (a total of 117) belonged to 20 coda series. Each series was produced by an individual, in most cases by a mature male in a small group, and consisted of between 2 and 16 codas, emitted in one or more "bursts" of 1 to 13 codas spaced fairly regularly in time. The mean number of codas in a burst was 3.46, and the standard deviation was 2.65. The time interval ratios within a coda are parameterized by the coda duration and by the first two interclick intervals normalized by coda duration. These three parameters remained highly stable within each coda series, with coefficients of variation within the series averaging less than 5%. The interval ratios varied somewhat across the data sets, but were highly stable over 8 of the 11 data sets, which span 11 years and widely dispersed geographic locations. Somewhat different interval ratios were observed in the other three data sets; in one of these data sets, the variant codas were produced by a young whale. Two sets of presumed sperm whale codas recorded in 1996 had 5- and 6-click patterns; the observation of these new patterns suggests that sperm whale codas in the Mediterranean may have more variations than previously believed.

Animal Communication↗
PubMed1994

Behavioral and electrocardiographic responses to social stress in male rats.

Telemetry ECGs were recorded from Wistar male rats during social stress induced by exposure to aggressive lactating female rats. Behavioral response to maternal attack was evaluated in terms of relative duration of passive submissive (p/s) and active/nonsubmissive (a/ns) patterns. A decrease of R-R interval (R-R) compared to baseline conditions was found, significantly more pronounced than that observed in control animals exposed just to novel environment. R-R variability during social stress was positively correlated with the amount of p/s behavior. R-R fluctuations, episodes of II degree A-V block, and ventricular arrhythmias were also observed. Most R-R fluctuations and II degree A-V blocks were temporally associated with phases of p/s behavior and periods of high R-R variability. Ventricular arrhythmias generally appeared during a/ns behavior and were temporally linked with periods of low R-R variability. Ventricular arrhythmias, low R-R variability, and concomitant a/ns behavior might be related to an increased sympathetic activity. R-R fluctuations and II degree A-V blocks, associated with high R-R variability and p/s behavior, might be related to a predominant inhibitory effect of vagal activation (accentuated antagonism).

Aggression↗
PubMedDate not supplied

Serum antibodies to diphtheria-tetanus-pertussis vaccine components in Argentine children.

The Argentine vaccination schedule against diphtheria, tetanus and pertussis (DTP) recommends three doses of DTP vaccine at 2, 4 and 6 months of age, two boosters at 18 months and 6 years, a booster dose of tetanus vaccine every 10 years and two doses during pregnancy. To evaluate the effect of this schedule, antibodies against pertussis toxin (PT) and filamentous hemagglutinin (FHA) and against tetanus and diphtheria toxoids were determined by ELISA in serum samples from children (1 month to 6 years) who received different doses of DPT vaccine: 0 dose (n = 50), 1 dose (n = 25), 2 doses (n = 25), 3 doses (n = 55), first and second booster (n = 25); 25 pregnant women and their offspring, and 45 adults. High antibody levels against PT (> 140 EU/ml) and FHA (> 80 EU/ml) were recorded in mothers and in the newborn. Antibody titers against PT increased with the number of doses given and decreased with time. Full protection against tetanus (titers > 0.1 IU/ml) was observed in the group of adults (0.37 IU/ml), in mothers (4.4 IU/ml) and their newborn offspring (5.5 IU/ml), and in children after receiving the second dose of DTP vaccine (1.86 IU/ml). The immune status for diphtheria was far lower, as most of the groups lacked adequate protection. After the third dose of DTP vaccine, only 78% of the children had antibody titers above the protective level (0.1 IU/ml). Since antibody levels considered to provide full protection were only achieved after the first booster dose of DTP vaccine, the primary three-dose schedule seems to be insufficient to confer adequate immunity in all vaccinees. Because of the high proportion of non-protected adults, a booster dose of Td vaccine should be considered for this group.

Adhesins, Bacterial↗