Biomedical subjects

A Gragnani

Publications and source records attributed to A Gragnani.

5 recordsLinked to original sources

PubMed2006

Coevolution of slow-fast populations: evolutionary sliding, evolutionary pseudo-equilibria and complex Red Queen dynamics.

We study the interplay of ecological and evolutionary dynamics in communities composed of populations with contrasting time-scales. In such communities, genetic variation of individual traits can cause population transitions between stationary and cyclic ecological regimes, hence abrupt variations in fitness. Such abrupt variations raise ridges in the adaptive landscape, where the populations are poised between equilibrium and cyclic coexistence and along which evolutionary trajectories can remain sliding for long times or halt at special points called evolutionary pseudo-equilibria. These novel phenomena should be generic to all systems in which ecological interactions cause fitness to vary discontinuously. They are demonstrated by the analysis of a predator-prey community, with one adaptive trait for each population. The eco-evolutionary dynamics of the system show a number of other distinctive features, including evolutionary extinction and two forms of Red Queen dynamics. One of them is characterized by intermittent bouts of cyclic oscillations of the two populations.

Adaptation, Physiological↗

PubMed1999

Obsessions and compulsions: normative data on the Padua Inventory from an Italian non-clinical adolescent sample.

In the present study the structure of obsessive-compulsive phenomena in non-clinical adolescents was investigated by 'The Padua Inventory' (PI). The PI is a self-report measure of obsessive and compulsive symptoms which is used in clinical and research settings. The use of PI in adolescents has been limited by the lack of normative data. Consequently, adolescent validation has both theoretical and practical implications. PI was administered to 566 normal Italian high school subjects, ranging in age from 15 to 18 years. The mean total score of PI and the mean score of 'mental activities', 'becoming contaminated' and 'urges and worries' sub-scales points to significant differences between males and females. Females reported more obsessions and cleaning rituals than males. Males show more urges and fears than females. Moreover, our data underline that younger subjects get higher mean scores than older subjects in all scales.

Adolescent↗

PubMed1998

Acidic deposition, plant pests, and the fate of forest ecosystems.

We present and analyze a nonlinear dynamical system modelling forest-pests interactions and the way they are affected by acidic deposition. The model includes mechanisms of carbon and nitrogen exchange between soil and vegetation, biomass decomposition and microbial mineralization, and defoliation by pest grazers, which are partially controlled by avian or mammalian predators. Acidic deposition is assumed to directly damage vegetation, to decrease soil pH, which in turn damages roots and inhibits microbial activity, and to predispose trees to increased pest attack. All the model parameters are set to realistic values except the inflow of protons to soil and the predation mortality inflicted to the pest which are allowed to vary inside reasonable ranges. A numerical bifurcation analysis with respect to these two parameters is carried out. Five functioning modes are uncovered: (i) pest-free equilibrium; (ii) pest persisting at endemic equilibrium; (iii) forest-pest permanent oscillations; (iv) bistable behavior with the system converging either to pest-free equilibrium or endemic pest presence in accordance with initial conditions; (v) bistable behavior with convergence to endemic pest presence or permanent oscillations depending on initial conditions. Catastrophic bifurcations between the different behavior modes are possible, provided the abundance of predators is not too small. Numerical simulation shows that increasing acidic load can lead the forest to collapse in a short time period without important warning signals.

Acid Rain↗

PubMed1997

Quantitative magnetic resonance analysis in vascular dementia.

The potential role of magnetic resonance imaging (MRI) in differentiating between specific causes of cognitive decline in patients with vascular dementia (VD) has not yet been fully established. We therefore decided to assess the supratentorial cerebral contents in 24 patients with a diagnosis of probable VD and in 24 normal subjects, matched for age and education level, using MRI volumetric parameters obtained by means of a quantitative method. The volumes of subarachnoid and ventricular spaces, cerebral tissue, and hyperintense areas on T2-weighted images were calculated. In order to reduce interindividual variability caused by differences in intracranial size, each absolute measurement was normalized to the relative size of the intracranial volume. In addition, we calculated the ratio between the areas of the corpus callosum (CC) and supratentorial brain at the same level on the T1-weighted image midsagittal plane. The MRI data were correlated with the deterioration of cognitive functions. Patients with VD showed significantly lower cerebral tissue volume and CC area, and higher ventricular space volume than normal subjects. Furthermore, the total volume of the T2 signal alterations was higher in VD patients than in normal subjects. In VD patients, this volume was found to be proportional to the increase in the volume of the ventricular space. On the other hand, no correlation was found between the volume of the T2 signal alterations and the area of the CC. The degree of global cognitive dysfunction and the score of each neuropsychological test did not show any correlation with the MRI data. Our results suggest that ventricular enlargement in VD patients is correlated with the increase in volume of the T2 signal abnormalities, but that the degree of global cognitive dysfunction is not influenced by the volume of these T2 signal abnormalities. Furthermore, the CC atrophy does not influence the score of any neuropsychological test or the degree of global cognitive dysfunction.

Age Distribution↗

PubMedDate not supplied

Differentiation and barrier formation of a cultured composite skin graft.

The differentiation and barrier formation of cultured composite skin grafts (CSGs) were assessed by histology and measurements of surface electrical capacitance (SEC) in vitro and in vivo. Keratinocytes cultured on the surface of acellular dermis were lifted to the air-liquid interface and analyzed for 30 days in vitro. Initially, SEC measurements of CSGs (n = 11) were high but quickly dropped between days 4 and 6 and remained steady for 30 days, indicating barrier formation by the epidermis. Histology of the CSGs (n = 6) demonstrated stratification of the epidermal cells and partial formation of the stratum corneum by day 3 that was complete by day 7. CSGs (n = 5) were transplanted to athymic mice, where they formed a stratified and differentiated epidermis. SEC measurements of CSGs remained low after transplant, suggesting that exposure to the air-liquid interface improved the maturation of CSGs in vitro prior to transplant.

Animals↗