Gaussian processes and neuronal modeling

This work is a contribution towards the understanding of certain features of mathematical models of single neurons. Emphasis is set on neuronal firing, for which the first passage time (FPT) problem bears a fundamental relevance. We focus the attention on modeling the change of the neuron membrane potential between two consecutive spikes by Gaussian stochastic processes, both of Markov and of non-Markov types. Methods to solve the FPT problems, both of a theoretical and of a computational nature, are sketched, including the case of random initial values. Significant similarities or diversities between computational and theoretical results are pointed out, disclosing the role played by the correlation time that has been used to characterize the neuronal activity. It is highlighted that any conclusion on this matter is strongly model-dependent. In conclusion, an outline of the asymptotic behavior of FPT densities is provided, which is particularly useful to discuss neuronal firing under certain slow activity conditions.     

Validation of the oxygen radical absorbance capacity (ORAC) parameter as a new index of quality and stability of virgin olive oil

The induction period (IP), determined using accelerated methods such as the Rancimat test, is a parameter that has been used to predict the shelf life of virgin olive oil. The oxygen radical absorbance capacity (ORAC) has recently been proposed as a quality index of virgin olive oil because it measures the efficiency of phenolic compounds in the protection against peroxyl radicals. This study aims to investigate relationships between the ORAC and IP values and proposes ORAC as a new parameter of virgin olive oil stability. The concentrations of phenolics, o-diphenols, tocopherol, β-carotene, lutein, and ORAC and IP values were determined in 33 virgin olive oils. Regression analyses showed that both ORAC and IP values correlate with total phenols and o-diphenols with highly significant indices, whereas the correlations of both ORAC and IP with tocopherols, β-carotene, and lutein were not significant. The ORAC values correlate with the IP values with low but significant indices (R=0.42; P<0.02). The results confirm the key role of phenolic compounds in accounting for the shelf life of virgin olive oil and suggest that the ORAC parameter may be used as a new index of quality and stability.     

Relationship between some Staphylococcus aureus pathogenic factors and growth rates and somatic cell counts

Staphylococcus aureus isolates produce several pathogenic factors. The combination of these products influences the pathogenic role of different isolates, but their specific effects are well known in the pathogenesis of udder infections. This study focused on the association of polymorphism of the coagulase gene, protein A gene, collagen-binding protein gene, and of fibrinogen-binding protein gene on somatic cell count (SCC) and on Staph. aureus growth rate. Fifty Staph. aureus isolates from 13 dairy cow herds, located in seven different provinces, were considered. The results showed a low frequency of cna gene, similar to the one observed in human isolates. Meanwhile, the high frequency of efb gene indirectly confirmed the role of this factor in bacterial pathogenesis, being associated with adhesion to epithelia. The association of these two single genes with SCC and growth rate showed to be not significant. The polymorphism of spa gene was confirmed to be significantly associated with inflammatory response and growth rate, albeit with a pattern different from the one suggested for human isolates. Sorting of isolates based on the clusters obtained by combining polymorphisms of spa and coa genes and the presence of cna and efb genes, showed that a single cluster (cluster V) was prevalent in the different herds and provinces, while the other six clusters identified were widely spread among the remaining 60% of the isolates. Results showed that clusters VI and VII had significantly higher growth rates at 3, 4, and 6 h in comparison with the other clusters. Meanwhile, quarters infected with these strains showed significantly lower SCC levels. The frequency of isolates from cluster V, suggested that they should possess pathogenic factors increasing their invasiveness, even if in the presence of a stronger inflammatory response. These results indirectly confirm previous findings on the different interactions between isolates and the udder immune system. They also suggest that isolates with higher growth rates and inducing a lower inflammatory response have better chances to spread among the herd. The relatively simple genomic method proposed in this study could be applied by an increasing number of diagnostic laboratories and could be useful in studying the epidemiology of Staph. aureus intra-mammary infections in dairy herds when collecting data from the field.     

Enantioselective hydrolysis of some 2-aryloxyalkanoic acid methyl esters and isosteric analogues using a penicillin G acylase-based HPLC monolithic silica column

A technique based on liquid chromatography has been developed to facilitate studies of enantioselectivity in penicillin G acylase (PGA)-catalyzed hydrolysis of some 2-aryloxyalkanoic acid methyl esters and isosteric analogues. PGA was covalently immobilized on an aminopropyl monolithic silica support to create an immobilized HPLC-enzyme reactor. Two sets of experimental data were drawn to calculate the enantioselectivity (E) of the kinetically controlled enantiomer-differentiating reaction, the degree of substrate conversion and the enantiomeric excess of the product. The developed enzymatic reactor was coupled through a switching valve to an achiral analytical column for separation and quantitation of the hydrolysis products. The enantiomeric excess was determined off-line on a PGA-chiral stationary phase. In this way, highly precise E values were determined. A computational study related to the hydrolysis of the considered racemic esters was also carried out in order to unambiguously clarify both the substrate specificity and the enantioselectivity displayed by PGA.     

Solid viscus injury predicts major hollow viscus injury in blunt abdominal trauma

BACKGROUND: As nonoperative management of blunt abdominal trauma has become more popular, reliable models for predicting the likelihood of concomitant hollow viscus injury in the hemodynamically stable patient with a solid viscus injury are increasingly important. METHODS: The Pennsylvania Trauma Systems Foundation registry was reviewed for the period from January 1992 to December 1995 for all adult (age > 12 years) patients with blunt trauma and an Abbreviated Injury Scale (AIS) score > or = 2 for a solid viscus (kidney, liver, pancreas, spleen). Patients with an initial systolic blood pressure < 90 mm Hg were excluded. Hollow viscus injuries included only lacerations or perforations of the gallbladder, gastrointestinal tract, or urinary tract. RESULTS: In the 4-year period, 3,089 patients sustained solid viscus injuries, 296 of whom had a hollow viscus injury (9.6%). The mean age was 35.6 years, mean Injury Severity Score was 22.2, and mean Revised Trauma Score was 7.3; 63.3% of the patients were male. A solitary solid viscus injury occurred in 2,437 patients (79%), 177 of whom (7.3%) had a hollow viscus injury. The frequency of hollow viscus injury increased with the number of solid organs injured: 15.4% of patients with two solid viscus injuries (n = 547) and 34.4% of patients with three solid viscus injuries (n = 96) suffered a concomitant hollow viscus injury (p < 0.001 vs. one organ). A hollow viscus injury was 2.3 times more likely for two solid viscus injuries and 6.7 times more likely for three solid viscus injuries compared with a solitary solid viscus injury. For solitary solid viscus injury, the frequency of hollow viscus injury varied little with increasing AIS score (AIS score 2, 6.6%; AIS score 3, 8.2%; AIS score 4, 9.2%; AIS score 5, 6.2%) (p = 0.27 between groups), suggesting that the incidence of hollow viscus injury is related more to the number of solid visceral injuries than the severity of individual organ injury. Also, when the sum of the AIS scores for solid viscus injuries was <6, the mean rate of hollow viscus injury was 7.8%. This increased to 22.8% when the sum of the AIS scores for solid viscus injury was > or =6 (p < 0.001). A pancreatic injury in combination with any other solid viscus injury had a rate of hollow viscus injury of >33%. CONCLUSION: A model of organ injury scaling predicted hollow viscus injury. Multiple solid viscus injuries, particularly pancreatic, or abdominal solid viscus injuries with an AIS score > or = 6, were predictive of hollow viscus injury. Identification of these injury patterns should prompt consideration for early operative intervention.     

Antibody covalent immobilization on carbon nanotubes and assessment of antigen binding

Controlling the covalent bonding of antibodies onto functionalized carbon nanotubes is a key step in the design and preparation of nanotube-based conjugates for targeting cancer cells. For this purpose, an anti-MUC1 antibody (Ab) is linked to both multi-walled (MWCNTs) and double-walled carbon nanotubes (DWCNTs) using different synthetic strategies. The presence of the Ab attached to the nanotubes is confirmed by gel electrophoresis and thermogravimetric analysis. Most importantly, molecular recognition of the antigen by surface plasmon resonance is able to determine similar Ab binding capacities for both Ab-DWCNTs and Ab-MWCNTs. These results are very relevant for the design of future receptor-targeting strategies using chemically functionalized carbon nanotubes.