Neuronal regulation: A mechanism for synaptic pruning during brain maturation

Human and animal studies show that mammalian brains undergo massive synaptic pruning during childhood, losing about half of the synapses by puberty. We have previously shown that maintaining the network performance while synapses are deleted requires that synapses be properly modified and pruned, with the weaker synapses removed. We now show that neuronal regulation, a mechanism recently observed to maintain the average neuronal input field of a postsynaptic neuron, results in a weight-dependent synaptic modification. Under the correct range of the degradation dimension and synaptic upper bound, neuronal regulation removes the weaker synapses and judiciously modifies the remaining synapses. By deriving optimal synaptic modification functions in an excitatory-inhibitory network, we prove that neuronal regulation implements near-optimal synaptic modification and maintains the performance of a network undergoing massive synaptic pruning. These findings support the possibility that neural regulation complements the action of Hebbian synaptic changes in the self-organization of the developing brain.     

Effect of stocking density on ewes' milk yield, udder health and microenvironment

Three groups of 12 lactating Comisana ewes were housed in separate rooms of the same building that contained straw-bedded pens with total areas of 12, 18 and 24 m2. The ewes were assigned to groups with different stocking densities: high (HSD, 1 m2/animal), medium (MSD, 1.5 m2/animal) or low (LSD, 2 m2/animal). The LSD treatment resulted in lower air concentrations of total microorganisms and coliform bacteria than the other two. Ewes in the LSD group gave greater yields of milk, total protein and fat than those in the other two groups. LSD treatment increased milk casein content and improved clotting time and clot firmness. LSD also resulted in ewes giving milk with lower somatic cell counts and smaller concentrations of mesophiles, psychrotrophs and faecal coliforms than MSD and HSD. Subclinical mastitis occurred in three ewes of the MSD groups and four ewes of the HSD group, while no cases were recorded in the LSD group. These results indicate that stocking density is a critical factor in dairy sheep housing and suggest that a space allocation < 2 m2/animal may adversely affect the performance and health of the lactating ewe.     

Rapid detection of stressed Salmonella spp. in dairy and egg products using immunomagnetic separation and PCR

The rapid detection of an average of 5.9 stressed Salmonella cells in 25 g of food product using immunomagnetic separation (IMS) and PCR is described. For pasteurised egg yolk, egg yolk powder, ice-cream, whole egg, egg white and cheeses made from pasteurised milk PCR was applied after 16 h of preenrichment in buffered peptone water (BPW) using IMS and alkaline lysis as sample preparation method. For whole egg and egg white the BPW was supplemented with iron. For milk powder, and raw milk cheeses, the 16-h preenrichment in BPW was followed by IMS and a 4-h enrichment in Rappaport-Vassiliadis broth. In the latter case, PCR was applied on the enrichment medium after centrifugation and alkaline lysis. For PCR the primers ST11 and ST15 (Aabo et al., 1993) producing a fragment of 429 bp were used. An internal PCR control, designed to be co-amplified with the target DNA using the same primers but producing a smaller fragment of 240 bp, was used.     

Cholesterol and fat contents of Spanish commercial pork cuts

A study was carried out to determine the fat and cholesterol contents of several commercial pork cuts as function of sex. Fat and cholesterol content ranged from 2.7% and 57 mg/100 g in loin to 30.3% and 116 mg/100 g in dewlap. The higher the fat content the higher was the cholesterol content. Sex did not influence fat content and the fat/cholesterol ratio, but cholesterol content was higher in females than in males.     

How to bring orphan genes into functional families

In the framework of the B1 Consortium of the EUROFAN-1 project, we set up a series of simple phenotypic tests that can be performed on a large number of strains at a time. This methodological approach was intended to help assign functions of putative genes coding for unknown proteins to several specific aspects of cell biology. The tests were chosen to study phenotypes which should be affected by numerous genes. In this report, we examined the sensitivity/resistance or the adaptation of the cell to physical or chemical stresses (thermotolerance, osmotolerance and ethanol sensitivity), the effects of the alteration of the level of protein phosphorylation (sensitivity or resistance to compounds affecting the activity of protein kinases or phosphatases) and the effects of compounds interfering with synthesis of nucleic acids or proteins. Deletions in 66 genes of unknown function have been tested in 21 different conditions. In many deletant strains, phenotypes were observed and, for the most promising candidates, tetrad analysis was performed in order to verify co-segregation of the deletion marker with the phenotype.     

High intensity pulsed electric fields applied to egg white: effect on Salmonella Enteritidis inactivation and protein denaturation

High-intensity electric fields have been successfully applied to the destruction of Salmonella Enteritidis in diaultrafiltered egg white. The effects of electric field strength (from 20 to 35 kV x cm(-1)), pulse frequency (from 100 to 900 Hz), pulse number (from 2 to 8), temperature (from 4 to 30 degrees C), pH (from 7 to 9), and inoculum size (from 10(3) to 10(7) CFU x ml(-1)) were tested through a multifactorial experimental design. Experimental results indicate that, for Salmonella inactivation, the electric field intensity is the dominant factor with a strongly positive effect, strengthened by its positive interaction with pulse number. Pulse number, temperature, and pH have also significant positive effects but to a lesser extent. In the most efficient conditions, the pulsed electric field (PEF) treatment is capable of 3.5 log10 reduction in viable salmonellae. Simultaneously, the measure of surface hydrophobicity does not indicate any increase after PEF treatment. These results suggest that no protein denaturation occurs, unlike what is observed after comparable heat treatment in terms of Salmonella inactivation (55 degrees C for 15 min).     

Effects of pH and acid resistance on the radiation resistance of enterohemorrhagic Escherichia coli

The effects of pH and the induction of pH-dependent stationary-phase acid resistance on the radiation resistance of Escherichia coli were determined for seven enterohemorrhagic strains and one nonenterohemorrhagic strain. The isolates were grown in acidogenic or nonacidogenic media to pH levels of approximately 4.7 and 7.2, respectively. The cells were then transferred to brain heart infusion (BHI) broth adjusted to pH 4.0, 4.5, 5.0, and 5.5 (with HCl) that was preequilibrated to 2 degrees C, and cultures were then irradiated using a 137Cs source. Surviving cells and the extent of injury were determined by plating on BHI and MacConkey agars both immediately after irradiation and after subsequent storage at 2 degrees C for 7 days. Decreasing the pH of the BHI in which E. coli was irradiated had relatively little effect on the microorganism's radiation resistance. Substantial differences in radiation resistance were noted among strains, and induction of acid resistance consistently increased radiation resistance. Comparison of E. coli levels immediately after irradiation and after 7 days of refrigerated storage suggested that irradiation enhanced pH-mediated inactivation of the pathogen. These results demonstrate that prior growth under conditions that induce a pH-dependent stationary phase cross-protects E. coli against radiation inactivation and must be taken into account when determining the microorganism's irradiation D value.     

Lactobacilli isolated from chicken intestines: potential use as probiotics

Lactobacillus strains were tested for their in vitro probiotic properties. Cell surface hydrophobicity was found to be very high for Lactobacillus fermentum subsp. cellobiosus and Salmonella Gallinarum; high values could indicate a greater ability to adhere to epithelial cells. Studies on Lactobacillus animalis indicated relative cell surface hydrophobicities smaller than those of L. fermentum subsp. cellobiosus and L. fermentum. L. animalis and Enterococcus faecalis were able to coaggregate with L. fermentum subsp. cellobiosus and L. fermentum, respectively, but not with Salmonella Gallinarum. After mixed-culture studies for determining suitable growth behavior, the pair of strains L. animalis plus L. fermentum subsp. cellobiosus was selected for an attempted challenge against Salmonella Gallinarum. Double and triple mixed-culture studies indicated that selected lactobacillus strains were able to retain their beneficial characteristics in the presence of Salmonella Gallinarum such as presence of lectins, production of antimicrobial compounds, and ability to grow and compete. The selected microorganisms can be considered as potential ingredients for a chicken probiotic feed formulation intended to control salmonellosis and also improve poultry sanitation.