Noise effects on robust synchronization of a small pacemaker neuronal ensemble via nonlinear controller: electronic circuit design

In this paper, we report on the synchronization of a pacemaker neuronal ensemble constituted of an AB neuron electrically coupled to two PD neurons. By the virtue of this electrical coupling, they can fire synchronous bursts of action potential. An external master neuron is used to induce to the whole system the desired dynamics, via a nonlinear controller. Such controller is obtained by a combination of sliding mode and feedback control. The proposed controller is able to offset uncertainties in the synchronized systems. We show how noise affects the synchronization of the pacemaker neuronal ensemble, and briefly discuss its potential benefits in our synchronization scheme. An extended Hindmarsh–Rose neuronal model is used to represent a single cell dynamic of the network. Numerical simulations and Pspice implementation of the synchronization scheme are presented. We found that, the proposed controller reduces the stochastic resonance of the network when its gain increases.     

Biosynthesis of hepatitis B virus e antigen: directed mutagenesis of the putative aspartyl protease site.

The C gene products of all mammalian hepadnaviruses contain a region with sequence similarities to the catalytic center of the aspartyl proteases. This region could have the capacity to cleave precore proteins, leading to the synthesis of e antigen. By site-directed mutagenesis on a plasmid containing the hepatitis B virus C gene, we have replaced either the Asp residue of the putative aspartyl protease catalytic center or an Asp residue located 3 amino acids upstream. Transient expression of the mutated hepatitis B virus C gene in human and mouse cells showed that none of these mutations prevented the secretion of an accurately processed HBe antigen. Thus, we demonstrated that the aspartyl protease responsible for e antigen precursor processing is not C gene encoded but is more likely to be a cellular enzyme. From these results, we suggest a model for the mechanism of e antigen synthesis.     

Effect of calcitonin on the prolactin surge of proestrus

The effect of calcitonin (CT) on the prolactin (PRL) surge of proestrus in rats was investigated under normal and perturbed lighting conditions. Salmon calcitonin (SCT) was injected i.p. on diestrus 2 or on proestrus, plasma PRL levels were measured by radioimmunoassay. SCT had no effect on the PRL surge under normal lighting conditions but it induced a small drop in PRL level measured on proestrus morning, 3 hours after CT injection. Animals submitted to perturbed light conditions had higher PRL levels than those kept under normal lighting. These data would indicate that for the female rats on proestrus the sensitivity to stress due to injection and blood sampling may be modulated by changing the photoperiod. SCT injection under these conditions may facilitate this destabilization in PRL level.     

expA: A conditional mutation affecting the expression of a group of exported proteins in Escherichia coli K-12

Summary A mutant of Escherichia coli K-12 was isolated as conditionally deficient in the expression of two exported proteins simultaneously (i.e. two acid phosphatases) The mutant was found to be thermosensitive on minimal medium at 37°C and above, but grew normally on rich media at these temperatures. The mutation, named expA and located at 22 min on the recalibrated linkage map, depressed the levels of six periplasmic enzymatic activities in bacteria grown at 37°C. At least ten proteins were greatly reduced in the periplasm under these conditions. The mutation also affected some outer membrane proteins, among which were the ompF protein and a protein which may be protein III, but had little effect on cytoplasmic membrane proteins. The gel patterns of the soluble cytoplasmic proteins were not modified except for one major protein of MW 47,000. The activities of -galactosidase and of aspartate transcarbamylase were unmodified. After growth at 30°C no difference was observed between expA and expA ⁺ isogenic strains. The results are discussed with respect to the mechanism of protein export.Enzymes E.C. 3.1.3.2 Acid phosphatase (optimum pH 2.5) - E.C. 3.1.3.2 Acid phosphatase (optimum pH 4.5) - E.C. 3.1.3.1 Alkaline phosphatase - E.C. 3.4.11 Aminopeptidase-N - E.C. 2.1.3.2 Aspartate transcarbamylase - E.C. 3.2.1.23 -galactosidase - E.C. 3.1.27.1 RNase I Abbreviations PNP-OH Para-nitro-phenol - PNA Para-nitro-anilide - PNP-P Para-nitro-phenyl-phosphate - Bis-PNP-P Bis-para-nitro-phenyl-phosphate - IPTG Isopropyl--thiogalactopyranoside, Nitrosoguanidine N-methyl, N'-nitro, N, Nitrosoguanidine, Tris Tris (hydromethyl) aminomethane     

The effect of calcitonin on prolactin secretion during gestation

The relationship between calcitonin (CT) and prolactin (PRL) was studied by means of the injection of salmon calcitonin (SCT) i.p. on day 1 of gestation. An estrogen inhibitor - clomiphene - was also administered to certain groups of animals on day 4 and 5 of gestation. SCT did not affect PRL levels on day 1 of gestation nor on days 5 or 7, but it prevented the rise of PRL levels observed in animals submitted to injection stress on days 4 and 5. In animals treated with clomiphene, the inhibition by SCT on PRL increase after injection stress was partially abolished. SCT while not affecting basal PRL level prevented the rise observed after stress and this effect occurred some days later. Thus SCT could exercise a delayed neuroendocrine control. This action of SCT seemed to be partially dependent upon the presence of estrogens.     

Coumarin and quinolone action in archaebacteria: evidence for the presence of a DNA gyrase-like enzyme.

The action of novobiocin and coumermycin (two coumarins which interact with the gyrB subunit of eubacterial DNA gyrase) and ciprofloxacin (a fluoroquinolone which interacts with the gyrA subunit of DNA gyrase) was tested on several archaebacteria, including five methanogens, two halobacteria, and a thermoacidophile. Most strains were sensitive to doses of coumarins (0.02 to 10 micrograms/ml) which specifically inhibit DNA gyrase in eubacteria. Ciprofloxacin inhibited growth of the haloalkaliphilic strain Natronobacterium gregoryi and of the methanogen Methanosarcina barkeri. In addition, ciprofloxacin partly relieved the sensitivity to coumarins (and vice versa). Novobiocin inhibited DNA replication in Halobacterium halobium rapidly and specifically. Topological analysis has shown that the 1.7-kilobase plasmid from Halobacterium sp. strain GRB is negatively supercoiled; this plasmid was relaxed after novobiocin treatment. These results support the existence in archaebacteria of a coumarin and quinolone target related to eubacterial DNA gyrase.     

Soluble factors and the immune response: in vitro studies of the immunosuppression induced by the graft-versus-host reaction

In vitro experiments were carried out to investigate the cause(s) of the immunosuppression induced by the graft-versus-host (GVH) reaction in F₁ hybrid mice injected with parental strain lymphoid cells. A modified Marbrook culture chamber, made up of two cell compartments separated by a cell impermeable membrane, was used in these studies. Spleen cells from either normal animals (NSC) or from animals experiencing a GVH reaction (GVH-SC) were cultured with sheep red blood cells (SRBC) and the direct plaque-forming cell (PFC) response to SRBC was measured. It was found that normal thymus, lymph node and spleen cells, separated from the GVH-SC by a cell impermeable membrane, restored partially or totally the immune response of the suppressed cells, while bone marrow cells did not. It was also found that GVH-SC inhibited the PFC response to SRBC of NSC when mixed in culture at a ratio of 1:5. Conversely the inhibitory effect of GVH-SC on the immune response of NSC was abrogated when the two cell populations were separated by a cell impermeable membrane. These observations demonstrate that GVH-induced immunosuppression is caused, at least in part, by the deficiency of a T-cell derived factor which is a necessary component of the normal immune response. It is suggested that the suppressive effect of GVH-SC on the immune response of NSC is mediated by a non-T cell which regulates the release and/or production of the T-cell derived factor.     

Seasonal habitat selection and temporal activity patterns determine the structure of bat assemblages in Dhana Biosphere Reserve,Jordan (Mammalia: Chiroptera)

We measured species richness, diversity, and diel activity patterns of insectivorous bats at four sites within Dhana Biosphere Reserve. A total of seven species belonging to five families at varying species compositions were recorded. Four to six species were present at these sites and total diversity ranged between 0.32 at Ain Lahtha and 0.65 at Al Khararah. Overall frequency of passes was highest at Shaq Kalbeh. The Common Pipistrelle, Pipistrellus pipistrellus, was the most prevalent at three sites, followed by the Arabian Horseshoe Bat, Rhinolophus clivosus, and Botta’s Serotine, Eptesicus bottae. Natterer’s Bat, Myotis nattereri, and the European Free-tailed Bat, Tadarida teniotis, occurred at low abundance. The Lesser Horseshoe Bat, Rhinolophus hipposideros, occurred at a higher abundance within Finan site (arid site at lower altitude), whereas the Egyptian Mouse-tailed Bat, Rhinopoma cystops, was restricted to Finan. The overall mean number of bat passes was not significantly different between sites. Average seasonal species diversity was low during winter (none at Ain Lahtha and Shaq Kalbeh) and highest during summer (0.68 at Al Kharrarah). Seasonal activity patterns for each site in terms of frequencies of bat passes on an hourly basis are given.     

Phylogenomics of the archaeal flagellum: rare horizontal gene transfer in a unique motility structure

Background  

As bacteria, motile archaeal species swim by means of rotating flagellum structures driven by a proton gradient force. Interestingly, experimental data have shown that the archaeal flagellum is non-homologous to the bacterial flagellum either in terms of overall structure, components and assembly. The growing number of complete archaeal genomes now permits to investigate the evolution of this unique motility system.