The theory of prey-predator oscillations.

A general prey-predator model is formulated and the conditions for the occurrence of limit cycles are discussed. The effects of random environmental fluctuations on a stable equilibrium and on a limit cycle are investigated. Data on the 4- and 10-yr cycles are analysed by computing the periodogram and the results are compared with the theoretical spectrum.     

Low oxygen concentrations inhibit trophoblast cell invasion from early gestation placental explants via alterations in levels of the urokinase plasminogen activator system

Extravillous trophoblast cell (EVT) invasion in early pregnancy occurs in a relatively low-oxygen environment. The role of oxygen in regulation of EVT invasion remains controversial. We hypothesized that 1) culture in 3% oxygen inhibits EVT invasion compared with culture at 8% or 20% oxygen and 2) inhibition of invasion is due to alterations in levels of components of the urokinase plasminogen activator (PLAU, uPA) system rather than through increased apoptosis and/or decreased proliferation. Placental samples (8-10, 12-14, and 16-20 wk gestation) were obtained from women undergoing elective surgical termination of pregnancy or after cesarean section delivery (term) at the Royal Victoria Infirmary, Newcastle upon Tyne, U.K. EVT invasion from placental explants cultured at 3%, 8%, or 20% oxygen was assessed using Matrigel invasion assays. Invasion was assessed on Day 6, explants were harvested for analysis of apoptosis and proliferation, and medium was stored for analysis of PLAU system components by ELISA and casein zymography. Culture at 3% oxygen inhibited EVT invasion. PLAU receptor and plasminogen activator inhibitor-2 protein levels were increased and PLAU activity decreased in these cultures. There was no difference in the proliferation in explants cultured at the three different oxygen concentrations. Apoptosis, assessed by M30 immunostaining, was increased in EVT at both 3% and 8% oxygen. The reduction in the invasive capacity of EVT cultured at 3% oxygen appears to be mediated both by a general inhibition of the PLAU system and a decrease in the number of cells available to invade.     

How to Write a Medical Research Paper for an International Journal

Western-raised scientists are taught with the traditional concepts of:purpose,method,observation and conclusion.This is not true for Chinese educated students.Since all international journals publish papers following these,or similar parameters,the Chinese scientist who wishes to publish in such a journal,must adjust his thinking to fit within this scheme.In this presentation we wish to assist our Chinese colleagues on how this thought process can be followed.     

Electrical and adaptive properties of rod photoreceptors in bufo marinus. I. Effects of altered extracellular Ca(2+) levels

The effects of altering extracellular Ca(2+) levels on the electrical and adaptive properties of toad rods have been examined. The retina was continually superfused in control (1.6 mM Ca(2+)) or test ringer’s solutions, and rod electrical activity was recorded intracellularly. Low-calcium ringer’s (10(-9)M Ca(2+)) superfused for up to 6 min caused a substantial depolarization of the resting membrane potential, an increase in light-evoked response amplitudes, and a change in the waveform of the light-evoked responses. High Ca(2+) ringer’s (3.2 mM) hyperpolarized the cell membrane and decreased response amplitudes. However, under conditions of either low or high Ca(2+) superfusion for up to 6 min, in both dark-adapted and partially light-adapted states, receptor sensitivity was virtually unaffected; i.e., the V-log I curve for the receptor potential was always located on the intensity scale at a position predicted by the prevailing light level, not by Ca(2+) concentration. Thus, we speculate that cytosol Ca(2+) concentration is capable of regulating membrane potential levels and light-evoked response amplitudes, but not the major component of rod sensitivity. Low Ca(2+) ringer’s also shortened the period of receptor response saturation after a bright but nonbleaching light flash, hence accelerating the onset of both membrane potential and sensitivity recovery during dark adaptation.

Exposure of the retina to low Ca(2+) (10(-9)M) ringer’s for long periods (7-15 min) caused dark-adapted rods to lose responsiveness. Response amplitudes gradually decreased, and the rods became desensitized. These severe conditions of low Ca(2+) caused changes in the dark-adapted rod that mimic those observed in rods during light adaptation. We suggest that loss of receptor sensitivity during prolonged exposure to low Ca(2+) ringer’s results from a decrease of intracellular (intradisk) stores of Ca(2+); i.e., less Ca(2+) is thereby released per quantum catch.

     

The antifungal action of dandruff shampoos

The disease commonly known as “dandruff” is caused by numerous host factors in conjunction with the normal flora yeast Malassezia furfur (Pityrosporumovale). Indeed, clinical studies have shown that administration of antifungal agents correlates with an improved clinical condition. Almost all commercially available hair shampoos publicize that they contain some form of antifungal agent(s). However, few studies have been published in which antifungal activity of commercially available hair shampoos have been contrasted experimentally. In this study six commercially available shampoos (in the Philippines) were assessed for antifungal activity against a human (dandruff) isolate of M. furfur: (a) Head & Shoulders (Proctor & Gamble); (b) Gard Violet (Colgate-Palmolive); (c) Nizoral 1% (Janssen); (d)Nizoral 2% (Janssen); (e) Pantene Blue (Proctor & Gamble); and (f) Selsun Blue (Abbott). The results demonstrated that all six of the assayed hair shampoos have some antifungal effect on the test yeast. However, there was consider variation in potency of antifungal activity. Nizoral 1% and Nizoral 2% shampoo preparations were the most effective. The 1% Nizoral shampoo was consistently 10X better at killing yeast cells than the next closest rival shampoo. The 2% Nizoral shampoo was 10X better than the Nizoral 1% product and 100 times better than any of the other products assayed. The study demonstrated that shampoos containing a proven antifungal compound were the most effective in controlling the causative yeast. This revised version was published online in June 2006 with corrections to the Cover Date.     

Human Pathogenic Fungi in China??Emerging Trends from Ongoing National Survey for 1986, 1996, and 2006

This epidemiological survey was a retrospective study on three nodes during the past three decades on fungal infections representing the China, including Taiwan. Owing to rare publications reporting on dynamic epidemiological trends in the pathogen epidemiology in China, we surveyed the isolation rates and pathogenic fungi from 8 representative districts in China using uniform identification with uniform methodology. The pathogenic fungi isolation rates and species obtained from 1986 (n=9,096), 1996 (n=19,009), and 2006 (n=33,022) suggested that Trichophyton rubrum was the commonest organism cultured in 1980s (45.4%) and 1990s (34.5%), but Candida albicans increased significantly and reaching to its peak (26.9%) in 2006s' survey, and has become the most common isolate of fungal infections in China currently. In addition, Candida glabrata became the most common non-albicans species of Candida in 2006s' survey. At the same time, the incidence of molds also gradually increased. According to comparative analysis of the results of these three surveys, we found apparent differences in the isolation rates of different pathogenic fungi and the forefront 10 species in China varied significantly, and the dermatophytes decreased markedly, while yeasts, especially the Candida species and the molds, increased gradually during the past three decades. Less dermatophytic infections may suggest better access to healthcare or increase in Candida species indicated higher incidence of hospital acquired infections.     

Salmonella Typhi sense host neuroendocrine stress hormones and release the toxin haemolysin E

Salmonella enterica serovar Typhi (S. typhi) causes typhoid fever. We show that exposure of S. typhi to neuroendocrine stress hormones results in haemolysis, which is associated with the release of haemolysin E in membrane vesicles. This effect is attributed to increased expression of the small RNA micA and RNA chaperone Hfq, with concomitant downregulation of outer membrane protein A. Deletion of micA or the two-component signal-transduction system, CpxAR, abolishes the phenotype. The hormone response is inhibited by the β-blocker propranolol. We provide mechanistic insights into the basis of neuroendocrine hormone-mediated haemolysis by S. typhi, increasing our understanding of inter-kingdom signalling.