Expression of outer membrane proteins by Salmonella enteritidis relating to pH

Abstract The pH of the environment influenced the expression of outer membrane protein by S. enteritidis PT4 growing in broth. Growth in broth at pH 5 to 7 resulted in variation in expression of outer membrane proteins of 18 to 22 kDa. Bacteria became acid-fixed and non-viable following prolonged incubation in broth with a pH below 5, and expression of flagella was repressed.     

The use of a hidden metal-capture reagent for the measurement of Na+--K+-ATPase activity: a new concept in cytochemistry

The original lead-trapping method for demonstrating Na+--K+-ATPase activity was discredited because of the effect that lead ions can have on the substrate and on the enzyme. Current methods, that measure this activity by the related K+-dependent phosphatase activity, do not appear to measure activity that is known, from microchemistry, to occur in proximal convoluted tubules. The disadvantages of using lead appear to have been overcome by the use of a new reagent in which the lead is complexed with ammonium citrate ions; phosphate, liberated enzymatically, successfully competes with these ions. The activities of total ATPase and of the ouabain sensitive Na+--K+-ATPase have been measured in three regions of the nephron in the guinea-pig and in the rat. The relative activities found, by this method, in the different regions of the latter, appear to be comparable with results found by others, using microchemical methods applied to isolated regions of the nephron.     

The occurrence and fission-track ages of late neogene and quaternary volcanic sediments,Siwalik group,Northern Pakistan

Volcanic sediments, now mostly bentonites and bentonitic mudstones, occur throughout the Late Neogene and Quaternary Siwalik Group of northern Pakistan. A number of these deposits have been dated by the fission-track method, utilizing zircon phenocrysts from these deposits, and provide the chronometric constraints upon which a paleomagnetic stratigraphy is developed for the Siwalik Group. Notable in the occurrence of these altered tuff horizons is an apparent mode in their stratigraphic development from approximately 3.0 to 1.5 m.y. B.P. which coincides with the period of activity of the Dacht-e-Nawar volcanic complex of east-central Afghanistan. Fission-track ages of certain tuffs for critical areas of northern Pakistan are reported herein.     

Geographic distribution of human skin colour: A selective compromise between natural selection and sexual selection?

Modern humans have been shaped by the cumulative action of natural selection, non-adaptive random change, and sexual selection. The last of these is not universal and has prevailed in one of two circumstances: (1) A surplus of females due to high male mortality, combined with ecological constraints on female participation in food procurement which discourage males from taking second wives; (2) A surplus of single males due to generalized polygyny with relatively low male mortality. These circumstances are most likely to occur in (1) Arctic tundra environments, specifically the vast expanse of tundra covering most of Europe up to 10,000 B.P., and in (2) regions dominated by generalized polygyny, notably sub-Saharan Africa. Sexual selection often acts on existing sex differences, including perhaps sexual dimorphism in human skin colour. Whereas women are universally fairer in complexion, men are browner and ruddier; parallel to this, most human societies see lighter skin as more feminine and darker skin as more masculine. Hence, sexual selection should favour lighter pigmented women when a surplus of single females must compete for a mate. Since skin colour is only mildly sex-linked, both sexes would lighten in pigmentation within the population in question. Similarly, when a surplus of single males must compete for a mate, both sexes would darken. Geographic variation in human skin colour may thus represent a selective compromise between two counterbalancing forces: natural selection, as determined by latitudinal variation in sunlight; and sexual selection, as determined by variations in the following: male mortality rates, incidence of polygyny, and ecological constraints on female participation in food procurement.     

Effects of Perinatal Vitamin B6 Deficiency on Dopaminergic Neurochemistry

Long-Evans dams were fed either a vitamin B6-deficient or a control diet from day 13-14 of gestation and throughout lactation. A control pair-fed group was also included because of differences in food intake between vitamin B6-deficient and control ad libitum dams. The progeny of vitamin B6-deficient dams had all the classic symptoms of B6 deficiency. These included weight loss, ataxia, tremor, and epileptic seizures. Concentrations of the neurotransmitter dopamine (DA), and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), as well as D-2 dopamine receptor binding, 3,4-dihydroxyphenylalanine (DOPA) decarboxylase activity, and vitamin B6 levels were measured in the corpus striatum of progeny at 7, 14, and 18 days after birth. Striatal DA and HVA levels were significantly decreased in B6-deficient animals when compared to ad libitum or pair-fed controls. Daily injections of vitamin B6 to deprived animals from the 14th to 18th day after birth improved the abnormal movement and normalized the concentration of DA but not of HVA in corpus striatum. Striatal D-2 dopamine receptor binding using [3H]spiperone as ligand was significantly reduced in 18-day-old animals as compared to ad libitum and pair-fed controls. No significant differences were found at 14 days. The administration of vitamin B6 to deprived animals did not raise the level of D-2 receptor binding during the period of observation. Scatchard plots indicated that the differences in binding were due to changes in receptor number and not in KD. Corpus striatum DOPA decarboxylase activity with and without the addition of exogenous pyridoxal phosphate was significantly reduced in 14- and 18-day-old animals when compared to pair-fed controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

The time factor in mortality: weather associations in a subtropical environment

 Mortality rates for a decade in Brisbane are analysed for dependence upon atmospheric factors. Time filters are applied to both the dependent and independent variables, and several models are developed to enable prediction, especially for weekly intervals. Statistically, deaths are observed to increase with colder and less humid weather with winds from a westerly, direction. Overall, taking account of both synoptic and seasonal influences, >90% of cumulative deviations from mean death rates are explained. Some differences are also noted in the association of death with the weather between sexes, age groups and causes of death. Received: 2 November 1995 / Accepted: 26 December 1996