Effect of gum Arabic on aminopyrine demethylation in rats

Summary Stimulation of aminopyrine demethylation induced in rats by oral or i.p. administration of phenobarbital was partially inhibited in animals receiving daily treatments of 2×200 mg/kg gum Arabic p.o.     

The end of world population growth

There has been enormous concern about the consequences of human population growth for the environment and for social and economic development. But this growth is likely to come to an end in the foreseeable future. Improving on earlier methods of probabilistic forecasting, here we show that there is around an 85 per cent chance that the world's population will stop growing before the end of the century. There is a 60 per cent probability that the world's population will not exceed 10 billion people before 2100, and around a 15 per cent probability that the world's population at the end of the century will be lower than it is today. For different regions, the date and size of the peak population will vary considerably.     

Dual effect of cannabinoid CB<Subscript>1</Subscript> receptor stimulation on a vanilloid VR1 receptor-mediated response

Cannabinoid CB1 receptors and vanilloid VR1 receptors are co-localized to some extent in sensory neurons of the spinal cord and dorsal root ganglia. In this study, we over-expressed both receptor types in human embryonic kidney (HEK)-293 cells and investigated the effect of the CB1 agonist HU-210 on the VR1-mediated increase in intracellular Ca2+ ([Ca2+]i), a well-known response of the prototypical VR1 agonist capsaicin. After a 5-min pre-treatment, HU-210 (0.1 microM) significantly enhanced the effect of several concentrations of capsaicin on [Ca2+]i in HEK-293 cells over-expressing both rat CB1 and human VR1 (CB1-VR1-HEK cells), but not in cells over-expressing only human VR1 (VR1-HEK cells). This effect was blocked by the CB1 receptor antagonist SR141716A (0.5 microM), and by phosphoinositide-3-kinase and phospholipase C inhibitors. The endogenous agonist of CB1 and VR1 receptors, anandamide, was more efficacious in inducing a VR1-mediated stimulation of [Ca2+]i in CB1-VR1-HEK cells than in VR1-HEK cells, and part of its effect on the former cells was blocked by SR141716A (0.5 microM). Pre-treatment of CB1-VR1-HEK cells with forskolin, an adenylate cyclase activator, enhanced the capsaicin effect on [Ca2+]i. HU-210, which in the same cells inhibits forskolin-induced enhancement of cAMP levels, blocked the stimulatory effect of forskolin on capsaicin. Our data suggest that in cells co-expressing both CB1 and VR1 receptors, pre-treatment with CB1 agonists inhibits or stimulates VR1 gating by capsaicin depending on whether or not cAMP-mediated signalling has been concomitantly activated.     

Organoplatinum crystals for gas-triggered switches

Considerable effort is being devoted to the fabrication of nanoscale devices. Molecular machines, motors and switches have been made, generally operating in solution, but for most device applications (such as electronics and opto-electronics), a maximal degree of order and regularity is required. Crystalline materials would be excellent systems for these purposes, as crystals comprise a vast number of self-assembled molecules, with a perfectly ordered three-dimensional structure. In non-porous crystals, however, the molecules are densely packed and any change in them (due, for example, to a reaction) is likely to destroy the crystal and its properties. Here we report the controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules. This process, including repetitive expansion-reduction sequences (on gas uptake and release) of the crystal lattice, modifies the structures of these molecules without affecting their crystallinity. The process is based on the incorporation of SO2 into the colourless crystals and its subsequent liberation from the orange adducts by reversible bond formation and cleavage. We therefore expect that these crystalline materials will find applications for gas storage devices and as opto-electronic switches.     

Covalent binding of aflatoxin B1 to liver DNA in rats pretreated with ethanol

Summary Male Fischer F-344 rats were given ethanol in the drinking water and/or by single oral administration. Following this, the animals received p.o. 100 ng/kg of the hepatocarcinogen [³H]aflatoxin B₁ (AFB₁). 24 h later, the level of DNA-bound AFB₁ was determined in the liver and was found not to be affected by any type of ethanol pretreatment. A cocarcinogenic effect of ethanol in the liver is therefore unlikely to be due to an effect on the metabolic activation and inactivation processes governing the formation of DNA-binding AFB₁ metabolites.To whom correspondence should be addressed.Acknowledgment. We thank the European Science Foundation for the Toxicology Research Fellowship awarded to M.M.     

Prey selection and food habits of Burrowing Owls in Colorado

Food habits of Burrowing Owls ( Speotyto cunicularia ) were studied during the breeding seasons of 1990 and 1991 in central Colorado. Concurrent insect availability studies were conducted to determine selection for specific insect families. Analysis of 1445 castings indicated use of only one insect family, the carrion beetles (Silphidae), at a rate greater than expected based on availability in one year. Castings and prey remains showed different dietary components. Prey remains showed greater use of small mammals, moths, amphibians, and passerines, and castings indicated greater use of mice and beetles. Methodology in raptor food habits studies may therefore bias results.     

Plasmid-related anaerobic autotrophy of the novel archaebacterium Sulfolobus ambivalens

Three different species of the genus Sulfolobus, S. acidocaldarius, S. solfataricus (= Caldariella) and S. brierleyi, have been distinguished by the conditions required for optimal growth, by the component patterns of their DNA-dependent RNA polymerases and by DNA sequence data. Many isolates of these species are able to grow chemolithoautotrophically using CO2 as the sole carbon source and the oxidation of S(0) with O2 yielding sulphuric acid, as the energy source, though a few others grow only heterotrophically. We show here that a strain of a novel Sulfolobus species, S. ambivalens, is alternatively able to live by an anaerobic mode of chemolithoautotrophy, also using CO2 as the sole carbon source, but using reduction of S(0) with H2, yielding H2S as the energy source. This mode of growth is correlated with the amplification of a plasmid, pSL10.     

Unexpected antibiotic properties of a cephalosporin]

The presence of an oximino group on the methylene of the (2-aminothiazol 4-yl)-acetyl side chain bound to the 7-amino cephalosporanic acid affords derivatives with syn or anti configuration. Whereas the anti isomers display low antibiotic activities, the syn isomers possess a surprising high efficiency against gram negative bacteria, enhanced a factor of 10 to 100 as compared with the cephalosporins known at the moment.     

Experimental demonstration of chaos in a microbial food web

Discovering why natural population densities change over time and vary with location is a central goal of ecological and evolutional disciplines. The recognition that even simple ecological systems can undergo chaotic behaviour has made chaos a topic of considerable interest among theoretical ecologists. However, there is still a lack of experimental evidence that chaotic behaviour occurs in the real world of coexisting populations in multi-species systems. Here we study the dynamics of a defined predator-prey system consisting of a bacterivorous ciliate and two bacterial prey species. The bacterial species preferred by the ciliate was the superior competitor. Experimental conditions were kept constant with continuous cultivation in a one-stage chemostat. We show that the dynamic behaviour of such a two-prey, one-predator system includes chaotic behaviour, as well as stable limit cycles and coexistence at equilibrium. Changes in the population dynamics were triggered by changes in the dilution rates of the chemostat. The observed dynamics were verified by estimating the corresponding Lyapunov exponents. Such a defined microbial food web offers a new possibility for the experimental study of deterministic chaos in real biological systems.