High impulsivity predicts the switch to compulsive cocaine-taking

Both impulsivity and novelty-seeking have been suggested to be behavioral markers of the propensity to take addictive drugs. However, their relevance for the vulnerability to compulsively seek and take drugs, which is a hallmark feature of addiction, is unknown. We report here that, whereas high reactivity to novelty predicts the propensity to initiate cocaine self-administration, high impulsivity predicts the development of addiction-like behavior in rats, including persistent or compulsive drug-taking in the face of aversive outcomes. This study shows experimental evidence that a shift from impulsivity to compulsivity occurs during the development of addictive behavior, which provides insights into the genesis and neural mechanisms of drug addiction.     

Enhanced enantioselectivity in excitation of chiral molecules by superchiral light

A molecule or larger body is chiral if it cannot be superimposed on its mirror image (enantiomer). Electromagnetic fields may be chiral, too, with circularly polarized light (CPL) as the paradigmatic example. A recently introduced measure of the local degree of chiral dissymmetry in electromagnetic fields suggested the existence of optical modes more selective than circularly polarized plane waves in preferentially exciting single enantiomers in certain regions of space. By probing induced fluorescence intensity, we demonstrated experimentally an 11-fold enhancement over CPL in discrimination of the enantiomers of a biperylene derivative by precisely sculpted electromagnetic fields. This result, which agrees to within 15% with theoretical predictions, establishes that optical chirality is a fundamental and tunable property of light, with possible applications ranging from plasmonic sensors to absolute asymmetric synthesis.     

Breast-feeding in sub-Saharan Africa: outlook for 2000

The World Health Organization (WHO) has stressed that 1.5 million infants die annually, unnecessarily, from deprival or from insufficiency of breast milk. Hence, the need for its maximal use, very particularly in impoverished populations, such as those in sub-Saharan Africa. In many developed populations, a generation ago the practice was very low, but now it has risen considerably. In contrast, in Africa and in most developing populations, despite the far greater need for breast-feeding, the practice is tending to decrease, especially among urban mothers. While the most common reasons given concern insufficiency of breast milk and employment of mothers, the latter, especially urban mothers, are under strong and increasing pressure to use proprietary replacement foods. These are often made up unsatisfactorily and are contaminated. Also influential are the often less than enthusiastic, and confusing, attitudes of staff at clinics and hospitals, albeit, due in part to their very heavy workloads. Additionally, there is society's relatively indifferent attitude to breast-feeding. Currently, a hugely adverse factor is the danger of human immunodeficiency virus (HIV) transference from seropositive mothers to their infants - in some African countries almost half of antenatal mothers are infected. Chances of early control of the infection are remote. However, apart from this danger, and from the pressure from replacement food companies, the outlook for breast-feeding practice in many African countries is unlikely to improve significantly until greater encouragement is given from State, local and other health authorities.     

Effect of Pb(NO3)2 on poplar tissue culture and the ultrastructural localization of lead in culture cells

In tissue cultures of Populus maximowiczii Henry, Pb(NO₃)₂ had a restraining effect on fresh weight increase and anthocyanin content. In ultrastructural research Pb deposits of various size were mainly present in the intercellular spaces, cell walls (mainly in the region of the middle lamella), in the paramural bodies and in the vacuoles. Small deposits of this metal were also observed in the endoplasmic reticulum (ER), dictyosomes and dictyosome derivated vesicles.     

Effects of Jatropha curcas on calves.

Jatropha curcas seed was fed to six calves at doses of 2.5, 1 and 0.25 g/kg once and to two other calves at 0.025 g/kg up to 14 days. The onset of toxic manifestations in the six calves was rapid and death occurred within 19 hours of administration. The two calves that received daily the lowest dose of J. curcas showed signs of poisoning and died within 10 to 14 days. The clinical signs of diarrhoea, dyspnoea, dehydration and loss of condition were well correlated with the pathological findings. There was an increase in aspartate aminotransferase, ammonia and potassium and a decrease in total protein and calcium in the serum of jatropha-poisoned calves.     

The bacillus spore coat

ABSTRACT Bacilli, which are abundant in the soil, form highly resistant dormant cell types, called spores, in response to starvation. The spore is organized into a series of concentrically arranged structures, each of which contribute in a different way to resistance against environmental stress. In certain bacteria, including Bacillus subtilis, the outermost of these structures is a multilayered protein shell, called the coat. The coat is both an armor plating and, almost certainly, possesses enzymatic activities, allowing it to have active roles as well. Assembly of the proteins comprising the coat is carefully controlled during spore assembly, resulting in a distinct pattern of layers, seen in cross section, and a discreet pattern of ridges on the surface. Although our understanding of spore coat composition and assembly is deepening, we still know little about the roles of the coat in interactions between spores and other organisms, particularly in the soil. Critical future directions for spore coat research include continued identification of the proteins that comprise the coat surface, characterization of the global chemical characteristics of this surface, and elucidation of how these features impact on other organisms in the soil.