Evening dietary increases in plasma tryptophan availability for uptake into the brain enhance sustained alertness early in the morning after an overnight sleep, most likely because of improved sleep.

No abstract

1. We use an individual-based model describing the life of a monarch butterfly, which utilises milkweeds both aggregated in patches and scattered across the wider landscape as a substrate for laying eggs. The model simplifies the metapopulation of milkweed habitat patches by representing them as a proportion of the overall landscape, with the rest of the landscape considered matrix, which may contain some low density of milkweed plants.2. The model simulates the number of eggs laid daily by a butterfly as it searches for hosts. The likelihood of finding hosts is related to the density of plants and the search ability of the butterfly. For an empty matrix, remaining in a habitat patch results in more eggs laid. However individuals that are good searchers have almost equivalent success without remaining in a habitat patch. These individuals are most affected by the presence of hosts in the matrix.3. Given realistic values of habitat patch availability, our model shows that the presence of plants at a low density in the matrix has a substantial impact on the number of eggs laid; removing these plants can reduce lifetime potential fecundity by ca. 20%. These results have implications for monarch butterflies inhabiting agricultural landscapes, in which genetically modified soybean that is resistant to herbicides has resulted in the decimation of milkweeds over large areas.

No abstract

Polychlorinated biphenyls (PCBs) and dioxins are potentially toxic compounds which occur widely in the environment. Their effects on the growth and development of infants at the levels currently found in highly industrialised western countries is not well known. This Dutch multicenter study, combining animal and human studies, tries to answer this question. Animal studies showed that PCB 169, given once during pregnancy at a dose of 1.8 g kg-1 bodyweight, has an effect on developmental parameters, dopamine regulation and fertility. Effects on thyroid hormones were also found in animals, probably due to both a competitive binding of PCB metabolites to the thyroxine binding protein and increased glucuronidation, Perhaps to compensate for this, an increased diodase activity in the brain was found. Human studies involved 400 mother-infant pairs, half of them being breast-fed, the other half were fed a formula devoid of PCBs and dioxins. PCB levels were measured in serum and dioxin and PCB levels in breastmilk. Levels were found to be as high as previously found in highly industrialised countries. Growth and development were carefully documented, but no data are as yet available. In pregnant women, a significant negative correlation was found between some dioxin and PCB congeners in milk and plasma thyroid hormones, while newborn infants showed higher thyroid stimulating hormone (TSH) at higher levels of dioxin exposure. In summary, data from this combined multicenter study involving animals and humans increases our insight into the potentially negative effects of PCBs and dioxins on growth and development.